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Sample records for repetition rate ultrafast

  1. Heat accumulation during high repetition rate ultrafast laser interaction: Waveguide writing in borosilicate glass

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Haibin; Eaton, Shane M; Li, Jianzhao; Herman, Peter R [The Edward S. Rogers Sr. Department of Electrical and Computer Engineering, University of Toronto, 10 King' s College Road, Toronto, ON, M5S 3G4 (Canada)

    2007-04-15

    During high repetition rate (>200 kHz) ultrafast laser waveguide writing, visible heat modified zones surrounding the formed waveguide occur as a result of heat accumulation. The radii of the heat-modified zones increase with the laser net fluence, and were found to correlate with the formation of low-loss and cylindrically symmetric optical waveguides. A numerical thermal model based on the finite difference method is applied here to account for cumulative heating and diffusion effects. The model successfully shows that heat propagation and accumulation accurately predict the radius of the 'heat modified' zones observed in borosilicate glass waveguides formed across a wide range of laser exposure conditions. Such modelling promises better control of thermal effects for optimizing the fabrication and performance of three-dimensional optical devices in transparent materials.

  2. Investigation on repetition rate and pulse duration influences on ablation efficiency of metals using a high average power Yb-doped ultrafast laser

    Directory of Open Access Journals (Sweden)

    Lopez J.

    2013-11-01

    Full Text Available Ultrafast lasers provide an outstanding processing quality but their main drawback is the low removal rate per pulse compared to longer pulses. This limitation could be overcome by increasing both average power and repetition rate. In this paper, we report on the influence of high repetition rate and pulse duration on both ablation efficiency and processing quality on metals. All trials have been performed with a single tunable ultrafast laser (350 fs to 10ps.

  3. Experimental and theoretical study of the laser micro-machining of glass using high-repetition-rate ultrafast laser

    Science.gov (United States)

    Yashkir, Yuri; Liu, Qiang

    2006-04-01

    We present a systematic study of the ultrafast laser micro-machining of glass using a Ti:Spp laser with moderate pulse energy (<5 μJ) at a high repetition rate (50 kHz). Optimal conditions were identified for high resolution surface laser etching, and via drilling. Several practical applications were developed: glass templates for micro fluid diffraction devices, phase gratings for excimer laser projection techniques, micro fluid vertical channel-connectors, etc. It is demonstrated that the interaction of ultrafast laser pulses with glass combines several different processes (direct ablation, explosive material ejection, and thermal material modification). A dynamic numerical model was developed for this process. It was successfully used for modelling of laser micro-machining with arbitrary 3D translations of the target.

  4. Electron diffraction using ultrafast electron bunches from a laser-wakefield accelerator at kHz repetition rate

    Science.gov (United States)

    He, Z.-H.; Thomas, A. G. R.; Beaurepaire, B.; Nees, J. A.; Hou, B.; Malka, V.; Krushelnick, K.; Faure, J.

    2013-02-01

    We show that electron bunches in the 50-100 keV range can be produced from a laser wakefield accelerator using 10 mJ, 35 fs laser pulses operating at 0.5 kHz. It is shown that using a solenoid magnetic lens, the electron bunch distribution can be shaped. The resulting transverse and longitudinal coherence is suitable for producing diffraction images from a polycrystalline 10 nm aluminum foil. The high repetition rate, the stability of the electron source, and the fact that its uncorrelated bunch duration is below 100 fs make this approach promising for the development of sub-100 fs ultrafast electron diffraction experiments.

  5. Multi-gigahertz repetition rate ultrafast waveguide lasers mode-locked with graphene saturable absorbers

    Science.gov (United States)

    Obraztsov, P. A.; Okhrimchuk, A. G.; Rybin, M. G.; Obraztsova, E. D.; Garnov, S. V.

    2016-08-01

    We report the development of an approach to build compact waveguide lasers that operate in the stable fundamental mode-locking regime with multigigahertz repetition rates. The approach is based on the use of depressed cladding multi- or single-mode waveguides fabricated directly in the active laser crystal using the femtosecond laser inscription method and a graphene saturable absorber. Using this approach we achieve the stable self-starting mode-locking operation of a diode-pumped waveguide Nd:YAG laser that delivers picosecond pulses at a repetition rate of up to 11.5 GHz with an average power of 12 mW at a central wavelength of 1064 nm. The saturable absorbers are formed through the chemical vapor deposition of single-layer graphene on the output coupler mirror or directly on the end facet of the laser crystal. The stable self-starting mode-locking operation is achieved by controlling the group delay dispersion in the laser cavity with an intracavity interferometer. The method developed for the creation of compact ultrashort pulse laser generators with gigahertz repetition rates can be extended further and applied for the development of compact high-repetition rate lasers that operate at a wide range of IR wavelengths.

  6. Ultrafast, high repetition rate, ultraviolet, fiber based laser source: application towards Yb+ fast quantum-logic

    CERN Document Server

    Hussain, Mahmood Irtiza; Bentley, Christopher D B; Taylor, Richard L; Carvalho, Andre R R; Hope, Joseph J; Streed, Erik W; Lobino, Mirko; Kielpinski, David

    2016-01-01

    Trapped ions are one of the most promising approaches for the realization of a universal quantum computer. Faster quantum logic gates could dramatically improve the performance of trapped-ion quantum computers, and require the development of suitable high repetition rate pulsed lasers. Here we report on a robust frequency upconverted fiber laser based source, able to deliver 2.5 ps ultraviolet (UV) pulses at a stabilized repetition rate of 300.00000 MHz with an average power of 190 mW. The laser wavelength is resonant with the strong transition in Ytterbium (Yb+) at 369.53 nm and its repetition rate can be scaled up using high harmonic mode locking. We show that our source can produce arbitrary pulse patterns using a programmable pulse pattern generator and fast modulating components. Finally, simulations demonstrate that our laser is capable of performing resonant, temperature-insensitive, two-qubit quantum logic gates on trapped Yb$^+$ ions faster than the trap period and with fidelity above 99%.

  7. High speed laser drilling of metals using a high repetition rate, high average power ultrafast fiber CPA system.

    Science.gov (United States)

    Ancona, A; Röser, F; Rademaker, K; Limpert, J; Nolte, S; Tünnermann, A

    2008-06-09

    We present an experimental study on the drilling of metal targets with ultrashort laser pulses at high repetition rates (from 50 kHz up to 975 kHz) and high average powers (up to 68 Watts), using an ytterbium-doped fiber CPA system. The number of pulses to drill through steel and copper sheets with thicknesses up to 1 mm have been measured as a function of the repetition rate and the pulse energy. Two distinctive effects, influencing the drilling efficiency at high repetition rates, have been experimentally found and studied: particle shielding and heat accumulation. While the shielding of subsequent pulses due to the ejected particles leads to a reduced ablation efficiency, this effect is counteracted by heat accumulation. The experimental data are in good qualitative agreement with simulations of the heat accumulation effect and previous studies on the particle emission. However, for materials with a high thermal conductivity as copper, both effects are negligible for the investigated processing parameters. Therefore, the full power of the fiber CPA system can be exploited, which allows to trepan high-quality holes in 0.5mm-thick copper samples with breakthrough times as low as 75 ms.

  8. Ultrafast, high repetition rate, ultraviolet, fiber-laser-based source: application towards Yb+ fast quantum-logic.

    Science.gov (United States)

    Hussain, Mahmood Irtiza; Petrasiunas, Matthew Joseph; Bentley, Christopher D B; Taylor, Richard L; Carvalho, André R R; Hope, Joseph J; Streed, Erik W; Lobino, Mirko; Kielpinski, David

    2016-07-25

    Trapped ions are one of the most promising approaches for the realization of a universal quantum computer. Faster quantum logic gates could dramatically improve the performance of trapped-ion quantum computers, and require the development of suitable high repetition rate pulsed lasers. Here we report on a robust frequency upconverted fiber laser based source, able to deliver 2.5 ps ultraviolet (UV) pulses at a stabilized repetition rate of 300.00000 MHz with an average power of 190 mW. The laser wavelength is resonant with the strong transition in Ytterbium (Yb+) at 369.53 nm and its repetition rate can be scaled up using high harmonic mode locking. We show that our source can produce arbitrary pulse patterns using a programmable pulse pattern generator and fast modulating components. Finally, simulations demonstrate that our laser is capable of performing resonant, temperature-insensitive, two-qubit quantum logic gates on trapped Yb+ ions faster than the trap period and with fidelity above 99%.

  9. Ultrafast high-repetition imaging of fuel sprays using picosecond fiber laser.

    Science.gov (United States)

    Purwar, Harsh; Wang, Hongjie; Tang, Mincheng; Idlahcen, Saïd; Rozé, Claude; Blaisot, Jean-Bernard; Godin, Thomas; Hideur, Ammar

    2015-12-28

    Modern diesel injectors operate at very high injection pressures of about 2000 bar resulting in injection velocities as high as 700 m/s near the nozzle outlet. In order to better predict the behavior of the atomization process at such high pressures, high-resolution spray images at high repetition rates must be recorded. However, due to extremely high velocity in the near-nozzle region, high-speed cameras fail to avoid blurring of the structures in the spray images due to their exposure time. Ultrafast imaging featuring ultra-short laser pulses to freeze the motion of the spray appears as an well suited solution to overcome this limitation. However, most commercial high-energy ultrafast sources are limited to a few kHz repetition rates. In the present work, we report the development of a custom-designed picosecond fiber laser generating ∼ 20 ps pulses with an average power of 2.5 W at a repetition rate of 8.2 MHz, suitable for high-speed imaging of high-pressure fuel jets. This fiber source has been proof tested by obtaining backlight images of diesel sprays issued from a single-orifice injector at an injection pressure of 300 bar. We observed a consequent improvement in terms of image resolution compared to standard white-light illumination. In addition, the compactness and stability against perturbations of our fiber laser system makes it particularly suitable for harsh experimental conditions.

  10. High power, high repetition rate, few picosecond Nd:LuVO₄ oscillator with cavity dumping.

    Science.gov (United States)

    Gao, Peng; Guo, Jie; Li, Jinfeng; Lin, Hua; Yu, Haohai; Zhang, Huaijin; Liang, Xiaoyan

    2015-12-28

    We investigate the potential use of Nd:LuVO4 in high average power, high repetition rate ultrafast lasers. Maximum mode-locked average power of 28 W is obtained at the repetition rate of 58 MHz. The shortest pulse duration is achieved at 4 ps without dispersion compensation. With a cavity dumping technique, the pulse energy is scaling up to 40.7 μJ at 300 kHz and 14.3 μJ at 1.5 MHz.

  11. A miniature high repetition rate shock tube.

    Science.gov (United States)

    Tranter, R S; Lynch, P T

    2013-09-01

    A miniature high repetition rate shock tube with excellent reproducibility has been constructed to facilitate high temperature, high pressure, gas phase experiments at facilities such as synchrotron light sources where space is limited and many experiments need to be averaged to obtain adequate signal levels. The shock tube is designed to generate reaction conditions of T > 600 K, P shock waves with predictable characteristics are created, repeatably. Two synchrotron-based experiments using this apparatus are also briefly described here, demonstrating the potential of the shock tube for research at synchrotron light sources.

  12. A high repetition rate XUV seeding source for FLASH2

    Energy Technology Data Exchange (ETDEWEB)

    Willner, Arik

    2012-05-15

    Improved performance of free-electron laser (FEL) light sources in terms of timing stability, pulse shape and spectral properties of the amplified FEL pulses is of interest in material science, the fields of ultrafast dynamics, biology, chemistry and even special branches in industry. A promising scheme for such an improvement is direct seeding with high harmonic generation (HHG) in a noble gas target. A free-electron laser seeded by an external extreme ultraviolet (XUV) source is planned for FLASH2 at DESY in Hamburg. The requirements for the XUV/soft X-ray source can be summarized as follows: A repetition rate of at least 100 kHz in a 10 Hz burst is needed at variable wavelengths from 10 to 40 nm and pulse energies of several nJ within a single laser harmonic. This application requires a laser amplifier system with exceptional parameters, mJ-level pulse energy, 10-15 fs pulse duration at 100 kHz (1 MHz) burst repetition rate. A new optical parametric chirped-pulse amplification (OPCPA) system is under development in order to meet these requirements, and very promising results have been achieved in the last three years. In parallel to this development, a new HHG concept is necessary to sustain high average power of the driving laser system and to generate harmonics with high conversion efficiencies. Currently, the highest conversion efficiency with HHG has been demonstrated using gas-filled capillary targets. For our application, only a free-jet target can be used for HHG, in order to overcome damage threshold limitations of HHG target optics at a high repetition rate. A novel dual-gas multijet gas target has been developed and first experiments show remarkable control of the degree of phase matching forming the basis for improved control of the harmonic photon flux and the XUV pulse characteristics. The basic idea behind the dual-gas concept is the insertion of matching zones in between multiple HHG sources. These matching sections are filled with hydrogen which

  13. KAPTURE-2. A picosecond sampling system for individual THz pulses with high repetition rate

    Science.gov (United States)

    Müller, A.-S.

    2017-01-01

    This paper presents a novel data acquisition system for continuous sampling of ultra-short pulses generated by terahertz (THz) detectors. Karlsruhe Pulse Taking Ultra-fast Readout Electronics (KAPTURE) is able to digitize pulse shapes with a sampling time down to 3 ps and pulse repetition rates up to 500 MHz. KAPTURE has been integrated as a permanent diagnostic device at ANKA and is used for investigating the emitted coherent synchrotron radiation in the THz range. A second version of KAPTURE has been developed to improve the performance and flexibility. The new version offers a better sampling accuracy for a pulse repetition rate up to 2 GHz. The higher data rate produced by the sampling system is processed in real-time by a heterogeneous FPGA and GPU architecture operating up to 6.5 GB/s continuously. Results in accelerator physics will be reported and the new design of KAPTURE be discussed.

  14. Soliton repetition rate in a silicon-nitride microresonator

    CERN Document Server

    Bao, Chengying; Wang, Cong; Jaramillo-Villegas, Jose A; Leaird, Daniel E; Qi, Minghao; Weiner, Andrew M

    2016-01-01

    The repetition rate of a Kerr comb comprising a single soliton in an anomalous dispersion silicon nitride microcavity is measured as a function of pump frequency tuning. The contributions from the Raman soliton self-frequency shift (SSFS) and from thermal effects are evaluated both experimentally and theoretically; the SSFS is found to dominate the changes in repetition rate. The relationship between the changes in repetition rate and pump frequency detuning is found to be independent of the nonlinearity coefficient and dispersion of the cavity. Modeling of the repetition rate change by using the generalized Lugiato-Lefever equation is discussed; the Kerr shock is found to have only a minor effect on repetition rate for cavity solitons with duration down to ~50 fs.

  15. Soliton repetition rate in a silicon-nitride microresonator.

    Science.gov (United States)

    Bao, Chengying; Xuan, Yi; Wang, Cong; Jaramillo-Villegas, Jose A; Leaird, Daniel E; Qi, Minghao; Weiner, Andrew M

    2017-02-15

    The repetition rate of a Kerr comb composed of a single soliton in an anomalous group velocity dispersion silicon-nitride microcavity is measured as a function of pump frequency. By comparing operation in the soliton and non-soliton states, the contributions from the Raman soliton self-frequency shift (SSFS) and the thermal effects are evaluated; the SSFS is found to dominate the changes in the repetition rate, similar to silica cavities. The relationship between the changes in the repetition rate and the pump frequency detuning is found to be independent of the nonlinearity coefficient and dispersion of the cavity. Modeling of the repetition rate change by using the generalized Lugiato-Lefever equation is discussed; the Kerr shock is found to have only a minor effect on repetition rate for cavity solitons with duration down to ∼50  fs.

  16. Generation of low-timing-jitter femtosecond pulse trains with 2 GHz repetition rate via external repetition rate multiplication.

    Science.gov (United States)

    Chen, Jian; Sickler, Jason W; Fendel, Peter; Ippen, Erich P; Kärtner, Franz X; Wilken, Tobias; Holzwarth, Ronald; Hänsch, Theodor W

    2008-05-01

    Generation of low-timing-jitter 150 fs pulse trains at 1560 nm with 2 GHz repetition rate is demonstrated by locking a 200 MHz fundamental polarization additive-pulse mode-locked erbium fiber laser to high-finesse external Fabry-Perot cavities. The timing jitter and relative intensity noise of the repetition-rate multiplied pulse train are investigated.

  17. Properties of water surface discharge at different pulse repetition rates

    Energy Technology Data Exchange (ETDEWEB)

    Ruma,; Yoshihara, K. [Graduate School of Science and Technology, Kumamoto University, Kumamoto 860-8555 (Japan); Hosseini, S. H. R., E-mail: hosseini@kumamoto-u.ac.jp; Sakugawa, T.; Akiyama, H. [Graduate School of Science and Technology, Kumamoto University, Kumamoto 860-8555 (Japan); Institute of Pulsed Power Science, Kumamoto University, Kumamoto 860-8555 (Japan); Akiyama, M. [Department of Electrical and Electronic Engineering, Kagoshima University, Kagoshima 890-0065 (Japan); Lukeš, P. [Institute of Plasma Physics, AS CR, Prague, Prague 18200 (Czech Republic)

    2014-09-28

    The properties of water surface discharge plasma for variety of pulse repetition rates are investigated. A magnetic pulse compression (MPC) pulsed power modulator able to deliver pulse repetition rates up to 1000 Hz, with 0.5 J per pulse energy output at 25 kV, was used as the pulsed power source. Positive pulse with a point-to-plane electrode configuration was used for the experiments. The concentration and production yield of hydrogen peroxide (H₂O₂) were quantitatively measured and orange II organic dye was treated, to evaluate the chemical properties of the discharge reactor. Experimental results show that the physical and chemical properties of water surface discharge are not influenced by pulse repetition rate, very different from those observed for under water discharge. The production yield of H₂O₂ and degradation rate per pulse of the dye did not significantly vary at different pulse repetition rates under a constant discharge mode on water surface. In addition, the solution temperature, pH, and conductivity for both water surface and underwater discharge reactors were measured to compare their plasma properties for different pulse repetition rates. The results confirm that surface discharge can be employed at high pulse repetition rates as a reliable and advantageous method for industrial and environmental decontamination applications.

  18. Breakdown behavior of electronics at variable pulse repetition rates

    OpenAIRE

    Korte, S.; H. Garbe

    2006-01-01

    The breakdown behavior of electronics exposed to single transient electromagnetic pulses is subject of investigations for several years. State-of-the-art pulse generators additionally provide the possibility to generate pulse sequences with variable pulse repetition rate. In this article the influence of this repetition rate variation on the breakdown behavior of electronic systems is described. For this purpose microcontroller systems are examined during line-led exposure to pulses with repe...

  19. Fast phosphor picosecond streak tube for ultrafast laser diagnostics in repetitive mode

    Science.gov (United States)

    Ageeva, N. V.; Gornostaev, P. B.; Ivanova, S. R.; Kulechenkova, T. P.; Levina, G. P.; Lozovoi, V. I.; Makushina, V. A.; Schelev, M. Ya; Shashkov, E. V.; Scaballanovich, T. A.; Smirnov, A. V.; Vereschagin, A. K.; Vereschagin, K. A.; Vorobiev, N. S.

    2015-08-01

    The well-established PIF-01/S1/P43 picosecond streak tube, designed 30 years ago and still manufactured at the A.M. Prokhorov General Physics Institute, was modified by replacing its traditional P43 phosphor screen with a P47 one having approximately three orders of magnitude shorter decay time. The experimental measurements of this decay time were provided by PIF-01/S1/P47 image tube photocathode irradiation either with a single or a train of 8 ps laser pulses separated by 8 ns from each other at a 1.08 μm wavelength. The results of our preliminary measurements of P47-BH phosphor (manufactured by Phosphor Technology Ltd) indicate the possibility of employing the PIF-01/S1/P47 streak tube for synchrotron diagnostics at a units megahertz repetition rate without the negative influence of ‘ghost images’ from the previous streak records.

  20. ROBUST REPETITIVE CONTROL FOR IMPROVING RATE SMOOTHNESS OF TEST TURNTABLE

    Institute of Scientific and Technical Information of China (English)

    LIUYu; ZENGMing; SUBao-ku

    2005-01-01

    A robust repetitive control scheme is used to improve the rate smoothness of a brushless DC motor (BLDCM) driven test turntable. The method synthesizes variable structure control (VSC) laws and repetitive control (RC) laws in a complementary manner. The VSC strategy can stabilize the system and suppress uncertainties, such as the aperiodic disturbance and noises, while RC strategy can eliminate the periodic rate fluctuation in a steady state. The convergence of the repetitive learning process is also guaranteed by VSC. A general nonlinear system model is discussed. The model can be considered as an extension of BLDCMs. The stability and asymptotic position tracking performance are validated by using Lyapunov functions. Simulation results show the effectiveness of the proposed approach for improving the rate smoothness.

  1. Demonstration of a high repetition rate capillary discharge waveguide

    Energy Technology Data Exchange (ETDEWEB)

    Gonsalves, A. J., E-mail: ajgonsalves@lbl.gov; Pieronek, C.; Daniels, J.; Bulanov, S. S.; Waldron, W. L.; Mittelberger, D. E.; Leemans, W. P. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Liu, F.; Antipov, S.; Butler, J. E. [Euclid TechLabs, Gaithersburg, Maryland 20879 (United States); Bobrova, N. A.; Sasorov, P. V. [Keldysh Institute of Applied Mathematics, Moscow (Russian Federation)

    2016-01-21

    A hydrogen-filled capillary discharge waveguide operating at kHz repetition rates is presented for parameters relevant to laser plasma acceleration (LPA). The discharge current pulse was optimized for erosion mitigation with laser guiding experiments and MHD simulation. Heat flow simulations and measurements showed modest temperature rise at the capillary wall due to the average heat load at kHz repetition rates with water-cooled capillaries, which is promising for applications of LPAs such as high average power radiation sources.

  2. Medium Repetition Rate TEA Laser For Industrial Applications

    Science.gov (United States)

    Walter, Bruno

    1987-09-01

    The design and performance of an inexpensive compact repetitively pulsed TEA CO2 laser is described. The device uses a modified corona preionization technique and a fast transverse gas flow to achieve high repetition rates. An output energy of 500 mJ per pulse and an out-put power of 6.2W at 40Hz have been obtained. Due to the small energy needed for preionization, the efficiency of the device is high, whereas the gas dissociation is low when compared with commercial laser systems. This results in the relatively small fresh laser gas exchange of 20 ltr h-1 for long term operation.

  3. Diagnostic for a high-repetition rate electron photo-gun and first measurements

    Science.gov (United States)

    Filippetto, D.; Doolittle, L.; Huang, G.; Norum, E.; Portmann, G.; Qian, H.; Sannibale, F.

    2015-05-01

    The APEX electron source at LBNL combines the high-repetition-rate with the high beam brightness typical of photoguns, delivering low emittance electron pulses at MHz frequency. Proving the high beam quality of the beam is an essential step for the success of the experiment, opening the doors of the high average power to brightness-hungry applications as X-Ray FELs, MHz ultrafast electron diffraction etc.. As first step, a complete characterization of the beam parameters is foreseen at the Gun beam energy of 750 keV. Diagnostics for low and high current measurements have been installed and tested, and measurements of cathode lifetime and thermal emittance in a RF environment with mA current performed. The recent installation of a double slit system, a deflecting cavity and a high precision spectrometer, allow the exploration of the full 6D phase space. Here we discuss the present layout of the machine and future upgrades, showing the latest results at low and high repetition rate, together with the tools and techniques used.

  4. High voltage high repetition rate pulse using Marx topology

    Science.gov (United States)

    Hakki, A.; Kashapov, N.

    2015-06-01

    The paper describes Marx topology using MOSFET transistors. Marx circuit with 10 stages has been done, to obtain pulses about 5.5KV amplitude, and the width of the pulses was about 30μsec with a high repetition rate (PPS > 100), Vdc = 535VDC is the input voltage for supplying the Marx circuit. Two Ferrite ring core transformers were used to control the MOSFET transistors of the Marx circuit (the first transformer to control the charging MOSFET transistors, the second transformer to control the discharging MOSFET transistors).

  5. Ultrafast electron diffraction with megahertz MeV electron pulses from a superconducting radio-frequency photoinjector

    Energy Technology Data Exchange (ETDEWEB)

    Feng, L. W.; Lin, L.; Huang, S. L.; Quan, S. W.; Hao, J. K.; Zhu, F.; Wang, F.; Liu, K. X., E-mail: kxliu@pku.edu.cn [Institute of Heavy Ion Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Jiang, T.; Zhu, P. F.; Fu, F.; Wang, R.; Zhao, L.; Xiang, D., E-mail: dxiang@sjtu.edu.cn [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240 (China)

    2015-11-30

    We report ultrafast relativistic electron diffraction operating at the megahertz repetition rate where the electron beam is produced in a superconducting radio-frequency (rf) photoinjector. We show that the beam quality is sufficiently high to provide clear diffraction patterns from gold and aluminium samples. With the number of electrons, several orders of magnitude higher than that from a normal conducting photocathode rf gun, such high repetition rate ultrafast MeV electron diffraction may open up many new opportunities in ultrafast science.

  6. Bottle microresonator broadband and low repetition rate frequency comb generator

    CERN Document Server

    Dvoyrin, V

    2016-01-01

    We propose a new type of broadband and low repetition rate frequency comb generator which has the shape of an elongated and nanoscale-shallow optical bottle microresonator created at the surface of an optical fiber. The free spectral range (FSR) of the broadband azimuthal eigenfrequency series of this resonator is the exact multiple of the FSR of the dense and narrowband axial series. The effective radius variation of the microresonator is close to a parabola with a nanoscale height which is greater or equal to lambda/2pi*n0 (here lambda is the characteristic radiation wavelength and n0 is the refractive index of the microresonator material). Overall, the microresonator possesses a broadband, small FSR, and accurately equidistant spectrum convenient for the generation of a broadband and low repetition rate optical frequency comb. It is shown that this comb can be generated by pumping with a cw laser, which radiation frequency matches a single axial eigenfrequency of the microresonator, or, alternatively, by p...

  7. Final Report, Photocathodes for High Repetition Rate Light Sources

    Energy Technology Data Exchange (ETDEWEB)

    Ben-Zvi, Ilan [Stony Brook University

    2014-04-20

    This proposal brought together teams at Brookhaven National Laboratory (BNL), Lawrence Berkeley National Laboratory (LBNL) and Stony Brook University (SBU) to study photocathodes for high repetition rate light sources such as Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). The work done under this grant comprises a comprehensive program on critical aspects of the production of the electron beams needed for future user facilities. Our program pioneered in situ and in operando diagnostics for alkali antimonide growth. The focus is on development of photocathodes for high repetition rate Free Electron Lasers (FELs) and Energy Recovery Linacs (ERLs), including testing SRF photoguns, both normal-conducting and superconducting. Teams from BNL, LBNL and Stony Brook University (SBU) led this research, and coordinated their work over a range of topics. The work leveraged a robust infrastructure of existing facilities and the support was used for carrying out the research at these facilities. The program concentrated in three areas: a) Physics and chemistry of alkali-antimonide cathodes b) Development and testing of a diamond amplifier for photocathodes c) Tests of both cathodes in superconducting RF photoguns and copper RF photoguns

  8. Wakefield-acceleration of relativistic electrons with few-cycle laser pulses at kHz-repetition-rate

    Science.gov (United States)

    Guenot, Diego; Gustas, Dominykas; Vernier, Aline; Boehle, Frederik; Beaurepaire, Benoit; Lopez-Martens, Rodrigo; Faure, Jerome; Appli Team

    2016-10-01

    The generation of relativistic electron beams using laser wakefield acceleration has become a standard technique, providing low emittance electron bunches with femtosecond durations. However, this technique usually requires multi-ten-terawatt lasers and is thus limited to low repetition-rate (typically 10 Hz or less). We have recently demonstrated the generation of few MeV electrons using 2.5-mJ, 4-fs, 1-kHz repetition-rate laser pulses, focused to relativistic intensity onto a gas jet with electron density 1020 cm-3. We have investigated the influence of the pulse duration, the gas density. We demonstrated that an electron beam with a charge in the range of 10-fC/shot, with a divergence of 20-mrad and a peaked spectrum with energies between 2 and 4 MeV can be generated at kHz repetition-rate. These results confirm the possibility of using few-cycle laser pulses with very low energy for exciting wakefields in the bubble regime and for trapping electrons, as predicted by PIC simulations. This kHz electron source is ideally suited for performing electron diffraction experiments with very high temporal resolution. Our results also open the way to other applications, such as the generation of a kHz ultrafast X-ray source. ERC femtoelec.

  9. Design of a high repetition rate S-band photocathode gun

    Science.gov (United States)

    Han, Jang-Hui; Cox, Matthew; Huang, Houcheng; Pande, Shivaji

    2011-08-01

    Photocathode RF guns have been developed in many laboratories for generating high quality electron beams for free-electron lasers based on linear accelerators. Such guns can generate electron beams with an exceptionally high peak current as well as a small transverse emittance. Their applications have been recently expanded for ultrafast electron diffraction, coherent terahertz radiation, and X-ray or γ-ray radiation by Compton scattering. In this paper, we design an S-band normal-conducting gun with capabilities of high quality beam generation and high repetition rate operation. The RF design and thermal analysis of the gun cavity and coupler are introduced. Optimal position of the gun focusing solenoid for low emittance beam generation is found by performing particle tracking simulations. Then, the gun system is designed to be able to afford the optimal solenoid position. The cooling-water channel surrounding the gun cavity and coupler is designed and analyzed numerically. The pressure in the gun is simulated with a vacuum model containing the detailed inner structure of the gun. An injector for a free-electron laser application is designed by using this gun and the beam dynamics simulation is shown. A cold test with a prototype gun for confirmation of the RF design is reported.

  10. Resistive Wall Heating of the Undulator in High Repetition Rate

    Energy Technology Data Exchange (ETDEWEB)

    Qiang, J; Corlett, J; Emma, P; Wu, J

    2012-05-20

    In next generation high repetition rate FELs, beam energy loss due to resistive wall wakefields will produce significant amount of heat. The heat load for a superconducting undulator (operating at low temperature), must be removed and will be expensive to remove. In this paper, we study this effect in an undulator proposed for a Next Generation Light Source (NGLS) at LBNL. We benchmark our calculations with measurements at the LCLS and carry out detailed parameter studies using beam from a start-to-end simulation. Our preliminarym results suggest that the heat load in the undulator is about 2 W/m or lower with an aperture size of 6 mm for nominal NGLS preliminary design parameters.

  11. Laser-diode pumped self-mode-locked praseodymium visible lasers with multi-gigahertz repetition rate.

    Science.gov (United States)

    Zhang, Yuxia; Yu, Haohai; Zhang, Huaijin; Di Lieto, Alberto; Tonelli, Mauro; Wang, Jiyang

    2016-06-15

    We demonstrate efficient laser-diode pumped multi-gigahertz (GHz) self-mode-locked praseodymium (Pr3+) visible lasers with broadband spectra from green to deep red for the first time to our knowledge. With a Pr3+-doped GdLiF4 crystal, stable self-mode-locked visible pulsed lasers at the wavelengths of 522 nm, 607 nm, 639 nm, and 720 nm have been obtained with the repetition rates of 2.8 GHz, 3.1 GHz, 3.1 GHz, and 3.0 GHz, respectively. The maximum output power was 612 mW with the slope efficiency of 46.9% at 639 nm. The mode-locking mechanism was theoretically analyzed. The stable second-harmonic mode-locking with doubled repetition frequency was also realized based on the Fabry-Perot effect formed in the laser cavity. In addition, we find that the polarization directions were turned with lasing wavelengths. This work may provide a new way for generating efficient ultrafast pulses with high- and changeable-repetition rates in the visible range.

  12. Ultrastable fiber amplifier delivering 145-fs pulses with 6-μJ energy at 10-MHz repetition rate.

    Science.gov (United States)

    Wunram, Marcel; Storz, Patrick; Brida, Daniele; Leitenstorfer, Alfred

    2015-03-01

    A high-power femtosecond Yb:fiber amplifier operating with exceptional noise performance and long-term stability is demonstrated. It generates a 10-MHz train of 145-fs pulses at 1.03 μm with peak powers above 36 MW. The system features a relative amplitude noise of 1.5·10⁻⁶  Hz(-1/2) at 1 MHz and drifts of the 60-W average power below 0.3% over 72 hours of continuous operation. The passively phase-stable Er:fiber seed system provides ultrabroadband pulses that are synchronized at a repetition rate of 40 MHz. This combination aims at new schemes for sensitive experiments in ultrafast scientific applications.

  13. Bright high-repetition-rate source of narrowband extreme-ultraviolet harmonics beyond 22 eV

    Energy Technology Data Exchange (ETDEWEB)

    Wang, He [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Xu, Yiming [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Ulonska, Stefan [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Robinson, Joseph S. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Ranitovic, Predrag [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Kaindl, Robert A. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division

    2015-06-11

    Novel table-top sources of extreme-ultraviolet light based on high-harmonic generation yield unique insight into the fundamental properties of molecules, nanomaterials or correlated solids, and enable advanced applications in imaging or metrology. Extending high-harmonic generation to high repetition rates portends great experimental benefits, yet efficient extreme-ultraviolet conversion of correspondingly weak driving pulses is challenging. In this article, we demonstrate a highly-efficient source of femtosecond extreme-ultraviolet pulses at 50-kHz repetition rate, utilizing the ultraviolet second-harmonic focused tightly into Kr gas. In this cascaded scheme, a photon flux beyond ≈3 × 1013 s-1 is generated at 22.3 eV, with 5 × 10-5 conversion efficiency that surpasses similar harmonics directly driven by the fundamental by two orders-of-magnitude. The enhancement arises from both wavelength scaling of the atomic dipole and improved spatio-temporal phase matching, confirmed by simulations. Finally, spectral isolation of a single 72-meV-wide harmonic renders this bright, 50-kHz extreme-ultraviolet source a powerful tool for ultrafast photoemission, nanoscale imaging and other applications.

  14. Repetition rate continuously tunable 10-GHz picosecond mode-locked fiber ring laser

    Institute of Scientific and Technical Information of China (English)

    Fang Wan; Ziyu Wang

    2006-01-01

    A couple of simple-structure phase modulators were used in active mode-locked fiber laser to implement repetition rate continuous tuning. The laser produces pulse as short as 5.7 ps whose repetition rate tuning can cover the spacing of the adjoining order mode-locking frequencies.

  15. High-repetition-rate XeCl waveguide laser without gas flow

    Energy Technology Data Exchange (ETDEWEB)

    Christensen, C.P.; Gordon C. III; Moutoulas, C.; Feldman, B.J.

    1987-03-01

    Operation of a microwave discharge XeCl laser at pulse-repetition rates extending to 8 kHz without flow of the laser gas is reported. Present limits on pulse-repetition rate appear to be imposed by thermally induced refractive-index gradients.

  16. Phase-stable, multi-µJ femtosecond pulses from a repetition-rate tunable Ti:Sa-oscillator-seeded Yb-fiber amplifier

    Science.gov (United States)

    Saule, T.; Holzberger, S.; De Vries, O.; Plötner, M.; Limpert, J.; Tünnermann, A.; Pupeza, I.

    2017-01-01

    We present a high-power, MHz-repetition-rate, phase-stable femtosecond laser system based on a phase-stabilized Ti:Sa oscillator and a multi-stage Yb-fiber chirped-pulse power amplifier. A 10-nm band around 1030 nm is split from the 7-fs oscillator output and serves as the seed for subsequent amplification by 54 dB to 80 W of average power. The µJ-level output is spectrally broadened in a solid-core fiber and compressed to 30 fs with chirped mirrors. A pulse picker prior to power amplification allows for decreasing the repetition rate from 74 MHz by a factor of up to 4 without affecting the pulse parameters. To compensate for phase jitter added by the amplifier to the feed-forward phase-stabilized seeding pulses, a self-referencing feed-back loop is implemented at the system output. An integrated out-of-loop phase noise of less than 100 mrad was measured in the band from 0.4 Hz to 400 kHz, which to the best of our knowledge corresponds to the highest phase stability ever demonstrated for high-power, multi-MHz-repetition-rate ultrafast lasers. This system will enable experiments in attosecond physics at unprecedented repetition rates, it offers ideal prerequisites for the generation and field-resolved electro-optical sampling of high-power, broadband infrared pulses, and it is suitable for phase-stable white light generation.

  17. Spin-state studies with XES and RIXS: From static to ultrafast

    DEFF Research Database (Denmark)

    Vankó, György; Bordage, Amélie; Glatzel, Pieter

    2013-01-01

    We report on extending hard X-ray emission spectroscopy (XES) along with resonant inelastic X-ray scattering (RIXS) to study ultrafast phenomena in a pump-probe scheme at MHz repetition rates. The investigated systems include low-spin (LS) FeII complex compounds, where optical pulses induce a spi...... exploited to study chemical and physical transformations on ultrafast time scales....

  18. Safety and efficacy of low fluence, high repetition rate versus high fluence, low repetition rate 810-nm diode laser for axillary hair removal in Chinese women.

    Science.gov (United States)

    Li, Wenhai; Liu, Chengyi; Chen, Zhou; Cai, Lin; Zhou, Cheng; Xu, Qianxi; Li, Houmin; Zhang, Jianzhong

    2016-11-01

    High-fluence diode lasers with contact cooling have emerged as the gold standard to remove unwanted hair. Lowering the energy should result in less pain and could theoretically affect the efficacy of the therapy. To compare the safety and efficacy of a low fluence high repetition rate 810-nm diode laser to those of a high fluence, low repetition rate diode laser for permanent axillary hair removal in Chinese women. Ninety-two Chinese women received four axillae laser hair removal treatments at 4-week intervals using the low fluence, high repetition rate 810-nm diode laser in super hair removal (SHR) mode on one side and the high fluence, low repetition rate diode laser in hair removal (HR) mode on the other side. Hair counts were done at each follow-up visit and 6-month follow-up after the final laser treatment using a "Hi Quality Hair Analysis Program System"; the immediate pain score after each treatment session was recorded by a visual analog scale. The overall median reduction of hair was 90.2% with the 810-nm diode laser in SHR mode and 87% with the same laser in HR mode at 6-month follow-up. The median pain scores in SHR mode and in HR mode were 2.75 and 6.75, respectively. Low fluence, high repetition rate diode laser can efficiently remove unwanted hair but also significantly improve tolerability and reduce adverse events during the course of treatment.

  19. Roadmap on ultrafast optics

    Science.gov (United States)

    Reid, Derryck T.; Heyl, Christoph M.; Thomson, Robert R.; Trebino, Rick; Steinmeyer, Günter; Fielding, Helen H.; Holzwarth, Ronald; Zhang, Zhigang; Del'Haye, Pascal; Südmeyer, Thomas; Mourou, Gérard; Tajima, Toshiki; Faccio, Daniele; Harren, Frans J. M.; Cerullo, Giulio

    2016-09-01

    The year 2015 marked the 25th anniversary of modern ultrafast optics, since the demonstration of the first Kerr lens modelocked Ti:sapphire laser in 1990 (Spence et al 1990 Conf. on Lasers and Electro-Optics, CLEO, pp 619-20) heralded an explosion of scientific and engineering innovation. The impact of this disruptive technology extended well beyond the previous discipline boundaries of lasers, reaching into biology labs, manufacturing facilities, and even consumer healthcare and electronics. In recognition of such a milestone, this roadmap on Ultrafast Optics draws together articles from some of the key opinion leaders in the field to provide a freeze-frame of the state-of-the-art, while also attempting to forecast the technical and scientific paradigms which will define the field over the next 25 years. While no roadmap can be fully comprehensive, the thirteen articles here reflect the most exciting technical opportunities presented at the current time in Ultrafast Optics. Several articles examine the future landscape for ultrafast light sources, from practical solid-state/fiber lasers and Raman microresonators to exotic attosecond extreme ultraviolet and possibly even zeptosecond x-ray pulses. Others address the control and measurement challenges, requiring radical approaches to harness nonlinear effects such as filamentation and parametric generation, coupled with the question of how to most accurately characterise the field of ultrafast pulses simultaneously in space and time. Applications of ultrafast sources in materials processing, spectroscopy and time-resolved chemistry are also discussed, highlighting the improvements in performance possible by using lasers of higher peak power and repetition rate, or by exploiting the phase stability of emerging new frequency comb sources.

  20. Femtosecond and picosecond laser drilling of metals at high repetition rates and average powers.

    Science.gov (United States)

    Ancona, A; Döring, S; Jauregui, C; Röser, F; Limpert, J; Nolte, S; Tünnermann, A

    2009-11-01

    The influence of pulse duration on the laser drilling of metals at repetition rates of up to 1 MHz and average powers of up to 70 W has been experimentally investigated using an ytterbium-doped-fiber chirped-pulse amplification system with pulses from 800 fs to 19 ps. At a few hundred kilohertz particle shielding causes an increase in the number of pulses for breakthrough, depending on the pulse energy and duration. At higher repetition rates, the heat accumulation effect overbalances particle shielding, but significant melt ejection affects the hole quality. Using femtosecond pulses, heat accumulation starts at higher repetition rates, and the ablation efficiency is higher compared with picosecond pulses.

  1. Pulsed pumped Yb-doped fiber amplifier at low repetition rate

    Institute of Scientific and Technical Information of China (English)

    Changgeng Ye; Ping Yan; Mali Gong; Ming Lei

    2005-01-01

    A pulsed pumped Yb-doped double-clad fiber (DCF) master-oscillator power amplifier (MOPA) at low repetition rate is reported. Seeded by a passive Q-switched Nd:YAG microchip laser, the fiber amplifier can generate 167-kW peak-power and 0.83-ns duration pulses at 200-Hz repetition rate. Because of the pulsed pump approach, the amplified spontaneous emission (ASE) and the spurious lasing between pulses are well avoided, and the repetition rate can be set freely from single-shot to 1 kHz. Peak power scaling limitations that arise from the fiber facet damage are discussed.

  2. Hydrodynamic size distribution of gold nanoparticles controlled by repetition rate during pulsed laser ablation in water

    Science.gov (United States)

    Menéndez-Manjón, Ana; Barcikowski, Stephan

    2011-02-01

    Most investigations on the laser generation and fragmentation of nanoparticles focus on Feret particle size, although the hydrodynamic size of nanoparticles is of great importance, for example in biotechnology for diffusion in living cells, or in engineering, for a tuned rheology of suspensions. In this sense, the formation and fragmentation of gold colloidal nanoparticles using femtosecond laser ablation at variable pulse repetition rates (100-5000 Hz) in deionized water were investigated through their plasmon resonance and hydrodynamic diameter, measured by Dynamic Light Scattering. The increment of the repetition rate does not influence the ablation efficiency, but produces a decrease of the hydrodynamic diameter and blue-shift of the plasmon resonance of the generated gold nanoparticles. Fragmentation, induced by inter-pulse irradiation of the colloids was measured online, showing to be more effective low repetition rates. The pulse repetition rate is shown to be an appropriate laser parameter for hydrodynamic size control of nanoparticles without further influence on the production efficiency.

  3. High Energy Single Frequency Fiber Laser at Low Repetition Rate Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This SBIR phase II project proposes a single frequency high energy fiber laser system operating at low repetition rate of 10 Hz to 1 kHz for coherent Lidar systems...

  4. Repetition rate tunable ultra-short optical pulse generation based on electrical pattern generator

    Institute of Scientific and Technical Information of China (English)

    Xin Fu; Hongming Zhang; Meng Yan; Minyu Yao

    2009-01-01

    @@ An actively mode-locked laser with tunable repetition rate is proposed and experimentally demonstrated based on a programmable electrical pattern generator.By changing the repetition rate of the electrical patterns applied on the in-cavity modulator, the repetition rate of the output optical pulse sequences changes accordingly while the pulse width of the optical pulse train remains almost constant.In other words, the output ultra-short pulse train has a tunable duty cycle.In a proof-of-principle experiment, optical pulses with repetition rates of 10, 5, 2.5 and 1.25 GHz are obtained by adjusting the electrical pattern applied on the in-cavity modulator while their pulse widths remain almost unchanged.

  5. Femtosecond Ti:sapphire cryogenic amplifier with high gain and MHz repetition rate.

    Science.gov (United States)

    Dantan, Aurélien; Laurat, Julien; Ourjoumtsev, Alexei; Tualle-Brouri, Rosa; Grangier, Philippe

    2007-07-09

    We demonstrate high gain amplification of 160-femtosecond pulses in a compact double-pass cryogenic Ti:sapphire amplifier. The setup involves a negative GVD mirrors recompression stage, and operates with a repetition rate between 0.2 and 4 MHz with a continuous pump laser. Amplification factors as high as 17 and 320 nJ Fourier-limited pulses are obtained at a 800 kHz repetition rate.

  6. High repetition rate femtosecond dye amplifier using a laser diode pumped neodymium:YAG laser

    Energy Technology Data Exchange (ETDEWEB)

    Zysset, B.; LaGasse, M.J.; Fujimoto, J.G.; Kafka, J.D.

    1989-02-06

    A high repetition rate femtosecond dye amplifier is demonstrated using a laser diode pumped Q-switched Nd:YAG laser. Amplification of wavelength tunable 300 fs pulses from a synchronously mode-locked rhodamine dye laser is achieved with a saturated gain of 70 and a small gain of 200 at a repetition rate of 800 Hz. Maximum pulse energies of 40 nJ are obtained, and pulse compression to as short as 30 fs is demonstrated.

  7. High repetition rate femtosecond dye amplifier using a laser diode pumped neodymium:YAG laser

    Science.gov (United States)

    Zysset, B.; LaGasse, M. J.; Fujimoto, J. G.; Kafka, J. D.

    1989-02-01

    A high repetition rate femtosecond dye amplifier is demonstrated using a laser diode pumped Q-switched Nd:YAG laser. Amplification of wavelength tunable 300 fs pulses from a synchronously mode-locked rhodamine dye laser is achieved with a saturated gain of 70 and a small gain of 200 at a repetition rate of 800 Hz. Maximum pulse energies of 40 nJ are obtained, and pulse compression to as short as 30 fs is demonstrated.

  8. Coupling coefficient for TEA CO2 laser propulsion with variable pulse repetition rate

    Institute of Scientific and Technical Information of China (English)

    Yijun Zheng; Rongqing Tan; Donglei Wang; Guang Zheng; Changjun Ke; Kuohai Zhang; Chongyi Wan; Jin Wu

    2006-01-01

    @@ Because pulse repetition rate affected directly the momentum coupling coefficient of transversely excited atmospheric (TEA) CO2 laser propulsion, a double pulse trigger, controlling high voltage switch of laser excitation circuit, was designed. The pulse interval ranged between 5 and 100 ms. The momentum coupling coefficient for air-breathing mode laser propulsion was studied experimentally. It was found that the momentum coupling coefficient decreased with the pulse repetition rate increasing.

  9. Relaxation rate for an ultrafast folding protein is independent of chemical denaturant concentration.

    Science.gov (United States)

    Cellmer, Troy; Henry, Eric R; Kubelka, Jan; Hofrichter, James; Eaton, William A

    2007-11-28

    The connection between free-energy surfaces and chevron plots has been investigated in a laser temperature jump kinetic study of a small ultrafast folding protein, the 35-residue subdomain from the villin headpiece. Unlike all other proteins that have been studied so far, no measurable dependence of the unfolding/refolding relaxation rate on denaturant concentration was observed over a wide range of guanidinium chloride concentration. Analysis with a simple Ising-like theoretical model shows that this denaturant-invariant relaxation rate can be explained by a large movement of the major free energy barrier, together with a denaturant- and reaction coordinate-dependent diffusion coefficient.

  10. Intense high repetition rate Mo Kα x-ray source generated from laser solid interaction for imaging application

    Energy Technology Data Exchange (ETDEWEB)

    Huang, K.; Li, M. H.; Yan, W. C.; Ma, Y.; Zhao, J. R.; Li, Y. F.; Chen, L. M., E-mail: lmchen@iphy.ac.cn [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China); Guo, X. [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China); Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); School of Optoelectronics, Beijing Institute of Technology, Beijing 100081 (China); Li, D. Z. [Institute of High Energy Physics, CAS, Beijing 100049 (China); Chen, Y. P.; Zhang, J. [Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China)

    2014-11-15

    We report an efficient Mo Kα x-ray source produced by interaction of femtosecond Ti: sapphire laser pulses with a solid Molybdenum target working at 1 kHz repetition rate. The generated Mo Kα x-ray intensity reaches to 4.7 × 10{sup 10} photons sr{sup −1} s{sup −1}, corresponding to an average power of 0.8 mW into 2π solid angle. The spatial resolution of this x-ray source is measured to be 26 lp/mm. With the high flux and high spatial resolution characteristics, high resolving in-line x-ray radiography was realized on test objects and large size biological samples within merely half a minute. This experiment shows the possibility of laser plasma hard x-ray source as a new low cost and high resolution system for radiography and its ability of ultrafast x-ray pump-probe study of matter.

  11. Switchable repetition rate bound solitons passively mode-locked fiber laser

    Science.gov (United States)

    Wang, Xuqin; Yao, Yong

    2016-11-01

    We present a kind of a switchable repetition rate mode-locked of bound-state solitons in a fiber laser based on Bi2Se3 saturable absorber (SA). In the fiber laser, two forms of the bound-state optical spectrum with central wavelength of 1532 nm are observed. The fiber laser is operate at the abnormal group velocity dispersion and the bound state pulses are equally distributed to the temporal domain. The fundamental cavity repetition-rate is 1.11 MHz with a pulse duration of 2.27 ps. The output average power and the pulse peak energy are 1.53 mW and 607 W respectively, which the pump power is 267 mW. The different repetition-rates are also achieved by changing the pump power or adjusting the angle of polarization controller. In the experiment, the repetition-rate is switched from 1.11 MHz to 41.32 MHz (37th-order, the highest repetition-rate).

  12. Multi-Rate Fractional-Order Repetitive Control of Shunt Active Power Filter

    DEFF Research Database (Denmark)

    Xie, Chuan; Zhao, Xin; Savaghebi, Mehdi

    2017-01-01

    This paper presents a multi-rate fractional-order repetitive control (MRFORC) scheme for three-phase shunt active power filter (APF). The proposed APF control scheme includes an inner proportional-integral (PI) control loop with a sampling rate identical to switching frequency and an external plug-in...

  13. Near- infrared, mode-locked waveguide lasers with multi-GHz repetition rates

    Science.gov (United States)

    Choudhary, A.; Lagatsky, A. A.; Zhang, Z. Y.; Zhou, K. J.; Wang, Q.; Hogg, R. A.; Pradeesh, K.; Rafailov, E. U.; Resan, B.; Oehler, A. E. H.; Weingarten, K. J.; Sibbett, W.; Brown, C. T. A.; Shepherd, D. P.

    2014-02-01

    In this work, we discuss mode-locking results obtained with low-loss, ion-exchanged waveguide lasers. With Yb3+-doped phosphate glass waveguide lasers, a repetition rate of up to 15.2 GHz was achieved at a wavelength of 1047 nm with an average power of 27 mW and pulse duration of 811 fs. The gap between the waveguide and the SESAM introduced negative group velocity dispersion via the Gires Tournois Interferometer (GTI) effect which allowed the soliton mode-locking of the device. A novel quantum dot SESAM was used to mode-lock Er3+, Yb3+-doped phosphate glass waveguide lasers around 1500 nm. Picosecond pulses were achieved at a maximum repetition rate of 6.8 GHz and an average output power of 30 mW. The repetition rate was tuned by more than 1 MHz by varying the pump power.

  14. Design of a low emittance and high repetition rate S-band photoinjector

    Science.gov (United States)

    Han, Jang-Hui

    2014-09-01

    As an electron beam injector of X-ray free-electron lasers (FELs), photoinjectors have been developed for the past few decades. Such an injector starting with a photocathode RF gun provides high brightness beams and therefore it is being adopted as an injector of X-ray FELs. In this paper we show how to improve photoinjector performance in terms of emittance and repetition rates by means of injector components optimization, especially with the gun. Transverse emittance at the end of an injector is reduced by optimizing the gun design, gun solenoid position, and accelerating section position. The repetition rate of an injector mainly depends on the gun. It is discussed that a repetition rate of 1 kHz at a normal-conducting S-band photoinjector is feasible by adopting a coaxial RF coupler and improving cooling-water channels surrounding the gun.

  15. Single Longitudinal Mode, High Repetition Rate, Q-switched Ho:YLF Laser for Remote Sensing

    Science.gov (United States)

    Bai, Yingxin; Yu, Jirong; Petzar, Paul; Petros, M.; Chen, Songsheng; Trieu, Bo; Lee, Nyung; Singh, U.

    2009-01-01

    Ho:YLF/LuLiF lasers have specific applications for remote sensing such as wind-speed measurement and carbon dioxide (CO2) concentration measurement in the atmosphere because the operating wavelength (around 2 m) is located in the eye-safe range and can be tuned to the characteristic lines of CO2 absorption and there is strong backward scattering signal from aerosol (Mie scattering). Experimentally, a diode pumped Ho:Tm:YLF laser has been successfully used as the transmitter of coherent differential absorption lidar for the measurement of with a repetition rate of 5 Hz and pulse energy of 75 mJ [1]. For highly precise CO2 measurements with coherent detection technique, a laser with high repetition rate is required to averaging out the speckle effect [2]. In addition, laser efficiency is critically important for the air/space borne lidar applications, because of the limited power supply. A diode pumped Ho:Tm:YLF laser is difficult to efficiently operate in high repetition rate due to the large heat loading and up-conversion. However, a Tm:fiber laser pumped Ho:YLF laser with low heat loading can be operated at high repetition rates efficiently [3]. No matter whether wind-speed or carbon dioxide (CO2) concentration measurement is the goal, a Ho:YLF/LuLiF laser as the transmitter should operate in a single longitudinal mode. Injection seeding is a valid technique for a Q-switched laser to obtain single longitudinal mode operation. In this paper, we will report the new results for a single longitudinal mode, high repetition rate, Q-switched Ho:YLF laser. In order to avoid spectral hole burning and make injection seeding easier, a four mirror ring cavity is designed for single longitudinal mode, high repetition rate Q-switched Ho:YLF laser. The ramp-fire technique is chosen for injection seeding.

  16. High repetition rate passively Q-switched fiber and microchip lasers for optical resolution photoacoustic imaging

    Science.gov (United States)

    Shi, Wei; Utkin, Ilya; Ranasinghesagara, Janaka; Pan, Lei; Godwal, Yogesh; Kerr, Shaun; Zemp, Roger J.; Fedosejevs, Robert

    2010-02-01

    Optical-resolution photoacoustic microscopy is a novel imaging technology for visualizing optically-absorbing superficial structures in vivo with lateral spatial resolution determined by optical focusing rather than acoustic detection. Since scanning of the illumination spot is required, the imaging speed is limited by the scanning speed and the laser pulse repetition rate. Unfortunately, lasers with high-repetition rate and suitable pulse durations and energies are difficult to find. We are developing compact laser sources for this application. Passively Q-switched fiber and microchip lasers with pulse repetition rates up to 300 kHz are demonstrated. Using a diode-pumped microchip laser fiber-coupled to a large mode-area Yb-doped fiber amplifier we obtained 60μJ 1-ns pulses at the frequency-doubled 532-nm wavelength. The pulse-repetition rate was determined by the power of the microchip laser pump source at 808nm and may exceed 10 kHz. Additionally, a passively Q-switched fiber laser utilizing a Yb-doped double-cladding fiber and an external saturable absorber has shown to produce 250ns pulses at repetition rates of 100-300 KHz. A photoacoustic probe enabling flexible scanning of the focused output of these lasers consisted of a 45-degree glass prism in an optical index-matching fluid. Photoacoustic signals exiting the sample are deflected by the prism to an ultrasound transducer. Phantom studies with a 7.5-micron carbon fiber demonstrate the ability to image with optical rather than acoustic resolution. We believe that the high pulse-repetition rates and the potentially compact and fiber-coupled nature of these lasers will prove important for clinical imaging applications where realtime imaging performance is essential.

  17. A contactless microwave-based diagnostic tool for high repetition rate laser systems

    CERN Document Server

    Braggio, C

    2014-01-01

    We report on a novel electro-optic device for the diagnostics of high repetition rate laser systems. It is composed of a microwave receiver and of a second order nonlinear crystal, whose irradiation with a train of short laser pulses produces a time-dependent polarization in the crystal itself as a consequence of optical rectification. This process gives rise to the emission of microwave radiation that is detected by a receiver and is analyzed to infer the repetition rate and intensity of the pulses. We believe that this new method may overcome some of the limitations of photodetection techniques.

  18. Low-loss waveguides fabricated in BK7 glass by high repetition rate femtosecond fiber laser.

    Science.gov (United States)

    Eaton, Shane M; Ng, Mi Li; Bonse, Jörn; Mermillod-Blondin, Alexandre; Zhang, Haibin; Rosenfeld, Arkadi; Herman, Peter R

    2008-04-20

    For the first time femtosecond-laser writing has inscribed low-loss optical waveguides in Schott BK7 glass, a commercially important type of borosilicate widely used in optical applications. The use of a variable repetition rate laser enabled the identification of a narrow processing window at 1 MHz repetition rate with optimal waveguides exhibiting propagation losses of 0.3 dB/cm and efficient mode matching to standard optical fibers at a 1550 nm wavelength. The waveguides were characterized by complementary phase contrast and optical transmission microscopy, identifying a micrometer-sized guiding region within a larger complex structure of both positive and negative refractive index variations.

  19. High-q microring resonator with narrow free spectral range for pulse repetition rate multiplication

    DEFF Research Database (Denmark)

    Pu, Minhao; Ji, Hua; Frandsen, Lars Hagedorn

    2009-01-01

    We demonstrate a silicon-on-insulator microring resonator with a free-spectral-range of 0.32 nm, an extinction ratio of 27 dB, and a quality factor of ~140900 at 1550 nm that is used for pulse repetition-rate multiplication from 10 to 40 GHz.......We demonstrate a silicon-on-insulator microring resonator with a free-spectral-range of 0.32 nm, an extinction ratio of 27 dB, and a quality factor of ~140900 at 1550 nm that is used for pulse repetition-rate multiplication from 10 to 40 GHz....

  20. Programmable Control of the Pulse Repetition Rate in the Multiwave Strontium Vapor Laser System

    Directory of Open Access Journals (Sweden)

    Soldatov Anatoly

    2016-01-01

    Full Text Available The aim of the present work was the development of laser systems for ablation of biological tissues with a programmable control over the lasing pulse repetition rate in a wide range. A two-stage laser system consisting of a master oscillator and a power amplifier based on strontium vapor laser has been developed. The operation of the laser system in a single-pulse mode operation, multipulse mode operation, and with a pulse repetition rate up to 20 kHz has been technically implemented. The possibility of a bone tissue ablation with no visible thermal damage is shown.

  1. Injector Beam Dynamics for a High-Repetition Rate 4th-Generation Light Source

    Energy Technology Data Exchange (ETDEWEB)

    Papadopoulos, C. F.; Corlett, J.; Emma, P.; Filippetto, D.; Penn, G.; Qiang, J.; Reinsch, M.; Sannibale, F.; Steier, C.; Venturini, M.; Wells, R.

    2013-05-20

    We report on the beam dynamics studies and optimization methods for a high repetition rate (1 MHz) photoinjector based on a VHF normal conducting electron source. The simultaneous goals of beamcompression and reservation of 6-dimensional beam brightness have to be achieved in the injector, in order to accommodate a linac driven FEL light source. For this, a parallel, multiobjective optimization algorithm is used. We discuss the relative merits of different injector design points, as well as the constraints imposed on the beam dynamics by technical considerations such as the high repetition rate.

  2. Frequency and amplitude characteristics of a high-repetition-rate hybrid TEA-CO/sub 2/ laser

    Energy Technology Data Exchange (ETDEWEB)

    Lachambre, J.L.; Lavigne, P.; Verreault, M.; Otis, G.

    1978-02-01

    The envelope and frequency characteristics of the output pulse of a high-repetition-rate hybrid TEA-CO/sub 2/ laser are presented. Both the intrapulse and interpulse laser frequency stability are experimentally determined at repetition rates up to 300 Hz. The recovery of the CW laser signal following the generation of the TEA laser pulse is analyzed theoretically and experimentally. Short term reproducibilities of + or - 2 MHz are observed at a pulse repetition rate of 300 Hz with initial chirp rates of about 1.5 MHz/microsec. Improvements and limits on power and repetition rate are discussed.

  3. Femtosecond Ti:sapphire cryogenic amplifier with high gain and MHz repetition rate

    DEFF Research Database (Denmark)

    Dantan, Aurelien Romain; Laurat, Julien; Ourjoumtsev, Alexei

    2007-01-01

    We demonstrate high gain amplification of 160-femtosecond pulses in a compact double-pass cryogenic Ti:sapphire amplifier. The setup involves a negative GVD mirrors recompression stage, and operates with a repetition rate between 0.2 and 4 MHz with a continuous pump laser. Amplification factors...

  4. Effect of the pulse repetition rate on fiber-assisted tissue ablation

    Science.gov (United States)

    Kang, Hyun Wook

    2016-07-01

    The effect of the pulse repetition rate on ablation performance was evaluated ex vivo at various fiber sweeping speeds for an effective 532-nm laser prostatectomy. Three pulse repetition rates (7.5, 15, and 30 kHz) at 100 W were delivered to bovine liver tissue at three sweeping speeds (2, 4, and 6 mm/s) to achieve bulky tissue removal. Ablation performance was quantitatively compared in terms of the ablation volume and the coagulation thickness. The lowest pulse repetition rate of 7.5 kHz attained the highest ablation volume (101.5 ± 12.0 mm3) and the thinnest coagulation (0.7 ± 0.1 mm) along with superficial carbonization. The highest pulse repetition rate of 30 kHz was associated with the least tissue removal (65.8 ± 5.0 mm3) and the deepest thermal denaturation (1.1 ± 0.2 mm). Quantitative evaluations of laser parameters can be instrumental in facilitating ablation efficiency and maintaining hemostatic coagulation during treatment of large-sized benign prostate hyperplasia.

  5. Operation and Thermal Modeling of the ISIS H– Source from 50 to 2 Hz Repetition Rates

    CERN Document Server

    Pereira, H; Lettry, J

    2013-01-01

    CERN’s Linac4 accelerator H− ion source, currently under construction, will operate at a 2 Hz repetition rate, with pulse length of 0.5 ms and a beam current of 80 mA. Its reliability must exceed 99 % with a mandatory 3 month uninterrupted operation period. A Penning ion source is successfully operated at ISIS; at 50 Hz repetition rate it reliably provides 55 mA H− pulses of 0.25 ms duration over 1 month. The discharge plasma ignition is very sensitive to the temperatures of the discharge region, especially of its cathode. The investigation by modeling and measurement of operation parameters suitable for arc ignition and H− production at 2 Hz is of paramount importance and must be understood prior to the implementation of discharge ion sources in the Linac4 accelerator. In its original configuration, the ISIS H− source delivers beam only if the repetition rate is above 12.5 Hz, this paper describes the implementation of a temperature control of the discharge region aiming at lower repetition rate op...

  6. High Repetition Rate and Frequency Stabilized Ho:YLF Laser for CO2 Differential Absorption Lidar

    Science.gov (United States)

    Bai, Yingxin; Yu, Jirong; Petros, M.; Petzar, Pau; Trieu, Bo; Lee, Hyung; Singh, U.

    2009-01-01

    High repetition rate operation of an injection seeded Ho:YLF laser has been demonstrated. For 1 kHz operation, the output pulse energy reaches 5.8mJ and the optical-to-optical efficiency is 39% when the pump power is 14.5W.

  7. DFB diode seeded low repetition rate fiber laser system operating in burst mode

    Science.gov (United States)

    Šajn, M.; Petelin, J.; Agrež, V.; Vidmar, M.; Petkovšek, R.

    2017-02-01

    A distributed feedback (DFB) diode, gain switched to produce pulses from 60 ps at high peak power of over 0.5 W, is used in burst mode to seed a fiber amplifier chain. High seed power, spectral filtering between amplifier stages and pulsed pumping are used to mitigate amplified spontaneous emission (ASE). The effect of pulse pumping synchronized with the seed on the ASE is explored for the power amplifier at low repetition. Different input and output energies at different burst repetition rates are examined and up to 85% reduction in ASE is achieved compared to continuous pumping. Finally, a numerical model is used to predict further reduction of ASE.

  8. Passively Mode-Locked Fiber Laser with a Sub-Megahertz Repetition Rate

    Institute of Scientific and Technical Information of China (English)

    CHEN Jiong; JIA Dong-Fang; WU Yong-Chao; WANG Chang-Le; WANG Zhao-Ying; YANG Tian-Xin

    2011-01-01

    We demonstrate an ultra-long cavity by which an all-fiber erbium-doped fiber laser is passively mode-locked by nonlinear polarization rotation.The length of the resonant cavity amounts to 466m,which can be achieved by incorporating a 420m highly nonlinear fiber.The laser generates stable mode-locked pulses with a 444 kHz fundamental repetition rate.A near transform-limited subpicosecond pulse is obtained without any dispersion compensation.The maximum average power of the output pulses is 5.16 mW,which corresponds to a per-pulse energy of 11.62nJ.A low-repetition-rate optical pulse train is required for many applications such as micromachining,biomedical diagnostics and lidar systems.[1-3] However,the repetition rate of conventional fiber lasers is normally tens of MHz.Pulse pickers such as Pockels cells or acousto-optic modulators are always used to lower the repetition rate,however,reduction in this way introduces significant energy losses,impairs the signal-to-noise ratio (SNR) and increases complexity.Because the pulse repetition rate of a modelocked laser is inversely proportional to its resonator length,longer cavities lead to lower pulse repetition rates and,consequently,to higher pulse energy at the same average power of radiation.%We demonstrate an ultra-long cavity by which an all-fiber erbium-doped fiber laser is passively mode-locked by nonlinear polarization rotation. The length of the resonant cavity amounts to 466 m, which can be achieved by incorporating a 420 m highly nonlinear fiber. The laser generates stable mode-locked pulses with a 444 kHz fundamental repetition rate. A near transform-limited subpicosecond pulse is obtained without any dispersion compensation. The maximum average power of the output pulses is 5.16mW, which corresponds to a per-pulse energy of 11.62 nJ.

  9. Effect of Repetition Rate on Femtosecond Laser-Induced Homogenous Microstructures

    Directory of Open Access Journals (Sweden)

    Sanchari Biswas

    2016-12-01

    Full Text Available We report on the effect of repetition rate on the formation and surface texture of the laser induced homogenous microstructures. Different microstructures were micromachined on copper (Cu and titanium (Ti using femtosecond pulses at 1 and 10 kHz. We studied the effect of the repetition rate on structure formation by comparing the threshold accumulated pulse ( F Σ p u l s e values and the effect on the surface texture through lacunarity analysis. Machining both metals at low F Σ p u l s e resulted in microstructures with higher lacunarity at 10 kHz compared to 1 kHz. On increasing F Σ p u l s e , the microstructures showed higher lacunarity at 1 kHz. The effect of the repetition rate on the threshold F Σ p u l s e values were, however, considerably different on the two metals. With an increase in repetition rate, we observed a decrease in the threshold F Σ p u l s e on Cu, while on Ti we observed an increase. These differences were successfully allied to the respective material characteristics and the resulting melt dynamics. While machining Ti at 10 kHz, the melt layer induced by one laser pulse persists until the next pulse arrives, acting as a dielectric for the subsequent pulse, thereby increasing F Σ p u l s e . However, on Cu, the melt layer quickly resolidifies and no such dielectric like phase is observed. Our study contributes to the current knowledge on the effect of the repetition rate as an irradiation parameter.

  10. Effect of Repetition Rate on Femtosecond Laser-Induced Homogenous Microstructures.

    Science.gov (United States)

    Biswas, Sanchari; Karthikeyan, Adya; Kietzig, Anne-Marie

    2016-12-19

    We report on the effect of repetition rate on the formation and surface texture of the laser induced homogenous microstructures. Different microstructures were micromachined on copper (Cu) and titanium (Ti) using femtosecond pulses at 1 and 10 kHz. We studied the effect of the repetition rate on structure formation by comparing the threshold accumulated pulse ( F Σ p u l s e ) values and the effect on the surface texture through lacunarity analysis. Machining both metals at low F Σ p u l s e resulted in microstructures with higher lacunarity at 10 kHz compared to 1 kHz. On increasing F Σ p u l s e , the microstructures showed higher lacunarity at 1 kHz. The effect of the repetition rate on the threshold F Σ p u l s e values were, however, considerably different on the two metals. With an increase in repetition rate, we observed a decrease in the threshold F Σ p u l s e on Cu, while on Ti we observed an increase. These differences were successfully allied to the respective material characteristics and the resulting melt dynamics. While machining Ti at 10 kHz, the melt layer induced by one laser pulse persists until the next pulse arrives, acting as a dielectric for the subsequent pulse, thereby increasing F Σ p u l s e . However, on Cu, the melt layer quickly resolidifies and no such dielectric like phase is observed. Our study contributes to the current knowledge on the effect of the repetition rate as an irradiation parameter.

  11. Longitudinally excited CO2 laser with short laser pulse operating at high repetition rate

    Science.gov (United States)

    Li, Jianhui; Uno, Kazuyuki; Akitsu, Tetsuya; Jitsuno, Takahisa

    2016-11-01

    A short-pulse longitudinally excited CO2 laser operating at a high repetition rate was developed. The discharge tube was made of a 45 cm-long or 60 cm-long dielectric tube with an inner diameter of 16 mm and two metallic electrodes at the ends of the tube. The optical cavity was formed by a ZnSe output coupler with a reflectivity of 85% and a high-reflection mirror. Mixed gas (CO2:N2:He = 1:1:2) was flowed into the discharge tube. A high voltage of about 33 kV with a rise time of about 200 ns was applied to the discharge tube. At a repetition rate of 300 Hz and a gas pressure of 3.4 kPa, the 45 cm-long discharge tube produced a short laser pulse with a laser pulse energy of 17.5 mJ, a spike pulse energy of 0.2 mJ, a spike width of 153 ns, and a pulse tail length of 90 μs. The output power was 5.3 W. The laser pulse waveform did not depend on the repetition rate, but the laser beam profile did. At a low repetition rate of less than 50 Hz, the laser beam had a doughnut-like shape. However, at a high repetition rate of more than 150 Hz, the discharge concentrated at the center of the discharge tube, and the intensity at the center of the laser beam was higher. The laser beam profile depended on the distribution of the discharge. An output power of 7.0 W was achieved by using the 60 cm-long tube.

  12. Ultrafast technologies for photonic networks

    Science.gov (United States)

    Prucnal, Paul R.; Baby, Varghese; Xu, Lei; Glesk, Ivan

    2004-10-01

    Considerable progress has been in the last decade in the fields of photonic networks and ultra-fast optics. The past few years has seen the widespread use of wavelength division multiplexing (WDM) to provide enormous point-to-point capacity in the backbone and metro area networks. Remarkable progress in electronics, in terms of both costs and performance speeds, has to some extent alleviated the 'electronic bottleneck'. Developments in fiber-optics such as novel fiber types and Raman amplification have opened up additional wavelength regions of operation resulting in great expansion of usable fiber bandwidth. There exist unique opportunities for ultrafast technologies - a subject of much interest in the last decade and reaching a point of maturity - to complement these advances and spark the next generation networks. In our talk, we will mention two networking environments very different from WDM - (1) optical time division multiplexing (OTDM) and (2) optical code division multiple access (OCDMA). We will look at the potential of both these scenarios for different applications, focusing in particular on the latter as an approach that provides maximum flexibility to utilize the immense bandwidth of the optical fiber. We will also describe various ultra-fast technologies that have been developed e.g. .high repetition rate pulsed lasers, ultra-fast optical switches, time delay elements etc. which have a direct relevance to both these types of networks.

  13. Effects of picosecond laser repetition rate on ablation of Cr12MoV cold work mold steel

    Science.gov (United States)

    Wu, Baoye; Deng, Leimin; Liu, Peng; Zhang, Fei; Duan, Jun; Zeng, Xiaoyan

    2017-07-01

    In this paper, the effects of pulse repetition rate on ablation efficiency and quality of Cr12MoV cold work mold steel have been studied using a picosecond (ps) pulse Nd:YVO4 laser system at λ= 1064 nm. The experimental results of area ablation on target surface reveal that laser repetition rate plays a significant role in controlling ablation efficiency and quality. Increasing the laser repetition rate, while keeping a constant mean power improves the ablation efficiency and quality. For each laser mean power, there is an optimal repetition rate to achieve a higher laser ablation efficiency with low surface roughness. A high ablation efficiency of 42.29, 44.11 and 47.52 μm3/mJ, with surface roughness of 0.476, 0.463 and 0.706 μm could be achieved at laser repetition rate of 10 MHz, for laser mean power of 15, 17 and 19 W, respectively. Scanning electron microcopy images revels that the surface morphology evolves from rough with numerous craters, to flat without pores when we increased the laser repetition rate. The effects of laser repetition rate on the heat accumulation, plasma shield and ablation threshold were analyzed by numerical simulation, spectral analysis and multi-laser shot, respectively. The synergetic effects of laser repetition rate on laser ablation rate and machining quality were analyzed and discussed systemically in this paper.

  14. Staggered Multiple-PRF Ultrafast Color Doppler.

    Science.gov (United States)

    Posada, Daniel; Poree, Jonathan; Pellissier, Arnaud; Chayer, Boris; Tournoux, Francois; Cloutier, Guy; Garcia, Damien

    2016-06-01

    Color Doppler imaging is an established pulsed ultrasound technique to visualize blood flow non-invasively. High-frame-rate (ultrafast) color Doppler, by emissions of plane or circular wavefronts, allows severalfold increase in frame rates. Conventional and ultrafast color Doppler are both limited by the range-velocity dilemma, which may result in velocity folding (aliasing) for large depths and/or large velocities. We investigated multiple pulse-repetition-frequency (PRF) emissions arranged in a series of staggered intervals to remove aliasing in ultrafast color Doppler. Staggered PRF is an emission process where time delays between successive pulse transmissions change in an alternating way. We tested staggered dual- and triple-PRF ultrafast color Doppler, 1) in vitro in a spinning disc and a free jet flow, and 2) in vivo in a human left ventricle. The in vitro results showed that the Nyquist velocity could be extended to up to 6 times the conventional limit. We found coefficients of determination r(2) ≥ 0.98 between the de-aliased and ground-truth velocities. Consistent de-aliased Doppler images were also obtained in the human left heart. Our results demonstrate that staggered multiple-PRF ultrafast color Doppler is efficient for high-velocity high-frame-rate blood flow imaging. This is particularly relevant for new developments in ultrasound imaging relying on accurate velocity measurements.

  15. The influence of the repetition rate on the nanosecond pulsed pin-to-pin microdischarges

    Science.gov (United States)

    Huang, Bang-Dou; Takashima, Keisuke; Zhu, Xi-Ming; Pu, Yi-Kang

    2014-10-01

    The effect of repetition rate on a nanosecond atmospheric pressure discharge is investigated. The discharge is generated between two pins in a mixture of Ne and Ar. The voltage, current, power waveforms and the temporally and spatially resolved electron density and an ‘effective’ electron temperature are measured, with a pulse interval between 1.5 and 200 µs. It is found that not only does the repetition rate have a strong influence on the breakdown voltage and the peak discharge power, but it can also affect the rise rate of the volume averaged electron density and its peak value. Temporally and spatially resolved measurement of the electron density and the effective electron temperature show that the spatial distributions of both quantities are also influenced by the repetition rate. In the initial discharge period of all cases, the sharp rise of the electron density correlates with the drastic drop of the effective electron temperature. It is suggested that the residual charges have a strong impact on the axial distribution of the electric field and energetic electrons between the electrodes during the breakdown period, as illustrated by a simple sheath model.

  16. A simple sub-nanosecond ultraviolet light pulse generator with high repetition rate and peak power.

    Science.gov (United States)

    Binh, P H; Trong, V D; Renucci, P; Marie, X

    2013-08-01

    We present a simple ultraviolet sub-nanosecond pulse generator using commercial ultraviolet light-emitting diodes with peak emission wavelengths of 290 nm, 318 nm, 338 nm, and 405 nm. The generator is based on step recovery diode, short-circuited transmission line, and current-shaping circuit. The narrowest pulses achieved have 630 ps full width at half maximum at repetition rate of 80 MHz. Optical pulse power in the range of several hundreds of microwatts depends on the applied bias voltage. The bias voltage dependences of the output optical pulse width and peak power are analysed and discussed. Compared to commercial UV sub-nanosecond generators, the proposed generator can produce much higher pulse repetition rate and peak power.

  17. A High Power and High Repetition Rate Modelocked Ti-Sapphire Laser for Photoinjectors

    Energy Technology Data Exchange (ETDEWEB)

    J. Hansknecht; M. Poelker

    2001-07-01

    A high power cw mode-locked Ti-sapphire laser has been constructed to drive the Jefferson Lab polarized photoinjector and provide > 500 mW average power with 50 ps pulsewidths at 499 MHz or 1497 MHz pulse repetition rates. This laser allows efficient, high current synchronous photoinjection for extended periods of time before intrusive steps must be taken to restore the quantum efficiency of the strained layer GaAs photocathode. The use of this laser has greatly enhanced the maximum high polarization beam current capability and operating lifetime of the Jefferson Lab photoinjector compared with previous performance using diode laser systems. A novel modelocking technique provides a simple means to phase-lock the optical pulse train of the laser to the accelerator and allows for operation at higher pulse repetition rates to {approx} 3 GHz without modification of the laser cavity. The laser design and characteristics are described below.

  18. Group velocity locked vector dissipative solitons in a high repetition rate fiber laser

    CERN Document Server

    Luo, Yiyang; Li, Lei; Sun, Qizhen; Wu, Zhichao; Xu, Zhilin; Fu, Songnian; Zhao, Luming

    2016-01-01

    Vectorial nature of dissipative solitons (DSs) with high repetition rates is studied for the first time in a normal-dispersion fiber laser. Despite the fact that the formed DSs are strongly chirped and the repetition rate is greater than 100 MHz, polarization locked and polarization rotating group velocity locked vector DSs can be formed under 129.3 MHz fundamental mode-locking and 258.6 MHz harmonic mode-locking of the fiber laser, respectively. The two orthogonally polarized components of these vector DSs possess distinctly different central wavelengths and travel together at the same group velocity in the laser cavity, resulting in a gradual spectral edge and small steps on the optical spectra, which can be considered as an auxiliary indicator of the group velocity locked vector DSs.

  19. Spectral-temporal encoding and decoding of the femtosecond pulses sequences with a THz repetition rate

    Science.gov (United States)

    Tcypkin, A. N.; Putilin, S. E.

    2017-01-01

    Experimental and numerical modeling techniques demonstrated the possibilities of the spectral-time encoding and decoding for time division multiplexing sequence of femtosecond subpulses with a repetition rate of up to 6.4 THz. The sequence was formed as a result of the interference of two phase-modulated pulses. We report the limits of the application of the developed method of controlling formed sequence at the spectral-temporal coding.

  20. High repetition rate, compact micro-pulse all-solid-state laser

    Institute of Scientific and Technical Information of China (English)

    Yutong Feng; Junqing Meng; Weibiao Chen

    2007-01-01

    A high repetition rate, compact micro-pulse all-solid-state laser is designed. The diffusion bonded crystal of YAG, Nd:YAG, and Cr4+:YAG is taken as a monolithic cavity. The optimized initial transmission,output coupling, and pumping size of Cr4+:YAG are calculated. The experimental results show that the laser satisfies the requirement of a spaceborne laser range finder.

  1. Impact of visual repetition rate on intrinsic properties of low frequency fluctuations in the visual network.

    Directory of Open Access Journals (Sweden)

    Yi-Chia Li

    Full Text Available BACKGROUND: Visual processing network is one of the functional networks which have been reliably identified to consistently exist in human resting brains. In our work, we focused on this network and investigated the intrinsic properties of low frequency (0.01-0.08 Hz fluctuations (LFFs during changes of visual stimuli. There were two main questions to be discussed in this study: intrinsic properties of LFFs regarding (1 interactions between visual stimuli and resting-state; (2 impact of repetition rate of visual stimuli. METHODOLOGY/PRINCIPAL FINDINGS: We analyzed scanning sessions that contained rest and visual stimuli in various repetition rates with a novel method. The method included three numerical approaches involving ICA (Independent Component Analyses, fALFF (fractional Amplitude of Low Frequency Fluctuation, and Coherence, to respectively investigate the modulations of visual network pattern, low frequency fluctuation power, and interregional functional connectivity during changes of visual stimuli. We discovered when resting-state was replaced by visual stimuli, more areas were involved in visual processing, and both stronger low frequency fluctuations and higher interregional functional connectivity occurred in visual network. With changes of visual repetition rate, the number of areas which were involved in visual processing, low frequency fluctuation power, and interregional functional connectivity in this network were also modulated. CONCLUSIONS/SIGNIFICANCE: To combine the results of prior literatures and our discoveries, intrinsic properties of LFFs in visual network are altered not only by modulations of endogenous factors (eye-open or eye-closed condition; alcohol administration and disordered behaviors (early blind, but also exogenous sensory stimuli (visual stimuli with various repetition rates. It demonstrates that the intrinsic properties of LFFs are valuable to represent physiological states of human brains.

  2. Generation of picosecond laser pulses at 1030 nm with gigahertz range continuously tunable repetition rate.

    Science.gov (United States)

    Aubourg, Adrien; Lhermite, Jérôme; Hocquet, Steve; Cormier, Eric; Santarelli, Giorgio

    2015-12-01

    We report on a watt range laser system generating picosecond pulses using electro-optical modulation of a 1030 nm single frequency low noise laser diode. Its repetition rate is continuously tunable between 11 and 18 GHz. Over this range, output spectra and pulse characteristics are measured and compared with a numerical simulation. Finally, amplitude and residual phase noise measurements of the source are also presented.

  3. Steady State Microbunching for High Brilliance and High Repetition Rate Storage Ring-Based Light Sources

    Energy Technology Data Exchange (ETDEWEB)

    Chao, Alex; Ratner, Daniel; /SLAC; Jiao, Yi; /Beijing, Inst. High Energy Phys.

    2012-09-06

    Electron-based light sources have proven to be effective sources of high brilliance, high frequency radiation. Such sources are typically either linac-Free Electron Laser (FEL) or storage ring types. The linac-FEL type has high brilliance (because the beam is microbunched) but low repetition rate. The storage ring type has high repetition rate (rapid beam circulation) but comparatively low brilliance or coherence. We propose to explore the feasibility of a microbunched beam in a storage ring that promises high repetition rate and high brilliance. The steady-state-micro-bunch (SSMB) beam in storage ring could provide CW sources for THz, EUV, or soft X-rays. Several SSMB mechanisms have been suggested recently, and in this report, we review a number of these SSMB concepts as promising directions for high brilliance, high repetition rate light sources of the future. The trick of SSMB lies in the RF system, together with the associated synchrotron beam dynamics, of the storage ring. Considering various different RF arrangements, there could be considered a number of scenarios of the SSMB. In this report, we arrange these scenarios more or less in order of the envisioned degree of technical challenge to the RF system, and not in the chronological order of their original references. Once the stored beam is steady-state microbunched in a storage ring, it passes through a radiator repeatedly every turn (or few turns). The radiator extracts a small fraction of the beam energy as coherent radiation with a wavelength corresponding to the microbunched period of the beam. In contrast to an FEL, this radiator is not needed to generate the microbunching (as required e.g. by SASE FELs or seeded FELs), so the radiator can be comparatively simple and short.

  4. Studies of a Linac Driver for a High Repetition Rate X-Ray FEL

    Energy Technology Data Exchange (ETDEWEB)

    Venturini, M.; Corlett, J.; Doolittle, L.; Filippetto, D.; Papadopoulos, C.; Penn, G.; Prosnitz, D.; Qiang, J.; Reinsch, M.; Ryne, R.; Sannibale, F.; Staples, J.; Wells, R.; Wurtele, J.; Zolotorev, M.; Zholents, A.

    2011-06-01

    We report on on-going studies of a superconducting CW linac driver intended to support a high repetition rate FEL operating in the soft x-rays spectrum. We present a pointdesign for a 1.8 GeV machine tuned for 300 pC bunches and delivering low-emittance, low-energy spread beams as needed for the SASE and seeded beamlines.

  5. Steady State Microbunching for High Brilliance and High Repetition Rate Storage Ring-Based Light Sources

    Energy Technology Data Exchange (ETDEWEB)

    Chao, Alex; Ratner, Daniel; /SLAC; Jiao, Yi; /Beijing, Inst. High Energy Phys.

    2012-09-06

    Electron-based light sources have proven to be effective sources of high brilliance, high frequency radiation. Such sources are typically either linac-Free Electron Laser (FEL) or storage ring types. The linac-FEL type has high brilliance (because the beam is microbunched) but low repetition rate. The storage ring type has high repetition rate (rapid beam circulation) but comparatively low brilliance or coherence. We propose to explore the feasibility of a microbunched beam in a storage ring that promises high repetition rate and high brilliance. The steady-state-micro-bunch (SSMB) beam in storage ring could provide CW sources for THz, EUV, or soft X-rays. Several SSMB mechanisms have been suggested recently, and in this report, we review a number of these SSMB concepts as promising directions for high brilliance, high repetition rate light sources of the future. The trick of SSMB lies in the RF system, together with the associated synchrotron beam dynamics, of the storage ring. Considering various different RF arrangements, there could be considered a number of scenarios of the SSMB. In this report, we arrange these scenarios more or less in order of the envisioned degree of technical challenge to the RF system, and not in the chronological order of their original references. Once the stored beam is steady-state microbunched in a storage ring, it passes through a radiator repeatedly every turn (or few turns). The radiator extracts a small fraction of the beam energy as coherent radiation with a wavelength corresponding to the microbunched period of the beam. In contrast to an FEL, this radiator is not needed to generate the microbunching (as required e.g. by SASE FELs or seeded FELs), so the radiator can be comparatively simple and short.

  6. Compact X-ray Source using a High Repetition Rate Laser and Copper Linac

    CERN Document Server

    Graves, W S; Brown, P; Carbajo, S; Dolgashev, V; Hong, K -H; Ihloff, E; Khaykovich, B; Lin, H; Murari, K; Nanni, E A; Resta, G; Tantawi, S; Zapata, L E; Kärtner, F X; Moncton, D E

    2014-01-01

    A design for a compact x-ray light source (CXLS) with flux and brilliance orders of magnitude beyond existing laboratory scale sources is presented. The source is based on inverse Compton scattering of a high brightness electron bunch on a picosecond laser pulse. The accelerator is a novel high-efficiency standing-wave linac and RF photoinjector powered by a single ultrastable RF transmitter at x-band RF frequency. The high efficiency permits operation at repetition rates up to 1 kHz, which is further boosted to 100 kHz by operating with trains of 100 bunches of 100 pC charge, each separated by 5 ns. The 100 kHz repetition rate is orders of magnitude beyond existing high brightness copper linacs. The entire accelerator is approximately 1 meter long and produces hard x-rays tunable over a wide range of photon energies. The colliding laser is a Yb:YAG solid-state amplifier producing 1030 nm, 100 mJ pulses at the same 1 kHz repetition rate as the accelerator. The laser pulse is frequency-doubled and stored for m...

  7. Relativistic electron beams driven by single-cycle laser pulses at kHz repetition rate (Conference Presentation)

    Science.gov (United States)

    Faure, Jérôme; Guénot, Diego; Gustas, Dominykas; Vernier, Aline; Beaurepaire, Benoît; Böhle, Frederik; López-Martens, Rodrigo; Lifschitz, Agustin

    2017-05-01

    Laser-plasma accelerators are usually driven by 100-TW class laser systems with rather low repetition rates. However, recent years have seen the emergence of laser-plasma accelerators operating with kHz lasers and energies lower than 10 mJ. The high repetition-rate is particularly interesting for applications requiring high stability and high signal-to-noise ratio but lower energy electrons. For example, our group recently demonstrated that kHz laser-driven electron beams could be used to capture ultrafast structural dynamics in Silicon nano-membranes via electron diffraction with picosecond resolution. In these first experiments, electrons were injected in the density gradients located at the plasma exit, resulting in rather low energies in the 100 keV range. The electrons being nonrelativistic, the bunch duration quickly becomes picosecond long. Relativistic energies are required to mitigate space charge effects and maintain femtosecond bunches. In this paper, we will show very recent results where electrons are accelerated in laser-driven wakefields to relativistic energies, reaching up to 5 MeV at kHz repetition rate. The electron energy was increased by nearly two orders of magnitude by using single-cycle laser pulses of 3.5 fs, with only 2.5 mJ of energy. Using such short pulses of light allowed us to resonantly excite high amplitude and nonlinear plasma waves at high plasma density, ne=1.5-2×1020 cm-3, in a regime close to the blow-out regime. Electrons had a peaked distribution around 5 MeV, with a relative energy spread of 30 %. Charges in the 100's fC/shot and up to pC/shot where measured depending on plasma density. The electron beam was fairly collimated, 20 mrad divergence at Full Width Half Maximum. The results show remarkable stability of the beam parameters in terms of beam pointing and electron distribution. 3D PIC simulations reproduce the results very well and indicate that electrons are injected by the ionization of Nitrogen atoms, N5+ to N6

  8. Effects of shifts in the rate of repetitive stimulation on sustained attention

    Science.gov (United States)

    Krulewitz, J. E.; Warm, J. S.; Wohl, T. H.

    1975-01-01

    The effects of shifts in the rate of presentation of repetitive neutral events (background event rate) were studied in a visual vigilance task. Four groups of subjects experienced either a high (21 events/min) or a low (6 events/min) event rate for 20 min and then experienced either the same or the alternate event rate for an additional 40 min. The temporal occurrence of critical target signals was identical for all groups, irrespective of event rate. The density of critical signals was 12 signals/20 min. By the end of the session, shifts in event rate were associated with changes in performance which resembled contrast effects found in other experimental situations in which shift paradigms were used. Relative to constant event rate control conditions, a shift from a low to a high event rate depressed the probability of signal detections, while a shift in the opposite direction enhanced the probability of signal detections.

  9. Acousto-optic pulse picking scheme with carrier-frequency-to-pulse-repetition-rate synchronization.

    Science.gov (United States)

    de Vries, Oliver; Saule, Tobias; Plötner, Marco; Lücking, Fabian; Eidam, Tino; Hoffmann, Armin; Klenke, Arno; Hädrich, Steffen; Limpert, Jens; Holzberger, Simon; Schreiber, Thomas; Eberhardt, Ramona; Pupeza, Ioachim; Tünnermann, Andreas

    2015-07-27

    We introduce and experimentally validate a pulse picking technique based on a travelling-wave-type acousto-optic modulator (AOM) having the AOM carrier frequency synchronized to the repetition rate of the original pulse train. As a consequence, the phase noise characteristic of the original pulse train is largely preserved, rendering this technique suitable for applications requiring carrier-envelope phase stabilization. In a proof-of-principle experiment, the 1030-nm spectral part of an 74-MHz, carrier-envelope phase stable Ti:sapphire oscillator is amplified and reduced in pulse repetition frequency by a factor of two, maintaining an unprecedentedly low carrier-envelope phase noise spectral density of below 68 mrad. Furthermore, a comparative analysis reveals that the pulse-picking-induced additional amplitude noise is minimized, when the AOM is operated under synchronicity. The proposed scheme is particularly suitable when the down-picked repetition rate is still in the multi-MHz-range, where Pockels cells cannot be applied due to piezoelectric ringing.

  10. Optimization of graffiti removal on natural stone by means of high repetition rate UV laser

    Science.gov (United States)

    Fiorucci, M. P.; López, A. J.; Ramil, A.; Pozo, S.; Rivas, T.

    2013-08-01

    The use of laser for graffiti removal is a promising alternative to conventional cleaning methods, though irradiation parameters must be carefully selected in order to achieve the effective cleaning without damaging the substrate, especially when referring to natural stone. From a practical point of view, once a safe working window is selected, it is necessary to determine the irradiation conditions to remove large paint areas, with minimal time consumption. The aim of this paper is to present a systematic procedure to select the optimum parameters for graffiti removal by means of the 3rd harmonic of a high repetition rate nanosecond Nd:YVO4 laser. Ablation thresholds of four spray paint colors were determined and the effect of pulse repetition frequency, beam diameter and line scan separation was analyzed, obtaining a set of values which optimize the ablation process.

  11. Optimization of graffiti removal on natural stone by means of high repetition rate UV laser

    Energy Technology Data Exchange (ETDEWEB)

    Fiorucci, M.P., E-mail: m.p.fiorucci@udc.es [Centro de Investigacións Tecnolóxicas, Universidade da Coruña, 15403 Ferrol (Spain); Dpto. Enxeñaría dos Recursos Naturais e Medio Ambiente, E.T.S.E. Minas, Universidade de Vigo, 36200 Vigo (Spain); López, A.J., E-mail: ana.xesus.lopez@udc.es [Centro de Investigacións Tecnolóxicas, Universidade da Coruña, 15403 Ferrol (Spain); Ramil, A., E-mail: alberto.ramil@udc.es [Centro de Investigacións Tecnolóxicas, Universidade da Coruña, 15403 Ferrol (Spain); Pozo, S., E-mail: ipozo@uvigo.es [Dpto. Enxeñaría dos Recursos Naturais e Medio Ambiente, E.T.S.E. Minas, Universidade de Vigo, 36200 Vigo (Spain); Rivas, T., E-mail: trivas@uvigo.es [Dpto. Enxeñaría dos Recursos Naturais e Medio Ambiente, E.T.S.E. Minas, Universidade de Vigo, 36200 Vigo (Spain)

    2013-08-01

    The use of laser for graffiti removal is a promising alternative to conventional cleaning methods, though irradiation parameters must be carefully selected in order to achieve the effective cleaning without damaging the substrate, especially when referring to natural stone. From a practical point of view, once a safe working window is selected, it is necessary to determine the irradiation conditions to remove large paint areas, with minimal time consumption. The aim of this paper is to present a systematic procedure to select the optimum parameters for graffiti removal by means of the 3rd harmonic of a high repetition rate nanosecond Nd:YVO{sub 4} laser. Ablation thresholds of four spray paint colors were determined and the effect of pulse repetition frequency, beam diameter and line scan separation was analyzed, obtaining a set of values which optimize the ablation process.

  12. 100 kV/2A three-phase constant-current repetitive-rate charging equipment

    CERN Document Server

    Tan Yu Gang; Chen Li Dong; Guo Zhi Gang; Zou Xiao Bing; Luo Min; Cao Shao Yun; Chang An Bi

    2002-01-01

    A 100 kV/2A three-phase constant-current repetitive-rate charging equipment was designed and constructed. A three-phase L-C converter is adopted as constant-current power source. Six Insulated Gate Bipolar Transistors (IGBTs) are connected in parallel to control the stop of charge. A Programmable Logical Controller (PLC) is the central element of the control unit. The equipment is used in the repetitive-rate discharge features test of the switch. It works stably under the conditions of 2A charging current, 10 Hz operating voltage, 100 kV repetitive rate and 1 mu F capacitor

  13. Ultraviolet excimer laser ablation: the effect of wavelength and repetition rate on in vivo guinea pig skin

    Energy Technology Data Exchange (ETDEWEB)

    Morelli, J.; Kibbi, A.G.; Farinelli, W.; Boll, J.; Tan, O.T.

    1987-06-01

    Multiple dermatologic conditions that are currently treated with traditional cold-knife surgery are amenable to laser therapy. The ideal surgical treatment would be precise and total removal of abnormal tissue with maximal sparing of remaining structures. The ultraviolet (UV) excimer laser is capable of such precise tissue removal due to the penetration depth of 193 nm and 248 nm irradiation of 1 micron per pulse. This type of ablative tissue removal requires a high repetition rate for efficient lesional destruction. Excimer laser radiation at 193 nm is capable of high repetition rates, which are necessary while 248 nm radiation causes increasing nonspecific thermal injury as the laser repetition rate is increased.

  14. Statistical analysis of laser driven protons using a high-repetition-rate tape drive target system

    Directory of Open Access Journals (Sweden)

    Muhammad Noaman-ul-Haq

    2017-04-01

    Full Text Available One of the challenges for laser-driven proton beams for many potential applications is their stability and reproducibility. We investigate the stability of the laser driven proton beams through statistical analysis of the data obtained by employing a high repetition rate tape driven target system. The characterization of the target system shows the positioning of the target within ∼15  μm in the focal plane of an off-axis parabola, with less than a micron variation in surface flatness. By employing this stable target system, we study the stability of the proton beams driven by ultrashort and intense laser pulses. Protons with maximum energies of ∼6±0.3  MeV were accelerated for a large number of laser shots taken at a rate of 0.2 Hz with a stability of less than 5% variations in cutoff energy. The development of high repetition rate target system may provide a platform to understand the dynamics of laser driven proton beams at the rate required for future applications.

  15. High energy high repetition-rate thin-disk amplifier for OPCPA pumping

    Energy Technology Data Exchange (ETDEWEB)

    Schulz, Michael

    2013-08-15

    The development of a pump laser system for a high power and high repetition rate optical parametric chirped-pulse amplification (OPCPA) is presented in this thesis. The OPCPA system requires pump pulse energies in the range of tens of millijoules at high repetition rates with sub-picosecond pulse durations. This can be achieved to some extend with Innoslab amplifier technology. However, scaling to higher pulse energies at high repetition rates may be problematic. With the thin-disk amplifier presented in this thesis, output energies of 140 mJ at 100 kHz repetition rate could be achieved in burst-mode operation, which is a world record for this type of laser amplifier. Due to its material and spectral properties, ytterbium doped YAG (Yb:YAG) is used as a gain medium for the high power amplifier stages. The low quantum defect and the comparatively large emission bandwidth makes this material the choice for high power operation and sub-picosecond compressed pulse durations. The output beam profile as well as the shape of the output bursts is ideal to pump an OPCPA system. An OPCPA output energy in the millijoule range with repetition rates of 100 kHz to 1 MHz is needed to generate seed pulses for the FEL and for the application as pump-probe laser at the FEL facility. Since the development of this laser system needs to meet requirements set by the Free-Electron Laser in Hamburg (FLASH), the amplifier is conceived for burst-mode operation. The main requirement is a high intra-burst pulse repetition rate of more than 100 kHz and a uniform pulse train (burst) with equal properties for every pulse. The burst-mode is an operation mode where the laser never reaches a lasing equilibrium, which means that the behavior of the amplifier is similar to a switch-on of the laser system for every burst. This makes the development of the amplifier system difficult. Therefore, an analytical model has been developed to study the amplification process during the burst. This includes the

  16. Single-pass high harmonic generation at high repetition rate and photon flux

    Science.gov (United States)

    Hädrich, Steffen; Rothhardt, Jan; Krebs, Manuel; Demmler, Stefan; Klenke, Arno; Tünnermann, Andreas; Limpert, Jens

    2016-09-01

    Sources of short wavelength radiation with femtosecond to attosecond pulse durations, such as synchrotrons or free electron lasers, have already made possible numerous, and will facilitate more, seminal studies aimed at understanding atomic and molecular processes on fundamental length and time scales. Table-top sources of coherent extreme ultraviolet to soft x-ray radiation enabled by high harmonic generation (HHG) of ultrashort pulse lasers have also gained significant attention in the last few years due to their enormous potential for addressing a plethora of applications, therefore constituting a complementary source to large-scale facilities (synchrotrons and free electron lasers). Ti:sapphire based laser systems have been the workhorses for HHG for decades, but are limited in repetition rate and average power. On the other hand, it has been widely recognized that fostering applications in fields such as photoelectron spectroscopy and microscopy, coincidence detection, coherent diffractive imaging and frequency metrology requires a high repetition rate and high photon flux HHG sources. In this article we will review recent developments in realizing the demanding requirement of producing a high photon flux and repetition rate at the same time. Particular emphasis will be put on suitable ultrashort pulse and high average power lasers, which directly drive harmonic generation without the need for external enhancement cavities. To this end we describe two complementary schemes that have been successfully employed for high power fiber lasers, i.e. optical parametric chirped pulse amplifiers and nonlinear pulse compression. Moreover, the issue of phase-matching in tight focusing geometries will be discussed and connected to recent experiments. We will highlight the latest results in fiber laser driven high harmonic generation that currently produce the highest photon flux of all existing sources. In addition, we demonstrate the first promising applications and

  17. All-optical repetition rate multiplication of pseudorandom bit sequences based on cascaded TOADs

    Science.gov (United States)

    Sun, Zhenchao; Wang, Zhi; Wu, Chongqing; Wang, Fu; Li, Qiang

    2016-03-01

    A scheme for all-optical repetition rate multiplication of pseudorandom bit sequences (PRBS) is demonstrated with all-optical wavelength conversion and optical logic gate 'OR' based on cascaded Tera-Hertz Optical Asymmetric Demultiplexers (TOADs). Its feasibility is verified by multiplication experiments from 500 Mb/s to 4 Gb/s for 23-1 PRBS and from 1 Gb/s to 4 Gb/s for 27-1 PRBS. This scheme can be employed for rate multiplication for much longer cycle PRBS at much higher bit rate over 40 Gb/s when the time-delay, the loss and the dispersion of the optical delay line are all precisely managed. The upper limit of bit rate will be restricted by the recovery time of semiconductor optical amplifier (SOA) finally.

  18. Development of a cryogenic hydrogen microjet for high-intensity, high-repetition rate experiments

    Science.gov (United States)

    Kim, J. B.; Göde, S.; Glenzer, S. H.

    2016-11-01

    The advent of high-intensity, high-repetition-rate lasers has led to the need for replenishing targets of interest for high energy density sciences. We describe the design and characterization of a cryogenic microjet source, which can deliver a continuous stream of liquid hydrogen with a diameter of a few microns. The jet has been imaged at 1 μm resolution by shadowgraphy with a short pulse laser. The pointing stability has been measured at well below a mrad, for a stable free-standing filament of solid-density hydrogen.

  19. Observation of Repetition-Rate Dependent Emission From an Un-Gated Thermionic Cathode Rf Gun

    Energy Technology Data Exchange (ETDEWEB)

    Edelen, J. P.; Sun, Y.; Harris, J.R.; Lewellen, J.W.

    2017-06-02

    Recent work at Fermilab in collaboration with the Advanced Photon Source and members of other national labs, designed an experiment to study the relationship between the RF repetition rate and the average current per RF pulse. While existing models anticipate a direct relationship between these two parameters we observed an inverse relationship. We believe this is a result of damage to the barium coating on the cathode surface caused by a change in back-bombardment power that is unaccounted for in the existing theories. These observations shed new light on the challenges and fundamental limitations associated with scaling an ungated thermionic cathode RF gun to high average current.

  20. Power scaling of supercontinuum seeded megahertz-repetition rate optical parametric chirped pulse amplifiers.

    Science.gov (United States)

    Riedel, R; Stephanides, A; Prandolini, M J; Gronloh, B; Jungbluth, B; Mans, T; Tavella, F

    2014-03-15

    Optical parametric chirped-pulse amplifiers with high average power are possible with novel high-power Yb:YAG amplifiers with kW-level output powers. We demonstrate a compact wavelength-tunable sub-30-fs amplifier with 11.4 W average power with 20.7% pump-to-signal conversion efficiency. For parametric amplification, a beta-barium borate crystal is pumped by a 140 W, 1 ps Yb:YAG InnoSlab amplifier at 3.25 MHz repetition rate. The broadband seed is generated via supercontinuum generation in a YAG crystal.

  1. OBSERVATION OF REPETITION-RATE DEPENDANT EMISSION FROM AN UN-GATED THERMIONIC CATHODE RF GUN

    Energy Technology Data Exchange (ETDEWEB)

    Edelen, J. P. [Fermilab; Sun, Y. [Argonne; Harris, J. R. [AFRL, NM; Lewellen, J. W. [Los Alamos Natl. Lab.

    2016-09-28

    Recent work at Fermilab in collaboration with the Advanced Photon Source and members of other national labs, designed an experiment to study the relationship between the RF repetition rate and the average current per RF pulse. While existing models anticipate a direct relationship between these two parameters we observed an inverse relationship. We believe this is a result of damage to the barium coating on the cathode surface caused by a change in back-bombardment power that is unaccounted for in the existing theories. These observations shed new light on the challenges and fundamental limitations associated with scaling an ungated thermionic cathode RF gun to high average current machines.

  2. Adjustable high-repetition-rate pulse trains in a passively-mode-locked fiber laser

    Science.gov (United States)

    Si Fodil, Rachid; Amrani, Foued; Yang, Changxi; Kellou, Abdelhamid; Grelu, Ph.

    2016-07-01

    We experimentally investigate multipulse regimes obtained within a passively-mode-locked fiber laser that includes a Mach-Zehnder (MZ) interferometer. By adjusting the time delay imbalance of the MZ, ultrashort pulse trains at multi-GHz repetition rates are generated. We compare the observed dynamics with high-harmonic mode locking, and show that the multi-GHz pulse trains display an inherent instability, which has been overlooked. By using a recirculation loop containing the MZ, we demonstrate a significant improvement of the pulse train stability.

  3. Optical Fiber Pumped High Repetition Rate and High Power Nd:YVO4 Picosecond Regenerative Amplifier

    Directory of Open Access Journals (Sweden)

    Zhen-Ao Bai

    2015-08-01

    Full Text Available We report a stable optical fiber pumped Nd:YVO4 all solid state regenerative amplifier with all fiber picosecond laser as seed source. 888 nm Yb optical fiber lasers was chosen as pump source to reduce quantum defect for improved thermal performance. At the repetition rate of 99.6 kHz, maximum power of 19.63 W with 36 ps pulse duration were achieved when seeded by a 150 mW picosecond oscillator. The wavelength delivered was 1064.07 nm with spectral width of 0.14 nm.

  4. HIGH REPETITION RATE MICROCHIP ER3+,YB3+:YAL3(BO34 DIODE-PUMPED LASER

    Directory of Open Access Journals (Sweden)

    K. N. Gorbachenya

    2012-01-01

    Full Text Available Diode-pumped passively Q-switched microchip Er,Yb:YAl3(BO34 laser for range-finding has been demonstrated. By using a Co2+:MgAl2O4 as a saturable absorber TEM00–mode Q-switched average output power of 315 mW was demonstrated at 1522 nm with pulse duration of 5 ns and pulse energy of 5,25 μJ at a repetition rate of 60 kHz.

  5. High-harmonic generation from plasma mirrors at kilohertz repetition rate

    OpenAIRE

    Quéré, Fabien

    2011-01-01

    International audience; We report the first demonstration of high-harmonic generation from plasma mirrors at a 1 kHz repetition rate. Harmonics up to nineteenth order are generated at peak intensities close to 1018 W=cm2 by focusing 1 mJ, 25 fs laser pulses down to 1:7 μm FWHM spot size without any prior wavefront correction onto a moving target. We minimize target surface motion with respect to the laser focus using online interferometry to ensure reproducible interaction conditions for ever...

  6. Spectrum analysis of all parameter noises in repetition-rate laser pulse train

    Institute of Scientific and Technical Information of China (English)

    Junhua Tang; Yuncai Wang

    2006-01-01

    @@ The theoretical investigation of all parameter noises in repetition-rate laser pulse train was presented. The expression of power spectrum of laser pulse trains with all parameter noises was derived, and the power spectra of pulse trains with different noise parameters were numerically simulated. By comparing the power spectra with and without pulse-width jitter, we noted that pulse-width jitter could not be neglected compared with amplitude noise and timing jitter and contributed a great amount of noise into the power spectrum under the condition that the product of pulse width and angular frequency was larger than 1.

  7. Choppers to optimise the repetition rate multiplication technique on a direct geometry neutron chopper spectrometer

    DEFF Research Database (Denmark)

    Vickery, Anette; Deen, P. P.

    2014-01-01

    In recent years the use of repetition rate multiplication (RRM) on direct geometry neutron spectrometers has been established and is the common mode of operation on a growing number of instruments. However, the chopper configurations are not ideally optimised for RRM with a resultant 100 fold flu...... in time resolution probed for a single European Spallation Source (ESS) period, which is ideal to probe complex relaxational behaviour. These two chopper configurations have been simulated for the Versatile Optimal Resolution direct geometry spectrometer, VOR, that will be built at ESS....

  8. Demonstration of a time-resolved x-ray scattering instrument utilizing the full-repetition rate of x-ray pulses at the Pohang Light Source

    Science.gov (United States)

    Jo, Wonhyuk; Eom, Intae; Landahl, Eric C.; Lee, Sooheyong; Yu, Chung-Jong

    2016-03-01

    We report on the development of a new experimental instrument for time-resolved x-ray scattering (TRXS) at the Pohang Light Source (PLS-II). It operates with a photon energy ranging from 5 to 18 keV. It is equipped with an amplified Ti:sappahire femtosecond laser, optical diagnostics, and laser beam delivery for pump-probe experiments. A high-speed single-element detector and high trigger-rate oscilloscope are used for rapid data acquisition. While this instrument is capable of measuring sub-nanosecond dynamics using standard laser pump/x-ray probe techniques, it also takes advantage of the dense 500 MHz standard fill pattern in the PLS-II storage ring to efficiently record nano-to-micro-second dynamics simultaneously. We demonstrate this capability by measuring both the (fast) impulsive strain and (slower) thermal recovery dynamics of a crystalline InSb sample following intense ultrafast laser excitation. Exploiting the full repetition rate of the storage ring results in a significant improvement in data collection rates compared to conventional bunch-tagging methods.

  9. High Repetition Rate Pulsed 2-Micron Laser Transmitter for Coherent CO2 DIAL Measurement

    Science.gov (United States)

    Singh, Uprendra N.; Bai, Yingxin; Yu, Jirong; Petros, Mulugeta; Petzar, Paul J.; Trieu, Bo C.; Lee, Hyung

    2009-01-01

    A high repetition rate, highly efficient, Q-switched 2-micron laser system as the transmitter of a coherent differential absorption lidar for CO2 measurement has been developed at NASA Langley Research Center. Such a laser transmitter is a master-slave laser system. The master laser operates in a single frequency, either on-line or off-line of a selected CO2 absorption line. The slave laser is a Q-switched ring-cavity Ho:YLF laser which is pumped by a Tm:fiber laser. The repetition rate can be adjusted from a few hundred Hz to 10 kHz. The injection seeding success rate is from 99.4% to 99.95%. For 1 kHz operation, the output pulse energy is 5.5mJ with the pulse length of approximately 50 ns. The optical-to-optical efficiency is 39% when the pump power is 14.5W. The measured standard deviation of the laser frequency jitter is about 3 MHz.

  10. High-repetition-rate femtosecond dye amplifier using a laser-diode-pumped neodymium:YAG laser

    Energy Technology Data Exchange (ETDEWEB)

    Zysset, B.; LaGasse, M.J.; Fujimoto, J.G.; Kafka, J.D.

    1989-02-06

    A high-repetition-rate femotosecond dye amplifier is demonstrated using a laser-diode-pumped Q-switched Nd:YAG laser. Amplification of wavelength-tunable 300-fs pulses from a synchronously mode-locked rhodamine dye laser is achieved with a saturated gain of 70 and a small gain of 200 at a repetition rate of 800 Hz. Maximum pulse energies of 40 nJ are obtained, and pulse compression to as short as 30 fs is demonstrated.

  11. Scheme for independently stabilizing the repetition rate and optical frequency of a laser using a regenerative mode-locking technique.

    Science.gov (United States)

    Nakazawa, Masataka; Yoshida, Masato

    2008-05-15

    We have succeeded in achieving independent control of the repetition rate and optical frequency of a pulse laser by employing a regenerative mode-locking technique. By adopting a voltage-controlled microwave phase shifter or an optical delay line in a regenerative feedback loop we can control the repetition rate of the laser without directly disturbing the optical frequencies. We experimentally show how this independent control can be realized by employing a 40 GHz harmonically and regeneratively mode-locked fiber laser.

  12. BEAM DYNAMICS STUDIES OF A HIGH-REPETITION RATE LINAC-DRIVER FOR A 4TH GENERATION LIGHT SOURCE

    Energy Technology Data Exchange (ETDEWEB)

    Ventturini, M.; Corlett, J.; Emma, P.; Papadopoulos, C.; Penn, G.; Placidi, M.; Qiang, J.; Reinsch, M.; Sannibale, F.; Steier, C.; Sun, C.; Wells, R.

    2012-05-18

    We present recent progress toward the design of a super-conducting linac driver for a high-repetition rate FEL-based soft x-ray light source. The machine is designed to accept beams generated by the APEX photo-cathode gun operating with MHz-range repetition rate and deliver them to an array of SASE and seeded FEL beamlines. We review the current baseline design and report results of beam dynamics studies.

  13. How Do Algebra I Course Repetition Rates Vary among English Learner Students by Length of Time to Reclassification as English Proficient? REL 2017-222

    Science.gov (United States)

    Jaquet, Karina; Fong, Anthony B.

    2017-01-01

    Research has found high repetition rates for students in Algebra I, with one study finding a repetition rate of 44 percent for students in a large urban high school district. Less is known about how math performance and Algebra I course repetition rates vary among students with different levels of English proficiency. This report examines Algebra…

  14. The effects of laser repetition rate on femtosecond laser ablation of dry bone: a thermal and LIBS study.

    Science.gov (United States)

    Gill, Ruby K; Smith, Zachary J; Lee, Changwon; Wachsmann-Hogiu, Sebastian

    2016-01-01

    The aim of this study is to understand the effect of varying laser repetition rate on thermal energy accumulation and dissipation as well as femtosecond Laser Induced Breakdown Spectroscopy (fsLIBS) signals, which may help create the framework for clinical translation of femtosecond lasers for surgical procedures. We study the effect of repetition rates on ablation widths, sample temperature, and LIBS signal of bone. SEM images were acquired to quantify the morphology of the ablated volume and fsLIBS was performed to characterize changes in signal intensity and background. We also report for the first time experimentally measured temperature distributions of bone irradiated with femtosecond lasers at repetition rates below and above carbonization conditions. While high repetition rates would allow for faster cutting, heat accumulation exceeds heat dissipation and results in carbonization of the sample. At repetition rates where carbonization occurs, the sample temperature increases to a level that is well above the threshold for irreversible cellular damage. These results highlight the importance of the need for careful selection of the repetition rate for a femtosecond laser surgery procedure to minimize the extent of thermal damage to surrounding tissues and prevent misclassification of tissue by fsLIBS analysis.

  15. Fetal Heart Rate Monitoring from Phonocardiograph Signal Using Repetition Frequency of Heart Sounds

    Directory of Open Access Journals (Sweden)

    Hong Tang

    2016-01-01

    Full Text Available As a passive, harmless, and low-cost diagnosis tool, fetal heart rate (FHR monitoring based on fetal phonocardiography (fPCG signal is alternative to ultrasonographic cardiotocography. Previous fPCG-based methods commonly relied on the time difference of detected heart sound bursts. However, the performance is unavoidable to degrade due to missed heart sounds in very low signal-to-noise ratio environments. This paper proposes a FHR monitoring method using repetition frequency of heart sounds. The proposed method can track time-varying heart rate without both heart sound burst identification and denoising. The average accuracy rate comparison to benchmark is 88.3% as the SNR ranges from −4.4 dB to −26.7 dB.

  16. Analyzing the effect of high repetition laser shock peening on dynamic corrosion rate of magnesium

    Science.gov (United States)

    Caralapatti, Vinodh Krishna; Narayanswamy, Sivakumar

    2017-08-01

    Magnesium as implant material is being investigated extensively due to its superior suitability. With corrosion rate being the major obstacle, this paper aims to determine the effects of high repetition laser shock peening (HRLSP) on the dynamic corrosion rate of magnesium. While there is lot of research on corrosion of magnesium, in this work, a specially designed test bench was used for characterization of dynamic corrosion to mimic the physiological conditions experienced by the implant inside human body. From the results, it can be inferred that corrosion rate of peened samples reduced by at least 6 times compared to unpeened sample and sample peened with 66% overlap 1 scans exhibited the least corrosion. The wettability of the samples was also determined as a measure to analyze the effects of HRLSP on biocompatibility. In addition, peening is seen to induce surface corrosion, which minimizes the risks of implant failure.

  17. What Controls the Rate of Ultrafast Charge Transfer and Charge Separation Efficiency in Organic Photovoltaic Blends.

    Science.gov (United States)

    Jakowetz, Andreas C; Böhm, Marcus L; Zhang, Jiangbin; Sadhanala, Aditya; Huettner, Sven; Bakulin, Artem A; Rao, Akshay; Friend, Richard H

    2016-09-14

    In solar energy harvesting devices based on molecular semiconductors, such as organic photovoltaics (OPVs) and artificial photosynthetic systems, Frenkel excitons must be dissociated via charge transfer at heterojunctions to yield free charges. What controls the rate and efficiency of charge transfer and charge separation is an important question, as it determines the overall power conversion efficiency (PCE) of these systems. In bulk heterojunctions between polymer donor and fullerene acceptors, which provide a model system to understand the fundamental dynamics of electron transfer in molecular systems, it has been established that the first step of photoinduced electron transfer can be fast, of order 100 fs. But here we report the first study which correlates differences in the electron transfer rate with electronic structure and morphology, achieved with sub-20 fs time resolution pump-probe spectroscopy. We vary both the fullerene substitution and donor/fullerene ratio which allow us to control both aggregate size and the energetic driving force for charge transfer. We observe a range of electron transfer times from polymer to fullerene, from 240 fs to as short as 37 fs. Using ultrafast electro-optical pump-push-photocurrent spectroscopy, we find the yield of free versus bound charges to be weakly dependent on the energetic driving force, but to be very strongly dependent on fullerene aggregate size and packing. Our results point toward the importance of state accessibility and charge delocalization and suggest that energetic offsets between donor and acceptor levels are not an important criterion for efficient charge generation. This provides design rules for next-generation materials to minimize losses related to driving energy and boost PCE.

  18. Crossatron switch as thyratron replacement in high repetition rate, high average power modulators

    Science.gov (United States)

    Sullivan, J. S.

    1988-06-01

    The Crossatron is a cold cathode, low pressure, gas discharge switch with opening and closing capabilities. Due to its cold cathode operation, the Crossatron may offer lifetime advantages compared to the hydrogen thyratron. Unfortunately, little information regarding Crossatron lifetime and performance in high repetition rate, high average power, pulse modulators exists. Four prototype Crossatron devices, fabricated by Hughes Aircraft, were obtained to evaluate their performance and lifetime in high repetition rate, high average power, pulse modulators that had previously been equipped with hydrogen thyratrons. The prototype Crossatrons were evaluated over a range of operating parameters. Various grid drive, keep alive power levels and triggering schemes were employed in the tests. Switch parameters such as trigger time, anode fall time, jitter, recovery time, peak di/dt, switch efficiency, and the gas pumping effect of the discharge were observed. One Crossatron prototype was also subjected to lifetime tests that accumulated tens of billions of pulses. Lifetime data will be compared to various thyratron models tested similarly.

  19. Repetition rate multiplication of frequency comb using all-pass fiber resonator

    Science.gov (United States)

    Yang, Lijun; Yang, Honglei; Zhang, Hongyuan; Wei, Haoyun; Li, Yan

    2016-09-01

    We propose a stable method for repetition rate multiplication of a 250-MHz Er-fiber frequency comb by a phase-locked all-pass fiber ring resonator, whose phase-locking configuration is simple. The optical path length of the fiber ring resonator is automatically controlled to be accurately an odd multiple of half of the original cavity length using an electronical phase-locking unit with an optical delay line. As for shorter cavity length of the comb, high-order odd multiple is preferable. Because the power loss depends only on the net-attenuation of the fiber ring resonator, the energetic efficiency of the proposed method is high. The input and output optical spectrums show that the spectral width of the frequency comb is clearly preserved. Besides, experimental results show less pulse intensity fluctuation and 35 dB suppression ratio of side-modes while providing a good long-term and short-term frequency stability. Higher-order repetition rate multiplication to several GHz can be obtained by using several fiber ring resonators in cascade configuration.

  20. Characterization of MHz pulse repetition rate femtosecond laser-irradiated gold-coated silicon surfaces

    Directory of Open Access Journals (Sweden)

    Venkatakrishnan Krishnan

    2011-01-01

    Full Text Available Abstract In this study, MHz pulse repetition rate femtosecond laser-irradiated gold-coated silicon surfaces under ambient condition were characterized by scanning electron microscopy (SEM, transmission electron microscopy (TEM, X-ray diffraction analysis (XRD, and X-ray photoelectron spectroscopy (XPS. The radiation fluence used was 0.5 J/cm2 at a pulse repetition rate of 25 MHz with 1 ms interaction time. SEM analysis of the irradiated surfaces showed self-assembled intermingled weblike nanofibrous structure in and around the laser-irradiated spots. Further TEM investigation on this nanostructure revealed that the nanofibrous structure is formed due to aggregation of Au-Si/Si nanoparticles. The XRD peaks at 32.2°, 39.7°, and 62.5° were identified as (200, (211, and (321 reflections, respectively, corresponding to gold silicide. In addition, the observed chemical shift of Au 4f and Si 2p lines in XPS spectrum of the irradiated surface illustrated the presence of gold silicide at the irradiated surface. The generation of Si/Au-Si alloy fibrous nanoparticles aggregate is explained by the nucleation and subsequent condensation of vapor in the plasma plume during irradiation and expulsion of molten material due to high plasma pressure.

  1. Investigation of bunch repetition rate deviations in FIR FEL driven by a magnetron-based microtron

    CERN Document Server

    Kazakevitch, Grigori M; Lee Byung Cheol; Lee, J

    2002-01-01

    The stability of the bunch repetition rate in a FIR FEL driven by a 2.8 GHz magnetron-based microtron was investigated using a heterodyne method with a low Q-factor straight-flight measuring cavity. The measuring cavity is located in the straight section of the FIR FEL injection beam line and is excited by the passage of electron bunches. The RF signal from the measuring cavity coupling loop was mixed with a precise heterodyne signal with a frequency difference of several MHz. The beat frequency was analyzed to obtain the temporal distribution of the bunch repetition rate deviation during the macro pulse of the electron beam. The time resolution and the accuracy of measurements are approximately 100 ns and a few kHz, respectively. Based on this data, we could determine the level and shape of the magnetron current and the initial frequency shift between magnetron and accelerating cavity for the FEL operation in the wavelength range 100-300 microns.

  2. 4D ultrafast ultrasound flow imaging: in vivo quantification of arterial volumetric flow rate in a single heartbeat

    Science.gov (United States)

    Correia, Mafalda; Provost, Jean; Tanter, Mickael; Pernot, Mathieu

    2016-12-01

    We present herein 4D ultrafast ultrasound flow imaging, a novel ultrasound-based volumetric imaging technique for the quantitative mapping of blood flow. Complete volumetric blood flow distribution imaging was achieved through 2D tilted plane-wave insonification, 2D multi-angle cross-beam beamforming, and 3D vector Doppler velocity components estimation by least-squares fitting. 4D ultrafast ultrasound flow imaging was performed in large volumetric fields of view at very high volume rate (>4000 volumes s-1) using a 1024-channel 4D ultrafast ultrasound scanner and a 2D matrix-array transducer. The precision of the technique was evaluated in vitro by using 3D velocity vector maps to estimate volumetric flow rates in a vessel phantom. Volumetric Flow rate errors of less than 5% were found when volumetric flow rates and peak velocities were respectively less than 360 ml min-1 and 100 cm s-1. The average volumetric flow rate error increased to 18.3% when volumetric flow rates and peak velocities were up to 490 ml min-1 and 1.3 m s-1, respectively. The in vivo feasibility of the technique was shown in the carotid arteries of two healthy volunteers. The 3D blood flow velocity distribution was assessed during one cardiac cycle in a full volume and it was used to quantify volumetric flow rates (375  ±  57 ml min-1 and 275  ±  43 ml min-1). Finally, the formation of 3D vortices at the carotid artery bifurcation was imaged at high volume rates.

  3. The ringer - An efficient, high repetition rate circuit for electromagnetic launchers

    Science.gov (United States)

    Giorgi, D.; Helava, H.; Lindner, K.; Long, J.; Zucker, O.

    1989-01-01

    The Meatgrinder is an efficient, current-multiplying circuit which can be used to optimize the energy transfer to various electromagnetic gun configurations. The authors present a simple variant of the Meatgrinder circuit which permits a first-order current profiling into the gun and recovery of the inductive energy in the barrel at a high repetition rate. The circuit is basically a one-stage Meatgrinder which utilizes the ringing of the energy storage capacitor (less than 40 percent reversal) to perform the opening switch function and a solid-state diode as the crowbar switch between the two mutually coupled inductors. With resonant charging, this results in a completely passive, high-repetiton-rate electromagnetic-gun power supply. Since most of the barrel energy is recovered, a railgun with negligible muzzle flash can be realized.

  4. Temporal dynamics of high repetition rate pulsed single longitudinal mode dye laser

    Indian Academy of Sciences (India)

    G Sridhar; V S Rawar; S Singh; L M Gantayet

    2013-08-01

    Theoretical and experimental studies of temporal dynamics of grazing incidence grating (GIG) cavity, single-mode dye laser pumped by high repetition rate copper vapour laser (CVL) are presented. Spectral chirp of the dye laser as they evolve in the cavity due to transient phase dynamics of the amplifier gain medium is studied. Effect of grating efficiency, focal spot size, pump power and other cavity parameters on the temporal behaviour of narrow band dye laser such as build-up time, pulse shape and pulse width is studied using the four level dye laser rate equation and photon evolution equation. These results are compared with experimental observations of GIG single-mode dye laser cavity. The effect of pulse stretching of CVL pump pulse on the temporal dynamics of the dye laser is studied.

  5. Cavity-enhanced field-free molecular alignment at high repetition rate

    CERN Document Server

    Benko, Craig; Allison, Thomas K; Labaye, François; Ye, Jun

    2015-01-01

    Extreme ultraviolet frequency combs are a versatile tool with applications including precision measurement, strong-field physics, and solid-state physics. Here we report on an application of extreme ultraviolet frequency combs and their driving lasers to studying strong-field effects in molecular systems. We perform field-free molecular alignment and high-order hamonic generation with aligned molecules in a gas jet at 154 MHz repetition rate using a high-powered optical frequency comb inside a femtosecond enhancement cavity. The cavity-enhanced system provides means to reach suitable intensities to study field-free molecular alignment and enhance the observable effects of the molecule-field interaction. We observe modulations of the driving field, arising from the nature of impulsive stimulated Raman scattering responsible for coherent molecular rotations. We foresee impact of this work on the study of molecule-based strong-field physics, with improved precision and a more fundamental understanding of the int...

  6. High repetition rate tunable femtosecond pulses and broadband amplification from fiber laser pumped parametric amplifier.

    Science.gov (United States)

    Andersen, T V; Schmidt, O; Bruchmann, C; Limpert, J; Aguergaray, C; Cormier, E; Tünnermann, A

    2006-05-29

    We report on the generation of high energy femtosecond pulses at 1 MHz repetition rate from a fiber laser pumped optical parametric amplifier (OPA). Nonlinear bandwidth enhancement in fibers provides the intrinsically synchronized signal for the parametric amplifier. We demonstrate large tunability extending from 700 nm to 1500 nm of femtosecond pulses with pulse energies as high as 1.2 muJ when the OPA is seeded by a supercontinuum generated in a photonic crystal fiber. Broadband amplification over more than 85 nm is achieved at a fixed wavelength. Subsequent compression in a prism sequence resulted in 46 fs pulses. With an average power of 0.5 W these pulses have a peak-power above 10 MW. In particular, the average power and pulse energy scalability of both involved concepts, the fiber laser and the parametric amplifier, will enable easy up-scaling to higher powers.

  7. Low-repetition rate femtosecond laser writing of optical waveguides in water-white glass slides.

    Science.gov (United States)

    Lazcano, H E; Vázquez, G V

    2016-04-20

    Energy dose ranges for fabrication of subsurface and ablated ridge waveguides were defined using a low repetition rate femtosecond laser. The waveguides were written along the width of water-white glass slides. The buried waveguides written between 0.23 and 0.62  μJ/μm3 energy dose show strong guidance at 633 nm, reaching in the best cases propagation losses of 0.7 dB/cm. Meanwhile, the ridge waveguides were fabricated between 2.04 and 31.9  μJ/μm3, with a best case of 3.1 dB/cm. Outcomes of this study are promising for use in the manufacturing of sensing devices.

  8. High-power, high repetition-rate, green-pumped, picosecond LBO optical parametric oscillator.

    Science.gov (United States)

    Kienle, Florian; Teh, Peh Siong; Lin, Dejiao; Alam, Shaif-Ul; Price, Jonathan H V; Hanna, D C; Richardson, David J; Shepherd, David P

    2012-03-26

    We report on a picosecond, green-pumped, lithium triborate optical parametric oscillator with record-high output power. It was synchronously pumped by a frequency-doubled (530 nm), pulse-compressed (4.4 ps), high-repetition-rate (230 MHz), fiber-amplified gain-switched laser diode. For a pump power of 17 W, a maximum signal and idler power of 3.7 W and 1.8 W was obtained from the optical parametric oscillator. A signal pulse duration of ~3.2 ps was measured and wide tunability from 651 nm to 1040 nm for the signal and from 1081 nm to 2851 nm for the idler was achieved.

  9. High repetition rate Q-switched radially polarized laser with a graphene-based output coupler

    Energy Technology Data Exchange (ETDEWEB)

    Li, Lifei; Jin, Chenjie; Qi, Mei; Chen, Xiaoming; Ren, Zhaoyu, E-mail: zhengxl@nwu.edu.cn, E-mail: rzy@nwu.edu.cn [National Key Laboratory of Photoelectric Technology and Functional Materials (Culture Base), and Institute of Photonics and Photon-Technology, Northwest University, Xi' an 710069 (China); Zheng, Xinliang, E-mail: zhengxl@nwu.edu.cn, E-mail: rzy@nwu.edu.cn [Department of Physics, Northwest University, Xi' an 710069 (China); Bai, Jintao [National Key Laboratory of Photoelectric Technology and Functional Materials (Culture Base), and Institute of Photonics and Photon-Technology, Northwest University, Xi' an 710069 (China); Department of Physics, Northwest University, Xi' an 710069 (China); Sun, Zhipei [Department of Micro- and Nanosciences, Aalto University, P.O. Box 13500, FI-00076 Aalto (Finland)

    2014-12-01

    We demonstrate a Q-switched radially polarized all-solid-state laser by transferring a graphene film directly onto an output coupler. The laser generates Q-switched radially polarized beam (QRPB) with a pulse width of 192 ns and 2.7 W average output power. The corresponding single pulse energy is up to 16.2 μJ with a high repetition rate of 167 kHz. The M{sup 2} factor and the polarization purity are ∼2.1 and 96%, respectively. Our QRPB source is a simple and low-cost source for a variety of applications, such as industrial material processing, optical trapping, and microscopy.

  10. A high repetition rate passively Q-switched microchip laser for controllable transverse laser modes

    Science.gov (United States)

    Dong, Jun; Bai, Sheng-Chuang; Liu, Sheng-Hui; Ueda, Ken-Ichi; Kaminskii, Alexander A.

    2016-05-01

    A Cr4+:YAG passively Q-switched Nd:YVO4 microchip laser for versatile controllable transverse laser modes has been demonstrated by adjusting the position of the Nd:YVO4 crystal along the tilted pump beam direction. The pump beam diameter-dependent asymmetric saturated inversion population inside the Nd:YVO4 crystal governs the oscillation of various Laguerre-Gaussian, Ince-Gaussian and Hermite-Gaussian modes. Controllable transverse laser modes with repetition rates over 25 kHz and up to 183 kHz, depending on the position of the Nd:YVO4 crystal, have been achieved. The controllable transverse laser beams with a nanosecond pulse width and peak power over hundreds of watts have been obtained for potential applications in optical trapping and quantum computation.

  11. Design Studies for a High-Repetition-Rate FEL Facility at LBNL.

    Energy Technology Data Exchange (ETDEWEB)

    CORLETT, J.; BELKACEM, A.; BYRD, J. M.; FAWLEY, W.; KIRZ, J.; LIDIA, S.; MCCURDY, W.; PADMORE, H.; PENN, G.; POGORELOV, I.; QIANG, J.; ROBIN, D.; SANNIBALE, F.; SCHOENLEIN, R.; STAPLES, J.; STEIER, C.; VENTURINI, M.; WAN, W.; WILCOX, R.; ZHOLENTS, A.

    2007-10-04

    Lawrence Berkeley National Laboratory (LBNL) is working to address the needs of the primary scientific Grand Challenges now being considered by the U.S. Department of Energy, Office of Basic Energy Sciences: we are exploring scientific discovery opportunities, and new areas of science, to be unlocked with the use of advanced photon sources. A partnership of several divisions at LBNL is working to define the science and instruments needed in the future. To meet these needs, we propose a seeded, high-repetition-rate, free-electron laser (FEL) facility. Temporally and spatially coherent photon pulses, of controlled duration ranging from picosecond to sub-femtosecond, are within reach in the vacuum ultraviolet (VUV) to soft X-ray regime, and LBNL is developing critical accelerator physics and technologies toward this goal. We envision a facility with an array of FELs, each independently configurable and tunable, providing a range of photon-beam properties with high average and peak flux and brightness.

  12. Compact, high-repetition-rate source for broadband sum-frequency generation spectroscopy

    Science.gov (United States)

    Heiner, Zsuzsanna; Petrov, Valentin; Mero, Mark

    2017-06-01

    We present a high-efficiency optical parametric source for broadband vibrational sum-frequency generation (BB-VSFG) for the chemically important mid-infrared spectral range at 2800-3600 cm-1 to study hydrogen bonding interactions affecting the structural organization of biomolecules at water interfaces. The source consists of a supercontinuum-seeded, dual-beam optical parametric amplifier with two broadband infrared output beams and a chirped sum-frequency mixing stage providing narrowband visible pulses with adjustable bandwidth. Utilizing a pulse energy of only 60 μJ from a turn-key, 1.03-μm pump laser operating at a repetition rate of 100 kHz, the source delivers 6-cycle infrared pulses at 1.5 and 3.2 μm with pulse energies of 4.6 and 1.8 μJ, respectively, and narrowband pulses at 0.515 μm with a pulse energy of 5.0 μJ. The 3.2-μm pulses are passively carrier envelope phase stabilized with fluctuations at the 180-mrad level over a 10-s time period. The 1.5-μm beamline can be exploited to deliver pump pulses for time-resolved studies after suitable frequency up-conversion. The high efficiency, stability, and two orders of magnitude higher repetition rate of the source compared to typically employed systems offer great potential for providing a boost in sensitivity in BB-VSFG experiments at a reduced cost.

  13. Assessing Sub-Antarctic Zone primary productivity from fast repetition rate fluorometry

    Science.gov (United States)

    Cheah, Wee; McMinn, Andrew; Griffiths, F. Brian; Westwood, Karen J.; Wright, Simon W.; Molina, Ernesto; Webb, Jason P.; van den Enden, Rick

    2011-11-01

    In situ primary productivity (PP) in the Sub-Antarctic Zone (SAZ) and the Polar Frontal Zone (PFZ) south of Australia was estimated using fast repetition rate fluorometry (FRRF). FRRF-derived PP at Process station 3 (P3) southeast of Tasmania (46°S, 153°E) were higher than P1 in the southwest of Tasmania (46°S, 140°E) and P2 in the Polar Frontal Zone (54°S, 146°E). The FRRF-derived PP rates were well correlated with 14C-uptake rates from one-hour incubations ( r2=0.85, slope=1.23±0.05, pMehler reaction, which are stimulated at high irradiance. Our results indicate that FRRF can be used to estimate photosynthesis rates in the SAZ and PFZ but to derive an accurate estimation of C-fixation requires a detailed understanding of the physiological properties of the cells and their response to oceanographic parameters under different environmental conditions.

  14. Advanced optic fabrication using ultrafast laser radiation

    Science.gov (United States)

    Taylor, Lauren L.; Qiao, Jun; Qiao, Jie

    2016-03-01

    Advanced fabrication and finishing techniques are desired for freeform optics and integrated photonics. Methods including grinding, polishing and magnetorheological finishing used for final figuring and polishing of such optics are time consuming, expensive, and may be unsuitable for complex surface features while common photonics fabrication techniques often limit devices to planar geometries. Laser processing has been investigated as an alternative method for optic forming, surface polishing, structure writing, and welding, as direct tuning of laser parameters and flexible beam delivery are advantageous for complex freeform or photonics elements and material-specific processing. Continuous wave and pulsed laser radiation down to the nanosecond regime have been implemented to achieve nanoscale surface finishes through localized material melting, but the temporal extent of the laser-material interaction often results in the formation of a sub-surface heat affected zone. The temporal brevity of ultrafast laser radiation can allow for the direct vaporization of rough surface asperities with minimal melting, offering the potential for smooth, final surface quality with negligible heat affected material. High intensities achieved in focused ultrafast laser radiation can easily induce phase changes in the bulk of materials for processing applications. We have experimentally tested the effectiveness of ultrafast laser radiation as an alternative laser source for surface processing of monocrystalline silicon. Simulation of material heating associated with ultrafast laser-material interaction has been performed and used to investigate optimized processing parameters including repetition rate. The parameter optimization process and results of experimental processing will be presented.

  15. Effect of Rolling Temperature and Ultrafast Cooling Rate on Microstructure and Mechanical Properties of Steel Plate

    Science.gov (United States)

    Ye, Qibin; Liu, Zhenyu; Yang, Yu; Wang, Guodong

    2016-07-01

    Microstructure can vary significantly through thickness after ultrafast cooling of rolled steel plates, impacting their mechanical properties. This study examined the microstructure, microstructural banding at centerline, and mechanical properties through thickness for different ultrafast cooling conditions and rolling temperatures. One set of steels (UC1 and UC2) were ultrafast-cooled (UFC) at 40 K/s after finish rolling at 1223 K and 1193 K (950 °C and 910 °C), respectively, while the second set (LC) was cooled by laminar cooling at 17 K/s after finish rolling at 1238 K (965 °C). UFC produced microstructural variation through thickness; highly dislocated lath-type bainitic ferrite was formed near the surface, whereas the primary microstructure was acicular ferrite and irregular polygonal ferrite in the interior of UC1 and UC2 steels, respectively. However, UFC has the advantage of suppression of microstructural banding in centerline segregation regions. The ferrite grain size in both UFC-cooled steels was refined to ~5 μm, increasing strength and toughness. The optimum combination of properties was obtained in UC2 steel with appropriate low finish rolling temperature, being attributed to the distinct microstructure resulting from work-hardened austenite before UFC.

  16. High-repetition rate industrial TEA CO2 laser with average output power of 1.5 kW

    Science.gov (United States)

    Wan, Chongyi; Liu, Shiming; Zhou, Jinwen; Qi, Jilan; Yang, Xiaola; Wu, Jin; Tan, Rongqing; Wang, Lichun; Mei, Qichu

    1995-03-01

    High power high repetition rate TEA CO2 laser has potential importance in material processing such as shock hardening, glazing, drilling, welding, and cutting for high damage threshold materials, as well as in chemical reaction and isotope separation. This paper describes a transverse-flow closed-cycle UV-preionized TEA CO2 laser with peak pulse power of 20 MW, maximum average power of 1.5 KW at repetition rate of 300 HZ. The laser has compact constructure of gas flow circulation system using tangential fans. With addition of small amounts of H2 and CO to the normal CO2-N2-He gas mixture, one filling sealed operating lifetime is up to millions of pulses. A novel spark gap switch has been developed for very high repetition rate laser discharge in the condition of high pulse power.

  17. Dynamics of dissipative solitons in a high repetition rate normal-dispersion erbium-doped fiber laser

    CERN Document Server

    Luo, Yiyang; Zhao, Luming; Sun, Qizhen; Wu, Zhichao; Xu, Zhilin; Fu, Songnian; Liu, Deming

    2016-01-01

    The dynamics of dissipative solitons (DSs) are explored in a high repetition rate normal-dispersion erbium-doped fiber laser for the first time. Despite of the high fundamental repetition rate of 129 MHz and thus the low pulse energy, a DS train with a dechirped pulse width of 418 fs, period-doubling of single and dual DSs, as well as 258 MHz 2nd-order harmonic mode-locking of DSs can be observed in the fiber laser with increasing pump power and appropriate settings. A transmitted semiconductor saturable absorber and a wavelength division multiplexer/isolator/tap hybrid module are employed to simplify the laser configuration, thus not only increasing the repetition rate, but also enhancing the stability and robustness of the fiber laser due to the commercial availability of all the components.

  18. Cavity-Enhanced Ultrafast Transient Absorption Spectroscopy

    CERN Document Server

    Reber, Melanie A R; Allison, Thomas K

    2015-01-01

    We present a new technique using a frequency comb laser and optical cavities for performing ultrafast transient absorption spectroscopy with improved sensitivity. Resonantly enhancing the probe pulses, we demonstrate a sensitivity of $\\Delta$OD $ = 1 \\times 10^{-9}/\\sqrt{\\mbox{Hz}}$ for averaging times as long as 30 s per delay point ($\\Delta$OD$_{min} = 2 \\times 10^{-10}$). Resonantly enhancing the pump pulses allows us to produce a high excitation fraction at high repetition-rate, so that signals can be recorded from samples with optical densities as low as OD $\\approx 10^{-8}$, or column densities $< 10^{10}$ molecules/cm$^2$. This high sensitivity enables new directions for ultrafast spectroscopy.

  19. A Real-Time Terahertz Time-Domain Polarization Analyzer with 80-MHz Repetition-Rate Femtosecond Laser Pulses

    Directory of Open Access Journals (Sweden)

    Takehiro Tachizaki

    2013-03-01

    Full Text Available We have developed a real-time terahertz time-domain polarization analyzer by using 80-MHz repetition-rate femtosecond laser pulses. Our technique is based on the spinning electro-optic sensor method, which we recently proposed and demonstrated by using a regenerative amplifier laser system; here we improve the detection scheme in order to be able to use it with a femtosecond laser oscillator with laser pulses of a much higher repetition rate. This improvement brings great advantages for realizing broadband, compact and stable real-time terahertz time-domain polarization measurement systems for scientific and industrial applications.

  20. A real-time terahertz time-domain polarization analyzer with 80-MHz repetition-rate femtosecond laser pulses.

    Science.gov (United States)

    Watanabe, Shinichi; Yasumatsu, Naoya; Oguchi, Kenichi; Takeda, Masatoshi; Suzuki, Takeshi; Tachizaki, Takehiro

    2013-03-11

    We have developed a real-time terahertz time-domain polarization analyzer by using 80-MHz repetition-rate femtosecond laser pulses. Our technique is based on the spinning electro-optic sensor method, which we recently proposed and demonstrated by using a regenerative amplifier laser system; here we improve the detection scheme in order to be able to use it with a femtosecond laser oscillator with laser pulses of a much higher repetition rate. This improvement brings great advantages for realizing broadband, compact and stable real-time terahertz time-domain polarization measurement systems for scientific and industrial applications.

  1. Compact and high repetition rate Kerr-lens mode-locked 532 nm Nd:YVO4 laser

    Science.gov (United States)

    Li, Zuohan; Peng, Jiying; Yuan, Ruixia; Wang, Tongtong; Yao, Jianquan; Zheng, Yi

    2015-11-01

    A compact and feasible CW Kerr-lens-induced mode-locked 532 nm Nd:YVO4 laser system was experimentally demonstrated for the first time with theoretical analysis. Kerr-lens mode locking with intracavity second harmonic generation provides a promising method to generate a high-repetition-rate picosecond green laser. With an incident pump power of 6 W, the average output power of mode locking was 258 mW at a high repetition rate of 1.1 GHz.

  2. Study of filamentation with a high power high repetition rate ps laser at 1.03 µm.

    Science.gov (United States)

    Houard, A; Jukna, V; Point, G; André, Y-B; Klingebiel, S; Schultze, M; Michel, K; Metzger, T; Mysyrowicz, A

    2016-04-01

    We study the propagation of intense, high repetition rate laser pulses of picosecond duration at 1.03 µm central wavelength through air. Evidence of filamentation is obtained from measurements of the beam profile as a function of distance, from photoemission imaging and from spatially resolved sonometric recordings. Good agreement is found with numerical simulations. Simulations reveal an important self shortening of the pulse duration, suggesting that laser pulses with few optical cycles could be obtained via double filamentation. An important lowering of the voltage required to induce guided electric discharges between charged electrodes is measured at high laser pulse repetition rate.

  3. Mode-locked Yb-doped fiber laser emitting broadband pulses at ultra-low repetition rates

    CERN Document Server

    Bowen, Patrick; Provo, Richard; Harvey, John D; Broderick, Neil G R

    2016-01-01

    We report on an environmentally stable, Yb-doped, all-normal dispersion, mode-locked fibre laser that is capable of creating broadband pulses with ultra-low repetition rates. Specifically, through careful positioning of fibre sections in an all-PM-fibre cavity mode-locked with a nonlinear amplifying loop mirror, we achieve stable pulse trains with repetition rates as low as 506 kHz. The pulses have several nanojules of energy and are compressible down to ultrashort (< 500 fs) durations.

  4. High-repetition rate relativistic electron beam generation from intense laser solid interactions

    Science.gov (United States)

    Batson, Thomas; Nees, John; Hou, Bixue; Thomas, A. G. R.; Krushelnick, Karl

    2015-05-01

    Relativistic electron beams have applications spanning materials science, medicine, and home- land security. Recent advances in short pulse laser technology have enabled the production of very high focused intensities at kHz rep rates. Consequently this has led to the generation of high ux sources of relativistic electrons- which is a necessary characteristic of these laser plasma sources for any potential application. In our experiments, through the generation of a plasma with the lambda cubed laser system at the University of Michigan (a 5 × 1018W=cm2, 500 Hz, Ti:Sapphire laser), we have measured electrons ejected from the surface of fused silica nd Cu targets having energies in excess of an MeV. The spectrum of these electrons was measured with respect to incident laser angle, prepulse timing, and focusing conditions. While taken at a high repetition rate, the pulse energy of the lambda cubed system was consistently on the order of 10 mJ. In order to predict scaling of the electron energy with laser pulse energy, simulations are underway which compare the spectrum generated with the lambda cubed system to the predicted spectrum generated on the petawatt scale HERCULES laser system at the University of Michigan.

  5. Research of application of high-repetition-rate green laser in underwater imaging system

    Science.gov (United States)

    Han, Jie-fei; Luo, Tao; Sun, Li-ying; Ding, Chi-zhu; Xia, Min; Yang, Ke-cheng

    2013-09-01

    It is commonly known that absorption and scattering are the main causes of reducing performance of imaging system, especially imaging distance and resolution. Generally, various techniques are applied to decrease the effect of scattering, such as synchronous scanning and range-gated technique. Continuous-laser imaging technique meets requirements of imaging objects in the large field of view in real time, but imaging distance is less than 2 attenuation lengths in natural water. High-repetition-rate green laser, called quasi-continuous wave (QCW) green laser, is a better light source for underwater imaging. It has 1 kHz-100 kHz modulated rate, and its single pulse peak power is KW magnitude, which can be applied to range-gated imaging as Canadian LUCIE system. In addition, its polarization property is excellent for underwater polarization imaging. Therefore, it has enormous potential to underwater imaging. In order to realize its performance in underwater imaging system, we setup a separated underwater staring imaging system. For this system, a theoretic model is built by the lidar equation and optic transmission theory, and the system is evaluated by modulation transfer function (MTF). The effects of laser and receiver's parameters for the system are analyzed. Then the comparative experiments are conducted in turbid water in laboratory. The results indicate that high pulse energy improves imaging distance. Aperture and polarization could reduce the effect of scattering effectively in staring system. The result shows that this underwater system performs better by choosing suitable parameters of source and receiver.

  6. Improved repetition rate mixed isotope CO{sub 2} TEA laser

    Energy Technology Data Exchange (ETDEWEB)

    Cohn, D. B., E-mail: dbctechnology@earthlink.net [DBC Technology Corp., 4221 Mesa St, Torrance, California 90505 (United States)

    2014-09-15

    A compact CO{sub 2} TEA laser has been developed for remote chemical detection that operates at a repetition rate of 250 Hz. It emits 700 mJ/pulse at 10.6 μm in a multimode beam with the {sup 12}C{sup 16}O{sub 2} isotope. With mixed {sup 12}C{sup 16}O{sub 2} plus {sup 13}C{sup 16}O{sub 2} isotopes it emits multiple lines in both isotope manifolds to improve detection of a broad range of chemicals. In particular, output pulse energies are 110 mJ/pulse at 9.77 μm, 250 mJ/pulse at 10 μm, and 550 mJ/pulse at 11.15 μm, useful for detection of the chemical agents Sarin, Tabun, and VX. Related work shows capability for long term sealed operation with a catalyst and an agile tuner at a wavelength shift rate of 200 Hz.

  7. Time-stretched real-time measurement technique for ultrafast absorption variations with TS/s sampling-rate.

    Science.gov (United States)

    Weber, Stefan; Waller, Erik H; Kaiser, Christoph; von Freymann, Georg

    2017-06-26

    We present a real-time measurement technique, based on time-stretching for measuring the temporal dynamic of ultrafast absorption variations with a sampling-rate of up to 1.1 TS/s. The single-shot captured data are stretched in a resonator-based time-stretch system with a variable stretch-factor of up to 13.8. The time-window of the time-stretch system for capturing the signal of interest is about 800 ps with an update-rate of 10 MHz. An adapted optical backpropagation algorithm is introduced for reconstructing the original unstretched event. As proof-of-principle the temporal characteristic of a picosecond semiconductor saturable absorber mirror is measured: The real-time results agree well with the results of a conventional pump-probe experiment. The time-stretch technique potentially allows to gain access to a large field of ultrafast absorption variations like semiconductor charge carrier dynamics, irreversible polymerization processes, and saturable absorber materials.

  8. Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory.

    Science.gov (United States)

    Weathersby, S P; Brown, G; Centurion, M; Chase, T F; Coffee, R; Corbett, J; Eichner, J P; Frisch, J C; Fry, A R; Gühr, M; Hartmann, N; Hast, C; Hettel, R; Jobe, R K; Jongewaard, E N; Lewandowski, J R; Li, R K; Lindenberg, A M; Makasyuk, I; May, J E; McCormick, D; Nguyen, M N; Reid, A H; Shen, X; Sokolowski-Tinten, K; Vecchione, T; Vetter, S L; Wu, J; Yang, J; Dürr, H A; Wang, X J

    2015-07-01

    Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used to study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. SLAC National Accelerator Laboratory recently launched the Ultrafast Electron Diffraction (UED) and microscopy Initiative aiming at developing the next generation ultrafast electron scattering instruments. As the first stage of the Initiative, a mega-electron-volt (MeV) UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at 120-Hz repetition rate with outstanding performance. In this paper, we report on the SLAC MeV UED system and its performance, including the reciprocal space resolution, temporal resolution, and machine stability.

  9. Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory

    Energy Technology Data Exchange (ETDEWEB)

    Weathersby, S. P. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Brown, G. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Centurion, M. [University of Nebraska-Lincoln, 855 N 16th Street, Lincoln, Nebraska 68588, USA; Chase, T. F. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Coffee, R. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Corbett, J. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Eichner, J. P. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Frisch, J. C. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Fry, A. R. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Gühr, M. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Hartmann, N. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Hast, C. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Hettel, R. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Jobe, R. K. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Jongewaard, E. N. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Lewandowski, J. R. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Li, R. K. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Lindenberg, A. M. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Makasyuk, I. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; May, J. E. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; McCormick, D. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Nguyen, M. N. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Reid, A. H. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Shen, X. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Sokolowski-Tinten, K. [University of Duisburg-Essen, Lotharstrasse 1, 47048 Duisburg, Germany; Vecchione, T. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Vetter, S. L. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Wu, J. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Yang, J. [University of Nebraska-Lincoln, 855 N 16th Street, Lincoln, Nebraska 68588, USA; Dürr, H. A. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA; Wang, X. J. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA

    2015-07-01

    Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used to study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. SLAC National Accelerator Laboratory recently launched the Ultrafast Electron Diffraction (UED) and microscopy Initiative aiming at developing the next generation ultrafast electron scattering instruments. As the first stage of the Initiative, a mega-electron-volt (MeV) UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at 120-Hz repetition rate with outstanding performance. In this paper, we report on the SLAC MeV UED system and its performance, including the reciprocal space resolution, temporal resolution, and machine stability.

  10. LUX - A recirculating linac-based ultrafast X-ray source

    Energy Technology Data Exchange (ETDEWEB)

    Corlett, J.N.; Barletta, W.A.; DeSantis, S.; Doolittle, L.; Fawley, W.M.; Green, M.A.; Heimann, P.; Leone, S.R.; Lidia, S.; Li, D.; Parmigiani, F.; Ratti, A.; Robinson, K.; Schoenlein, R.; Staples, J.; Wan, W.; Wells, R.; Wilcox, R.; Wolski, A.; Zholents, A.

    2003-08-01

    We describe the design of a proposed source of ultra-fast synchrotron radiation x-ray pulses based on a recirculating superconducting linac, with an integrated array of ultrafast laser systems. The source produces x-ray pulses with duration of 10-50 fs at a 10 kHz repetition rate, with tunability from EUV to hard x-ray regimes, and optimized for the study of ultra-fast dynamics. A high-brightness rf photocathode provides electron bunches. An injector linac accelerates the beam to the 100 MeV range, and is followed by four passes through a 700 MeV recirculating linac. Ultrafast hard x-ray pulses are obtained by a combination of electron bunch manipulation, transverse temporal correlation of the electrons, and x-ray pulse compression. EUV and soft x-ray pulses as short as 10 fs are generated in a harmonic-cascade free electron laser scheme.

  11. Heart Rate Variability and Skin Conductance During Repetitive TMS Course in Children with Autism.

    Science.gov (United States)

    Wang, Yao; Hensley, Marie K; Tasman, Allan; Sears, Lonnie; Casanova, Manuel F; Sokhadze, Estate M

    2016-03-01

    Autism spectrum disorder (ASD) is a developmental disorder marked by difficulty in social interactions and communication. ASD also often present symptoms of autonomic nervous system (ANS) functioning abnormalities. In individuals with autism the sympathetic branch of the ANS presents an over-activation on a background of the parasympathetic activity deficits, creating an autonomic imbalance, evidenced by a faster heart rate with little variation and increased tonic electrodermal activity. The objective of this study was to explore the effect of 12 sessions of 0.5 Hz repetitive transcranial magnetic stimulation (rTMS) over dorsolateral prefrontal cortex (DLPFC) on autonomic activity in children with ASD. Electrocardiogram and skin conductance level (SCL) were recorded and analyzed during each session of rTMS. The measures of interest were time domain (i.e., R-R intervals, standard deviation of cardiac intervals, NN50-cardio-intervals >50 ms different from preceding interval) and frequency domain heart rate variability (HRV) indices [i.e., power of high frequency (HF) and low frequency (LF) components of HRV spectrum, LF/HF ratio]. Based on our prior pilot studies it was proposed that the course of 12 weekly inhibitory low-frequency rTMS bilaterally applied to the DLPFC will improve autonomic balance probably through improved frontal inhibition of the ANS activity, and will be manifested in an increased length of cardiointervals and their variability, and in higher frequency-domain HRV in a form of increased HF power, decreased LF power, resulting in decreased LF/HF ratio, and in decreased SCL. Our post-12 TMS results showed significant increases in cardiac intervals variability measures and decrease of tonic SCL indicative of increased cardiac vagal control and reduced sympathetic arousal. Behavioral evaluations showed decreased irritability, hyperactivity, stereotype behavior and compulsive behavior ratings that correlated with several autonomic variables.

  12. Generation of low jitter and discrete tunable dual-wavelength optical pulses at arbitrary repetition rates

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ming-jiang; WANG Yun-cai

    2006-01-01

    A novel and simple method to generate low timing jitter and discrete tunable dual-wavelength optical pulses at arbitrary repetition rates is demonstrated in this paper.Two multiple quantum wells distributed feedback laser diodes,were used as the external seeding sources to inject the external photons into a gain-switched Fabry-Perot laser diode.The output wavelengths can be tuned discretely to coincide with any two lasing modes in the gain spectra range of the Fabry-Perot Laser diode,and the output side mode suppression ratio was better than 25 dB.Moreover,the timing jitter of optical pulses was reduced from 1.89 ps to 0.83 ps.It was empirically found that the lowest timing jitter operation occurred when the injected light wavelength is 0.2-0.3 nm shorter than the locked mode of the Fabry-Perot laser diode.To our knowledge,this is the first report of using two DFB laser diodes as a seeding source to reduce pulses jitter and select lasing dual-wavelength simultaneously.

  13. [INVITED] Laser welding of glasses at high repetition rates - Fundamentals and prospects

    Science.gov (United States)

    Richter, Sören; Zimmermann, Felix; Tünnermann, Andreas; Nolte, Stefan

    2016-09-01

    We report on the welding of various glasses with ultrashort laser pulses. Femtosecond laser pulses at repetition rates in the MHz range are focused at the interface between two substrates, resulting in multiphoton absorption and heat accumulation from successive pulses. This leads to local melting and subsequent resolidification which can be used to weld the glasses. The fundamental interaction process was studied using an in-situ micro Raman setup to measure the laser induced temperature distribution and its temporal decay. The induced network changes were analyzed by Raman spectrocopy identifying an increase of three and four membered silicon rings within the laser irradiated area. In order to determine the stability of the laser welded samples a three point bending test was used. Thereby, we identified that the maximal achievable breaking strength is limited by laser induced stress surrounding the modified material. To minimize the amount of stress bursts of laser pulses or an post processing annealing step can be applied. Besides fused silica, we welded borosilicate glasses and glasses with a low thermal expansion coefficient. Even the welding of different glass combinations is possible demonstrating the versatility of ultrashort pulse induced laser welding.

  14. Bottle microresonator broadband and low-repetition-rate frequency comb generator.

    Science.gov (United States)

    Dvoyrin, V; Sumetsky, M

    2016-12-01

    We propose a new type of broadband and low repetition rate (RR) frequency comb generator that has the shape of an elongated and nanoscale-shallow optical bottle microresonator created at the surface of an optical fiber. The free spectral range (FSR) of the broadband azimuthal eigenfrequency series of this resonator is the exact multiple of the FSR of the dense and narrowband axial series. The effective radius variation of the microresonator is close to a parabola with a nanoscale height that is greater or equal to λ/2πn0. (Here λ is the characteristic radiation wavelength and n0 is the refractive index of the microresonator material.) Overall, the microresonator possesses a broadband, small FSR and accurately equidistant spectrum convenient for the generation of a broadband and low RR optical frequency comb. It is shown that this comb can be generated by pumping with a cw laser, with a radiation frequency that matches a single axial eigenfrequency of the microresonator or, alternatively, by pumping with a mode-locked laser, which generates a narrowband low RR comb matching a series of equidistant axial eigenfrequencies situated between adjacent azimuthal eigenfrequencies.

  15. A high repetition rate experimental setup for quantum non-linear optics with cold Rydberg atoms

    Science.gov (United States)

    Busche, Hannes; Ball, Simon W.; Huillery, Paul

    2016-12-01

    Using electromagnetically induced transparency and photon storage, the strong dipolar interactions between Rydberg atoms and the resulting dipole blockade can be mapped onto light fields to realise optical non-linearities and interactions at the single photon level. We report on the realisation of an experimental apparatus designed to study interactions between single photons stored as Rydberg excitations in optically trapped microscopic ensembles of ultracold 87Rb atoms. A pair of in-vacuum high numerical aperture lenses focus excitation and trapping beams down to 1 μm, well below the Rydberg blockade. Thanks to efficient magneto-optical trap (MOT) loading from an atomic beam generated by a 2D MOT and the ability to recycle the microscopic ensembles more than 20000 times without significant atom loss, we achieve effective repetition rates exceeding 110 kHz to obtain good photon counting statistics on reasonable time scales. To demonstrate the functionality of the setup, we present evidence of strong photon interactions including saturation of photon storage and the retrieval of non-classical light. Using in-vacuum antennae operating at up to 40 GHz, we perform microwave spectroscopy on photons stored as Rydberg excitations and observe an interaction induced change in lineshape depending on the number of stored photons.

  16. Design of high gradient, high repetition rate damped C -band rf structures

    Science.gov (United States)

    Alesini, David; Bellaveglia, Marco; Bini, Simone; Gallo, Alessandro; Lollo, Valerio; Pellegrino, Luigi; Piersanti, Luca; Cardelli, Fabio; Migliorati, Mauro; Mostacci, Andrea; Palumbo, Luigi; Tocci, Simone; Ficcadenti, Luca; Pettinacci, Valerio

    2017-03-01

    The gamma beam system of the European Extreme Light Infrastructure-Nuclear Physics project foresees the use of a multibunch train colliding with a high intensity recirculated laser pulse. The linac energy booster is composed of 12 traveling wave C -band structures, 1.8 m long with a field phase advance per cell of 2 π /3 and a repetition rate of 100 Hz. Because of the multibunch operation, the structures have been designed with a dipole higher order mode (HOM) damping system to avoid beam breakup (BBU). They are quasiconstant gradient structures with symmetric input couplers and a very effective damping of the HOMs in each cell based on silicon carbide (SiC) rf absorbers coupled to each cell through waveguides. An optimization of the electromagnetic and mechanical design has been done to simplify the fabrication and to reduce the cost of the structures. In the paper, after a review of the beam dynamics issues related to the BBU effects, we discuss the electromagnetic and thermomechanic design criteria of the structures. We also illustrate the criteria to compensate the beam loading and the rf measurements that show the effectiveness of the HOM damping.

  17. A high repetition rate transverse beam profile diagnostic for laser-plasma proton sources

    Science.gov (United States)

    Dover, Nicholas; Nishiuchi, Mamiko; Sakaki, Hironao; Kando, Masaki; Nishitani, Keita

    2016-10-01

    The recently upgraded J-KAREN-P laser can provide PW peak power and intensities approaching 1022 Wcm-2 at 0.1 Hz. Scaling of sheath acceleration to such high intensities predicts generation of protons to near 100 MeV, but changes in electron heating mechanisms may affect the emitted proton beam properties, such as divergence and pointing. High repetition rate simultaneous measurement of the transverse proton distribution and energy spectrum are therefore key to understanding and optimising the source. Recently plastic scintillators have been used to measure online proton beam transverse profiles, removing the need for time consuming post-processing. We are therefore developing a scintillator based transverse proton beam profile diagnostic for use in ion acceleration experiments using the J-KAREN-P laser. Differential filtering provides a coarse energy spectrum measurement, and time-gating allows differentiation of protons from other radiation. We will discuss the design and implementation of the diagnostic, as well as proof-of-principle results from initial experiments on the J-KAREN-P system demonstrating the measurement of sheath accelerated proton beams up to 20 MeV.

  18. A HIGH REPETITION RATE VUV-SOFT X-RAY FEL CONCEPT

    Energy Technology Data Exchange (ETDEWEB)

    Corlett, J.; Byrd, J.; Fawley, W.M.; Gullans, M.; Li, D.; Lidia,S.M.; Padmore, H.; Penn, G.; Pogorelov, I.; Qiang, J.; Robin, D.; Sannibale, F.; Staples, J.W.; Steier, C.; Venturini, M.; Virostek, S.; Wan, W.; Wells, R.; Wilcox, R.; Wurtele, J.; Zholents, A.

    2007-06-24

    We report on design studies for a seeded FEL light source that is responsive to the scientific needs of the future. The FEL process increases radiation flux by several orders of magnitude above existing incoherent sources, and offers the additional enhancements attainable by optical manipulations of the electron beam: control of the temporal duration and bandwidth of the coherent output, reduced gain length in the FEL, utilization of harmonics to attain shorter wavelengths, and precise synchronization of the x-ray pulse with seed laser systems. We describe an FEL facility concept based on a high repetition rate RF photocathode gun, that would allow simultaneous operation of multiple independent FEL's, each producing high average brightness, tunable over the VUV-soft x-ray range, and each with individual performance characteristics determined by the configuration of the FEL. SASE, enhanced-SASE (ESASE), seeded, harmonic generation, and other configurations making use of optical manipulations of the electron beam may be employed, providing a wide range of photon beam properties to meet varied user demands.

  19. Design of a VHF-band RF Photoinjector with Megahertz BeamRepetition Rate

    Energy Technology Data Exchange (ETDEWEB)

    Staples, J.W.; Baptiste, K.M.; Corlett, J.N.; Kwiatkowski, S.; Lidia, S.M.; Qiang, J.; Sannibale, F.; Sonnad, K.G.; Virostek, S.P.; Wells, R.P.

    2007-06-01

    New generation accelerator-based X-ray light sources require high quality beams with high average brightness. Normal conducting L- and S-band photoinjectors are limited in repetition rate and D-C (photo)injectors are limited in field strength at the cathode. We propose a low frequency normal-conducting cavity, operating at 50 to 100MHz CW, to provide beam bunches of up to the cavity frequency. The photoinjector uses a re-entrant cavity structure, requiring less than 100 kW CW, with a peak wall power density less than 10 W/cm{sup 2}. The cavity will support a vacuum down to 10 picoTorr, with a load-lock mechanism for easy replacement of photocathodes. The photocathode can be embedded in a magnetic field to provide correlations useful for emittance exchange. Beam dynamics simulations indicate that normalized emittances smaller than 1 mm-mrad are possible with gap voltage of 750 kV, with fields up to 20 MV/m at the photocathode, for 1 nanocoulomb charge per bunch after acceleration and emittance compensation. Long-bunch operation (10's of picosecond) is made possible by the low cavity frequency, permitting low bunch current at the 750 kV gap voltage.

  20. High-repetition-rate picosecond pump laser based on a Yb:YAG disk amplifier for optical parametric amplification.

    Science.gov (United States)

    Metzger, Thomas; Schwarz, Alexander; Teisset, Catherine Yuriko; Sutter, Dirk; Killi, Alexander; Kienberger, Reinhard; Krausz, Ferenc

    2009-07-15

    We report an optically synchronized picosecond pump laser for optical parametric amplifiers based on an Yb:YAG thin-disk amplifier. At 3 kHz repetition rate, pulse energies of 25 mJ with 1.6 ps pulse duration were achieved with an rms fluctuation in pulse energy of pumped regenerative amplifier.

  1. High-repetition-rate optical delay line using a micromirror array and galvanometer mirror for a terahertz system.

    Science.gov (United States)

    Kitahara, Hideaki; Tani, Masahiko; Hangyo, Masanori

    2009-07-01

    We developed a high-repetition-rate optical delay line based on a micromirror array and galvanometer mirror for terahertz time-domain spectroscopy. The micromirror array is fabricated by using the x-ray lithographic technology. The measurement of terahertz time-domain waveforms with the new optical delay line is demonstrated successfully up to 25 Hz.

  2. High Repetition Rate Electron Beam RF-Acceleration and Sub-Millimeter Wave Generation Via a Free Electron Laser.

    Science.gov (United States)

    1986-02-14

    Period, Including Journal References: (a) D.B. McDermott, W.J. Nunan and N.C. Luhmann, Jr., "A High Duty Cycle, Compact 94 GHz Free Electron Laser...34 submitted to Journal IR and am-Waves. (b) W.J. Nunan , D.B. McDermott and N.C. Luhmann, Jr., "A High Repetition *Rate, Compact 94 GHz Free Electron Laser...34 Bulletin of the American Phy- * ) sical Society 30, 1543 (1985). L J (c) D.B. McDermott, W.J. Nunan and N.C. Luhmann, Jr., "A High RepetitionLL

  3. Design study of a low-emittance high-repetition rate thermionic rf gun

    Science.gov (United States)

    Opanasenko, A.; Mytrochenko, V.; Zhaunerchyk, V.; Goryashko, V. A.

    2017-05-01

    We propose a novel gridless continuous-wave radiofrequency (rf) thermionic gun capable of generating nC ns electron bunches with a rms normalized slice emittance close to the thermal level of 0.3 mm mrad. In order to gate the electron emission, an externally heated thermionic cathode is installed into a stripline-loop conductor. Two high-voltage pulses propagating towards each other in the stripline-loop overlap in the cathode region and create a quasielectrostatic field gating the electron emission. The repetition rate of pulses is variable and can reach up to one MHz with modern solid-state pulsers. The stripline attached to a rf gun cavity wall has with the wall a common aperture that allows the electrons to be injected into the rf cavity for further acceleration. Thanks to this innovative gridless design, simulations suggest that the bunch emittance is approximately at the thermal level after the bunch injection into the cavity provided that the geometry of the cathode and aperture are properly designed. Specifically, a concave cathode is adopted to imprint an Ƨ-shaped distribution onto the beam transverse phase-space to compensate for an S-shaped beam distribution created by the spherical aberration of the aperture-cavity region. In order to compensate for the energy spread caused by rf fields of the rf gun cavity, a 3rd harmonic cavity is used. A detailed study of the electrodynamics of the stripline and rf gun cavity as well as the beam optics and bunch dynamics are presented.

  4. Oral-diadochokinetic rates for Hebrew-speaking healthy ageing population: non-word versus real-word repetition.

    Science.gov (United States)

    Ben-David, Boaz M; Icht, Michal

    2017-05-01

    Oral-diadochokinesis (oral-DDK) tasks are extensively used in the evaluation of motor speech abilities. Currently, validated normative data for older adults (aged 65 years and older) are missing in Hebrew. The effect of task stimuli (non-word versus real-word repetition) is also non-clear in the population of older adult Hebrew speakers. (1) To establish a norm for oral-DDK rate for older adult (aged 65 years and older) Hebrew speakers, and to investigate the possible effect of age and gender on performance rate; and (2) to examine the effects of stimuli (non-word versus real word) on oral-DDK rates. In experiment 1, 88 healthy older Hebrew speakers (60-95 years, 48 females and 40 males) were audio-recorded while performing an oral-DDK task (repetition of /pataka/), and repetition rates (syllables/s) were coded. In experiment 2, the effect of real-word repetition was evaluated. Sixty-eight older Hebrew speakers (aged 66-95 years, 43 females and 25 males) were asked to repeat 'pataka' (non-word) and 'bodeket' (Hebrew real word). Experiment 1: Oral-DDK performance for older adult Hebrew speakers was 5.07 syllables/s (SD = 1.16 syllables/s), across age groups and gender. Comparison of this data with Hebrew norms for younger adults (and equivalent data in English) shows the following gradient of oral-DDK rates: ages 15-45 > 65-74 > 75-86 years. Gender was not a significant factor in our data. Experiment 2: Repetition of real words was faster than that of non-words, by 13.5%. The paper provides normative values for oral-DDK rates for older Hebrew speakers. The data show the large impact of ageing on oro-motor functions. The analysis further indicates that speech and language pathologists should consider separate norms for clients of 65-74 years and those of 75-86 years. Hebrew rates were found to be different from English norms for the oldest group, shedding light on the impact of language on these norms. Finally, the data support using a dual-protocol (real- and non

  5. Engineering model for ultrafast laser microprocessing

    Science.gov (United States)

    Audouard, E.; Mottay, E.

    2016-03-01

    Ultrafast laser micro-machining relies on complex laser-matter interaction processes, leading to a virtually athermal laser ablation. The development of industrial ultrafast laser applications benefits from a better understanding of these processes. To this end, a number of sophisticated scientific models have been developed, providing valuable insights in the physics of the interaction. Yet, from an engineering point of view, they are often difficult to use, and require a number of adjustable parameters. We present a simple engineering model for ultrafast laser processing, applied in various real life applications: percussion drilling, line engraving, and non normal incidence trepanning. The model requires only two global parameters. Analytical results are derived for single pulse percussion drilling or simple pass engraving. Simple assumptions allow to predict the effect of non normal incident beams to obtain key parameters for trepanning drilling. The model is compared to experimental data on stainless steel with a wide range of laser characteristics (time duration, repetition rate, pulse energy) and machining conditions (sample or beam speed). Ablation depth and volume ablation rate are modeled for pulse durations from 100 fs to 1 ps. Trepanning time of 5.4 s with a conicity of 0.15° is obtained for a hole of 900 μm depth and 100 μm diameter.

  6. A Device and Methodology for Measuring Repetitive Lifting VO2max (Oxygen Consumption Rate)

    Science.gov (United States)

    1987-08-01

    and its estimate from skinfold thicknesses ; measurements on 481 men and women aged from 16 to 72 years. Br J Nutr 32:77-92. 3. Intaranont K, Ayoub MM...Justificaton --. By ......... AvaI~bty Co’der, L Ust Avdi iUl I r /1- Table of Contents Table of Contents iii List of Figures iv List of Tables v...during 28 repetitive lifting exercise iv List of Tables 1. Repetitive lifting device specifications 15 2. Subject sample descriptive data 24 3

  7. Repetition rate stabilization of an erbium-doped all-fiber laser via opto-mechanical control of the intracavity group velocity

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Xuling; He, Boqu; Zhao, Jian; Liu, Yang; Bai, Dongbi; Wang, Chao; Liu, Geping; Luo, Daping; Liu, Fengjiang; Li, Wenxue; Zeng, Heping, E-mail: hpzeng@phy.ecnu.edu.cn [State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062 (China); Yang, Kangwen; Hao, Qiang [Shanghai Key Laboratory of Modern Optical System, Engineering Research Center of Optical Instrument and System (Ministry of Education), School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093 (China)

    2015-01-19

    We present a method for stabilizing the repetition rate of an erbium-doped all-fiber laser by inserting an electronic polarization controller (EPC) in the fiber laser cavity. The device exhibited good integration, low cost, and convenient operation. Such a repetition rate stabilization may facilitate an all-fiber laser comb system with high integration. The repetition rate was phase-locked to a Rb reference more than 72 h with a low feedback voltage applied to one channel of the EPC. The repetition rate was 74.6 MHz. The standard deviation and the repetition rate linewidth were 1.4 and 1.7 mHz, respectively.

  8. Pulse shortening of an ultrafast VECSEL

    Science.gov (United States)

    Waldburger, D.; Alfieri, C. G. E.; Link, S. M.; Gini, E.; Golling, M.; Mangold, M.; Tilma, B. W.; Keller, U.

    2016-03-01

    Ultrafast, optically pumped, passively modelocked vertical external-cavity surface-emitting lasers (VECSELs) are excellent sources for industrial and scientific applications that benefit from compact semiconductor based high-power ultrafast lasers with gigahertz repetition rates and excellent beam quality. Applications such as self-referenced frequency combs and multi-photon imaging require sub-200-fs pulse duration combined with high pulse peak power. Here, we present a semiconductor saturable absorber mirror (SESAM) modelocked VECSEL with a pulse duration of 147 fs and 328 W of pulse peak power. The average output power was 100 mW with a repetition rate of 1.82 GHz at a center wavelength of 1034 nm. The laser has optimal beam quality operating in a fundamental transverse mode with a M2 value of organic vapor phase epitaxy (MOVPE) with five pairs of strain-compensated InGaAs quantum wells (QWs). The QWs are placed symmetrical around the antinodes of the standing electric field at a reduced average field enhancement in the QWs of ≈ 0.5 (normalized to 4 outside the structure). These results overcome the trade-off between pulse duration and peak power of the state-of-the-art threshold values of 4.35 kW peak power for a pulse duration of 400 fs and 3.3 W peak power for a pulse duration of 107 fs.

  9. Design criteria for ultrafast optical parametric amplifiers

    Science.gov (United States)

    Manzoni, C.; Cerullo, G.

    2016-10-01

    Optical parametric amplifiers (OPAs) exploit second-order nonlinearity to transfer energy from a fixed frequency pump pulse to a variable frequency signal pulse, and represent an easy way of tuning over a broad range the frequency of an otherwise fixed femtosecond laser system. OPAs can also act as broadband amplifiers, transferring energy from a narrowband pump to a broadband signal and thus considerably shortening the duration of the pump pulse. Due to these unique properties, OPAs are nowadays ubiquitous in ultrafast laser laboratories, and are employed by many users, such as solid state physicists, atomic/molecular physicists, chemists and biologists, who are not experts in ultrafast optics. This tutorial paper aims at providing the non-specialist reader with a self-consistent guide to the physical foundations of OPAs, deriving the main equations describing their performance and discussing how they can be used to understand their most important working parameters (frequency tunability, bandwidth, pulse energy/repetition rate scalability, control over the carrier-envelope phase of the generated pulses). Based on this analysis, we derive practical design criteria for OPAs, showing how their performance depends on the type of the nonlinear interaction (crystal type, phase-matching configuration, crystal length), on the characteristics of the pump pulse (frequency, duration, energy, repetition rate) and on the OPA architecture.

  10. Real-time energy measurement of high repetition rate ultrashort laser pulses using pulse integration and FPGA processing.

    Science.gov (United States)

    Tang, Qi-Jie; Yang, Dong-Xu; Wang, Jian; Feng, Yi; Zhang, Hong-Fei; Chen, Teng-Yun

    2016-11-01

    Real-time energy measurement using pulse integration method for high repetition rate ultrashort laser pulses based on FPGA (Field-Programmable Gate Array) and high-speed pipeline ADC (Analog-to-Digital Convertor) is introduced in this paper. There are two parts contained in this method: pulse integration and real-time data processing. The pulse integration circuit will convert the pulse to the step type signals which are linear to the laser pulse energy. Through the real-time data processing part, the amplitude of the step signals will be obtained by ADC sampling and conducting calculation in real time in FPGA. The test result shows that the method with good linearity (4.770%) and without pulse measurement missing is suitable for ultrashort laser pulses with high repetition rate up to 100 MHz.

  11. 1  J, 0.5  kHz repetition rate picosecond laser.

    Science.gov (United States)

    Baumgarten, Cory; Pedicone, Michael; Bravo, Herman; Wang, Hanchen; Yin, Liang; Menoni, Carmen S; Rocca, Jorge J; Reagan, Brendan A

    2016-07-15

    We report the demonstration of a diode-pumped chirped pulse amplification Yb:YAG laser that produces λ=1.03  μm pulses of up to 1.5 J energy compressible to sub-5 ps duration at a repetition rate of 500 Hz (750 W average power). Amplification to high energy takes place in cryogenically cooled Yb:YAG active mirrors designed for kilowatt average power laser operation. This compact laser system will enable new advances in high-average-power ultrashort-pulse lasers and high-repetition-rate tabletop soft x-ray lasers. As a first application, the laser was used to pump a 400 Hz λ=18.9  nm laser.

  12. High-peak-power, high-repetition-rate intracavity optical parametric oscillator at 1.57μm

    Institute of Scientific and Technical Information of China (English)

    Yuye Wang; Degang Xu; Yizhong Yu; Wuqi Wen; Jingping Xiong; Peng Wang; Jianquan Yao

    2007-01-01

    We report a high-peak-power, high-repetition-rate diode-side-pumped Nd:YAG Q-switched intracavity optical parametric oscillator (IOPO) at 1.57μm with a type-Ⅱ non-critically phase-matched x-cut KTP crystal. The average power of 1.15 W at 1.57μm is obtained at 4.3-kHz repetition rate. The peak power of the pulses amounts to 33.4 kW with 8-ns duration. The average conversion efficiency from Q-switched 1.064-μm-wavelength input power to OPO signal output power is up to 10.5%.

  13. Real-time energy measurement of high repetition rate ultrashort laser pulses using pulse integration and FPGA processing

    Science.gov (United States)

    Tang, Qi-jie; Yang, Dong-xu; Wang, Jian; Feng, Yi; Zhang, Hong-fei; Chen, Teng-yun

    2016-11-01

    Real-time energy measurement using pulse integration method for high repetition rate ultrashort laser pulses based on FPGA (Field-Programmable Gate Array) and high-speed pipeline ADC (Analog-to-Digital Convertor) is introduced in this paper. There are two parts contained in this method: pulse integration and real-time data processing. The pulse integration circuit will convert the pulse to the step type signals which are linear to the laser pulse energy. Through the real-time data processing part, the amplitude of the step signals will be obtained by ADC sampling and conducting calculation in real time in FPGA. The test result shows that the method with good linearity (4.770%) and without pulse measurement missing is suitable for ultrashort laser pulses with high repetition rate up to 100 MHz.

  14. Optical breakdown and filamentation of femtosecond laser pulses propagating in air at a kHz repetition rate

    Institute of Scientific and Technical Information of China (English)

    Duan Zuo-Liang; Chen Jian-Ping; Li Ru-Xin; Lin Li-Huang; Xu Zhi-Zhan

    2004-01-01

    We report the experiments on the optical breakdown and filamentation of femtosecond laser pulses propagating in air at a kHz repetition rate and with several hundreds micro-joule-energy. A 10m-long filament and its breakup and merging at the nonlinear focal region produced by modulational instability of femtosecond laser pulses in air are observed. A simple model based on the nonlinear Schrodinger equation coupled with multiphoton ionization law is presented to explain the several experimental results.

  15. High energy picosecond Yb:YAG CPA system at 10 Hz repetition rate for pumping optical parametric amplifiers.

    Science.gov (United States)

    Klingebiel, Sandro; Wandt, Christoph; Skrobol, Christoph; Ahmad, Izhar; Trushin, Sergei A; Major, Zsuzsanna; Krausz, Ferenc; Karsch, Stefan

    2011-03-14

    We present a chirped pulse amplification (CPA) system based on diode-pumped Yb:YAG. The stretched ns-pulses are amplified and have been compressed to less than 900 fs with an energy of 200 mJ and a repetition rate of 10 Hz. This system is optically synchronized with a broadband seed laser and therefore ideally suited for pumping optical parametric chirped pulse amplification (OPCPA) stages on a ps-timescale.

  16. Generation of a Sub-10 fs Laser Pulse by a Ring Oscillator with a High Repetition Rate

    Institute of Scientific and Technical Information of China (English)

    ZHANG Qing; ZHAO Yan-Ying; WEI Zhi-Yi

    2009-01-01

    @@ A compact femtoescond Ti:sapphire ring oscillator composed of chirped mirrors is designed. By accurately optimizing the intra-cavity dispersion and the mode locking range of the ring configuration, we generate laser pulses as short as 7.7 fs with a repetition rate as high as 745 MHz. The spectrum spans from 660nm to 940nm and the average output power is 480row under the cw pump laser of 7.5 W.

  17. High repetition rate Yb:CaF2 multipass amplifiers operating in the 100 mJ range

    OpenAIRE

    Dimitrios PAPADOPOULOS; Friebel, Florence; Pellegrina, Alain; Hanna, Marc; Camy, Patrice; Doualan, Jean-Louis; Moncorgé, Richard; Georges, Patrick; Druon, Frédéric

    2014-01-01

    International audience; — We present the research advances on the development of 50-200 mJ energy range diode-pumped Yb:CaF 2-based multipass amplifiers operating at relatively high repetition rates. These laser amplifiers are based on diverse innovative geometries. All these innovations aim to design compact, stable and reliable amplifiers adapted to our application that consists in pumping ultrashort-pulse OPCPA (optical parametric chirped pulse amplifier) systems in the frame of the Apollo...

  18. Neodymium glass laser with a pulse energy of 220 J and a pulse repetition rate of 0.02 Hz

    Energy Technology Data Exchange (ETDEWEB)

    Kuzmin, A A; Kulagin, O V; Khazanov, Efim A; Shaykin, A A [Institute of Applied Physics, Russian Academy of Sciences, Nizhnii Novgorod (Russian Federation)

    2013-07-31

    A compact neodymium glass laser with a pulse energy of 220 J and a record-high pulse repetition rate of 0.02 Hz (pulse duration 30 ns) is developed. Thermally induced phase distortions are compensated using wave phase conjugation. The integral depolarisation of radiation is decreased to 0.4% by using linear compensation schemes. The second harmonic of laser radiation can be used for pumping Ti : sapphire multipetawatt complexes. (letters)

  19. Effects of high-repetition-rate femtosecond laser micromachining on the physical and chemical properties of polylactide (PLA).

    Science.gov (United States)

    Jia, Wei; Luo, Yiming; Yu, Jian; Liu, Bowen; Hu, Minglie; Chai, Lu; Wang, Chingyue

    2015-10-19

    The effects of femtosecond laser ablation, with 115 fs pulses at 1040 nm wavelength and 57 MHz repetition-rate, on the physical and chemical properties of polylactide (PLA) were studied in air and in water. The surface of the PLA sample ablated by high-repetition-rate femtosecond laser was analysed using field emission scanning electron microscopy, infrared spectroscopy, raman spectroscopy, as well as X-ray photoelectron spectroscopy. Compared with the experiments in the air at ambient temperature, melting resolidification was negligible for the experiments conducted under water. Neither in air nor under water did oxidation and crystallization process take place in the laser ablated surface. In addition, the intensity of some oxygen related peaks increased for water experiments, probably due to the hydrolysis. Meantime, the chemical shift to higher energies appeared in C1s XPS spectrum of laser processing in water. Interestingly, a large amount of defects were observed after laser processing in air, while no significant change was shown under water experiments. This indicates that thermal and mechanical effects by high-repetition-rate femtosecond laser ablation in water are quite limited, which could be even ignored.

  20. A Simulation of the Effects of Varying Repetition Rate and Pulse Width of Nanosecond Discharges on Premixed Lean Methane-Air Combustion

    Directory of Open Access Journals (Sweden)

    Moon Soo Bak

    2012-01-01

    Full Text Available Two-dimensional kinetic simulation has been carried out to investigate the effects of repetition rate and pulse width of nanosecond repetitively pulsed discharges on stabilizing premixed lean methane-air combustion. The repetition rate and pulse width are varied from 10 kHz to 50 kHz and from 9 ns to 2 ns while the total power is kept constant. The lower repetition rates provide larger amounts of radicals such as O, H, and OH. However, the effect on stabilization is found to be the same for all of the tested repetition rates. The shorter pulse width is found to favor the production of species in higher electronic states, but the varying effects on stabilization are also found to be small. Our results indicate that the total deposited power is the critical element that determines the extent of stabilization over this range of discharge properties studied.

  1. Design concept and performance considerations for fast high power semiconductor switching for high repetition rate and high power excimer laser

    Science.gov (United States)

    Goto, Tatsumi; Kakizaki, Kouji; Takagi, Shigeyuki; Satoh, Saburoh; Shinohe, Takashi; Ohashi, Hiromichi; Endo, Fumihiko; Okamura, Katsuya; Ishii, Akira; Teranishi, Tsuneharu; Yasuoka, Koichi

    1997-07-01

    A semiconductor switching power supply has been developed, in which a novel structure semiconductor device, metal-oxide-semiconductor assisted gate-triggered thyristor (MAGT) was incorporated with a single stage magnetic pulse compression circuit (MPC). The MAGT was specially designed to directly replace thyratrons in a power supply for a high repetition rate laser. Compared with conventional high power semiconductor switching devices, it was designed to enable a fast switching, retaining a high blocking voltage and to extremely reduce the transient turn-on power losses, enduring a higher peak current. A maximum peak current density of 32 kA/cm2 and a current density risetime rate di/dt of 142 kA/(cm2×μs) were obtained at the chip area with an applied anode voltage of 1.5 kV. A MAGT switching unit connecting 32 MAGTs in series was capable of switching on more than 25 kV-300 A at a repetition rate of 5 kHz, which, coupled with the MPC, was equivalent to the capability of a high power thyratron. A high repetition rate and high power XeCl excimer laser was excited by the power supply. The results confirmed the stable laser operation of a repetition rate of up to 5 kHz, the world record to our knowledge. An average output power of 0.56 kW was obtained at 5 kHz where the shortage of the total discharge current was subjoined by a conventional power supply with seven parallel switching thyratrons, simultaneously working, for the MAGT power supply could not switch a greater current than that switched by one thyratron. It was confirmed by those excitations that the MAGT unit with the MPC could replace a high power commercial thyratron directly for excimer lasers. The switching stability was significantly superior to that of the thyratron in a high repetition rate region, judging from the discharge current wave forms. It should be possible for the MAGT unit, in the future, to directly switch the discharge current within a rise time of 0.1 μs with a magnetic assist.

  2. Thermal distortion and birefringence in repetition-rate plasma electrode Pockels cell for high average power

    Institute of Scientific and Technical Information of China (English)

    Dingxiang Cao; Xiongjun Zhang; Wanguo Zheng; Shaobo He; Zhan Sui

    2007-01-01

    We numerically study thermally induced birefringence and distortion in plasma electrode Pockels cell based on KD*P as the electro-optic material. This device can repetitively operate under the heat capacity mode.Simulation results indicate that the excellent switching performances and low wave-front distortion are achieved within several tens seconds working time at average power in excess of 1 kW.

  3. The effect of laser repetition rate on the LASiS synthesis of biocompatible silver nanoparticles in aqueous starch solution

    Directory of Open Access Journals (Sweden)

    Zamiri R

    2013-01-01

    Full Text Available Reza Zamiri,1 Azmi Zakaria,1,* Hossein Abbastabar Ahangar,2 Majid Darroudi,3 Golnoosh Zamiri,1 Zahid Rizwan,1 Gregor PC Drummen4,* 1Department of Physics, Faculty of Science, Universiti Putra Malaysia, Serdang, Selangor, Malaysia; 2Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, Selangor Darul Ehsan, Malaysia; 3Advanced Materials and Nanotechnology Laboratory, Institute of Advanced Technology (ITMA, Universiti Putra Malaysia, Serdang, Selangor, Malaysia; 4Bionanoscience and Bio-Imaging Program, Cellular Stress and Ageing Program, Bio&Nano-Solutions, Düsseldorf, Germany*These authors contributed to this work equallyAbstract: Laser ablation-based nanoparticle synthesis in solution is rapidly becoming popular, particularly for potential biomedical and life science applications. This method promises one pot synthesis and concomitant bio-functionalization, is devoid of toxic chemicals, does not require complicated apparatus, can be combined with natural stabilizers, is directly biocompatible, and has high particle size uniformity. Size control and reduction is generally determined by the laser settings; that the size and size distribution scales with laser fluence is well described. Conversely, the effect of the laser repetition rate on the final nanoparticle product in laser ablation is less well-documented, especially in the presence of stabilizers. Here, the influence of the laser repetition rate during laser ablation synthesis of silver nanoparticles in the presence of starch as a stabilizer was investigated. The increment of the repetition rate does not negatively influence the ablation efficiency, but rather shows increased productivity, causes a red-shift in the plasmon resonance peak of the silver–starch nanoparticles, an increase in mean particle size and size distribution, and a distinct lack of agglomerate formation. Optimal results were achieved at 10 Hz repetition rate, with a mean particle size of ~10 nm and a

  4. Investigations on the heat transport capability of a cryogenic oscillating heat pipe and its application in achieving ultra-fast cooling rates for cell vitrification cryopreservation☆

    OpenAIRE

    Han, Xu; Ma, Hongbin; Jiao, Anjun; Critser, John K.

    2008-01-01

    Theoretically, direct vitrification of cell suspensions with relatively low concentrations (~1 M) of permeating cryoprotective agents (CPA) is suitable for cryopreservation of almost all cell types and can be accomplished by ultra-fast cooling rates that are on the order of 106–7 K/min. However, the methods and devices currently available for cell cryopreservation cannot achieve such high cooling rates. In this study, we constructed a novel cryogenic oscillating heat pipe (COHP) using liquid ...

  5. Oral-diadochokinetic rates for Hebrew-speaking school-age children: real words vs. non-words repetition.

    Science.gov (United States)

    Icht, Michal; Ben-David, Boaz M

    2015-02-01

    Oral-diadochokinesis (DDK) tasks are a common tool for evaluating speech disorders. Usually, these tasks involve repetitions of non-words. It has been suggested that repeating real words can be more suitable for preschool children. But, the impact of using real words with elementary school children has not been studied yet. This study evaluated oral-DDK rates for Hebrew-speaking elementary school children using non-words and real words. The participants were 60 children, 9-11 years old, with normal speech and language development, who were asked to repeat "pataka" (non-word) and "bodeket" (Hebrew real word). Data replicate the advantage generally found for real word repetition with preschoolers. Children produced real words faster than non-words for all age groups, and repetition rates were higher for the older children. The findings suggest that adding real words to the standard oral-DDK task with elementary school children may provide a more comprehensive picture of oro-motor function.

  6. 3.7 GHz repetition rate operated narrow-bandwidth picosecond pulsed Yb fiber amplifier with an all-fiber multiplier

    Science.gov (United States)

    Wei, K. H.; Wen, R. H.; Guo, Y.

    2016-04-01

    A high power picosecond pulsed Yb fiber amplifier with a pulse repetition rate of 3.7 GHz is experimentally demonstrated. The seed is a gain switched distributed Bragg reflection (DBR) structured laser diode (LD) with a pulse duration of 130 ps and a repetition rate of 460 MHz. The pulse repetition rate is increased to 3.7 GHz by introducing an all-fiber multiplier, which is composed of four 2  ×  2 structured fiber couplers. The multiplied pulse train is amplified to 81 W through two stage Yb fiber amplifiers.

  7. End-pumped all solid-state high repetition rate Tm, Ho:LuLF laser

    Institute of Scientific and Technical Information of China (English)

    Shijiang Shu; Ting Yu; Junyan Hou; Rongtao Liu; Minjie Huang; Weibiao Chen

    2011-01-01

    @@ The characteristics of diode end-pumped Tm,Ho:LuLiF for continuous wave (CW) running and high pulse repetition frequency (PRF) Q-switched operation are illustrated. In the CW mode, 950-mW output power with a slope efficiency of 24% is obtained. In the Q-switched mode, output energy of 78 μJ under 10 kHz with a slope efficiency of 23% is achieved. The pulse stability, pulse width as a function of pump intensity, and spectral characteristics are also analyzed.%The characteristics of diode end-pumped Tm,Ho:LuLiF for continuous wave (CW) running and high pulse repetition frequency (PRF) Q-switched operation are illustrated. In the CW mode, 950-mW output power with a slope efficiency of 24% is obtained. In the Q-switched mode, output energy of 78μJ under 10 kHz with a slope efficiency of 23% is achieved. The pulse stability, pulse width as a function of pump intensity, and spectral characteristics are also analyzed.

  8. SU-E-T-460: Impact of the LINAC Repetition Rate On a High-Resolution Liquid Ionization Chamber Array for Patient-Specific QA

    Energy Technology Data Exchange (ETDEWEB)

    Wang, S; Driewer, J; Zheng, D; Lei, Y; Zhang, Q; Zhu, X; Li, S; Enke, C; Zhou, S [University of Nebraska Medical Center, Omaha, NE (United States); Xu, B [The Fujian Medical University Union Hospital, Fu Zhou, Fu Jian (China)

    2015-06-15

    Purpose: The purpose of this study is to investigate the LINAC repetition-rate (dose-rate) dependence of OCTAVIUS 1000SRS liquid ionization chamber (LIC) array for patient specific QA of SRT plans delivered with flattening-filter-free (FFF) beams. Methods: 1) The repetition-rate dependence of 1000SRS was measured in a phantom constructed with 5-cm solid water above and below the array for build-up and backscatter. A 0.3cc calibrated ion chamber was also placed along the central axis 2.3cm below the center chamber of the array for normalizing LINAC output fluctuation. The signals from the center chamber of the array under different repetition rates in the range of 400–2400 MU/min for 6xFFF and 10xFFF beams on a Varian TrueBeamSTx LINAC, normalized by the independent chamber readings, were analyzed for the array response dependence on repetition rates. 2) Twelve Step-and-shoot IMRS QA plans (6xFFF and 10xFFF) were delivered to the array under different repetition rates for analysis and comparison. 3) The absolute doses measured by the center chamber were compared to measurements using an independent ionization chamber with the identical setup, taken as the gold standard. 4) The correction factors based on the actual delivery repetition rate were applied to the measurements, and the results were compared again to the gold standard. Results: 1) The 1000SRS array exhibited repetition-rate dependence for FFF beams, up to 5% for 6xFFF and 10% for 10xFFF; 2) The array showed clinically-acceptable repetition-rate dependence for regular flattened beams; 3) This repetition-rate dependence significantly affected the measurement accuracy, thereby affecting IMRS QA results; 4) By applying an empirical repetition-rate correction, the corrected measurements agreed better with the gold standard ion chamber measurements. Conclusion: OCTAVIUS 1000SRS LIC array exhibited considerable repetition-rate dependence for FFF beams, which will affect the accuracy of the absolute QA

  9. Efficient intracavity frequency doubling of a high-repetition-rate diode-pumped Nd:YAG laser.

    Science.gov (United States)

    Hanson, F; Poirier, P

    1994-10-01

    Efficient operation of a pulsed, high-repetition-rate diode-pumped and intracavity frequency-doubled Nd:YAG laser is reported. A 3-mm-diameter laser rod was side-pumped with a 5-bar stack of high-duty-cycle 1-cm diodearrays. The average Q-switched power at 1.06microum was 3.8 W at 1.33 kH(z), and more than 4 W at 0.532 ,microm wasobtained through intracavity frequency doubling with LiB(3)O(5).

  10. Femtosecond laser ablation: Experimental study of the repetition rate influence on inductively coupled plasma mass spectrometry performance

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez, Jhanis J. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Fernandez, Alberto [Centro de Fisicoquimica. Escuela de Quimica, Universidad Central de Venezuela, Caracas 1020-A (Venezuela); Oropeza, Dayana; Mao Xianglei [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Russo, Richard E. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)], E-mail: RERusso@lbl.gov

    2008-02-15

    This paper demonstrates the feasibility of performing bulk chemical analysis based on laser ablation for good lateral resolution with only nominal mass ablated per pulse. The influence of repetition rate (1-1000 Hz) and scan speed (1-200 {mu}m/s) using a low energy (30 {mu}J) and a small spot size ({approx} 10 {mu}m) UV-femtosecond laser beam was evaluated for chemical analysis of silica glass samples, based on laser ablation sampling and inductively coupled plasma mass spectrometry (ICP-MS). Accuracy to approximately 14% and precision of 6% relative standard deviation (RSD) were measured.

  11. Mechanisms of high-regularity periodic structuring of silicon surface by sub-MHz repetition rate ultrashort laser pulses

    Science.gov (United States)

    Gnilitskyi, Iaroslav; Gruzdev, Vitaly; Bulgakova, Nadezhda M.; Mocek, Tomáš; Orazi, Leonardo

    2016-10-01

    Silicon is one of the most abundant materials which is used in many areas of modern research and technology. A variety of those applications require surface nanopatterning with minimum structure defects. However, the high-quality nanostructuring of large areas of silicon surface at industrially acceptable speed is still a challenge. Here, we report a rapid formation of highly regular laser-induced periodic surface structures (HR-LIPSS) in the regime of strong ablation by infrared femtosecond laser pulses at sub-MHz repetition rate. Parameters of the laser-surface interactions and obtained experimental results suggest an important role of electrostatically assisted bond softening in initiating the HR-LIPSS formation.

  12. A Compact, Transportable, Microchip-Based System for High Repetition Rate Production of Bose-Einstein Condensates

    CERN Document Server

    Farkas, Daniel M; Salim, Evan A; Segal, Stephen R; Squires, Matthew B; Anderson, Dana Z

    2009-01-01

    We present a compact, transportable system that produces Bose-Einstein condensates (BECs) near the surface of an integrated atom microchip. The system occupies a volume of 0.4 m^3 and operates at a repetition rate as high as 0.3 Hz. Evaporative cooling in a chip trap with trap frequencies of several kHz leads to nearly pure condensates containing 1.9x10^4 87Rb atoms. Partial condensates are observed at a temperature of 1.58(8) \\mu K, close to the theoretical transition temperature of 1.1 \\mu K.

  13. Actual laser removal of black soiling crust from siliceous sandstone by high pulse repetition rate equipment: effects on surface morphology

    Directory of Open Access Journals (Sweden)

    Iglesias-Campos, M. A.

    2016-03-01

    Full Text Available This research project studies the role of pulse repetition rate in laser removal of black soiling crust from siliceous sandstone, and specifically, how laser fluence correlates with high pulse repetition rates in cleaning practice. The aim is to define practical cleaning processes and determine simple techniques for evaluation based on end-users’ perspective (restorers. Spot and surface tests were made using a Q-switched Nd:YAG laser system with a wide range of pulse repetition rates (5–200 Hz, systematically analysed and compared by macrophotography, portable microscope, stereomicroscope with 3D visualizing and area roughness measurements, SEM imaging and spectrophotometry. The results allow the conclusion that for operation under high pulse repetition rates the average of total energy applied per spot on a treated surface should be attendant upon fluence values in order to provide a systematic and accurate description of an actual laser cleaning intervention.En este trabajo se estudia el papel de la frecuencia de repetición en la limpieza láser de costras de contaminación sobre una arenisca silícea, y concretamente, como se relaciona fluencia y frecuencias elevadas en una limpieza real. Se pretende definir un procedimiento práctico de limpieza y determinar técnicas sencillas de evaluación desde el punto de vista de los usuarios finales (restauradores. Para el estudio se realizaron diferentes ensayos en spot y en superficie mediante un equipo Q-switched Nd:YAG con un amplio rango de frecuencias (5–200 Hz, que se analizaron y compararon sistemáticamente mediante macrofotografía, microscopio portátil, estereomicroscopio con visualización 3D y mediciones de rugosidad en área, imágenes SEM y espectrofotometría. Los resultados permiten proponer que, al trabajar con altas frecuencias, la media de la energía total depositada por spot en la superficie debería acompañar los valores de fluencia para describir y comprender mejor una

  14. Performance Optimization of a High-Repetition-Rate KrF Laser Plasma X-Ray Source for Microlithography.

    Science.gov (United States)

    Bukerk, F; Louis, E; Turcu, E C; Tallents, G J; Batani, D

    1992-01-01

    In order to develop a high-intensity laser plasma x-ray source appropriate for industrial application of x-ray lithography, experiments have been carried out using a high-repetition-rate (up to 40 Hz) excimer laser (249 nm, 300 mJ) with a power density of 2 × 1013 W/ cm2 in the laser focus. In this study emphasis is given to remedying specific problems inherent in operating the laser plasma x-ray source at high repetition rates and in its prolonged operation. Two different methods of minimizing the production of target debris are investigated. First, the use of helium as a quenching gas results in a reduction of the amount of atomic debris particles by more than two orders of magnitude with negligible x-ray absorption. Second, a tape target as opposed to a solid target reduces the production of larger debris particles by a further factor of 100. Remaining debris is stopped by an aluminized plastic or beryllium filter used to avoid exposure of the resist by plasma ultraviolet radiation. The x-ray source has been used to image x-ray transmission mask structures down to 0.3 μm onto general purpose x-ray photo-resist. Results have been analyzed with SEM. The x-ray emission spectrum of the repetitive laser plasmas created from an iron target has been recorded and the conversion efficiency of the laser light into x-rays that contribute to exposure of the resist was measured to be 0.3% over 2π sr.

  15. High-power, highly stable KrF laser with a 4-kHz pulse repetition rate

    Science.gov (United States)

    Borisov, V. M.; El'tsov, A. V.; Khristoforov, O. B.

    2015-08-01

    An electric-discharge KrF laser (248 nm) with an average output power of 300 W is developed and studied. A number of new design features are related to the use of a laser chamber based on an Al2O3 ceramic tube. A high power and pulse repetition rate are achieved by using a volume discharge with lateral preionisation by the UV radiation of a creeping discharge in the form of a homogeneous plasma sheet on the surface of a plane sapphire plate. Various generators for pumping the laser are studied. The maximum laser efficiency is 3.1%, the maximum laser energy is 160 mJ pulse-1, and the pulse duration at half maximum is 7.5 ns. In the case of long-term operation at a pulse repetition rate of 4 kHz and an output power of 300 W, high stability of laser output energy (σ <= 0.7%) is achieved using an all-solid-state pump system.

  16. Fiber-laser-based, high-repetition-rate, picosecond ultraviolet source tunable across 329-348  nm.

    Science.gov (United States)

    Devi, Kavita; Chaitanya Kumar, S; Ebrahim-Zadeh, M

    2016-10-15

    We report a compact, fiber-laser-based, high-repetition-rate picosecond source for the ultraviolet (UV), providing multi-tens of milliwatt of average power across 329-348 nm. The source is based on internal sum-frequency-generation (SFG) in a singly resonant optical parametric oscillator (OPO), synchronously pumped at 532 nm by the second harmonic of a picosecond Yb-fiber laser at 80 MHz repetition rate. Using a 30-mm-long single-grating MgO:sPPLT crystal for the OPO and a 5-mm-long BiB3O6 crystal for intracavity SFG, we generate up to 115 mW of average UV power at 339.9 nm, with >50  mW over 73% of the tuning range, for 1.6 W of input pump power. The UV output exhibits a passive rms power stability of ∼2.9% rms over 1 min and 6.5% rms over 2 h in high beam quality. Angular acceptance bandwidth and cavity detuning effects have also been studied.

  17. Monolithic all-fiber repetition-rate tunable gain-switched single-frequency Yb-doped fiber laser.

    Science.gov (United States)

    Hou, Yubin; Zhang, Qian; Qi, Shuxian; Feng, Xian; Wang, Pu

    2016-12-12

    We report a monolithic gain-switched single-frequency Yb-doped fiber laser with widely tunable repetition rate. The single-frequency laser operation is realized by using an Yb-doped distributed Bragg reflection (DBR) fiber cavity, which is pumped by a commercial-available laser diode (LD) at 974 nm. The LD is electronically modulated by the driving current and the diode output contains both continuous wave (CW) and pulsed components. The CW component is set just below the threshold of the single-frequency fiber laser for reducing the requirement of the pump pulse energy. Above the threshold, the gain-switched oscillation is trigged by the pulsed component of the diode. Single-frequency pulsed laser output is achieved at 1.063 μm with a pulse duration of ~150 ns and a linewidth of 14 MHz. The repetition rate of the laser output can be tuned between 10 kHz and 400 kHz by tuning the electronic trigger signal. This kind of lasers shows potential for the applications in the area of coherent LIDAR etc.

  18. Cavity-Enhanced Ultrafast Spectroscopy: Ultrafast Meets Ultrasensitive

    Science.gov (United States)

    Allison, Thomas K.; Reber, Melanie Roberts; Chen, Yuning

    2016-06-01

    Ultrafast optical spectroscopy methods, such as transient absorption spectroscopy and 2D-spectroscopy, are widely used across many disciplines. However, these techniques are typically restricted to optically thick samples, such as solids and liquid solutions. Using a frequency comb laser and optical cavities, we present a new technique for performing ultrafast optical spectroscopy with high sensitivity, enabling work in dilute gas-phase molecular beams. Resonantly enhancing the probe pulses, we demonstrate transient absorption measurements with a detection limit of ΔOD = 2 × 10-10 (1 × 10-9/√{Hz}). Resonantly enhancing the pump pulses allows us to produce a high excitation fraction at high repetition-rate, so that signals can be recorded from samples with optical densities as low as OD ≈ 10-8, or column densities oise performance of CE-TAS. (a), Transient absorption measurements taken with reduced gas flow and perpendicular polarizations. The red dots represent the average of 60 consecutive scans taken over a 1 hour period. Black curves are every 10th scan from the data set. Inset: Zoom-in around 0.8 ps delay. Error bars represent the uncertainty in the mean. (b), The green squares show the average of the Allan deviations obtained independently for each delay point. Error bars here are the standard deviation (not the uncertainty in the mean) of this ensemble, to represent the spread in the data. The blue diamond is the average of the error bars of (a), along with their standard deviation. The grey line has a slope of -1/2 on the log-log plot, the expected slope for white noise performance

  19. Filamentation effect in a gas attenuator for high-repetition-rate X-ray FELs

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Yiping; Krzywinski, Jacek; Schafer, Donald W.; Ortiz, Eliazar; Rowen, Michael; Raubenheimer, Tor O.

    2016-01-01

    A sustained filamentation or density depression phenomenon in an argon gas attenuator servicing a high-repetition femtosecond X-ray free-electron laser has been studied using a finite-difference method applied to the thermal diffusion equation for an ideal gas. A steady-state solution was obtained by assuming continuous-wave input of an equivalent time-averaged beam power and that the pressure of the entire gas volume has reached equilibrium. Both radial and axial temperature/density gradients were found and describable as filamentation or density depression previously reported for a femtosecond optical laser of similar attributes. The effect exhibits complex dependence on the input power, the desired attenuation, and the geometries of the beam and the attenuator. Time-dependent simulations were carried out to further elucidate the evolution of the temperature/density gradients in between pulses, from which the actual attenuation received by any given pulse can be properly calculated.

  20. High Speed Pump-Probe Apparatus for Observation of Transitional Effects in Ultrafast Laser Micromachining Processes

    Directory of Open Access Journals (Sweden)

    Ilya Alexeev

    2015-12-01

    Full Text Available A pump-probe experimental approach has been shown to be a very efficient tool for the observation and analysis of various laser matter interaction effects. In those setups, synchronized laser pulses are used to create an event (pump and to simultaneously observe it (probe. In general, the physical effects that can be investigated with such an apparatus are restricted by the temporal resolution of the probe pulse and the observation window. The latter can be greatly extended by adjusting the pump-probe time delay under the assumption that the interaction process remains fairly reproducible. Unfortunately, this assumption becomes invalid in the case of high-repetition-rate ultrafast laser material processing, where the irradiation history strongly affects the ongoing interaction process. In this contribution, the authors present an extension of the pump-probe setup that allows to investigate transitional and dynamic effects present during ultrafast laser machining performed at high pulse repetition frequencies.

  1. Real Time Quantification of Ultrafast Photoinduced Bimolecular Electron Transfer Rate: Direct Probing of the Transient Intermediate.

    Science.gov (United States)

    Mukherjee, Puspal; Biswas, Somnath; Sen, Pratik

    2015-08-27

    Fluorescence quenching studies through steady-state and time-resolved measurements are inadequate to quantify the bimolecular electron transfer rate in bulk homogeneous solution due to constraints from diffusion. To nullify the effect of diffusion, direct evaluation of the rate of formation of a transient intermediate produced upon the electron transfer is essential. Methyl viologen, a well-known electron acceptor, produces a radical cation after accepting an electron, which has a characteristic strong and broad absorption band centered at 600 nm. Hence it is a good choice to evaluate the rate of photoinduced electron transfer reaction employing femtosecond broadband transient absorption spectroscopy. The time constant of the aforementioned process between pyrene and methyl viologen in methanol has been estimated to be 2.5 ± 0.4 ps using the same technique. The time constant for the backward reaction was found to be 14 ± 1 ps. These values did not change with variation of concentration of quencher, i.e., methyl viologen. Hence, we can infer that diffusion has no contribution in the estimation of rate constants. However, on changing the solvent from methanol to ethanol, the time constant of the electron transfer reaction has been found to increase and has accounted for the change in solvent reorganization energy.

  2. Fluid dynamics analysis of a gas attenuator for X-ray FELs under high-repetition-rate operation

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Bo; Wu, Juhao; Raubenheimer, Tor O.; Feng, Yiping

    2017-04-18

    Newtonian fluid dynamics simulations were performed using the Navier–Stokes–Fourier formulations to elucidate the short time-scale (µs and longer) evolution of the density and temperature distributions in an argon-gas-filled attenuator for an X-ray free-electron laser under high-repetition-rate operation. Both hydrodynamic motions of the gas molecules and thermal conductions were included in a finite-volume calculation. It was found that the hydrodynamic wave motions play the primary role in creating a density depression (also known as a filament) by advectively transporting gas particles away from the X-ray laser–gas interaction region, where large pressure and temperature gradients have been built upon the initial energy depositionviaX-ray photoelectric absorption and subsequent thermalization. Concurrent outward heat conduction tends to reduce the pressure in the filament core region, generating a counter gas flow to backfill the filament, but on an initially slower time scale. If the inter-pulse separation is sufficiently short so the filament cannot recover, the depth of the filament progressively increases as the trailing pulses remove additional gas particles. Since the rate of hydrodynamic removal decreases while the rate of heat conduction back flow increases as time elapses, the two competing mechanisms ultimately reach a dynamic balance, establishing a repeating pattern for each pulse cycle. By performing simulations at higher repetition rates but lower per pulse energies while maintaining a constant time-averaged power, the amplitude of the hydrodynamic motion per pulse becomes smaller, and the evolution of the temperature and density distributions approach asymptotically towards, as expected, those calculated for a continuous-wave input of the equivalent power.

  3. Silicon chip based wavelength conversion of ultra-high repetition rate data signals

    DEFF Research Database (Denmark)

    Hu, Hao; Ji, Hua; Galili, Michael

    2011-01-01

    We report on all-optical wavelength conversion of 160, 320 and 640 Gbit/s line-rate data signals using four-wave mixing in a 3.6 mm long silicon waveguide. Bit error rate measurements validate the performance within FEC limits.......We report on all-optical wavelength conversion of 160, 320 and 640 Gbit/s line-rate data signals using four-wave mixing in a 3.6 mm long silicon waveguide. Bit error rate measurements validate the performance within FEC limits....

  4. Flexible graphene-based lithium ion batteries with ultrafast charge and discharge rates.

    Science.gov (United States)

    Li, Na; Chen, Zongping; Ren, Wencai; Li, Feng; Cheng, Hui-Ming

    2012-10-23

    There is growing interest in thin, lightweight, and flexible energy storage devices to meet the special needs for next-generation, high-performance, flexible electronics. Here we report a thin, lightweight, and flexible lithium ion battery made from graphene foam, a three-dimensional, flexible, and conductive interconnected network, as a current collector, loaded with Li(4)Ti(5)O(12) and LiFePO(4), for use as anode and cathode, respectively. No metal current collectors, conducting additives, or binders are used. The excellent electrical conductivity and pore structure of the hybrid electrodes enable rapid electron and ion transport. For example, the Li(4)Ti(5)O(12)/graphene foam electrode shows a high rate up to 200 C, equivalent to a full discharge in 18 s. Using them, we demonstrate a thin, lightweight, and flexible full lithium ion battery with a high-rate performance and energy density that can be repeatedly bent to a radius of 5 mm without structural failure and performance loss.

  5. High Repetition-Rate Wakefield Electron Source Generated by Few-millijoule, 30 femtosecond Laser Pulses on a Density Downramp

    CERN Document Server

    He, Z -H; Easter, J H; Krushelnick, K; Nees, J A; Thomas, A G R

    2012-01-01

    We report on an experimental demonstration of laser wakefield electron acceleration using a sub-TW power laser by tightly focusing 30-fs laser pulses with only 8 mJ pulse energy on a 100 \\mu m scale gas target. The experiments are carried out at an unprecedented 0.5 kHz repetition rate, allowing "real time" optimization of accelerator parameters. Well-collimated and stable electron beams with a quasi-monoenergetic peak in excess of 100 keV are measured. Particle-in-cell simulations show excellent agreement with the experimental results and suggest an acceleration mechanism based on electron trapping on the density downramp, due to the time varying phase velocity of the plasma waves.

  6. Octave-spanning spectrum of femtosecond Yb:fiber ring laser at 528 MHz repetition rate in microstructured tellurite fiber.

    Science.gov (United States)

    Wang, Guizhong; Jiang, Tongxiao; Li, Chen; Yang, Hongyu; Wang, Aimin; Zhang, Zhigang

    2013-02-25

    The octave-spanning spectrum was generated in a tellurite glass based microstructured fiber pumped by a 528 MHz repetition rate Yb:fiber ring laser without amplification. The laser achieved 40% output optical-to-optical efficiency with the output power of 410 mW. By adjusting the grating pair in the cavity, this oscillator can work at different cavity dispersion regimes with the shortest dechirped pulse width of 46 fs. The output pulses were then launched into a high-nonlinearity tellurite fiber, which has the zero-dispersion wavelength at ~1 μm. The high nonlinearity coefficient (1348 km⁻¹W⁻¹) and the matched zero-dispersion wavelength with pump laser enable the octave-spanning supercontinuum generated from 750 nm to 1700 nm with the coupled pulse energy above 10 pJ.

  7. Time-gated single-photon detection module with 110 ps transition time and up to 80 MHz repetition rate

    Energy Technology Data Exchange (ETDEWEB)

    Buttafava, Mauro, E-mail: mauro.buttafava@polimi.it; Boso, Gianluca; Ruggeri, Alessandro; Tosi, Alberto [Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Dalla Mora, Alberto [Politecnico di Milano, Dipartimento di Fisica, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy)

    2014-08-15

    We present the design and characterization of a complete single-photon counting module capable of time-gating a silicon single-photon avalanche diode with ON and OFF transition times down to 110 ps, at repetition rates up to 80 MHz. Thanks to this sharp temporal filtering of incoming photons, it is possible to reject undesired strong light pulses preceding (or following) the signal of interest, allowing to increase the dynamic range of optical acquisitions up to 7 decades. A complete experimental characterization of the module highlights its very flat temporal response, with a time resolution of the order of 30 ps. The instrument is fully user-configurable via a PC interface and can be easily integrated in any optical setup, thanks to its small and compact form factor.

  8. Development of a 16 kHz repetition rate, 110 W average power copper HyBrID laser

    Indian Academy of Sciences (India)

    R Biswal; P K Agrawal; G K Mishra; S V Nakhe; S K Dixit; J K Mittal

    2010-11-01

    This paper presents the design and performance analysis of an indigenously developed 110 W average output power copper HyBrID laser operating at 16 kHz pulse repetition rate. The laser active medium was confined within a fused silica tube of ∼ 6 cm diameter and ∼ 200 cm active length. An in-house developed high-power (∼ 10 kW) solid-state pulser was used as the electrical excitation source. A simple estimation of deposited electrical power, at the laser head, was carried out and based on it, the laser tube efficiency was found to be 2.9% at 70 W and 2.2% at 110 W laser power levels.

  9. Periodic disruptions induced by high repetition rate femtosecond pulses on magnesium-oxide-doped lithium niobate surfaces

    Science.gov (United States)

    Zhang, Shuanggen; Kan, Hongli; Zhai, Kaili; Ma, Xiurong; Luo, Yiming; Hu, Minglie; Wang, Qingyue

    2017-02-01

    In this paper, we demonstrate the periodic disruption formation on magnesium-oxide-doped lithium niobate surfaces by a femtosecond fiber laser system with wavelength and repetition rate of 1040 nm and 52 MHz, respectively. Three main experimental conditions, laser average power, scanning speed, and orientation of sample were systematically studied. In particular, the ablation morphologies of periodic disruptions under different crystal orientations were specifically researched. The result shows that such disruptions consisting of a bamboo-like inner structure appears periodically for focusing on the surface of X-, Y- and Z-cut wafers, which are formed by a rapid quenching of the material. Meanwhile, due to the anisotropic property, the bamboo-like inner structures consist of a cavity only arise from X- and Z-cut orientation.

  10. The readout of the LHC beam luminosity monitor: accurate shower energy measurements at a 40 MHz repetition rate

    Energy Technology Data Exchange (ETDEWEB)

    Manfredi, P.F. E-mail: pfmanfredi@lbl.gov; Ratti, L.; Speziali, V.; Traversi, G.; Manghisoni, M.; Re, V.; Denes, P.; Placidi, M.; Ratti, A.; Turner, W.C.; Datte, P.S.; Millaud, J.E

    2004-02-01

    The LHC beam luminosity monitor is based on the following principle. The neutrals that originate in LHC at every PP interaction develop showers of minimum ionizing particles in the absorbers placed in front of the separation dipoles. The shower energy, measured by suitable detectors in the absorbers is proportional to the number of neutral particles and, therefore, to the luminosity. The principle lends itself to a luminosity measurement on a bunch-by-bunch basis. However, to make such a measurement feasible, the system must comply with extremely stringent requirements. Its speed of operation must match the 40 MHz bunch repetition rate of LHC. Besides, the detector must stand extremely high radiation doses. This paper discusses the solutions adopted to comply with these requirements.

  11. The readout of the LHC beam luminosity monitor Accurate shower energy measurements at a 40 MHz repetition rate

    CERN Document Server

    Manfredi, P F; Speziali, V; Traversi, G; Manghisoni, M; Re, V; Denes, P; Placidi, Massimo; Ratti, A; Turner, W C; Datte, P S; Millaud, J E

    2004-01-01

    The LHC beam luminosity monitor is based on the following principle. The neutrals that originate in LHC at every PP interaction develop showers of minimum ionizing particles in the absorbers placed in front of the separation dipoles. The shower energy, measured by suitable detectors in the absorbers is proportional to the number of neutral particles and, therefore, to the luminosity. The principle lends itself to a luminosity measurement on a bunch-by-bunch basis. However, to make such a measurement feasible, the system must comply with extremely stringent requirements. Its speed of operation must match the 40 MHz bunch repetition rate of LHC. Besides, the detector must stand extremely high radiation doses. This paper discusses the solutions adopted to comply with these requirements.

  12. Miniaturized two-stack Blumlein pulser with a variable repetition-rate for non-thermal irreversible-electroporation experiments

    Science.gov (United States)

    Min, Sun-Hong; Kwon, Ohjoon; Sattorov, Matlabjon; Baek, In-Keun; Kim, Seontae; Jeong, Jin-Young; Hong, Dongpyo; Park, Seunghyuk; Park, Gun-Sik

    2017-01-01

    Non-thermal irreversible electroporation (NTIRE) to avoid thermal damage to cells during intense DC ns pulsed electric fields (nsPEFs) is a recent modality for medical applications. This mechanism, related to bioelectrical dynamics of the cell, is linked to the effect of a DC electric field and a threshold effect with an electrically stimulated membrane for the charge distribution in the cell. To create the NTIRE condition, the pulse width of the nsPEF should be shorter than the charging time constant of the membrane related to the cell radius, membrane capacitance, cytoplasm resistivity, and medium resistivity. It is necessary to design and fabricate a very intense nanosecond DC electric field pulser that is capable of producing voltages up to the level of 100 kV/cm with an artificial pulse width (˜ns) with controllable repetition rates. Many devices to generate intense DC nsPEF using various pulse-forming line technologies have been introduced thus far. However, the previous Blumlein pulse-generating devices are clearly inefficient due to the energy loss between the input voltage and the output voltage. An improved two-stage stacked Blumlein pulse-forming line can overcome this limitation and decrease the energy loss from a DC power supply. A metal oxide silicon field-effect transistor switch with a fast rise and fall time would enable a high repetition rate (max. 100 kHz) and good endurance against very high voltages (DC ˜ 30 kV). The load is designed to match the sample for exposure to cell suspensions consisting of a 200 Ω resistor matched with a Blumlein circuit and two electrodes without the characteristic RC time effect of the circuit (capacitance =0.174 pF).

  13. Generation of tunable, high repetition rate frequency combs with equalized spectra using carrier injection based silicon modulators

    Science.gov (United States)

    Nagarjun, K. P.; Selvaraja, Shankar Kumar; Supradeepa, V. R.

    2016-03-01

    High repetition-rate frequency combs with tunable repetition rate and carrier frequency are extensively used in areas like Optical communications, Microwave Photonics and Metrology. A common technique for their generation is strong phase modulation of a CW-laser. This is commonly implemented using Lithium-Niobate based modulators. With phase modulation alone, the combs have poor spectral flatness and significant number of missing lines. To overcome this, a complex cascade of multiple intensity and phase modulators are used. A comb generator on Silicon based on these principles is desirable to enable on-chip integration with other functionalities while reducing power consumption and footprint. In this work, we analyse frequency comb generation in carrier injection based Silicon modulators. We observe an interesting effect in these comb generators. Enhanced absorption accompanying carrier injection, an undesirable effect in data modulators, shapes the amplitude here to enable high quality combs from a single modulator. Thus, along with reduced power consumption to generate a specific number of lines, the complexity has also been significantly reduced. We use a drift-diffusion solver and mode solver (Silvaco TCAD) along with Soref-Bennett relations to calculate the variations in refractive indices and absorption of an optimized Silicon PIN - waveguide modulator driven by an unbiased high frequency (10 Ghz) voltage signal. Our simulations demonstrate that with a device length of 1 cm, a driving voltage of 2V and minor shaping with a passive ring-resonator filter, we obtain 37 lines with a flatness better than 5-dB across the band and power consumption an order of magnitude smaller than Lithium-Niobate modulators.

  14. High rate particle tracking and ultra-fast timing with a thin hybrid silicon pixel detector

    Science.gov (United States)

    Fiorini, M.; Aglieri Rinella, G.; Carassiti, V.; Ceccucci, A.; Cortina Gil, E.; Cotta Ramusino, A.; Dellacasa, G.; Garbolino, S.; Jarron, P.; Kaplon, J.; Kluge, A.; Marchetto, F.; Mapelli, A.; Martin, E.; Mazza, G.; Morel, M.; Noy, M.; Nuessle, G.; Perktold, L.; Petagna, P.; Petrucci, F.; Poltorak, K.; Riedler, P.; Rivetti, A.; Statera, M.; Velghe, B.

    2013-08-01

    The Gigatracker (GTK) is a hybrid silicon pixel detector designed for the NA62 experiment at CERN. The beam spectrometer, made of three GTK stations, has to sustain high and non-uniform particle rate (∼ 1 GHz in total) and measure momentum and angles of each beam track with a combined time resolution of 150 ps. In order to reduce multiple scattering and hadronic interactions of beam particles, the material budget of a single GTK station has been fixed to 0.5% X0. The expected fluence for 100 days of running is 2 ×1014 1 MeV neq /cm2, comparable to the one foreseen in the inner trackers of LHC detectors during 10 years of operation. To comply with these requirements, an efficient and very low-mass (architectures have been produced as small-scale prototypes: one is based on a Time-over-Threshold circuit followed by a TDC shared by a group of pixels, while the other makes use of a constant-fraction discriminator followed by an on-pixel TDC. The read-out ASICs are produced in 130 nm IBM CMOS technology and will be thinned down to 100 μm or less. An overview of the Gigatracker detector system will be presented. Experimental results from laboratory and beam tests of prototype bump-bonded assemblies will be described as well. These results show a time resolution of about 170 ps for single hits from minimum ionizing particles, using 200 μm thick silicon sensors.

  15. High rate particle tracking and ultra-fast timing with a thin hybrid silicon pixel detector

    Energy Technology Data Exchange (ETDEWEB)

    Fiorini, M., E-mail: Massimiliano.Fiorini@cern.ch [CERN, CH-1211 Geneva 23 (Switzerland); Aglieri Rinella, G. [CERN, CH-1211 Geneva 23 (Switzerland); Carassiti, V. [INFN Sezione di Ferrara (Italy); Ceccucci, A. [CERN, CH-1211 Geneva 23 (Switzerland); Cortina Gil, E. [Université Catholique de Louvain, Louvain-la-Neuve (Belgium); Cotta Ramusino, A. [INFN Sezione di Ferrara (Italy); Dellacasa, G.; Garbolino, S.; Jarron, P. [INFN Sezione di Torino (Italy); Kaplon, J.; Kluge, A.; Marchetto, F.; Mapelli, A. [CERN, CH-1211 Geneva 23 (Switzerland); Martin, E. [Université Catholique de Louvain, Louvain-la-Neuve (Belgium); Mazza, G. [INFN Sezione di Torino (Italy); Morel, M.; Noy, M. [CERN, CH-1211 Geneva 23 (Switzerland); Nuessle, G. [Université Catholique de Louvain, Louvain-la-Neuve (Belgium); Perktold, L.; Petagna, P. [CERN, CH-1211 Geneva 23 (Switzerland); and others

    2013-08-01

    The Gigatracker (GTK) is a hybrid silicon pixel detector designed for the NA62 experiment at CERN. The beam spectrometer, made of three GTK stations, has to sustain high and non-uniform particle rate (∼1GHz in total) and measure momentum and angles of each beam track with a combined time resolution of 150 ps. In order to reduce multiple scattering and hadronic interactions of beam particles, the material budget of a single GTK station has been fixed to 0.5% X{sub 0}. The expected fluence for 100 days of running is 2×10{sup 14} 1 MeV n{sub eq}/cm{sup 2}, comparable to the one foreseen in the inner trackers of LHC detectors during 10 years of operation. To comply with these requirements, an efficient and very low-mass (<0.15%X{sub 0}) cooling system is being constructed, using a novel microchannel cooling silicon plate. Two complementary read-out architectures have been produced as small-scale prototypes: one is based on a Time-over-Threshold circuit followed by a TDC shared by a group of pixels, while the other makes use of a constant-fraction discriminator followed by an on-pixel TDC. The read-out ASICs are produced in 130 nm IBM CMOS technology and will be thinned down to 100μm or less. An overview of the Gigatracker detector system will be presented. Experimental results from laboratory and beam tests of prototype bump-bonded assemblies will be described as well. These results show a time resolution of about 170 ps for single hits from minimum ionizing particles, using 200μm thick silicon sensors.

  16. Effect of laser annealing using high repetition rate pulsed laser on optical properties of phosphorus-ion-implanted ZnO nanorods

    Science.gov (United States)

    Shimogaki, Tetsuya; Ofuji, Taihei; Tetsuyama, Norihiro; Okazaki, Kota; Higashihata, Mitsuhiro; Nakamura, Daisuke; Ikenoue, Hiroshi; Asano, Tanemasa; Okada, Tatsuo

    2014-02-01

    The effect of high repetition rate pulsed laser annealing with a KrF excimer laser on the optical properties of phosphorus-ion-implanted zinc oxide nanorods has been investigated. The recovery levels of phosphorus-ion-implanted zinc oxide nanorods have been measured by photoluminescence spectra and cathode luminescence images. Cathode luminescence disappeared over 300 nm below the surface due to the damage caused by ion implantation with an acceleration voltage of 25 kV. When the annealing was performed at a low repetition rate of the KrF excimer laser, cathode luminescence was recovered only in a shallow area below the surface. The depth of the annealed area was increased along with the repetition rate of the annealing laser. By optimizing the annealing conditions such as the repetition rate, the irradiation fluence and so on, we have succeeded in annealing the whole damaged area of over 300 nm in depth and in observing cathode luminescence. Thus, the effectiveness of high repetition rate pulsed laser annealing on phosphorus-ion-implanted zinc oxide nanorods was demonstrated.

  17. A 600 VOLT MULTI-STAGE, HIGH REPETITION RATE GAN FET SWITCH

    Energy Technology Data Exchange (ETDEWEB)

    Frolov, D. [Fermilab; Pfeffer, H. [Fermilab; Saewert, G. [Fermilab

    2016-10-05

    Using recently available GaN FETs, a 600 Volt three- stage, multi-FET switch has been developed having 2 nanosecond rise time driving a 200 Ohm load with the potential of approaching 30 MHz average switching rates. Possible applications include driving particle beam choppers kicking bunch-by-bunch and beam deflectors where the rise time needs to be custom tailored. This paper reports on the engineering issues addressed, the design approach taken and some performance results of this switch.

  18. Investigations on the heat transport capability of a cryogenic oscillating heat pipe and its application in achieving ultra-fast cooling rates for cell vitrification cryopreservation.

    Science.gov (United States)

    Han, Xu; Ma, Hongbin; Jiao, Anjun; Critser, John K

    2008-06-01

    Theoretically, direct vitrification of cell suspensions with relatively low concentrations ( approximately 1 M) of permeating cryoprotective agents (CPA) is suitable for cryopreservation of almost all cell types and can be accomplished by ultra-fast cooling rates that are on the order of 10(6-7) K/min. However, the methods and devices currently available for cell cryopreservation cannot achieve such high cooling rates. In this study, we constructed a novel cryogenic oscillating heat pipe (COHP) using liquid nitrogen as its working fluid and investigated its heat transport capability to assess its application for achieving ultra-fast cooling rates for cell cryopreservation. The experimental results showed that the apparent heat transfer coefficient of the COHP can reach 2 x 10(5) W/m(2).K, which is two orders of the magnitude higher than traditional heat pipes. Theoretical analyzes showed that the average local heat transfer coefficient in the thin film evaporation region of the COHP can reach 1.2 x 10(6) W/m(2).K, which is approximately 10(3) times higher than that achievable with standard pool-boiling approaches. Based on these results, a novel device design applying the COHP and microfabrication techniques is proposed and its efficiency for cell vitrification is demonstrated through numerical simulation. The estimated average cooling rates achieved through this approach is 10(6-7)K/min, which is much faster than the currently available methods and sufficient for achieving vitrification with relatively low concentrations of CPA.

  19. Femtosecond laser bone ablation with a high repetition rate fiber laser source.

    Science.gov (United States)

    Mortensen, Luke J; Alt, Clemens; Turcotte, Raphaël; Masek, Marissa; Liu, Tzu-Ming; Côté, Daniel C; Xu, Chris; Intini, Giuseppe; Lin, Charles P

    2015-01-01

    Femtosecond laser pulses can be used to perform very precise cutting of material, including biological samples from subcellular organelles to large areas of bone, through plasma-mediated ablation. The use of a kilohertz regenerative amplifier is usually needed to obtain the pulse energy required for ablation. This work investigates a 5 megahertz compact fiber laser for near-video rate imaging and ablation in bone. After optimization of ablation efficiency and reduction in autofluorescence, the system is demonstrated for the in vivo study of bone regeneration. Image-guided creation of a bone defect and longitudinal evaluation of cellular injury response in the defect provides insight into the bone regeneration process.

  20. Implementation of time-resolved step-scan fourier transform infrared (FT-IR) spectroscopy using a kHz repetition rate pump laser.

    Science.gov (United States)

    Magana, Donny; Parul, Dzmitry; Dyer, R Brian; Shreve, Andrew P

    2011-05-01

    Time-resolved step-scan Fourier transform infrared (FT-IR) spectroscopy has been shown to be invaluable for studying excited-state structures and dynamics in both biological and inorganic systems. Despite the established utility of this method, technical challenges continue to limit the data quality and more wide ranging applications. A critical problem has been the low laser repetition rate and interferometer stepping rate (both are typically 10 Hz) used for data acquisition. Here we demonstrate significant improvement in the quality of time-resolved spectra through the use of a kHz repetition rate laser to achieve kHz excitation and data collection rates while stepping the spectrometer at 200 Hz. We have studied the metal-to-ligand charge transfer excited state of Ru(bipyridine)(3)Cl(2) in deuterated acetonitrile to test and optimize high repetition rate data collection. Comparison of different interferometer stepping rates reveals an optimum rate of 200 Hz due to minimization of long-term baseline drift. With the improved collection efficiency and signal-to-noise ratio, better assignments of the MLCT excited-state bands can be made. Using optimized parameters, carbonmonoxy myoglobin in deuterated buffer is also studied by observing the infrared signatures of carbon monoxide photolysis upon excitation of the heme. We conclude from these studies that a substantial increase in performance of ss-FT-IR instrumentation is achieved by coupling commercial infrared benches with kHz repetition rate lasers.

  1. High-average-power 2 μm few-cycle optical parametric chirped pulse amplifier at 100 kHz repetition rate.

    Science.gov (United States)

    Shamir, Yariv; Rothhardt, Jan; Hädrich, Steffen; Demmler, Stefan; Tschernajew, Maxim; Limpert, Jens; Tünnermann, Andreas

    2015-12-01

    Sources of long wavelengths few-cycle high repetition rate pulses are becoming increasingly important for a plethora of applications, e.g., in high-field physics. Here, we report on the realization of a tunable optical parametric chirped pulse amplifier at 100 kHz repetition rate. At a central wavelength of 2 μm, the system delivered 33 fs pulses and a 6 W average power corresponding to 60 μJ pulse energy with gigawatt-level peak powers. Idler absorption and its crystal heating is experimentally investigated for a BBO. Strategies for further power scaling to several tens of watts of average power are discussed.

  2. Repetition-rate-selectable high-speed optical gating in a VO{sub 2} thin film based on gain modulation of optical amplifier

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Yong Wook; Kim, Bong Jun; Choi, Sung Youl; Chae, Byung Gyu; Kim, Hyun Tak [Electronics and Telecommunications Research Institute, Daejeon (Korea, Republic of); Lee, Yong Wook [Pukyong National University, Busan (Korea, Republic of); Seo, Gi Wan [University of Science and Technology, Daejeon (Korea, Republic of); Lee, Yong Wan [University of Minnesota, Minneapolis, MN (United States)

    2010-12-15

    In this research, we investigated the dependence of the saturation-induced gain modulation (SIGM) on the modulation frequency of the input signal in an erbium-doped fiber amplifier (EDFA). By finding and incorporating the modulation frequency invariance of the SIGM realizable within some frequency range, we demonstrated a repetition-rate-selectable high-speed optical gating in two-terminal electrical devices based on vanadium-dioxide thin films. In the implemented optical gating system, the repetition rate could be freely chosen as an arbitrary frequency between 0.27 and 10 kHz without any degradation of the gating speed and the signal-to-noise ratio.

  3. Strong modulation of ectopic focus as a mechanism of repetitive interpolated ventricular bigeminy with heart rate doubling.

    Science.gov (United States)

    Takayanagi, Kan; Nakahara, Shiro; Toratani, Noritaka; Chida, Ryuji; Kobayashi, Sayuki; Sakai, Yoshihiko; Takeuchi, Akihiro; Ikeda, Noriaki

    2013-10-01

    Repetitive interpolated ventricular bigeminy (RIVB) can introduce a doubling of the ventricular rate. To clarify the mechanism of RIVB, we hypothesized that it was introduced by a strong modulation of the ventricular automatic focus. RIVB, defined as more than 7 bigeminy events, was detected by instantaneous heart rate and bigeminy interval (BI) tachograms in 1450 successive patients with frequent ventricular premature contractions (≥3000 per day). Postextrasystolic interval bigeminy interval curves were plotted to determine the degree of modulation. Mean sinus cycle length bigeminy interval curves were plotted for selection. RIVB was simulated by using a computer-based parasystole model. RIVB was observed in 7 patients (age 60 ± 16 years; 2 men and 5 women) with a heart rate of 58.2 ± 6.5 beats/min during a rest period both during the day and at night. The tachograms disclosed the onset of the RIVB with a doubled ventricular rate to 112.3 ± 8.5 beats/min. On the postextrasystolic interval bigeminy interval curves, compensatory bigeminy and interpolated bigeminy constituted overlapping regression lines with slopes close to 1.00 and RIVB was located in the lower left portion. RIVB lasting for up to 3 hours was quickly detected by mean sinus cycle length bigeminy interval curve. The PQ interval immediately after RIVB was prolonged in comparison with baseline (0.18 ± 0.02 to 0.21 ± 0.02 seconds; P heart rate. Our findings support the hypothesis that RIVB was introduced by strongly modulated ventricular pacemaker accelerated by an intervening normal QRS. © 2013 Heart Rhythm Society. All rights reserved.

  4. 300 microJ noncollinear optical parametric amplifier in the visible at 1 kHz repetition rate.

    Science.gov (United States)

    Tzankov, Pancho; Zheng, Jiaan; Mero, Mark; Polli, Dario; Manzoni, Cristian; Cerullo, Giulio

    2006-12-15

    We demonstrate an order-of-magnitude energy scaling of a white-light seeded noncollinear optical parametric amplifier in the visible. The generated pulses, tunable between 520 and 650 nm with sub-25-fs duration, had energies up to 310 microJ with 20% blue-pump-to-signal energy conversion efficiency at 540 nm. This new ultrafast source will make possible numerous extreme nonlinear optics applications. As a first application, we demonstrate the generation of tunable vacuum ultraviolet pulses.

  5. 500 MW peak power degenerated optical parametric amplifier delivering 52 fs pulses at 97 kHz repetition rate.

    Science.gov (United States)

    Rothhardt, J; Hädrich, S; Röser, F; Limpert, J; Tünnermann, A

    2008-06-09

    We present a high peak power degenerated parametric amplifier operating at 1030 nm and 97 kHz repetition rate. Pulses of a state-of-the art fiber chirped-pulse amplification (FCPA) system with 840 fs pulse duration and 410 microJ pulse energy are used as pump and seed source for a two stage optical parametric amplifier. Additional spectral broadening of the seed signal in a photonic crystal fiber creates enough bandwidth for ultrashort pulse generation. Subsequent amplification of the broadband seed signal in two 1 mm BBO crystals results in 41 microJ output pulse energy. Compression in a SF 11 prism compressor yields 37 microJ pulses as short as 52 fs. Thus, pulse shortening of more than one order of magnitude is achieved. Further scaling in terms of average power and pulse energy seems possible and will be discussed, since both concepts involved, the fiber laser and the parametric amplifier have the reputation to be immune against thermo-optical effects.

  6. Synthesis, characterization and evaluation of CO-oxidation catalysts for high repetition rate CO2 TEA lasers

    Science.gov (United States)

    Moser, Thomas P.

    1990-06-01

    An extremely active class of noble metal catalysts supported on titania was developed and fabricated at Hughes for the recombination of oxygen (O2) and carbon monoxide (CO) in closed-cycle CO2 TEA lasers. The incipient wetness technique was used to impregnate titania and alumina pellets with precious metals including platinum and palladium. In particular, the addition of cerium (used as an oxygen storage promoter) produced an extremely active Pt/Ce/TiO2 catalyst. By comparison, the complementary Pt/Ce/ gamma-Al2O3 catalyst was considerably less active. In general, chloride-free catalyst precursors proved critical in obtaining an active catalyst while also providing uniform metal distributions throughout the support structure. Detailed characterization of the Pt/Ce/TiO2 catalyst demonstrated uniform dendritic crystal growth of the metals throughout the support. Electron spectroscopy for Chemical Analysis (ESCA) analysis was used to characterize the oxidation states of Pt, Ce and Ti. The performance of the catalysts was evaluated with an integral flow reactor system incorporating real time analysis of O2 and CO. With this system, the transient and steady-state behavior of the catalysts were evaluated. The kinetic evaluation was complemented by tests in a compact, closed-cycle Hughes CO2 TEA laser operating at a pulse repetition rate of 100 Hz with a catalyst temperature of 75 to 95 C. The Pt/Ce/TiO2 catalyst was compatible with a C(13)O(16)2 gas fill.

  7. Low-repetition rate femtosecond laser writing of optical waveguides in KTP crystals: analysis of anisotropic refractive index changes.

    Science.gov (United States)

    Butt, Muhammad Ali; Nguyen, Huu-Dat; Ródenas, Airán; Romero, Carolina; Moreno, Pablo; Vázquez de Aldana, Javier R; Aguiló, Magdalena; Solé, Rosa Maria; Pujol, Maria Cinta; Díaz, Francesc

    2015-06-15

    We report on the direct low-repetition rate femtosecond pulse laser microfabrication of optical waveguides in KTP crystals and the characterization of refractive index changes after the thermal annealing of the sample, with the focus on studying the potential for direct laser fabricating Mach-Zehnder optical modulators. We have fabricated square cladding waveguides by means of stacking damage tracks, and found that the refractive index decrease is large for vertically polarized light (c-axis; TM polarized) but rather weak for horizontally polarized light (a-axis; TE polarized), this leading to good near-infrared light confinement for TM modes but poor for TE modes. However, after performing a sample thermal annealing we have found that the thermal process enables a refractive index increment of around 1.5x10(-3) for TE polarized light, while maintaining the negative index change of around -1x10(-2) for TM polarized light. In order to evaluate the local refractive index changes we have followed a multistep procedure: We have first characterized the waveguide cross-sections by means of Raman micro-mapping to access the lattice micro-modifications and their spatial extent. Secondly we have modeled the waveguides following the modified region sizes obtained by micro-Raman with finite element method software to obtain a best match between the experimental propagation modes and the simulated ones. Furthermore we also report the fabrication of Mach-Zehnder structures and the evaluation of propagation losses.

  8. Vernier effect within a versatile femtosecond optical parametric oscillator for broad-tunable, high-repetition-rate oscillator

    CERN Document Server

    Jin, Yuwei; Harren, Frans J M; Mandon, Julien

    2015-01-01

    Within a synchronously pumped optical parametric oscillator (SPOPO), the inherent synchronism between the pump and the resonating signal is the magic to partly transfer the coherence property of the pump to the signal. In our demonstration, Vernier effect is observed within a femtosecond SPOPO by simply detuning the FSR of the cavity, generating signal pulses at tunable repetition rate from several GHz to 1 THz with a maximum 22.58 nm full width half maximum (FWHM) bandwidth supporting 160 fs pulses covering the C- and L-bands of the telecom wavelength region. This technique offers a simple method of active ?filtering of dense frequency comb lines instead of using Fabry-P?erot (FP) cavities with complex locking system for astro-comb generation. Beside, as a promising source for frequency combs with tunable and large comb-spacing, it offers potential opportunities for applications such as high speed coherent data transmission, line-by-line pulse shaping, optical clocks and precision metrology.

  9. In-situ, variable thickness, liquid crystal film target formation at moderate repetition rate for intense laser applications

    CERN Document Server

    Poole, P L; Cochran, G E; Hanna, R J; Andereck, C D; Schumacher, D W

    2015-01-01

    Liquid crystal films have recently been demonstrated as variable thickness, planar targets for ultra-intense laser matter experiments and applications such as ion acceleration. By controlling the parameters of film formation, including liquid crystal temperature and volume, their thickness can be varied on-demand from 10 $nm$ to above 10 $\\mu m$. This thickness range enables for the first time real-time selection and optimization of various ion acceleration mechanisms using low cost, high quality targets. Our previous work employed these targets in single shot configuration, requiring chamber cycling after the pre-made films were expended. Presented here is a film formation device capable of drawing films from a bulk liquid crystal source volume to any thickness in the aforementioned range. This device will form films under vacuum within 2 $\\mu m$ of the same location each time, well within the Rayleigh range of even tight $F/ \\#$ systems. The repetition rate of the device exceeds 0.1 $Hz$ for sub-100 $nm$ fi...

  10. Low-timing-jitter, stretched-pulse passively mode-locked fiber laser with tunable repetition rate and high operation stability

    Science.gov (United States)

    Liu, Yuanshan; Zhang, Jian-Guo; Chen, Guofu; Zhao, Wei; Bai, Jing

    2010-09-01

    We design a low-timing-jitter, repetition-rate-tunable, stretched-pulse passively mode-locked fiber laser by using a nonlinear amplifying loop mirror (NALM), a semiconductor saturable absorber mirror (SESAM), and a tunable optical delay line in the laser configuration. Low-timing-jitter optical pulses are stably produced when a SESAM and a 0.16 m dispersion compensation fiber are employed in the laser cavity. By inserting a tunable optical delay line between NALM and SESAM, the variable repetition-rate operation of a self-starting, passively mode-locked fiber laser is successfully demonstrated over a range from 49.65 to 50.47 MHz. The experimental results show that the newly designed fiber laser can maintain the mode locking at the pumping power of 160 mW to stably generate periodic optical pulses with width less than 170 fs and timing jitter lower than 75 fs in the 1.55 µm wavelength region, when the fundamental repetition rate of the laser is continuously tuned between 49.65 and 50.47 MHz. Moreover, this fiber laser has a feature of turn-key operation with high repeatability of its fundamental repetition rate in practice.

  11. Sub-picosecond Graphene-based Harmonically Mode-Locked Fiber Laser With Repetition Rates up to 2.22 GHz

    Directory of Open Access Journals (Sweden)

    Abramski K.M.

    2013-03-01

    Full Text Available Passive harmonic-mode locking (PHML of erbium-doped fiber laser with multilayer graphene is presented. The laser could operate at several harmonics (from 2nd to 21st of the fundamental repetition frequency of the ring resonator (106 MHz. The highest achieved repetition rate was 2.22 GHz (which corresponds to the 21st harmonic with 900 fs pulse duration and 50 dB of the supermode noise suppression. The saturable absorber was formed by multilayer graphene, mechanically exfoliated from pure graphite block through Scotch-tape and deposited on the fiber ferrule.

  12. In vivo functional imaging of blood flow and wall strain rate in outflow tract of embryonic chick heart using ultrafast spectral domain optical coherence tomography

    Science.gov (United States)

    Li, Peng; Yin, Xin; Shi, Liang; Rugonyi, Sandra; Wang, Ruikang K.

    2012-09-01

    During cardiac development, the cardiac wall and flowing blood are two important cardiac tissues that constantly interact with each other. This dynamic interaction defines appropriate biomechanical environment to which the embryonic heart is exposed. Quantitative assessment of the dynamic parameters of wall tissues and blood flow is required to further our understanding of cardiac development. We report the use of an ultrafast 1310-nm dual-camera spectral domain optical coherence tomography (SDOCT) system to characterize/image, in parallel, the dynamic radial strain rate of the myocardial wall and the Doppler velocity of the underlying flowing blood within an in vivo beating chick embryo. The OCT system operates at 184-kHz line scan rate, providing the flexibility of imaging the fast blood flow and the slow tissue deformation within one scan. The ability to simultaneously characterize tissue motion and blood flow provides a useful approach to better understand cardiac dynamics during early developmental stages.

  13. High-repetition-rate compact excimer laser: UV light source for metrology, inspection, direct writing, and material testing

    Science.gov (United States)

    Huber, Heinz P.; Pflanz, Tobias; Goertler, Andreas; Schillinger, Helmut

    2003-06-01

    The discharge pumped excimer laser is a gas laser providing ultra violet (UV) radiation with well defined spectral, temporal and spatial properties. The fast development of excimer lasers in recent years has succeeded in designing very compact, table-top and turn-key systems delivering up to 20 W of radiation at 248 nm, 10 W at 193 nm and 2 W at 157 nm with repetition rates up to 2000 Hz (1, 5). Due to their short emission wavelength and compactness they are continuously replacing other light sources, like lamps and ion lasers, in applications as metrology, inspection, direct writing and material testing. Spatial and temporal beam properties of compact excimer lasers are very suitable to be utilized as illumination source in these applications. The compact excimer laser is combining the advantages of both, lamp and laser sources. It displays low temporal and spatial coherence, but has a narrow spectral emission range of a few hundred pm. The beam area is approximately 1/2 cm2, the divergence is in the order of 1 mrad. Variation of beam position and beam direction are negligible for most illumination applications. Compact excimer lasers are easy to integrate in measurement and inspection systems. Typically their footprint area is 0.25 m2. The power consumption is less than 1 kW, enabling single phase electrical supply and air cooling. State-of-the-art compact excimer lasers are compliant to all relevant SEMI regulations. The laser optics exceeds the life time of the laser tube, thus no optics cleaning and exchange is necessary in a whole life time of a laser tube of a few billion pulses (6).

  14. Confirmation of gravitationally induced attitude drift of spinning satellite Ajisai with Graz high repetition rate SLR data

    Science.gov (United States)

    Kucharski, Daniel; Kirchner, Georg; Otsubo, Toshimichi; Lim, Hyung-Chul; Bennett, James; Koidl, Franz; Kim, Young-Rok; Hwang, Joo-Yeon

    2016-02-01

    The high repetition rate Satellite Laser Ranging system Graz delivers the millimeter precision range measurements to the corner cube reflector panels of Ajisai. The analysis of 4599 passes measured from October 2003 until November 2014 reveals the secular precession and nutation of Ajisai spin axis due to the gravitational forces as predicted by Kubo (1987) with the periods of 35.6 years and 116.5 days respectively. The observed precession cone is oriented at RA = 88.9°, Dec = -88.85° (J2000) and has a radius of 1.08°. The radius of the nutation cone increases from 1.32° to 1.57° over the 11 years of the measurements. We also detect a draconitic wobbling of Ajisai orientation due to the 'motion' of the Sun about the satellite's orbit. The observed spin period of Ajisai increases exponentially over the investigated time span according to the trend function: T = 1.492277·exp(0.0148388·Y) [s], where Y is in years since launch (1986.6133), RMS = 0.412 ms. The physical simulation model fitted to the observed spin parameters proves a very low interaction between Ajisai and the Earth's magnetic field, what assures that the satellite's angular momentum vector will remain in the vicinity of the south celestial pole for the coming decades. The developed empirical model of the spin axis orientation can improve the accuracy of the range determination between the ground SLR systems and the satellite's center-of-mass (Kucharski et al., 2015) and enable the accurate attitude prediction of Ajisai for the laser time-transfer experiments (Kunimori et al., 1992).

  15. Ultrafast biophotonics

    CERN Document Server

    Vasa, P

    2016-01-01

    This book presents emerging contemporary optical techniques of ultrafast science which have opened entirely new vistas for probing biological entities and processes. The spectrum reaches from time-resolved imaging and multiphoton microscopy to cancer therapy and studies of DNA damage. The book displays interdisciplinary research at the interface of physics and biology. Emerging topics on the horizon are also discussed, like the use of squeezed light, frequency combs and terahertz imaging as the possibility of mimicking biological systems. The book is written in a manner to make it readily accessible to researchers, postgraduate biologists, chemists, engineers, and physicists and students of optics, biomedical optics, photonics and biotechnology.

  16. 10  GHz pulse repetition rate Er:Yb:glass laser modelocked with quantum dot semiconductor saturable absorber mirror.

    Science.gov (United States)

    Resan, B; Kurmulis, S; Zhang, Z Y; Oehler, A E H; Markovic, V; Mangold, M; Südmeyer, T; Keller, U; Hogg, R A; Weingarten, K J

    2016-05-10

    Semiconductor saturable absorber mirror (SESAM) modelocked high pulse repetition rate (≥10  GHz) diode-pumped solid-state lasers are proven as an enabling technology for high data rate coherent communication systems owing to their low noise and high pulse-to-pulse optical phase-coherence. Compared to quantum well, quantum dot (QD)-based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the first 10 GHz pulse repetition rate QD-SESAM modelocked laser at 1.55 μm, exhibiting 2 ps pulse width from an Er-doped glass oscillator (ERGO). The 10 GHz ERGO laser is modelocked with InAs/GaAs QD-SESAM with saturation fluence as low as 9  μJ/cm2.

  17. PREFACE: Ultrafast biophotonics Ultrafast biophotonics

    Science.gov (United States)

    Gu, Min; Reid, Derryck; Ben-Yakar, Adela

    2010-08-01

    The use of light to explore biology can be traced to the first observations of tissue made with early microscopes in the mid-seventeenth century, and has today evolved into the discipline which we now know as biophotonics. This field encompasses a diverse range of activities, each of which shares the common theme of exploiting the interaction of light with biological material. With the rapid advancement of ultrafast optical technologies over the last few decades, ultrafast lasers have increasingly found applications in biophotonics, to the extent that the distinctive new field of ultrafast biophotonics has now emerged, where robust turnkey ultrafast laser systems are facilitating cutting-edge studies in the life sciences to take place in everyday laboratories. The broad spectral bandwidths, precision timing resolution, low coherence and high peak powers of ultrafast optical pulses provide unique opportunities for imaging and manipulating biological systems. Time-resolved studies of bio-molecular dynamics exploit the short pulse durations from such lasers, while other applications such as optical coherence tomography benefit from the broad optical bandwidths possible by using super-continuum generation and additionally allowing for high speed imaging with speeds as high as 47 000 scans per second. Continuing progress in laser-system technology is accelerating the adoption of ultrafast techniques across the life sciences, both in research laboratories and in clinical applications, such as laser-assisted in situ keratomileusis (LASIK) eye surgery. Revolutionizing the field of optical microscopy, two-photon excitation fluorescence (TPEF) microscopy has enabled higher spatial resolution with improved depth penetration into biological specimens. Advantages of this nonlinear optical process include: reduced photo-interactions, allowing for extensive imaging time periods; simultaneously exciting multiple fluorescent molecules with only one excitation wavelength; and

  18. Derivation of a formula describing the saturation correction of plane-parallel ionization chambers in pulsed fields with arbitrary repetition rate.

    Science.gov (United States)

    Karsch, Leonhard

    2016-04-21

    Gas-filled ionization chambers are widely used radiation detectors in radiotherapy. A quantitative description and correction of the recombination effects exists for two cases, for continuous radiation exposure and for pulsed radiation fields with short single pulses. This work gives a derivation of a formula for pulsed beams with arbitrary pulse rate for which the prerequisites of the two existing descriptions are not fulfilled. Furthermore, an extension of the validity of the two known cases is investigated. The temporal evolution of idealized charge density distributions within a plane parallel chamber volume is described for pulsed beams of vanishing pulse duration and arbitrary pulse repetition rate. First, the radiation induced release, movement and collection of the charge carriers without recombination are considered. Then, charge recombination is calculated basing on these simplified charge distributions and the time dependent spatial overlap of positive and negative charge carrier distributions. Finally, a formula for the calculation of the saturation correction factor is derived by calculation and simplification of the first two terms of a Taylor expansion for small recombination. The new formula of saturation correction contains the two existing cases, descriptions for exposure by single pulses and continuous irradiation, as limiting cases. Furthermore, it is possible to determine the pulse rate range for which each of the three descriptions is applicable by comparing the dependencies of the new formula with the two existing cases. As long as the time between two pulses is lower than one third of the collection time of the chamber, the formalism for a continuous exposure can be used. The known description for single pulse irradiation is only valid if the repetition rate is less than 1.2 times the inverse collection time. For all other repetition rates in between the new formula should be used. The experimental determination by Jaffe diagrams can be

  19. Derivation of a formula describing the saturation correction of plane-parallel ionization chambers in pulsed fields with arbitrary repetition rate

    Science.gov (United States)

    Karsch, Leonhard

    2016-04-01

    Gas-filled ionization chambers are widely used radiation detectors in radiotherapy. A quantitative description and correction of the recombination effects exists for two cases, for continuous radiation exposure and for pulsed radiation fields with short single pulses. This work gives a derivation of a formula for pulsed beams with arbitrary pulse rate for which the prerequisites of the two existing descriptions are not fulfilled. Furthermore, an extension of the validity of the two known cases is investigated. The temporal evolution of idealized charge density distributions within a plane parallel chamber volume is described for pulsed beams of vanishing pulse duration and arbitrary pulse repetition rate. First, the radiation induced release, movement and collection of the charge carriers without recombination are considered. Then, charge recombination is calculated basing on these simplified charge distributions and the time dependent spatial overlap of positive and negative charge carrier distributions. Finally, a formula for the calculation of the saturation correction factor is derived by calculation and simplification of the first two terms of a Taylor expansion for small recombination. The new formula of saturation correction contains the two existing cases, descriptions for exposure by single pulses and continuous irradiation, as limiting cases. Furthermore, it is possible to determine the pulse rate range for which each of the three descriptions is applicable by comparing the dependencies of the new formula with the two existing cases. As long as the time between two pulses is lower than one third of the collection time of the chamber, the formalism for a continuous exposure can be used. The known description for single pulse irradiation is only valid if the repetition rate is less than 1.2 times the inverse collection time. For all other repetition rates in between the new formula should be used. The experimental determination by Jaffe diagrams can be

  20. LUX — A Recirculating Linac-based Ultrafast X-ray Source

    Science.gov (United States)

    Corlett, J. N.; Barletta, W. A.; DeSantis, S.; Doolittle, L.; Fawley, W. M.; Green, M. A.; Heimann, P.; Leone, S. R.; Lidia, S.; Li, D.; Parmigiani, F.; Ratti, A.; Robinson, K.; Schoenlein, R.; Staples, J.; Wan, W.; Wells, R.; Wilcox, R.; Wolski, A.; Zholents, A.

    2004-05-01

    We describe the design of a proposed source of ultra-fast synchrotron radiation x-ray pulses based on a recirculating superconducting linac, with an integrated array of ultrafast laser systems. The source produces x-ray pulses with duration of 10-50 fs at a 10 kHz repetition rate, with tunability from EUV to hard x-ray regimes, and optimized for the study of ultra-fast dynamics. A high-brightness rf photocathode provides electron bunches. An injector linac accelerates the beam to the 100 MeV range, and is followed by four passes through a 700 MeV recirculating linac. Ultrafast hard x-ray pulses are obtained by a combination of electron bunch manipulation, transverse temporal correlation of the electrons, and x-ray pulse compression. EUV and soft x-ray pulses as short as 10 fs are generated in a harmonic-cascade free electron laser scheme. We describe the facility major systems and peformance.

  1. Oral-Diadochokinetic Rates for Hebrew-Speaking Healthy Ageing Population: Non-Word versus Real-Word Repetition

    Science.gov (United States)

    Ben-David, Boaz M.; Icht, Michal

    2017-01-01

    Background: Oral-diadochokinesis (oral-DDK) tasks are extensively used in the evaluation of motor speech abilities. Currently, validated normative data for older adults (aged 65 years and older) are missing in Hebrew. The effect of task stimuli (non-word versus real-word repetition) is also non-clear in the population of older adult Hebrew…

  2. Optimizing stimulus repetition rate for recording ocular vestibular evoked myogenic potential elicited by air-conduction tone bursts of 500 Hz

    Directory of Open Access Journals (Sweden)

    Niraj Kumar Singh

    2014-03-01

    Full Text Available Amidst several publications reporting the effects of stimulus-related parameters on ocular vestibular evoked myogenic potential (oVEMP, the effect of the repetition rate on oVEMP responses has largely gone unexplored. Studies have used a repetition rate of ~5.1 Hz mainly due to a presumption that oVEMP, like cervical VEMP, should produce best responses for ~5 Hz, although there is paucity of experimental evidence to support this hypothesis. 52 healthy individuals in the age range of 17-35 years underwent air-conduction oVEMP elicited by 500 Hz tone-bursts using seven different repetition rates (3.1, 5.1, 10.1, 15.1, 20.1, 25.1 and 30.1 Hz. The results revealed a tendency for prolongation of latencies and reduction in amplitude with increasing repetition rate. However, significantly longer latencies were observed only for 20.1 Hz and larger amplitudes for 3.1 and 5.1 Hz (P<0.05. There was no significant difference between the rates of 3.1 Hz and 5.1 Hz. However 3.1 Hz produced poorer signal-to-noise ratio and required considerably longer time and thereby had lesser efficiency than 5.1 Hz (P<0.05. This would also result in higher fatigue and irritation levels considering the physical act of maintaining a supero-medial gaze. Thus the use of 5.1 Hz is recommended for clinical recording of oVEMP.

  3. Optimizing Stimulus Repetition Rate for Recording Ocular Vestibular Evoked Myogenic Potential Elicited by Air-Conduction Tone Bursts of 500 Hz.

    Science.gov (United States)

    Singh, Niraj Kumar; Kadisonga, Peter; Ashitha, Palliyath

    2014-03-06

    Amidst several publications reporting the effects of stimulus-related parameters on ocular vestibular evoked myogenic potential (oVEMP), the effect of the repetition rate on oVEMP responses has largely gone unexplored. Studies have used a repetition rate of ~5.1 Hz mainly due to a presumption that oVEMP, like cervical VEMP, should produce best responses for ~5 Hz, although there is paucity of experimental evidence to support this hypothesis. 52 healthy individuals in the age range of 17-35 years underwent air-conduction oVEMP elicited by 500 Hz tone-bursts using seven different repetition rates (3.1, 5.1, 10.1, 15.1, 20.1, 25.1 and 30.1 Hz). The results revealed a tendency for prolongation of latencies and reduction in amplitude with increasing repetition rate. However, significantly longer latencies were observed only for 20.1 Hz and larger amplitudes for 3.1 and 5.1 Hz (P<0.05). There was no significant difference between the rates of 3.1 Hz and 5.1 Hz. However 3.1 Hz produced poorer signal-to-noise ratio and required considerably longer time and thereby had lesser efficiency than 5.1 Hz (P<0.05). This would also result in higher fatigue and irritation levels considering the physical act of maintaining a supero-medial gaze. Thus the use of 5.1 Hz is recommended for clinical recording of oVEMP.

  4. Disturbance and recovery of trunk mechanical and neuromuscular behaviours following repetitive lifting: influences of flexion angle and lift rate on creep-induced effects.

    Science.gov (United States)

    Toosizadeh, Nima; Bazrgari, Babak; Hendershot, Brad; Muslim, Khoirul; Nussbaum, Maury A; Madigan, Michael L

    2013-01-01

    Repetitive lifting is associated with an increased risk of occupational low back disorders, yet potential adverse effects of such exposure on trunk mechanical and neuromuscular behaviours were not well described. Here, 12 participants, gender balanced, completed 40 min of repetitive lifting in all combinations of three flexion angles (33, 66, and 100% of each participant's full flexion angle) and two lift rates (2 and 4 lifts/min). Trunk behaviours were obtained pre- and post-exposure and during recovery using sudden perturbations. Intrinsic trunk stiffness and reflexive responses were compromised after lifting exposures, with larger decreases in stiffness and reflexive force caused by larger flexion angles, which also delayed reflexive responses. Consistent effects of lift rate were not found. Except for reflex delay no measures returned to pre-exposure values after 20 min of recovery. Simultaneous changes in both trunk stiffness and neuromuscular behaviours may impose an increased risk of trunk instability and low back injury. An elevated risk of low back disorders is attributed to repetitive lifting. Here, the effects of flexion angle and lift rate on trunk mechanical and neuromuscular behaviours were investigated. Increasing flexion angle had adverse effects on these outcomes, although lift rate had inconsistent effects and recovery time was more than 20 min.

  5. High-repetition-rate quasi-CW side-pumped mJ eye-safe laser with a monolithic KTP crystal for intracavity optical parametric oscillator.

    Science.gov (United States)

    Cho, C Y; Chen, Y C; Huang, Y P; Huang, Y J; Su, K W; Chen, Y F

    2014-04-01

    We demonstrate a high-repetition-rate millijoule passively Q-switched eye-safe Nd:YVO(4) laser pumped by a quasi-CW diode stack. A theoretical analysis has been explored for the design criteria of generating TEM(n,0) mode in the diode-stack directly side-pumping configuration. We successfully generate TEM(n,0) modes at 1064 nm by adjusting the gain medium with respected to the laser axis. We further observe the spatial cleaning ability for generating an nearly TEM(0,0) mode output at 1573 nm with a monolithic OPO cavity. At the repetition rate up to 200 Hz, the output pulse energy reaches 1.21 mJ with the threshold pump energy of 17.9 mJ.

  6. Dual-frequency comb generation with differing GHz repetition rates by parallel Fabry-Perot cavity filtering of a single broadband frequency comb source

    Science.gov (United States)

    Mildner, Jutta; Meiners-Hagen, Karl; Pollinger, Florian

    2016-07-01

    We present a dual-comb-generator based on a coupled Fabry-Perot filtering cavity doublet and a single seed laser source. By filtering a commercial erbium-doped fiber-based optical frequency comb with CEO-stabilisation and 250 MHz repetition rate, two broadband coherent combs of different repetition rates in the GHz range are generated. The filtering doublet consists of two Fabry-Perot cavities with a tunable spacing and Pound-Drever-Hall stabilisation scheme. As a prerequisite for the development of such a filtering unit, we present a method to determine the actual free spectral range and transmission bandwidth of a Fabry-Perot cavity in situ. The transmitted beat signal of two diode lasers is measured as a function of their tunable frequency difference. Finally, the filtering performance and resulting beat signals of the heterodyned combs are discussed as well as the optimisation measures of the whole system.

  7. Testing of super conducting low-beta 704 Mhz cavities at 50 Hz pulse repetition rate in view of SPL- first results

    CERN Document Server

    Höfle, W; Lollierou, J; Valuch, D; Chel, S; Devanz, G; Desmons, M; Piquet, O; Paparella, R; Pierini, P

    2010-01-01

    In the framework of the preparatory phase for the luminosity upgrade of the LHC (SLHC-PP ) it is foreseen to characterize two superconducting RF cavities and demonstrate compliance of the required SPL field stability in amplitude and phase using a prototype LLRF system. We report on the preparation for testing of two superconducting low-beta cavities at 50 Hz pulse repetition rate including the setting-up of the low level RF control system to evaluate the performance of the piezo-tuning system and cavity field stability in amplitude and phase. Results from tests with 50 Hz pulse repetition rate are presented. Simulations of the RF system will be used to predict the necessary specifications for power and bandwidth to control the cavity field and derive specifications for the RF system and its control. Exemplary results of the simulation are presented.

  8. A high-repetition rate scheme for synchrotron-based picosecond laser pump/x-ray probe experiments on chemical and biological systems in solution.

    Science.gov (United States)

    Lima, Frederico A; Milne, Christopher J; Amarasinghe, Dimali C V; Rittmann-Frank, Mercedes Hannelore; van der Veen, Renske M; Reinhard, Marco; Pham, Van-Thai; Karlsson, Susanne; Johnson, Steven L; Grolimund, Daniel; Borca, Camelia; Huthwelker, Thomas; Janousch, Markus; van Mourik, Frank; Abela, Rafael; Chergui, Majed

    2011-06-01

    We present the extension of time-resolved optical pump/x-ray absorption spectroscopy (XAS) probe experiments towards data collection at MHz repetition rates. The use of a high-power picosecond laser operating at an integer fraction of the repetition rate of the storage ring allows exploitation of up to two orders of magnitude more x-ray photons than in previous schemes based on the use of kHz lasers. Consequently, we demonstrate an order of magnitude increase in the signal-to-noise of time-resolved XAS of molecular systems in solution. This makes it possible to investigate highly dilute samples at concentrations approaching physiological conditions for biological systems. The simplicity and compactness of the scheme allows for straightforward implementation at any synchrotron beamline and for a wide range of x-ray probe techniques, such as time-resolved diffraction or x-ray emission studies.

  9. Broadly wavelength- and pulse width-tunable high-repetition rate light pulses from soliton self-frequency shifting photonic crystal fiber integrated with a frequency doubling crystal.

    Science.gov (United States)

    Lanin, Aleksandr A; Fedotov, Andrei B; Zheltikov, Aleksei M

    2012-09-01

    Soliton self-frequency shift (SSFS) in a photonic crystal fiber (PCF) pumped by a long-cavity mode-locked Cr:forsterite laser is integrated with second harmonic generation (SHG) in a nonlinear crystal to generate ultrashort light pulses tunable within the range of wavelengths from 680 to 1800 nm at a repetition rate of 20 MHz. The pulse width of the second harmonic output is tuned from 70 to 600 fs by varying the thickness of the nonlinear crystal, beam-focusing geometry, and the wavelength of the soliton PCF output. Wavelength-tunable pulses generated through a combination of SSFS and SHG are ideally suited for coherent Raman microspectroscopy at high repetition rates, as verified by experiments on synthetic diamond and polystyrene films.

  10. Gigahertz repetition rate, sub-femtosecond timing jitter optical pulse train directly generated from a mode-locked Yb:KYW laser

    CERN Document Server

    Yang, Heewon; Shin, Junho; Kim, Chur; Choi, Sun Young; Kim, Guang-Hoon; Rotermund, Fabian; Kim, Jungwon

    2014-01-01

    We show that a 1.13-GHz repetition rate optical pulse train with 0.70 fs high-frequency timing jitter (integration bandwidth of 17.5 kHz - 10 MHz, where the measurement instrument-limited noise floor contributes 0.41 fs in 10 MHz bandwidth) can be directly generated from a free-running, single-mode diode-pumped Yb:KYW laser mode-locked by single-walled carbon nanotube (SWCNT)-coated mirrors. To our knowledge, this is the lowest timing jitter optical pulse train with the GHz repetition rate ever measured. If this pulse train is used for direct sampling of 565-MHz signals (Nyquist frequency of the pulse train), the demonstrated jitter level corresponds to the projected effective-number-of-bit (ENOB) of 17.8, which is much higher than the thermal noise limit of 50-ohm load resistance (~14 bits).

  11. Compact High-Repetition-Rate Monochromatic Terahertz Source Based on Difference Frequency Generation from a Dual-Wavelength Nd:YAG Laser and DAST Crystal

    Science.gov (United States)

    Zhong, Kai; Mei, Jialin; Wang, Maorong; Liu, Pengxiang; Xu, Degang; Wang, Yuye; Shi, Wei; Yao, Jianquan; Teng, Bing; Xiao, Yong

    2017-01-01

    Although high-repetition-rate dual-wavelength Nd:YAG lasers at 1319 and 1338 nm have been realized for quite a long time, we have employed it in generating monochromatic terahertz (THz) wave in this paper for the first time. The dual-wavelength laser was LD-end-pumped and acousto-optically (AO) Q-switched with the output power of watt level operating at different repetition rates from 5.5 to 30 kHz. Using a 0.6-mm-thick organic nonlinear crystal DAST for difference frequency generation (DFG), a compact terahertz source was achieved at 3.28 THz. The maximum average output power was about 0.58 μW obtained at a repetition rate of 5.5 kHz, corresponding to the conversion efficiency of about 6.4 × 10-7. The output power scaling is still feasible with higher pump power and a longer nonlinear DFG crystal. Owing to the compactness of the dual-wavelength laser and the nonlinear crystal, a palm-top terahertz source is expected for portable applications such as imaging and so on.

  12. Tunable GHz pulse repetition rate operation in high-power TEM(00)-mode Nd:YLF lasers at 1047 nm and 1053 nm with self mode locking.

    Science.gov (United States)

    Huang, Y J; Tzeng, Y S; Tang, C Y; Huang, Y P; Chen, Y F

    2012-07-30

    We report on a high-power diode-pumped self-mode-locked Nd:YLF laser with the pulse repetition rate up to several GHz. A novel tactic is developed to efficiently select the output polarization state for achieving the stable TEM(00)-mode self-mode-locked operations at 1053 nm and 1047 nm, respectively. At an incident pump power of 6.93 W and a pulse repetition rate of 2.717 GHz, output powers as high as 2.15 W and 1.35 W are generated for the σ- and π-polarization, respectively. We experimentally find that decreasing the separation between the gain medium and the input mirror not only brings in the pulse shortening thanks to the enhanced effect of the spatial hole burning, but also effectively introduces the effect of the spectral filtering to lead the Nd:YLF laser to be in a second harmonic mode-locked status. Consequently, pulse durations as short as 8 ps and 8.5 ps are obtained at 1053 nm and 1047 nm with a pulse repetition rate of 5.434 GHz.

  13. Highly efficient, versatile, self-Q-switched, high-repetition-rate microchip laser generating Ince-Gaussian modes for optical trapping

    Science.gov (United States)

    Dong, Jun; He, Yu; Zhou, Xiao; Bai, Shengchuang

    2016-03-01

    Lasers operating in the Ince-Gaussian (IG) mode have potential applications for optical manipulation of microparticles and formation of optical vortices, as well as for optical trapping and optical tweezers. Versatile, self-Q-switched, high-peak-power, high-repetition-rate Cr, Nd:YAG microchip lasers operating in the IG mode are implemented under tilted, tightly focused laser-diode pumping. An average output power of over 2 W is obtained at an absorbed pump power of 6.4 W. The highest optical-to-optical efficiency of 33.2% is achieved at an absorbed pump power of 3.9 W. Laser pulses with a pulse energy of 7.5 μJ, pulse width of 3.5 ns and peak power of over 2 kW are obtained. A repetition rate up to 335 kHz is reached at an absorbed pump power of 5.8 W. Highly efficient, versatile, IG-mode lasers with a high repetition rate and a high peak power ensure a better flexibility in particle manipulation and optical trapping.

  14. Highly efficient, versatile, self-Q-switched, high-repetition-rate microchip laser generating Ince–Gaussian modes for optical trapping

    Energy Technology Data Exchange (ETDEWEB)

    Jun Dong; Yu He; Xiao Zhou; Shengchuang Bai [Department of Electronics Engineering, School of Information Science and Engineering, Xiamen, 361005 (China)

    2016-03-31

    Lasers operating in the Ince-Gaussian (IG) mode have potential applications for optical manipulation of microparticles and formation of optical vortices, as well as for optical trapping and optical tweezers. Versatile, self-Q-switched, high-peak-power, high-repetition-rate Cr, Nd:YAG microchip lasers operating in the IG mode are implemented under tilted, tightly focused laser-diode pumping. An average output power of over 2 W is obtained at an absorbed pump power of 6.4 W. The highest optical-to-optical efficiency of 33.2% is achieved at an absorbed pump power of 3.9 W. Laser pulses with a pulse energy of 7.5 μJ, pulse width of 3.5 ns and peak power of over 2 kW are obtained. A repetition rate up to 335 kHz is reached at an absorbed pump power of 5.8 W. Highly efficient, versatile, IG-mode lasers with a high repetition rate and a high peak power ensure a better flexibility in particle manipulation and optical trapping. (control of laser radiation parameters)

  15. Bandwidth and repetition rate programmable Nyquist sinc-shaped pulse train source based on intensity modulators and four-wave mixing.

    Science.gov (United States)

    Cordette, S; Vedadi, A; Shoaie, M A; Brès, C-S

    2014-12-01

    We propose and experimentally demonstrate an all-optical Nyquist sinc-shaped pulse train source based on intensity modulation and four-wave mixing. The proposed scheme allows for the tunability of the bandwidth and the full flexibility of the repetition rate in the limit of the electronic bandwidth of the modulators used through the flexible synthesis of rectangular frequency combs. Bandwidth up to 360 GHz at 40 GHz rate and up to 45 frequency lines at 5 GHz rate are demonstrated with 40 GHz modulators.

  16. Single-pulse picking at kHz repetition rates using a Ge plasma switch at the free-electron laser FELBE.

    Science.gov (United States)

    Schmidt, J; Winnerl, S; Seidel, W; Bauer, C; Gensch, M; Schneider, H; Helm, M

    2015-06-01

    We demonstrate a system for picking of mid-infrared and terahertz (THz) radiation pulses from the free-electron laser (FEL) FELBE operating at a repetition rate of 13 MHz. Single pulses are reflected by a dense electron-hole plasma in a Ge slab that is photoexcited by amplified near-infrared (NIR) laser systems operating at repetition rates of 1 kHz and 100 kHz, respectively. The peak intensity of picked pulses is up to 400 times larger than the peak intensity of residual pulses. The required NIR fluence for picking pulses at wavelengths in the range from 5 μm to 30 μm is discussed. In addition, we show that the reflectivity of the plasma decays on a time scale from 100 ps to 1 ns dependent on the wavelengths of the FEL and the NIR laser. The plasma switch enables experiments with the FEL that require high peak power but lower average power. Furthermore, the system is well suited to investigate processes with decay times in the μs to ms regime, i.e., much longer than the 77 ns long pulse repetition period of FELBE.

  17. Ultrafast acoustics in the middle UV range: coherent phonons at higher frequencies and in smaller objects.

    Science.gov (United States)

    Ayrinhac, S; Devos, A; Le Louarn, A; Mante, P-A; Emery, P

    2010-10-15

    We show that the propagation of coherent acoustic phonons generated by femtosecond optical excitation can be clearly resolved using a probe laser in the middle UV (MUV) range. The MUV probe is easily produced from a high-repetition-rate femtosecond laser and a homemade frequency tripler. We present various experimental results that demonstrate efficient and high frequency detection of acoustic phonons. Thus, we show that the MUV range offers a unique way to reach higher frequencies and probe smaller objects in ultrafast acoustics.

  18. Ultrafast pulse generation in a mode-locked Erbium chip waveguide laser

    CERN Document Server

    Khurmi, Champak; Zhang, Wen Qi; V., Shahraam Afshar; Chen, George; Genest, Jérôme; Monro, Tanya M; Lancaster, David G

    2016-01-01

    We report mode-locked ~1550 nm output of transform-limited ~180 fs pulses from a large mode-area (diameter ~ 50 {\\mu}m) guided-wave erbium fluorozirconate glass laser. The passively mode-locked oscillator generates pulses with 25 nm bandwidth at 156 MHz repetition rate and peak-power of 260 W. Scalability to higher repetition rate is demonstrated by transform-limited 410 fs pulse output at 1.3 GHz. To understand the origins of the broad spectral output, the laser cavity is simulated by using a numerical solution to the Ginzburg-Landau equation. This paper reports the widest bandwidth and shortest pulses achieved from an ultra-fast laser inscribed waveguide laser.

  19. Advanced ultrafast fiber laser sources enabled by fiber nonlinearities

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wei

    2017-05-15

    Development of high power/energy ultrafast fiber lasers for scientific research and industrial applications is one of the most exciting fields in ultrafast optics. This thesis demonstrated new means to improve two essential properties - which are indispensable for novel applications such as high-harmonic generation (HHG) and multiphoton microscopy (MPM) - of an ultrafast fiber laser system: energy scaling capability and wavelength tunability. High photon-flux extreme ultraviolet sources enabled by HHG desire high power (>100 W), high repetition-rate (>1 MHz) ultrafast driving laser sources. We have constructed from scratch a high-power Yb-fiber laser system using the well-known chirped-pulse amplification (CPA) technique. Such a CPA system capable of producing ∝200-W average power consists of a monolithic Yb-fiber oscillator, an all-fiber stretcher, a pre-amplifier chain, a main amplifier constructed from rode-type large pitch fiber, and a diffraction-grating based compressor. To increase the HHG efficiency, ultrafast pulses with duration <60 fs are highly desired. We proposed and demonstrated a novel amplification technique, named as pre-chirp managed amplification (PCMA). We successfully constructed an Yb-fiber based PCMA system that outputs 75-MHz spectrally broadened pulses with >130-W average power. The amplified pulses are compressed to 60-fs pulses with 100-W average power, constituting a suitable HHG driving source. MPM is a powerful biomedical imaging tool, featuring larger penetration depth while providing the capability of optical sectioning. Although femtosecond solid-state lasers have been widely accepted as the standard option as MPM driving sources, fiber-based sources have received growing research efforts due to their superior performance. In the second part of this thesis, we both theoretically and experimentally demonstrated a new method of producing wavelength widely tunable femtosecond pulses for driving MPM. We employed self-phase modulation

  20. Ultrafast pulse generation with black phosphorus solution saturable absorber

    Science.gov (United States)

    Li, Lu; Wang, Yonggang; Wang, Xi

    2017-08-01

    The study presents the mode-locked Er-doped fiber (EDF) laser with a black phosphorus (BP) solution saturable absorber (SSA). The saturable absorber (SA) is fabricated based on a D-shaped fiber (DF) embedded in BP nanosheets N-Methylpyrrolidone solution. Such a BP solution method has the virtues of good antioxidant capacity, high heat dissipation and high damage threshold. This kind of SA shows a modulation depth of 7.75% and a nonsaturable loss of 10%. By employing the EDF-BP SSA, a repetition rate of 15.2 MHz mode-locked fiber laser is achieved. The pulse duration is 580 fs and the signal-to-noise ratio is 65 dB. The results indicate that the DF-BP solution can work as a potential SA for ultrafast nonlinear optics.

  1. High-power, high-repetition-rate performance characteristics of β-BaB₂O₄ for single-pass picosecond ultraviolet generation at 266 nm.

    Science.gov (United States)

    Kumar, S Chaitanya; Casals, J Canals; Wei, Junxiong; Ebrahim-Zadeh, M

    2015-10-19

    We report a systematic study on the performance characteristics of a high-power, high-repetition-rate, picosecond ultraviolet (UV) source at 266 nm based on β-BaB2O4 (BBO). The source, based on single-pass fourth harmonic generation (FHG) of a compact Yb-fiber laser in a two-crystal spatial walk-off compensation scheme, generates up to 2.9 W of average power at 266 nm at a pulse repetition rate of ~80 MHz with a single-pass FHG efficiency of 35% from the green to UV. Detrimental issues such as thermal effects have been studied and confirmed by performing relevant measurements. Angular and temperature acceptance bandwidths in BBO for FHG to 266 nm are experimentally determined, indicating that the effective interaction length is limited by spatial walk-off and thermal gradients under high-power operation. The origin of dynamic color center formation due to two-photon absorption in BBO is investigated by measurements of intensity-dependent transmission at 266 nm. Using a suitable theoretical model, two-photon absorption coefficients as well as the color center densities have been estimated at different temperatures. The measurements show that the two-photon absorption coefficient in BBO at 266 nm is ~3.5 times lower at 200°C compared to that at room temperature. The long-term power stability as well as beam pointing stability is analyzed at different output power levels and focusing conditions. Using cylindrical optics, we have circularized the generated elliptic UV beam to a circularity of >90%. To our knowledge, this is the first time such high average powers and temperature-dependent two-photon absorption measurements at 266 nm are reported at repetition rates as high as ~80 MHz.

  2. μJ-level, kHz-repetition rate femtosecond fiber-CPA system at 1555 nm

    Science.gov (United States)

    Sobon, Grzegorz; Kaczmarek, Pawel; Gluszek, Aleksander; Sotor, Jaroslaw; Abramski, Krzysztof M.

    2015-07-01

    In this work, we demonstrate a high-power, fiber-based chirped pulse amplification (CPA) setup utilizing Er- and Er/Yb-doped fibers, operating at 1555 nm central wavelength. The integrated all-fiber pulse-picker allows to reduce the repetition frequency down to the kHz-range, which enables generation of sub-picosecond pulses with energies above 2 μJ and pulse peak power exceeding 1 MW. The system utilizes an Er/Yb co-doped large mode area fiber in the final amplification stage. Thanks to the used mode-field adapters and fiber-based components, the setup is almost fully fiberized, except the bulk grating pulse compressor. In order to provide compactness and simplicity, the compressor was designed using dense 1100 lines per millimeter gratings, that allow to keep the small grating separation.

  3. 1-J operation of monolithic composite ceramics with Yb:YAG thin layers: multi-TRAM at 10-Hz repetition rate and prospects for 100-Hz operation.

    Science.gov (United States)

    Divoky, Martin; Tokita, Shigeki; Hwang, Sungin; Kawashima, Toshiyuki; Kan, Hirofumi; Lucianetti, Antonio; Mocek, Tomas; Kawanaka, Junji

    2015-03-15

    Experimental amplification of 10-ns pulses to energy of 1 J at repetition rate of 10-100 Hz in cryogenic multipass total-reflection active-mirror (TRAM) amplifier is reported for the first time. By using a monolithic multi-TRAM, which is a YAG ceramic composite with three thin Yb:YAG active layers, efficient energy extraction was achieved without parasitic lasing. A detailed measurement of output characteristics of the laser amplifier is presented; results are discussed and compared with numerical calculations.

  4. 615 fs pulses with 17 mJ energy generated by an Yb:thin-disk amplifier at 3 kHz repetition rate.

    Science.gov (United States)

    Fischer, Jonathan; Heinrich, Alexander-Cornelius; Maier, Simon; Jungwirth, Julian; Brida, Daniele; Leitenstorfer, Alfred

    2016-01-15

    A combination of Er/Yb:fiber and Yb:thin-disk technology produces 615 fs pulses at 1030 nm with an average output power of 72 W. The regenerative amplifier allows variation of the repetition rate between 3 and 5 kHz with pulse energies from 13 to 17 mJ. A broadband and intense seed provided by the compact and versatile fiber front-end minimizes gain narrowing. The resulting sub-ps performance is ideal for nonlinear frequency conversion and pulse compression. Operating in the upper branch of a bifurcated pulse train, the system exhibits exceptional noise performance and stability.

  5. Generation of 220 mJ nanosecond pulses at a 10 Hz repetition rate with excellent beam quality in a diode-pumped Yb:YAG MOPA system.

    Science.gov (United States)

    Wandt, Christoph; Klingebiel, Sandro; Siebold, Mathias; Major, Zsuzsanna; Hein, Joachim; Krausz, Ferenc; Karsch, Stefan

    2008-05-15

    A novel all-diode-pumped master oscillator power amplifier system based on Yb:YAG crystal rods has been developed. It consists of a Q-switched oscillator delivering 3 mJ, 6.4 ns pulses at a 10 Hz repetition rate and an additional four-pass amplifier, which boosts the output energy to 220 mJ, while a close to TEM(00) beam quality could be observed. Additionally a simulation of the amplification was written that allows for further scaling considerations.

  6. 1-MW peak power, 574-kHz repetition rate picosecond pulses at 515 nm from a frequency-doubled fiber amplifier

    Science.gov (United States)

    Zou, Feng; Wang, Ziwei; Wang, Zhaokun; Bai, Yang; Li, Qiurui; Zhou, Jun

    2016-11-01

    1-MW peak power picosecond, 574-kHz repetition rate green laser at 515-nm is generated from a frequency-doubled fiber amplifier. 12-ps pulses with 13.9-μJ energy at 515 nm are achieved with a noncritically phase-matched lithium triborate (LBO) crystal through second harmonic generation of a 1030 nm infrared source. The infrared source employs ultra-large-mode-area rod-type photonic crystal fiber (Rod-PCF) for direct picosecond amplification and delivers 20-W 11.6-ps 2.97-MW pulse train with near-diffraction-limited beam quality (M2 = 1.01).

  7. Laser-induced backside wet etching of silica glass with ns-pulsed DPSS UV laser at the repetition rate of 40 kHz

    Energy Technology Data Exchange (ETDEWEB)

    Niino, Hiroyuki; Kawaguchi, Yoshizo; Sato, Tadatake; Narazaki, Aiko; Gumpenberger, Thomas; Kurosaki, Ryozo [Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, Higashi, Tsukuba, Ibaraki 305-8565 (Japan)

    2007-04-15

    Surface micro-structuring of silica glass plates was performed by using laser- induced backside wet etching (LIBWE) upon irradiation with a single-mode laser beam from a diode-pumped solid-state (DPSS) UV laser with 40 kHz repetition rate at 266 nm. We have succeeded in a well-defined micro-pattern formation without debris and microcrack generation around the etched area on the basis of a galvanometer scanning system for the laser beam. Bubble dynamics after liquid ablation was monitored by impulse pressure detection with a fast- response piezoelectric pressure gauge.

  8. A K-alpha x-ray source using high energy and high repetition rate laser system for phase contrast imaging

    OpenAIRE

    Serbanescu, Cristina; Fourmaux, Sylvain; Kieffer, Jean-Claude; Kincaid, Russell; Krol, Andrzej

    2009-01-01

    K-alpha x-ray sources from laser produced plasmas provide completely new possibilities for x-ray phase-contrast imaging applications. By tightly focusing intense femtosecond laser pulses onto a solid target K-alpha x-ray pulses are generated through the interaction of energetic electrons created in the plasma with the bulk target. In this paper, we present a continuous and efficient Mo K-alpha x-ray source produced by a femtosecond laser system operating at 100 Hz repetition rate with maximum...

  9. Subharmonic resonant optical excitation of confined acoustic modes in a free-standing semiconductor membrane at GHz frequencies with a high-repetition-rate femtosecond laser.

    Science.gov (United States)

    Bruchhausen, A; Gebs, R; Hudert, F; Issenmann, D; Klatt, G; Bartels, A; Schecker, O; Waitz, R; Erbe, A; Scheer, E; Huntzinger, J-R; Mlayah, A; Dekorsy, T

    2011-02-18

    We propose subharmonic resonant optical excitation with femtosecond lasers as a new method for the characterization of phononic and nanomechanical systems in the gigahertz to terahertz frequency range. This method is applied for the investigation of confined acoustic modes in a free-standing semiconductor membrane. By tuning the repetition rate of a femtosecond laser through a subharmonic of a mechanical resonance we amplify the mechanical amplitude, directly measure the linewidth with megahertz resolution, infer the lifetime of the coherently excited vibrational states, accurately determine the system's quality factor, and determine the amplitude of the mechanical motion with femtometer resolution.

  10. Phosphorene quantum dot saturable absorbers for ultrafast fiber lasers

    Science.gov (United States)

    Du, J.; Zhang, M.; Guo, Z.; Chen, J.; Zhu, X.; Hu, G.; Peng, P.; Zheng, Z.; Zhang, H.

    2017-01-01

    We fabricate ultrasmall phosphorene quantum dots (PQDs) with an average size of 2.6 ± 0.9 nm using a liquid exfoliation method involving ultrasound probe sonication followed by bath sonication. By coupling the as-prepared PQDs with microfiber evanescent light field, the PQD-based saturable absorber (SA) device exhibits ultrafast nonlinear saturable absorption property, with an optical modulation depth of 8.1% at the telecommunication band. With the integration of the all-fiber PQD-based SA, a continuous-wave passively mode-locked erbium-doped (Er-doped) laser cavity delivers stable, self-starting pulses with a pulse duration of 0.88 ps and at the cavity repetition rate of 5.47 MHz. Our results contribute to the growing body of work studying the nonlinear optical properties of ultrasmall PQDs that present new opportunities of this two-dimensional (2D) nanomaterial for future ultrafast photonic technologies. PMID:28211471

  11. Phosphorene quantum dot saturable absorbers for ultrafast fiber lasers

    Science.gov (United States)

    Du, J.; Zhang, M.; Guo, Z.; Chen, J.; Zhu, X.; Hu, G.; Peng, P.; Zheng, Z.; Zhang, H.

    2017-02-01

    We fabricate ultrasmall phosphorene quantum dots (PQDs) with an average size of 2.6 ± 0.9 nm using a liquid exfoliation method involving ultrasound probe sonication followed by bath sonication. By coupling the as-prepared PQDs with microfiber evanescent light field, the PQD-based saturable absorber (SA) device exhibits ultrafast nonlinear saturable absorption property, with an optical modulation depth of 8.1% at the telecommunication band. With the integration of the all-fiber PQD-based SA, a continuous-wave passively mode-locked erbium-doped (Er-doped) laser cavity delivers stable, self-starting pulses with a pulse duration of 0.88 ps and at the cavity repetition rate of 5.47 MHz. Our results contribute to the growing body of work studying the nonlinear optical properties of ultrasmall PQDs that present new opportunities of this two-dimensional (2D) nanomaterial for future ultrafast photonic technologies.

  12. Ultrafast laser pump/x-ray probe experiments

    Energy Technology Data Exchange (ETDEWEB)

    Larsson, J.; Judd, E.; Schuck, P.J. [Univ. of California, Berkeley, CA (United States)] [and others

    1997-04-01

    In an ongoing project aimed at probing solids using x-rays obtained at the ALS synchrotron with a sub-picosecond time resolution following interactions with a 100 fs laser pulse, the authors have successfully performed pump-probe experiments limited by the temporal duration of ALS-pulse. They observe a drop in the diffraction efficiency following laser heating. They can attribute this to a disordering of the crystal. Studies with higher temporal resolution are required to determine the mechanism. The authors have also incorporated a low-jitter streakcamera as a diagnostic for observing time-dependant x-ray diffraction. The streakcamera triggered by a photoconductive switch was operated at kHz repetition rates. Using UV-pulses, the authors obtain a temporal response of 2 ps when averaging 5000 laser pulses. They demonstrate the ability to detect monochromatized x-ray radiation from a bend-magnet with the streak camera by measuring the pulse duration of a x-ray pulse to 70 ps. In conclusion, the authors show a rapid disordering of an InSb crystal. The resolution was determined by the duration of the ALS pulse. They also demonstrate that they can detect x-ray radiation from a synchrotron source with a temporal resolution of 2ps, by using an ultrafast x-ray streak camera. Their set-up will allow them to pursue laser pump/x-ray probe experiments to monitor structural changes in materials with ultrafast time resolution.

  13. Active Q-switching in an erbium-doped fiber laser using an ultrafast silicon-based variable optical attenuator.

    Science.gov (United States)

    Chang, You Min; Lee, Junsu; Jhon, Young Min; Lee, Ju Han

    2011-12-19

    Presented herein is the use of an ultrafast Si-based variable optical attenuator (VOA) as a Q-switch for rare earth-doped fiber lasers. The ultrafast VOA is based on a forward-biased p-i-n diode integrated with a ridge waveguide, which was originally designed and optimized for WDM channel power equalization in optical communication systems. By incorporating a Si-based VOA with a transient time of ~410 ns into an erbium-doped fiber-based Fabry-Perot cavity it has been shown that stable Q-switched pulses possessing a temporal width of less than ~86 ns can be readily obtained at a repetition rate of up to ~1 MHz. The laser's peak power of ~38 W is shown to be obtainable at 20 kHz with a slope efficiency of ~21%.

  14. Gain-switched laser diode seeded Yb-doped fiber amplifier delivering 11-ps pulses at repetition rates up to 40-MHz

    CERN Document Server

    Ryser, Manuel; Pilz, Soenke; Burn, Andreas; Romano, Valerio

    2014-01-01

    Here, we demonstrate all-fiber direct amplification of 11 picosecond pulses from a gain-switched laser diode at 1063nm. The diode was driven at a repetition rate of 40MHz and delivered 13$\\mu$W of fiber-coupled average output power. For the low output pulse energy of 0.33pJ we have designed a multi-stage core pumped preamplifier based on single clad Yb-doped fibers in order to keep the contribution of undesired amplified spontaneous emission as low as possible and to minimize temporal and spectral broadening. After the preamplifier we reduced the 40MHz repetition rate to 1MHz using a fiber coupled pulse-picker. The final amplification was done with a cladding pumped Yb-doped large mode area fiber and a subsequent Yb-doped rod-type fiber. With our setup we achieved amplification of 72dBs to an output pulse energy of 5.7$\\mu$J, pulse duration of 11ps and peak power of >0.6MW.

  15. On the Optimality of Repetition Coding among Rate-1 DC-offset STBCs for MIMO Optical Wireless Communications

    KAUST Repository

    Sapenov, Yerzhan

    2017-07-06

    In this paper, an optical wireless multiple-input multiple-output communication system employing intensity-modulation direct-detection is considered. The performance of direct current offset space-time block codes (DC-STBC) is studied in terms of pairwise error probability (PEP). It is shown that among the class of DC-STBCs, the worst case PEP corresponding to the minimum distance between two codewords is minimized by repetition coding (RC), under both electrical and optical individual power constraints. It follows that among all DC-STBCs, RC is optimal in terms of worst-case PEP for static channels and also for varying channels under any turbulence statistics. This result agrees with previously published numerical results showing the superiority of RC in such systems. It also agrees with previously published analytic results on this topic under log-normal turbulence and further extends it to arbitrary turbulence statistics. This shows the redundancy of the time-dimension of the DC-STBC in this system. This result is further extended to sum power constraints with static and turbulent channels, where it is also shown that the time dimension is redundant, and the optimal DC-STBC has a spatial beamforming structure. Numerical results are provided to demonstrate the difference in performance for systems with different numbers of receiving apertures and different throughput.

  16. Spin-state studies with XES and RIXS: From static to ultrafast

    Energy Technology Data Exchange (ETDEWEB)

    Vankó, György, E-mail: vanko.gyorgy@wigner.mta.hu [Wigner Research Centre for Physics, Hungarian Academy Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Bordage, Amélie [Wigner Research Centre for Physics, Hungarian Academy Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Glatzel, Pieter; Gallo, Erik; Rovezzi, Mauro [European Synchrotron Radiation Facility (ESRF), 6 Rue Jules Horowitz, BP220, 38043 Grenoble Cedex 9 (France); Gawelda, Wojciech; Galler, Andreas; Bressler, Christian [European XFEL, Albert-Einstein Ring 19, D-22 761 Hamburg (Germany); Doumy, Gilles; March, Anne Marie; Kanter, Elliot P.; Young, Linda; Southworth, Stephen H. [X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 (United States); Canton, Sophie E. [Department of Synchrotron Instrumentation, MAXlab, Lund University, Box 118, SE-22100 Lund (Sweden); Uhlig, Jens; Smolentsev, Grigory; Sundström, Villy [Department of Chemical Physics, Lund University, Box 124, SE-22100 Lund (Sweden); Haldrup, Kristoffer; Brandt van Driel, Tim; Nielsen, Martin M. [Centre for Molecular Movies, Department of Physics, Technical University of Denmark, DK-2800 Lyngby (Denmark); and others

    2013-06-15

    Highlights: ► We study light-induced spin-state transition of Fe(II) complexes in solution. ► Laser-pump-X-ray-probe spectroscopy is extended to MHz repetition rates. ► XES and RIXS compare well with the static spectra at thermal spin transition. ► The typical assumptions used in XES line shape analysis are validated. -- Abstract: We report on extending hard X-ray emission spectroscopy (XES) along with resonant inelastic X-ray scattering (RIXS) to study ultrafast phenomena in a pump-probe scheme at MHz repetition rates. The investigated systems include low-spin (LS) Fe{sup II} complex compounds, where optical pulses induce a spin-state transition to their (sub)nanosecond-lived high-spin (HS) state. Time-resolved XES clearly reflects the spin-state variations with very high signal-to-noise ratio, in agreement with HS–LS difference spectra measured at thermal spin crossover, and reference HS–LS systems in static experiments, next to multiplet calculations. The 1s2p RIXS, measured at the Fe 1s pre-edge region, shows variations after laser excitation, which are consistent with the formation of the HS state. Our results demonstrate that X-ray spectroscopy experiments with overall rather weak signals, such as RIXS, can now be reliably exploited to study chemical and physical transformations on ultrafast time scales.

  17. Human sensory-evoked responses differ coincident with either "fusion-memory" or "flash-memory", as shown by stimulus repetition-rate effects

    Directory of Open Access Journals (Sweden)

    Baird Bill

    2006-02-01

    Full Text Available Abstract Background: A new method has been used to obtain human sensory evoked-responses whose time-domain waveforms have been undetectable by previous methods. These newly discovered evoked-responses have durations that exceed the time between the stimuli in a continuous stream, thus causing an overlap which, up to now, has prevented their detection. We have named them "A-waves", and added a prefix to show the sensory system from which the responses were obtained (visA-waves, audA-waves, somA-waves. Results: When A-waves were studied as a function of stimulus repetition-rate, it was found that there were systematic differences in waveshape at repetition-rates above and below the psychophysical region in which the sensation of individual stimuli fuse into a continuity. The fusion phenomena is sometimes measured by a "Critical Fusion Frequency", but for this research we can only identify a frequency-region [which we call the STZ (Sensation-Transition Zone]. Thus, the A-waves above the STZ differed from those below the STZ, as did the sensations. Study of the psychophysical differences in auditory and visual stimuli, as shown in this paper, suggest that different stimulus features are detected, and remembered, at stimulation rates above and below STZ. Conclusion: The results motivate us to speculate that: 1 Stimulus repetition-rates above the STZ generate waveforms which underlie "fusion-memory" whereas rates below the STZ show neuronal processing in which "flash-memory" occurs. 2 These two memories differ in both duration and mechanism, though they may occur in the same cell groups. 3 The differences in neuronal processing may be related to "figure" and "ground" differentiation. We conclude that A-waves provide a novel measure of neural processes that can be detected on the human scalp, and speculate that they may extend clinical applications of evoked response recordings. If A-waves also occur in animals, it is likely that A-waves will provide

  18. Theoretical investigation on nonlinear optical effects in laser trapping of dielectric nanoparticles with ultrafast pulsed excitation.

    Science.gov (United States)

    Devi, Anita; De, Arijit K

    2016-09-19

    The use of low-power high-repetition-rate ultrafast pulsed excitation in stable optical trapping of dielectric nanoparticles has been demonstrated in the recent past; the high peak power of each pulse leads to instantaneous trapping of a nanoparticle with fast inertial response and the high repetition-rate ensures repetitive trapping by successive pulses However, with such high peak power pulsed excitation under a tight focusing condition, nonlinear optical effects on trapping efficiency also become significant and cannot be ignored. Thus, in addition to the above mentioned repetitive instantaneous trapping, trapping efficiency under pulsed excitation is also influenced by the optical Kerr effect, which we theoretically investigate here. Using dipole approximation we show that with an increase in laser power the radial component of the trapping potential becomes progressively more stable but the axial component is dramatically modulated due to increased Kerr nonlinearity. We justify that the relevant parameter to quantify the trapping efficiency is not the absolute depth of the highly asymmetric axial trapping potential but the height of the potential barrier along the beam propagation direction. We also discuss the optimal excitation parameters leading to the most stable dipole trap. Our results show excellent agreement with previous experiments.

  19. A Recirculating Linac-Based Facility for Ultrafast X-Ray Science

    Energy Technology Data Exchange (ETDEWEB)

    J. N. Corlett; W. A. Barletta; S. DeSantis; L. Doolittle; W. M. Fawley; M.A. Green; P. Heimann; S. Leone; S. Lidia; D. Li; A. Ratti; K. Robinson; R. Schoenlein; J. Staples; W. Wan; R. Wells; A.Wolski; A. Zholents; F. Parmigiani; M. Placidi; W. Pirkl; R. A. Rimmer; S. Wang

    2003-05-01

    We present an updated design for a proposed source of ultra-fast synchrotron radiation pulses based on a recirculating superconducting linac [1,2], in particular the incorporation of EUV and soft x-ray production. The project has been named LUX--Linac-based Ultrafast X-ray facility. The source produces intense x-ray pulses with duration of 10-100 fs at a 10 kHz repetition rate, with synchronization of 10's fs, optimized for the study of ultra-fast dynamics. The photon range covers the EUV to hard x-ray spectrum by use of seeded harmonic generation in undulators, and a specialized technique for ultra-short pulse photon production in the 1-10 keV range. High brightness rf photocathodes produce electron bunches which are optimized either for coherent emission in free electron lasers, or to provide a large x/y emittance ration and small vertical emittance which allows for manipulation to produce short-pulse hard x-rays. An injector linac accelerates the beam to 120 MeV, and is followed by f our passes through a 600-720 MeV recirculating linac. We outline the major technical components of the proposed facility.

  20. A recirculating linac-based facility for ultrafast X-ray science

    Energy Technology Data Exchange (ETDEWEB)

    Corlett, J.N; Barletta, W.A.; DeSantis, S.; Doolittle, L.; Fawley, W.M.; Green, M.A.; Heimann, P.; Leone, S.; Lidia, S.; Li, D.; Ratti, A.; Robinson, K.; Schoenlein, R.; Staples, J.; Wan, W.; Wells, R.; Wolski, A.; Zholents, A.; Placidi, M.; Pirkl, W.; Parmigiani, F.

    2003-05-06

    We present an updated design for a proposed source of ultra-fast synchrotron radiation pulses based on a recirculating superconducting linac, in particular the incorporation of EUV and soft x-ray production. The project has been named LUX - Linac-based Ultrafast X-ray facility. The source produces intense x-ray pulses with duration of 10-100 fs at a 10 kHz repetition rate, with synchronization of 10 s fs, optimized for the study of ultra-fast dynamics. The photon range covers the EUV to hard x-ray spectrum by use of seeded harmonic generation in undulators, and a specialized technique for ultra-short-pulse photon production in the 1-10 keV range. High-brightness rf photocathodes produce electron bunches which are optimized either for coherent emission in free-electron lasers, or to provide a large x/y emittance ration and small vertical emittance which allows for manipulation to produce short-pulse hard x-rays. An injector linac accelerates the beam to 120 MeV, and is followed by four passes through a 600-720 MeV recirculating linac. We outline the major technical components of the proposed facility.

  1. Probing ultrafast dynamics of condensed matter with pump and probe experiments with X-rays

    Energy Technology Data Exchange (ETDEWEB)

    Giles, Carlos; Celestre, Rafael; Tasca, Kelin R.; Vescovi, Rafael; Faria, Guilherme; Dias, Carlos S.; Tomm, Natasha; Cordeiro, Cristiano M.B. [Universidade Estadual de Campinas (IFGW/UNICAMP), SP (Brazil). Inst. de Fisica Gleb Wataghin; Silva, Rene Nome [Universidade Estadual de Campinas (IQ/UNICAMP), SP (Brazil). Inst. de Quimica

    2012-07-01

    Full text: In this presentation we will describe recent advances in the route to start ultrafast studies with X-rays in Brazil. From one side pump and probe experiments using synchrotron radiation facilities will be described, showing how the thermal expansion of an invar alloy is not occurring at the picosecond time scales after heating the sample with a femtosecond infrared laser pulse. We will also describe the experimental setup at the LNLS in Campinas were we probe the fast response of a piezoelectric material to a 1 ns electric pulse recorded by a pump and probe X-ray diffraction experiment at the XRD2 LNLS beamline. We will also present the first results of the production of sub-picosecond X-ray pulses using an amplified infrared laser at the Ultrafast Laboratory of DEQ/IFGW. The instrumentation developed at UNICAMP together with the first setup for a pump and probe experiment will be presented. Characteristic radiation of various targets (TiK{alpha}, FeK{alpha}, CuK{alpha}) have been measured at a repetition rate of 1 kHz showing unambiguously our capability of producing a pulsed X-ray source for time resolved x-ray diffraction experiments. Experiments to measure the pulse width of the X-ray radiation are under development and the latest results will be presented. All these efforts open the path to the nucleation of a research group in ultrafast studies using X-rays in Brazil. (author)

  2. Phase-matched high-order harmonics by interaction of Ar atoms with high-repetition-rate low-energy femtosecond laser pulses

    Institute of Scientific and Technical Information of China (English)

    XIE Xinhua; ZENG Zhinan; LI Ruxin; CHEN Shu; LU Haihe; YIN Dingjun; XU Zhizhan

    2004-01-01

    Phase-matched high-order harmonic generation in Ar gas-filled cell was investigated experimentally. We obtained phase-matched 27th order harmonic driven by a commercially available solid-state femtosecond laser system at 0.55 m J/pulse energy level and 1 kHz repetition rate. To our knowledge, this is the lowest driving laser energy used to obtain phase-matched 27th order harmonic in a static gas cell. High-order harmonic generation at different gas density was studied systematically. Spectral blueshift and broadening of high harmonics under different pressure were analyzed. We found that the source size and spatial distribution of high-order harmonics are quite different under the phase-matching condition from those of the phase-mismatching case.

  3. Generation of microwave radiation by nonlinear interaction of a high-power, high-repetition rate, 1064-nm laser in KTP crystals

    CERN Document Server

    Borghesani, A F; Carugno, G

    2013-01-01

    We report measurements of microwave (RF) generation in the centimeter band accomplished by irradiating a nonlinear KTiOPO$_4$ (KTP) crystal with a home-made, infrared laser at $1064\\,$nm as a result of optical rectification (OR). The laser delivers pulse trains of duration up to $1\\,\\mu$s. Each train consists of several high-intensity pulses at an adjustable repetition rate of approximately $ 4.6\\,$GHz. The duration of the generated RF pulses is determined by that of the pulse trains. We have investigated both microwave- and second harmonic (SHG) generation as a function of the laser intensity and of the orientation of the laser polarization with respect to the crystallographic axes of KTP.

  4. PULSAR: A High-Repetition-Rate, High-Power, CE Phase-Locked Laser for the J.R. Macdonald Laboratory at Kansas State University

    Energy Technology Data Exchange (ETDEWEB)

    Ben-Itzhak, Itzik (Itzhak) [J.R. Macdonald Laboratory, Physics Department, Kansas State University; Carnes, Kevin D. [J.R. Macdonald Laboratory, Physics Department, Kansas State University; Cocke, C. Lew [J.R. Macdonald Laboratory, Physics Department, Kansas State University; Fehrenbach, Charles W. [J.R. Macdonald Laboratory, Physics Department, Kansas State University; Kumarappan, Vinod [PULSAR: A High-Repetition-Rate, High-Power, CE Phase-Locked Laser for the J.R. Macdonald Laboratory at Kansas State University; Rudenko, Artem [J.R. Macdonald Laboratory, Physics Department, Kansas State University; Trallero, Carlos [J.R. Macdonald Laboratory, Physics Department, Kansas State University

    2014-05-09

    This instrumentation grant funded the development and installation of a state-of-the-art laser system to be used for the DOE funded research at the J.R. Macdonald Laboratory at Kansas State University. Specifically, we purchased a laser based on the KMLABs Red-Dragon design, which has a high repetition rate of 10-20 kHz crucial for multi-parameter coincidence measurements conducted in our lab. This laser system is carrier-envelope phase (CEP) locked and provides pulses as short as 21 fs directly from the amplifier (see details below). In addition, we have developed a pulse compression setup that provides sub 5 fs pulses and a CEP tagging capability that allows for long measurements of CEP dependent processes.

  5. Nanosecond pulsed power generator for a voltage amplitude up to 300 kV and a repetition rate up to 16 Hz for fine disintegration of quartz

    Energy Technology Data Exchange (ETDEWEB)

    Krastelev, E. G., E-mail: ekrastelev@yandex.ru; Sedin, A. A.; Tugushev, V. I. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

    2015-12-15

    A generator of high-power high-voltage nanosecond pulses is intended for electrical discharge disintegration of mineral quartz and other nonconducting minerals. It includes a 320 kV Marx pulsed voltage generator, a high-voltage glycerin-insulated coaxial peaking capacitor, and an output gas spark switch followed by a load, an electric discharge disintegration chamber. The main parameters of the generator are as follows: a voltage pulse amplitude of up to 300 kV, an output impedance of ≈10 Ω, a discharge current amplitude of up to 25 kA for a half-period of 80–90 ns, and a pulse repetition rate of up to 16 Hz.

  6. Laser ablation efficiency during the production of Ag nanoparticles in ethanol at a low pulse repetition rate (1-10 Hz)

    Science.gov (United States)

    Valverde-Alva, M. A.; García-Fernández, T.; Esparza-Alegría, E.; Villagrán-Muniz, M.; Sánchez-Aké, C.; Castañeda-Guzmán, R.; de la Mora, M. B.; Márquez-Herrera, C. E.; Sánchez Llamazares, J. L.

    2016-10-01

    We studied the effect of the repetition rate of laser pulses (RRLP) in the range from 1-10 Hz in the production of silver nanoparticles (Ag-NPs) by laser ablation in ethanol. Laser pulses with a duration of 7 ns, a wavelength of 1064 nm and an energy of 60 mJ were used to ablate a 99.99% pure silver target immersed in 10 ml of ethanol. Transmittance analysis and atomic absorption spectroscopy were used to study the silver concentration in the colloidal solutions. The ablation process was studied by measuring the transmission of the laser pulses through the colloid. It is shown that for a fixed number of laser pulses (NLP) the ablation efficiency, in terms of the ablated silver mass per laser pulse, increases with the RRLP. This result contradicts what had previously been established in the literature.

  7. Effect of pulse repetition rate and number of pulses in the analysis of polypropylene and high density polyethylene by nanosecond infrared laser induced breakdown spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Leme, Flavio O. [Laboratorio de Quimica Analitica ' Henrique Bergamin Filho' , Centro de Energia Nuclear na Agricultura, Universidade de Sao Paulo, Av. Centenario 303, 13416-000 Piracicaba, SP (Brazil); Godoi, Quienly [Laboratorio de Quimica Analitica ' Henrique Bergamin Filho' , Centro de Energia Nuclear na Agricultura, Universidade de Sao Paulo, Av. Centenario 303, 13416-000 Piracicaba, SP (Brazil); Departamento de Quimica, Universidade Federal de Sao Carlos, Rod. Washington Luis, km 235, 13565-905 Sao Carlos, SP (Brazil); Kiyataka, Paulo H.M. [Centro de Tecnologia de Embalagens, Instituto de Tecnologia de Alimentos, Av. Brasil 2880, 13070-178 Campinas, SP (Brazil); Santos, Dario [Departamento de Ciencias Exatas e da Terra, Universidade Federal de Sao Paulo, Rua Prof. Artur Riedel 275, 09972-270 Diadema, SP (Brazil); Agnelli, Jose A.M. [Departamento de Engenharia de Materiais, Universidade Federal de Sao Carlos, Rod. Washington Luis, km 235, 13565-905 Sao Carlos, SP (Brazil); and others

    2012-02-01

    Pulse repetition rates and the number of laser pulses are among the most important parameters that do affect the analysis of solid materials by laser induced breakdown spectroscopy, and the knowledge of their effects is of fundamental importance for suggesting analytical strategies when dealing with laser ablation processes of polymers. In this contribution, the influence of these parameters in the ablated mass and in the features of craters was evaluated in polypropylene and high density polyethylene plates containing pigment-based PbCrO{sub 4}. Surface characterization and craters profile were carried out by perfilometry and scanning electron microscopy. Area, volume and profile of craters were obtained using Taylor Map software. A laser induced breakdown spectroscopy system consisted of a Q-Switched Nd:YAG laser (1064 nm, 5 ns) and an Echelle spectrometer equipped with ICCD detector were used. The evaluated operating conditions consisted of 10, 25 and 50 laser pulses at 1, 5 and 10 Hz, 250 mJ/pulse (85 J cm{sup -2}), 2 {mu}s delay time and 6 {mu}s integration time gate. Differences in the topographical features among craters of both polymers were observed. The decrease in the repetition rate resulted in irregular craters and formation of edges, especially in polypropylene sample. The differences in the topographical features and ablated masses were attributed to the influence of the degree of crystallinity, crystalline melting temperature and glass transition temperature in the ablation process of the high density polyethylene and polypropylene. It was also observed that the intensities of chromium and lead emission signals obtained at 10 Hz were two times higher than at 5 Hz by keeping the number of laser pulses constant.

  8. Tunable Yb-doped fiber laser based on a FBG array and a theta ring resonator ensuring a constant repetition rate (Conference Presentation)

    Science.gov (United States)

    Tiess, Tobias; Becker, Martin; Rothhardt, Manfred; Bartelt, Hartmut; Jäger, Matthias L.

    2017-03-01

    Fiber lasers provide the perfect basis to develop broadly tunable lasers with high efficiency, excellent beam quality and user-friendly operation as they are increasingly demanded by applications in biophotonics and spectroscopy. Recently, a novel tuning scheme has been presented using fiber Bragg grating (FBG) arrays as fiber-integrated spectral filters containing many standard FBGs with different feedback wavelengths. Based on the discrete spectral sampling, these reflective filters uniquely enable tailored tuning ranges and broad bandwidths to be implemented into fiber lasers. Even though the first implementation of FBG arrays in pulsed tunable lasers based on a sigma ring resonators works with good emission properties, the laser wavelength is tuned by a changing repetition rate, which causes problems with applications in synchronized environments. In this work, we present a modified resonator scheme to maintain a constant repetition rate over the tuning range and still benefit from the advantages of FBG arrays as filters. With a theta ring cavity and two counter propagating filter passes, the distributed feedback of the FBG array is compensated resulting in a constant pulse round trip time for each filter wavelength. Together with an adapted gating scheme controlling the emission wavelength with a modulator, the tuning principle has been realized based on a Ytterbium-doped fiber laser. We present first experimental results demonstrating a tuning range of 25nm, high signal contrast and pulse durations of about 10ns. With the prospect of tailored tuning ranges, this pulsed fiber-integrated laser may be the basis to tackle challenging applications in spectroscopy.

  9. Experimental study of the inverse diffusion flame using high repetition rate OH/acetone PLIF and PIV

    KAUST Repository

    Elbaz, Ayman M.

    2015-10-29

    Most previous work on inverse diffusion flames (IDFs) has focused on laminar IDF emissions and the soot formation characteristics. Here, we investigate the characteristics and structure of methane IDFs using high speed planar laser-induced fluorescence (PLIF) images of OH, particle image velocimetry (PIV), and acetone PLIF imaging for non-reacting cases. First, the flame appearance was investigated with fixed methane loading (mass flux) but with varying airflow rates, yielding a central air jet Reynolds number (Re) of 1,000 to 6,000 (when blow-off occurs). Next, it was investigated a fixed central air jet Re of 4500, but with varied methane mass flux such that the global equivalence ratio spanned 0.5 to 4. It was observed that at Re smaller than 2000, the inner air jet promotes the establishment of an inverse diffusion flame surrounded by a normal diffusion flame. However, when the Re was increased to 2500, two distinct zones became apparent in the flame, a lower entrainment zone and an upper mixing and combustion zone. 10 kHz OH-PLIF images, and 2D PIV allow the identification of the fate and spatial flame structure. Many flame features were identified and further analyzed using simple but effective image processing methods, where three types of structure in all the flames investigated here: flame holes or breaks; closures; and growing kernels. Insights about the rate of evolution of these features, the dynamics of local extinction, and the sequence of events that lead to re-ignition are reported here. In the lower entrainment zone, the occurrence of the flame break events is counterbalanced by closure events, and the edge propagation appears to control the rate at which the flame holes and closures propagate. The rate of propagation of holes was found to be statistically faster than the rate of closure. As the flames approach blow-off, flame kernels become the main mechanism for flame re-ignition further downstream. The simultaneous OH-PLIF/Stereo PIV

  10. A self-consistent model for the discharge kinetics in a high-repetition-rate copper-vapor laser

    Energy Technology Data Exchange (ETDEWEB)

    Carman, R.J.; Brown, D.J.W.; Piper, J.A. (Macquarie Univ., Sydney (Australia). Centre for Lasers and Applications)

    1994-08-01

    A self-consistent computer model has been developed to simulate the discharge kinetics and lasing characteristics of a copper-vapor laser (CVL) for typical operating conditions. Using a detailed rate-equation analysis, the model calculates the spatio-temporal evolution of the population densities of 11 atomic and ionic copper levels, four neon levels, and includes 70 collisional and radiative processes, in addition to radial particle transport. The long-term evolution of the plasma is taken into account by integrating the set of coupled rate equations describing the discharge and electrical circuit through multiple excitation-afterglow cycles. A time-dependent two-electron group model, based on a bi-Maxwellian electron energy distribution function, has been used to evaluate the energy partitioning between the copper vapor and the neon-buffer gas. The behavior of the plasma in the cooler end regions of the discharge tube near the electrodes, where the plasma kinetics are dominated by the buffer gas, has also been modeled. Results from the model have been compared to experimental data for a narrow-bore ([phi] = 1.8 cm) CVL operating under optimum conditions.

  11. Efficient generation of twin photons at telecom wavelengths with 2.5 GHz repetition-rate-tunable comb laser

    Science.gov (United States)

    Jin, Rui-Bo; Shimizu, Ryosuke; Morohashi, Isao; Wakui, Kentaro; Takeoka, Masahiro; Izumi, Shuro; Sakamoto, Takahide; Fujiwara, Mikio; Yamashita, Taro; Miki, Shigehito; Terai, Hirotaka; Wang, Zhen; Sasaki, Masahide

    2014-12-01

    Efficient generation and detection of indistinguishable twin photons are at the core of quantum information and communications technology (Q-ICT). These photons are conventionally generated by spontaneous parametric down conversion (SPDC), which is a probabilistic process, and hence occurs at a limited rate, which restricts wider applications of Q-ICT. To increase the rate, one had to excite SPDC by higher pump power, while it inevitably produced more unwanted multi-photon components, harmfully degrading quantum interference visibility. Here we solve this problem by using recently developed 10 GHz repetition-rate-tunable comb laser, combined with a group-velocity-matched nonlinear crystal, and superconducting nanowire single photon detectors. They operate at telecom wavelengths more efficiently with less noises than conventional schemes, those typically operate at visible and near infrared wavelengths generated by a 76 MHz Ti Sapphire laser and detected by Si detectors. We could show high interference visibilities, which are free from the pump-power induced degradation. Our laser, nonlinear crystal, and detectors constitute a powerful tool box, which will pave a way to implementing quantum photonics circuits with variety of good and low-cost telecom components, and will eventually realize scalable Q-ICT in optical infra-structures.

  12. Estimation of the dust production rate from the tungsten armour after repetitive ELM-like heat loads

    Science.gov (United States)

    Pestchanyi, S.; Garkusha, I.; Makhlaj, V.; Landman, I.

    2011-12-01

    Experimental simulations for the erosion rate of tungsten targets under ITER edge-localized mode (ELM)-like surface heat loads of 0.75 MJ m-2 causing surface melting and of 0.45 MJ m-2 without melting have been performed in the QSPA-Kh50 plasma accelerator. Analytical considerations allow us to conclude that for both energy deposition values the erosion mechanism is solid dust ejection during surface cracking under the action of thermo-stress. Tungsten influx into the ITER containment of NW~5×1018 W per medium size ELM of 0.75 MJ m-2 and 0.25 ms time duration has been estimated. The radiation cooling power of Prad=150-300 MW due to such influx of tungsten is intolerable: it should cool the ITER core to 1 keV within a few seconds.

  13. Exploring the physics of efficient optical trapping of dielectric nanoparticles with ultrafast pulsed excitation.

    Science.gov (United States)

    Roy, Debjit; Goswami, Debabrata; De, Arijit K

    2015-08-10

    Stable optical trapping of dielectric nanoparticles with low power high-repetition-rate ultrafast pulsed excitation has received considerable attention in recent years. However, the exact role of such excitation has been quite illusive so far since, for dielectric micron-sized particles, the trapping efficiency turns out to be similar to that of continuous-wave excitation and independent of pulse chirping. In order to provide a coherent explanation of this apparently puzzling phenomenon, we justify the superior role of high-repetition-rate pulsed excitation in dielectric nanoparticle trapping which is otherwise not possible with continuous-wave excitation at a similar average power level. We quantitatively estimate the optimal combination of pulse peak power and pulse repetition rate leading to a stable trap and discuss the role of inertial response on the dependence of trapping efficiency on pulse width. In addition, we report gradual trapping of individual quantum dots detected by a stepwise rise in a two-photon fluorescence signal from the trapped quantum dots which conclusively proves individual particle trapping.

  14. Comparative effect of order based resistance exercises on number of repetitions, rating of perceived exertion and muscle damage biomarkers in men

    Directory of Open Access Journals (Sweden)

    H. Arazi

    2015-12-01

    Conclusion: It can be concluded that both of the resistance exercise orders were equally effective in muscle damage parameters (CK, lactate, RPE and the average of the total number of exercise repetitions, although when the exercise session progressed, the number of repetitions performed to volitional failure decreased in last exercise in one single order, and the exercise order can influence performance.

  15. Guest–Host Interactions Investigated by Time-Resolved X-ray Spectroscopies and Scattering at MHz Rates

    DEFF Research Database (Denmark)

    Haldrup, Martin Kristoffer; Vanko, G.; Gawelda, W.

    2012-01-01

    We have studied the photoinduced low spin (LS) to high spin (HS) conversion of [Fe(bipy)3]2+ in aqueous solution. In a laser pump/X-ray probe synchrotron setup permitting simultaneous, time-resolved X-ray diffuse scattering (XDS) and X-ray spectroscopic measurements at a 3.26 MHz repetition rate...... lifetime, allowing the detection of an ultrafast change in bulk solvent density. An analysis approach directly utilizing the spectroscopic data in the XDS analysis effectively reduces the number of free parameters, and both combined permit extraction of information about the ultrafast structural dynamics...

  16. Handheld nonlinear microscope system comprising a 2 MHz repetition rate, mode-locked Yb-fiber laser for in vivo biomedical imaging.

    Science.gov (United States)

    Krolopp, Ádám; Csákányi, Attila; Haluszka, Dóra; Csáti, Dániel; Vass, Lajos; Kolonics, Attila; Wikonkál, Norbert; Szipőcs, Róbert

    2016-09-01

    A novel, Yb-fiber laser based, handheld 2PEF/SHG microscope imaging system is introduced. It is suitable for in vivo imaging of murine skin at an average power level as low as 5 mW at 200 kHz sampling rate. Amplified and compressed laser pulses having a spectral bandwidth of 8 to 12 nm at around 1030 nm excite the biological samples at a ~1.89 MHz repetition rate, which explains how the high quality two-photon excitation fluorescence (2PEF) and second harmonic generation (SHG) images are obtained at the average power level of a laser pointer. The scanning, imaging and detection head, which comprises a conventional microscope objective for beam focusing, has a physical length of ~180 mm owing to the custom designed imaging telescope system between the laser scanner mirrors and the entrance aperture of the microscope objective. Operation of the all-fiber, all-normal dispersion Yb-fiber ring laser oscillator is electronically controlled by a two-channel polarization controller for Q-switching free mode-locked operation. The whole nonlinear microscope imaging system has the main advantages of the low price of the fs laser applied, fiber optics flexibility, a relatively small, light-weight scanning and detection head, and a very low risk of thermal or photochemical damage of the skin samples.

  17. High-rate low-temperature dc pulsed magnetron sputtering of photocatalytic TiO2films: the effect of repetition frequency

    Directory of Open Access Journals (Sweden)

    Strýhal Z

    2007-01-01

    Full Text Available AbstractThe article reports on low-temperature high-rate sputtering of hydrophilic transparent TiO2thin films using dc dual magnetron (DM sputtering in Ar + O2mixture on unheated glass substrates. The DM was operated in a bipolar asymmetric mode and was equipped with Ti(99.5 targets of 50 mm in diameter. The substrate surface temperature Tsurfmeasured by a thermostrip was less than 180 °C for all experiments. The effect of the repetition frequency frwas investigated in detail. It was found that the increase of frfrom 100 to 350 kHz leads to (a an improvement of the efficiency of the deposition process that results in a significant increase of the deposition rate aDof sputtered TiO2films and (b a decrease of peak pulse voltage and sustaining of the magnetron discharge at higher target power densities. It was demonstrated that several hundreds nm thick hydrophilic TiO2films can be sputtered on unheated glass substrates at aD = 80 nm/min, Tsurf < 180 °C when high value of fr = 350 kHz was used. Properties of a thin hydrophilic TiO2film deposited on a polycarbonate substrate are given.

  18. 新型高重复频率脉冲CO2激光器%Novel high repetition-rate pulse CO2 laser

    Institute of Scientific and Technical Information of China (English)

    郑义军; 刁伟伦; 谭荣清; 王东雷; 张阔海; 黄文武; 刘世明; 李能文; 孙科; 卢远添

    2013-01-01

    A novel transversely excited atmospheric (TEA) CO2 laser with high repetition- rate was reported. The size of laser is 300 mmí300 mmí300 mm. The discharge volume is 12í103 mm3, the length of cavity is 310 mm. The ultraviolet preionization makes the discharge even and stable, the output energy can be as high as 15 mJ under the circumstance of free oscillation, and the full width at half maximum of the light pulse is 70 ns. To acquire the high wind velocity, a turbocharger was used in the system of the fast- gas flow cycle. When the pressure in the cavity is 100 kPa, the wind speed is 100 m/s, and the repetition rate of the TEA CO2 laser is up to 1.5 kHz. On the basis of preliminary experiment, the system of the grating tuning line selection can be applied to the high repetition- rate pulse laser to abtain the output of grating line selection accurately and fast.%报道了一种新型高重复频率的脉冲CO2激光器。该型激光器结构紧凑,激光器外型尺寸为300 mm×300 mm×300 mm,工作气体放电增益体积为12×103 mm3,谐振腔的长度为310 mm。为了获得大体积均匀稳定的气体放电,激光器采用了紫外电晕预电离方式。在激光器自由运转时,单脉冲激光的输出能量达到15 mJ ,输出脉冲的半高全宽为70 ns。激光器采用紧凑型高速涡轮增压风机,在一个大气压的条件下,气流循环速度超过100 m/s,激光脉冲重复频率为1.5 kHz,采用大体积强迫冷却和气体主动置换技术,可以获得较长时间激光稳定输出。在已有的实验基础上,采用光栅调谐,可快速准确地实现高重复频率脉冲CO2激光器的谱线选支输出。

  19. Reaching white-light radiation source of ultrafast laser pulses with tunable peak power using nonlinear self-phase modulation in neon gas

    Science.gov (United States)

    Tawfik, Walid

    2016-08-01

    A source of white-light radiation that generates few-cycle pulses with controlled peak power values has been developed. These ultrafast pulses have been observed by spectral broadening of 32 fs pulses through nonlinear self-phase modulation in a neon-filled hollow-fiber then compressed with a pair of chirped mirrors for dispersion compensation. The observed pulses reached transform-limited duration of 5.77 fs and their peak power values varied from 57 GW up to 104 GW at repetition rate of 1 kHz. Moreover, the applied method is used for a direct tuning of the peak power of the output pulses through varying the chirping of the input pulses at different neon pressures. The observed results may give an opportunity to control the ultrafast interaction dynamics on the femtosecond time scale and facilitate the regeneration of attosecond pulses.

  20. Ultrafast Magnetic Light

    CERN Document Server

    Makarov, Sergey V; Krasnok, Alexander E; Belov, Pavel A

    2015-01-01

    We propose a novel concept for efficient dynamic tuning of optical properties of a high refractive index subwavelength nanoparticle with a magnetic Mie-type resonance by means of femtosecond laser radiation. This concept is based on ultrafast generation of electron-hole plasma within such nanoparticle, drastically changing its transient dielectric permittivity. This allows to manipulate by both electric and magnetic nanoparticle responses, resulting in dramatic changes of its extinction cross section and scattering diagram. Specifically, we demonstrate the effect of ultrafast switching-on a Huygens source in the vicinity of the magnetic dipole resonance. This approach enables to design ultrafast and compact optical switchers and modulators based on the "ultrafast magnetic light" concept.

  1. Short-time X-ray diffraction with an efficient-optimized, high repetition-rate laser-plasma X-ray-source; Kurzzeit-Roentgenbeugung mit Hilfe einer Effizienz-optimierten, hochrepetierenden Laser-Plasma-Roentgenquelle

    Energy Technology Data Exchange (ETDEWEB)

    Kaehle, Stephan

    2009-04-23

    This thesis deals with the production and application of ultrashort X-ray pulses. In the beginning different possibilities for the production of X-ray pulses with pulse durations of below one picosecond are presented, whereby the main topic lies on the so called laser-plasma X-ray sources with high repetition rate. In this case ultrashort laser pulses are focused on a metal, so that in the focus intensities of above 10{sup 16} W/cm{sup 2} dominate. In the ideal case in such way ultrafast electrons are produced, which are responsible for line radiation. In these experiments titanium K{sub {alpha}} radiation is produced, thes photons possess an energy of 4.51 keV. For the efficient production of line radiation here the Ti:Sa laser is optimized in view of the laser energy and the pulse shape and the influence of the different parameters on the K{sub {alpha}} production systematically studied. The influences of laser intensity, system-conditioned pre-pulses and of phase modulation are checked. It turns out that beside the increasement of the K{sub {alpha}} radiation by a suited laser intensity a reduction of the X-ray background radiation is of deciding importance for the obtaining of clear diffraction images. This background radiation is mainly composed of bremsstrahlung. It can be suppressed by the avoidance of intrinsic pre-pulses and by means of 2nd-order phase modulation. By means of optical excitation and X-ray exploration experiments the production of acoustic waves after ultrashort optical excitation in a 150 nm thick Ge(111) film on Si(111) is studied. These acoustic waves are driven by thermal (in this time scale time-independent) and electronic (time dependent) pressure amounts. As essential results it turns out that the relative amount of the electronic pressure increases with decreasing excitation density. [German] Diese Arbeit befasst sich mit der Erzeugung und Anwendung ultrakurzer Roentgenimpulse. Zu Beginn werden verschiedene Moeglichkeiten zur

  2. Three-dimensional polymer nanostructures for applications in cell biology generated by high-repetition rate sub-15 fs near-infrared laser pulses

    Science.gov (United States)

    Licht, Martin; Straub, Martin; König, Karsten; Afshar, Maziar; Feili, Dara; Seidel, Helmut

    2011-03-01

    In recent years two-photon photopolymerization has emerged as a novel and extremely powerful technique of three-dimensional nanostructure formation. Complex-shaped structures can be generated using appropriate beam steering or nanopositioning systems. Here, we report on the fabrication of three-dimensional arrangements made of biocompatible polymer material, which can be used as templates for cell growth. Using three-dimensional cell cages as cell culture substrates is advantageous, as cells may develop in a more natural environment as compared to conventional planar growth methods. The two-photon fabrication experiments were carried out on a commercial microscope setup. Sub-15 fs pulsed Ti:Sapphire laser light (centre wavelength 800 nm, bandwidth 120 nm, repetition rate 85 MHz) was focused into the polymer material by a high-numerical aperture oil immersion objective. Due to the high peak intensities picojoule pulse energies in the focal spot are sufficient to polymerize the material at sub-100 nm structural element dimensions. Therefore, cell cages of sophisticated architecture can be constructed involving very fine features which take into account the specific needs of various types of cells. Ultimately, our research aims at three-dimensional assemblies of photopolymerized structural elements involving sub-100 nm features, which provide cell culture substrates far superior to those currently existing.

  3. Welding of glasses in optical and partial-optical contact via focal position adjustment of femtosecond-laser pulses at moderately high repetition rate

    Science.gov (United States)

    Tan, Hua; Duan, Ji'an

    2017-07-01

    We used 1030-nm femtosecond-laser pulses focused above/at/below the interface of two fused-silica glass substrates in optical and partial-optical contact to successfully weld them at a moderately high repetition rate of 600 kHz. Variation in the laser focal position for these two gap-distance regimes (optical and partial-optical contact) yields different bonding strengths (BSs) and machining mechanisms. The maximum bonding strength (58.2 MPa) can be achieved for a gap distance ≤λ /4 for optical-contact welding when laser focused below the interface, and the corresponding height of the welding seam was 23 μm. In addition, our results demonstrated that the "filamentation welding technique" is critical to the femtosecond-laser direct welding of glasses. Furthermore, line welding is significantly easier to realize when the femtosecond laser focuses at the interface in partial-optical-contact welding applications due to the combined effects of filamentation welding and ablation.

  4. Fast repetition rate (FRR) fluorometry: variability of chlorophyll a fluorescence yields in colonies of the corals, Montastraea faveolata (w.) and Diploria labyrinthiformes (h.) recovering from bleaching.

    Science.gov (United States)

    Lombardi; Lesser; Gorbunov

    2000-09-05

    Recently, an underwater version of a fast repetition rate fluorometer (FRRF) was developed for the non-destructive study of fluorescence yields in benthic photoautotrophs. We used an FRRF to study bleached colonies of the corals, Montastraea faveolata and Diploria labyrinthiformes at sites surrounding Lee Stocking Island, Exuma, Bahamas, to assess their recovery from bleaching ( approximately 1 year after the initial bleaching event) induced by elevated temperatures. The steady state quantum yields of chlorophyll a fluorescence (DeltaF'/F'(m)) from photosystem II (PSII) within coral colonies were separated into three categories representing visibly distinct degrees of bleaching ranging from no bleaching to completely bleached areas. Differences in DeltaF'/F'(m) were significantly different from bleached to unbleached regions within colonies. Dark, unbleached regions within colonies exhibited significantly higher DeltaF'/F'(m) values (0.438+/-0.019; mean+/-S.D.) when compared to lighter regions, and occupied a majority of the colonies' surface area (46-73%). Bleached regions exhibited significantly lower DeltaF'/F'(m) (0.337+/-0.014) and covered only 7-25% of the colonies' surface area. The observations from this study suggest that zooxanthellae in bleached regions of a colony exhibit reduced photosynthetic activity as long as one year after a bleaching event and that in situ fluorescence techniques such as FRRF are an effective means of studying coral responses and recovery from natural or anthropogenic stress in a non-destructive manner.

  5. A shock tube with a high-repetition-rate time-of-flight mass spectrometer for investigations of complex reaction systems

    Science.gov (United States)

    Dürrstein, Steffen H.; Aghsaee, Mohammad; Jerig, Ludger; Fikri, Mustapha; Schulz, Christof

    2011-08-01

    A conventional membrane-type stainless steel shock tube has been coupled to a high-repetition-rate time-of-flight mass spectrometer (HRR-TOF-MS) to be used to study complex reaction systems such as the formation of pollutants in combustion processes or formation of nanoparticles from metal containing organic compounds. Opposed to other TOF-MS shock tubes, our instrument is equipped with a modular sampling unit that allows to sample with or without a skimmer. The skimmer unit can be mounted or removed in less than 10 min. Thus, it is possible to adjust the sampling procedure, namely, the mass flux into the ionization chamber of the HRR-TOF-MS, to the experimental situation imposed by species-specific ionization cross sections and vapor pressures. The whole sampling section was optimized with respect to a minimal distance between the nozzle tip inside the shock tube and the ion source inside the TOF-MS. The design of the apparatus is presented and the influence of the skimmer on the measured spectra is demonstrated by comparing data from both operation modes for conditions typical for chemical kinetics experiments. The well-studied thermal decomposition of acetylene has been used as a test system to validate the new setup against kinetics mechanisms reported in literature.

  6. Texturing of titanium (Ti6Al4V) medical implant surfaces with MHz-repetition-rate femtosecond and picosecond Yb-doped fiber lasers.

    Science.gov (United States)

    Erdoğan, Mutlu; Öktem, Bülent; Kalaycıoğlu, Hamit; Yavaş, Seydi; Mukhopadhyay, Pranab K; Eken, Koray; Ozgören, Kıvanç; Aykaç, Yaşar; Tazebay, Uygar H; Ilday, F Ömer

    2011-05-23

    We propose and demonstrate the use of short pulsed fiber lasers in surface texturing using MHz-repetition-rate, microjoule- and sub-microjoule-energy pulses. Texturing of titanium-based (Ti6Al4V) dental implant surfaces is achieved using femtosecond, picosecond and (for comparison) nanosecond pulses with the aim of controlling attachment of human cells onto the surface. Femtosecond and picosecond pulses yield similar results in the creation of micron-scale textures with greatly reduced or no thermal heat effects, whereas nanosecond pulses result in strong thermal effects. Various surface textures are created with excellent uniformity and repeatability on a desired portion of the surface. The effects of the surface texturing on the attachment and proliferation of cells are characterized under cell culture conditions. Our data indicate that picosecond-pulsed laser modification can be utilized effectively in low-cost laser surface engineering of medical implants, where different areas on the surface can be made cell-attachment friendly or hostile through the use of different patterns.

  7. High-power LD side-pump Nd: YAG regenerative amplifier at 1 kHz repetition rate with volume Bragg gratings (VBG) for broadening and compressor

    Science.gov (United States)

    Long, Ming-Liang; Chen, Li-Yuan; Chen, Meng; Li, Gang

    2016-05-01

    Pulse width of 8.7 ps was broadened to 102.2, 198 ps with single and double pass the VBG respectively. When the 102.2 ps pulse was injected into 1 kHz repetition rate of LD side-pump Nd: YAG regenerative amplifier (RA), pulse width of 87.5 ps at 1 kHz was obtained with the pulse energy of 9.4 mJ, the beam quality of M^2 factor was 1.2. The pulse width was compressed to 32.7 ps with a single pass VBG and the pulse energy reduced to 8.8 mJ, and the power density was up to 15.2 GW/cm2, the stability for pulse to pulse rms is about 0.6 %, beam pointing was about 35 μrad. In addition, when 198 ps pulse was injected into RA, pulse width of 156 ps was obtained which energy was 9.6 mJ, the pulse width was compressed to 38 ps by double passing the VBG, the pulse energy decreased to 8.5 mJ. Chirped VBG is a new way to obtain high-intensity picosecond pulse laser system simple and smaller.

  8. A shock tube with a high-repetition-rate time-of-flight mass spectrometer for investigations of complex reaction systems.

    Science.gov (United States)

    Dürrstein, Steffen H; Aghsaee, Mohammad; Jerig, Ludger; Fikri, Mustapha; Schulz, Christof

    2011-08-01

    A conventional membrane-type stainless steel shock tube has been coupled to a high-repetition-rate time-of-flight mass spectrometer (HRR-TOF-MS) to be used to study complex reaction systems such as the formation of pollutants in combustion processes or formation of nanoparticles from metal containing organic compounds. Opposed to other TOF-MS shock tubes, our instrument is equipped with a modular sampling unit that allows to sample with or without a skimmer. The skimmer unit can be mounted or removed in less than 10 min. Thus, it is possible to adjust the sampling procedure, namely, the mass flux into the ionization chamber of the HRR-TOF-MS, to the experimental situation imposed by species-specific ionization cross sections and vapor pressures. The whole sampling section was optimized with respect to a minimal distance between the nozzle tip inside the shock tube and the ion source inside the TOF-MS. The design of the apparatus is presented and the influence of the skimmer on the measured spectra is demonstrated by comparing data from both operation modes for conditions typical for chemical kinetics experiments. The well-studied thermal decomposition of acetylene has been used as a test system to validate the new setup against kinetics mechanisms reported in literature.

  9. High-repetition-rate and high-photon-flux 70 eV high-harmonic source for coincidence ion imaging of gas-phase molecules

    CERN Document Server

    Rothhardt, Jan; Shamir, Yariv; Tschnernajew, Maxim; Klas, Robert; Hoffmann, Armin; Tadesse, Getnet K; Klenke, Arno; Gottschall, Thomas; Eidam, Tino; Boll, Rebecca; Bomme, Cedric; Dachraoui, Hatem; Erk, Benjamin; Di Fraia, Michele; Horke, Daniel A; Kierspel, Thomas; Mullins, Terence; Przystawik, Andreas; Savelyev, Evgeny; Wiese, Joss; Laarmann, Tim; Küpper, Jochen; Rolles, Daniel; Limpert, Jens; Tünnermann, Andreas

    2016-01-01

    Unraveling and controlling chemical dynamics requires techniques to image structural changes of molecules with femtosecond temporal and picometer spatial resolution. Ultrashort-pulse x-ray free-electron lasers have significantly advanced the field by enabling advanced pump-probe schemes. There is an increasing interest in using table-top photon sources enabled by high-harmonic generation of ultrashort-pulse lasers for such studies. We present a novel high-harmonic source driven by a 100 kHz fiber laser system, which delivers 10$^{11}$ photons/s in a single 1.3 eV bandwidth harmonic at 68.6 eV. The combination of record-high photon flux and high repetition rate paves the way for time-resolved studies of the dissociation dynamics of inner-shell ionized molecules in a coincidence detection scheme. First coincidence measurements on CH$_3$I are shown and it is outlined how the anticipated advancement of fiber laser technology and improved sample delivery will, in the next step, allow pump-probe studies of ultrafas...

  10. A high-repetition rate edge localised mode replication system for the Magnum-PSI and Pilot-PSI linear devices

    Science.gov (United States)

    Morgan, T. W.; de Kruif, T. M.; van der Meiden, H. J.; van den Berg, M. A.; Scholten, J.; Melissen, W.; Krijger, B. J. M.; Bardin, S.; De Temmerman, G.

    2014-09-01

    A high-power edge-localized mode (ELM) striking onto divertor components presents one of the strongest lifetime and performance challenges for plasma facing components in future fusion reactors. A high-repetition-rate ELM replication system has been constructed and was commissioned at the Magnum-PSI linear device to investigate the synergy between steady state plasma exposure and the large increase in heat and particle flux to the plasma facing surface during repeated ELM transients in conditions aiming to mimic as closely as possible those in the ITER divertor. This system is capable of increasing the electron density and temperature from ˜1 × 1020 m-3 to ˜1 × 1021 m-3 and from 1 to 5 eV respectively, leading to a heat flux increase at the surface to ˜130 MW m-2. By combining Thomson scattering measurements with heat fluxes determined using the THEODOR code, the sheath heat transmission factor during the pulses was determined to be ≈7.7, in agreement with sheath theory. The heat flux is found to be linearly dependent upon the strength of the magnetic field at the target position, and, by adapting the system to Pilot-PSI, tests at 1.6 T showed heat fluxes of more than 600 MW m-2. This gives confidence that with the installation of a 2.5 T superconducting magnetic solenoid at Magnum-PSI the heat flux will reach the ITER-relevant gigawatt per square metre heat flux regime.

  11. High-energy femtosecond Yb-doped all-fiber monolithic chirped-pulse amplifier at repetition rate of 1 MHz

    Science.gov (United States)

    Lv, Zhi-Guo; Teng, Hao; Wang, Li-Na; Wang, Jun-Li; Wei, Zhi-Yi

    2016-09-01

    A high-energy femtosecond all ytterbium fiber amplifier based on a chirped-pulse amplification (CPA) technique at a repetition rate of 1 MHz seeded by a dispersion-management mode-locked picosecond broadband oscillator is studied. We find that the compressed pulse duration is dependent on the amplified energy, the pulse duration of 804 fs corresponds to the maximum amplified energy of 10.5 μJ, while the shortest pulse duration of 424 fs corresponds to the amplified energy of 6.75 μJ. The measured energy fluctuation is approximately 0.46% root mean square (RMS) over 2 h. The low-cost femtosecond fiber laser source with super-stability will be widely used in industrial micromachines, medical therapy, and scientific studies. Project supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Grant No. 2012BAC23B03), the National Key Basic Research Program of China (Grant No. 2013CB922401), and the National Natural Science Foundation of China (Grant No. 11474002).

  12. A K-alpha x-ray source using high energy and high repetition rate laser system for phase contrast imaging.

    Science.gov (United States)

    Serbanescu, Cristina; Fourmaux, Sylvain; Kieffer, Jean-Claude; Kincaid, Russell; Krol, Andrzej

    2009-01-01

    K-alpha x-ray sources from laser produced plasmas provide completely new possibilities for x-ray phase-contrast imaging applications. By tightly focusing intense femtosecond laser pulses onto a solid target K-alpha x-ray pulses are generated through the interaction of energetic electrons created in the plasma with the bulk target. In this paper, we present a continuous and efficient Mo K-alpha x-ray source produced by a femtosecond laser system operating at 100 Hz repetition rate with maximum pulse energy of 110 mJ before compression. The source has an x-ray conversion efficiency of greater than 10(-5) into K-alpha line emission. In preparation for phase contrast imaging applications, the size of the resultant K-alpha x-ray emission spot has been also characterized. The source exhibits sufficient spatial coherence to observe phase contrast. We observe a relatively small broadening of the K-alpha source size compared to the size of the laser beam itself. Detailed characterization of the source including the x-ray spectrum and the x-ray average yield along with phase contrast images of test objects will be presented.

  13. High speed inscription of uniform, large-area laser-induced periodic surface structures in Cr films using a high repetition rate fs laser.

    Science.gov (United States)

    Ruiz de la Cruz, A; Lahoz, R; Siegel, J; de la Fuente, G F; Solis, J

    2014-04-15

    We report on the fabrication of laser-induced periodic surface structures in Cr films upon high repetition rate fs laser irradiation (up to 1 MHz, 500 fs, 1030 nm), employing beam scanning. Highly regular large-area (9  cm2) gratings with a relative diffraction efficiency of 42% can be produced within less than 6 min. The ripple period at moderate and high fluences is 0.9 μm, with a small period of 0.5 μm appearing at lower energies. The role of the irradiation parameters on the characteristics of the laser-induced periodic surface structures (LIPSS) is studied and discussed in the frame of the models presently used. We have identified the polarization vector orientation with respect to the scan direction as a key parameter for the fabrication of high-quality, large-area LIPSS, which, for perpendicular orientation, allows the coherent extension of the sub-wavelength structure over macroscopic distances. The processing strategy is robust in terms of broad parameter windows and applicable to other materials featuring LIPSS.

  14. High Repetition-Rate Neutron Generation by Several-mJ, 35 fs pulses interacting with Free-Flowing D2O

    Science.gov (United States)

    Hah, Jungmoo; Petrov, George; Nees, John; He, Zhaohan; Hammig, Mark; Krushelnick, Karl; Thomas, Alexander

    2016-10-01

    Recent advance in ultra-high power laser technology allows a development of laser-based neutron sources. Here we demonstrate heavy-water based neutron source. Using several-mJ energy pulses from a high-repetition rate (½kHz), ultrashort (35 fs) pulsed laser interacting with a 10 μm diameter stream of free-flowing heavy water (D2O), we get a 2.45 MeV neutron flux of 105/s. In the intentionally generated pre-plasma, laser pulse energy is efficiently absorbed, and energetic deuterons are generated. As a convertor, the bulk heavy water stream target and the large volume of low density D2O vapor near the target are collided with accelerated deuterons, generating neutron through d(d,n)3He reactions. As laser pulse energy increased from 6mJ to 12mJ, the neutron flux increased. From the 2D particle-in-cell simulation, comparable neutron fluxes are shown at the similar laser characteristics to the experiment. Also, simulation shows forward and backward moving deuterons, which are main distributing ions impinging upon D2O stream and vapor, respectively. This material is based upon work supported by the Air Force Office of Scien- tific Research under Award Numbers FA9550-12-1-0310 (Young Investigator Program) and FA9550-14-1-0282.

  15. High-throughput machining using high average power ultrashort pulse lasers and ultrafast polygon scanner

    Science.gov (United States)

    Schille, Joerg; Schneider, Lutz; Streek, André; Kloetzer, Sascha; Loeschner, Udo

    2016-03-01

    In this paper, high-throughput ultrashort pulse laser machining is investigated on various industrial grade metals (Aluminium, Copper, Stainless steel) and Al2O3 ceramic at unprecedented processing speeds. This is achieved by using a high pulse repetition frequency picosecond laser with maximum average output power of 270 W in conjunction with a unique, in-house developed two-axis polygon scanner. Initially, different concepts of polygon scanners are engineered and tested to find out the optimal architecture for ultrafast and precision laser beam scanning. Remarkable 1,000 m/s scan speed is achieved on the substrate, and thanks to the resulting low pulse overlap, thermal accumulation and plasma absorption effects are avoided at up to 20 MHz pulse repetition frequencies. In order to identify optimum processing conditions for efficient high-average power laser machining, the depths of cavities produced under varied parameter settings are analyzed and, from the results obtained, the characteristic removal values are specified. The maximum removal rate is achieved as high as 27.8 mm3/min for Aluminium, 21.4 mm3/min for Copper, 15.3 mm3/min for Stainless steel and 129.1 mm3/min for Al2O3 when full available laser power is irradiated at optimum pulse repetition frequency.

  16. Spaced planar laminations formed by repetitive basal erosion and resurgence to high-sedimentation-rate regime: new insight from a bedform-like structures and laterally continuous exposures

    Science.gov (United States)

    Ishihara, Yoshiro; Yuri, Onishi; Tsuda, Keisuke; Yokokawa, Miwa

    2017-04-01

    Spaced planar laminations (SPL), or so-called traction carpet deposits, are frequently observed in deposits of sediment gravity flows. Several sedimentation models for a succession of inversely graded units have been suggested from field observations and flume experiments. The formation of the inversely graded unit could be summarized as follows: (1) abrupt sedimentation on freezing of an inversely graded layer, or (2) interruptions in flow causing a freezing of an inversely graded layer at the most basal part of flow. In either case, traction carpets as a bed load overlying the erosive boundary at the base of flow are required. Although some descriptions have reported SPLs forming antidune bedform-like structures and the association of SPLs with structureless massive deposits have not been clearly explained. In this study, we suggest a novel model of SPL formation by repetition of basal erosion and resurgence to high-sedimentation rates, based on detail examinations of SPLs both showing bedform-like structures and lateral extents of hundreds of meters. SPLs were investigated in the Mio-Pliocene Kiyosumi Formation in central Japan and the Miocene Aoshima Formation in southwest Japan. In a turbidite in the Kiyosumi Formation, SPLs show three mound-like structures, suggesting antidune bedforms with wavelengths of about 6 to 7 m. On the upcurrent flanks, SPLs show lenticular cross laminations or pinching out of units; those units do not show clear inverse grading. Rip-up mud clasts and relatively high-angle imbrications are also observed. On the other hand, SPLs on the downcurrent flanks show relatively clear inverse grading and transition downcurrent into a massive structureless bed. In the Aoshima Formation, SPLs with ca. 1 cm unit thickness continue approximately 50 m along a palaeocurrent direction without changes in thickness. These SPLs gradually transition upward into a massive structureless unit. From the observations described above, in addition to

  17. Ultra-high-resolution inelastic X-ray scattering at high-repetition-rate self-seeded X-ray free-electron lasers

    Energy Technology Data Exchange (ETDEWEB)

    Chubar, Oleg [Brookhaven National Laboratory, Upton, NY 11973 (United States); Geloni, Gianluca [European X-ray Free-Electron Laser, Albert-Einstein-Ring 19, 22761 Hamburg (Germany); Kocharyan, Vitali [Deutsches Elektronen-Synchrotron, 22761 Hamburg (Germany); Madsen, Anders [European X-ray Free-Electron Laser, Albert-Einstein-Ring 19, 22761 Hamburg (Germany); Saldin, Evgeni; Serkez, Svitozar [Deutsches Elektronen-Synchrotron, 22761 Hamburg (Germany); Shvyd’ko, Yuri, E-mail: shvydko@aps.anl.gov [Argonne National Laboratory, Argonne, IL 60439 (United States); Sutter, John [Diamond Light Source Ltd, Didcot OX11 0DE (United Kingdom)

    2016-02-12

    This article explores novel opportunities for ultra-high-resolution inelastic X-ray scattering (IXS) at high-repetition-rate self-seeded XFELs. These next-generation light sources are promising a more than three orders of magnitude increase in average spectral flux compared with what is possible with storage-ring-based radiation sources. In combination with the advanced IXS spectrometer described here, this may become a real game-changer for ultra-high-resolution X-ray spectroscopies, and hence for the studies of dynamics in condensed matter systems. Inelastic X-ray scattering (IXS) is an important tool for studies of equilibrium dynamics in condensed matter. A new spectrometer recently proposed for ultra-high-resolution IXS (UHRIX) has achieved 0.6 meV and 0.25 nm{sup −1} spectral and momentum-transfer resolutions, respectively. However, further improvements down to 0.1 meV and 0.02 nm{sup −1} are required to close the gap in energy–momentum space between high- and low-frequency probes. It is shown that this goal can be achieved by further optimizing the X-ray optics and by increasing the spectral flux of the incident X-ray pulses. UHRIX performs best at energies from 5 to 10 keV, where a combination of self-seeding and undulator tapering at the SASE-2 beamline of the European XFEL promises up to a 100-fold increase in average spectral flux compared with nominal SASE pulses at saturation, or three orders of magnitude more than what is possible with storage-ring-based radiation sources. Wave-optics calculations show that about 7 × 10{sup 12} photons s{sup −1} in a 90 µeV bandwidth can be achieved on the sample. This will provide unique new possibilities for dynamics studies by IXS.

  18. Single-shot compressed ultrafast photography at one hundred billion frames per second

    Science.gov (United States)

    Gao, Liang; Liang, Jinyang; Li, Chiye; Wang, Lihong V.

    2014-12-01

    The capture of transient scenes at high imaging speed has been long sought by photographers, with early examples being the well known recording in 1878 of a horse in motion and the 1887 photograph of a supersonic bullet. However, not until the late twentieth century were breakthroughs achieved in demonstrating ultrahigh-speed imaging (more than 105 frames per second). In particular, the introduction of electronic imaging sensors based on the charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) technology revolutionized high-speed photography, enabling acquisition rates of up to 107 frames per second. Despite these sensors' widespread impact, further increasing frame rates using CCD or CMOS technology is fundamentally limited by their on-chip storage and electronic readout speed. Here we demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 1011 frames per second. Compared with existing ultrafast imaging techniques, CUP has the prominent advantage of measuring an x-y-t (x, y, spatial coordinates; t, time) scene with a single camera snapshot, thereby allowing observation of transient events with temporal resolution as tens of picoseconds. Furthermore, akin to traditional photography, CUP is receive-only, and so does not need the specialized active illumination required by other single-shot ultrafast imagers. As a result, CUP can image a variety of luminescent--such as fluorescent or bioluminescent--objects. Using CUP, we visualize four fundamental physical phenomena with single laser shots only: laser pulse reflection and refraction, photon racing in two media, and faster-than-light propagation of non-information (that is, motion that appears faster than the speed of light but cannot convey information). Given CUP's capability, we expect it to find widespread applications in both fundamental and applied sciences, including biomedical

  19. Single-shot compressed ultrafast photography at one hundred billion frames per second.

    Science.gov (United States)

    Gao, Liang; Liang, Jinyang; Li, Chiye; Wang, Lihong V

    2014-12-04

    The capture of transient scenes at high imaging speed has been long sought by photographers, with early examples being the well known recording in 1878 of a horse in motion and the 1887 photograph of a supersonic bullet. However, not until the late twentieth century were breakthroughs achieved in demonstrating ultrahigh-speed imaging (more than 10(5) frames per second). In particular, the introduction of electronic imaging sensors based on the charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) technology revolutionized high-speed photography, enabling acquisition rates of up to 10(7) frames per second. Despite these sensors' widespread impact, further increasing frame rates using CCD or CMOS technology is fundamentally limited by their on-chip storage and electronic readout speed. Here we demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 10(11) frames per second. Compared with existing ultrafast imaging techniques, CUP has the prominent advantage of measuring an x-y-t (x, y, spatial coordinates; t, time) scene with a single camera snapshot, thereby allowing observation of transient events with temporal resolution as tens of picoseconds. Furthermore, akin to traditional photography, CUP is receive-only, and so does not need the specialized active illumination required by other single-shot ultrafast imagers. As a result, CUP can image a variety of luminescent--such as fluorescent or bioluminescent--objects. Using CUP, we visualize four fundamental physical phenomena with single laser shots only: laser pulse reflection and refraction, photon racing in two media, and faster-than-light propagation of non-information (that is, motion that appears faster than the speed of light but cannot convey information). Given CUP's capability, we expect it to find widespread applications in both fundamental and applied sciences, including

  20. Ablation-cooled material removal with ultrafast bursts of pulses

    Science.gov (United States)

    Kerse, Can; Kalaycıoğlu, Hamit; Elahi, Parviz; Çetin, Barbaros; Kesim, Denizhan K.; Akçaalan, Önder; Yavaş, Seydi; Aşık, Mehmet D.; Öktem, Bülent; Hoogland, Heinar; Holzwarth, Ronald; Ilday, Fatih Ömer

    2016-09-01

    The use of femtosecond laser pulses allows precise and thermal-damage-free removal of material (ablation) with wide-ranging scientific, medical and industrial applications. However, its potential is limited by the low speeds at which material can be removed and the complexity of the associated laser technology. The complexity of the laser design arises from the need to overcome the high pulse energy threshold for efficient ablation. However, the use of more powerful lasers to increase the ablation rate results in unwanted effects such as shielding, saturation and collateral damage from heat accumulation at higher laser powers. Here we circumvent this limitation by exploiting ablation cooling, in analogy to a technique routinely used in aerospace engineering. We apply ultrafast successions (bursts) of laser pulses to ablate the target material before the residual heat deposited by previous pulses diffuses away from the processing region. Proof-of-principle experiments on various substrates demonstrate that extremely high repetition rates, which make ablation cooling possible, reduce the laser pulse energies needed for ablation and increase the efficiency of the removal process by an order of magnitude over previously used laser parameters. We also demonstrate the removal of brain tissue at two cubic millimetres per minute and dentine at three cubic millimetres per minute without any thermal damage to the bulk.

  1. An ultrafast angle-resolved photoemission apparatus for measuring complex materials

    Energy Technology Data Exchange (ETDEWEB)

    Smallwood, Christopher L.; Lanzara, Alessandra [Department of Physics, University of California, Berkeley, California 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Jozwiak, Christopher [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Zhang Wentao [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2012-12-15

    We present technical specifications for a high resolution time- and angle-resolved photoemission spectroscopy setup based on a hemispherical electron analyzer and cavity-dumped solid state Ti:sapphire laser used to generate pump and probe beams, respectively, at 1.48 and 5.93 eV. The pulse repetition rate can be tuned from 209 Hz to 54.3 MHz. Under typical operating settings the system has an overall energy resolution of 23 meV, an overall momentum resolution of 0.003 A{sup -1}, and an overall time resolution of 310 fs. We illustrate the system capabilities with representative data on the cuprate superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}. The descriptions and analyses presented here will inform new developments in ultrafast electron spectroscopy.

  2. An ultrafast angle-resolved photoemission apparatus for measuring complex materials.

    Science.gov (United States)

    Smallwood, Christopher L; Jozwiak, Christopher; Zhang, Wentao; Lanzara, Alessandra

    2012-12-01

    We present technical specifications for a high resolution time- and angle-resolved photoemission spectroscopy setup based on a hemispherical electron analyzer and cavity-dumped solid state Ti:sapphire laser used to generate pump and probe beams, respectively, at 1.48 and 5.93 eV. The pulse repetition rate can be tuned from 209 Hz to 54.3 MHz. Under typical operating settings the system has an overall energy resolution of 23 meV, an overall momentum resolution of 0.003 Å(-1), and an overall time resolution of 310 fs. We illustrate the system capabilities with representative data on the cuprate superconductor Bi(2)Sr(2)CaCu(2)O(8+δ). The descriptions and analyses presented here will inform new developments in ultrafast electron spectroscopy.

  3. An injector for the proposed Berkeley Ultrafast X-Ray Light Source

    Energy Technology Data Exchange (ETDEWEB)

    Lidia, Steven; Corlett, John; Pusina, Jan; Staples, John; Zholents, Alexander

    2003-05-19

    Berkeley Lab has proposed to build a recirculating linac based X-ray source for ultra-fast dynamic studies [1]. This machine requires a flat electron beam with a small vertical emittance and large x/y emittance ratio to allow for compression of spontaneous undulator emission of soft and hard x-ray pulses, and a low-emittance, round electron beam for coherent emission of soft x-rays via the FEL process based on cascaded harmonic generation [2]. We propose an injector system consisting of two high gradient high repetition rate photo cathode guns [3] (one for each application), an {approx}120 MeV super conducting linear accelerator, a 3rd harmonic cavity for linearization of the longitudinal phase space, and a bunch compressor. We present details of the design and the results of particle tracking studies using several computer codes.

  4. Ultrafast nonlinear optics

    CERN Document Server

    Leburn, Christopher; Reid, Derryck

    2013-01-01

    The field of ultrafast nonlinear optics is broad and multidisciplinary, and encompasses areas concerned with both the generation and measurement of ultrashort pulses of light, as well as those concerned with the applications of such pulses. Ultrashort pulses are extreme events – both in terms of their durations, and also the high peak powers which their short durations can facilitate. These extreme properties make them powerful experiment tools. On one hand, their ultrashort durations facilitate the probing and manipulation of matter on incredibly short timescales. On the other, their ultrashort durations can facilitate high peak powers which can drive highly nonlinear light-matter interaction processes. Ultrafast Nonlinear Optics covers a complete range of topics, both applied and fundamental in nature, within the area of ultrafast nonlinear optics. Chapters 1 to 4 are concerned with the generation and measurement of ultrashort pulses. Chapters 5 to 7 are concerned with fundamental applications of ultrasho...

  5. Ultrafast and nanoscale diodes

    Science.gov (United States)

    Zhang, Peng; Lau, Y. Y.

    2016-10-01

    Charge carrier transport across interfaces of dissimilar materials (including vacuum) is the essence of all electronic devices. Ultrafast charge transport across a nanometre length scale is of fundamental importance in the miniaturization of vacuum and plasma electronics. With the combination of recent advances in electronics, photonics and nanotechnology, these miniature devices may integrate with solid-state platforms, achieving superior performance. This paper reviews recent modelling efforts on quantum tunnelling, ultrafast electron emission and transport, and electrical contact resistance. Unsolved problems and challenges in these areas are addressed.

  6. Carrier-Envelope Offset Stabilized Ultrafast Diode-Pumped Solid-State Lasers

    Directory of Open Access Journals (Sweden)

    Stéphane Schilt

    2015-10-01

    Full Text Available Optical frequency combs have been revolutionizing many research areas and are finding a growing number of real-world applications. While initially dominated by Ti:Sapphire and fiber lasers, optical frequency combs from modelocked diode-pumped solid-state lasers (DPSSLs have become an attractive alternative with state-of-the-art performance. In this article, we review the main achievements in ultrafast DPSSLs for frequency combs. We present the current status of carrier-envelope offset (CEO frequency-stabilized DPSSLs based on various approaches and operating in different wavelength regimes. Feedback to the pump current provides a reliable scheme for frequency comb CEO stabilization, but also other methods with faster feedback not limited by the lifetime of the gain material have been applied. Pumping DPSSLs with high power multi-transverse-mode diodes enabled a new class of high power oscillators and gigahertz repetition rate lasers, which were initially not believed to be suitable for CEO stabilization due to the pump noise. However, this challenge has been overcome, and recently both high power and gigahertz DPSSL combs have been demonstrated. Thin disk lasers have demonstrated the highest pulse energy and average power emitted from any ultrafast oscillator and present a high potential for the future generation of stabilized frequency combs with hundreds of watts average output power.

  7. Investigation of an Ultrafast Harmonic Resonant RF Kicker

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Yulu [Univ. of Chinese Academy of Sciences (CAS), Beijing (China)

    2016-10-01

    An Energy Recovery Linac (ERL) based multi-turn electron Circulator Cooler Ring (CCR) is envisaged in the proposed Jefferson Lab Electron Ion Collider (JLEIC) to cool the ion bunches with high energy (55 MeV), high current (1.5 A), high repetition frequency (476.3 MHz), high quality magnetized electron bunches. A critical component in this scheme is a pair of ultrafast kickers for the exchange of electron bunches between the ERL and the CCR. The ultrafast kicker should operate with the rise and fall time in less than 2.1 ns, at the repetition rate of ~10s MHz, and should be able to run continuously during the whole period of cooling. These -and-fall time being combined together, are well beyond the state-of-art of traditional pulsed power supplies and magnet kickers. To solve this technical challenge, an alternative method is to generate this high repetition rate, fast rise-and-fall time short pulse continuous waveform by summing several finite number of (co)sine waves at harmonic frequencies of the kicking repetition frequency, and these harmonic modes can be generated by the Quarter Wave Resonater (QWR) based multifrequency cavities. Assuming the recirculator factor is 10, 10 harmonic modes (from 47.63 MHz to 476.3 MHz) with proper amplitudes and phases, plus a DC offset are combined together, a continuous short pulse waveform with the rise-and-fall time in less than 2.1 ns, repetition rate of 47.63 MHz waveform can be generated. With the compact and matured technology of QWR cavities, the total cost of both hardware development and operation can be reduced to a modest level. Focuse on the technical scheme, three main topics will be discussed in this thesis: the synthetization of the kicking pulse, the design and optimization of the deflecting QWR multi-integer harmonic frequency resonator and the fabrication and bench measurements of a half scale copper prototype. In the kicking pulse synthetization part, we begin with the Fourier Series expansion of an ideal

  8. LD-pumped high repetition rate Q-switched Nd:YVO4 laser by using La3Ga5SiO14 single crystal electro-optic modulator

    Institute of Scientific and Technical Information of China (English)

    Chunyu Wang; Huaguo Zang; Xiaoli Li; Yutian Lu; Xiaolei Zhu

    2006-01-01

    A diode-end-pumped electro-optic (EO) Q-switched Nd:YVO4 laser operating at repetition rate of 10 kpps (pulses per second) was reported. A block of La3Ga5SiO14 (LGS) single crystal was used as a Q-switch and the driver was a metal oxide semiconductor field effect transistor (MOS-FET) pulser of high repetition rate and high voltage. At continuous wave (CW) operation, the slope efficiency of the laser was 46%, and maximum optical-to-optical efficiency was 38.5%. Using an output coupler with transmission of 70%, a 10-kpps Q-switched pulse train with 0.4-mJ monopulse energy and 8.2-ns pulse width was achieved, the optical conversion efficiency was around 15%, and the beam quality M2 factor was less than 1.2.

  9. Modeling normal tissue complication probability from repetitive computed tomography scans during fractionated high-dose-rate brachytherapy and external beam radiotherapy of the uterine cervix.

    Science.gov (United States)

    Dale, E; Hellebust, T P; Skjønsberg, A; Høgberg, T; Olsen, D R

    2000-07-01

    To calculate the normal tissue complication probability (NTCP) of late radiation effects on the rectum and bladder from repetitive CT scans during fractionated high-dose-rate brachytherapy (HDRB) and external beam radiotherapy (EBRT) of the uterine cervix and compare the NTCP with the clinical frequency of late effects. Fourteen patients with cancer of the uterine cervix (Stage IIb-IVa) underwent 3-6 (mean, 4.9) CT scans in treatment position during their course of HDRB using a ring applicator with an Iridium stepping source. The rectal and bladder walls were delineated on the treatment-planning system, such that a constant wall volume independent of organ filling was achieved. Dose-volume histograms (DVH) of the rectal and bladder walls were acquired. A method of summing multiple DVHs accounting for variable dose per fraction were applied to the DVHs of HDRB and EBRT together with the Lyman-Kutcher NTCP model fitted to clinical dose-volume tolerance data from recent studies. The D(mean) of the DVH from EBRT was close to the D(max) for both the rectum and bladder, confirming that the DVH from EBRT corresponded with homogeneous whole-organ irradiation. The NTCP of the rectum was 19.7% (13.5%, 25. 9%) (mean and 95% confidence interval), whereas the clinical frequency of late rectal sequelae (Grade 3-4, RTOG/EORTC) was 13% based on material from 200 patients. For the bladder the NTCP was 61. 9% (46.8%, 76.9%) as compared to the clinical frequency of Grade 3-4 late effects of 14%. If only 1 CT scan from HDRB was assumed available, the relative uncertainty (standard deviation or SD) of the NTCP value for an arbitrary patient was 20-30%, whereas 4 CT scans provided an uncertainty of 12-13%. The NTCP for the rectum was almost consistent with the clinical frequency of late effects, whereas the NTCP for bladder was too high. To obtain reliable (SD of 12-13%) NTCP values, 3-4 CT scans are needed during 5-7 fractions of HDRB treatments.

  10. Quasi-flat-top frequency-doubled Nd:glass laser for pumping of high-power Ti:sapphire amplifiers at a 0.1 Hz repetition rate.

    Science.gov (United States)

    Yanovsky, Victor; Kalinchenko, Galina; Rousseau, Pascal; Chvykov, Vladimir; Mourou, Gerard; Krushelnick, Karl

    2008-04-20

    A Nd:glass laser based on a novel design delivers up to 120 J energy pulses with a quasi-flat-top spatial profile at a 0.1 Hz repetition rate. The laser output is frequency-doubled with 50% efficiency and used to pump Ti:sapphire amplifiers. The developed design is perspective for use in the currently contemplated next step in ultra-high-intensity laser development.

  11. Stable mode-locked operation of a low repetition rate diode-pumped Nd:GdVO4 laser by combining quadratic polarisation switching and a semiconductor saturable absorber mirror.

    Science.gov (United States)

    Gerhard, Christoph; Druon, Frédéric; Georges, Patrick; Couderc, Vincent; Leproux, Philippe

    2006-08-07

    In this paper, we present the mode-locked operation of an ultra-robustly stabilised Nd:GdVO(4) laser with low repetition rate by combining quadratic polarisation switching and a semiconductor saturable absorber mirror (SESAM). In addition, similar experiment was also done with Nd:YVO(4). For Nd:GdVO(4), 16-ps pulses at 1063 nm with a repetition rate of 3.95 MHz have been obtained for a laser average output power of 1.4 W. For Nd:YVO(4), the performance was 2.5 W of average power for 15-ps pulses at 1064 nm. Moreover, we demonstrate experimentally the advantage of combining these two passive mode locking techniques in terms of stability ranges. We show how the dual mode-locking technique is crucial to obtain a stable and long-term mode-locked regime in our case of a diode-pumped Nd:GdVO(4) laser operating at low repetition rate and more generally how this dual mode-locking technique improves the stability range of the mode-locked operation giving more flexibility on different parameters.

  12. Task Repetition and Second Language Speech Processing

    Science.gov (United States)

    Lambert, Craig; Kormos, Judit; Minn, Danny

    2017-01-01

    This study examines the relationship between the repetition of oral monologue tasks and immediate gains in L2 fluency. It considers the effect of aural-oral task repetition on speech rate, frequency of clause-final and midclause filled pauses, and overt self-repairs across different task types and proficiency levels and relates these findings to…

  13. Ultrafast fiber lasers for homeland security

    Science.gov (United States)

    Okhotnikov, O. G.

    2005-09-01

    properties, technical challenges and methods to achieve stable short pulse operation with high average and peak powers from all-fiber devices. The important aspects of the mode-locked fiber lasers relevant to practical security systems are presented. Particularly, the effect of the amplified spontaneous emission (ASE) on the performance of the SESAMs in mode-locked fiber lasers has been investigated. We show that high level of ASE intensity typical for fiber lasers can saturate the absorption and degrade significantly the nonlinear response of the SESAM. We studied the effect of the absorber recovery time and demonstrated that the ion-irradiated SESAMs with fast nonlinear response are less affected by the ASE radiation and, consequently, in the presence of the high-power ASE they exhibit better self-starting capability compared with slow absorbers. The promising method for noise suppression based on the cavity-enhanced optical limiting is another important issue described. Optical limiting and saturable absorption are studied by placing two-photon absorption material and InGaAs quantum wells in a microcavity. We show that field enhancement that occurs in a cavity affects strongly the limiting threshold and dynamic range of roll-over in the nonlinear response. To achieve energy levels sufficient for different security systems, power scaling technique should be employed. We present a stretched-pulse double-clad ytterbium-doped fiber laser mode-locked with SESAM. High modulation depth in the nonlinear response of the SESAM allows for self-starting pulse operation without any dispersion compensation in the laser cavity. The chirp on the output pulses is highly linear and can be compensated for with dispersion in photonic bandgap fiber. The results is a fully self-starting source of 150-fs pulse with 63-nJ of energy at a 8-MHz repetition rate.

  14. Repetitive maladaptive behavior: beyond repetition compulsion.

    Science.gov (United States)

    Bowins, Brad

    2010-09-01

    Maladaptive behavior that repeats, typically known as repetition compulsion, is one of the primary reasons that people seek psychotherapy. However, even with psychotherapeutic advances it continues to be extremely difficult to treat. Despite wishes and efforts to the contrary repetition compulsion does not actually achieve mastery, as evidenced by the problem rarely resolving without therapeutic intervention, and the difficulty involved in producing treatment gains. A new framework is proposed, whereby such behavior is divided into behavior of non-traumatic origin and traumatic origin with some overlap occurring. Repetitive maladaptive behavior of non-traumatic origin arises from an evolutionary-based process whereby patterns of behavior frequently displayed by caregivers and compatible with a child's temperament are acquired and repeated. It has a familiarity and ego-syntonic aspect that strongly motivates the person to retain the behavior. Repetitive maladaptive behavior of traumatic origin is characterized by defensive dissociation of the cognitive and emotional components of trauma, making it very difficult for the person to integrate the experience. The strong resistance of repetitive maladaptive behavior to change is based on the influence of both types on personality, and also factors specific to each. Psychotherapy, although very challenging at the best of times, can achieve the mastery wished and strived for, with the aid of several suggestions provided.

  15. Studies on nanosecond 532nm and 355nm and ultrafast 515nm and 532nm laser cutting super-hard materials

    Science.gov (United States)

    Zhang, Jie; Tao, Sha; Wang, Brian; Zhao, Jay

    2017-02-01

    In this paper, micro-processing of three kinds of super-hard materials of poly-crystal diamond (PCD)/tungsten-carbide (WC), CVD-diamond and cubic boron nitride (CNB) has been systematically studied using nanosecond laser (532nm and 355nm), and ultrafast laser (532nm and 515nm). Our purpose is to investigate a full laser micro-cutting solution to achieve a ready-to-use cutting tool insert (CTI). The results show a clean cut with little burns and recasting at edge. The cutting speed of 2-10mm/min depending on thickness was obtained. The laser ablation process was also studied by varying laser parameters (wavelength, pulse width, pulse energy, repetition rate) and tool path to improve cutting speed. Also, studies on material removal efficiency (MRE) of PCD/WC with 355nm-ns and 515nm-fs laser as a function of laser fluence show that 355nm-ns laser is able to achieve higher MRE for PCD and WC. Thus, ultrafast laser is not necessarily used for superhard material cutting. Instead, post-polishing with ultrafast laser can be used to clean cutting surface and improve smoothness.

  16. Ultrafast magnetization dynamics

    OpenAIRE

    Woodford, S.

    2008-01-01

    This thesis addresses ultrafast magnetization dynamics from a theoretical perspective. The manipulation of magnetization using the inverse Faraday effect has been studied, as well as magnetic relaxation processes in quantum dots. The inverse Faraday effect – the generation of a magnetic field by nonresonant, circularly polarized light – offers the possibility to control and reverse magnetization on a timescale of a few hundred femtoseconds. This is important both for the technological advant...

  17. Ptychographic ultrafast pulse reconstruction

    CERN Document Server

    Spangenberg, D; Brügmann, M H; Feurer, T

    2014-01-01

    We demonstrate a new ultrafast pulse reconstruction modality which is somewhat reminiscent of frequency resolved optical gating but uses a modified setup and a conceptually different reconstruction algorithm that is derived from ptychography. Even though it is a second order correlation scheme it shows no time ambiguity. Moreover, the number of spectra to record is considerably smaller than in most other related schemes which, together with a robust algorithm, leads to extremely fast convergence of the reconstruction.

  18. Ultrafast Magnetization Dynamics

    OpenAIRE

    Woodford, S.

    2008-01-01

    This thesis addresses ultrafast magnetization dynamics from a theoretical perspective. The manipulation of magnetization using the inverse Faraday effect has been studied, as well as magnetic relaxation processes in quantum dots. The inverse Faraday effect – the generation of a magnetic field by nonresonant, circularly polarized light – offers the possibility to control and reverse magnetization on a timescale of a few hundred femtoseconds. This is important both for the technological advant...

  19. Scanning ultrafast electron microscopy.

    Science.gov (United States)

    Yang, Ding-Shyue; Mohammed, Omar F; Zewail, Ahmed H

    2010-08-24

    Progress has been made in the development of four-dimensional ultrafast electron microscopy, which enables space-time imaging of structural dynamics in the condensed phase. In ultrafast electron microscopy, the electrons are accelerated, typically to 200 keV, and the microscope operates in the transmission mode. Here, we report the development of scanning ultrafast electron microscopy using a field-emission-source configuration. Scanning of pulses is made in the single-electron mode, for which the pulse contains at most one or a few electrons, thus achieving imaging without the space-charge effect between electrons, and still in ten(s) of seconds. For imaging, the secondary electrons from surface structures are detected, as demonstrated here for material surfaces and biological specimens. By recording backscattered electrons, diffraction patterns from single crystals were also obtained. Scanning pulsed-electron microscopy with the acquired spatiotemporal resolutions, and its efficient heat-dissipation feature, is now poised to provide in situ 4D imaging and with environmental capability.

  20. Scanning ultrafast electron microscopy

    Science.gov (United States)

    Yang, Ding-Shyue; Mohammed, Omar F.; Zewail, Ahmed H.

    2010-01-01

    Progress has been made in the development of four-dimensional ultrafast electron microscopy, which enables space-time imaging of structural dynamics in the condensed phase. In ultrafast electron microscopy, the electrons are accelerated, typically to 200 keV, and the microscope operates in the transmission mode. Here, we report the development of scanning ultrafast electron microscopy using a field-emission-source configuration. Scanning of pulses is made in the single-electron mode, for which the pulse contains at most one or a few electrons, thus achieving imaging without the space-charge effect between electrons, and still in ten(s) of seconds. For imaging, the secondary electrons from surface structures are detected, as demonstrated here for material surfaces and biological specimens. By recording backscattered electrons, diffraction patterns from single crystals were also obtained. Scanning pulsed-electron microscopy with the acquired spatiotemporal resolutions, and its efficient heat-dissipation feature, is now poised to provide in situ 4D imaging and with environmental capability. PMID:20696933

  1. Grammatical Change through Repetition.

    Science.gov (United States)

    Arevart, Supot

    1989-01-01

    The effect of repetition on grammatical change in an unrehearsed talk is examined based on a case study of a single learner. It was found that repetition allows for accuracy monitoring in that errors committed in repeated contexts undergo correction. Implications for teaching are discussed. (23 references) (LB)

  2. The Negative Repetition Effect

    Science.gov (United States)

    Mulligan, Neil W.; Peterson, Daniel J.

    2013-01-01

    A fundamental property of human memory is that repetition enhances memory. Peterson and Mulligan (2012) recently documented a surprising "negative repetition effect," in which participants who studied a list of cue-target pairs twice recalled fewer targets than a group who studied the pairs only once. Words within a pair rhymed, and…

  3. Roles of repetitive sequences

    Energy Technology Data Exchange (ETDEWEB)

    Bell, G.I.

    1991-12-31

    The DNA of higher eukaryotes contains many repetitive sequences. The study of repetitive sequences is important, not only because many have important biological function, but also because they provide information on genome organization, evolution and dynamics. In this paper, I will first discuss some generic effects that repetitive sequences will have upon genome dynamics and evolution. In particular, it will be shown that repetitive sequences foster recombination among, and turnover of, the elements of a genome. I will then consider some examples of repetitive sequences, notably minisatellite sequences and telomere sequences as examples of tandem repeats, without and with respectively known function, and Alu sequences as an example of interspersed repeats. Some other examples will also be considered in less detail.

  4. Roles of repetitive sequences

    Energy Technology Data Exchange (ETDEWEB)

    Bell, G.I.

    1991-12-31

    The DNA of higher eukaryotes contains many repetitive sequences. The study of repetitive sequences is important, not only because many have important biological function, but also because they provide information on genome organization, evolution and dynamics. In this paper, I will first discuss some generic effects that repetitive sequences will have upon genome dynamics and evolution. In particular, it will be shown that repetitive sequences foster recombination among, and turnover of, the elements of a genome. I will then consider some examples of repetitive sequences, notably minisatellite sequences and telomere sequences as examples of tandem repeats, without and with respectively known function, and Alu sequences as an example of interspersed repeats. Some other examples will also be considered in less detail.

  5. Applications of Ultrafast Terahertz Pulses for Intra-ExcitonicSpectroscopy of Quasi-2D Electron-Hole Gases

    Energy Technology Data Exchange (ETDEWEB)

    Kaindl, Robert A.; Carnahan, Marc A.; Hagele, Daniel; Chemla, D.S.

    2006-09-02

    Excitons are of fundamental interest and of importance foropto-electronic applications of bulk and nano-structured semiconductors.This paper discusses the utilization of ultrafast terahertz (THz) pulsesfor the study of characteristic low-energy excitations of photoexcitedquasi 2D electron-hole (e-h) gases. Optical-pump THz-probe spectroscopyat 250-kHz repetition rate is employed to detect characteristic THzsignatures of excitons and unbound e-h pairs in GaAs quantum wells.Exciton and free-carrier densities are extracted from the data using atwo-component model. We report the detailed THz response and pairdensities for different photoexcitation energies resonant to heavy-holeexcitons, light-hole excitons, or the continuum of unbound pairs. Suchexperiments can provide quantitative insights into wavelength, time, andtemperature dependence of the low-energy response and composition ofoptically excited e-h gases in low-dimensionalsemiconductors.

  6. WS2 as a saturable absorber for ultrafast photonic applications of mode-locked and Q-switched lasers

    CERN Document Server

    Wu, Kan; Wang, Jun; Li, Xing; Chen, Jianping

    2014-01-01

    Two-dimensional (2D) nanomaterials, especially the transition metal sulfide semiconductors, have drawn great interests due to their potential applications in viable photonic and optoelectronic devices, such as saturable absorbers (SAs) and optical switches, etc. In this work, tungsten disulfide (WS2) based SA for ultrafast photonic applications was demonstrated. WS2 nanosheets were prepared using liquid-phase exfoliation method and embedded in polyvinyl alcohol (PVA) thin film for the practical usage. Saturable absorption was observed in the WS2-PVA SA at the telecommunication waveband near 1550 nm. By incorporating WS2-PVA SA into a fiber laser cavity, both stable mode locking operation and Q-switching operation were achieved. In the mode locking operation, the laser obtained femtosecond output pulse width and high spectral purity in the radio frequency spectrum. In the Q-switching operation, the laser had tunable repetition rate and output pulse energy of a few tens of nano joule. Our findings suggest that ...

  7. Ultrafast soliton mode-locked Zirconia-based Erbium-doped fiber laser with carbon nanotubes saturable absorber

    Science.gov (United States)

    Munira Markom, Arni; Wey Sen-Winson, Mah; Paul, Mukul Chandra; Wadi Harun, Sulaiman

    2017-06-01

    Ultrafast soliton mode-locked fiber laser was successfully generated in zirconia-yttria-alumina (Zr-Y-Al) co-doped erbium-doped fiber laser cavity using a single-wall carbon nanotubes (SWCNTs) as saturable absorber. The laser cavity was 11.5 m long with the group delay dispersion of -0.04 ps2. The laser generates soliton pulse train with a center wavelength and 3 dB bandwidth of 1564.2 nm and 3.8 nm, respectively at pump power of 92 mW. Meanwhile, the repetition rate, pulse duration and pulse energy were 17.7 MHz, 770 fs and 51.4 nJ.

  8. Advancing non-equilibrium ARPES experiments by a 9.3 eV coherent ultrafast photon source

    Energy Technology Data Exchange (ETDEWEB)

    Cilento, F., E-mail: federico.cilento@elettra.eu [Elettra – Sincrotrone Trieste S.C.p.A., Strada Statale 14, km 163.5, Trieste 34149 (Italy); C.N.R. – I.O.M., Strada Statale 14, km 163.5, Trieste 34149 (Italy); Crepaldi, A. [Elettra – Sincrotrone Trieste S.C.p.A., Strada Statale 14, km 163.5, Trieste 34149 (Italy); Manzoni, G.; Sterzi, A. [Universitá degli Studi di Trieste, Via A. Valerio 2, Trieste 34127 (Italy); Zacchigna, M. [C.N.R. – I.O.M., Strada Statale 14, km 163.5, Trieste 34149 (Italy); Bugnon, Ph.; Berger, H. [Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Parmigiani, F. [Elettra – Sincrotrone Trieste S.C.p.A., Strada Statale 14, km 163.5, Trieste 34149 (Italy); Universitá degli Studi di Trieste, Via A. Valerio 2, Trieste 34127 (Italy); International Faculty, University of Köln, 50937 Köln (Germany)

    2016-02-15

    The quest for investigating the non-equilibrium dynamics of the band structure of strongly-correlated materials over their entire Brillouin zone is a primary objective. However, the actual ultrafast UV light sources are not suitable for addressing several critical questions in the field. Here we report on a novel light source generating sub-250 fs, 9.3 eV photon energy light pulses at 250 kHz repetition rate, obtained via third-harmonic generation in Xe of frequency-doubled 50 fs laser pulses at 1.55 eV. By reporting the measured band dispersion of a Cu(111) crystal and the non-equilibrium dynamics of the Bi{sub 2}Se{sub 3} topological insulator, we prove that this source is suitable for studying the non-equilibrium dynamics of the entire Fermi surface of several complex materials, with high signal statistics and limited space-charge effect.

  9. 50-GHz repetition-rate, 280-fs pulse generation at 100-mW average power from a mode-locked laser diode externally compressed in a pedestal-free pulse compressor

    Science.gov (United States)

    Tamura, Kohichi R.; Sato, Kenji

    2002-07-01

    280-fs pedestal-free pulses are generated at average output powers exceeding 100 mW at a repetition rate of 50 GHz by compression of the output of a mode-locked laser diode (MLLD) by use of a pedestal-free pulse compressor (PFPC). The MLLD consists of a monolithically integrated chirped distributed Bragg reflector, a gain section, and an electroabsorption modulator. The PFPC is composed of a dispersion-flattened dispersion-decreasing fiber and a dispersion-flattened dispersion-imbalanced nonlinear optical loop mirror. Frequency modulation for linewidth broadening is used to overcome the power limitation imposed by stimulated Brillouin scattering.

  10. Repetition and Translation Shifts

    Directory of Open Access Journals (Sweden)

    Simon Zupan

    2006-06-01

    Full Text Available Repetition manifests itself in different ways and at different levels of the text. The first basic type of repetition involves complete recurrences; in which a particular textual feature repeats in its entirety. The second type involves partial recurrences; in which the second repetition of the same textual feature includes certain modifications to the first occurrence. In the article; repetitive patterns in Edgar Allan Poe’s short story “The Fall of the House of Usher” and its Slovene translation; “Konec Usherjeve hiše”; are compared. The author examines different kinds of repetitive patterns. Repetitions are compared at both the micro- and macrostructural levels. As detailed analyses have shown; considerable microstructural translation shifts occur in certain types of repetitive patterns. Since these are not only occasional; sporadic phenomena; but are of a relatively high frequency; they reduce the translated text’s potential for achieving some of the gothic effects. The macrostructural textual property particularly affected by these shifts is the narrator’s experience as described by the narrative; which suffers a reduction in intensity.

  11. Ultrafast gain recovery and modulation limitations in self-assembled quantum-dot devices

    DEFF Research Database (Denmark)

    Berg, Tommy Winther; Bischoff, Svend; Magnúsdóttir, Ingibjörg

    2001-01-01

    Measurements of ultrafast gain recovery in self-assembled InAs quantum-dot (QD) amplifiers are explained by a comprehensive numerical model. The on excited state carriers are found to act as a reservoir for the optically active ground state carriers resulting in an ultrafast gain recovery as long...... as the excited state is well populated. However, when pulses are injected into the device at high-repetition frequencies, the response of a on amplifier is found to be limited by the wetting-layer dynamics....

  12. Precision markedly attenuates repetitive lift capacity.

    Science.gov (United States)

    Collier, Brooke R; Holland, Laura; McGhee, Deirdre; Sampson, John A; Bell, Alison; Stapley, Paul J; Groeller, Herbert

    2014-01-01

    This study investigated the effect of precision on time to task failure in a repetitive whole-body manual handling task. Twelve participants were required to repetitively lift a box weighing 65% of their single repetition maximum to shoulder height using either precise or unconstrained box placement. Muscle activity, forces exerted at the ground, 2D body kinematics, box acceleration and psychophysical measures of performance were recorded until task failure was reached. With precision, time to task failure for repetitive lifting was reduced by 72%, whereas the duration taken to complete a single lift and anterior deltoid muscle activation increased by 39% and 25%, respectively. Yet, no significant difference was observed in ratings of perceived exertion or heart rate at task failure. In conclusion, our results suggest that when accuracy is a characteristic of a repetitive manual handling task, physical work capacity will decline markedly. The capacity to lift repetitively to shoulder height was reduced by 72% when increased accuracy was required to place a box upon a shelf. Lifting strategy and muscle activity were also modified, confirming practitioners should take into consideration movement precision when evaluating the demands of repetitive manual handling tasks.

  13. Diagnosis of high-repetition-rate pulse laser with pyroelectric detector%基于热释电探测器的重频脉冲激光诊断

    Institute of Scientific and Technical Information of China (English)

    张磊; 邵碧波; 杨鹏翎; 王振宝; 闫燕

    2011-01-01

    Based on the working principles of a pyroelectric detector, the transient response of the detector to the pulse laser is researched. The model of pyroelectric detector is built, and the response in practical application is simulated according to the parameters of materials and structures. Signal process circuits which are suitable for a high-repetition-rate pulse laser are designed. Finally', a number of the repetition frequency laser radiation experiments on the pyroelectric detector are carried out. The experiments on frequency response and pulse width of the detector are completed, and the feasibility of applying the pyroelectric detector to the energy measurement of the high-repetition-rate and narrow pulse laser is verified.%摘以热释电探测器的工作原理为基础,研究了热释电探测器对重频脉冲激光的瞬态响应特性,建立了热释电探测器对单脉冲激光辐照响应的工作模型,分析了影响探测器频率特性的主要因素。根据材料和结构参数模拟计算了实际应用中的响应模型。设计了信号检测电路并对其进行计算仿事。完成了探测器的频率响应、脉宽响应等实验测量,验证了热释电探测器用于高重频、窄脉冲激光能量测量的可行性。

  14. Perceptual Repetition Blindness Effects

    Science.gov (United States)

    Hochhaus, Larry; Johnston, James C.; Null, Cynthia H. (Technical Monitor)

    1994-01-01

    The phenomenon of repetition blindness (RB) may reveal a new limitation on human perceptual processing. Recently, however, researchers have attributed RB to post-perceptual processes such as memory retrieval and/or reporting biases. The standard rapid serial visual presentation (RSVP) paradigm used in most RB studies is, indeed, open to such objections. Here we investigate RB using a "single-frame" paradigm introduced by Johnston and Hale (1984) in which memory demands are minimal. Subjects made only a single judgement about whether one masked target word was the same or different than a post-target probe. Confidence ratings permitted use of signal detection methods to assess sensitivity and bias effects. In the critical condition for RB a precue of the post-target word was provided prior to the target stimulus (identity precue), so that the required judgement amounted to whether the target did or did not repeat the precue word. In control treatments, the precue was either an unrelated word or a dummy.

  15. Trialogue: Preparation, Repetition and...

    Science.gov (United States)

    Oberg, Antoinette; And Others

    1996-01-01

    This paper interrogates both curriculum theory and the limits and potentials of textual forms. A set of overlapping discourses (a trialogue) focuses on inquiring into the roles of obsession and repetition in creating deeply interpretive locations for understanding. (SM)

  16. Assessing the performance of ultrafast vector flow imaging in the neonatal heart via multiphysics modeling and in-vitro experiments.

    Science.gov (United States)

    Van Cauwenberge, Joris; Lovstakken, Lasse; Fadnes, Solveig; Rodriguez-Molares, Alfonso; Vierendeels, Jan; Segers, Patrick; Swillens, Abigail

    2016-08-01

    Ultrafast vector flow imaging would benefit newborn patients with congenital heart disorders, but still requires thorough validation before translation to clinical practice. This study investigates 2D speckle tracking of intraventricular blood flow in neonates when transmitting diverging waves at ultrafast frame rate. Computational and in-vitro studies enabled us to quantify the performance and identify artefacts related to the flow and the imaging sequence. First, synthetic ultrasound images of a neonate's left ventricular flow pattern were obtained with the ultrasound simulator Field II by propagating point scatterers according to 3D intraventricular flow fields obtained with computational fluid dynamics (CFD). Non-compounded diverging waves (opening angle of 60°) were transmitted at a pulse repetition frequency of 9 kHz. Speckle tracking of the B-mode data provided 2D flow estimates at 180 Hz, which were compared to the CFD flow field. We demonstrated that the diastolic inflow jet showed a strong bias in the lateral velocity estimates at the edges of the jet, as confirmed by additional in-vitro tests on a jet flow phantom. Further, speckle tracking performance was highly dependent on the cardiac phase with low flows (flow gradients and out-of-plane flow as deteriorating factors. Despite the observed artefacts, a good overall performance of 2D speckle tracking was obtained with a median magnitude underestimation and angular deviation of respectively 28% and 13.5° during systole, and 16% and 10.5° during diastole.

  17. Assessing the Performance of Ultrafast Vector Flow Imaging in the Neonatal Heart via Multiphysics Modeling and In Vitro Experiments.

    Science.gov (United States)

    Van Cauwenberge, Joris; Lovstakken, Lasse; Fadnes, Solveig; Rodriguez-Morales, Alfonso; Vierendeels, Jan; Segers, Patrick; Swillens, Abigail

    2016-11-01

    Ultrafast vector flow imaging would benefit newborn patients with congenital heart disorders, but still requires thorough validation before translation to clinical practice. This paper investigates 2-D speckle tracking (ST) of intraventricular blood flow in neonates when transmitting diverging waves at ultrafast frame rate. Computational and in vitro studies enabled us to quantify the performance and identify artifacts related to the flow and the imaging sequence. First, synthetic ultrasound images of a neonate's left ventricular flow pattern were obtained with the ultrasound simulator Field II by propagating point scatterers according to 3-D intraventricular flow fields obtained with computational fluid dynamics (CFD). Noncompounded diverging waves (opening angle of 60°) were transmitted at a pulse repetition frequency of 9 kHz. ST of the B-mode data provided 2-D flow estimates at 180 Hz, which were compared with the CFD flow field. We demonstrated that the diastolic inflow jet showed a strong bias in the lateral velocity estimates at the edges of the jet, as confirmed by additional in vitro tests on a jet flow phantom. Furthermore, ST performance was highly dependent on the cardiac phase with low flows (flow gradients, and out-of-plane flow as deteriorating factors. Despite the observed artifacts, a good overall performance of 2-D ST was obtained with a median magnitude underestimation and angular deviation of, respectively, 28% and 13.5° during systole and 16% and 10.5° during diastole.

  18. Ultrafast scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Botkin, D.A. [California Univ., Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States)

    1995-09-01

    I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.

  19. Pulsed UV-C disinfection of Escherichia coli with light-emitting diodes, emitted at various repetition rates and duty cycles.

    Science.gov (United States)

    Wengraitis, Stephen; McCubbin, Patrick; Wade, Mary Margaret; Biggs, Tracey D; Hall, Shane; Williams, Leslie I; Zulich, Alan W

    2013-01-01

    A 2010 study exposed Staphylococcus aureus to ultraviolet (UV) radiation and thermal heating from pulsed xenon flash lamps. The results suggested that disinfection could be caused not only by photochemical changes from UV radiation, but also by photophysical stress damage caused by the disturbance from incoming pulses. The study called for more research in this area. The recent advances in light-emitting diode (LED) technology include the development of LEDs that emit in narrow bands in the ultraviolet-C (UV-C) range (100-280 nm), which is highly effective for UV disinfection of organisms. Further, LEDs would use less power, and allow more flexibility than other sources of UV energy in that the user may select various pulse repetition frequencies (PRFs), pulse irradiances, pulse widths, duty cycles and types of waveform output (e.g. square waves, sine waves, triangular waves, etc.). Our study exposed Escherichia coli samples to square pulses of 272 nm radiation at various PRFs and duty cycles. A statistically significant correlation was found between E. coli's disinfection sensitivity and these parameters. Although our sample size was small, these results show promise and are worthy of further investigation. Comparisons are also made with pulsed disinfection by LEDs emitting at 365 nm, and pulsed disinfection by xenon flash lamps. © 2012 U.S. Government. Photochemistry and Photobiology © 2012 The American Society of Photobiology.

  20. EDITORIAL: Ultrafast magnetization processes

    Science.gov (United States)

    Hillebrands, Burkard

    2008-09-01

    This Cluster Issue of Journal of Physics D: Applied Physics is devoted to ultrafast magnetization processes. It reports on the scientific yield of the Priority Programme 1133 'Ultrafast Magnetization Processes' which was funded by the Deutsche Forschungsgemeinschaft in the period 2002-2008 in three successive two-year funding periods, supporting research of 17-18 groups in Germany. Now, at the end of this Priority Programme, the members feel that the achievements made in the course of the programme merit communication to the international scientific community in a concerted way. Therefore, each of the projects of the last funding period presents a key result in a published contribution to this Cluster Issue. The purpose of the funding by a Priority Programme is to advance knowledge in an emerging field of research through collaborative networked support over several locations. Priority Programmes are characterized by their enhanced quality of research through the use of new methods and forms of collaboration in emerging fields, by added value through interdisciplinary cooperation, and by networking. The aim of the Priority Programme 1133 'Ultrafast Magnetization Processes' may be well characterized by the call for projects in June 2001 after the programme was approved by the Deutsche Forschungsgemeinschaft: 'The aim of the priority programme is the achievement of a basic understanding of the temporal evolution of fast magnetization processes in magnetically ordered films, multilayers and micro-structured systems. The challenge lies in the advancement of the field of ultrafast magnetization processes into the regime of a few femtoseconds to nanoseconds, a topic not yet well explored. A general aim is to understand the fundamental mechanisms needed for applications in ultrafast magneto-electronic devices. The fundamental topic to be addressed is the response of the magnetization of small structures upon the application of pulsed magnetic fields, laser pulses or

  1. Experiment on damage in K9 glass due to repetition rate pulsed CO2 laser radiation%重频脉冲CO2激光损伤K9玻璃的实验

    Institute of Scientific and Technical Information of China (English)

    王玺; 卞进田; 李华; 聂劲松; 孙晓泉; 尹学忠; 雷鹏

    2013-01-01

      对脉冲CO2激光在不同重频模式下损伤K9玻璃进行了实验研究。采用输出能量为10 J,脉宽为90 ns,重复频率在100 Hz至300 Hz之间连续可调的脉冲CO2激光器,对K9玻璃样品进行了激光损伤实验,观察到两次不同重频条件下样品的损伤形貌。实验结果表明,重频越高,对样品的损伤程度就越严重;应力损伤成为K9玻璃激光损伤的最主要的原因,在重频强激光的辐照下,K9玻璃表面出现强烈的等离子体闪光,伴随明显的熔融气化破坏,并形成等离子体爆轰波。爆轰波对玻璃材料产生了严重的力学冲击作用,这种应力作用足以对K9玻璃造成毁灭性破坏。运用有限元分析对激光辐照K9玻璃的温度与应力分布进行仿真,其计算结果与实验基本吻合。%  In this paper, the experiment on damage in K9 glass induced by pulsed CO2 laser under different repetition rates was carried out, which had a pulse width of 90 ns. The laser pulse energy was 10 J and the repetition rate was kept within the range of 100 Hz to 300 Hz. The damage morphologies of two kind repetition rates after laser irradiation were characterized. The experimental results indicate that the effect of laser irradiation on samples can be affected considerably by the change of laser repetition rate, and the intensity of damage morphology on the sample increases with the laser repetition rate, and the damage in K9 glass induced by pulsed CO2 laser is dominated by stress. As a result, the plasma detonation wave induced by laser occured, the material was broken result from the melting and evaporation of K9 glass. It is shown that the plasma detonation wave affected stress damage considerably, and this mechanical effect almost destroyed K9 glass sample. A numerical simulation was performed to calculate temperature and stress distributions in K9 glass sample irradiated by pulsed CO2 laser using finite element method. The model

  2. Enhanced rate performance of flexible and stretchable linear supercapacitors based on polyaniline@Au@carbon nanotube with ultrafast axial electron transport

    Science.gov (United States)

    Xu, Jiang; Ding, Jianning; Zhou, Xiaoshuang; Zhang, Yang; Zhu, Wenjun; Liu, Zunfen; Ge, Shanhai; Yuan, Ningyi; Fang, Shaoli; Baughman, Ray H.

    2017-02-01

    Linear supercapacitors suffer a severe loss of capacity at high rates due to the trade-off of radial ion diffusion and axial electron transport. Optimizing axial conductivity of electrodes is a key to circumvent this trade-off. We report here the synthesis of Au nanograin decorated aligned multiwall carbon nanotube (CNT) sheets, followed by the incorporation of polyaniline (PANI). The embedded Au nanograins results in fast radial ion diffusion and enhance axial electron transport in the linear electrodes. The flexible linear solid supercapacitor fabricated by twisting two PANI@Au@CNT yarns exhibits an outstanding electrochemical performance with a total volumetric capacitance of ∼6 F cm-3 at scan rate up to 10 V s-1. Diameter of the electrode has little effect on volumetric capacitance even at high scan rates because of its high electrical conductivity. Highly stretchable supercapacitors with high rate performance and excellent cycling and stretching stability have been also fabricated using buckled linear electrodes made by wrapping PANI@Au@CNT sheet on elastic rubber fibers. The stretchable linear supercapacitor possesses a stable total volumetric capacitance of up to ∼0.2 F cm-3 at scan rate of 1 V s-1 and at 400% strain, and remarkable capacitance retention of about 95% over 1000 stretch/release cycles.

  3. Ultrafast Graphene Photonics and Optoelectronics

    Science.gov (United States)

    2017-04-14

    structures that consist of a sheet of graphene and a plasma substrate such as a metal, a doped semiconductor, or another graphene layer. Using these...AFRL-AFOSR-JP-TR-2017-0032 Ultrafast Graphene Photonics and Optoelectronics Kuang-Hsiung Wu National Chiao Tung University Final Report 04/14/2017...DATES COVERED (From - To) 18 Apr 2013 to 17 Apr 2016 4. TITLE AND SUBTITLE Ultrafast Graphene Photonics and Optoelectronics 5a.  CONTRACT NUMBER 5b

  4. Partially coherent ultrafast spectrography.

    Science.gov (United States)

    Bourassin-Bouchet, C; Couprie, M-E

    2015-03-06

    Modern ultrafast metrology relies on the postulate that the pulse to be measured is fully coherent, that is, that it can be completely described by its spectrum and spectral phase. However, synthesizing fully coherent pulses is not always possible in practice, especially in the domain of emerging ultrashort X-ray sources where temporal metrology is strongly needed. Here we demonstrate how frequency-resolved optical gating (FROG), the first and one of the most widespread techniques for pulse characterization, can be adapted to measure partially coherent pulses even down to the attosecond timescale. No modification of experimental apparatuses is required; only the processing of the measurement changes. To do so, we take our inspiration from other branches of physics where partial coherence is routinely dealt with, such as quantum optics and coherent diffractive imaging. This will have important and immediate applications, such as enabling the measurement of X-ray free-electron laser pulses despite timing jitter.

  5. Ultrafast photophysics of transition metal complexes.

    Science.gov (United States)

    Chergui, Majed

    2015-03-17

    The properties of transition metal complexes are interesting not only for their potential applications in solar energy conversion, OLEDs, molecular electronics, biology, photochemistry, etc. but also for their fascinating photophysical properties that call for a rethinking of fundamental concepts. With the advent of ultrafast spectroscopy over 25 years ago and, more particularly, with improvements in the past 10-15 years, a new area of study was opened that has led to insightful observations of the intramolecular relaxation processes such as internal conversion (IC), intersystem crossing (ISC), and intramolecular vibrational redistribution (IVR). Indeed, ultrafast optical spectroscopic tools, such as fluorescence up-conversion, show that in many cases, intramolecular relaxation processes can be extremely fast and even shorter than time scales of vibrations. In addition, more and more examples are appearing showing that ultrafast ISC rates do not scale with the magnitude of the metal spin-orbit coupling constant, that is, that there is no heavy-atom effect on ultrafast time scales. It appears that the structural dynamics of the system and the density of states play a crucial role therein. While optical spectroscopy delivers an insightful picture of electronic relaxation processes involving valence orbitals, the photophysics of metal complexes involves excitations that may be centered on the metal (called metal-centered or MC) or the ligand (called ligand-centered or LC) or involve a transition from one to the other or vice versa (called MLCT or LMCT). These excitations call for an element-specific probe of the photophysics, which is achieved by X-ray absorption spectroscopy. In this case, transitions from core orbitals to valence orbitals or higher allow probing the electronic structure changes induced by the optical excitation of the valence orbitals, while also delivering information about the geometrical rearrangement of the neighbor atoms around the atom of

  6. Error correction and fast detectors implemented by ultrafast neuronal plasticity.

    Science.gov (United States)

    Vardi, Roni; Marmari, Hagar; Kanter, Ido

    2014-04-01

    We experimentally show that the neuron functions as a precise time integrator, where the accumulated changes in neuronal response latencies, under complex and random stimulation patterns, are solely a function of a global quantity, the average time lag between stimulations. In contrast, momentary leaps in the neuronal response latency follow trends of consecutive stimulations, indicating ultrafast neuronal plasticity. On a circuit level, this ultrafast neuronal plasticity phenomenon implements error-correction mechanisms and fast detectors for misplaced stimulations. Additionally, at moderate (high) stimulation rates this phenomenon destabilizes (stabilizes) a periodic neuronal activity disrupted by misplaced stimulations.

  7. Ultrafast dynamics of correlated electrons

    Energy Technology Data Exchange (ETDEWEB)

    Rettig, Laurenz

    2012-07-09

    This work investigates the ultrafast electron dynamics in correlated, low-dimensional model systems using femtosecond time- and angle-resolved photoemission spectroscopy (trARPES) directly in the time domain. In such materials, the strong electron-electron (e-e) correlations or coupling to other degrees of freedom such as phonons within the complex many-body quantum system lead to new, emergent properties that are characterized by phase transitions into broken-symmetry ground states such as magnetic, superconducting or charge density wave (CDW) phases. The dynamical processes related to order like transient phase changes, collective excitations or the energy relaxation within the system allow deeper insight into the complex physics governing the emergence of the broken-symmetry state. In this work, several model systems for broken-symmetry ground states and for the dynamical charge balance at interfaces have been studied. In the quantum well state (QWS) model system Pb/Si(111), the charge transfer across the Pb/Si interface leads to an ultrafast energetic stabilization of occupied QWSs, which is the result of an increase of the electronic confinement to the metal film. In addition, a coherently excited surface phonon mode is observed. In antiferromagnetic (AFM) Fe pnictide compounds, a strong momentum-dependent asymmetry of electron and hole relaxation rates allows to separate the recovery dynamics of the AFM phase from electron-phonon (e-ph) relaxation. The strong modulation of the chemical potential by coherent phonon modes demonstrates the importance of e-ph coupling in these materials. However, the average e-ph coupling constant is found to be small. The investigation of the excited quasiparticle (QP) relaxation dynamics in the high-T{sub c}4 superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} reveals a striking momentum and fluence independence of the QP life times. In combination with the momentum-dependent density of excited QPs, this demonstrates the

  8. High-power, narrow-band, high-repetition-rate, 5.9 eV coherent light source using passive optical cavity for laser-based angle-resolved photoelectron spectroscopy.

    Science.gov (United States)

    Omachi, J; Yoshioka, K; Kuwata-Gonokami, M

    2012-10-08

    We demonstrate a scheme for efficient generation of a 5.9 eV coherent light source with an average power of 23 mW, 0.34 meV linewidth, and 73 MHz repetition rate from a Ti: sapphire picosecond mode-locked laser with an output power of 1 W. Second-harmonic light is generated in a passive optical cavity by a BiB(3)O(6) crystal with a conversion efficiency as high as 67%. By focusing the second-harmonic light transmitted from the cavity into a β-BaB(2)O(4) crystal, we obtain fourth-harmonic light at 5.9 eV. This light source offers stable operation for at least a week. We discuss the suitability of the laser light source for high-resolution angle-resolved photoelectron spectroscopy by comparing it with other sources (synchrotron radiation facilities and gas discharge lamp).

  9. 基于光导开关的重复频率闪光X光机%Repetitive rate flash X-ray generator with photo conductive semiconductor switches

    Institute of Scientific and Technical Information of China (English)

    马勋; 袁建强; 刘宏伟; 王凌云; 姜苹; 李洪涛

    2016-01-01

    A repetitive rate flash X-ray generator was developed recently to meet the demands in scientific research and in-dustrial area.A repetitive pulsed power supply was fabricated with GaAs photo conductive semiconductor switches and stacked Blumlein pulse forming networks to drive industrial X-ray diode,and a novel X-ray diode was proposed with spoked metal ceramic flashover cathode.The results show that 2 pulse burst X rays were generated under 1 kHz frame rate with novel cathode,and the two power pulses of diode and X-ray signals were identical.%采用砷化镓光导开关和Blumlein 型脉冲形成网络以级联的拓扑形式构建平顶输出功率源,驱动工业 X 光二极管产生 X 射线。提出了一种轮辐状金属-陶瓷沿面阴极,并与普通金属阴极工业 X 光二极管重复频率实验结果进行比较。研究表明:受限于阴极重复频率下的电流发射能力,普通金属阴极工业 X 光二极管难以实现1 kHz 重复频率,采用新型阴极二极管实现了1 kHz 重复频率2猝发脉冲 X 光输出,这两个脉冲的二极管功率、X 射线信号基本一致。

  10. Novel porcine repetitive elements

    Directory of Open Access Journals (Sweden)

    Nonneman Dan J

    2006-12-01

    Full Text Available Abstract Background Repetitive elements comprise ~45% of mammalian genomes and are increasingly known to impact genomic function by contributing to the genomic architecture, by direct regulation of gene expression and by affecting genomic size, diversity and evolution. The ubiquity and increasingly understood importance of repetitive elements contribute to the need to identify and annotate them. We set out to identify previously uncharacterized repetitive DNA in the porcine genome. Once found, we characterized the prevalence of these repeats in other mammals. Results We discovered 27 repetitive elements in 220 BACs covering 1% of the porcine genome (Comparative Vertebrate Sequencing Initiative; CVSI. These repeats varied in length from 55 to 1059 nucleotides. To estimate copy numbers, we went to an independent source of data, the BAC-end sequences (Wellcome Trust Sanger Institute, covering approximately 15% of the porcine genome. Copy numbers in BAC-ends were less than one hundred for 6 repeat elements, between 100 and 1000 for 16 and between 1,000 and 10,000 for 5. Several of the repeat elements were found in the bovine genome and we have identified two with orthologous sites, indicating that these elements were present in their common ancestor. None of the repeat elements were found in primate, rodent or dog genomes. We were unable to identify any of the replication machinery common to active transposable elements in these newly identified repeats. Conclusion The presence of both orthologous and non-orthologous sites indicates that some sites existed prior to speciation and some were generated later. The identification of low to moderate copy number repetitive DNA that is specific to artiodactyls will be critical in the assembly of livestock genomes and studies of comparative genomics.

  11. Ultrafast erbium-doped fiber laser mode-locked by a CVD-grown molybdenum disulfide (MoS2) saturable absorber.

    Science.gov (United States)

    Xia, Handing; Li, Heping; Lan, Changyong; Li, Chun; Zhang, Xiaoxia; Zhang, Shangjian; Liu, Yong

    2014-07-14

    We demonstrate an erbium-doped fiber laser passively mode-locked by a multilayer molybdenum disulfide (MoS(2)) saturable absorber (SA). The multilayer MoS(2) is prepared by the chemical vapor deposition (CVD) method and transferred onto the end-face of a fiber connector. Taking advantage of the excellent saturable absorption of the fabricated MoS(2)-based SA, stable mode locking is obtained at a pump threshold of 31 mW. Resultant output soliton pulses have central wavelength, spectral width, pulse duration, and repetition rate of 1568.9 nm, 2.6 nm, 1.28 ps, and 8.288 MHz, respectively. The experimental results show that multilayer MoS(2) is a promising material for ultrafast laser systems.

  12. 19th International Conference on Ultrafast Phenomena

    CERN Document Server

    Cundiff, Steven; Vivie-Riedle, Regina; Kuwata-Gonokami, Makoto; DiMauro, Louis

    2015-01-01

    This book presents the latest advances in ultrafast science, including both ultrafast optical technology and the study of ultrafast phenomena. It covers picosecond, femtosecond, and attosecond processes relevant to applications in physics, chemistry, biology, and engineering. Ultrafast technology has a profound impact in a wide range of applications, amongst them biomedical imaging, chemical dynamics, frequency standards, material processing, and ultrahigh-speed communications. This book summarizes the results presented at the 19th International Conference on Ultrafast Phenomena and provides an up-to-date view of this important and rapidly advancing field.

  13. Ultrafast nanoimprint lithography (Invited Paper)

    Science.gov (United States)

    Xia, Qiangfei; Chou, Stephen Y.

    2005-04-01

    Both ultrafast thermal and photocurable nanoimprint lithography (NIL) are studied and high fidelity transfers of nanopatterns from molds to resists have been achieved. In ultrafast thermal NIL, we use a single excimer laser pulse to melt a NIL resist polymer and imprint it using a fused silica mold. The entire imprint process, from melting the polymer to completion of the imprint, takes less than 200 ns. This technique, termed laser assisted nanoimprint lithography (LAN), has patterned nanostructures in various polymer films with high fidelity over the entire mold area. In LAN, the short laser pulse is absorbed primarily by the resist and the laser energy is minute, hence substrate heating and distortion are negligible. In ultrafast photocurable NIL, a flash lamp (pulse width 94 μs) is used to crosslink photo curable resists over a 4 in. wafer with high uniformity by a single pulse. The significant reduction of the heating of the substrate and mold will greatly benefit overlay alignment.

  14. Photodynamic therapy with ultrafast lasers

    Science.gov (United States)

    Wachter, Eric A.; Petersen, Mark G.; Dees, Craig

    1999-06-01

    The photodynamic properties of several photosensitive compounds have been evaluated in vivo using simultaneous two-photon excitation (TPE) and multi-photon excitation (MPE). TPE and MPE are effected using a mode-locked laser, such as the mode-locked titanium:sapphire or Nd:YLF laser, the near infrared output of which allows direct promotion of various non-resonant transitions. Such lasers are exceptionally well suited for non-linear activation of exogenous or endogenous PDT agents in biological systems due to their extremely short pulse width, modest pulse energy, and high repetition rate; these features combine to effect efficient PDT activation with minimal potential for non- specific biological damage, improved spatial localization of activation, and enhanced depth of penetration. Results in several murine models are presented.

  15. Multi-purpose two- and three-dimensional momentum imaging of charged particles for attosecond experiments at 1 kHz repetition rate.

    Science.gov (United States)

    Månsson, Erik P; Sorensen, Stacey L; Arnold, Cord L; Kroon, David; Guénot, Diego; Fordell, Thomas; Lépine, Franck; Johnsson, Per; L'Huillier, Anne; Gisselbrecht, Mathieu

    2014-12-01

    We report on the versatile design and operation of a two-sided spectrometer for the imaging of charged-particle momenta in two dimensions (2D) and three dimensions (3D). The benefits of 3D detection are to discern particles of different mass and to study correlations between fragments from multi-ionization processes, while 2D detectors are more efficient for single-ionization applications. Combining these detector types in one instrument allows us to detect positive and negative particles simultaneously and to reduce acquisition times by using the 2D detector at a higher ionization rate when the third dimension is not required. The combined access to electronic and nuclear dynamics available when both sides are used together is important for studying photoreactions in samples of increasing complexity. The possibilities and limitations of 3D momentum imaging of electrons or ions in the same spectrometer geometry are investigated analytically and three different modes of operation demonstrated experimentally, with infrared or extreme ultraviolet light and an atomic/molecular beam.

  16. 降低焦炉机车电器运行重复故障率%Reduce the Repetition Rate of Electric Operation of the Coke Oven Locomotive

    Institute of Scientific and Technical Information of China (English)

    姜玉怀

    2016-01-01

    the coking coal coking company of masteel outdated 1 # 4 # coke oven in order to real-ize the coal charging and coke pushing, blocking water coke dry quenching, quenching, screen coke and dust removal, etc. By the four major locomotive ( coke pusher, coal car, stop coke car, coke quenching car) , due to the special environment of the equipment operation ( mobile, high tempera-ture, dust, stop frequent restart, etc. ) , make the equipment in the process of running frequent fail-ure, not only increase the workload of maintenance, because maintenance delayed production at the same time, reduces the coke oven coke rate, thus the ascension of the whole economic benefit of mas-teel.%马钢煤焦化公司老区焦化1#-4#焦炉为了实现装煤、推焦、拦焦、干熄焦、水熄焦、筛焦、除尘等工艺。由四大机车(推焦车、装煤车、拦焦车、熄焦车)来实现,由于设备运行的特殊环境(移动、高温、多灰尘、停启动频繁等),使得设备在运行过程中故障频发,这不仅仅增加了维修工作量,同时因为检修耽误了生产,降低了焦炉的出焦率,从而影响了整个马钢的经济效益的提升。

  17. Topological insulator: Bi{sub 2}Se{sub 3}/polyvinyl alcohol film-assisted multi-wavelength ultrafast erbium-doped fiber laser

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Bo; Yao, Yong, E-mail: yaoyong@hit.edu.cn; Yang, Yan-Fu; Yuan, Yi-Jun; Wang, Rui-Lai [Department of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055 (China); Wang, Shu-Guang; Ren, Zhong-Hua [Department of Materials Science and Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055 (China); Yan, Bo [College of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450052 (China)

    2015-02-14

    We experimentally demonstrate a multi-wavelength ultrafast erbium-doped fiber laser incorporating a μm-scale topological insulator: Bi{sub 2}Se{sub 3}/Polyvinyl Alcohol film as both an excellent saturable absorber for mode-locking and a high-nonlinear medium to induce a giant third order optical nonlinear effect for mitigating the mode competition of erbium-doped fiber laser and stabilizing the multi-wavelength oscillation. By properly adjusting the pump power and the polarization state, the single-, dual-, triple-, four-wavelength mode-locking pulse could be stably initiated. For the four-wavelength operation, we obtain its pulse width of ∼22 ps and a fundamental repetition rate of 8.83 MHz. The fiber laser exhibits the maximum output power of 9.7 mW with the pulse energy of 1.1 nJ and peak power of 50 W at the pump power of 155 mW. Our study shows that the simple, stable, low-cost multi-wavelength ultrafast fiber laser could be applied in various potential fields, such as optical communication, biomedical research, and radar system.

  18. All-solid-state high-repetition-rate magnetic pulse compression generator%全固态高重复频率磁脉冲压缩发生器

    Institute of Scientific and Technical Information of China (English)

    张东东; 周媛; 李文峰; 许家雨; 王珏; 邵涛; 赵莹; 徐蓉

    2012-01-01

    The paper presents an all-solid-state high-repetition-rate pulse generator with adjustable output amplitude based on magnetic pulse compression (MPC) technique. The pulse compression network makes use of commercially available IGBTs switching a capacitor bank into a metglas transformer together with a voltage doubling circuit. The capacitor bank is charged to 500 V by a resonant LC charger, and also switched by a commercial diode. The output of the pulse generator is controlled by the gate voltage of the IGBTs. Pulses with a width of 70 ns can be generated with repetition rates up to 5 kHz. The amplitude can be controlled from 4 kV to 40 kV into a 500 Ω load. Equivalent circuits for the final operation stage of the compressor accounting for pre-pulse in magnetic switches are presented and analyzed, and the pre-pulse generation process of the MPC system is discussed. Simulation results show that, increasing the unsaturated inductance of the magnetic switch and reducing the load resistance enhance the pre-pulse peak. Thus to diminish the pre-pulse, a better ferrite core with higher permeability should be considered.%设计制作了全固态高重复频率磁脉冲压缩发生器,最高重复频率5 kHz,脉宽70 ns,通过调节初始储能电容上的电压可在500 Ω阻性负载上获得4~40 kV连续可调的输出电压.通过分析简化的磁压缩末级回路,分析了预脉冲产生的过程,得出了预脉冲的电压表达式,选取适当的磁芯相对磁导率,经过求解,得出在磁开关未饱和电感一定时预脉冲随负载阻值变化的曲线簇,从曲线中可以看出:随着负载的阻值的增大,预脉冲的峰值绝对值也增大;在负载恒定的情况下,增大磁开关未饱和电感的大小可以显著地减小负载两端预脉冲的峰值绝对值,这要求磁开关磁芯有更高的相对磁导率.

  19. Ultrafast Spectroscopy of Semiconductor Devices

    DEFF Research Database (Denmark)

    Borri, Paola; Langbein, Wolfgang; Hvam, Jørn Marcher

    1999-01-01

    In this work we present an experimental technique for investigating ultrafast carrier dynamics in semiconductor optical amplifiers at room temperature. These dynamics, influenced by carrier heating, spectral hole-burning and two-photon absorption, are very important for device applications...

  20. Ultrafast vibrations of gold nanorings

    DEFF Research Database (Denmark)

    Kelf, T; Tanaka, Y; Matsuda, O

    2011-01-01

    We investigate the vibrational modes of gold nanorings on a silica substrate with an ultrafast optical technique. By comparison with numerical simulations, we identify several resonances in the gigahertz range associated with axially symmetric deformations of the nanoring and substrate. We...

  1. Ultrafast optical spectroscopy of quasi one dimensional Ta{sub 2}NiSe{sub 5}

    Energy Technology Data Exchange (ETDEWEB)

    Mor, Selene; Herzog, Marc; Monney, Claude; Staehler, Julia; Wolf, Martin [Fritz-Haber-Institut der MPG, Dept. of Phys. Chem., Berlin (Germany)

    2015-07-01

    Ta2NiSe5 is a layered compound in which atomic chains are aligned in the layers, forming a quasi one dimensional crystal structure. At 328 K, the system shows a structural change, which is accompanied by an electronic phase transition from a semiconductor to an excitonic insulator, with an estimated energy gap of about few hundreds millielectronvolts. Our aim is to unveil the microscopic mechanisms underlying the phase transition in Ta{sub 2}NiSe{sub 5}. The system is excited with a femtosecond Ti:sapphire fundamental laser pulse and the mid-infrared (MIR) transient optical response is monitored by ultrafast optical spectroscopy. We observe a fast rise of transient reflectivity, which decays exponentially. This incoherent response is superimposed by a coherent phonon oscillation. A preliminary study with white light (WL) probe beam shows that low repetition rate is mandatory to study the response of the photoexcited system. The analysis unveils the presence of two phonons at 3 and 4 THz, that dominate at high (HT) and low (LT) temperature, respectively. We study the time evolution of the two phonons in the LT phase. We reveal a finite lifetime for the LT phase phonon, whose amplitude decays within few picoseconds, while the HT phase phonon amplitude remains almost constant. The picture is supported by temperature-dependent Raman spectroscopy.

  2. An ultrafast optics undergraduate advanced laboratory with a mode-locked fiber laser

    Science.gov (United States)

    Schaffer, Andrew; Fredrick, Connor; Hoyt, Chad; Jones, Jason

    2015-05-01

    We describe an ultrafast optics undergraduate advanced laboratory comprising a mode-locked erbium fiber laser, auto-correlation measurements, and an external, free-space parallel grating dispersion compensation apparatus. The simple design of the stretched pulse laser uses nonlinear polarization rotation mode-locking to produce pulses at a repetition rate of 55 MHz and average power of 5.5 mW. Interferometric and intensity auto-correlation measurements are made using a Michelson interferometer that takes advantage of the two-photon nonlinear response of a common silicon photodiode for the second order correlation between 1550 nm laser pulses. After a pre-amplifier and compression, pulse widths as narrow as 108 fs are measured at 17 mW average power. A detailed parts list includes previously owned and common components used by the telecommunications industry, which may decrease the cost of the lab to within reach of many undergraduate and graduate departments. We also describe progress toward a relatively low-cost optical frequency comb advanced laboratory. NSF EIR #1208930.

  3. Towards circularly polarized (sub-) femtosecond XUV pulses for ultrafast pump-probe experiments

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Juergen; Chew, Soo Hoon; Kranjec, Mihael; Kleineberg, Ulf [LMU Muenchen, Physik-Department, Garching (Germany); Guggenmos, Alexander; Hofstetter, Michael [MPQ fuer Quantenoptik, Garching (Germany)

    2012-07-01

    Circularly polarized (CP) XUV radiation has been demonstrated to be a useful probe for the experimental investigation of electronic effects in magnetic materials such as magnetic circular dichroism, spin-polarized photoemission, magneto-optical Kerr-effect and others. On the laboratory scale, High Harmonic (HH) gas jet sources which inherently provide coherent and ultrashort linearly polarized XUV pulses in the sub-fs domain, suitable to study ultrafast dynamics, have emerged. In our setup we aim at incorporating in-house fabricated broadband transmission multilayer phase shifters into a laser driven 10kHz repetition rate HH Source in the 50-70eV photon energy range. To our knowledge only little investigation on such polarizers intended for use in HH radiation has been made so far. We examine our phase shifters regarding tunability of energy range, phase retardation, transmission efficiency and spectral bandwidth. For this purpose we use a home-made XUV flat-field spectrometer and a multilayer mirror based polarization analyzer. Combining the expected CP pulses with our TOF-PEEM and ARPES spectrometer will pave the way towards time resolved measurements of exchange-coupled electron dynamics.

  4. Nd:YVO4 amplifier for ultrafast low-power lasers.

    Science.gov (United States)

    Agnesi, Antonio; Carrà, Luca; Piccoli, Riccardo; Pirzio, Federico; Reali, Giancarlo

    2012-09-01

    An Nd:YVO4 amplifier consisting of two modules end pumped at 808 nm at 30 W total absorbed power has been designed for efficient, diffraction-limited amplification of ultrafast pulses from low-power seeders. We investigated amplification with a 50 mW, 7 ps Nd:YVO4 oscillator, a 2 mW, 15 ps Yb fiber laser, and a 30 mW, 300 fs Nd:glass laser. Output power as high as 9.5 W with 8 ps pulses was achieved with the 250 MHz vanadate seeder, whereas the 20 MHz fiber laser was amplified to 6 W. The femtosecond seeder allowed extracting Fourier-limited 4 ps pulses at 7 W output power. To our knowledge, these are the shortest pulses from any Nd:YVO4 laser device with at least 7 W output power. This suggests a novel approach to exploit the gain bandwidth of vanadate amplifiers with high output power levels. Such amplifier technology promises to offer an interesting alternative to high-power thin disk oscillators at few picoseconds duration, as well as to regenerative amplifiers with low-repetition-rate fiber seeders.

  5. MIMICRY, DIFFERENCE AND REPETITION

    Directory of Open Access Journals (Sweden)

    Marcelo Mendes de Souza

    2008-07-01

    Full Text Available This article addresses Homi K. Bhabha’s concept of mimicry in a broader context, other than that of cultural studies and post-colonial studies, bringing together other concepts, such as that of Gilles Deleuze in Difference and repetition, among other texts, and other names, such as Silviano Santiago, Jorge Luís Borges, Franz Kafka and Giorgio Agamben. As a partial conclusion, the article intends to oppose Bhabha’s freudian-marxist view to Five propositions on Psychoanalysis (1973, Gilles Deleuze’s text about Psychoanalysis published right after his book The Anti-Oedipus.

  6. High Repetition Rate Thermometry System And Method

    KAUST Repository

    Chrystie, Robin

    2015-05-14

    A system and method for rapid thermometry using intrapulse spectroscopy can include a laser for propagating pulses of electromagnetic radiation to a region. Each of the pulses can be chirped. The pulses from the region can be detected. An intrapulse absorbance spectrum can be determined from the pulses. An instantaneous temperature of the region based on the intrapulse absorbance spectrum can be determined.

  7. Superheating in linear polymers studied by ultrafast nanocalorimetry.

    Science.gov (United States)

    Minakov, A A; Wurm, A; Schick, C

    2007-05-01

    To study phase transition kinetics on submillisecond time scale a sensitive ultrafast nanocalorimeter was constructed. Controlled ultrafast cooling, as well as heating, up to 10(6) K/s was attained. The method was applied for the measurements of the superheating phenomenon in a set of linear polymers: iPS, PBT, PET, and iPP. A power law relation between the superheating and the heating rate holds in the heating rate range 10(-2) - 10(4) K/s. A limiting superheating of about 10% of the melting temperature was observed at rates above 10(4) - 10(5) K/s. This limit depends on annealing conditions before sample melting. The observed superheating limit, as well as the power law, can be accounted for the internal stresses near the crystalline amorphous interface in semicrystalline polymers induced by heating, which are related to the thermal expansion gradients inherent in a semicrystalline material.

  8. A single-pulse shock tube coupled with high-repetition-rate time-of-flight mass spectrometry and gas chromatography for high-temperature gas-phase kinetics studies

    Science.gov (United States)

    Sela, P.; Shu, B.; Aghsaee, M.; Herzler, J.; Welz, O.; Fikri, M.; Schulz, C.

    2016-10-01

    Shock tubes are frequently used to investigate the kinetics of chemical reactions in the gas phase at high temperatures. Conventionally, two complementary arrangements are used where either time-resolved intermediate species measurements are conducted after the initiation of the reaction or where the product composition is determined after rapid initiation and quenching of the reaction through gas-dynamic processes. This paper presents a facility that combines both approaches to determine comprehensive information. A single-pulse shock tube is combined with high-sensitivity gas chromatography/mass spectrometry for product composition and concentration measurement as well as high-repetition-rate time-of-flight mass spectrometry for time-dependent intermediate concentration determination with 10 μs time resolution. Both methods can be applied simultaneously. The arrangement is validated with investigations of the well-documented thermal unimolecular decomposition of cyclohexene towards ethylene and 1,3-butadiene at temperatures between 1000 and 1500 K and pressures ranging from 0.8 to 2.4 bars. The comparison shows that the experimental results for both detections are in very good agreement with each other and with literature data.

  9. DOE-HEP Final Report for 2013-2016: Studies of plasma wakefields for high repetition-rate plasma collider, and Theoretical study of laser-plasma proton and ion acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Katsouleas, Thomas C. [Duke Univ., Durham, NC (United States). Dept. of Electrical and Computer Engineering; Sahai, Aakash A. [Imperial College, London (United Kingdom). Dept. of Physics

    2016-08-08

    There were two goals for this funded project: 1. Studies of plasma wakefields for high repetition-rate plasma collider, and 2. Theoretical study of laser-plasma proton and ion acceleration. For goal 1, an analytical model was developed to determine the ion-motion resulting from the interaction of non-linear “blow-out” wakefields excited by beam-plasma and laser-plasma interactions. This is key to understanding the state of the plasma at timescales of 1 picosecond to a few 10s of picoseconds behind the driver-energy pulse. More information can be found in the document. For goal 2, we analytically and computationally analyzed the longitudinal instabilities of the laser-plasma interactions at the critical layer. Specifically, the process of “Doppler-shifted Ponderomotive bunching” is significant to eliminate the very high-energy spread and understand the importance of chirping the laser pulse frequency. We intend to publish the results of the mixing process in 2-D. We intend to publish Chirp-induced transparency. More information can be found in the document.

  10. Laser radiation frequency conversion in carbon- and cluster-containing plasma plumes under conditions of single and two-color pumping by pulses with a 10-Hz repetition rate

    Science.gov (United States)

    Ganeev, R. A.

    2013-07-01

    This work reviews a series of investigations of different plasma plumes using single- and two-color laser systems that emit femtosecond pulses with a 10-Hz repetition rate. Results of investigation of the resonant enhancement of harmonics in tin plasma with the use of two types of pumps are analyzed, and it is shown that the tuning of the wavelengths of harmonics to ion-resonance levels plays an important role in increasing the conversion efficiency to high-order harmonics of the radiation to be converted. Investigations of different carbon-containing plasma media (carbon nanotubes, graphite, carbon aerogel, etc.) exhibit attractive properties of the nonlinear medium of this type for efficient generation of high-order harmonics. The results of the first experiments on the use of nanoparticles produced directly in the course of laser ablation of metals for increasing the efficiency of harmonics generated in this cluster-containing medium are analyzed. It is shown that new approaches realized in these investigations give hope that the nonlinear optical response of plasma media in the far-ultraviolet range can be further increased.

  11. Nonlinear Transient Dynamics of Photoexcited Silicon Nanoantenna for Ultrafast All-Optical Signal Processing

    CERN Document Server

    Baranov, Denis G; Milichko, Valentin A; Kudryashov, Sergey I; Krasnok, Alexander E; Belov, Pavel A

    2016-01-01

    Optically generated electron-hole plasma in high-index dielectric nanostructures was demonstrated as a means of tuning of their optical properties. However, until now an ultrafast operation regime of such plasma driven nanostructures has not been attained. Here, we perform pump-probe experiments with resonant silicon nanoparticles and report on dense optical plasma generation near the magnetic dipole resonance with ultrafast (about 2.5 ps) relaxation rate. Basing on experimental results, we develop an analytical model describing transient response of a nanocrystalline silicon nanoparticle to an intense laser pulse and show theoretically that plasma induced optical nonlinearity leads to ultrafast reconfiguration of the scattering power pattern. We demonstrate 100 fs switching to unidirectional scattering regime upon irradiation of the nanoparticle by an intense femtosecond pulse. Our work lays the foundation for developing ultracompact and ultrafast all-optical signal processing devices.

  12. Repetition in Waiting for Godot

    Institute of Scientific and Technical Information of China (English)

    李想; 魏妍

    2015-01-01

    Waiting for Godot is one of the most famous plays written by Samuel Barclay Beckett, and also is the founding work of“Theatre of the Absurd”. In the drama, repetitive phenomena shed light on the whole construction considerably. All the charac-ters were helpless and unthinking. Their dialogues were simple, nonsense and repetitive. Two scenes were cyclical. Repetition was used subtly in order to express the theme of the play, showing mental crisis after depravation of WWII.

  13. Active power filter for harmonic compensation using a digital dual-mode-structure repetitive control approach

    DEFF Research Database (Denmark)

    Zou, Zhixiang; Wang, Zheng; Cheng, Ming;

    2012-01-01

    This paper presents an digital dual-mode-structure repetitive control approach for the single-phase shunt active power filter (APF), which aims to enhance the tracking ability and eliminate arbitrary order harmonic. The proposed repetitive control scheme blends the characteristics of both odd......-harmonic repetitive control and even-harmonic repetitive control. Moreover, the convergence rate is faster than conventional repetitive controller. Additionally, the parameters have been designed and optimized for the dual-mode structure repetitive control to improve the performance of APF system. Experimental...... results on a laboratory setup are given to verify the proposed control scheme....

  14. Ultrafast photonic crystal optical switching

    Institute of Scientific and Technical Information of China (English)

    GONG Qi-huang; HU Xiao-yong

    2006-01-01

    Photonic crystal,a novel and artificial photonic material with periodic dielectric distribution,possesses photonic bandgap and can control the propagation states of photons.Photonic crystal has been considered to be a promising candidate for the future integrated photonic devices.The properties and the fabrication method of photonic crystal are expounded.The progresses of the study of ultrafast photonic crystal optical switching are discussed in detail.

  15. Ultrafast Dynamics of Energetic Materials

    Science.gov (United States)

    2014-01-23

    make tens of thousands of shocks on the same sample. As shown in Fig. 5, the original sample used a monolayer of nitrobenzoic acid ( NBA ). Also...there is a few micrometer thick polymer tamping layer. The NBA molecule is an EM simulant with a nitro group. We are focused on the nitro groups due...in Fig. 5d. We have 13 Fig.5. Sample construction for ultrafast shock vibrational spectroscopy. A monolayer of NBA is deposited onto a metal

  16. Ultrafast Imaging using Spectral Resonance Modulation.

    Science.gov (United States)

    Huang, Eric; Ma, Qian; Liu, Zhaowei

    2016-04-28

    CCD cameras are ubiquitous in research labs, industry, and hospitals for a huge variety of applications, but there are many dynamic processes in nature that unfold too quickly to be captured. Although tradeoffs can be made between exposure time, sensitivity, and area of interest, ultimately the speed limit of a CCD camera is constrained by the electronic readout rate of the sensors. One potential way to improve the imaging speed is with compressive sensing (CS), a technique that allows for a reduction in the number of measurements needed to record an image. However, most CS imaging methods require spatial light modulators (SLMs), which are subject to mechanical speed limitations. Here, we demonstrate an etalon array based SLM without any moving elements that is unconstrained by either mechanical or electronic speed limitations. This novel spectral resonance modulator (SRM) shows great potential in an ultrafast compressive single pixel camera.

  17. Repetitive energy transfer from an inductive energy store

    Energy Technology Data Exchange (ETDEWEB)

    Honig, E.M.

    1984-01-01

    The theoretical and experimental results of a research program aimed at finding practical ways to transfer energy repetitively from an inductive energy store to various loads are discussed. The objectives were to investigate and develop the high power opening switches and transfer circuits needed to enable high-repetition-rate operation of such systems, including a feasibility demonstration at a current level near 10 kA and a pulse repetition rate of 1-10 kpps with a 1-ohm load. The requirements of nonlinear, time-varying loads, such as the railgun electromagnetic launcher, were also addressed. Energy storage capability is needed for proper power conditioning in systems where the duty factor of the output pulse train is low. Inductive energy storage is attractive because it has both a high energy storage density and a fast discharge capability. By producing a pulse train with a peak power of 75 MW at a pulse repetition rate of 5 kpps in a one-ohm load system, this research program was the first to demonstrate fully-controlled, high-power, high-repetition-rate operation of an inductive energy storage and transfer system with survivable switches. Success was made possible by using triggered vacuum gap switches as repetitive, current-zero opening switches and developing several new repetitive transfer circuits using the counterpulse technique.

  18. Understanding maximal repetitions in strings

    CERN Document Server

    Crochemore, Maxime

    2008-01-01

    The cornerstone of any algorithm computing all repetitions in a string of length n in O(n) time is the fact that the number of runs (or maximal repetitions) is O(n). We give a simple proof of this result. As a consequence of our approach, the stronger result concerning the linearity of the sum of exponents of all runs follows easily.

  19. Basin-scale spatio-temporal variability and control of phytoplankton photosynthesis in the Baltic Sea: The first multiwavelength fast repetition rate fluorescence study operated on a ship-of-opportunity

    Science.gov (United States)

    Houliez, Emilie; Simis, Stefan; Nenonen, Susanna; Ylöstalo, Pasi; Seppälä, Jukka

    2017-05-01

    This study presents the results of the first field application of a flow-through multi-wavelength Fast Repetition Rate fluorometer (FRRF) equipped with two excitation channels (458 and 593 nm). This device aims to improve the measurement of mixed cyanobacteria and algae community's photosynthetic parameters and was designed to be easily incorporated into existing ferrybox systems. We present a spatiotemporal analysis of the maximum photochemical efficiency (Fv/Fm) and functional absorption cross section (σPSII) recorded from April to August 2014 on a ship-of-opportunity commuting twice per week between Helsinki (Finland) and Travemünde (Germany). Temporal variations of Fv/Fm and σPSII differed between areas of the Baltic Sea. However, even though the Baltic Sea is characterized by several physico-chemical gradients, no gradient was observed in Fv/Fm and σPSII spatial distribution suggesting complex interactions between biotic and abiotic controls. σPSII was sensitive to phytoplankton seasonal succession and thus differed according to the wavelength used to excite photosystems II (PSII) pigments. This was particularly true in summer when high σPSII(593) values were observed later and longer than high σPSII(458) values, reflecting the role of cyanobacteria in photosynthetic light uptake measured at community scale. In contrast, Fv/Fm variations were similar after excitation at 458 nm or 593 nm suggesting that the adjustment of Fv/Fm in response to environmental factors was similar for the different groups (algae vs. cyanobacteria) present within the phytoplankton community.

  20. On the repetitive operation of a self-switched transversely excited atmosphere CO2 laser

    Indian Academy of Sciences (India)

    Pallavi Raote; Gautam Patil; J Padma Nilaya; D J Biswas

    2010-11-01

    The repetition rate capability of self-switched transversely excited atmosphere (TEA) CO2 laser was studied for different gas flow configurations. For an optimized gas flow configuration, repetitive operation was achieved at a much smaller gas replenishment factor between two successive pulses when compared with repetitive systems energized by conventional pulsers.

  1. Ultrafast Hierarchical OTDM/WDM Network

    Directory of Open Access Journals (Sweden)

    Hideyuki Sotobayashi

    2003-12-01

    Full Text Available Ultrafast hierarchical OTDM/WDM network is proposed for the future core-network. We review its enabling technologies: C- and L-wavelength-band generation, OTDM-WDM mutual multiplexing format conversions, and ultrafast OTDM wavelengthband conversions.

  2. Avant-Garde Ultrafast Laser Writing

    Directory of Open Access Journals (Sweden)

    Kazansky P. G.

    2013-11-01

    Full Text Available Ultrafast laser processing of transparent materials reveals new phenomena. Reviewed, are recent demonstrations of 5D optical memory, vortex polarization and Airy beam converters employing self-assembled nanostructuring, ultrafast laser calligraphy and polarization writing control using pulses with tilted front.

  3. WE-B-210-02: The Advent of Ultrafast Imaging in Biomedical Ultrasound

    Energy Technology Data Exchange (ETDEWEB)

    Tanter, M. [Laboratoire Ondes et Acoustique (France)

    2015-06-15

    In the last fifteen years, the introduction of plane or diverging wave transmissions rather than line by line scanning focused beams has broken the conventional barriers of ultrasound imaging. By using such large field of view transmissions, the frame rate reaches the theoretical limit of physics dictated by the ultrasound speed and an ultrasonic map can be provided typically in tens of micro-seconds (several thousands of frames per second). Interestingly, this leap in frame rate is not only a technological breakthrough but it permits the advent of completely new ultrasound imaging modes, including shear wave elastography, electromechanical wave imaging, ultrafast doppler, ultrafast contrast imaging, and even functional ultrasound imaging of brain activity (fUltrasound) introducing Ultrasound as an emerging full-fledged neuroimaging modality. At ultrafast frame rates, it becomes possible to track in real time the transient vibrations – known as shear waves – propagating through organs. Such “human body seismology” provides quantitative maps of local tissue stiffness whose added value for diagnosis has been recently demonstrated in many fields of radiology (breast, prostate and liver cancer, cardiovascular imaging, …). Today, Supersonic Imagine company is commercializing the first clinical ultrafast ultrasound scanner, Aixplorer with real time Shear Wave Elastography. This is the first example of an ultrafast Ultrasound approach surpassing the research phase and now widely spread in the clinical medical ultrasound community with an installed base of more than 1000 Aixplorer systems in 54 countries worldwide. For blood flow imaging, ultrafast Doppler permits high-precision characterization of complex vascular and cardiac flows. It also gives ultrasound the ability to detect very subtle blood flow in very small vessels. In the brain, such ultrasensitive Doppler paves the way for fUltrasound (functional ultrasound imaging) of brain activity with unprecedented

  4. Ultrafast THz saturable absorption in doped semiconductors at room temperature

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Hoffmann, M. V.

    2011-01-01

    Ultrafast Phenomena XVII presents the latest advances in ultrafast science, including both ultrafast optical technology and the study of ultrafast phenomena. It covers picosecond, femtosecond and attosecond processes relevant to applications in physics, chemistry, biology, and engineering. Ultraf...... and provides an up-to-date view of this important and rapidly advancing field....

  5. Ultrafast Science Opportunities with Electron Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    DURR, HERMANN; Wang, X.J., ed.

    2016-04-28

    X-rays and electrons are two of the most fundamental probes of matter. When the Linac Coherent Light Source (LCLS), the world’s first x-ray free electron laser, began operation in 2009, it transformed ultrafast science with the ability to generate laser-like x-ray pulses from the manipulation of relativistic electron beams. This document describes a similar future transformation. In Transmission Electron Microscopy, ultrafast relativistic (MeV energy) electron pulses can achieve unsurpassed spatial and temporal resolution. Ultrafast temporal resolution will be the next frontier in electron microscopy and can ideally complement ultrafast x-ray science done with free electron lasers. This document describes the Grand Challenge science opportunities in chemistry, material science, physics and biology that arise from an MeV ultrafast electron diffraction & microscopy facility, especially when coupled with linac-based intense THz and X-ray pump capabilities.

  6. Emotional arousal enhances word repetition priming

    OpenAIRE

    Thomas, Laura A.; LaBar, Kevin S.

    2005-01-01

    Three experiments were conducted to determine if emotional content increases repetition priming magnitude. In the study phase of Experiment 1, participants rated high-arousing negative (taboo) words and neutral words for concreteness. In the test phase, they made lexical decision judgements for the studied words intermixed with novel words (half taboo, half neutral) and pseudowords. In Experiment 2, low-arousing negative (LAN) words were substituted for the taboo words, and in Experiment 3 al...

  7. Ultrafast vibrations of gold nanorings

    DEFF Research Database (Denmark)

    Kelf, T; Tanaka, Y; Matsuda, O;

    2011-01-01

    elucidate the corresponding mode shapes and find that the substrate plays an important role in determining the mode damping. This study demonstrates the need for a plasmonic nano-optics approach to understand the optical excitation and detection mechanisms for the vibrations of plasmonic nanostructures.......We investigate the vibrational modes of gold nanorings on a silica substrate with an ultrafast optical technique. By comparison with numerical simulations, we identify several resonances in the gigahertz range associated with axially symmetric deformations of the nanoring and substrate. We...

  8. FRB repetition and non-Poissonian statistics

    CERN Document Server

    Connor, Liam; Oppermann, Niels

    2016-01-01

    We discuss some of the claims that have been made regarding the statistics of fast radio bursts (FRBs). In an earlier paper \\citep{2015arXiv150505535C} we conjectured that flicker noise associated with FRB repetition could show up in non-cataclysmic neutron star emission models, like supergiant pulses. We show how the current limits of repetition would be significantly weakened if their repeat rate really were non-Poissonian and had a pink or red spectrum. Repetition and its statistics have implications for observing strategy, generally favouring shallow wide-field surveys, since in the non-repeating scenario survey depth is unimportant. We also discuss the statistics of the apparent latitudinal dependence of FRBs, and offer a simple method for calculating the significance of this effect. We provide a generalized Bayesian framework for addressing this problem, which allows for direct model comparison. It is shown how the evidence for a steep latitudinal gradient of the FRB rate is less strong than initially s...

  9. A broadband ultrafast transient absorption spectrometer covering the range from near-infrared (NIR) down to green.

    Science.gov (United States)

    Schmidhammer, Uli; Jeunesse, Pierre; Stresing, Gerhard; Mostafavi, Mehran

    2014-01-01

    We present a new development for pump-probe absorption spectroscopy that allows the simultaneous measurement from the green part of the visible spectrum (510 nm) over the whole near-infrared range to >1600 nm, corresponding to 0.77-2.40 eV. The system is based on a sub-picosecond supercontinuum generated in bulk material used as a broadband probe that is dispersed with a custom-made prism spectrometer and detected by an InGaAs array with extended sensitivity to the visible. Two versions, with and without probe referencing, are implemented for operation at laser repetition rates of a few hertz and kilohertz, respectively. After presentation of the optical configuration of the spectrometer, its performance is characterized and further illustrated on two time scales, with the ultrafast radiolysis of isopropanol induced by a picosecond electron pulse and with the instantaneous response of a BK7 plate to a femtosecond light pulse. The photophysics of the dye IR-140 is resolved from the femto- to picosecond regime. Stable and easy day-to-day routine use of the spectrometer also can be achieved in non-optical laboratory surroundings. For operation in a hazardous environment, the optical probe beams can be transported to the detector unit by optical fibers.

  10. LUX - a recirculating linac-based facility for ultrafast X-ray science

    Energy Technology Data Exchange (ETDEWEB)

    Corlett, J.N.; Barletta, W.A.; DeSantis, S.; Doolittle, L.; Fawley, W.M.; Heimann, P.; Leone, S.; Lidia, S.; Li, D.; Penn, G.; Ratti, A.; Reinsch, M.; Schoenlein, R.; Staples, J.; Stover, G.; Virostek, S.; Wan, W.; Wells, R.; Wilcox, R.; Wolski, A.; Wurtele, J.; Zholents, A.

    2004-06-29

    We present recent developments in design concepts for LUX - a source of ultra-short synchrotron radiation pulses based on a recirculating superconducting linac. The source produces high-flux x-ray pulses with duration of 100 fs or less at a 10 kHz repetition rate, optimized for the study of ultra-fast dynamics across many fields of science [1]. Cascaded harmonic generation in free-electron lasers (FEL's) produces coherent radiation in the VUV-soft x-ray regime, and a specialized technique is used to compress spontaneous emission for ultra-short-pulse photon production in the 1-10 keV range. High-brightness electron bunches of 2-3 mm-mrad emittance at 1 nC charge in 30 ps duration are produced in an rf photocathode gun and compressed to 3 ps duration following an injector linac, and recirculated three times through a 1 GeV main linac. In each return path, independently tunable harmonic cascades are inserted to produce seeded FEL radiation in selected photon energy ranges from approximately 20 eV with a single stage of harmonic generation, to 1 keV with a four-stage cascade. The lattice is designed to minimize emittance growth from effects such as coherent synchrotron radiation (CSR), and resistive wall wakefields. Timing jitter between pump lasers and x-ray pulses is minimized by use of a stable optical master oscillator, distributing timing signals over actively stabilized fiber-optic, phase-locking all lasers to the master oscillator, and generating all rf signals from the master oscillator. We describe technical developments including techniques for minimizing power dissipation in a high repetition rate rf photocathode gun, beam dynamics in two injector configurations, independently tunable beamlines for VUV and soft x-ray production by cascaded harmonic generation, a fast kicker design, timing systems for providing synchronization between experimental pump lasers and the x-ray pulse, and beamline design for maintaining nm-scale density modulation.

  11. Ultrafast optomechanical pulse picking

    Science.gov (United States)

    Lilienfein, Nikolai; Holzberger, Simon; Pupeza, Ioachim

    2017-01-01

    State-of-the-art optical switches for coupling pulses into and/or out of resonators are based on either the electro-optic or the acousto-optic effect in transmissive elements. In high-power applications, the damage threshold and other nonlinear and thermal effects in these elements impede further improvements in pulse energy, duration, and average power. We propose a new optomechanical switching concept which is based solely on reflective elements and is suitable for switching times down to the ten-nanosecond range. To this end, an isolated section of a beam path is moved in a system comprising mirrors rotating at a high angular velocity and stationary imaging mirrors, without affecting the propagation of the beam thereafter. We discuss three variants of the concept and exemplify practical parameters for its application in regenerative amplifiers and stack-and-dump enhancement cavities. We find that optomechanical pulse picking has the potential to achieve switching rates of up to a few tens of kilohertz while supporting pulse energies of up to several joules.

  12. Repetition in English Political Public Speaking

    Institute of Scientific and Technical Information of China (English)

    李红梅

    2010-01-01

    Repetition is frequently used in English political public speaking to make it easy to be remembered and powerful to move the feelings of the public. This paper is intended to analyze the functions of repetition and different levels of repetition to highlight the significance of repetition in English political public speaking and the ability of using it in practice.

  13. Four-dimensional ultrafast electron microscopy.

    Science.gov (United States)

    Lobastov, Vladimir A; Srinivasan, Ramesh; Zewail, Ahmed H

    2005-05-17

    Electron microscopy is arguably the most powerful tool for spatial imaging of structures. As such, 2D and 3D microscopies provide static structures with subnanometer and increasingly with angstrom-scale spatial resolution. Here we report the development of 4D ultrafast electron microscopy, whose capability imparts another dimension to imaging in general and to dynamics in particular. We demonstrate its versatility by recording images and diffraction patterns of crystalline and amorphous materials and images of biological cells. The electron packets, which were generated with femtosecond laser pulses, have a de Broglie wavelength of 0.0335 angstroms at 120 keV and have as low as one electron per pulse. With such few particles, doses of few electrons per square ångstrom, and ultrafast temporal duration, the long sought after but hitherto unrealized quest for ultrafast electron microscopy has been realized. Ultrafast electron microscopy should have an impact on all areas of microscopy, including biological imaging.

  14. Ultrafast pulse generation with black phosphorus

    CERN Document Server

    Li, Diao; Karvonen, Lasse; Ye, Guojun; Lipsanen, Harri; Chen, Xianhui; Sun, Zhipei

    2015-01-01

    Black phosphorus has been recently rediscovered as a new and interesting two-dimensional material due to its unique electronic and optical properties. Here, we study the linear and nonlinear optical properties of black phosphorus thin films, indicating that both linear and nonlinear optical properties are anisotropic and can be tuned by the film thickness. Then we employ the nonlinear optical property of black phosphorus for ultrafast (pulse duration down to ~786 fs in mode-locking) and large-energy (pulse energy up to >18 nJ in Q-switching) pulse generation in fiber lasers at the near-infrared telecommunication band ~1.5 {\\mu}m. Our results underscore relatively large optical nonlinearity in black phosphorus and its prospective for ultrafast pulse generation, paving the way to black phosphorus based nonlinear and ultrafast photonics applications (e.g., ultrafast all-optical switches/modulators, frequency converters etc.).

  15. Ultrafast THz Saturable Absorption in Doped Semiconductors

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Hoffmann, Matthias C.

    2011-01-01

    We demonstrate ultrafast THz saturable absorption in n-doped semiconductors by nonlinear THz time-domain spectroscopy. This effect is caused by the semiconductor conductivity modulation due to electron heating and satellite-valley scattering in strong THz fields.......We demonstrate ultrafast THz saturable absorption in n-doped semiconductors by nonlinear THz time-domain spectroscopy. This effect is caused by the semiconductor conductivity modulation due to electron heating and satellite-valley scattering in strong THz fields....

  16. Unlocking the Constraints of Cyanobacterial Productivity: Acclimations Enabling Ultrafast Growth

    Energy Technology Data Exchange (ETDEWEB)

    Bernstein, Hans C.; McClure, Ryan S.; Hill, Eric A.; Markillie, Lye Meng; Chrisler, William B.; Romine, Margie F.; McDermott, Jason E.; Posewitz, Matthew C.; Bryant, Donald A.; Konopka, Allan E.; Fredrickson, James K.; Beliaev, Alexander S.

    2016-07-26

    ABSTRACT

    Harnessing the metabolic potential of photosynthetic microbes for next-generation biotechnology objectives requires detailed scientific understanding of the physiological constraints and regulatory controls affecting carbon partitioning between biomass, metabolite storage pools, and bioproduct synthesis. We dissected the cellular mechanisms underlying the remarkable physiological robustness of the euryhaline unicellular cyanobacteriumSynechococcussp. strain PCC 7002 (Synechococcus7002) and identify key mechanisms that allow cyanobacteria to achieve unprecedented photoautotrophic productivities (~2.5-h doubling time). Ultrafast growth ofSynechococcus7002 was supported by high rates of photosynthetic electron transfer and linked to significantly elevated transcription of precursor biosynthesis and protein translation machinery. Notably, no growth or photosynthesis inhibition signatures were observed under any of the tested experimental conditions. Finally, the ultrafast growth inSynechococcus7002 was also linked to a 300% expansion of average cell volume. We hypothesize that this cellular adaptation is required at high irradiances to support higher cell division rates and reduce deleterious effects, corresponding to high light, through increased carbon and reductant sequestration.

    IMPORTANCEEfficient coupling between photosynthesis and productivity is central to the development of biotechnology based on solar energy. Therefore, understanding the factors constraining maximum rates of carbon processing is necessary to identify regulatory mechanisms and devise strategies to overcome productivity constraints. Here, we interrogate the molecular mechanisms that operate at a systems level to allow cyanobacteria to achieve ultrafast growth. This was done by considering growth and photosynthetic kinetics with global transcription patterns. We have delineated

  17. Varianish: Jamming with Pattern Repetition

    Directory of Open Access Journals (Sweden)

    Jort Band

    2014-10-01

    Full Text Available In music, patterns and pattern repetition are often regarded as a machine-like task, indeed often delegated to drum Machines and sequencers. Nevertheless, human players add subtle differences and variations to repeated patterns that are musically interesting and often unique. Especially when looking at minimal music, pattern repetitions create hypnotic effects and the human mind blends out the actual pattern to focus on variation and tiny differences over time. Varianish is a musical instrument that aims at turning this phenomenon into a new musical experience for musician and audience: Musical pattern repetitions are found in live music and Varianish generates additional (musical output accordingly that adds substantially to the overall musical expression. Apart from the theory behind the pattern finding and matching and the conceptual design, a demonstrator implementation of Varianish is presented and evaluated.

  18. Ultrafast spectroscopy of quantum dots

    CERN Document Server

    Foo, E

    2001-01-01

    exchange-correlation interactions among the confined carriers inside the dots are suggested to be responsible. A density functional calculation for BGR of the ground state transition shows good agreement with our experimental results, especially in the high dot occupancy regime. Many-particle state scattering gives rise to large homogeneous spectral broadening of the PL peaks, from which an intradot relaxation time approx 300 fs is estimated. This observation supports the results obtained by direct excitation of carriers within the QDs. Femtosecond time-resolved photoluminescence measured by frequency up-conversion has been used to investigate carrier dynamics in InAs/GaAs self-assembled quantum dots (QDs). Our results reveal ultrafast carrier relaxation and sequential state filling. Carrier relaxation is proposed to occur by Auger-type processes, and the sequential state filling suggests that intradot relaxation is much faster than carrier capture from the InAs wetting layer. Measurements obtained by direct ...

  19. Ultrafast infrared spectroscopy in photosynthesis.

    Science.gov (United States)

    Di Donato, Mariangela; Groot, Marie Louise

    2015-01-01

    In recent years visible pump/mid-infrared (IR) probe spectroscopy has established itself as a key technology to unravel structure-function relationships underlying the photo-dynamics of complex molecular systems. In this contribution we review the most important applications of mid-infrared absorption difference spectroscopy with sub-picosecond time-resolution to photosynthetic complexes. Considering several examples, such as energy transfer in photosynthetic antennas and electron transfer in reaction centers and even more intact structures, we show that the acquisition of ultrafast time resolved mid-IR spectra has led to new insights into the photo-dynamics of the considered systems and allows establishing a direct link between dynamics and structure, further strengthened by the possibility of investigating the protein response signal to the energy or electron transfer processes. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems.

  20. Ultrafast measurements of optical spectral coherence by single-shot time-stretch interferometry

    Science.gov (United States)

    Xu, Yiqing; Wei, Xiaoming; Ren, Zhibo; Wong, Kenneth K. Y.; Tsia, Kevin K.

    2016-06-01

    The palette of laser technology has significantly been enriched by the innovations in ultrafast optical pulse generation. Our knowledge of the complex pulse dynamics, which is often highly nonlinear and stochastic in nature, is however limited by the scarcity of technologies that can measure fast variation/fluctuation of the spectral phase (or coherence) and amplitude in real-time, continuously. To achieve this goal, we demonstrate ultrafast interferometry enabled by optical time-stretch for real- time spectral coherence characterization with microsecond-resolution. Accessing the single-shot interferograms continuously, it further reveals the degree of second-order coherence, defined by the cross-spectral density function, at high speed-a capability absent in any existing spectroscopic measurement tools. As the technique can simultaneously measure both the high-speed variations of spectrally resolved coherence and intensity, time-stretch interferometry could create a new arena for ultrafast pulse characterization, especially favorable for probing and understanding the non-repetitive or stochastic dynamics in real-time.

  1. REPETITIVE CLUSTER-TILTED ALGEBRAS

    Institute of Scientific and Technical Information of China (English)

    Zhang Shunhua; Zhang Yuehui

    2012-01-01

    Let H be a finite-dimensional hereditary algebra over an algebraically closed field k and CFm be the repetitive cluster category of H with m ≥ 1.We investigate the properties of cluster tilting objects in CFm and the structure of repetitive clustertilted algebras.Moreover,we generalize Theorem 4.2 in [12](Buan A,Marsh R,Reiten I.Cluster-tilted algebra,Trans.Amer.Math.Soc.,359(1)(2007),323-332.) to the situation of CFm,and prove that the tilting graph KCFm of CFm is connected.

  2. Ultrafast circular polarization oscillations in spin-polarized vertical-cavity surface-emitting laser devices

    Science.gov (United States)

    Gerhardt, N. C.; Li, M.; Jaehme, H.; Soldat, H.; Hofmann, M. R.; Ackemann, T.

    2010-02-01

    Spin-polarized lasers offer new encouraging possibilities for future devices. We investigate the polarization dynamics of electrically pumped vertical-cavity surface-emitting lasers after additional spin injection at room temperature. We find that the circular polarization degree exhibits faster dynamics than the emitted light. Moreover the experimental results demonstrate a strongly damped ultrafast circular polarization oscillation due to spin injection with an oscillation frequency of approximately 11GHz depending on the birefringence in the VCSEL device. We compare our experimental results with theoretical calculations based on rate-equations. This allows us to predict undamped long persisting ultrafast polarization oscillations, which reveal the potential of spin-VCSELs for ultrafast modulation applications.

  3. Ultrafast spontaneous emission modulation of graphene quantum dots interacting with Ag nanoparticles in solution

    Science.gov (United States)

    Zhao, Jianwei; Lu, Jian; Wang, Liang; Tian, Linfan; Deng, Xingxia; Tian, Lijun; Pan, Dengyu; Wang, Zhongyang

    2016-07-01

    We investigated the strong interaction between graphene quantum dots and silver nanoparticles in solution using time-resolved photoluminescence techniques. In solution, the silver nanoparticles are surrounded by graphene quantum dots and interacted with graphene quantum dots through exciton-plasmon coupling. An ultrafast spontaneous emission process (lifetime 27 ps) was observed in such a mixed solution. This ultrafast lifetime corresponds to the emission rate exceeding 35 GHz, with the purcell enhancement by a factor of ˜12. These experiment results pave the way for the realization of future high speed light sources applications.

  4. Ultrafast demagnetizing fields from first principles

    Science.gov (United States)

    Simoni, Jacopo; Stamenova, Maria; Sanvito, Stefano

    2017-01-01

    We examine the ultrafast demagnetization process of iron-based materials, namely, Fe6 clusters and bulk bcc Fe, with time-dependent spin-density functional theory (TDSDFT). The magnetization continuity equation is reformulated and the torque due to the spin-current divergence is written in terms of an effective time-dependent kinetic magnetic field, an object already introduced in the literature. Its time evolution, as extracted from the TDSDFT simulations, is identified as one of the main sources of the local out-of-equilibrium spin dynamics and it plays a major role in the demagnetization process in combination with the spin orbit interaction. Such demagnetization is particularly strong in hot spots where the kinetic torque is maximized. Finally, we find the rate of demagnetization in Fe6 to be strongly dependent on the direction of polarization of the exciting electric field and this can be linked to the out-of-equilibrium distribution of the kinetic field in two comparative cases.

  5. Repetitive elements in parasitic protozoa

    Directory of Open Access Journals (Sweden)

    Clayton Christine

    2010-05-01

    Full Text Available Abstract A recent paper published in BMC Genomics suggests that retrotransposition may be active in the human gut parasite Entamoeba histolytica. This adds to our knowledge of the various types of repetitive elements in parasitic protists and the potential influence of such elements on pathogenicity. See research article http://www.biomedcentral.com/1471-2164/11/321

  6. Ultrafast electrooptic dual-comb interferometry

    CERN Document Server

    Duran, Vicente; Torres-Company, Victor

    2015-01-01

    The femtosecond laser frequency comb has enabled the 21st century revolution in optical synthesis and metrology. A particularly compelling technique that relies on the broadband coherence of two laser frequency combs is dual-comb interferometry. This method is rapidly advancing the field of optical spectroscopy and empowering new applications, from nonlinear microscopy to laser ranging. Up to now, most dual-comb interferometers were based on modelocked lasers, whose repetition rates have restricted the measurement speed to ~ kHz. Here we demonstrate a novel dual-comb interferometer that is based on electrooptic frequency comb technology and measures consecutive complex spectra at a record-high refresh rate of 25 MHz. These results pave the way for novel scientific and metrology applications of frequency comb generators beyond the realm of molecular spectroscopy, where the measurement of ultrabroadband waveforms is of paramount relevance.

  7. Ultrafast laser spectroscopy in complex solid state materials

    Energy Technology Data Exchange (ETDEWEB)

    Li, Tianqi [Iowa State Univ., Ames, IA (United States)

    2014-12-01

    This thesis summarizes my work on applying the ultrafast laser spectroscopy to the complex solid state materials. It shows that the ultrafast laser pulse can coherently control the material properties in the femtosecond time scale. And the ultrafast laser spectroscopy can be employed as a dynamical method for revealing the fundamental physical problems in the complex material systems.

  8. Repetition suppression and repetition priming are processing outcomes.

    Science.gov (United States)

    Wig, Gagan S

    2012-01-01

    Abstract There is considerable evidence that repetition suppression (RS) is a cortical signature of previous exposure to the environment. In many instances RS in specific brain regions is accompanied by improvements in specific behavioral measures; both observations are outcomes of repeated processing. In understanding the mechanism by which brain changes give rise to behavioral changes, it is important to consider what aspect of the environment a given brain area or set of areas processes, and how this might be expressed behaviorally.

  9. Frequency modulated few-cycle optical pulse trains induced controllable ultrafast coherent population oscillations in three-level atomic systems

    CERN Document Server

    Kumar, Parvendra

    2012-01-01

    We report a study on the ultrafast coherent population oscillations (UCPO) in sodium atoms induced by the frequency modulated few-cycle optical pulse trains. The phenomenon of UCPO is investigated by numerically solving the appropriate density matrix equations beyond the rotating wave approximation. We demonstrate that the quantum state of the atoms and the frequency of UCPO may be controlled by controlling the number of pulses in the pulse trains and the pulse repetition time respectively. Moreover, the robustness of population transfer against the variation of laser pulse parameters is also investigated. The proposed scheme may be useful for the creation of atomic beam in selected quantum state for desired time duration and may have potential applications in ultrafast optical switching.

  10. Hot Rolled Strip Re-reddening Temperature Changing Law during Ultra-fast Cooling

    Institute of Scientific and Technical Information of China (English)

    Lian-yun JIANG; Chun-jiang ZHAO; Jian-hui SHI; Guo YUAN; Xue-qiang WANG; Qing-xue HUANG

    2015-01-01

    Temperature deviation between surface and the center of hot rolled strip is formed during ultra-fast cooling (UFC). Surface temperature would rise when temperature deviation goes up to an extent, and strip re-reddening phenomenon will appear. Strip re-reddening affects the stability of strip microstructure, property and temperature control precision. Thus, it is necessary to conduct research on re-reddening temperature changing law to improve strip property and temperature control precision. Strip temperature trends for various strip thicknesses and ultra-fast cooling rates were obtained by numerical calculation method. Re-reddening temperature, temperature deviation between surface and center, and boundary layer position changing law were obtained. By comparison, some conclusions were obtained: UFC re-reddening temperature and laminar cooling (LC) re-reddening temperature were linear to ultra-fast cooling rate respectively. Ultra-fast cooling rate affected UFC re-reddening temperature greatly, but it had little effect on LC re-reddening temperature. Equations which were used to calculate UFC re-reddening temperature, LC re-reddening temperature and maximum temperature deviation were obtained. The position of boundary layer stayed in 1/4 strip thickness.

  11. Case-Based Reasoning(CBR) Model for Ultra-Fast Cooling in Plate Mill

    Institute of Scientific and Technical Information of China (English)

    HU Xiao,WANG Zhaodong,; WANG Guodong

    2014-01-01

    New generation thermo-mechanical control process(TMCP) based on ultra-fast cooling is being widely adopted in plate mill to product high-performance steel material at low cost. Ultra-fast cooling system is complex because of optimizing the temperature control error generated by heat transfer mathematical model and process parameters. In order to simplify the system and improve the temperature control precision in ultra-fast cooling process, several existing models of case-based reasoning(CBR) model are reviewed. Combining with ultra-fast cooling process, a developed R5 CBR model is proposed, which mainly improves the case representation, similarity relation and retrieval module. Certainty factor is defined in semantics memory unit of plate case which provides not only internal data reliability but also product performance reliability. Similarity relation is improved by defined power index similarity membership function. Retrieval process is simplified and retrieval efficiency is improved apparently by windmill retrieval algorithm. The proposed CBR model is used for predicting the case of cooling strategy and its capability is superior to traditional process model. In order to perform comprehensive investigations on ultra-fast cooling process, different steel plates are considered for the experiment. The validation experiment and industrial production of proposed CBR model are carried out, which demonstrated that finish cooling temperature(FCT) error is controlled within±25℃ and quality rate of product is more than 97%. The proposed CBR model can simplify ultra-fast cooling system and give quality performance for steel product.

  12. Case-based reasoning(CBR) model for ultra-fast cooling in plate mill

    Science.gov (United States)

    Hu, Xiao; Wang, Zhaodong; Wang, Guodong

    2014-11-01

    New generation thermo-mechanical control process(TMCP) based on ultra-fast cooling is being widely adopted in plate mill to product high-performance steel material at low cost. Ultra-fast cooling system is complex because of optimizing the temperature control error generated by heat transfer mathematical model and process parameters. In order to simplify the system and improve the temperature control precision in ultra-fast cooling process, several existing models of case-based reasoning(CBR) model are reviewed. Combining with ultra-fast cooling process, a developed R5 CBR model is proposed, which mainly improves the case representation, similarity relation and retrieval module. Certainty factor is defined in semantics memory unit of plate case which provides not only internal data reliability but also product performance reliability. Similarity relation is improved by defined power index similarity membership function. Retrieval process is simplified and retrieval efficiency is improved apparently by windmill retrieval algorithm. The proposed CBR model is used for predicting the case of cooling strategy and its capability is superior to traditional process model. In order to perform comprehensive investigations on ultra-fast cooling process, different steel plates are considered for the experiment. The validation experiment and industrial production of proposed CBR model are carried out, which demonstrated that finish cooling temperature(FCT) error is controlled within ±25°C and quality rate of product is more than 97%. The proposed CBR model can simplify ultra-fast cooling system and give quality performance for steel product.

  13. Cohesive Function of Lexical Repetition in Text

    Institute of Scientific and Technical Information of China (English)

    张莉; 卢沛沛

    2013-01-01

    Lexical repetition is the most direct form of lexical cohesion,which is the central device for making texts hang together. Although repetition is the most direct way to emphasize,it performs the cohesive effect more apparently.

  14. Ultrafast disk lasers and amplifiers

    Science.gov (United States)

    Sutter, Dirk H.; Kleinbauer, Jochen; Bauer, Dominik; Wolf, Martin; Tan, Chuong; Gebs, Raphael; Budnicki, Aleksander; Wagenblast, Philipp; Weiler, Sascha

    2012-03-01

    Disk lasers with multi-kW continuous wave (CW) output power are widely used in manufacturing, primarily for cutting and welding applications, notably in the automotive industry. The ytterbium disk technology combines high power (average and/or peak power), excellent beam quality, high efficiency, and high reliability with low investment and operating costs. Fundamental mode picosecond disk lasers are well established in micro machining at high throughput and perfect precision. Following the world's first market introduction of industrial grade 50 W picosecond lasers (TruMicro 5050) at the Photonics West 2008, the second generation of the TruMicro series 5000 now provides twice the average power (100 W at 1030 nm, or 60 W frequency doubled, green output) at a significantly reduced footprint. Mode-locked disk oscillators achieve by far the highest average power of any unamplified lasers, significantly exceeding the 100 W level in laboratory set-ups. With robust long resonators their multi-microjoule pulse energies begin to compete with typical ultrafast amplifiers. In addition, significant interest in disk technology has recently come from the extreme light laser community, aiming for ultra-high peak powers of petawatts and beyond.

  15. Ultrafast palladium diffusion in germanium

    KAUST Repository

    Tahini, Hassan Ali

    2015-01-01

    The slow transport of dopants through crystal lattices has hindered the development of novel devices. Typically atoms are contained within deep potential energy wells which necessitates multiple attempts to hop between minimum energy positions. This is because the bonds that constrain atoms are strongest at the minimum positions. As they hop between sites the bonds must be broken, only to re-form as the atoms slide into adjacent minima. Here we demonstrate that the Pd atoms introduced into the Ge lattice behave differently. They retain bonds as the atoms shift across so that at the energy maximum between sites Pd still exhibits strong bonding characteristics. This reduces the energy maximum to almost nothing (a migration energy of only 0.03 eV) and means that the transport of Pd through the Ge lattice is ultrafast. We scrutinize the bonding characteristics at the atomic level using quantum mechanical simulation tools and demonstrate why Pd behaves so differently to other metals we investigated (i.e. Li, Cu, Ag, Pt and Au). Consequently, this fundamental understanding can be extended to systems where extremely rapid diffusion is desired, such as radiation sensors, batteries and solid oxide fuel cells.

  16. Progress in ultrafast intense laser science IX

    CERN Document Server

    Midorikawa, Katsumi

    2013-01-01

    The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance and attractions of the research topic at hand; these are followed by reports of cutting-edge discoveries. This ninth volume covers a broad range of topics from this interdisciplinary research field, focusing on ultrafast molecular responses to an intense laser field, advanced techniques for attosecond pulse generation, atomic and molecular responses to attosecond pulses, photoelectron spectroscopy of atoms and molecules...

  17. Ultrafast structural dynamics of perovskite superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Woerner, M.; Korff Schmising, C. von; Zhavoronkov, N.; Elsaesser, T. [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie, Berlin (Germany); Bargheer, M. [Universitaet Potsdam, Institut fuer Physik und Astronomie, Potsdam (Germany); Vrejoiu, I.; Hesse, D.; Alexe, M. [Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Germany)

    2009-07-15

    Femtosecond X-ray diffraction provides direct insight into the ultrafast reversible lattice dynamics of materials with a perovskite structure. Superlattice (SL) structures consisting of a sequence of nanometer-thick layer pairs allow for optically inducing a tailored stress profile that drives the lattice motions and for limiting the influence of strain propagation on the observed dynamics. We demonstrate this concept in a series of diffraction experiments with femtosecond time resolution, giving detailed information on the ultrafast lattice dynamics of ferroelectric and ferromagnetic superlattices. Anharmonically coupled lattice motions in a SrRuO{sub 3}/PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} (SRO/PZT) SL lead to a switch-off of the electric polarizations on a time scale of the order of 1 ps. Ultrafast magnetostriction of photoexcited SRO layers is demonstrated in a SRO/SrTiO{sub 3} (STO) SL. (orig.)

  18. Unlocking the Constraints of Cyanobacterial Productivity: Acclimations Enabling Ultrafast Growth

    Directory of Open Access Journals (Sweden)

    Hans C. Bernstein

    2016-07-01

    Full Text Available Harnessing the metabolic potential of photosynthetic microbes for next-generation biotechnology objectives requires detailed scientific understanding of the physiological constraints and regulatory controls affecting carbon partitioning between biomass, metabolite storage pools, and bioproduct synthesis. We dissected the cellular mechanisms underlying the remarkable physiological robustness of the euryhaline unicellular cyanobacterium Synechococcus sp. strain PCC 7002 (Synechococcus 7002 and identify key mechanisms that allow cyanobacteria to achieve unprecedented photoautotrophic productivities (~2.5-h doubling time. Ultrafast growth of Synechococcus 7002 was supported by high rates of photosynthetic electron transfer and linked to significantly elevated transcription of precursor biosynthesis and protein translation machinery. Notably, no growth or photosynthesis inhibition signatures were observed under any of the tested experimental conditions. Finally, the ultrafast growth in Synechococcus 7002 was also linked to a 300% expansion of average cell volume. We hypothesize that this cellular adaptation is required at high irradiances to support higher cell division rates and reduce deleterious effects, corresponding to high light, through increased carbon and reductant sequestration.

  19. Progress in ultrafast intense laser science XI

    CERN Document Server

    Yamanouchi, Kaoru; Martin, Philippe

    2014-01-01

    The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance

  20. Progress in ultrafast intense laser science

    CERN Document Server

    Yamanouchi, Kaoru; Mathur, Deepak

    2014-01-01

    The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance

  1. Ultrafast cyclic voltammetry with asymmetrical potential scan

    Institute of Scientific and Technical Information of China (English)

    Zhi Yong Guo; Xiang Qin Lin

    2008-01-01

    Based on the perfect ohmic drop compensation by online electronic positive feedback, ultrafast cyclic voltammetry withasymmetrical potential scan is achieved for the first time, with the reduction of anthracene acting as the test system. Compared withthe traditional cyclic voltammetry utilizing symmetrical triangular waveform as the excitation one, the new method allows a simplerapproach to mechanistic analysis of ultrafast chemical reactions coupled with a charge transfer. And perhaps more important, it alsoprovides a way to eliminate the interference of the adsorbed product in dynamic monitoring.

  2. Ultrafast Nonlinear Signal Processing in Silicon Waveguides

    DEFF Research Database (Denmark)

    Oxenløwe, Leif Katsuo; Mulvad, Hans Christian Hansen; Hu, Hao;

    2012-01-01

    We describe recent demonstrations of exploiting highly nonlinear silicon waveguides for ultrafast optical signal processing. We describe wavelength conversion and serial-to-parallel conversion of 640 Gbit/s data signals and 1.28 Tbit/s demultiplexing and all-optical sampling.......We describe recent demonstrations of exploiting highly nonlinear silicon waveguides for ultrafast optical signal processing. We describe wavelength conversion and serial-to-parallel conversion of 640 Gbit/s data signals and 1.28 Tbit/s demultiplexing and all-optical sampling....

  3. Ultrafast Terahertz Conductivity of Photoexcited Nanocrystalline Silicon

    DEFF Research Database (Denmark)

    Cooke, David; MacDonald, A. Nicole; Hryciw, Aaron;

    2007-01-01

    The ultrafast transient ac conductivity of nanocrystalline silicon films is investigated using time-resolved terahertz spectroscopy. While epitaxial silicon on sapphire exhibits a free carrier Drude response, silicon nanocrystals embedded in glass show a response that is best described by a class......The ultrafast transient ac conductivity of nanocrystalline silicon films is investigated using time-resolved terahertz spectroscopy. While epitaxial silicon on sapphire exhibits a free carrier Drude response, silicon nanocrystals embedded in glass show a response that is best described...

  4. Microdroplet target synthesis for kilohertz ultrafast lasers

    CERN Document Server

    Chvykov, Pavel; Easter, James; Hou, Bixue; Nees, John; Krushelnick, Karl; 10.1063/1.3516158

    2012-01-01

    We have developed a method for producing spatially stable micron-scale liquid targets of flexible shapes at kilohertz repetition rate for use in air and vacuum, by perturbing 5 and 30 \\mu m diameter streams with femtosecond laser pulses and monitoring the temporal development of the perturbation. Using water, we have produced features such as 2.1 \\mu m diameter droplet and 1.3 \\mu m diameter neck with less than 0.3 \\mu m shot-to-shot variation, with prospects for further reduction in size and variability. The use of such micron-scale targets can be expected to prevent conductive heat dissipation, enhance field strength for ion acceleration and allow spatially-deterministic laser-cluster experiments.

  5. Ultrafast impact dynamics of reactive materials (Dlott)

    Science.gov (United States)

    2013-04-16

    Submitted Patents Awarded Awards Jupiter Laser Facility Program Advisory Committee, Lawrence Livermore National Laboratory, 2008, 2011 Executive...related materials such as B/Teflon) to ultrafast laser flash heating. 36-39 In fact during the project period we wrapped up the flash-heating

  6. Silicon based ultrafast optical waveform sampling

    DEFF Research Database (Denmark)

    Ji, Hua; Galili, Michael; Pu, Minhao

    2010-01-01

    A 300 nmx450 nmx5 mm silicon nanowire is designed and fabricated for a four wave mixing based non-linear optical gate. Based on this silicon nanowire, an ultra-fast optical sampling system is successfully demonstrated using a free-running fiber laser with a carbon nanotube-based mode-locker...

  7. Ultrafast angular momentum transfer in multisublattice ferrimagnets.

    Science.gov (United States)

    Bergeard, N; López-Flores, V; Halté, V; Hehn, M; Stamm, C; Pontius, N; Beaurepaire, E; Boeglin, C

    2014-03-11

    Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. However, one of the unsolved questions is that of conservation of the total angular momentum during the ultrafast demagnetization. Here we report the ultrafast transfer of angular momentum during the first hundred femtoseconds in ferrimagnetic Co0.8Gd0.2 and Co0.74Tb0.26 films. Using time-resolved X-ray magnetic circular dichroism allowed for time-resolved determination of spin and orbital momenta for each element. We report an ultrafast quenching of the magnetocrystalline anisotropy and show that at early times the demagnetization in ferrimagnetic alloys is driven by the local transfer of angular momenta between the two exchange-coupled sublattices while the total angular momentum stays constant. In Co0.74Tb0.26 we have observed a transfer of the total angular momentum to an external bath, which is delayed by ~150 fs.

  8. Dynamic optics for ultrafast laser processing

    Directory of Open Access Journals (Sweden)

    Salter Patrick

    2013-11-01

    Full Text Available We present a range of dynamic optical methods to control focal fields for material processing using ultrafast lasers. Adaptive aberration correction maintains focal quality when focusing deep into materials. Dynamic parallelisation methods permit independent control of hundreds of fabrication spots. New adaptive methods for control of pulse front tilt are also presented.

  9. Performance of Ultra-Fast Silicon Detectors

    CERN Document Server

    Cartiglia, N; Ely, S; Fadeyev, V; Galloway, Z; Marchetto, F; Mazza, G; Ngo, J; Obertino, M; Parker, C; Rivetti, A; Shumacher, D; Sadrozinski, H F-W; Seiden, A; Zatserklyaniy, A

    2013-01-01

    The development of Low-Gain Avalanche Detectors has opened up the possibility of manufacturing silicon detectors with signal larger than that of traditional sensors. In this paper we explore the timing performance of Low-Gain Avalanche Detectors, and in particular we demonstrate the possibility of obtaining ultra-fast silicon detector with time resolution of less than 20 picosecond.

  10. Ultrafast chemistry in complex and confined systems

    Indian Academy of Sciences (India)

    Partha Dutta; Kankan Bhattacharyya

    2004-01-01

    Self-organized molecular assemblies play a crucial role in many natural and biological processes. Recent applications of ultrafast laser spectroscopy and computer simulations revealed that chemistry in a confined environment is fundamentally different from that in ordinary solutions. Many recent examples of slow dynamics in constrained environments and their biological implications are discussed.

  11. Quantum dot waveguides: ultrafast dynamics and applications

    DEFF Research Database (Denmark)

    Chen, Yaohui; Mørk, Jesper

    2009-01-01

    In this paper we analyze, based on numerical simulations, the dynamics of semiconductor devices incorporating quantum dots (QDs). In particular we emphasize the unique ultrafast carrier dynamics occurring between discrete QD bound states, and its influence on QD semiconductor optical amplifiers...... (SOAs). Also the possibility of realizing an all-optical regenerator by incorporating a QD absorber section in an amplifier structure is discussed....

  12. Photonic-assisted ultrafast THz wireless access

    DEFF Research Database (Denmark)

    Yu, Xianbin; Chen, Ying; Galili, Michael

    THz technology has been considered feasible for ultrafast wireless data communi- cation, to meet the increasing demand on next-generation fast wireless access, e.g., huge data file transferring and fast mobile data stream access. This talk reviews recent progress in high-speed THz wireless...

  13. Ultrafast spectroscopy of model biological membranes

    NARCIS (Netherlands)

    Ghosh, Avishek

    2009-01-01

    In this PhD thesis, I have described the novel time-resolved sum-frequency generation (TR-SFG) spectroscopic technique that I developed during the course of my PhD research and used it study the ultrafast vibrational, structural and orientational dynamics of water molecules at model biological membr

  14. Circuit considerations for repetitive railguns

    Energy Technology Data Exchange (ETDEWEB)

    Honih, E.M.

    1986-01-01

    Railgun electromagnetic launchers have significant military and scientific potential. They provide direct conversion of electrical energy to projectile kinetic energy, and they offer the hope of achieving projectile velocities greatly exceeding the limits of conventional guns. With over 10 km/sec already demonstrated, railguns are attracting attention for tactical and strategic weapons systems and for scientific equation-of-state research. The full utilization of railguns will require significant improvements in every aspect of system design - projectile, barrel, and power source - to achieve operation on a large scale. This paper will review fundamental aspects of railguns, with emphasis on circuit considerations and repetitive operation.

  15. Ultrafast action potentials mediate kilohertz signaling at a central synapse.

    Science.gov (United States)

    Ritzau-Jost, Andreas; Delvendahl, Igor; Rings, Annika; Byczkowicz, Niklas; Harada, Harumi; Shigemoto, Ryuichi; Hirrlinger, Johannes; Eilers, Jens; Hallermann, Stefan

    2014-10-01

    Fast synaptic transmission is important for rapid information processing. To explore the maximal rate of neuronal signaling and to analyze the presynaptic mechanisms, we focused on the input layer of the cerebellar cortex, where exceptionally high action potential (AP) frequencies have been reported in vivo. With paired recordings between presynaptic cerebellar mossy fiber boutons and postsynaptic granule cells, we demonstrate reliable neurotransmission up to ∼1 kHz. Presynaptic APs are ultrafast, with ∼100 μs half-duration. Both Kv1 and Kv3 potassium channels mediate the fast repolarization, rapidly inactivating sodium channels ensure metabolic efficiency, and little AP broadening occurs during bursts of up to 1.5 kHz. Presynaptic Cav2.1 (P/Q-type) calcium channels open efficiently during ultrafast APs. Furthermore, a subset of synaptic vesicles is tightly coupled to Ca(2+) channels, and vesicles are rapidly recruited to the release site. These data reveal mechanisms of presynaptic AP generation and transmitter release underlying neuronal kHz signaling.

  16. Atomic origin of ultrafast resistance switching in nanoscale electrometallization cells.

    Science.gov (United States)

    Onofrio, Nicolas; Guzman, David; Strachan, Alejandro

    2015-04-01

    Nanoscale resistance-switching cells that operate via the electrochemical formation and disruption of metallic filaments that bridge two electrodes are among the most promising devices for post-CMOS electronics. Despite their importance, the mechanisms that govern their remarkable properties are not fully understood, especially for nanoscale devices operating at ultrafast rates, limiting our ability to assess the ultimate performance and scalability of this technology. We present the first atomistic simulations of the operation of conductive bridging cells using reactive molecular dynamics with a charge equilibration method extended to describe electrochemical reactions. The simulations predict the ultrafast switching observed in these devices, with timescales ranging from hundreds of picoseconds to a few nanoseconds for devices consisting of Cu active electrodes and amorphous silica dielectrics and with dimensions corresponding to their scaling limit (cross-sections below 10 nm). We find that single-atom-chain bridges often form during device operation but that they are metastable, with lifetimes below a nanosecond. The formation of stable filaments involves the aggregation of ions into small metallic clusters, followed by a progressive chemical reduction as they become connected to the cathode. Contrary to observations in larger cells, the nanoscale conductive bridges often lack crystalline order. An atomic-level mechanistic understanding of the switching process provides guidelines for materials optimization for such applications and the quantitative predictions over an ensemble of devices provide insight into their ultimate scaling and performance.

  17. Effect of repetitive mckenzie lumbar spine exercises on cardiovascular system

    Directory of Open Access Journals (Sweden)

    Agrawal Sonal S

    2014-07-01

    Full Text Available Background & Purpose: McKenzie exercises for the lumbar spine, which are done repeatedly, such as flexion in standing (FIS, extension in standing flexion in lying (FIL & extension in lying (EIL have been used in the management of low back pain for over three decades. The cardiovascular effects of exercises that involve postural stabilization, arm exercises and of exercises performed in lying are well known, but there are seldom studies performed to assess the cardiovascular effects of these commonly used McKenzie exercises. Therefore the study focused on evaluating the effects of 4 commonly used McKenzie exercises on the cardiovascular system. Methods: 80 subjects in the age group of 20-59 years were randomly assigned into 4 groups according to their age, such that such that each group comprised of an equal number of subjects & equal number of males & females. Each subject performed all the 4 exercises (FIS, EIS, FIL & EIL for 10, 15 & 20 repetitions respectively. Heart rate, blood pressure & rate pressure product were recorded before & after each set of repetitions & after each type of exercise. Results: Repetitive McKenzie lumbar spine exercises had cardiovascular effects in apparently healthy subjects (both male & female. Exercises performed in lying were hemodynamically more demanding than that performed in standing, also exercises involving flexion of the lumbar spine elicited greater cardiovascular demand as compared to extension exercises i.e. FIL>EIL>FIS>EIS irrespective of the number of repetitions, 10, 15 or 20. The cardiovascular demand for a given subject increased as the number of repetitions increased, for all the 4 exercises. Conclusion: McKenzie exercises when done repetitively have cardiovascular effects in healthy subjects.

  18. Analysis on multiple-component synchronization of ultra-fast time-interleaved analog-to-digital conversion systems and its novel parameterized hardware solution.

    Science.gov (United States)

    Huang, Wuhuang; Wang, Houjun; Tian, Shulin; Ye, Peng; Zeng, Hao; Qiu, Duyu

    2014-10-01

    Parallelism-based technique of time-interleaved analog-to-digital conversion (TIADC) has become an effective solution for the higher sampling rate acquisition system to acquire non-repetitive waveforms. With the increase of sampling frequency, the indeterminacy of combining sequence of sampled data among multiple components has become a highlighted barrier for the reset operation of high-speed acquisition systems, and this is especially obvious for the ultra-fast TIADC systems. In this paper, we clarify the root of the problem in multiple-component synchronization (MCS) caused by such reset operation. Also we propose a novel and reliable hardware solution to precisely condition each reset signal, including three key circuit design parameters, i.e., the best time interval, required edge uncertainty, and the minimum delay precision. Besides, the designing scheme and debugging procedures are presented in detail in a generalized platform of this system type. Finally, in order to demonstrate the feasibility, parametric materialization and testing verification are gradually accomplished in a 20 Giga Samples Per Second (GSPS) TIADC system composed of four 5 GSPS ADC components. The results show that the proposed method is feasible and effective for ensuring the combined determinacy of multiple groups of sampled data and solving the MCS problem. In comparison with other existing solutions, it adopts some simple logic components more easily and flexibly, and this is significant for the development of congeneric systems or instruments featuring the MCS.

  19. Ultrafast science using Laser Wakefield Accelerators

    Science.gov (United States)

    Thomas, Alec G. R.

    2016-10-01

    Recent progress in laser wakefield acceleration has led to the emergence of a new generation of electron and X-ray sources that may have considerable benefits for ultrafast science. Laser wakefield acceleration provides radiation pulses that have femtosecond duration and intrinsic synchronisation with the laser source, allowing for pump-probe measurements with unprecedented temporal resolution. These pulses can be used to study ultrafast dynamical phenomena in plasma and dense material, such as transient magnetic fields, rapidly evolving plasma dynamics and crystal lattice oscillations. In this talk, I will review recent experiments in laser wakefield acceleration and energetic photon generation using the laser systems HERCULES and Lambda-Cubed at the University of Michigan and their use for capturing the dynamics of laser-pumped samples. Studies of the electron beam hosing instability and the generation of annular phase space distributions increase X-ray flux while maintaining its femtosecond duration. Single-shot, spectrally resolved absorption measurements in laser pumped foils can be made on ultrafast timescales using this broadband photon source. Ultrafast electron radiography is able to temporally resolve relativistically expanding magnetic fields in high-intensity laser-solid interactions and the evolution of electric fields in low density plasma. Time-resolved electron diffraction captures structural dynamics in crystalline silicon. I will also discuss the technological needs for and potential impact of such revolutionary compact radiation sources for ultrafast science in the future. US Air Force Office of Scientific Research under Award Number FA9550-12-1-0310, the US National Science Foundation Grants No. 1054164, 0935197, 1535628 and 0810979, US Department of Energy Grant No. DE-NA0002372 and Army Research Office Grant No. W911NF1.

  20. Perspective: Ultrafast magnetism and THz spintronics

    Energy Technology Data Exchange (ETDEWEB)

    Walowski, Jakob; Münzenberg, Markus [Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, 17489 Greifswald (Germany)

    2016-10-14

    This year the discovery of femtosecond demagnetization by laser pulses is 20 years old. For the first time, this milestone work by Bigot and coworkers gave insight directly into the time scales of microscopic interactions that connect the spin and electron system. While intense discussions in the field were fueled by the complexity of the processes in the past, it now became evident that it is a puzzle of many different parts. Rather than providing an overview that has been presented in previous reviews on ultrafast processes in ferromagnets, this perspective will show that with our current depth of knowledge the first applications are developed: THz spintronics and all-optical spin manipulation are becoming more and more feasible. The aim of this perspective is to point out where we can connect the different puzzle pieces of understanding gathered over 20 years to develop novel applications. Based on many observations in a large number of experiments. Differences in the theoretical models arise from the localized and delocalized nature of ferromagnetism. Transport effects are intrinsically non-local in spintronic devices and at interfaces. We review the need for multiscale modeling to address the processes starting from electronic excitation of the spin system on the picometer length scale and sub-femtosecond time scale, to spin wave generation, and towards the modeling of ultrafast phase transitions that altogether determine the response time of the ferromagnetic system. Today, our current understanding gives rise to the first usage of ultrafast spin physics for ultrafast magnetism control: THz spintronic devices. This makes the field of ultrafast spin-dynamics an emerging topic open for many researchers right now.

  1. Perspective: Ultrafast magnetism and THz spintronics

    Science.gov (United States)

    Walowski, Jakob; Münzenberg, Markus

    2016-10-01

    This year the discovery of femtosecond demagnetization by laser pulses is 20 years old. For the first time, this milestone work by Bigot and coworkers gave insight directly into the time scales of microscopic interactions that connect the spin and electron system. While intense discussions in the field were fueled by the complexity of the processes in the past, it now became evident that it is a puzzle of many different parts. Rather than providing an overview that has been presented in previous reviews on ultrafast processes in ferromagnets, this perspective will show that with our current depth of knowledge the first applications are developed: THz spintronics and all-optical spin manipulation are becoming more and more feasible. The aim of this perspective is to point out where we can connect the different puzzle pieces of understanding gathered over 20 years to develop novel applications. Based on many observations in a large number of experiments. Differences in the theoretical models arise from the localized and delocalized nature of ferromagnetism. Transport effects are intrinsically non-local in spintronic devices and at interfaces. We review the need for multiscale modeling to address the processes starting from electronic excitation of the spin system on the picometer length scale and sub-femtosecond time scale, to spin wave generation, and towards the modeling of ultrafast phase transitions that altogether determine the response time of the ferromagnetic system. Today, our current understanding gives rise to the first usage of ultrafast spin physics for ultrafast magnetism control: THz spintronic devices. This makes the field of ultrafast spin-dynamics an emerging topic open for many researchers right now.

  2. Ultrafast optical imaging technology: principles and applications of emerging methods

    Science.gov (United States)

    Mikami, Hideharu; Gao, Liang; Goda, Keisuke

    2016-09-01

    High-speed optical imaging is an indispensable technology for blur-free observation of fast transient dynamics in virtually all areas including science, industry, defense, energy, and medicine. High temporal resolution is particularly important for microscopy as even a slow event appears to occur "fast" in a small field of view. Unfortunately, the shutter speed and frame rate of conventional cameras based on electronic image sensors are significantly constrained by their electrical operation and limited storage. Over the recent years, several unique and unconventional approaches to high-speed optical imaging have been reported to circumvent these technical challenges and achieve a frame rate and shutter speed far beyond what can be reached with the conventional image sensors. In this article, we review the concepts and principles of such ultrafast optical imaging methods, compare their advantages and disadvantages, and discuss an entirely new class of applications that are possible using them.

  3. Ultrafast optical measurements of charge generation and transfer mechanisms of pi-conjugated polymers for solar cell applications

    Science.gov (United States)

    Holt, Joshua Michael

    Current developments in organic solar cells based on donor-acceptor blends require understanding and control of photoinduced charge transfer and electronic state dynamics. In this work the ultrafast dynamics of photoexcitations in pi-conjugated organic semiconductors were studied using a low-intensity, high-repetition rate laser system in the broad mid- to near-infrared (IR) spectral range from 0.25 to 1.1 eV, and a high-intensity, low-repetition rate laser system in the spectral range from 1.2 to 2.5 eV, in the time domain up to 1 ns with 150 fs resolution. We also applied CW photomodulation spectroscopy along with excitation spectrum, modulation frequency sweeps, photoluminescence and electroabsorption to study the excited states of pi-conjugated polymers and acceptor-donor blends. One current drawback to organic solar cell efficiency is negligible absorption in the near infrared spectral range of the solar spectrum. We provide and compare evidence that poly(2-methoxy-5(2'-ethyl)hexoxy-phenylenevinylene) (MEH-PPV) [electron donor] blended with 2,4,7-trinitrofluorenone (TNF) [strong electron acceptor] form a below-gap charge transfer complex (CTC) state that can extend absorption into the near infrared. The transient PA measurements also show that significant charge species are initially photogenerated, a majority of which geminately recombine within 8-10 ps, but the few that escape geminate recombination are subsequently captured in long-lived traps. In addition polarons could be also photogenerated with high efficiency at near-IR excitation, with similar fate. This demonstrates that a CTC state exists below the MEH-PPV polymer optical gap, but with low dissociation efficiency. We compare our results to those in blends of MEH-PPV/C60 where apparently a charge transport pathway to the electrodes is formed and the obtained CTC state has higher dissociation efficiency. The most efficient all-organic photovoltaic (OPV) cells to date (˜6% power conversion efficiency

  4. Research on the ultrafast fluorescence property of thylakoid membranes of the wild-type and mutant rice

    Institute of Scientific and Technical Information of China (English)

    任兆玉; 许晓明; 王水才; 辛越勇; 贺俊芳; 侯洵

    2003-01-01

    A high yielding rice variety mutant (Oryza sativa L., Zhenhui 249) with low chlorophyll b (Chl b) has been discovered in natural fields. It has a quality character controlled by a pair of recessive genes (nuclear gene). The partial loss of Chl b in content affects the efficiency of light harvest in a light harvest complex (LHC), thus producing the difference of the exciting energy transfer and the efficiency of photochemistry conversion between the mutant and wild-type rice in photosynthetic unit. The efficiency of utilizing light energy is higher in the mutant than that in the wildtype rice relatively. For further discussion of the above-mentioned difference and learning about the mechanism of the increase in the photochemical efficiency of the mutant, the pico-second resolution fluorescence spectrum measurement with delay-frame-scanning single photon counting technique is adopted. Thylakoid membranes of the mutant and the wild-type rice are excited by an Ar+ laser with a pulse width of 120ps, repetition rate of 4MHz and wavelength of 514nm. Compared with the time and spectrum property of exciting fluorescence, conclusions of those ultrafast dynamic experiments are: 1) The speeds of the exciting energy transferred in photo-system I are faster than that in photo-system II in both samples. 2) The speeds of the exciting energy transfer of mutant sample are faster than those of the wildtype. This might be one of the major reasons why the efficiency of photosynthesis is higher in mutant than that in the wild-type rice.

  5. 40 MHz high-frequency ultrafast ultrasound imaging.

    Science.gov (United States)

    Huang, Chih-Chung; Chen, Pei-Yu; Peng, Po-Hsun; Lee, Po-Yang

    2017-06-01

    Ultrafast high-frame-rate ultrasound imaging based on coherent-plane-wave compounding has been developed for many biomedical applications. Most coherent-plane-wave compounding systems typically operate at 3-15 MHz, and the image resolution for this frequency range is not sufficient for visualizing microstructure tissues. Therefore, the purpose of this study was to implement a high-frequency ultrafast ultrasound imaging operating at 40 MHz. The plane-wave compounding imaging and conventional multifocus B-mode imaging were performed using the Field II toolbox of MATLAB in simulation study. In experiments, plane-wave compounding images were obtained from a 256 channel ultrasound research platform with a 40 MHz array transducer. All images were produced by point-spread functions and cyst phantoms. The in vivo experiment was performed from zebrafish. Since high-frequency ultrasound exhibits a lower penetration, chirp excitation was applied to increase the imaging depth in simulation. The simulation results showed that a lateral resolution of up to 66.93 μm and a contrast of up to 56.41 dB were achieved when using 75-angles plane waves in compounding imaging. The experimental results showed that a lateral resolution of up to 74.83 μm and a contrast of up to 44.62 dB were achieved when using 75-angles plane waves in compounding imaging. The dead zone and compounding noise are about 1.2 mm and 2.0 mm in depth for experimental compounding imaging, respectively. The structure of zebrafish heart was observed clearly using plane-wave compounding imaging. The use of fewer than 23 angles for compounding allowed a frame rate higher than 1000 frames per second. However, the compounding imaging exhibits a similar lateral resolution of about 72 μm as the angle of plane wave is higher than 10 angles. This study shows the highest operational frequency for ultrafast high-frame-rate ultrasound imaging. © 2017 American Association of Physicists in Medicine.

  6. Digital repetitive control under varying frequency conditions

    OpenAIRE

    Ramos Fuentes, Germán Andrés

    2012-01-01

    The tracking/rejection of periodic signals constitutes a wide field of research in the control theory and applications area and Repetitive Control has proven to be an efficient way to face this topic; however, in some applications the period of the signal to be tracked/rejected changes in time or is uncertain, which causes and important performance degradation in the standard repetitive controller. This thesis presents some contributions to the open topic of repetitive control workin...

  7. A repetitive 0.14 THz relativistic surface wave oscillator

    Energy Technology Data Exchange (ETDEWEB)

    Wang Guangqiang; Tong Changjiang; Li Xiaoze; Wang Xuefeng; Li Shuang; Lu Xicheng [Northwest Institute of Nuclear Technology, P.O. Box 69-1, Xi' an 710024 (China); Wang Jianguo [Northwest Institute of Nuclear Technology, P.O. Box 69-1, Xi' an 710024 (China); School of Electronic and Information Engineering, Xi' an Jiaotong University, Xi' an 710049 (China)

    2013-04-15

    Preliminary experimental results of a repetitive 0.14 THz overmoded relativistic surface wave oscillator (RSWO) are presented in this paper. The repetitive RSWO is developed by using a rectangularly corrugated slow-wave structure with overmoded ratio of 3 and a foilless diode emitting annular electron beam with thickness of 0.5 mm. The high quality electron beams at the repetition rate of 10 are obtained over a wide range of diode voltage (180 kV < U < 240 kV) and current (700 A < I < 1.2 kA). The generation experiments of RSWO are conducted at an axial pulsed magnetic field whose maximum strength and duration can reach about 2.7 T and 1 s, respectively. The experimental results show that the RSWO successfully produces reasonable uniform terahertz pulses at repetition rate of 10, and the pulse duration, frequency, and power of a single pulse are about 1.5 ns, 0.154 THz, and 2.6 MW, respectively, whereas the dominated radiation mode of the RSWO is TM{sub 02}.

  8. Optimization and practical implementation of ultrafast 2D NMR experiments

    OpenAIRE

    Queiroz Júnior,Luiz H. K.; Antonio G. Ferreira; Patrick Giraudeau

    2013-01-01

    Ultrafast 2D NMR is a powerful methodology that allows recording of a 2D NMR spectrum in a fraction of second. However, due to the numerous non-conventional parameters involved in this methodology its implementation is no trivial task. Here, an optimized experimental protocol is carefully described to ensure efficient implementation of ultrafast NMR. The ultrafast spectra resulting from this implementation are presented based on the example of two widely used 2D NMR experiments, COSY and HSQC...

  9. [Repetition and fear of dying].

    Science.gov (United States)

    Lerner, B D

    1995-03-01

    In this paper a revision is made of the qualifications of Repetition (R) in Freuds work, i.e. its being at the service of the Pleasure Principle and, beyond it, the binding of free energy due to trauma. Freud intends to explain with this last concept the "fort-da" and the traumatic dreams (obsessively reiterated self-reproaches may be added to them). The main thesis of this work is that R. is not only a defense against the recollection of the ominous past (as in the metaphorical deaths of abandonment and desertion) but also a way of maintaining life and identify fighting against the inescapable omninous future (known but yet experienced), i.e. our own death. Some forms of R. like habits, identificatory behaviors and sometimes even magic, are geared to serve the life instinct. A literary illustration shows this desperate fight.

  10. Pressure rig for repetitive casting

    Science.gov (United States)

    Vasquez, Peter (Inventor); Hutto, William R. (Inventor); Philips, Albert R. (Inventor)

    1989-01-01

    The invention is a pressure rig for repetitive casting of metal. The pressure rig performs like a piston for feeding molten metal into a mold. Pressure is applied to an expandable rubber diaphragm which expands like a balloon to force the metal into the mold. A ceramic cavity which holds molten metal is lined with blanket-type insulating material, necessitating only a relining for subsequent use and eliminating the lengthy cavity preparation inherent in previous rigs. In addition, the expandable rubber diaphragm is protected by the insulating material thereby decreasing its vulnerability to heat damage. As a result of the improved design the life expectancy of the pressure rig contemplated by the present invention is more than doubled. Moreover, the improved heat protection has allowed the casting of brass and other alloys with higher melting temperatures than possible in the conventional pressure rigs.

  11. BEAM DYNAMICS ANALYSIS FOR THE ULTRA-FAST KICKER IN CIRCULAR COOLER RING OF JLEIC

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Yulu [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Inst. Modern Phys., Chinese Academy of Sciences, Lanzhou, China; Wang, Haipeng [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Rimmer, Robert A. [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Wang, Shaoheng [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

    2016-05-01

    An ultra-fast kicker system consisting of four quarter wavelength resonator based deflecting cavities was developed that simultaneously resonates at 10 subharmonic modes of the 476.3MHz bunch repetition frequency. Thus every 10th bunch in the bunch train will experience a transverse kick while all the other bunches are undisturbed. This fast kicker is being developed for the Energy Recovery Linac (ERL) based electron Circular Cooler Ring (CCR) in the proposed Jefferson Lab Electron Ion Collider (JLEIC, previously MEIC). The electron bunches can be reused 10-30 turns thus the beam current in the ERL can be reduced to 1/10 - 1/30 (150mA - 50mA) of the cooling bunch current (1.5A). In this paper, several methods to synthesize such a kicker waveform and the comparison made by the beam dynamics tracking in Elegant will be discussed.

  12. Interaction of Repetitively Pulsed High Energy Laser Radiation With Matter

    Science.gov (United States)

    Hugenschmidt, Manfred

    1986-10-01

    The paper is concerned with laser target interaction processes involving new methods of improving the overall energy balance. As expected theoretically, this can be achieved with high repetition rate pulsed lasers even for initially highly reflecting materials, such as metals. Experiments were performed by using a pulsed CO2 laser at mean powers up to 2 kW and repetition rates up to 100 Hz. The rates of temperature rise of aluminium for example were thereby increased by lore than a factor of 3 as compared to cw-radiation of comparable power density. Similar improvements were found for the overall absorptivities that were increased by this method by more than an order of magnitude.

  13. Output Characteristics of LD End-pumping Nd:YVO_4 Laser with Pulse Repetition Rates up to 1 kHz%LD端面抽运1KHz电光调Q Nd:YVO_4激光器输出功率特性研究

    Institute of Scientific and Technical Information of China (English)

    宋标; 李传起; 谢爱根; 王铁邦

    2009-01-01

    A laser diode (LD) continuous-wave (CW) end-pumping high repetition rate electro-optic ( EO) Q-switching Nd : YVO_4 laser was experimentally and theoretically studied. In experiments , using BBO single crystal as an EO Q-switch,with 10 W pump power ,about 170 mW average power was obtained at 1 kHz repetition rate. The dips in the output power curves were analyzed, A reasonable explaination was given and a way of improving the output was pointed out through the graphic analysis of the transmitting and transforming circle.%报道了全固态激光器连续抽运高重复率电光调Q Nd:YVO_4激光器的实验和理论分析结果,用BBO晶体作电光调Q元件,在激光二极管(LD)端面抽运Nd:YVO_4激光器中实现了较高重复率的电光调Q输出.实验中在1 kHz重复率下,抽运功率为10 W时,平均功率超过170 mW.对输出功率曲线中的凹陷现象进行了分析,指出了制约激光器的内在诸因素,并用传播圆-变换圆图解分析方法给出了合理的解释.

  14. Efeito da ordem dos exercícios no número de repetições e na percepção subjetiva de esforço em homens treinados em força The effect of the exercises order on number of repetitions and rate of perceived effort in resistance trained men

    Directory of Open Access Journals (Sweden)

    Saulo Gil

    2011-03-01

    Full Text Available A ordem dos exercícios refere-se à sequência de execução durante uma sessão de treinamento. Evidências demonstram que essa ordem pode afetar o número de repetições realizadas nos exercícios. A percepção subjetiva de esforço (PSE, assim como o número de repetições realizadas, depende da sobrecarga utilizada. Assim, alterações no número de repetições podem afetar a PSE. O volume total de trabalho (VTT influencia nas adaptações crônicas ao treinamento e também pode ser afetado pela ordem dos exercícios. O objetivo foi verificar o efeito da ordem dos exercícios para membros inferiores no número de repetições realizadas, na PSE e no VTT. Doze homens treinados (19,3 ± 2,1 anos, 71,1 ± 9,8 kg, 172,4 ± 6,1 cm, 23,3 ± 11,5 meses/treino realizaram duas sessões com os exercícios "leg-press" (L, mesa flexora (F e cadeira extensora (E em diferentes ordens (LFE ou EFL. Foram utilizados testes t de "Student" pareados com ajuste de Bonferroni para comparações múltiplas. O número de repetições em L e E diminuiu quando realizados no final da sessão. As repetições realizadas em F diminuíram na LFE. A PSE de E foi maior quando realizada no final da sessão, porém de L e de F não foram afetadas pelas diferentes ordens. O volume de trabalho total de LFE foi maior. Em conclusão, a ordem dos exercícios envolvendo membros inferiores afeta o número de repetições e a PSE de um exercício além do VTT, ressaltando a importância da ordem dos exercícios como uma importante variável na prescrição do treinamento.The order of exercises refers to the sequence during a training bout. Some evidence shows that the number of repetitions may be affected by the order of exercises. Both the number of repetitions and the rate of perceived effort (PSE are influenced by exercise load. Thus, changes in the number of repetitions may affect PSE. Additionally, total work volume influences long term training adaptations and can be

  15. Ultrafast spectroscopic imaging of exfoliated graphene

    Energy Technology Data Exchange (ETDEWEB)

    Grancini, Giulia; Martino, Nicola; Petrozza, Annamaria; Lanzani, Guglielmo [Center for Nano Science and Technology rate at PoliMi, Istituto Italiano di Tecnologia, Via Giovanni Pascoli, 70/3, 20133 Milano (Italy); Bianchi, Massimiliano; Rizzi, Laura Giorgia; Sordan, Roman [L-NESS, Department of Physics, Polo di Como, Politecnico di Milano, Via Anzani 42, 22100 Como (Italy); Russo, Valeria [Department of Energetics, Politecnico di Milano, Via Lambruschini 4, 20156 Milano (Italy); Li Bassi, Andrea; Casari, Carlo Spartaco [Center for Nano Science and Technology rate at PoliMi, Istituto Italiano di Tecnologia, Via Giovanni Pascoli, 70/3, 20133 Milano (Italy); Department of Energetics, Politecnico di Milano, Via Lambruschini 4, 20156 Milano (Italy)

    2012-12-15

    In this paper we investigate the carrier cooling dynamics in graphene flakes exploiting ultrafast transient absorption imaging technique. This tool enables us to combine nanoscale spatial resolution and sub-picosecond (ps) time resolution. It provides many advantages over the standard transient absorption techniques because it directly investigates the excited state dynamics at a local scale that would be usually averaged out. The local dynamics show a photobleaching recovery in the first ps, assigned to cooling by electron-phonon scattering. We found that the photoexcited carrier dynamics is spatially uniform over the micrometer-sized exfoliated graphene layer. Ultrafast pump-probe technique is combined with an optical microscope to investigate the local excited state dynamics in graphene flakes. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Progress in Ultrafast Intense Laser Science VIII

    CERN Document Server

    Nisoli, Mauro; Hill, Wendell; III, III

    2012-01-01

    The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science and optical science which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield as well as graduate students can grasp the importance and attractions of the research topic at hand. These are followed by reports of cutting-edge discoveries. This eighth volume covers a broad range of topics from this interdisciplinary research field, focusing on molecules interacting with ultrashort and intense laser fields, advanced technologies for the characterization of ultrashort laser pulses and their applications, laser plasma formation and laser acceleration.

  17. Ultrafast and Gigantic Spin Injection in Semiconductors

    Science.gov (United States)

    Battiato, M.; Held, K.

    2016-05-01

    The injection of spin currents in semiconductors is one of the big challenges of spintronics. Motivated by the ultrafast demagnetization and spin injection into metals, we propose an alternative femtosecond route based on the laser excitation of superdiffusive spin currents in a ferromagnet such as Ni. Our calculations show that even though only a fraction of the current crosses the Ni-Si interface, the laser-induced creation of strong transient electrical fields at a ferromagnet-semiconductor interface allows for the injection of chargeless spin currents with record spin polarizations of 80%. Beyond that they are pulsed on the time scale of 100 fs which opens the door for new experiments and ultrafast spintronics.

  18. Progress in ultrafast intense laser science XII

    CERN Document Server

    Roso, Luis; Li, Ruxin; Mathur, Deepak; Normand, Didier

    2015-01-01

    This  volume covers a broad range of topics focusing on atoms, molecules, and clusters interacting in intense laser field, laser induced filamentation, and laser plasma interaction and application. The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance and attractions of the research topic at hand; these are followed by reports of cutting-edge discoveries. .

  19. Dual-tip-enhanced ultrafast CARS nanoscopy

    CERN Document Server

    Ballmann, Charles W; Sinyukov, Alexander M; Sokolov, Alexei V; Voronine, Dmitri V

    2013-01-01

    Coherent anti-Stokes Raman scattering (CARS) and, in particular, femtosecond adaptive spectroscopic techniques (FAST CARS) have been successfully used for molecular spectroscopy and microscopic imaging. Recent progress in ultrafast nanooptics provides flexibility in generation and control of optical near fields, and holds promise to extend CARS techniques to the nanoscale. In this theoretical study, we demonstrate ultrafast subwavelentgh control of coherent Raman spectra of molecules in the vicinity of a plasmonic nanostructure excited by ultrashort laser pulses. The simulated nanostructure design provides localized excitation sources for CARS by focusing incident laser pulses into subwavelength hot spots via two self-similar nanolens antennas connected by a waveguide. Hot-spot-selective dual-tip-enhanced CARS (2TECARS) nanospectra of DNA nucleobases are obtained by simulating optimized pump, Stokes and probe near fields using tips, laser polarization- and pulse-shaping. This technique may be used to explore ...

  20. Progress in Ultrafast Intense Laser Science

    CERN Document Server

    Yamanouchi, Kaoru; Li, Ruxin; Chin, See Leang

    2009-01-01

    The PUILS series presents Progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science. PUILS has been stimulated by the recent development of ultrafast laser technologies. Each volume contains approximately 15 chapters, authored by researchers at the forefront. Each chapter opens with an overview of the topics to be discussed, so that researchers, who are not experts in the specific topics, as well as graduate students can grasp the importance and attractions of this sub-field of research, and these are followed by reports of cutting-edge discoveries. This fourth volume covers a broad range of topics from this interdisciplinary research field, focusing on strong field ionization of atoms; excitation, ionization and fragmentation of molecules; nonlinear intense optical phenomena and attosecond pulses; and laser - solid interactions and photoemission.

  1. Development of Scanning Ultrafast Electron Microscope Capability.

    Energy Technology Data Exchange (ETDEWEB)

    Collins, Kimberlee Chiyoko [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Talin, Albert Alec [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Chandler, David W. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Michael, Joseph R. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2016-11-01

    Modern semiconductor devices rely on the transport of minority charge carriers. Direct examination of minority carrier lifetimes in real devices with nanometer-scale features requires a measurement method with simultaneously high spatial and temporal resolutions. Achieving nanometer spatial resolutions at sub-nanosecond temporal resolution is possible with pump-probe methods that utilize electrons as probes. Recently, a stroboscopic scanning electron microscope was developed at Caltech, and used to study carrier transport across a Si p-n junction [ 1 , 2 , 3 ] . In this report, we detail our development of a prototype scanning ultrafast electron microscope system at Sandia National Laboratories based on the original Caltech design. This effort represents Sandia's first exploration into ultrafast electron microscopy.

  2. Progress in Ultrafast Intense Laser Science III

    CERN Document Server

    Yamanouchi, Kaoru; Agostini, Pierre; Ferrante, Gaetano

    2008-01-01

    The PUILS series presents Progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science. PUILS has been stimulated by the recent development of ultrafast laser technologies. Each volume contains approximately 15 chapters, authored by researchers at the forefront. Each chapter opens with an overview of the topics to be discussed, so that researchers, who are not experts in the specific topics, as well as graduate students can grasp the importance and attractions of this sub-field of research, and these are followed by reports of cutting-edge discoveries. This third volume covers a diverse range of disciplines, focusing on such topics as strong field ionization of atoms, ionization and fragmentation of molecules and clusters, generation of high-order harmonics and attosecond pulses, filamentation and laser plasma interaction, and the development of ultrashort and ultrahigh-intensity light sources.

  3. Ultra-fast framing camera tube

    Science.gov (United States)

    Kalibjian, Ralph

    1981-01-01

    An electronic framing camera tube features focal plane image dissection and synchronized restoration of the dissected electron line images to form two-dimensional framed images. Ultra-fast framing is performed by first streaking a two-dimensional electron image across a narrow slit, thereby dissecting the two-dimensional electron image into sequential electron line images. The dissected electron line images are then restored into a framed image by a restorer deflector operated synchronously with the dissector deflector. The number of framed images on the tube's viewing screen is equal to the number of dissecting slits in the tube. The distinguishing features of this ultra-fast framing camera tube are the focal plane dissecting slits, and the synchronously-operated restorer deflector which restores the dissected electron line images into a two-dimensional framed image. The framing camera tube can produce image frames having high spatial resolution of optical events in the sub-100 picosecond range.

  4. Progress in Ultrafast Intense Laser Science VI

    CERN Document Server

    Yamanouchi, Kaoru; Bandrauk, André D

    2010-01-01

    The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance and attractions of the research topic at hand; these are followed by reports of cutting-edge discoveries. This sixth volume covers a broad range of topics from this interdisciplinary research field, focusing on responses of molecules to ultrashort intense laser pulses, generation and characterization of attosecond pulses and high-order harmonics, and filamentation and laser-plasma interaction.

  5. Ultrafast two dimensional infrared chemical exchange spectroscopy

    Science.gov (United States)

    Fayer, Michael

    2011-03-01

    The method of ultrafast two dimensional infrared (2D IR) vibrational echo spectroscopy is described. Three ultrashort IR pulses tuned to the frequencies of the vibrational transitions of interest are directed into the sample. The interaction of these pulses with the molecular vibrational oscillators produces a polarization that gives rise to a fourth pulse, the vibrational echo. The vibrational echo pulse is combined with another pulse, the local oscillator, for heterodyne detection of the signal. For fixed time between the second and third pulses, the waiting time, the first pulse is scanned. Two Fourier transforms of the data yield a 2D IR spectrum. The waiting time is increased, and another spectrum is obtained. The change in the 2D IR spectra with increased waiting time provides information on the time evolution of the structure of the molecular system under observation. In a 2D IR chemical exchange experiment, two species A and B, are undergoing chemical exchange. A's are turning into B's, and B's are turning into A's, but the overall concentrations of the species are not changing. The kinetics of the chemical exchange on the ground electronic state under thermal equilibrium conditions can be obtained 2D IR spectroscopy. A vibration that has a different frequency for the two species is monitored. At very short time, there will be two peaks on the diagonal of the 2D IR spectrum, one for A and one for B. As the waiting time is increased, chemical exchange causes off-diagonal peaks to grow in. The time dependence of the growth of these off-diagonal peaks gives the chemical exchange rate. The method is applied to organic solute-solvent complex formation, orientational isomerization about a carbon-carbon single bond, migration of a hydrogen bond from one position on a molecule to another, protein structural substate interconversion, and water hydrogen bond switching between ions and water molecules. This work was supported by the Air Force Office of Scientific

  6. Ultrafast electron dynamics in gold nanoshells

    Science.gov (United States)

    Westcott, Sarah Linda

    2001-10-01

    In metallic nanostructures, the interaction of excited electrons with the nanostructure surface may result in electron relaxation dynamics that are significantly different than those predicted by electron-lattice coupling. These ultrafast electron dynamics were monitored by pump-probe measurements of the time-resolved change in transmission. Using femtosecond pulses from a cavity-dumped titanium-doped sapphire laser, two types of nanoparticles with a core-shell geometry were studied. Nanoshells are nanoparticles with a dielectric core surrounded by a continuous thin metal shell. For nanoshells, the plasmon resonance wavelength is tunable by changing the core and shell dimensions. For nanoshells with a gold sulfide core and a gold shell, two conditions were observed under which electron relaxation was different than predicted by electron-phonon coupling. First, electron relaxation occurred more rapidly for gold-gold sulfide nanoshells embedded in polymer films than for nanoshells dispersed in water, with lifetimes of 1.6 ps and 3 to 5 ps, respectively. Second, for nanoshells dispersed in water, the electron relaxation lifetime decreased with adsorption of p-aminobenzoic acid (to 1.7 ps) or aniline (to 1.9 ps) on the nanoshells. With adsorbed n-propylamine or p-mercaptobenzoic acid, electron relaxation transpired in 2.8 ps or 2.4 ps, respectively. Density functional theory calculations indicated that the molecules leading to the fastest electron relaxation possessed the largest induced dipole moments near a metal surface. Semicontinuous gold films grown around a silica nanoparticle core exhibited spectral and dynamical optical signatures of the percolation threshold. Compared to continuous shells, the electron dynamics in the semicontinuous shell layer were dramatically different as additional induced bleaching was observed in the first 500 fs. The observed dynamics are consistent with a rate equation model in which the electrons are initially excited in localized

  7. Development of an ultrafast electron source based on a cold-field emission gun for ultrafast coherent TEM

    Science.gov (United States)

    Caruso, Giuseppe Mario; Houdellier, Florent; Abeilhou, Pierre; Arbouet, Arnaud

    2017-07-01

    We report on the design of a femtosecond laser-driven electron source for ultrafast coherent transmission electron microscopy. The proposed architecture allows introducing an ultrafast laser beam inside the cold field emission source of a commercial TEM, aligning and focusing the laser spot on the apex of the nanoemitter. The modifications of the gun assembly do not deteriorate the performances of the electron source in conventional DC mode and allow easy switching between the conventional and ultrafast laser-driven emission modes. We describe here this ultrafast electron source and discuss its properties.

  8. Ultrafast (picosecond) laser oscillator for educational use

    Science.gov (United States)

    Alexeev, I.; Ugurlu, A.; Seerdar, G.; Pflaum, C.

    2016-07-01

    Here, we present a description of an inexpensive ultrafast self-starting passively mode-locked laser oscillator that can be constructed using widely available off-the-shelf optical components. Such a laser system can be used to teach students the principles of solid state laser engineering, demonstrate a number of nonlinear optical phenomena, and perform qualitative and quantitative comparisons between numerical laser modeling and experimental results.

  9. Ultrafast Photovoltaic Response in Ferroelectric Nanolayers

    Science.gov (United States)

    2016-04-19

    1Department of Chemistry, Stanford University, Stanford, CA 94305 2PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory...9Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, Menlo Park, CA 94025 10Linac Coherent Light Source, SLAC ...of this research were carried out at the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory. LCLS is an Office of Science

  10. Probing Transient Electron Dynamics Using Ultrafast X Rays

    Science.gov (United States)

    Bucksbaum, Philip

    2016-05-01

    Linear x-ray absorption in atoms or molecules creates highly excited multi-electron quantum systems, which relax rapidly by fluorescence or Auger emission. These relaxation rates are usually less than a few femtoseconds in duration, and so they can reveal transient elecronic states in molecules as they undergo photo-induced transformations. I will show recent results from femtosecond x-ray experiments that display this phenomenon. There are efforts underway to push the temporal resolving power of ultrafast x-ray pulses into the attosecond regime, using stronger fields to initiate nonlinear absorption processes such as transient stimulated electronic Raman scattering. I will discuss current progress and future prospects for research in this area. This research is supported through Stanford PULSE Institute, SLAC National Accelerator Lab by the U.S. Department of Energy, Office of Basic Energy Sciences, Atomic, Molecular, and Optical Science Program.

  11. Comparing repetition-based melody segmentation models

    NARCIS (Netherlands)

    Rodríguez López, M.E.; de Haas, Bas; Volk, Anja

    2014-01-01

    This paper reports on a comparative study of computational melody segmentation models based on repetition detection. For the comparison we implemented five repetition-based segmentation models, and subsequently evaluated their capacity to automatically find melodic phrase boundaries in a corpus of 2

  12. Repetitions: A Cross-Cultural Study.

    Science.gov (United States)

    Murata, Kumiko

    1995-01-01

    This study investigated how repetition is used in conversation among native speakers of British English, native speakers of Japanese, and Japanese speakers of English. Five interactional functions of repetition (interruption-orientated, solidarity, silence-avoidance, hesitation, and reformulation) were identified, as well as the cultural factors…

  13. Digital repetitive control under varying frequency conditions

    CERN Document Server

    Ramos, Germán A; Olm, Josep M

    2013-01-01

    The tracking/rejection of periodic signals constitutes a wide field of research in the control theory and applications area. Repetitive Control has proven to be an efficient way to face this topic. However, in some applications the frequency of the reference/disturbance signal is time-varying or uncertain. This causes an important performance degradation in the standard Repetitive Control scheme. This book presents some solutions to apply Repetitive Control in varying frequency conditions without loosing steady-state performance. It also includes a complete theoretical development and experimental results in two representative systems. The presented solutions are organized in two complementary branches: varying sampling period Repetitive Control and High Order Repetitive Control. The first approach allows dealing with large range frequency variations while the second allows dealing with small range frequency variations. The book also presents applications of the described techniques to a Roto-magnet plant and...

  14. Investigation on the effect of exposure time on scintillator afterglow for ultra-fast tomography acquisition

    Science.gov (United States)

    Zefreh, K. Z.; Welford, F. M.; Sijbers, Jan

    2016-12-01

    Thanks to the ultra-fast endstation of the TOMCAT beamline, it is possible to do a tomographic scan with a sub-second temporal resolution which allows following dynamic processes in 4D (3D space + time). This ultra- high-rate tomography acquisition, exploiting the distinctive peculiarities of synchrotron radiation, provides nondestructive investigation of many dynamic processes which were not possible in the past. For example a continuous tensile test has been conducted recently in-situ for the first time with a frequency of 20 tomograms per second (20 Hz acquisition frequency). In the ultra-fast endstation a scintillator is used to convert X-ray to visible photons that can be detected by the camera. However, this conversion is not ideal and the scintillator response decays exponentially with afterglow. Afterglow can cause resolution degradation and artifacts (such as ring and band) especially with high rotation speed. On the other hand, to achieve a higher scan speed, thicker scintillators are more common because they result in higher emission intensities that can compensate the short exposure time in fast scans. However, the resolution deteriorates as the scintillator's thickness increases and thicker scintillators show higher afterglow. Performing many ultra-fast scans at the TOMCAT beamline with different acquisition rate, we demonstrate how the exposure time effects on the projection data and reconstructed images. Using two different thicknesses of LAG scintillator we also investigate the afterglow artifacts for different acquisition rate and exposure time.

  15. Optical beam dynamics in a gas repetitively heated by femtosecond filaments

    CERN Document Server

    Jhajj, N; Wahlstrand, J K; Milchberg, H M

    2013-01-01

    We investigate beam pointing dynamics in filamentation in gases driven by high repetition rate femtosecond laser pulses. Upon suddenly exposing a gas to a kilohertz train of filamenting pulses, the filament is steered from its original direction to a new stable direction whose equilibrium is determined by a balance among buoyant, viscous, and diffusive processes in the gas. Results are shown for Xe and air, but are broadly applicable to all configurations employing high repetition rate femtosecond laser propagation in gases.

  16. Strategies for Using Repetition as a Powerful Teaching Tool

    Science.gov (United States)

    Saville, Kirt

    2011-01-01

    Brain research indicates that repetition is of vital importance in the learning process. Repetition is an especially useful tool in the area of music education. The success of repetition can be enhanced by accurate and timely feedback. From "simple repetition" to "repetition with the addition or subtraction of degrees of freedom," there are many…

  17. Strategies for Using Repetition as a Powerful Teaching Tool

    Science.gov (United States)

    Saville, Kirt

    2011-01-01

    Brain research indicates that repetition is of vital importance in the learning process. Repetition is an especially useful tool in the area of music education. The success of repetition can be enhanced by accurate and timely feedback. From "simple repetition" to "repetition with the addition or subtraction of degrees of freedom," there are many…

  18. Environmental conditions associated with repetitive behavior in a group of African elephants.

    Science.gov (United States)

    Hasenjager, Matthew J; Bergl, Richard A

    2015-01-01

    Repetitive movement patterns are commonly observed in zoo elephants. The extent to which these behaviors constitute a welfare concern varies, as their expression ranges from stereotypies to potentially beneficial anticipatory behaviors. Nevertheless, their occurrence in zoo animals is often viewed negatively. To better identify conditions that prompt their performance, observations were conducted on six African elephants (Loxodonta africana) at the North Carolina Zoo. Individuals spent most of their time engaged in feeding, locomotion, resting, and repetitive behavior. Both generalized estimating equation and zero-inflated negative binomial models were used to identify factors associated with increased rates of repetitive behavior. Time of day in conjunction with location on- or off-exhibit best explained patterns of repetitive behavior. Repetitive behaviors occurred at a lower rate in the morning when on-exhibit, as compared to afternoons on-exhibit or at any time of day off-exhibit. Increased repetitive behavior rates observed on-exhibit in the afternoon prior to the evening transfer and feeding were possibly anticipatory responses towards those events. In contrast, consistently elevated frequencies of repetitive behavior off-exhibit at all times of day could be related to differences in exhibit complexity between off-exhibit and on-exhibit areas, as well as a lack of additional foraging opportunities. Our study contributes valuable information on captive elephant behavior and represents a good example of how behavioral research can be employed to improve management of zoo animals.

  19. Ultrafast dephasing of interband transitions in semiconductors

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Haichao

    2001-01-01

    [1]Becker, P. C., Fragnito, H. L., Brito, C. C. H. et al., Femtosecond photon echoes from band-to-band transitions in GaAs, Phys. Rev. Lett., 1988, 61: 1647—1649.[2]Lin, W. Z., Schoenlein, R. W., Fujimoto, J. G. et al., Femtosecond absorption saturation of hot carriers in GaAs and AlGaAs, IEEE JQE, 1988, 24: 267—275.[3]Gurevich, V. L., Muradov, M. I., Parshin, D. A., On the theory of femtosecond photon echoes from band-to -band transitions in semiconductors, Europhys. Lett., 1990, 12(4): 375—379.[4]Sayed, K. E., Bányai, L., Haug, H., Coulomb quantum kinetics and optical dephasing on the femtosecond time scale, Phys. Rev. B, 1994, 50:1541—1550.[5]Arlt, S., Siegner, U., Kunde, J. et al., Ultrafast dephasing of continuum transitions in bulk semiconductors, Phys. Rev. B, 1999, 59: 14860—14863.[6]Hügel, W. A., Heinrich, M. F., Wegener, M. et al., Photon echoes from semiconductor band-to -band continuum transitions in the regime of Coulomb quantum kinetics, Phys. Rev. Lett., 1999, 83(16): 3313—3316.[7]Scott, D. C., Binder, R., Koch, S. W., Ultrafast dephasing through acoustic plasmon undamping in nonequilibrium electron-hole plasmas, Phys. Rev. Lett., 1992, 69(2): 347—350.[8]Binder, R., Scott, D., Paul, A. E. et al., Carrier-carrier scattering and optical dephasing in highly excited semiconductors, Phys. Rev., B 1991, 45: 1107—1114.[9]Schilp, J., Kuhn, T., Mahler, G., Electron-phonon quantum kinetics in pulse-excited semiconductors: Memory and renormalization effects, Phys. Rev. B, 1994, 50: 5435—5447.[10]Snoke, D. W., Density dependence of electron scattering at low density, Phys. Rev., B 1994, 50: 11583—11591.[11]Leitenstorfer, A., Lohner, A., Rick, K. et al., Excitonic and free-carrier polarizations of bulk GaAs studied by femtosecond coherent spectroscopy, Phys. Rev., 1994B 49: 16372—16380.[12]Zhang, H. C., Wen, J. H., Guo, B. Hole-hole scattering of photoexcited heavy-holes in GaAs, Acta Physica

  20. Repetition priming from moving faces.

    Science.gov (United States)

    Lander, Karen; Bruce, Vicki

    2004-06-01

    Recent experiments have suggested that seeing a familiar face move provides additional dynamic information to the viewer, useful in the recognition of identity. In four experiments, repetition priming was used to investigate whether dynamic information is intrinsic to the underlying face representations. The results suggest that a moving image primes more effectively than a static image, even when the same static image is shown in the prime and the test phases (Experiment 1). Furthermore, when moving images are presented in the test phase (Experiment 2), there is an advantage for moving prime images. The most priming advantage is found with naturally moving faces, rather than with those shown in slow motion (Experiment 3). Finally, showing the same moving sequence at prime and test produced more priming than that found when different moving sequences were shown (Experiment 4). The results suggest that dynamic information is intrinsic to the face representations and that there is an advantage to viewing the same moving sequence at prime and test.