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Sample records for femtosecond pulse shaping

  1. Femtosecond profiling of shaped x-ray pulses

    Science.gov (United States)

    Hoffmann, M. C.; Grguraš, I.; Behrens, C.; Bostedt, C.; Bozek, J.; Bromberger, H.; Coffee, R.; Costello, J. T.; DiMauro, L. F.; Ding, Y.; Doumy, G.; Helml, W.; Ilchen, M.; Kienberger, R.; Lee, S.; Maier, A. R.; Mazza, T.; Meyer, M.; Messerschmidt, M.; Schorb, S.; Schweinberger, W.; Zhang, K.; Cavalieri, A. L.

    2018-03-01

    Arbitrary manipulation of the temporal and spectral properties of x-ray pulses at free-electron lasers would revolutionize many experimental applications. At the Linac Coherent Light Source at Stanford National Accelerator Laboratory, the momentum phase-space of the free-electron laser driving electron bunch can be tuned to emit a pair of x-ray pulses with independently variable photon energy and femtosecond delay. However, while accelerator parameters can easily be adjusted to tune the electron bunch phase-space, the final impact of these actuators on the x-ray pulse cannot be predicted with sufficient precision. Furthermore, shot-to-shot instabilities that distort the pulse shape unpredictably cannot be fully suppressed. Therefore, the ability to directly characterize the x-rays is essential to ensure precise and consistent control. In this work, we have generated x-ray pulse pairs via electron bunch shaping and characterized them on a single-shot basis with femtosecond resolution through time-resolved photoelectron streaking spectroscopy. This achievement completes an important step toward future x-ray pulse shaping techniques.

  2. Generating shaped femtosecond pulses in the far infrared using a spatial light modulator and difference frequency generation

    CSIR Research Space (South Africa)

    Botha, N

    2010-08-31

    Full Text Available Femtosecond pulse shaping can be done by different kinds of pulse shapers, such as liquid crystal spatial light modulators (LC SLM), acousto optic modulators (AOM) and deformable and movable mirrors. A few applications where pulse shaping...

  3. Thermally controlled femtosecond pulse shaping using metasurface based optical filters

    Science.gov (United States)

    Rahimi, Eesa; Şendur, Kürşat

    2018-02-01

    Shaping of the temporal distribution of the ultrashort pulses, compensation of pulse deformations due to phase shift in transmission and amplification are of interest in various optical applications. To address these problems, in this study, we have demonstrated an ultra-thin reconfigurable localized surface plasmon (LSP) band-stop optical filter driven by insulator-metal phase transition of vanadium dioxide. A Joule heating mechanism is proposed to control the thermal phase transition of the material. The resulting permittivity variation of vanadium dioxide tailors spectral response of the transmitted pulse from the stack. Depending on how the pulse's spectrum is located with respect to the resonance of the band-stop filter, the thin film stack can dynamically compress/expand the output pulse span up to 20% or shift its phase up to 360°. Multi-stacked filters have shown the ability to dynamically compensate input carrier frequency shifts and pulse span variations besides their higher span expansion rates.

  4. Thermally controlled femtosecond pulse shaping using metasurface based optical filters

    Directory of Open Access Journals (Sweden)

    Rahimi Eesa

    2018-02-01

    Full Text Available Shaping of the temporal distribution of the ultrashort pulses, compensation of pulse deformations due to phase shift in transmission and amplification are of interest in various optical applications. To address these problems, in this study, we have demonstrated an ultra-thin reconfigurable localized surface plasmon (LSP band-stop optical filter driven by insulator-metal phase transition of vanadium dioxide. A Joule heating mechanism is proposed to control the thermal phase transition of the material. The resulting permittivity variation of vanadium dioxide tailors spectral response of the transmitted pulse from the stack. Depending on how the pulse’s spectrum is located with respect to the resonance of the band-stop filter, the thin film stack can dynamically compress/expand the output pulse span up to 20% or shift its phase up to 360°. Multi-stacked filters have shown the ability to dynamically compensate input carrier frequency shifts and pulse span variations besides their higher span expansion rates.

  5. Adaptive control of lasers and their interactions with matter using femtosecond pulse shaping

    Science.gov (United States)

    Efimov, Anatoly

    Coherent control of chemical reactions, atomic and molecular systems, lattice dynamics, and electronic motion rely on femtosecond laser sources capable of producing programmable arbitrarily shaped waveforms. To enter the time scale of natural dynamic processes in many systems, femtosecond pulse shaping techniques must be extended to the ultrashort pulse domain (ISRS). We chose this material as a candidate for possible nonlinear oscillations regime for its wide band gap and superior optical properties allowing for high-energy excitation. To enter a nonlinear regime, however, complex asymmetric multiple-pulse excitation is required. Therefore, we make a detailed proposal of the experimental adaptive feedback implementation for optimization of phonon amplitude based on the coherent probe scattering and a novel phase mask calculation algorithm for the real-time asymmetric pulse train generation.

  6. Diffraction characteristics of spatial and temporal Gaussian-shaped femtosecond laser pulse by rectangle reflection grating.

    Science.gov (United States)

    Liu, Guohua; Xu, Rongrong; Yu, Wenbing; Wu, Hanping

    2011-02-20

    The exact intensity distribution expression for the spatial and temporal Gaussian-shaped femtosecond laser pulse diffracted by a rectangle reflection grating is derived. The spatial and temporal diffraction characteristics are theoretically investigated in detail, and a criterion for judging whether or not the diffraction pulse is just split into two independent pulses in the temporal domain is obtained. The results show that the diffraction intensity in the temporal domain consists of three parts: the intensity diffracted by the upper reflection surface of the grating, the intensity diffracted by the nether reflection surface, and their temporal coherent intensity. The temporal coherent intensity becomes weaker, even is zero, for the higher height from the nether surface to the upper surface of the grating. The principal maximum becomes more sharply bright for the bigger waist width of the femtosecond laser pulse in the spatial domain.

  7. Pulse shaping using a spatial light modulator

    CSIR Research Space (South Africa)

    Botha, N

    2009-07-01

    Full Text Available Femtosecond pulse shaping can be done by different kinds of pulse shapers, such as liquid crystal spatial light modulators (LC SLM), acousto optic modulators (AOM) and deformable and movable mirrors. A few applications where pulse shaping...

  8. Laser-Induced Damage with Femtosecond Pulses

    Science.gov (United States)

    Kafka, Kyle R. P.

    The strong electric fields of focused femtosecond laser pulses lead to non-equilibrium dynamics in materials, which, beyond a threshold intensity, causes laser-induced damage (LID). Such a strongly non-linear and non-perturbative process renders important LID observables like fluence and intensity thresholds and damage morphology (crater) extremely difficult to predict quantitatively. However, femtosecond LID carries a high degree of precision, which has been exploited in various micro/nano-machining and surface engineering applications, such as human eye surgery and super-hydrophobic surfaces. This dissertation presents an array of experimental studies which have measured the damage behavior of various materials under femtosecond irradiation. Precision experiments were performed to produce extreme spatio-temporal confinement of the femtosecond laser-solid damage interaction on monocrystalline Cu, which made possible the first successful direct-benchmarking of LID simulation with realistic damage craters. A technique was developed to produce laser-induced periodic surface structures (LIPSS) in a single pulse (typically a multi-pulse phenomenon), and was used to perform a pump-probe study which revealed asynchronous LIPSS formation on copper. Combined with 1-D calculations, this new experimental result suggests more drastic electron heating than expected. Few-cycle pulses were used to study the LID performance and morphology of commercial ultra-broadband optics, which had not been systematically studied before. With extensive surface analysis, various morphologies were observed, including LIPSS, swelling (blisters), simple craters, and even ring-shaped structures, which varied depending on the coating design, number of pulses, and air/vacuum test environment. Mechanisms leading to these morphologies are discussed, many of which are ultrafast in nature. The applied damage behavior of multi-layer dielectric mirrors was measured and compared between long pulse (150 ps

  9. Instantaneous nonvertical electronic transitions with shaped femtosecond laser pulses: Is it possible?

    DEFF Research Database (Denmark)

    Henriksen, Niels Engholm; Møller, Klaus Braagaard

    2003-01-01

    In molecular electronic transitions, a vertical transition can be induced by an ultrashort laser pulse. That is, a replica of the initial nuclear state-times the transition dipole moment of the electronic transition-can be created instantaneously (on the time scale of nuclear motion) in the excited...

  10. Fast Shape Evolution of Laser Filaments in the Wake of Femtosecond Driving Pulse

    Science.gov (United States)

    Romanov, Dmitri; Levis, Robert

    2013-05-01

    A theoretical model is developed for subnanosecond evolution of highly nonequilibrium, inhomogeneous free-electron gas in a laser filament/microfilament wake channel. The evolution is driven by two interrelated mechanisms: (i) impact ionization of residual neutral atoms inside the channel and on its surface, and (ii) thermal conduction in the electron gas. The simulation results for the cases of weak and moderate initial ionization show crucial importance of incorporating the spread effects, especially as regards the electron temperature. The calculated evolution patterns determine the transient optical and electronic properties of filament wake channels. Accordingly, we propose tracing the wake channel evolution via linear and nonlinear light-scattering experiments. The evolving shape of the electron density distribution can be extracted from longitudinal and/or transverse Fraunhofer diffraction patterns. Complementarily, the evolving temperature distribution may be deduced either from angular-resolved four-wave-mixing experiments or from the spatial-spectral patterns of giant Rabi sidebands. Medium-specific estimates are made for atmospheric-pressure argon gas. In molecular-gas cases, the model can be straightforwardly augmented to incorporate the processes of dissociative recombination and vibrational excitations. Support from the Air Force Office of Scientific Research, Grant No. N00014-10-0293, is gratefully acknowledged.

  11. Optical reprogramming of human somatic cells using ultrashort Bessel-shaped near-infrared femtosecond laser pulses

    Science.gov (United States)

    Uchugonova, Aisada; Breunig, Hans Georg; Batista, Ana; König, Karsten

    2015-11-01

    We report a virus-free optical approach to human cell reprogramming into induced pluripotent stem cells with low-power nanoporation using ultrashort Bessel-shaped laser pulses. Picojoule near-infrared sub-20 fs laser pulses at a high 85 MHz repetition frequency are employed to generate transient nanopores in the membrane of dermal fibroblasts for the introduction of four transcription factors to induce the reprogramming process. In contrast to conventional approaches which utilize retro- or lentiviruses to deliver genes or transcription factors into the host genome, the laser method is virus-free; hence, the risk of virus-induced cancer generation limiting clinical application is avoided.

  12. Generation of Femtosecond Electron and Photon Pulses

    CERN Document Server

    Thongbai, Chitrlada; Kangrang, Nopadol; Kusoljariyakul, Keerati; Rhodes, Michael W; Rimjaem, Sakhorn; Saisut, Jatuporn; Vilaithong, Thiraphat; Wichaisirimongkol, Pathom; Wiedemann, Helmut

    2005-01-01

    Femtosecond electron and photon pulses become a tool of interesting important to study dynamics at molecular or atomic levels. Such short pulses can be generated from a system consisting of an RF-gun with a thermionic cathode, an alpha magnet as a magnetic bunch compressor, and a linear accelerator. The femtosecond electron pulses can be used directly or used as sources to produce electromagnetic radiation of equally short pulses by choosing certain kind of radiation pruduction processes. At the Fast Neutron Research Facility (Thailand), we are especially interested in production of radiation in Far-infrared and X-ray regime. In the far-infrared wavelengths which are longer than the femtosecond pulse length, the radiation is emitted coherently producing intense radiation. In the X-ray regime, development of femtosecond X-ray source is crucial for application in ultrafast science.

  13. Characterization and modulation of femtosecond laser pulse

    International Nuclear Information System (INIS)

    Dorrer, Christophe

    1999-01-01

    This work brings some solutions to the characterization and control of femtosecond laser pulses. Spectral interferometry has been extensively studied; whereas this is a rather old technique, it has found new specific applications to short pulses. Several important points concerning the experimental implementation of this technique are treated. Sources of errors have been tracked and simple solutions have been found to enhance its reliability. A recently demonstrated technique for the complete characterization of short pulses has been used to characterize short pulses from Chirped Pulse Amplification Systems. This transposition of shearing interferometry to the optical frequency domain, known as Spectral Phase Interferometry for Direct Electric-field Reconstruction (SPlDER), is conceptually very interesting: for example, the inversion from the experimental data to the electric field to be characterized is completely algebraic. A reliable tool for the characterization and optimization of Chirped pulse amplification systems has been built on this principle. This is the first single-shot real-time characterization implementation of this technique. An improvement of the method has also allowed the first single-shot real-time characterization of a short pulse using a single mono-dimensional integrative detector and an algebraic inversion of the experimental data. The control of these pulses is also of prior interest. Through a collaboration with Thomson CSF-LCR, the demonstration of the use of an optically addressed light valve at the Fourier plane of a zero-dispersion line for spectral phase modulation has been made. This device allows a high-resolution control of the spectral phase of a short pulse. It is a well-adapted tool for the correction of the residual spectral phase, at the output of Chirped Pulse Amplification systems and the temporal synthesis of shaped pulses for specific experiments. (author) [fr

  14. Amorphization of silicon by femtosecond laser pulses

    International Nuclear Information System (INIS)

    Jia, Jimmy; Li Ming; Thompson, Carl V.

    2004-01-01

    We have used femtosecond laser pulses to drill submicron holes in single crystal silicon films in silicon-on-insulator structures. Cross-sectional transmission electron microscopy and energy dispersive x-ray analysis of material adjacent to the ablated holes indicates the formation of a layer of amorphous Si. This demonstrates that even when material is ablated using femtosecond pulses near the single pulse ablation threshold, sufficient heating of the surrounding material occurs to create a molten zone which solidifies so rapidly that crystallization is bypassed

  15. Growth and shape of indium islands on molybdenum at micro-roughened spots created by femtosecond laser pulses

    Science.gov (United States)

    Ringleb, F.; Eylers, K.; Teubner, Th.; Schramm, H.-P.; Symietz, C.; Bonse, J.; Andree, S.; Heidmann, B.; Schmid, M.; Krüger, J.; Boeck, T.

    2017-10-01

    Indium islands on molybdenum coated glass can be grown in ordered arrays by surface structuring using a femtosecond laser. The effect of varying the molybdenum coated glass substrate temperature and the indium deposition rate on island areal density, volume and geometry is investigated and evaluated in a physical vapor deposition (PVD) process. The joined impact of growth conditions and spacing of the femtosecond laser structured spots on the arrangement and morphology of indium islands is demonstrated. The results yield a deeper understanding of the island growth and its precise adjustment to industrial requirements, which is indispensable for a technological application of such structures at a high throughput, for instance as precursors for the preparation of Cu(In,Ga)Se2 micro concentrator solar cells.

  16. Improvement of aluminum drilling efficiency and precision by shaped femtosecond laser

    Energy Technology Data Exchange (ETDEWEB)

    Qi, Ying; Qi, Hongxia; Chen, Anmin, E-mail: amchen@jlu.edu.cn; Hu, Zhan, E-mail: huzhan@jlu.edu.cn

    2014-10-30

    Highlights: • The ablation accuracy can be improved by the shaped femtosecond laser pulse. • The ablation rate can be improved by the shaped femtosecond laser pulse with higher laser fluence. • The results can be used to optimize femtosecond micromachining metal. - Abstract: Shaped femtosecond laser pulses with the plain phase (transform-limited pulse) and sine phase (A = 1.2566, T = 30, T = 10, and T = 5) were used to drill Al sheet in vacuum. Using different phase, the number of pulses required to drill through the sheet was different. With lower laser pulse energy, the ablation rate was the highest when plain phase (corresponding to transform limited pulse) was used. With higher laser energy, the optimized ablation rate can be achieved by increasing the time separation between the subpulses of pulse train produced from the sine phase function. And, with the shaped femtosecond laser, the diameter of ablation holes produced was smaller, the ablation precision was also improved. The results showed that shaped femtosecond laser pulse has great advantages in the context of femtosecond laser drilling.

  17. Cascaded Soliton Compression of Energetic Femtosecond Pulses at 1030 nm

    DEFF Research Database (Denmark)

    Bache, Morten; Zhou, Binbin

    2012-01-01

    We discuss soliton compression with cascaded second-harmonic generation of energetic femtosecond pulses at 1030 nm. We discuss problems encountered with soliton compression of long pulses and show that sub-10 fs compressed pulses can be achieved.......We discuss soliton compression with cascaded second-harmonic generation of energetic femtosecond pulses at 1030 nm. We discuss problems encountered with soliton compression of long pulses and show that sub-10 fs compressed pulses can be achieved....

  18. Characteristics and Applications of Spatiotemporally Focused Femtosecond Laser Pulses

    Directory of Open Access Journals (Sweden)

    Chenrui Jing

    2016-12-01

    Full Text Available Simultaneous spatial and temporal focusing (SSTF of femtosecond laser pulses gives rise to strong suppression of nonlinear self-focusing during the propagation of the femtosecond laser beam. In this paper, we begin with an introduction of the principle of SSTF, followed by a review of our recent experimental results on the characterization and application of the spatiotemporally focused pulses for femtosecond laser micromachining. Finally, we summarize all of the results and give a future perspective of this technique.

  19. Optical reprogramming with ultrashort femtosecond laser pulses

    Science.gov (United States)

    Uchugonova, Aisada; Breunig, Hans G.; Batista, Ana; König, Karsten

    2015-03-01

    The use of sub-15 femtosecond laser pulses in stem cell research is explored with particular emphasis on the optical reprogramming of somatic cells. The reprogramming of somatic cells into induced pluripotent stem (iPS) cells can be evoked through the ectopic expression of defined transcription factors. Conventional approaches utilize retro/lenti-viruses to deliver genes/transcription factors as well as to facilitate the integration of transcription factors into that of the host genome. However, the use of viruses may result in insertional mutations caused by the random integration of genes and as a result, this may limit the use within clinical applications due to the risk of the formation of cancer. In this study, a new approach is demonstrated in realizing non-viral reprogramming through the use of ultrashort laser pulses, to introduce transcription factors into the cell so as to generate iPS cells.

  20. Generation and patterning of Si nanoparticles by femtosecond laser pulses

    Science.gov (United States)

    Zywietz, Urs; Reinhardt, Carsten; Evlyukhin, Andrey B.; Birr, Tobias; Chichkov, Boris N.

    2014-01-01

    The unique optical properties of nanoparticles are highly sensitive in respect to particle shapes, sizes, and localization on a sample. This demands for a fully controlled fabrication process. The use of femtosecond laser pulses to generate and transfer nanoparticles from a bulk target towards a collector substrate is a promising approach. This process allows a controlled fabrication of spherical nanoparticles with a very smooth surface. Several process parameters can be varied to achieve the desired nanoparticle characteristics. In this paper, the influence of two of these parameters, i.e. the applied pulse energy and the laser beam shape, on the generation of Si nanoparticles from a bulk Si target are studied in detail. By changing the laser intensity distribution on the target surface one can influence the dynamics of molten material inducing its flow to the edges or to the center of the focal spot. Due to this dynamics of molten material, a single femtosecond laser pulse with a Gaussian beam shape generates multiple spherical nanoparticles from a bulk Si target. The statistical properties of this process, with respect to number of generated nanoparticles and laser pulse energy are investigated. We demonstrate for the first time that a ring-shaped intensity distribution on the target surface results in the generation of a single silicon nanoparticle with a controllable size. Furthermore, the generated silicon nanoparticles presented in this paper show strong electric and magnetic dipole resonances in the visible and near-infrared spectral range. Theoretical simulations as well as optical scattering measurements of single silicon nanoparticles are discussed and compared.

  1. Kilohertz generation of high contrast polarization states for visible femtosecond pulses via phase-locked acousto-optic pulse shapers

    Energy Technology Data Exchange (ETDEWEB)

    Seiler, Hélène; Walsh, Brenna; Palato, Samuel; Kambhampati, Patanjali, E-mail: pat.kambhampati@mcgill.ca [Department of Chemistry, McGill University, Montreal, Quebec H3A 0B8 (Canada); Thai, Alexandre; Forget, Nicolas [Fastlite, 1900 route des Crêtes, 06560 Valbonne (France); Crozatier, Vincent [Fastlite, Centre Scientifique d' Orsay, Bât.503, Plateau du Moulon, BP 45 Orsay (France)

    2015-09-14

    We present a detailed analysis of a setup capable of arbitrary amplitude, phase, and polarization shaping of broadband visible femtosecond pulses at 1 kHz via a pair of actively phase stabilized acousto-optic programmable dispersive filters arranged in a Mach-Zehnder interferometer geometry. The setup features phase stability values around λ/225 at 580 nm as well as degrees of polarization of at least 0.9 for any polarization state. Both numbers are important metrics to evaluate a setup's potential for applications based on polarization-shaped femtosecond pulses, such as fully coherent multi-dimensional electronic spectroscopy.

  2. Green synthesis of gold nanoparticles of different sizes and shapes using agar-agar water solution and femtosecond pulse laser irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Almeida de Matos, Ricardo [Universidade Federal de Sao Paulo (UNIFESP) - Campus Diadema, Instituto de Ciencias Ambientais, Quimicas e Farmaceuticas (ICAQF), Departamento de Ciencias Exatas e da Terra (DCET), Diadema, SP (Brazil); Universidade Federal de Sao Paulo - UNIFESP, Sao Paulo (Brazil); Silva Cordeiro, Thiago da; Elgul Samad, Ricardo; Dias Vieira, Nilson [Instituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP, Sao Paulo (Brazil); Coronato Courrol, Lilia [Universidade Federal de Sao Paulo - UNIFESP, Sao Paulo (Brazil); Instituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP, Sao Paulo (Brazil)

    2012-11-15

    We report a method to create gold nanoparticles of different sizes and shapes using agar-agar water solution and irradiation with light from a xenon lamp, followed by ultrashort laser pulses. No additives, such as solvents, surfactants or reducing agents, were used in the procedure. Laser irradiation (laser ablation) was important to the reduction of the nanoparticles diameter and formation of another shapes. Distilled water was used as solvent and agar-agar (hydrophilic colloid extracted from certain seaweeds) was important for the stabilization of gold nanoparticles, avoiding their agglomeration. The formation of gold nanoparticles was confirmed with ultraviolet-visible absorption and TEM microscopy. The gold nanoparticles acquired spherical, prism, and rod shapes depending on the laser parameters. Variation of laser irradiation parameters as pulse energy, irradiation time and repetition rate was assessed. The relevant mechanisms contributing for the gold nanoparticles production are discussed. (orig.)

  3. Nanospallation induced by a femtosecond laser pulse

    Science.gov (United States)

    Agranat, M. B.; Anisimov, S. I.; Ashitkov, S. I.; Zhakhovskii, V. V.; Inogamov, N. A.; Nishihara, K.; Petrov, Yu. V.

    2008-01-01

    In the present work phenomena are considered related to the interaction of ultra-short laser pulses, τ L~0.1 ps, with metallic targets. The absorption of laser pulse results in formation of thin layer of hot electrons strongly superheated (T e>>T i) relative to the ion temperature, T i. Initial thickness of the layer d heat is small, d heat~δ, where δ~10 nm is the skin layer thickness. Subsequent developments include the following stages: (1) Propagation of electron thermal wave which expands the hot layer d heat; (2) Cooling of electrons due to energy transfer to cold ions; (3) Onset of hydrodynamic motion that constitutes the rarefaction wave with positive pressure; (4) Further expansion of target material leading to the appearance of negative pressure; and (5) Long separation process which begins with nucleation of voids and goes on to the total separation of spallation plate. The thickness of the plate is ~10 nm (we call it nanospallation). Theoretical model involves two-temperature hydrodynamic equations with semiempirical EOS for a metal, electron heat conduction and electron-ion energy exchange. The decay of metastable strongly stretched matter is described by molecular dynamics (MD) simulation with extremely large number of atoms. The experimental setup includes femtosecond chromium-forsterite laser operating in the pump-probe regime. The experiments are performed with gold target. Measured ablation threshold for gold is 1.35 J/cm2 of incident pump light at inclination 45°, p-polarization. Calorimeter measurements give for the absorbed fluence F abs=0.3F inc, therefore the threshold value of F abs is 0.4 J/cm2.

  4. Pulse radiolysis based on a femtosecond electron beam and a femtosecond laser light with double-pulse injection technique

    International Nuclear Information System (INIS)

    Yang Jinfeng; Kondoh, Takafumi; Kozawa, Takahiro; Yoshida, Youichi; Tagawa, Seiichi

    2006-01-01

    A new pulse radiolysis system based on a femtosecond electron beam and a femtosecond laser light with oblique double-pulse injection was developed for studying ultrafast chemical kinetics and primary processes of radiation chemistry. The time resolution of 5.2 ps was obtained by measuring transient absorption kinetics of hydrated electrons in water. The optical density of hydrated electrons was measured as a function of the electron charge. The data indicate that the double-laser-pulse injection technique was a powerful tool for observing the transient absorptions with a good signal to noise ratio in pulse radiolysis

  5. Piecewise Adiabatic Passage with a Series of Femtosecond Pulses

    International Nuclear Information System (INIS)

    Shapiro, E. A.; Milner, V.; Menzel-Jones, C.; Shapiro, M.

    2007-01-01

    We develop a method of executing complete population transfers between quantum states in a piecewise manner using a series of femtosecond laser pulses. The method can be applied to a large class of problems as it benefits from the high peak powers and large spectral bandwidths afforded by femtosecond pulses. The degree of population transfer is robust to a wide variation in the absolute and relative intensities, durations, and time ordering of the pulses. The method is studied in detail for atomic sodium where piecewise adiabatic population transfer, as well as the induction of Ramsey-type interferences, is demonstrated

  6. Correlation functions formed by a femtosecond pulse interferometer

    NARCIS (Netherlands)

    Cui, M.; Bhattacharya, N.; Urbach, H.P.; Van den berg, S.A.

    2008-01-01

    We experimentally demonstrate that a stabilized femtosecond frequency comb can be applied as a tool for distance measurement. The scheme is based on optical interference between individual pulses in a Michelson type interferometer. The cross-correlation functions between individual pulses with a

  7. High aspect ratio nanoholes in glass generated by femtosecond laser pulses with picosecond intervals

    Science.gov (United States)

    Ahn, Sanghoon; Choi, Jiyeon; Noh, Jiwhan; Cho, Sung-Hak

    2018-02-01

    Because of its potential uses, high aspect ratio nanostructures have been interested for last few decades. In order to generate nanostructures, various techniques have been attempted. Femtosecond laser ablation is one of techniques for generating nanostructures inside a transparent material. For generating nanostructures by femtosecond laser ablation, previous studies have been attempted beam shaping such as Bessel beam and temporal tailored beam. Both methods suppress electron excitation at near surface and initiate interference of photons at certain depth. Recent researches indicate that shape of nanostructures is related with temporal change of electron density and number of self-trapped excitons. In this study, we try to use the temporal change of electron density induced by femtosecond laser pulse for generating high aspect ratio nanoholes. In order to reveal the effect of temporal change of electron density, secondary pulses are irradiated from 100 to 1000 ps after the irradiation of first pulse. Our result shows that diameter of nanoholes is increasing and depth of nanoholes is decreasing as pulse to pulse interval is getting longer. With manipulating of pulse to pulse interval, we could generate high aspect ratio nanoholes with diameter of 250-350 nm and depth of 4∼6 μm inside a glass.

  8. Patterning of silicon differences between nanosecond and femtosecond laser pulses

    Science.gov (United States)

    Weingärtner, M.; Elschner, R.; Bostanjoglo, O.

    1999-01-01

    Si (100) surfaces were exposed to 8 ns and 100 fs laser pulses with fluences≤3 J/cm 2 and ≤0.5 J/cm 2, respectively. Transient stages and final patterns were investigated by pulsed photoelectron microscopy and scanning electron plus light interference microscopy. Though the pattern formation extends for both pulse lengths over the same time of some 10 ns, the patterns are different. Nanosecond pulses produce smooth craters and remove a covering oxide. Femtosecond pulses ablate an oxide-free Si surface and produce flat pits covered by nanodrops, whereas oxide-covered surfaces are converted to a foam, which solidifies to a blistered structure.

  9. Digital pulse shape discrimination

    International Nuclear Information System (INIS)

    Miller, L. F.; Preston, J.; Pozzi, S.; Flaska, M.; Neal, J.

    2007-01-01

    Pulse-shape discrimination (PSD) has been utilised for about 40 years as a method to obtain estimates for dose in mixed neutron and photon fields. Digitizers that operate close to GHz are currently available at a reasonable cost, and they can be used to directly sample signals from photomultiplier tubes. This permits one to perform digital PSD rather than the traditional, and well-established, analogous techniques. One issue that complicates PSD for neutrons in mixed fields is that the light output characteristics of typical scintillators available for PSD, such as BC501A, vary as a function of energy deposited in the detector. This behaviour is more easily accommodated with digital processing of signals than with analogous signal processing. Results illustrate the effectiveness of digital PSD. (authors)

  10. Tracking Femtosecond Laser Pulses in Space and Time

    NARCIS (Netherlands)

    Balistreri, M.L.M.; Gersen, H.; Korterik, Jeroen P.; Kuipers, L.; van Hulst, N.F.

    2001-01-01

    We show that the propagation of a femtosecond laser pulse inside a photonic structure can be directly visualized and tracked as it propagates using a time-resolved photon scanning tunneling microscope. From the time-dependent and phase- sensitive measurements, both the group velocity and the phase

  11. Propagation delay of femtosecond pulses in an optical amplifier

    DEFF Research Database (Denmark)

    Poel, Mike van der; Mørk, Jesper; Hvam, Jørn Märcher

    of 2.6 THz, through a quantum-dot (QD) semiconductor amplifier (SOA) at room temperature. This extremely large bandwidth, on the other hand, is at the cost of a rather small group index change of ?ng=4*10-3. We have performed two types of femtosecond pulse slow-down and advancement experiments....... In the first experiment, we prepare a narrow peak or dip in the SOA gain spectrum by injection of a strong pump pulse4. The resulting dispersion feature is then probed by a weak pulse. In the second experiment, we measure self-slowdown or advancement as pulse energy isincreased5. In both cases, we perform...

  12. Enhancement of peak intensity in a filament core with spatiotemporally focused femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Zeng Bin; Chu Wei; Li Guihua; Zhang Haisu; Ni Jielei [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Graduate School of Chinese Academy of Sciences, Beijing 100080 (China); Gao Hui; Liu Weiwei [Institute of Modern Optics, Nankai University, Tianjin, 300071 (China); Yao Jinping; Cheng Ya; Xu Zhizhan [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Chin, See Leang [Center for Optics, Photonics and Laser (COPL) and Department of Physics, Engineering Physics and Optics, Universite Laval, Quebec City, QC, G1V 0A6 (Canada)

    2011-12-15

    We demonstrate that the peak intensity in the filament core, which is inherently limited by the intensity clamping effect during femtosecond laser filamentation, can be significantly enhanced using spatiotemporally focused femtosecond laser pulses. In addition, the filament length obtained by spatiotemporally focused femtosecond laser pulses is {approx}25 times shorter than that obtained by a conventional focusing scheme, resulting in improved high spatial resolution.

  13. Development of a new picosecond pulse radiolysis system by using a femtosecond laser synchronized with a picosecond linac. A step to femtosecond pulse radiolysis

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, Yoichi; Yamamoto, Tamotsu; Miki, Miyako; Seki, Shu; Okuda, Shuichi; Honda, Yoshihide; Kimura, Norio; Tagawa, Seiichi [Osaka Univ., Ibaraki (Japan). Inst. of Scientific and Industrial Research; Ushida, Kiminori

    1997-03-01

    A new picosecond pulse radiolysis system by using a Ti sapphire femtosecond laser synchronized with a 20 ps electron pulse from the 38 MeV L-band linac has been developed for the research of the ultra fast reactions in primary processes of radiation chemistry. The timing jitter in the synchronization of the laser pulse with the electron pulse is less than several picosecond. The technique can be used in the next femtosecond pulse radiolysis. (author)

  14. Colorizing metals with femtosecond laser pulses

    International Nuclear Information System (INIS)

    Vorobyev, A. Y.; Guo Chunlei

    2008-01-01

    For centuries, it had been the dream of alchemists to turn inexpensive metals into gold. Certainly, it is not enough from an alchemist's point of view to transfer only the appearance of a metal to gold. However, the possibility of rendering a certain metal to a completely different color without coating can be very interesting in its own right. In this work, we demonstrate a femtosecond laser processing technique that allows us to create a variety of colors on a metal that ultimately leads us to control its optical properties from UV to terahertz

  15. Rapid microfabrication of transparent materials using filamented femtosecond laser pulses

    Science.gov (United States)

    Butkus, S.; Gaižauskas, E.; Paipulas, D.; Viburys, Ž.; Kaškelyė, D.; Barkauskas, M.; Alesenkov, A.; Sirutkaitis, V.

    2014-01-01

    Microfabrication of transparent materials using femtosecond laser pulses has showed good potential towards industrial application. Maintaining pulse energies exceeding the critical self-focusing threshold by more than 100-fold produced filaments that were used for micromachining purposes. This article demonstrates two different micromachining techniques using femtosecond filaments generated in different transparent media (water and glass). The stated micromachining techniques are cutting and welding of transparent samples. In addition, cutting and drilling experiments were backed by theoretical modelling giving a deeper insight into the whole process. We demonstrate cut-out holes in soda-lime glass having thickness up to 1 mm and aspect ratios close to 20, moreover, the fabrication time is of the order of tens of seconds, in addition, grooves and holes were fabricated in hardened 1.1 mm thick glass (Corning Gorilla glass). Glass welding was made possible and welded samples were achieved after several seconds of laser fabrication.

  16. Desorption by Femtosecond Laser Pulses : An Electron-Hole Effect?

    OpenAIRE

    D. M., NEWNS; T. F., HEINZ; J. A., MISEWICH; IBM Research Division, T. J. Watson Research Center; IBM Research Division, T. J. Watson Research Center; IBM Research Division, T. J. Watson Research Center

    1992-01-01

    Desorption of molecules from metal surfaces induced by femtosecond visible laser pulses has been reported. Since the lattice temperature rise is insufficient to explain desorption, an electronic mechanism is clearly responsible. It is shown that a theory based on direct coupling between the center-of-mass degree of freedom of the adsorbate and the electron-hole excitations of the substrate provides a satisfactory explanation of the various experimental findings.

  17. Femtosecond Pulse Propagation in a Highly Nonlinear Photonic Crystal Fiber

    OpenAIRE

    J. F. Gabayno; C. A. Alonzo; W. O. Garcia

    2004-01-01

    Femtosecond pulses are launched into a highly nonlinear photonic crystal fiber (PCF). The input and output spectra were measured using a monochromator and streak camera. The spectrum of the output from a 50 cm PCF pumped at 794 nm for different pump powers features asymmetric side lobes due to intrapulse Raman scattering. Similar measurements on a 100 cm PCF pumped at 795 nm highlight the appearance of blueshifted peaks as a result of energy transfer of solitons to dispersive waves. Broadenin...

  18. Conical Double Frequency Emission by Femtosecond Laser Pulses from DKDP

    International Nuclear Information System (INIS)

    Xi-Peng, Zhang; Hong-Bing, Jiang; Shan-Chun, Tang; Qi-Huang, Gong

    2009-01-01

    Conical double frequency emission is investigated by femtosecond laser pulses at a wavelength of 800 nm in a DKDP crystal. It is demonstrated that the sum frequency of incident wave and its scattering wave accounts for the conical double frequency emission. The gaps on the conical rings are observed and they are very sensitive to the propagation direction, and thus could be used to detect the small angle deviation of surface direction. (fundamental areas of phenomenology (including applications))

  19. Communication: The electronic structure of matter probed with a single femtosecond hard x-ray pulse

    Directory of Open Access Journals (Sweden)

    J. Szlachetko

    2014-03-01

    Full Text Available Physical, biological, and chemical transformations are initiated by changes in the electronic configuration of the species involved. These electronic changes occur on the timescales of attoseconds (10−18 s to femtoseconds (10−15 s and drive all subsequent electronic reorganization as the system moves to a new equilibrium or quasi-equilibrium state. The ability to detect the dynamics of these electronic changes is crucial for understanding the potential energy surfaces upon which chemical and biological reactions take place. Here, we report on the determination of the electronic structure of matter using a single self-seeded femtosecond x-ray pulse from the Linac Coherent Light Source hard x-ray free electron laser. By measuring the high energy resolution off-resonant spectrum (HEROS, we were able to obtain information about the electronic density of states with a single femtosecond x-ray pulse. We show that the unoccupied electronic states of the scattering atom may be determined on a shot-to-shot basis and that the measured spectral shape is independent of the large intensity fluctuations of the incoming x-ray beam. Moreover, we demonstrate the chemical sensitivity and single-shot capability and limitations of HEROS, which enables the technique to track the electronic structural dynamics in matter on femtosecond time scales, making it an ideal probe technique for time-resolved X-ray experiments.

  20. Femtosecond laser pulses principles and experiments

    CERN Document Server

    1998-01-01

    This smooth introduction for advanced undergraduate students starts with the fundamentals of lasers and pulsed optics Thus prepared, the student learns how to generate short and ultrashort laser pulses, how to manipulate them, and how to measure them Finally, spectroscopic implications are discussed This rounded text gives the student an up-to-date introduction to one of the most exciting fields in laser physics

  1. Optical trapping with femtosecond laser pulses

    Science.gov (United States)

    Devi, Anita; Dhamija, Shaina; De, Arijit K.

    2017-08-01

    Laser trapping of 100nm diameter polystyrene bead under high repetition rate ultrafast pulsed excitation is studied theoretically as well as experimentally. In our theoretical analysis, we explore the role of optical Kerr effect at 50mW average power under pulsed excitation. In our experiment, we use a CMOS camera to record two-photon fluorescence signal from the trapped particle which decays with time due to photo-bleaching.

  2. Femtosecond few-cycle mid-infrared laser pulses

    DEFF Research Database (Denmark)

    Liu, Xing

    The few-cycle pulses of mid-infrared (mid-IR, wavelength 2-10 microns) have attracted increasing attention owing to their great potentials for high order harmonic generation, time-resolved spectroscopy, precision of cutting and biomedical science.In this thesis, mid-IR frequency conversion.......2 - 5.5 μm with only one fixed pump wavelength, a feature absent in Kerr media. Finally, we experimentally observe supercontinuum generation spanning 1.5 octaves, generated in a 10 mm long silicon-rich nitride waveguide pumped by 100 pJ femtosecond pulses from an erbium fiber laser. The waveguide has...

  3. Formation of multiscale surface structures on nickel via above surface growth and below surface growth mechanisms using femtosecond laser pulses.

    Science.gov (United States)

    Zuhlke, Craig A; Anderson, Troy P; Alexander, Dennis R

    2013-04-08

    The formation of self-organized micro- and nano-structured surfaces on nickel via both above surface growth (ASG) and below surface growth (BSG) mechanisms using femtosecond laser pulse illumination is reported. Detailed stepped growth experiments demonstrate that conical mound-shaped surface structure development is characterized by a balance of growth mechanisms including scattering from surface structures and geometric effects causing preferential ablation of the valleys, flow of the surface melt, and redeposition of ablated material; all of which are influenced by the laser fluence and the number of laser shots on the sample. BSG-mound formation is dominated by scattering, while ASG-mound formation is dominated by material flow and redeposition. This is the first demonstration to our knowledge of the use of femtosecond laser pulses to fabricate metallic surface structures that rise above the original surface. These results are useful in understanding the details of multi-pulse femtosecond laser interaction with metals.

  4. High efficiency, monolithic fiber chirped pulse amplification system for high energy femtosecond pulse generation.

    Science.gov (United States)

    Peng, Xiang; Kim, Kyungbum; Mielke, Michael; Jennings, Stephen; Masor, Gordon; Stohl, Dave; Chavez-Pirson, Arturo; Nguyen, Dan T; Rhonehouse, Dan; Zong, Jie; Churin, Dmitriy; Peyghambarian, N

    2013-10-21

    A novel monolithic fiber-optic chirped pulse amplification (CPA) system for high energy, femtosecond pulse generation is proposed and experimentally demonstrated. By employing a high gain amplifier comprising merely 20 cm of high efficiency media (HEM) gain fiber, an optimal balance of output pulse energy, optical efficiency, and B-integral is achieved. The HEM amplifier is fabricated from erbium-doped phosphate glass fiber and yields gain of 1.443 dB/cm with slope efficiency >45%. We experimentally demonstrate near diffraction-limited beam quality and near transform-limited femtosecond pulse quality at 1.55 µm wavelength. With pulse energy >100 µJ and pulse duration of 636 fs (FWHM), the peak power is estimated to be ~160 MW. NAVAIR Public Release Distribution Statement A-"Approved for Public release; distribution is unlimited".

  5. Influence of SOD on THG for femtosecond laser pulse

    Science.gov (United States)

    Trofimov, Vyacheslav A.; Sidorov, Pavel S.

    2017-02-01

    THG is used nowadays in many practical applications such as a substance diagnostics, and biological objects imaging, and etc. Therefore, THG features understanding are urgent problem and this problem attracts an attention of many researchers. In this paper we analyze THG efficiency of a femtosecond laser pulse. Consideration is based on computer simulation of the laser pulse propagation with taking into account a selfand cross- modulation of the interacting waves, and their SOD, and phase mismatching. Moreover, we analyze an influence of the non-homogeneous phase mismatching along laser pulse propagation coordinate. In this case, a phase matching occurs only in narrow area of longitudinal coordinate. Due to strong self- and crossmodulation of interacting waves it is possible to manage effective THG. Using the frame-work of long pulse duration approximation and plane wave approximation as well as an original approach we write the explicit solution of Schrödinger equations describing the frequency tripling of femtosecond pulse. It should be stressed, that the main feature of our approach consists in conservation laws using corresponding to wave interaction process.

  6. Dual-pulse laser-induced breakdown spectroscopy with combinations of femtosecond and nanosecond laser pulses.

    Science.gov (United States)

    Scaffidi, Jon; Pender, Jack; Pearman, William; Goode, Scott R; Colston, Bill W; Carter, J Chance; Angel, S Michael

    2003-10-20

    Nanosecond and femtosecond laser pulses were combined in an orthogonal preablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS) configuration. Even without full optimization of interpulse alignment, ablation focus, large signal, signal-to-noise ratio, and signal-to-background ratio enhancements were observed for both copper and aluminum targets. Despite the preliminary nature of this study, these results have significant implications in the attempt to explain the sources of dual-pulse LIBS enhancements.

  7. Polarization dependent nanostructuring of silicon with femtosecond vortex pulse

    Directory of Open Access Journals (Sweden)

    M. G. Rahimian

    2017-08-01

    Full Text Available We fabricated conical nanostructures on silicon with a tip dimension of ∼ 70 nm using a single twisted femtosecond light pulse carrying orbital angular momentum (ℓ=±1. The height of the nano-cone, encircled by a smooth rim, increased from ∼ 350 nm to ∼ 1 μm with the pulse energy and number of pulses, whereas the apex angle remained constant. The nano-cone height was independent of the helicity of the twisted light; however, it is reduced for linear polarization compared to circular at higher pulse energies. Fluid dynamics simulations show nano-cones formation when compressive forces arising from the radial inward motion of the molten material push it perpendicular to the surface and undergo re-solidification. Simultaneously, the radial outward motion of the molten material re-solidifies after reaching the cold boundary to form a rim. Overlapping of two irradiated spots conforms to the fluid dynamics model.

  8. Testing of a femtosecond pulse laser in outer space.

    Science.gov (United States)

    Lee, Joohyung; Lee, Keunwoo; Jang, Yoon-Soo; Jang, Heesuk; Han, Seongheum; Lee, Sang-Hyun; Kang, Kyung-In; Lim, Chul-Woo; Kim, Young-Jin; Kim, Seung-Woo

    2014-05-30

    We report a test operation of an Er-doped fibre femtosecond laser which was conducted for the first time in outer space. The fibre-based ultrashort pulse laser payload was designed to meet space-use requirements, undergone through ground qualification tests and finally launched into a low-earth orbit early in 2013. Test results obtained during a one-year mission lifetime confirmed stable mode-locking all the way through although the radiation induced attenuation (RIA) in the Er-doped gain fibre caused an 8.6% reduction in the output power. This successful test operation would help facilitate diverse scientific and technological applications of femtosecond lasers in space and earth atmosphere in the near future.

  9. Testing of a femtosecond pulse laser in outer space

    Science.gov (United States)

    Lee, Joohyung; Lee, Keunwoo; Jang, Yoon-Soo; Jang, Heesuk; Han, Seongheum; Lee, Sang-Hyun; Kang, Kyung-In; Lim, Chul-Woo; Kim, Young-Jin; Kim, Seung-Woo

    2014-01-01

    We report a test operation of an Er-doped fibre femtosecond laser which was conducted for the first time in outer space. The fibre-based ultrashort pulse laser payload was designed to meet space-use requirements, undergone through ground qualification tests and finally launched into a low-earth orbit early in 2013. Test results obtained during a one-year mission lifetime confirmed stable mode-locking all the way through although the radiation induced attenuation (RIA) in the Er-doped gain fibre caused an 8.6% reduction in the output power. This successful test operation would help facilitate diverse scientific and technological applications of femtosecond lasers in space and earth atmosphere in the near future. PMID:24875665

  10. Femtosecond Pulse Propagation in a Highly Nonlinear Photonic Crystal Fiber

    Directory of Open Access Journals (Sweden)

    J. F. Gabayno

    2004-12-01

    Full Text Available Femtosecond pulses are launched into a highly nonlinear photonic crystal fiber (PCF. The input and output spectra were measured using a monochromator and streak camera. The spectrum of the output from a 50 cm PCF pumped at 794 nm for different pump powers features asymmetric side lobes due to intrapulse Raman scattering. Similar measurements on a 100 cm PCF pumped at 795 nm highlight the appearance of blueshifted peaks as a result of energy transfer of solitons to dispersive waves. Broadening in the spectrum is observed and attributed to Raman-scattering-induced soliton self-frequency shift. Spectrograms of both input and output pulses into a 50 cm PCF are captured using a streak camera. The spectrum reveals that individual modes observed on the spectrogram are actually a decomposition of the input pulse.

  11. Periodic refractive index modifications inscribed in polymer optical fibre by focussed IR femtosecond pulses

    DEFF Research Database (Denmark)

    Stecher, Matthias; Williams, Robert J.; Bang, Ole

    Focussed femtosecond laser pulses were used to inscribe a periodic array of modifications in the core of a polymer optical fibre. Structural and refractive-index modifications have been observed at different pulse energies using DIC microscopy.......Focussed femtosecond laser pulses were used to inscribe a periodic array of modifications in the core of a polymer optical fibre. Structural and refractive-index modifications have been observed at different pulse energies using DIC microscopy....

  12. Femtosecond pulsed laser deposition of biological and biocompatible thin layers

    Energy Technology Data Exchange (ETDEWEB)

    Hopp, B. [Hungarian Academy of Sciences, University of Szeged, Research Group on Laser Physics, Dom ter 9, H-6720 Szeged (Hungary)]. E-mail: bhopp@physx.u-szeged.hu; Smausz, T. [Hungarian Academy of Sciences, University of Szeged, Research Group on Laser Physics, Dom ter 9, H-6720 Szeged (Hungary); Kecskemeti, G. [Department of Optics and Quantum Electronics, University of Szeged, Dom ter 9, H-6720 Szeged (Hungary); Klini, A. [Institute of Electronic Structure and Laser (I.E.S.L.), Foundation for Research and Technology-Hellas (F.O.R.T.H.), P.O. Box 1527, GR-711 10 Heraklion, Crete (Greece); Bor, Zs. [Department of Optics and Quantum Electronics, University of Szeged, Dom ter 9, H-6720 Szeged (Hungary)

    2007-07-31

    In our study we investigate and report the femtosecond pulsed laser deposition of biological and biocompatible materials. Teflon, polyhydroxybutyrate, polyglycolic-acid, pepsin and tooth in the form of pressed pellets were used as target materials. Thin layers were deposited using pulses from a femtosecond KrF excimer laser system (FWHM = 450 fs, {lambda} = 248 nm, f = 10 Hz) at different fluences: 0.6, 0.9, 1.6, 2.2, 2.8 and 3.5 J/cm{sup 2}, respectively. Potassium bromide were used as substrates for diagnostic measurements of the films on a FTIR spectrometer. The pressure in the PLD chamber was 1 x 10{sup -3} Pa, and in the case of tooth and Teflon the substrates were heated at 250 deg. C. Under the optimized conditions the chemical structure of the deposited materials seemed to be largely preserved as evidenced by the corresponding IR spectra. The polyglycolic-acid films showed new spectral features indicating considerable morphological changes during PLD. Surface structure and thickness of the layers deposited on Si substrates were examined by an atomic force microscopy (AFM) and a surface profilometer. An empirical model has been elaborated for the description of the femtosecond PLD process. According to this the laser photons are absorbed in the surface layer of target resulting in chemical dissociation of molecules. The fast decomposition causes explosion-like gas expansion generating recoil forces which can tear off and accelerate solid particles. These grains containing target molecules without any chemical damages are ejected from the target and deposited onto the substrate forming a thin layer.

  13. Measurements of femtosecond pulse temporal profile by means of a Michelson interferometer with a Schottky junction.

    Science.gov (United States)

    Ling, Yan; Lu, Fang

    2006-12-20

    We introduce a new method for femtosecond pulse shape measurement. The interference of two pulses is employed rather than the second-harmonic generation (SHG). Usually, the measurements of the femtosecond pulse is realized by an interferometer in combination with a nonlinear optical material, while the measurement that we describe is realized by means of a Michelson interferometer with a Schottky junction. Only a metal-semiconductor junction (Schottky junction) is needed, and neither the nonlinear optical material nor a photodetector is included. The two-photon absorption arises when the light is strong enough, while there is only a one-photon absorption when the light is weak. And the calculations are in good agreement with the experimental results. In principle, the new technique could be used for the measuring of pulses with any duration and with very low power. Unlike the SHG scheme, in the new method the quality of optics, mechanics, and other elements of the scheme are not essential, and the measurement is easily realized, but the results are quite precise and very sensitive to the light.

  14. Microcrystal delivery by pulsed liquid droplet for serial femtosecond crystallography.

    Science.gov (United States)

    Mafuné, Fumitaka; Miyajima, Ken; Tono, Kensuke; Takeda, Yoshihiro; Kohno, Jun-ya; Miyauchi, Naoya; Kobayashi, Jun; Joti, Yasumasa; Nango, Eriko; Iwata, So; Yabashi, Makina

    2016-04-01

    A liquid-droplet injector has been developed that delivers pristine microcrystals to an X-ray irradiation area for conducting serial femtosecond crystallography (SFX) with an X-ray free-electron laser (XFEL). By finely tuning the pulsed liquid droplets in time and space, a high hit rate of the XFEL pulses to microcrystals in the droplets was achieved for measurements using 5 µm tetragonal lysozyme crystals, which produced 4265 indexable diffraction images in about 30 min. The structure was determined at a resolution of 2.3 Å from <0.3 mg of protein. With further improvements such as reduction of the droplet size, liquid droplets have considerable potential as a crystal carrier for SFX with low sample consumption.

  15. Control of molecular breakup by an infrared pulse and a femtosecond pulse train

    Science.gov (United States)

    Singh, Kamal P.; Kenfack, A.; Rost, Jan M.; Pfeifer, Thomas

    2018-03-01

    We investigate the dissociation dynamics of diatomic molecules subjected to both a femtosecond infrared (IR) laser pulse and a femtosecond pulse train (FPT) within the framework of the Morse potential model. When the IR and FPT are phase delayed, we observe well-resolved oscillations in dissociation probability, corresponding to multiple integers of the IR period, exhibiting enhancement and suppression of bond dissociation. These oscillations reveal a rich dynamics as a function of the IR and FPT parameters including chaotic fields. A frequency-resolved profile of dressed molecular states shows that these oscillations are due to interference of many quantum paths analogous to the recently observed control of photoionization of atoms under IR and XUV pulses. By manipulating phases of FPTs we demonstrate an enhancement of molecular dissociation compared to the transform-limited case.

  16. Simulation of condensed matter dynamics in strong femtosecond laser pulses

    International Nuclear Information System (INIS)

    Wachter, G.

    2014-01-01

    Ultrashort custom-tailored laser pulses can be employed to observe and control the motion of electrons in atoms and small molecules on the (sub-) femtosecond time scale. Very recently, efforts are underway to extend these concepts to solid matter. This monograph theoretically explores first applications of electron control by ultrashort laser pulses in three paradigmatic systems of solid-state density: a metal nano-structure (nanometric metal tip), a bulk dielectric (quartz glass), and the buckminsterfullerene molecule (C60) as arguably the smallest possible nano-particle. The electron motion is resolved on the atomic length and time scale by ab-initio simulations based on time-dependent density functional theory. Our quantum simulations are complemented by classical and semi-classical models elucidating the underlying mechanisms. We compare our results to experiments where already available and find good agreement. With increasing laser intensity, we find a transition from vertical photoexcitation to tunneling-like excitation. For nanostructures, that leads to temporally confined electron photoemission and thereby to quantum interferences in the energy spectra of emitted electrons. Similarly, tunneling can be induced between neighboring atoms inside an insulator. This provides a mechanism for ultrafast light-field controlled currents and modification of the optical properties of the solid, promising to eventually realize light-field electronic devices operating on the femtosecond time scale and nanometer length scale. Electron-electron interaction leads to near field enhancement and spatial localization of the non-linear response and is investigated both classically by solving the Maxwell equations near a nanostructure as well as quantum mechanically for the fullerene molecule. For the latter, we discuss scrutiny of the molecular near-field by the attosecond streaking technique. Our results demonstrate that ultrashort laser pulses can be employed to steer the

  17. Femtosecond-laser experiment for Master II students: generation, measurement and control of femtoseconds pulses

    Science.gov (United States)

    Druon, Fréderic; Peyrot, Tom; Larrouy, Arthur; Courvoisier, Arnaud; Lejeune, Cédric; Avignon, Thierry

    2015-10-01

    In the framework of the experiment platform LEnsE (Laboratoire d'Enseignement Expérimental) of the Institut d'Optique Graduate School in Palaiseau, we present a new lab work dedicated to Master-­-II-­-level students. This lab work is integrated in the formation in the field of ultrashort-­-pulse lasers and its objective is to train students to this specific technology. The varied topics include generation, measurement and basic control of ultrashort pulses. Key concepts are studied, such as the time-­-frequency duality, nonlinear effects, the group velocity dispersion (GVD) and more generally managing spectral and temporal phase. The lab work is based on a totally accessible Ti:sapphire laser (Mira 800 from Coherent). It is used to understand crucial concepts in the generation process such as GVD and self-­-phase-­-modulation in the solitonic regime and Kerr lens mode-­-locking. Because the pulse measurement is a crucial issue to address in ultrafast optics, the lab work also studies different apparatus commonly used to fully characterize fs pulse train: photodiode, spectrometer, and more specifically second-­-order autocorrelator. The autocorrelation concept is detailed using a homemade accessible apparatus. For a simple manipulation of femtosecond pulses, we propose to realize a spectral-­-phase control with high-­-dispersive glass to temporally stretch the pulses. GTI mirrors then re-­-compress them. The three pillars generation-­-measurement-­-control will be described with a practical approach at the conference.

  18. Femtosecond pulse radiolysis based on photocathode electron accelerator

    International Nuclear Information System (INIS)

    Yoshida, Y.; Yang, Jinfeng; Kondoh, T.; Kozawa, T.; Tagawa, S.

    2006-01-01

    Pulse radiolysis is a powerful tool for studying chemical kinetics and primary processes or reactions of radiation chemistry. In the pulse radiolysis, a short electron beam, which is almost produced by radio-frequency (RF) electron linear accelerator with energy from a few MeV to a few tens MeV, is used as an irradiative source. The electron-induced reactions or phenomena in matter are analyzed by a short-pulse analyzing light (e.g. synchronized lasers) with the time-resolved stroboscopic technique. The time resolution of pulse radiolysis is not only dependent on the electron bunch length, the analyzing light pulse width, the time jitter between the electron bunch and the analyzing light, but also determined by degradation due to the velocity difference between light and the electron in the sample because of the refractive index. In order to improve the time resolution into femtosecond time region, we have develop a new pulse radiolysis based on a concept of 'Equivalent Velocity Spectroscopy (EVS)' to avoid the degradation of the time resolution caused by the velocity difference between the light and the electron beam in sample. In EVS as shown in Fig.1, a femtosecond electron beam produced by a photocathode electron linear accelerator was used, and a synchronized femtosecond laser was used as the analyzing light source. The electron beam and the laser light were injected into sample with an angle (θ), which is determined by the refractive index (n) of the sample. The electron bunch was also rotated with a same angle to make an overlap of the electron bunch with the laser pulse. The degradation of the time resolution caused by the velocity difference between the light and the electron beam can be calculated as g(L)=L[n/c-1/(vcos θ)], where L is the optical path length and v is the velocity of the electron in sample (we can assume v=c for a few tens MeV electron beam).We can thus obtained g(L)=0 by adjusting the incident angle to cos θ=1/n. However, the rotation

  19. Burst train generator of high energy femtosecond laser pulses for driving heat accumulation effect during micromachining.

    Science.gov (United States)

    Rezaei, Saeid; Li, Jianzhao; Herman, Peter R

    2015-05-01

    A new method for generating high-repetition-rate (12.7-38.2 MHz) burst trains of femtosecond laser pulses has been demonstrated for the purpose of tailoring ultrashort laser interactions in material processing that can harness the heat accumulation effect among pulses separated by a short interval (i.e., 26 ns). Computer-controlled time delays were applied to synchronously trigger the high frequency switching of a high voltage Pockels cell to specify distinctive values of polarization rotation for each round-trip of a laser pulse cycling within a passive resonator. Polarization dependent output coupling facilitated the flexible shaping of the burst envelope profile to provide burst trains of up to ∼1  mJ of burst energy divided over a selectable number (1 to 25) of pulses. Individual pulses of variable energy up to 150 μJ and with pulse duration tunable over 70 fs to 2 ps, were applied in burst trains to generate deep and high aspect ratio holes that could not form with low-repetition-rate laser pulses.

  20. Non-radially polarized THz pulse emitted from femtosecond laser filament in air.

    Science.gov (United States)

    Zhang, Y; Chen, Y; Marceau, C; Liu, W; Sun, Z-D; Xu, S; Théberge, F; Châteauneuf, M; Dubois, J; Chin, S L

    2008-09-29

    Femtosecond laser filament could produce THz wave in forward direction. In our experiment, THz pulse emitted from a femtosecond laser filament has been investigated. It was found that the polarization of the studied THz pulse mainly appears as elliptical. This observation supplements the previous conclusion obtained by C. D'Amico et al. that THz wave emitted by a filament is radially polarized. The mechanism of generating elliptically polarized THz wave has been interpreted by either four-wave optical rectification or second order optical rectification inside the filament zone where centro-symmetry of the air is broken by the femtosecond laser pulse.

  1. Selective Deactivation of M13 Bacteriophage in E. Coli using Femtosecond Laser Pulses

    CSIR Research Space (South Africa)

    Molukanele, P

    2010-09-01

    Full Text Available Deactivation of M13 Bacteriophage in E. Coli using Femtosecond Laser Pulses P. Molukanele 1, 3, A. Du Plessis 1, T. Roberts 1, L. Botha 1, M. Khati 2,3, W. Campos 2, 3 1CSIR National Laser Centre, Femtosecond Science group, Pretoria, South Africa 2CSIR...

  2. Photo-transfection of mouse embryonic stem cells with plasmid DNA using femtosecond laser pulses

    CSIR Research Space (South Africa)

    Thobakgale, Lebogang

    2017-01-01

    Full Text Available This presentation is about the photo-transfection of mouse embryonic stem cells with plasmid DNA using femtosecond laser pulses. It outlines the background on embryonic stem cells (ES) and phototransfection....

  3. Nanosurgery of cells and chromosomes using near-infrared twelve-femtosecond laser pulses.

    Science.gov (United States)

    Uchugonova, Aisada; Lessel, Matthias; Nietzsche, Sander; Zeitz, Christian; Jacobs, Karin; Lemke, Cornelius; König, Karsten

    2012-10-01

    ABSTRACT. Laser-assisted surgery based on multiphoton absorption of near-infrared laser light has great potential for high precision surgery at various depths within the cells and tissues. Clinical applications include refractive surgery (fs-LASIK). The non-contact laser method also supports contamination-free cell nanosurgery. In this paper we describe usage of an ultrashort femtosecond laser scanning microscope for sub-100 nm surgery of human cells and metaphase chromosomes. A mode-locked 85 MHz Ti:Sapphire laser with an M-shaped ultrabroad band spectrum (maxima: 770  nm/830  nm) and an in situ pulse duration at the target ranging from 12 fs up to 3 ps was employed. The effects of laser nanoprocessing in cells and chromosomes have been quantified by atomic force microscopy. These studies demonstrate the potential of extreme ultrashort femtosecond laser pulses at low mean milliwatt powers for sub-100 nm surgery of cells and cellular organelles.

  4. Fast pulses and slow atoms: making microKelvin molecules using femtosecond lasers

    Science.gov (United States)

    Walmsley, Ian

    2008-05-01

    We discuss a general approach to the formation of ultracold ground state molecules by synthesis from pairs of cold atoms using shaped ultrashort optical pulses. This method combines an effective and widely applicable control technology to the problem of preparing molecules is the ground state of all their degrees of freedom. The broad bandwidth of femtosecond pulses provides and number of options for removing energy from a pair of colliding atoms, and binding them with little or no vibrational energy. We shall give examples of possible strategies, and report on experiments demonstrating photoassocation using coherent control, and measuring wavepacket dynamics by femtosecond pump probe molecular ionization. Prospects for stabilizing the molecules by protecting them from further collisions, and for increasing the range of internuclear separations that can be associated will be pointed out. This work is funded by the UK EPSRC, and has contributions from J. Petrovic, A. Wyatt, A. Dicks, D. McCabe, D. England, M. Friedman, H. Martay, T. Koehler, C. Foot and collaborations with F. Masnou-Seeuws and J. Mur-Petit.

  5. Laser photoionization of triacetone triperoxide (TATP) by femtosecond and nanosecond laser pulses

    Science.gov (United States)

    Mullen, Christopher; Huestis, David; Coggiola, Michael; Oser, Harald

    2006-05-01

    Laser ionization time-of-flight mass spectrometry has been applied to the study of triacetone triperoxide (TATP), an improvised explosive. Wavelength dependent mass spectra in two time regimes were acquired using nanosecond (5 ns) and femtosecond (130 fs) laser pulses. We find the major difference between the two time regimes to be the detection of the parent molecular ion when femtosecond laser pulses are employed.

  6. Long lifetime air plasma channel generated by femtosecond laser pulse sequence.

    Science.gov (United States)

    Liu, Xiao-Long; Lu, Xin; Ma, Jing-Long; Feng, Liu-Bin; Ge, Xu-Lei; Zheng, Yi; Li, Yu-Tong; Chen, Li-Ming; Dong, Quan-Li; Wang, Wei-Min; Wang, Zhao-Hua; Teng, Hao; Wei, Zhi-Yi; Zhang, Jie

    2012-03-12

    Lifetime of laser plasma channel is significantly prolonged using femtosecond laser pulse sequence, which is generated from a chirped pulse amplification laser system with pure multi-pass amplification chain. Time-resolved fluorescence images and electrical conductivity measurement are used to characterize the lifetime of the plasma channel. Prolongation of plasma channel lifetime up to microsecond level is observed using the pulse sequence.

  7. Generation of electromagnetic pulses from plasma channels induced by femtosecond light strings

    OpenAIRE

    Cheng, Chung-Chieh; Wright, E. M.; Moloney, J. V.

    2000-01-01

    We present a model that elucidates the physics underlying the generation of an electromagnetic pulse from a femtosecond laser induced plasma channel. The radiation pressure force from the laser pulse spatially separates the ionized electrons from the heavier ions and the induced dipole moment subsequently oscillates at the plasma frequency and radiates an electromagnetic pulse.

  8. Volumetric graphics in liquid using holographic femtosecond laser pulse excitations

    Science.gov (United States)

    Kumagai, Kota; Hayasaki, Yoshio

    2017-06-01

    Much attention has been paid to the development of three-dimensional volumetric displays in the fields of optics and computer graphics, and it is a dream of we display researchers. However, full-color volumetric displays are challenging because many voxels with different colors have to be formed to render volumetric graphics in real three-dimensional space. Here, we show a new volumetric display in which microbubble voxels are three-dimensionally generated in a liquid by focused femtosecond laser pulses. Use of a high-viscosity liquid, which is the key idea of this system, slows down the movement of the microbubbles, and as a result, volumetric graphics can be displayed. This "volumetric bubble display" has a wide viewing angle and simple refresh and requires no addressing wires because it involves optical access to transparent liquid and achieves full-color graphics composed on light-scattering voxels controlled by illumination light sources. In addition, a bursting of bubble graphics system using an ultrasonic vibrator also has been demonstrated. This technology will open up a wide range of applications in three-dimensional displays, augmented reality and computer graphics.

  9. Femtosecond pulsed laser deposition of cobalt ferrite thin films

    Science.gov (United States)

    Dascalu, Georgiana; Pompilian, Gloria; Chazallon, Bertrand; Caltun, Ovidiu Florin; Gurlui, Silviu; Focsa, Cristian

    2013-08-01

    The insertion of different elements in the cobalt ferrite spinel structure can drastically change the electric and magnetic characteristics of CoFe2O4 bulks and thin films. Pulsed Laser Deposition (PLD) is a widely used technique that allows the growth of thin films with complex chemical formula. We present the results obtained for stoichiometric and Gadolinium-doped cobalt ferrite thin films deposited by PLD using a femtosecond laser with 1 kHz repetition rate. The structural properties of the as obtained samples were compared with other thin films deposited by ns-PLD. The structural characteristics and chemical composition of the samples were investigated using profilometry, Raman spectroscopy, X-Ray diffraction measurements and ToF-SIMS analysis. Cobalt ferrite thin films with a single spinel structure and a preferential growth direction have been obtained. The structural analysis results indicated the presence of internal stress for all the studied samples. By fs-PLD, uniform thin films were obtained in a short deposition time.

  10. Laser surface and subsurface modification of sapphire using femtosecond pulses

    Energy Technology Data Exchange (ETDEWEB)

    Eberle, G., E-mail: eberle@iwf.mavt.ethz.ch [Institute of Machine Tools and Manufacturing, ETH Zurich, Leonhardstrasse 21, 8092 Zurich (Switzerland); Schmidt, M. [Chair of Photonic Technologies, University of Erlangen-Nuremberg, Konrad-Zuse-Strasse 3-5, 91052 Erlangen (Germany); Pude, F. [Inspire AG, Technoparkstrasse 1, 8005 Zurich (Switzerland); Wegener, K. [Institute of Machine Tools and Manufacturing, ETH Zurich, Leonhardstrasse 21, 8092 Zurich (Switzerland); Inspire AG, Technoparkstrasse 1, 8005 Zurich (Switzerland)

    2016-08-15

    Highlights: • Single and multipulse ablation threshold of aluminium oxide is determined. • Laser ablation, and in-volume modification followed by wet etching are demonstrated. • Quality following laser processing and laser-material interactions are studied. - Abstract: Two methods to process sapphire using femtosecond laser pulses are demonstrated, namely ablation (surface), and in-volume laser modification followed by wet etching (subsurface). Firstly, the single and multipulse ablation threshold is determined and compared with previous literature results. A unique application of ablation is demonstrated by modifying the entrance aperture of water jet orifices. Laser ablation exhibits advantages in terms of geometric flexibility and resolution, however, defects in the form of edge outbreaks and poor surface quality are evident. Secondly, the role of material transformation, polarisation state and formation of multi-focus structures after in-volume laser modification is investigated in order to explain their influence during the wet etching process. Laser scanning and electron microscopy as well as electron backscatter diffraction measurements supported by ion beam polishing are used to better understand quality and laser-material interactions of the two demonstrated methods of processing.

  11. Dissociative Ionization of Argon Dimer by Intense Femtosecond Laser Pulses.

    Science.gov (United States)

    Cheng, Qian; Xie, Xiguo; Yuan, Zongqiang; Zhong, Xunqi; Liu, Yunquan; Gong, Qihuang; Wu, Chengyin

    2017-05-25

    We experimentally and theoretically studied dissociative ionization of argon dimer driven by intense femtosecond laser pulses. In the experiment, we measured the ion yield and the angular distribution of fragmental ions generated from the dissociative ionization channels of (1,1) (Ar 2 2+ → Ar + + Ar + ) and (2,1) (Ar 2 3+ → Ar 2+ + Ar + ) using a cold target recoil ion momentum spectroscopy. The channel ratio of (2,1)/(1,1) is 4.5-7.5 times of the yield ratio of double ionization to single ionization of argon monomer depending on the laser intensity. The measurement verified that the ionization of Ar + is greatly enhanced if there exists a neighboring Ar + separated by a critical distance. In addition, the fragmental ions exhibit an anisotropic angular distribution with the peak along the laser polarization direction and the full width at half maximum becomes broader with increasing laser intensity. Using a full three-dimensional classical ensemble model, we calculated the angle-dependent multiple ionization probability of argon dimer in intense laser fields. The results show that the experimentally observed anisotropic angular distribution of fragmental ions can be attributed to the angle-dependent enhanced ionization of the argon dimer in intense laser fields.

  12. Pulse-analysis-pulse investigation of femtosecond laser-induced periodic surface structures on silicon in air

    NARCIS (Netherlands)

    Vincenc Obona, J.; Skolski, J.Z.P.; Römer, Gerardus Richardus, Bernardus, Engelina; Huis in 't Veld, Bert

    2014-01-01

    A new approach to experimentally investigate laser-induced periodic surface structures (LIPSSs) is introduced. Silicon was iteratively exposed to femtosecond laser pulses at λ = 800 nm and normal incidence in ambient air and at a fluence slightly over the single-pulse modification threshold. After

  13. Coherent scatter-controlled phase-change grating structures in silicon using femtosecond laser pulses.

    Science.gov (United States)

    Fuentes-Edfuf, Yasser; Garcia-Lechuga, Mario; Puerto, Daniel; Florian, Camilo; Garcia-Leis, Adianez; Sanchez-Cortes, Santiago; Solis, Javier; Siegel, Jan

    2017-07-04

    Periodic structures of alternating amorphous-crystalline fringes have been fabricated in silicon using repetitive femtosecond laser exposure (800 nm wavelength and 120 fs duration). The method is based on the interference of the incident laser light with far- and near-field scattered light, leading to local melting at the interference maxima, as demonstrated by femtosecond microscopy. Exploiting this strategy, lines of highly regular amorphous fringes can be written. The fringes have been characterized in detail using optical microscopy combined modelling, which enables a determination of the three-dimensional shape of individual fringes. 2D micro-Raman spectroscopy reveals that the space between amorphous fringes remains crystalline. We demonstrate that the fringe period can be tuned over a range of 410 nm - 13 µm by changing the angle of incidence and inverting the beam scan direction. Fine control over the lateral dimensions, thickness, surface depression and optical contrast of the fringes is obtained via adjustment of pulse number, fluence and spot size. Large-area, highly homogeneous gratings composed of amorphous fringes with micrometer width and millimeter length can readily be fabricated. The here presented fabrication technique is expected to have applications in the fields of optics, nanoelectronics, and mechatronics and should be applicable to other materials.

  14. Pulse shaping for all-optical signal processing of ultra-high bit rate serial data signals

    DEFF Research Database (Denmark)

    Palushani, Evarist

    The following thesis concerns pulse shaping and optical waveform manipulation for all-optical signal processing of ultra-high bit rate serial data signals, including generation of optical pulses in the femtosecond regime, serial-to-parallel conversion and terabaud coherent optical time division...

  15. Measurement of temperature rises in the femtosecond laser pulsed three-dimensional atom probe

    International Nuclear Information System (INIS)

    Cerezo, A.; Smith, G.D.W.; Clifton, P.H.

    2006-01-01

    A previous Letter [B. Gault et al., Appl. Phys. Lett. 86, 094101 (2005)] interpreted measurements of the field evaporation enhancement under femtosecond pulsed laser irradiation of a field emitter in terms of a direct electric field enhancement by the intrinsic field of the laser light. We show that, on the contrary, the field evaporation enhancement is predominantly a thermal heating effect. Indirect measurements of the peak specimen temperature under irradiation by femtosecond laser pulses are consistent with temperature rises obtained using longer laser pulses in a range of earlier work

  16. Compression of XUV FEL pulses in the few-femtosecond regime

    International Nuclear Information System (INIS)

    Frassetto, Fabio; Giannessi, Luca; Poletto, Luca

    2008-01-01

    This work presents the design of a grating compressor for XUV FEL pulses able to compress chirped pulses from some hundreds to some tens of femtoseconds. The instrument adopts the conical diffraction mounts of gratings to reach high efficiency. We discuss the general design of the compressor and present an example of application to FEL emission at 13.5 nm

  17. Femtosecond Bessel light pulse formation by a multi-circular diaphragm

    International Nuclear Information System (INIS)

    Ushakova, E.E.; Kurilkina, S.N.

    2010-01-01

    The dynamics of the envelope of a new type of light field, a femtosecond Bessel light pulse (FBLP) formed from a Gaussian pulsed beam by means of a multi-circular diaphragm, has been investigated theoretically. It is shown that the FBLP possesses a steady structure that features a narrow central maximum and significantly suppressed subordinate maxima. (authors)

  18. Quantum Computation with Ultrafast Laser Pulse Shaping

    Indian Academy of Sciences (India)

    Quantum Computation with Ultrafast. Laser Pulse Shaping. Debabrata Goswami is at the Department of. Chemistry, Indian. Institute of Technology,. Kanpur, where he explores the applications of ultrafast shaped pulses to bio-imaging, coherent control, high-speed communication and quantum computing. Keywords. Qubit ...

  19. Determination of ablation threshold for composite resins and amalgam irradiated with femtosecond laser pulses

    Science.gov (United States)

    Freitas, A. Z.; Freschi, L. R.; Samad, R. E.; Zezell, D. M.; Gouw-Soares, S. C.; Vieira, N. D., Jr.

    2010-03-01

    The use of laser for caries removal and cavity preparation is already a reality in the dental clinic. The objective of the present study was to consider the viability of ultrashort laser pulses for restorative material selective removal, by determining the ablation threshold fluence for composite resins and amalgam irradiated with femtosecond laser pulses. Lasers pulses centered at 830 nm with 50 fs of duration and 1 kHz of repetition rate, with energies in the range of 300 to 770 μJ were used to irradiate the samples. The samples were irradiated using two different geometrical methods for ablation threshold fluence determinations and the volume ablation was measured by optical coherence tomography. The shape of the ablated surfaces were analyzed by optical microscopy and scanning electron microscopy. The determined ablation threshold fluence is 0.35 J/cm2 for the composite resins Z-100 and Z-350, and 0.25 J/cm2 for the amalgam. These values are half of the value for enamel in this temporal regime. Thermal damages were not observed in the samples. Using the OCT technique (optical coherence tomography) was possible to determine the ablated volume and the total mass removed.

  20. 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.

  1. High power all-polarization-maintaining photonic crystal fiber monolithic femtosecond nonlinear chirped-pulse amplifier

    Science.gov (United States)

    Lv, Zhiguo; Yang, Zhi; Li, Feng; Yang, Xiaojun; Li, Qianglong; Zhang, Xin; Wang, Yishan; Zhao, Wei

    2018-03-01

    We report on an experimental study on fully fusion spliced high power all-polarization-maintaining Yb-doped photonic crystal fiber (PCF) femtosecond nonlinear chirped-pulse amplifier (CPA), which features large values of the positive third-order dispersion (TOD) superposed from the single-mode fiber stretcher (SMFs) and grating-pair compressor. Compensation of the TOD is realized by means of self-phase modulation (SPM) induced nonlinear phase shift during amplification. Up to 9.8 W of compressed average power at 275 kHz repetition rates with 36 μJ pulse energy and 495 fs pulse width has been obtained. To the best of our knowledge, this is the highest output power generated from the strictly all-fiber nonlinear CPA amplifier in femtosecond domain, which provides a possibility for the industrialized promotion and development of the high energy femtosecond fiber laser.

  2. A new multifunctional device for femtosecond pulse characterization with a wide operating range

    International Nuclear Information System (INIS)

    Li, F J; Zhang, S X; Liu, Q F; Zhao, G K; Liu, J

    2014-01-01

    We demonstrate a novel and simple device for femtosecond pulse characterization, which combines the frequency-resolved optical gating (FROG) and the self-referenced spectral interferometry (SRSI) methods in the frequency-resolved optical gating and self-referenced spectral interferometry (FASI) method. It was found that the comparative advantages of FROG and SRSI can complement each other. Therefore FASI can be used to characterize femtosecond pulses in different conditions, which may need different devices when using either the FROG or the SRSI method independently. With our multifunctional FASI device, the TG-FROG, SHG-FROG and TG-SRSI methods were used to fully characterize femtosecond pulses at 800 nm with different dispersions. The experimental results obtained by all three methods were compared with each other and also with the calculated data. These results proved the reliability and the wide operating range of our FASI device. (letter)

  3. Noncollinear SHG with compensation of phase mismatch by controlling frequency chirp and tilted pulse fronts of femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Aoyama, Makoto; Nakano, Fumihiko; Akahane, Yutaka; Yamakawa, Koichi [Japan Atomic Energy Research Inst., Kizu, Kyoto (Japan). Kansai Research Establishment; Harimoto, Tetsuo [Yamanashi Univ., Faculty of Engineering, Yamanashi (Japan)

    2001-10-01

    In order to achieve efficient second-harmonic generation with femtosecond laser pulses, we studied noncollinear second-harmonic generation with tilted pulse fronts and a suitable frequency chirp of fundamental pulses. We discussed the compensation of a phase-mismatch by controlling the frequency chirp of fundamental pulses and an improvement of the energy conversion efficiency using our method. When the energy conversion efficiency was less than 0.4% under a phase-mismatch condition, we experimentally obtained a 30% energy conversion efficiency with a proper frequency chirp of fundamental pulses. (author)

  4. Photofragmentation of colloidal solutions of gold nanoparticles under femtosecond laser pulses in IR and visible ranges

    International Nuclear Information System (INIS)

    Danilov, P A; Zayarnyi, D A; Ionin, A A; Kudryashov, S I; Makarov, S V; Rudenko, A A; Saraeva, I N; Yurovskikh, V I; Lednev, V N; Pershin, S M

    2015-01-01

    The specific features of photofragmentation of sols of gold nanoparticles under focused femtosecond laser pulses in IR (1030 nm) and visible (515 nm) ranges is experimentally investigated. A high photofragmentation efficiency of nanoparticles in the waist of a pulsed laser beam in the visible range (at moderate radiation scattering) is demonstrated; this efficiency is related to the excitation of plasmon resonance in nanoparticles on the blue shoulder of its spectrum, in contrast to the regime of very weak photofragmentation in an IR-laser field of comparable intensity. Possible mechanisms of femtosecond laser photofragmentation of gold nanoparticles are discussed. (extreme light fields and their applications)

  5. Bragg grating photo-inscription in doped microstructured polymer optical fiber by 400 nm femtosecond laser pulses.

    OpenAIRE

    Hu, X.; Woyessa, Getinet; Kinet, D.; Janting, Jakob; Nielsen, Kristian; Bang, Ole; Mégret, P.; Caucheteur, C.

    2016-01-01

    In this paper, we report the manufacturing of high-quality endlessly single-mode doped microstructured poly(methyl methacrylate) (PMMA) optical fibers. Bragg gratings are photo-inscribed in such fibers by means of 400 nm femtosecond laser pulses through a 1060-nm-period uniform phase mask. Preliminary results show a rapid growing process of the reflection band. To preserve a good spectral shape, the photo-inscription process was limited to ~20 seconds, yielding an FBG reflectivity close to 40 %.

  6. High-power pre-chirp managed amplification of femtosecond pulses at high repetition rates

    International Nuclear Information System (INIS)

    Liu, Yang; Li, Wenxue; Zhao, Jian; Bai, Dongbi; Luo, Daping; Zeng, Heping

    2015-01-01

    Femtosecond pulses at 250 MHz repetition rate from a mode-locked fiber laser are amplified to high power in a pre-chirp managed amplifier. The experimental strategy offers a potential towards high-power ultrashort laser pulses at high repetition rates. By investigating the laser pulse evolution in the amplification processes, we show that self-similar evolution, finite gain bandwidth and mode instabilities determine pulse characteristics in different regimes. Further average power scaling is limited by the mode instabilities. Nevertheless, this laser system enables us to achieve sub-50 fs pulses with an average power of 93 W. (letter)

  7. Surface texturing of sialon ceramic by femtosecond pulsed laser

    CSIR Research Space (South Africa)

    Tshabalala, Lerato C

    2017-01-01

    Full Text Available AlONSi(sub3)N(sub4) ceramic using the Ti: Sapphire Femtosecond laser system was investigated. Parametric analysis was conducted using surface drilling, unidirectional and cross-hatching machining procedures performed on the substrate at a varied power...

  8. Nano- and femtosecond UV laser pulses to immobilize biomolecules onto surfaces with preferential orientation

    Science.gov (United States)

    Lettieri, S.; Avitabile, A.; Della Ventura, B.; Funari, R.; Ambrosio, A.; Maddalena, P.; Valadan, M.; Velotta, R.; Altucci, C.

    2014-10-01

    By relying on the photonic immobilization technique of antibodies onto surfaces, we realized portable biosensors for light molecules based on the use of quartz crystal microbalances, given the linear dependence of the method on the laser pulse intensity. Here, we compare the quality of the anchoring method when using nanosecond (260 nm, 25 mJ/pulse, 5 ns, 10 Hz rep. rate) and femtosecond (258 nm, 25 μJ/pulse, 150 fs, 10 kHz rep. rate) laser source, delivering the same energy to the sample with the same average power. As a reference, we also tethered untreated antibodies by means of the passive adsorption. The results are striking: When the antibodies are irradiated with the femtosecond pulses, the deposition on the gold plate is much more ordered than in the other two cases. The effects of UV pulses irradiation onto the antibodies are also analyzed by measuring absorption and fluorescence and suggest the occurrence of remarkable degradation when nanosecond pulses are used likely induced by a larger thermal coupling. In view of the high average power required to activate the antibodies for the achievement of the photonic immobilization technique, we conclude that femtosecond rather than nanosecond laser pulses have to be used.

  9. Oval-like hollow intensity distribution of tightly focused femtosecond laser pulses in air.

    Science.gov (United States)

    Li, Y T; Xi, T T; Hao, Z Q; Zhang, Z; Peng, X Y; Li, K; Jin, Z; Zheng, Z Y; Yu, Q Z; Lu, X; Zhang, J

    2007-12-24

    The propagation of a tightly focused femtosecond laser pulse in air has been investigated. Unlike long-distance self-guided propagation of short laser pulses, a novel oval-like hollow distribution of the laser intensity is observed in the experiments and reproduced by the numerical simulations. The formation of the hollow structures can be explained by the interplay between ionization-induced refraction and Kerr self-focusing.

  10. Pulse-shaping strategies in short-pulse fiber amplifiers

    Energy Technology Data Exchange (ETDEWEB)

    Schimpf, Damian Nikolaus

    2010-02-09

    Ultrashort pulse lasers are an important tool in scientific and industrial applications. However, many applications are demanding higher average powers from these ultrashort pulse sources. This can be achieved by combining direct diode pumping with novel gain media designs. In particular, ultrashort pulse fiber lasers are now delivering average powers in the kW range. However, the design of fiber lasers, producing pulses with high peak-powers, is challenging due to the impact of nonlinear effects. To significantly reduce these detrimental effects in ultrashort pulse fiber amplifers, the combination of chirped pulse amplification (CPA) and large mode area fibers is employed. Using these methods, the pulse energy of fiber lasers has been steadily increasing for the past few years. Recently, a fiber-based CPA-system has been demonstrated which produces pulse energies of around 1 mJ. However, both the stretching and the enlargement of the mode area are limited, and therefore, the impact of nonlinearity is still noticed in systems employing such devices. The aim of this thesis is the analysis of CPA-systems operated beyond the conventional nonlinear limit, which corresponds to accumulated nonlinear phase-shifts around 1 rad. This includes a detailed discussion of the influence of the nonlinear effect self-phase modulation on the output pulse of CPA-systems. An analytical model is presented. Emphasis is placed on the design of novel concepts to control the impact of self-phase modulation. Pulse-shaping is regarded as a powerful tool to accomplish this goal. Novel methods to control the impact of SPM are experimentally demonstrated. The design of these concepts is based on the theoretical findings. Both amplitude- and phase-shaping are studied. Model-based phase-shaping is implemented in a state-of-the-art fiber CPA-system. The influence of the polarization state is also highlighted. Additionally, existing techniques and recent advances are put into context. (orig.)

  11. Pulse-shaping strategies in short-pulse fiber amplifiers

    International Nuclear Information System (INIS)

    Schimpf, Damian Nikolaus

    2010-01-01

    Ultrashort pulse lasers are an important tool in scientific and industrial applications. However, many applications are demanding higher average powers from these ultrashort pulse sources. This can be achieved by combining direct diode pumping with novel gain media designs. In particular, ultrashort pulse fiber lasers are now delivering average powers in the kW range. However, the design of fiber lasers, producing pulses with high peak-powers, is challenging due to the impact of nonlinear effects. To significantly reduce these detrimental effects in ultrashort pulse fiber amplifers, the combination of chirped pulse amplification (CPA) and large mode area fibers is employed. Using these methods, the pulse energy of fiber lasers has been steadily increasing for the past few years. Recently, a fiber-based CPA-system has been demonstrated which produces pulse energies of around 1 mJ. However, both the stretching and the enlargement of the mode area are limited, and therefore, the impact of nonlinearity is still noticed in systems employing such devices. The aim of this thesis is the analysis of CPA-systems operated beyond the conventional nonlinear limit, which corresponds to accumulated nonlinear phase-shifts around 1 rad. This includes a detailed discussion of the influence of the nonlinear effect self-phase modulation on the output pulse of CPA-systems. An analytical model is presented. Emphasis is placed on the design of novel concepts to control the impact of self-phase modulation. Pulse-shaping is regarded as a powerful tool to accomplish this goal. Novel methods to control the impact of SPM are experimentally demonstrated. The design of these concepts is based on the theoretical findings. Both amplitude- and phase-shaping are studied. Model-based phase-shaping is implemented in a state-of-the-art fiber CPA-system. The influence of the polarization state is also highlighted. Additionally, existing techniques and recent advances are put into context. (orig.)

  12. Flexible and rapidly configurable femtosecond pulse generation in the mid-IR.

    Science.gov (United States)

    Foreman, Seth M; Jones, David J; Ye, Jun

    2003-03-01

    We demonstrate a new experimental approach for flexible femtosecond pulse generation in the mid-IR by use of difference-frequency generation from two tightly synchronized Ti:sapphire lasers. The resultant mid-IR pulse train can be easily tuned, with an adjustable repetition frequency up to 100 MHz, a pulse energy of approximately 1.5 x 10(-13) J, and an intensity noise similar to that of the Ti:sapphire. Rapid switching of the mid-IR wavelength and programmable amplitude modulation are achieved by precision setting of the time delay between two original pulses.

  13. Extension of supercontinuum spectrum, generated in polarization-maintaining photonic crystal fiber, using chirped femtosecond pulses

    Science.gov (United States)

    Vengelis, Julius; Jarutis, Vygandas; Sirutkaitis, Valdas

    2018-01-01

    We present results of experimental and numerical investigation of supercontinuum (SC) generation in polarization-maintaining photonic crystal fiber (PCF) using chirped femtosecond pulses. The initial unchirped pump pulse source was a mode-locked Yb:KGW laser generating 52-nJ energy, 110-fs duration pulses at 1030 nm with a 76-MHz repetition rate. The nonlinear medium was a 32-cm-long polarization-maintaining PCF manufactured by NKT Photonics A/S. We demonstrated the influence of pump pulse chirp on spectral characteristics of a SC. We showed that by chirping pump pulses positively or negatively one can obtain a broader SC spectrum than in the case of unchirped pump pulses at the same peak power. Moreover, the extension can be controlled by changing the amount of pump pulse chirp. Numerical simulation results also indicated that pump pulse chirp yields an extension of SC spectrum.

  14. Optimization methods of pulse-to-pulse alignment using femtosecond pulse laser based on temporal coherence function for practical distance measurement

    Science.gov (United States)

    Liu, Yang; Yang, Linghui; Guo, Yin; Lin, Jiarui; Cui, Pengfei; Zhu, Jigui

    2018-02-01

    An interferometer technique based on temporal coherence function of femtosecond pulses is demonstrated for practical distance measurement. Here, the pulse-to-pulse alignment is analyzed for large delay distance measurement. Firstly, a temporal coherence function model between two femtosecond pulses is developed in the time domain for the dispersive unbalanced Michelson interferometer. Then, according to this model, the fringes analysis and the envelope extraction process are discussed. Meanwhile, optimization methods of pulse-to-pulse alignment for practical long distance measurement are presented. The order of the curve fitting and the selection of points for envelope extraction are analyzed. Furthermore, an averaging method based on the symmetry of the coherence function is demonstrated. Finally, the performance of the proposed methods is evaluated in the absolute distance measurement of 20 μ m with path length difference of 9 m. The improvement of standard deviation in experimental results shows that these approaches have the potential for practical distance measurement.

  15. Spatial and temporal dependence of interspark interactions in femtosecond-nanosecond dual-pulse laser-induced breakdown spectroscopy.

    Science.gov (United States)

    Scaffidi, Jon; Pearman, William; Lawrence, Marion; Carter, J Chance; Colston, Bill W; Angel, S Michael

    2004-09-20

    A femtosecond air spark has recently been combined with a nanosecond ablative pulse in order to map the spatial and temporal interactions of the two plasmas in femtosecond-nanosecond orthogonal preablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS). Good spatial and temporal correlation was found for reduced atomic emission from atmospheric species (nitrogen and oxygen) and increased atomic emission from ablated species (copper and aluminum) in the femtosecond-nanosecond plasma, suggesting a potential role for atmospheric pressure or nitrogen/oxygen concentration reduction following air spark formation in generating atomic emission enhancements in dual-pulse LIBS.

  16. Nonlinear spatial focusing in random layered media by spectral pulse shaping

    Science.gov (United States)

    Han, Alex C.; Milner, Valery

    2016-02-01

    We demonstrate numerically a method of focusing two-photon fields inside one-dimensional random media. The approach is based on coherent control of backscattering achieved by adaptive spectral pulse shaping. The spectral phases of a femtosecond laser pulse are adjusted for the constructive interference of its backward-traveling components, resulting in an enhanced reflection from within the random system. A delayed forward-propagating second pulse overlaps with the controlled reflection, increasing the interpulse multiphoton field at a location determined by the delay between the two pulses. The technique is shown to be robust against the variations of the disorder and to work with realistic pulse-shaping parameters, hence enabling applications in controlling random lasing and multiphoton imaging in scattering materials.

  17. Synchronized femtosecond laser pulse switching system based nano-patterning technology

    Science.gov (United States)

    Sohn, Ik-Bu; Choi, Hun-Kook; Yoo, Dongyoon; Noh, Young-Chul; Sung, Jae-Hee; Lee, Seong-Ku; Ahsan, Md. Shamim; Lee, Ho

    2017-07-01

    This paper demonstrates the design and development of a synchronized femtosecond laser pulse switching system and its applications in nano-patterning of transparent materials. Due to synchronization, we are able to control the location of each irradiated laser pulse in any kind of substrate. The control over the scanning speed and scanning step of the laser beam enables us to pattern periodic micro/nano-metric holes, voids, and/or lines in various materials. Using the synchronized laser system, we pattern synchronized nano-holes on the surface of and inside various transparent materials including fused silica glass and polymethyl methacrylate to replicate any image or pattern on the surface of or inside (transparent) materials. We also investigate the application areas of the proposed synchronized femtosecond laser pulse switching system in a diverse field of science and technology, especially in optical memory, color marking, and synchronized micro/nano-scale patterning of materials.

  18. Laser pulse shaping for high gradient accelerators

    Energy Technology Data Exchange (ETDEWEB)

    Villa, F., E-mail: fabio.villa@lnf.infn.it [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy); Anania, M.P.; Bellaveglia, M. [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy); Bisesto, F. [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy); Università La Sapienza di Roma, Via A. Scarpa 14, Rome (Italy); Chiadroni, E. [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy); Cianchi, A. [INFN-Roma Tor Vergata and Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome (Italy); Curcio, A.; Galletti, M.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Gatti, G. [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy); Moreno, M.; Petrarca, M. [Università La Sapienza di Roma, Via A. Scarpa 14, Rome (Italy); Pompili, R.; Vaccarezza, C. [INFN-Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati (Italy)

    2016-09-01

    In many high gradient accelerator schemes, i.e. with plasma or dielectric wakefield induced by particles, many electron pulses are required to drive the acceleration of one of them. Those electron bunches, that generally should have very short duration and low emittance, can be generated in photoinjectors driven by a train of laser pulses coming inside the same RF bucket. We present the system used to shape and characterize the laser pulses used in multibunch operations at Sparc-lab. Our system gives us control over the main parameter useful to produce a train of up to five high brightness bunches with tailored intensity and time distribution.

  19. Developing of CIAE2170 pulse shape discriminator

    International Nuclear Information System (INIS)

    Shen Guanren; Wuru Gongsang; Zhou Zuying; Guo Li; Gao Weixiang; Ni Hefeng; Sun Gong

    1995-01-01

    The pulse shape discriminator is very important electronics for reducing γ rays background. The CIAE2170 pulse shape discriminator is developed and is applied to the experiments on neutron and fission physics and measurements of nuclear data for more than 1500 h. It's very stable and reliable, and continually worked for more than 200 h. The main performance is carefully tested and is in the lead in china and arrived at international advanced level. Specially, the temperature stability is less than 0.10 ns/degree C in 5-45 degree C range

  20. Ablation of silicon with bursts of femtosecond laser pulses

    Science.gov (United States)

    Gaudiuso, Caterina; Kämmer, Helena; Dreisow, Felix; Ancona, Antonio; Tünnermann, Andreas; Nolte, Stefan

    2016-03-01

    We report on an experimental investigation of ultrafast laser ablation of silicon with bursts of pulses. The pristine 1030nm-wavelength 200-fs pulses were split into bursts of up to 16 sub-pulses with time separation ranging from 0.5ps to 4080ps. The total ablation threshold fluence was measured depending on the burst features, finding that it strongly increases with the number of sub-pulses for longer sub-pulse delays, while a slowly increasing trend is observed for shorter separation time. The ablation depth per burst follows two different trends according to the time separation between the sub-pulses, as well as the total threshold fluence. For delays shorter than 4ps it decreases with the number of pulses, while for time separations longer than 510ps, deeper craters were achieved by increasing the number of subpulses in the burst, probably due to a change of the effective penetration depth.

  1. Spatial-temporal distribution of femtosecond pulses at the focal region of a mirror with aberrations

    Science.gov (United States)

    Anaya-Vera, S.; Rosete-Aguilar, M.; Rodríguez-Herrera, O. G.; Garduño-Mejía, J.; Bruce, N. C.

    2017-11-01

    The spatial-temporal distribution of femtosecond pulses around the focal region of lenses has been extensively studied in recent years [1-6] due to the rapid progress in the technology of femtosecond lasers and their applications in many experiments in physics [7,8]. In this paper we present the time and spatial distribution of a few optical-cycle optical pulses around the focal region of a perfectly conducting spherical mirror which is a dispersionless system, by calculating the aberrations introduced when an off-axis collimated beam is incident on the mirror. The Seidel aberration theory has been used to calculate the wavefront aberration and the corresponding phase change for each frequency at the pupil of the mirror. The propagation of the beam from the exit pupil to the focal region is calculated by using the scalar diffraction theory [9]. The effect of aberrations in the focusing pulses has been analyzed in the literature by approximating the wavenumber of the pulse-frequencies by the wavenumber of the carrier frequency [4, 5]. In this paper we show that the monochromatic aberrations change the temporal duration of few-optical-cycle pulses when this approximation is removed. When this approximation is used, monochromatic aberrations do not introduce any temporal change in the focusing pulse even for pulses as short as 2.7fs@810nm which corresponds to a oneoptical-cycle pulse. Examples are presented for homogeneous and Gaussian illumination on the entrance pupil.

  2. Crystallization of Ge2Sb2Te5 films by amplified femtosecond optical pulses

    Science.gov (United States)

    Liu, Y.; Aziz, M. M.; Shalini, A.; Wright, C. D.; Hicken, R. J.

    2012-12-01

    The phase transition between the amorphous and crystalline states of Ge2Sb2Te5 has been studied by exposure of thin films to series of 60 femtosecond (fs) amplified laser pulses. The analysis of microscope images of marks of tens of microns in size provide an opportunity to examine the effect of a continuous range of optical fluence. For a fixed number of pulses, the dependence of the area of the crystalline mark upon the fluence is well described by simple algebraic results that provide strong evidence that thermal transport within the sample is one-dimensional (vertical). The crystalline mark area was thus defined by the incident fs laser beam profile rather than by lateral heat diffusion, with a sharp transition between the crystalline and amorphous materials as confirmed from line scans of the microscope images. A simplified, one-dimensional model that accounts for optical absorption, thermal transport and thermally activated crystallization provides values of the optical reflectivity and mark area that are in very good quantitative agreement with the experimental data, further justifying the one-dimensional heat flow assumption. Typically, for fluences below the damage threshold, the crystalline mark has annular shape, with the fluence at the centre of the irradiated mark being sufficient to induce melting. The fluence at the centre of the mark was correlated with the melt depth from the thermal model to correctly predict the observed melt fluence thresholds and to explain the closure and persistence of the annular crystalline marks as functions of laser fluence and pulse number. A solid elliptical mark may be obtained for smaller fluences. The analysis of marks made by amplified fs pulses present a new and effective means of observing the crystallization dynamics of phase-change material at elevated temperatures near the melting point, which provided estimates of the growth velocity in the range 7-9 m/s. Furthermore, finer control over the crystallization

  3. Optical cell cleaning with NIR femtosecond laser pulses

    Science.gov (United States)

    Uchugonova, Aisada; Breunig, Hans Georg; Batista, Ana; König, Karsten

    2015-03-01

    Femtosecond laser microscopes have been used as both micro and nanosurgery tools. The optical knock-out of undesired cells in multiplex cell clusters shall be further reported on in this study. Femtosecond laser-induced cell death is beneficial due to the reduced collateral side effects and therefore can be used to selectively destroy target cells within monolayers, as well as within 3D tissues, all the while preserving cells of interest. This is an important characteristic for the application in stem cell research and cancer treatment. Non-precise damage compromises the viability of neighboring cells by inducing side effects such as stress to the cells surrounding the target due to the changes in the microenvironment, resulting from both the laser and laser-exposed cells. In this study, optimum laser parameters for optical cleaning by isolating single cells and cell colonies are exploited through the use of automated software control. Physiological equilibrium and cellular responses to the laser induced damages are also investigated. Cell death dependence on laser focus, determination and selectivity of intensity/dosage, controllable damage and cell recovery mechanisms are discussed.

  4. Femtosecond-Laser-Pulse Characterization and Optimization for CARS Microscopy.

    Directory of Open Access Journals (Sweden)

    Vincenzo Piazza

    Full Text Available We present a simple method and its experimental implementation to determine the pulse durations and linear chirps of the pump-and-probe pulse and the Stokes pulse in a coherent anti-Stokes Raman scattering microscope at sample level without additional autocorrelators. Our approach exploits the delay line, ubiquitous in such microscopes, to perform a convolution of the pump-and-probe and Stokes pulses as a function of their relative delay and it is based on the detection of the photons emitted from an appropriate non-linear sample. The analysis of the non-resonant four-wave-mixing and sum-frequency-generation signals allows for the direct retrieval of the pulse duration on the sample and the linear chirp of each pulse. This knowledge is crucial in maximizing the spectral-resolution and contrast in CARS imaging.

  5. Characteristics of micro air plasma produced by double femtosecond laser pulses.

    Science.gov (United States)

    Zhang, Nan; Wu, Zehua; Xu, Kuanhong; Zhu, Xiaonong

    2012-01-30

    Dynamic characteristics of air plasma generated by focused double collinear femtosecond laser pulses with a time interval of 10 ns are experimentally investigated. The air plasma emission changes significantly when altering the energy ratio between the two laser pulses. Time-resolved shadowgraphic measurements reveal that a small volume of transient vacuum is formed inside the air shock wave produced by the first laser pulse, which causes the second laser pulse induced ionization zone to present as two separate sections in space. Also recorded is strong scattering of the second laser pulse by the ionized air just behind the ionization front of the first laser pulse produced shock wave. Due to the high intensity of the scattered light, coherent Thomson scattering enhanced by plasma instabilities is believed to be the main scattering mechanism in this case.

  6. Laser chirp effect on femtosecond laser filamentation generated for pulse compression.

    Science.gov (United States)

    Park, Juyun; Lee, Jae-Hwan; Nam, Chang H

    2008-03-31

    The influence of laser chirp on the formation of femtosecond laser filamentation in Ar was investigated for the generation of few-cycle high-power laser pulses. The condition for the formation of a single filament has been carefully examined using 28-fs laser pulses with energy over 3 mJ. The filament formation and output spectrum changed very sensitively to the initial laser chirp and gas pressure. Much larger spectral broadening was obtained with positively chirped pulses, compared to the case of negatively chirped pulses that generated much longer filament, and compressed pulses of 5.5 fs with energy of 0.5 mJ were obtained from the filamentation of positively chirped 30-fs laser pulses in a single Ar cell.

  7. Effect of nonlinear crystal thickness on the parameters of the autocorrelator of femtosecond light pulses

    International Nuclear Information System (INIS)

    Masalov, Anatolii V; Chudnovsky, Aleksandr V

    2004-01-01

    It is shown that the finite thickness of the second-harmonic crystal distorts the results of measurements in nonlinear autocorrelators intended for measuring the durations and fields of femtosecond light pulses mainly due to dispersive broadening (or compression) of the pulses being measured, as well as due to the group velocity mismatch between the fundamental and sum-frequency pulses. The refractive index dispersion of the crystal, scaled by half its thickness, distorts the pulse duration to a certain extent depending on its initial chirp and thus determines the width of the energy distribution recorded in the autocorrelator. As the crystal thickness increases, the group velocity mismatch leads to a transformation of the recorded distribution from the correlation function of intensity to the squared modulus of the field correlation function. In the case of Gaussian pulses, such a transformation does not affect significantly the recorded distribution. Errors of pulse duration measurements are estimated. (nonlinear optical phenomena)

  8. Femtosecond pulsed laser ablation to enhance drug delivery across the skin.

    Science.gov (United States)

    Garvie-Cook, Hazel; Stone, James M; Yu, Fei; Guy, Richard H; Gordeev, Sergey N

    2016-01-01

    Laser poration of the skin locally removes its outermost, barrier layer, and thereby provides a route for the diffusion of topically applied drugs. Ideally, no thermal damage would surround the pores created in the skin, as tissue coagulation would be expected to limit drug diffusion. Here, a femtosecond pulsed fiber laser is used to porate mammalian skin ex vivo. This first application of a hollow core negative curvature fiber (HC-NCF) to convey a femtosecond pulsed, visible laser beam results in reproducible skin poration. The effect of applying ink to the skin surface, prior to ultra-short pulsed ablation, has been examined and Raman spectroscopy reveals that the least, collateral thermal damage occurs in inked skin. Pre-application of ink reduces the laser power threshold for poration, an effect attributed to the initiation of plasma formation by thermionic electron emission from the dye in the ink. Poration under these conditions significantly increases the percutaneous permeation of caffeine in vitro. Dye-enhanced, plasma-mediated ablation of the skin is therefore a potentially advantageous approach to enhance topical/transdermal drug absorption. The combination of a fiber laser and a HC-NCF, capable of emitting and delivering femtosecond pulsed, visible light, may permit a compact poration device to be developed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Selective ablation of dental enamel and dentin using femtosecond laser pulses

    International Nuclear Information System (INIS)

    Lizarelli, R F Z; Costa, M M; Carvalho-Filho, E; Bagnato, V S; Nunes, F D

    2008-01-01

    The study of the interaction of intense laser light with matter, as well as transient response of atoms and molecules is very appropriated because of the laser energy concentration in a femtosecond optical pulses. The fundamental problem to be solved is to find tools and techniques which allow us to observe and manipulate on a femtosecond time scale the photonics events on and into the matter. Six third human extracted molars were exposed to a femtosecond Ti:Sapphire Q-switched and mode locked laser (Libra-S, Coherent, Palo Alto, CA, USA), emitting pulses with 70 fs width, radiation wavelength of 801 nm, at a constant pulse repetition rate of 1 KHz. The laser was operated at different power levels (70 to 400 mW) with constant exposition time of 10 seconds, at focused and defocused mode. Enamel and dentin surfaces were evaluated concerned ablation rate and morphological aspects under scanning electron microscopic. The results in this present experiment suggest that at the focused mode and under higher average power, enamel tissues present microcavities with higher depth and very precise edges, but, while dentin shows a larger melt-flushing, lower depth and melting and solidification aspect. In conclusion, it is possible to choose hard or soft ablation, under lower and higher average power, respectively, revealing different aspects of dental enamel and dentin, depending on the average power, fluence and distance from the focal point of the ultra-short pulse laser on the tooth surface

  10. Quantum Computation with Ultrafast Laser Pulse Shaping

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 10; Issue 6. Quantum Computation with Ultrafast Laser Pulse Shaping. Debabrata Goswami. General Article Volume 10 Issue 6 June 2005 pp 8-14. Fulltext. Click here to view fulltext PDF. Permanent link:

  11. Light pulse shapes from plastic scintillators

    International Nuclear Information System (INIS)

    Moszynski, M.; Bengtson, B.

    1977-01-01

    A detailed study of the light pulse shape from the binary NE 111 and the ternary Pilot U, Naton 136, KL 236, NE 102A, NE 104 and NE 110 plastic scintillators was performed by the single photon method using XP 1021 and C 31024 photomultipliers. The analysis of the shape of the light pulses determined experimentally for several samples of different dimensions gave the following conclusions. The original light pulse shape from the binary NE 111 scintillator, as measured with a 5 mm thick polished sample is described analytically by the convolution integral of a Gaussian and an exponential function. The Gaussian function may reflect a deexcitation of several higher levels of the solvent molecules excited by nuclear particles preceding an intermolecular energy transfer in the scintillator. It may introduce a rather important limitation of the speed of plastic scintillators as the standard deviation of the Gaussian function is equal to 0.2 ns. The light pulse shape from the ternary plastics is described by the convolution integral of a Gaussian and two exponential functions. The Gaussian function presents the rate of energy transfer from nuclear particles to the primary solute as in the binary plastics. The exponential functions describe the energy transfer from the primary solute to the wavelength shifter and the final emission of the light. (Auth.)

  12. Type-I cascaded quadratic soliton compression in lithium niobate: Compressing femtosecond pulses from high-power fiber lasers

    DEFF Research Database (Denmark)

    Bache, Morten; Wise, Frank W.

    2010-01-01

    The output pulses of a commercial high-power femtosecond fiber laser or amplifier are typically around 300–500 fs with wavelengths of approximately 1030 nm and tens of microjoules of pulse energy. Here, we present a numerical study of cascaded quadratic soliton compression of such pulses in LiNbO3...

  13. Dual-scale nanoripple/nanoparticle-covered microspikes on silicon by femtosecond double pulse train irradiation in water

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Ge; Jiang, Lan [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Li, Xin, E-mail: lixin02@bit.edu.cn [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Xu, Yongda; Shi, Xuesong; Yan, Ruyu [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Lu, Yongfeng [Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511 (United States)

    2017-07-15

    Highlights: • A simple method to fabricate dual-scale structures on silicon is proposed. • Nanoripple-covered or nanoparticle-covered microspikes are obtained on Si firstly. • They are obtained by temporally-shaped fs laser one-step irradiation in water. • Their application in SERS was proved with a high sensitivity of up to 10{sup 8}. - Abstract: Novel dual-scale structures were obtained by femtosecond double pulse train (subpulse delay Δt > 0 ps) one-step irradiating silicon in water. The dual-scale structures consist of microspikes of ∼2 μm width and ∼0.5 μm height, and nanoripples with a mean period of 146 nm or nanoparticles with a mean diameter of 90 nm which entirely cover on the microspikes, for linearly polarized or circularly polarized femtosecond laser respectively. The formation of dual-scale structures involves the following processes: (1) Continuously laser energy deposited at femtosecond to picosecond timescales within silicon surfaces and central regions, will result in enhanced capillary waves and thinner melted silicon layers. Hence, the microspikes can be induced at laser fluences below ablation threshold; (2) Later (>500–800 pulses), a mass of debris and bubbles produced will lead to the remarkably and uniformly scattering or shielding of subsequent incident laser energy. Hence, the nanostructures can be induced. The novel structures exhibit high-sensitive surface enhanced Raman scattering with an enhancement factor of 10{sup 8} for Rhodamine 6G detecting. Besides, the novel structures have application potentials in improving the silicon hydrophobicity, antireflection, etc.

  14. Dual-scale nanoripple/nanoparticle-covered microspikes on silicon by femtosecond double pulse train irradiation in water

    International Nuclear Information System (INIS)

    Meng, Ge; Jiang, Lan; Li, Xin; Xu, Yongda; Shi, Xuesong; Yan, Ruyu; Lu, Yongfeng

    2017-01-01

    Highlights: • A simple method to fabricate dual-scale structures on silicon is proposed. • Nanoripple-covered or nanoparticle-covered microspikes are obtained on Si firstly. • They are obtained by temporally-shaped fs laser one-step irradiation in water. • Their application in SERS was proved with a high sensitivity of up to 10 8 . - Abstract: Novel dual-scale structures were obtained by femtosecond double pulse train (subpulse delay Δt > 0 ps) one-step irradiating silicon in water. The dual-scale structures consist of microspikes of ∼2 μm width and ∼0.5 μm height, and nanoripples with a mean period of 146 nm or nanoparticles with a mean diameter of 90 nm which entirely cover on the microspikes, for linearly polarized or circularly polarized femtosecond laser respectively. The formation of dual-scale structures involves the following processes: (1) Continuously laser energy deposited at femtosecond to picosecond timescales within silicon surfaces and central regions, will result in enhanced capillary waves and thinner melted silicon layers. Hence, the microspikes can be induced at laser fluences below ablation threshold; (2) Later (>500–800 pulses), a mass of debris and bubbles produced will lead to the remarkably and uniformly scattering or shielding of subsequent incident laser energy. Hence, the nanostructures can be induced. The novel structures exhibit high-sensitive surface enhanced Raman scattering with an enhancement factor of 10 8 for Rhodamine 6G detecting. Besides, the novel structures have application potentials in improving the silicon hydrophobicity, antireflection, etc.

  15. Influence of Nonlinear Environmental Properties on the Process of Pulse-Stimulated Compulsory Combined Scattering under Femtosecond Pumping Conditions

    Directory of Open Access Journals (Sweden)

    V.L. Dobryakov

    2017-12-01

    Full Text Available Impulsive stimulated Raman scattering (ISRS observed by pump-probe experiments was considered. The response from the model system for ISRS-process is calculated for femtosecond laser pump pulse. The response of the model system for the processes of the is-SRS type under the conditions of femtosecond pumping is calculated: the time behavior of the ISC signal is theoretically calculated, and also the frequency dependence of the amplitude of the oscillations excited by the laser pulse with a femtosecond duration. Qualitative agreement is demonstrated for the case of the experiment with the perylene molecule.

  16. Filming Femtosecond Molecular Movies with X-ray Pulses

    DEFF Research Database (Denmark)

    Kjær, Kasper Skov

    This thesis describes the investigation of time-resolved phenomena using X-ray techniques, and in particular the new possibilities and challenges arising from the application of these techniques on the femtosecond time-scale. The thesis will review the processes following laser excitation...... of molecular species in solution, describing the interplay between electronic and structural dynamics, as well as the role of the solvent. This will be followed by an introduction of the three X-ray techniques used in this work, and it will be shown how the application of these techniques in a laser pump / X-ray...... probe framework can help elucidate the excited state dynamics. The theoretical information content of the X-ray techniques will be discussed, as well as the practical experimental considerations for their implementation. This is done in order to demonstrate the potential increase in information content...

  17. Femtosecond Pulse Characterization as Applied to One-Dimensional Photonic Band Edge Structures

    Science.gov (United States)

    Fork, Richard L.; Gamble, Lisa J.; Diffey, William M.

    1999-01-01

    The ability to control the group velocity and phase of an optical pulse is important to many current active areas of research. Electronically addressable one-dimensional photonic crystals are an attractive candidate to achieve this control. This report details work done toward the characterization of photonic crystals and improvement of the characterization technique. As part of the work, the spectral dependence of the group delay imparted by a GaAs/AlAs photonic crystal was characterized. Also, a first generation an electrically addressable photonic crystal was tested for the ability to electronically control the group delay. The measurement technique, using 100 femtosecond continuum pulses was improved to yield high spectral resolution (1.7 nanometers) and concurrently with high temporal resolution (tens of femtoseconds). Conclusions and recommendations based upon the work done are also presented.

  18. Synchronization of femtosecond UV-IR laser with electron beam for pulse radiolysis studies

    International Nuclear Information System (INIS)

    Saeki, Akinori; Kozawa, Takahiro; Kashiwagi, Shigeru; Okamoto, Kazumasa; Isoyama, Goro; Yoshida, Yoichi; Tagawa, Seiichi

    2005-01-01

    A picosecond stroboscopic pulse radiolysis system which consists of a femtosecond laser and a picosecond L-band linear accelerator (linac) is demonstrated. A newly installed femtosecond laser system operated at 960 Hz can cover a wide region of wavelength ranging from <300 nm to 10 μm, although the upper limit is 1.7 μm to date because of the sensitivity of photodetectors. In order to achieve a high accuracy of synchronization between the laser and the linac, a new timing and synchronization circuit was developed. A double pulse detection method was applied for the new system, resulting in doubling of the improvement in signal-to-noise ratio. The time resolution and time jitter were estimated from the rise time of hydrated electrons at 600 nm, and the transient absorption kinetics of electrons in n-dodecane was measured at 1300 nm

  19. Momentum distributions of selected rare-gas atoms probed by intense femtosecond laser pulses

    DEFF Research Database (Denmark)

    Abu-Samha, Mahmoud; Madsen, Lars Bojer

    2011-01-01

    We provide a direct comparison between numerical and experimental (Rudenko et al 2004 J. Phys. B: At. Mol. Opt. Phys. 37 L407) photoelectron momentum distributions in strong-field ionization of selected rare-gas atoms (He, Ne and Ar), probed by femtosecond linearly polarized laser pulses. The cal......We provide a direct comparison between numerical and experimental (Rudenko et al 2004 J. Phys. B: At. Mol. Opt. Phys. 37 L407) photoelectron momentum distributions in strong-field ionization of selected rare-gas atoms (He, Ne and Ar), probed by femtosecond linearly polarized laser pulses....... The calculations are performed by solving the time-dependent Schrödinger equation within the single-active-electron approximation, and focal-volume effects are taken into account by appropriately averaging the results. The resulting momentum distributions are in quantitative agreement with the experimental...

  20. Formation of array microstructures on silicon by multibeam interfered femtosecond laser pulses

    International Nuclear Information System (INIS)

    Zhao Quanzhong; Qiu Jianrong; Zhao Chongjun; Jiang Xiongwei; Zhu Congshan

    2005-01-01

    We report on an optical interference method to fabricate array microstructures on the surface of silicon wafers by means of five-beam interference of femtosecond laser pulses. Optical microscope and scanning electron microscope observations revealed microstructures with micrometer-order were fabricated. The diffraction characteristics of the fabricated structures were evaluated. The present technique allows one-step realization of functional optoelectronic devices on silicon surface

  1. Noncontact microsurgery of cell membranes using femtosecond laser pulses for optoinjection of specified substances into cells

    Science.gov (United States)

    Il'ina, I. V.; Ovchinnikov, A. V.; Chefonov, O. V.; Sitnikov, D. S.; Agranat, Mikhail B.; Mikaelyan, A. S.

    2013-04-01

    IR femtosecond laser pulses were used for microsurgery of a cell membrane aimed at local and short-duration change in its permeability and injection of specified extracellular substances into the cells. The possibility of noncontact laser delivery of the propidium iodide fluorescent dye and the pEGFP plasmid, encoding the green fluorescent protein, into the cells with preservation of the cell viability was demonstrated.

  2. Optical fiber link for transmission of 1-nJ femtosecond laser pulses at 1550 nm

    DEFF Research Database (Denmark)

    Eichhorn, Finn; Olsson, Rasmus Kjelsmark; Buron, Jonas Christian Due

    2010-01-01

    a distance of 5.3 m. The fiber link consists of dispersion-compensating fiber (DCF) and standard single-mode fiber. The optical pulses at different positions in the fiber link are measured using frequency-resolved optical gating (FROG). The results are compared with numerical simulations of the pulse......We report on numerical and experimental characterization of the performance of a fiber link optimized for the delivery of sub-100-fs laser pulses at 1550 nm over several meters of fiber. We investigate the power handling capacity of the link, and demonstrate all-fiber delivery of 1-nJ pulses over...... propagation based on the generalized nonlinear Schrödinger equation. The high input power capacity of the fiber link allows the splitting and distribution of femtosecond pulses to an array of fibers with applications in multi-channel fiber-coupled terahertz time-domain spectroscopy and imaging systems. We...

  3. Magnetic phases in Pt/Co/Pt films induced by single and multiple femtosecond laser pulses

    International Nuclear Information System (INIS)

    Kisielewski, J.; Kurant, Z.; Sveklo, I.; Tekielak, M.; Maziewski, A.; Wawro, A.

    2016-01-01

    Ultrathin Pt/Co/Pt trilayers with initial in-plane magnetization were irradiated with femtosecond laser pulses. In this way, an irreversible structural modification was introduced, which resulted in the creation of numerous pulse fluence-dependent magnetic phases. This was particularly true with the out-of-plane magnetization state, which exhibited a submicrometer domain structure. This effect was studied in a broad range of pulse fluences up to the point of ablation of the metallic films. In addition to this single-pulse experiment, multiple exposure spots were also investigated, which exhibited an extended area of out-of-plane magnetization phases and a decreased damage threshold. Using a double exposure with partially overlapped spots, a two-dimensional diagram of the magnetic phases as a function of the two energy densities was built, which showed a strong inequality between the first and second incoming pulses.

  4. Soliton filtering from a supercontinuum: a tunable femtosecond pulse source

    Energy Technology Data Exchange (ETDEWEB)

    Licea-Rodriguez, Jacob; Rangel-Rojo, Raul [Centro de Investigacion CientIfica y de Educacion Superior de Ensenada, Apartado Postal 2732, Ensenada B.C., 22860 (Mexico); Garay-Palmett, Karina, E-mail: rrangel@cicese.mx [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543, Mexico DF. 04510 (Mexico)

    2011-01-01

    In this article we report experimental results related with the generation of a supercontinuum in a microstructured fiber, from which the soliton with the longest wavelength is filtered out of the continuum and is used to construct a tunable ultrashort pulses source by varying the pump power. Pulses of an 80 fs duration (FWHM) from a Ti:sapphire oscillator were input into a 2 m long fiber to generate the continuum. The duration of the solitons at the fiber output was preserved by using a zero dispersion filtering system, which selected the longest wavelength soliton, while avoiding temporal spreading of the solitons. We present a complete characterization of the filtered pulses that are continuously tunable in the 850-1100 nm range. We also show that the experimental results have a qualitative agreement with theory. An important property of the proposed near-infrared pulsed source is that the soliton pulse energies obtained after filtering are large enough for applications in nonlinear microscopy.

  5. Study and realisation of a femtosecond dye laser operating at different wavelengths. Ultrashort pulses compression and amplification

    International Nuclear Information System (INIS)

    Georges, Patrick

    1989-01-01

    We present the study and the realization of a passively mode-locked dye laser producing pulses shorter than 100 femto-seconds (10 -13 s). In a ring cavity with an amplifier medium (Rhodamine 60) and a saturable absorber (DODCI), a sequence of four prisms controls the group velocity dispersion and allows the generation of very short pulses. Then we have studied the production of femtosecond pulses at other wavelengths directly from the femtosecond dye laser. For the first rime, 60 fs pulses at 685 nm and pulses shorter than 50 fs between 775 nm and 800 nm have been produced by passive mode locking. These near infrared pulses have been used to study the absorption saturation kinetics in semiconductors multiple quantum wells GaAs/GaAlAs. We have observed a singular behavior of the laser operating at 685 nm and analyzed the produced pulses in terms of optical solitons. To perform time resolved spectroscopy with shortest pulses, we have studied a pulse compressor and a multipass amplifier to increase the pulses energy. Pulses of 20 fs and 10 micro-joules (peak power: 0.5 GW) have been obtained at low repetition rate (10 Hz) and pulses of 16 fs and 0.6 micro-joules pulses have been generated at high repetition rate (11 kHz) using a copper vapor laser. These pulses have been used to study the absorption saturation kinetics of an organic dye (the Malachite Green). (author) [fr

  6. Absorption of femtosecond laser pulses by atomic clusters

    International Nuclear Information System (INIS)

    Lin Jingquan; Zhang Jie; Li Yingjun; Chen Liming; Lu Tiezheng; Teng Hao

    2001-01-01

    Energy absorption by Xe, Ar, He atomic clusters are investigated using laser pulses with 5 mJ energy in 150 fs duration. Experimental results show that the size of cluster and laser absorption efficiency are strongly dependent on several factors, such as the working pressure of pulse valve, atomic number Z of the gas. Absorption fraction of Xe clusters is as high as 45% at a laser intensity of 1 x 10 15 W/cm 2 with 20 x 10 5 Pa gas jet backing pressure. Absorption of the atomic clusters is greatly reduced by introducing pre-pulses. Ion energy measurements confirm that the efficient energy deposition results in a plasma with very high ion temperature

  7. Frequency conversion of high-intensity, femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Banks, P S

    1997-06-01

    Almost since the invention of the laser, frequency conversion of optical pulses via non- linear processes has been an area of active interest. However, third harmonic generation using ~(~1 (THG) in solids is an area that has not received much attention because of ma- terial damage limits. Recently, the short, high-intensity pulses possible with chirped-pulse amplification (CPA) laser systems allow the use of intensities on the order of 1 TW/cm2 in thin solids without damage. As a light source to examine single-crystal THG in solids and other high field inter- actions, the design and construction of a Ti:sapphire-based CPA laser system capable of ultimately producing peak powers of 100 TW is presented. Of special interest is a novel, all-reflective pulse stretcher design which can stretch a pulse temporally by a factor of 20,000. The stretcher design can also compensate for the added material dispersion due to propagation through the amplifier chain and produce transform-limited 45 fs pulses upon compression. A series of laser-pumped amplifiers brings the peak power up to the terawatt level at 10 Hz, and the design calls for additional amplifiers to bring the power level to the 100 TW level for single shot operation. The theory for frequency conversion of these short pulses is presented, focusing on conversion to the third harmonic in single crystals of BBO, KD*P, and d-LAP (deuterated I-arginine phosphate). Conversion efficiencies of up to 6% are obtained with 500 fs pulses at 1053 nm in a 3 mm thick BBO crystal at 200 GW/cm 2. Contributions to this process by unphasematched, cascaded second harmonic generation and sum frequency generation are shown to be very significant. The angular relationship between the two orders is used to measure the tensor elements of C = xt3)/4 with Crs = -1.8 x 1O-23 m2/V2 and .15Cri + .54Crs = 4.0 x 1O-23 m2/V2. Conversion efficiency in d-LAP is about 20% that in BBO and conversion efficiency in KD*P is 1% that of BBO. It is calculated

  8. New organic crystals for pulse shape discrimination

    Energy Technology Data Exchange (ETDEWEB)

    Hull, G; Zaitseva, N; Cherepy, N; Newby, J; Stoeffl, W; Payne, S

    2008-07-16

    Efficient, readily-available, low-cost, high-energy neutron detectors can play a central role in detecting illicit nuclear weapons since neutrons are a strong indication for the presence of fissile material such as Plutonium and Highly-Enriched Uranium. The main challenge in detecting fast neutrons consists in the discrimination of the signal from the gamma radiation background. At present, the only well-investigated organic crystal scintillator for fast neutron detection, in a n/{gamma} mixed field, is stilbene, which while offering good pulse shape discrimination, is not widely used because of its limited availability and high cost. In this work we report the results of our studies made with a number of new organic crystals, which exhibit pulse shape discrimination for detection of fast neutrons. In particular 1,1,4,4-tetraphenyl-1,3-butadiene features a light yield higher than anthracene and a Figure of Merit (FOM) for the pulse shape discrimination better than stilbene. New crystals are good candidates for the low-cost solution growth method, thus representing promising organic scintillators for widespread deployment for high-energy neutron detection.

  9. Monochromatization of femtosecond XUV light pulses with the use of reflection zone plates.

    Science.gov (United States)

    Metje, Jan; Borgwardt, Mario; Moguilevski, Alexandre; Kothe, Alexander; Engel, Nicholas; Wilke, Martin; Al-Obaidi, Ruba; Tolksdorf, Daniel; Firsov, Alexander; Brzhezinskaya, Maria; Erko, Alexei; Kiyan, Igor Yu; Aziz, Emad F

    2014-05-05

    We report on a newly built laser-based tabletop setup which enables generation of femtosecond light pulses in the XUV range employing the process of high-order harmonic generation (HHG) in a gas medium. The spatial, spectral, and temporal characteristics of the XUV beam are presented. Monochromatization of XUV light with minimum temporal pulse distortion is the central issue of this work. Off-center reflection zone plates are shown to be advantageous when selection of a desired harmonic is carried out with the use of a single optical element. A cross correlation technique was applied to characterize the performance of the zone plates in the time domain. By using laser pulses of 25 fs length to pump the HHG process, a pulse duration of 45 fs for monochromatized harmonics was achieved in the present setup.

  10. High-energy infrared femtosecond pulses generated by dual-chirped optical parametric amplification.

    Science.gov (United States)

    Fu, Yuxi; Takahashi, Eiji J; Midorikawa, Katsumi

    2015-11-01

    We demonstrate high-energy infrared femtosecond pulse generation by a dual-chirped optical parametric amplification (DC-OPA) scheme [Opt. Express19, 7190 (2011)]. By employing a 100 mJ pump laser, a signal pulse energy exceeding 20 mJ at a wavelength of 1.4 μm was achieved before dispersion compensation. A total output energy of 33 mJ was recorded. Under a further energy scaling condition, the signal pulse was compressed to an almost transform-limited duration of 27 fs using a fused silica prism compressor. Since the DC-OPA scheme is efficient and energy scalable, design parameters for obtaining 100 mJ level infrared pulses are presented, which are suitable as driver lasers for the energy scaling of high-order harmonic generation with sub-keV photon energy.

  11. Femtosecond X-ray Pulses from a Spatially Chirped Electron Bunch in a SASE FEL

    Energy Technology Data Exchange (ETDEWEB)

    Emma, P.

    2003-01-14

    We propose a simple method to produce short x-ray pulses using a spatially chirped electron bunch in a SASE FEL. The spatial chirp is generated using an rf deflector which produces a transverse offset (in y and/or y') correlated with the longitudinal bunch position. Since the FEL gain is very sensitive to an initial offset in the transverse phase space at the entrance of the undulator, only a small portion of the electron bunch with relatively small transverse offset will interact significantly with the radiation, resulting in an x-ray pulse length much shorter than the electron bunch length. The x-ray pulse is also naturally phase locked to the rf deflector and so allows high precision timing synchronization. We discuss the generation and transport of such a spatially chirped electron beam and show that tens of femtosecond long pulse can be generated for the linac coherent light source (LCLS).

  12. Single- and multi-pulse formation of surface structures under static femtosecond irradiation

    Science.gov (United States)

    Guillermin, M.; Garrelie, F.; Sanner, N.; Audouard, E.; Soder, H.

    2007-07-01

    Femtosecond surface structure modifications are investigated under irradiation with laser pulses of 150 fs at 800 nm, on copper and silicon. We report sub-wavelength periodic structures formation (ripples) with a periodicity of 500 nm for both materials. These ripples are perpendicular to the laser polarization and can be obtained with only one pulse. The formation of these ripples corresponds to a fluence threshold of 1 J/cm 2 for copper and 0.15 J/cm 2 for silicon. We find several morphologies when more pulses are applied: larger ripples parallel to the polarization are formed with a periodicity of 1 μm and degenerate into a worm-like morphology with a higher number of pulses. In addition, walls of deep holes also show sub-wavelength and large ripples.

  13. Production and utilization of synchronized femtosecond electron and laser single pulses

    International Nuclear Information System (INIS)

    Uesaka, M.; Watanabe, T.; Ueda, T.; Nakajima, K.; Kotaki, H.; Ogata, A.

    1997-01-01

    A subpicosecond (700 fs at FWHM) electron pulse from the S-band (2.856 GHz) linear accelerator (linac) of the NERL (Nuclear Engineering Research Laboratory) was synchronized with a femtosecond (100 fs at FWHM) laser pulse from a T 3 (table-top terawatts) laser with a picosecond time whose standard deviation is 3.7 ps. Then we generated a picosecond characteristic X-ray pulse by irradiating through the electron pulse a Cu target (Kα, 8.1 keV, 1.54 A) and obstained the Bragg diffraction from a NaCl ionic monocrystal using a high sensitivity X-ray imaging plate. Further, we discuss its applications to observe lattice vibration of the monocrystal by using the synchronized laser (pump) and X-ray (probe). (orig.)

  14. Optimal Control of Atomic, Molecular and Electron Dynamics with Tailored Femtosecond Laser Pulses

    Science.gov (United States)

    Brixner, Tobias; Pfeifer, Thomas; Gerber, Gustav; Wollenhaupt, Matthias; Baumert, Thomas

    With the invention of the laser, the dream was realized to actively exert control over quantum systems. Active control over the dynamics of quantum mechanical systems is a fascinating perspective in modern physics. Cleavage and creation of predetermined chemical bonds, selective population transfer in atoms and molecules, and steering the dynamics of bound and free electrons have been important milestones along this way. A promising tool for this purpose is available with femtosecond laser technologies. In this chapter we review some of our work on adaptive femtosecond quantum control where a learning algorithm and direct experimental feedback signals are employed to optimize user-defined objectives. Femtosecond laser pulses are modified in frequency-domain pulse shapers, which apart from phase- and intensity-modulation can also modify the polarization state as a function of time. We will highlight the major advances in the field of optimal control by presenting our own illustrative experimental examples such as gas-phase and liquid-phase femtochemistry, control in weak and strong laser fields, and control of electron dynamics.

  15. Characteristic measurement for femtosecond laser pulses using a GaAs PIN photodiode as a two-photon photovoltaic receiver

    Science.gov (United States)

    Chen, Junbao; Xia, Wei; Wang, Ming

    2017-06-01

    Photodiodes that exhibit a two-photon absorption effect within the spectral communication band region can be useful for building an ultra-compact autocorrelator for the characteristic inspection of optical pulses. In this work, we develop an autocorrelator for measuring the temporal profile of pulses at 1550 nm from an erbium-doped fiber laser based on the two-photon photovoltaic (TPP) effect in a GaAs PIN photodiode. The temporal envelope of the autocorrelation function contains two symmetrical temporal side lobes due to the third order dispersion of the laser pulses. Moreover, the joint time-frequency distribution of the dispersive pulses and the dissimilar two-photon response spectrum of GaAs and Si result in different delays for the appearance of the temporal side lobes. Compared with Si, GaAs displays a greater sensitivity for pulse shape reconstruction at 1550 nm, benefiting from the higher signal-to-noise ratio of the side lobes and the more centralized waveform of the autocorrelation trace. We also measure the pulse width using the GaAs PIN photodiode, and the resolution of the measured full width at half maximum of the TPP autocorrelation trace is 0.89 fs, which is consistent with a conventional second-harmonic generation crystal autocorrelator. The GaAs PIN photodiode is shown to be highly suitable for real-time second-order autocorrelation measurements of femtosecond optical pulses. It is used both for the generation and detection of the autocorrelation signal, allowing the construction of a compact and inexpensive intensity autocorrelator.

  16. Acceleration of a ground-state reaction by selective femtosecond-infrared-laser-pulse excitation

    Science.gov (United States)

    Stensitzki, Till; Yang, Yang; Kozich, Valeri; Ahmed, Ashour A.; Kössl, Florian; Kühn, Oliver; Heyne, Karsten

    2018-02-01

    Infrared (IR) excitation of vibrations that participate in the reaction coordinate of an otherwise thermally driven chemical reaction are believed to lead to its acceleration. Attempts at the practical realization of this concept have been hampered so far by competing processes leading to sample heating. Here we demonstrate, using femtosecond IR-pump IR-probe experiments, the acceleration of urethane and polyurethane formation due to vibrational excitation of the reactants for 1:1 mixtures of phenylisocyanate and cyclohexanol, and toluene-2,4-diisocyanate and 2,2,2-trichloroethane-1,1-diol, respectively. We measured reaction rate changes upon selective vibrational excitation with negligible heating of the sample and observed an increase of the reaction rate up to 24%. The observation is rationalized using reactant and transition-state structures obtained from quantum chemical calculations. We subsequently used IR-driven reaction acceleration to write a polyurethane square on sample windows using a femtosecond IR pulse.

  17. X-ray emission from stainless steel foils irradiated by femtosecond petawatt laser pulses

    Science.gov (United States)

    Alkhimova, M. A.; Faenov, A. Ya; Pikuz, T. A.; Skobelev, I. Yu; Pikuz, S. A.; Nishiuchi, M.; Sakaki, H.; Pirozhkov, A. S.; Sagisaka, S.; Dover, N. P.; Kondo, Ko; Ogura, K.; Fukuda, Y.; Kiriyama, H.; Esirkepov, T.; Bulanov, S. V.; Andreev, A.; Kando, M.; Zhidkov, A.; Nishitani, K.; Miyahara, T.; Watanabe, Y.; Kodama, R.; Kondo, K.

    2018-01-01

    We report about nonlinear growth of x-ray emission intensity emitted from plasma generated by femtosecond petawatt laser pulses irradiating stainless steel foils. X-ray emission intensity increases as ∼ I 4.5 with laser intensity I on a target. High spectrally resolved x-ray emission from front and rear surfaces of 5 μm thickness stainless steel targets were obtained at the wavelength range 1.7–2.1 Å, for the first time in experiments at femtosecond petawatt laser facility J-KAREN-P. Total intensity of front x-ray spectra three times dominates to rear side spectra for maximum laser intensity I ≈ 3.2×1021 W/cm2. Growth of x-ray emission is mostly determined by contribution of bremsstrahlung radiation that allowed estimating bulk electron plasma temperature for various magnitude of laser intensity on target.

  18. Cylindrical shockwave-induced compression mechanism in femtosecond laser Bessel pulse micro-drilling of PMMA

    Science.gov (United States)

    Wang, Guoyan; Yu, Yanwu; Jiang, Lan; Li, Xiaowei; Xie, Qian; Lu, Yongfeng

    2017-04-01

    Femtosecond (fs) laser Bessel pulses can be employed for high-quality and high-speed fabrication of high-aspect-ratio uniform microhole arrays. This technique exhibits prominent potential in three-dimensional packaging, fluidic devices, fiber sensing, biomedical devices, and aeronautics. However, the fundamental mechanisms remain mysterious. Using the femtosecond time-resolved pump-probe shadowgraph technique, this study revealed that the generation of cylindrical shockwaves inside the bulk material and the corresponding compression mechanism play key roles in the formation of high-aspect-ratio microholes. The phenomena were observed in all experiments of Bessel beam drilling of polymethyl methacrylate. In the aforementioned cases, the compression mechanism was confirmed by measuring sample mass losses that were experimentally determined to be negligible. By contrast, neither cylindrical shockwave nor compression mechanism was observed when a fused silica or Gaussian laser beam was involved.

  19. Evaluation of ablation efficiency and surface morphology of human teeth upon irradiation with femtosecond laser pulses

    Science.gov (United States)

    Shaheen, M. E.; Gagnon, J. E.; Fryer, B. J.

    2014-11-01

    This study investigates changes in ablation efficiency and surface morphology induced in human dental enamel and dentin upon interaction with femtosecond laser pulses at variable energies and number of laser pulses. Craters were created using a Ti:sapphire femtosecond laser ablation system operating at a wavelength of 785 nm, pulse width of 130 fs, and repetition rate of 20 Hz. Various techniques, such as optical and scanning electron microscopy and inductively coupled plasma mass spectrometry (ICP-MS), were used to evaluate ablation depth, amount of material ablated, and surface morphology of the craters. Ablation rate (ablation depth per pulse) was found to be lower in enamel than dentin with the maximum rate occurring at fluence of 12.4 J cm-2 in both materials. A drop in ablation rate was observed for fluence greater than 12.4 J cm-2 and was attributed to attenuation of laser energy due to interaction with the laser-generated particles. Above this fluence, signs of thermal effects, such as melting and formation of droplets of molten material at the sample surface, were observed. The response of the ICP-MS indicated that the amount of ablated material removed from dentin is greater than that removed from enamel by a factor of 1.5 or more at all investigated fluence.

  20. Generation of femtosecond soft x-ray pulse by interaction between laser and electron beam in an electron storage ring

    CERN Document Server

    Inoue, T; Amano, S; Mochizuki, T; Yatsuzaka, M

    2002-01-01

    A femtosecond synchrotron radiation pulse train can be extracted from an electron storage ring by interaction between an ultrashort laser pulse and an electron beam in an undulator. Generation system of a femtosecond soft x-ray pulse by the slicing technique was studied with numerical calculations for its performance, as applicable for the NewSUBARU synchrotron radiation facility at LASTI. The femtosecond electron pulse, that is energy-modulated with a Ti:sapphire laser at a pulse energy of 100 mu J, a pulse width of 150 fs, and repetition frequency of 20 kHz, can be sufficiently separated in a bending magnet. A femtosecond soft x-ray pulse (the critical photon energy of 0.69 keV and a pulse width of 250 fs) is obtained with a collimator (diameter of 800 mu m phi), and it has an average brightness 3 x 10 sup 6 photons/s/mm sup 2 /mrad sup 2 /0.1 %BW and an average photon flux 10 sup 5 photons/s/0.1 %BW. (author)

  1. Femtosecond and nanosecond pulsed laser deposition of silicon and germanium

    Energy Technology Data Exchange (ETDEWEB)

    Reenaas, Turid Worren [Department of Physics, Norwegian University of Science and Technology, 7491 Trondheim (Norway); Lee, Yen Sian [Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur (Malaysia); Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Chowdhury, Fatema Rezwana; Gupta, Manisha; Tsui, Ying Yin [Department of Electrical and Computer Engineering, University of Alberta (Canada); Tou, Teck Yong [Faculty of Engineering, Multimedia University, 63100 Cyberjaya, Selangor (Malaysia); Yap, Seong Ling [Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Kok, Soon Yie [Faculty of Engineering, Multimedia University, 63100 Cyberjaya, Selangor (Malaysia); Yap, Seong Shan, E-mail: seongshan@gmail.com [Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    2015-11-01

    Highlights: • Ge and Si were deposited by fs and ns laser at room temperature and at vacuum. • Ion of 10{sup 4} ms{sup −1} and 30–200 eV was obtained for ns ablation for Ge and Si. • Highly energetic ions of 10{sup 5} ms{sup −1} with 2–7 KeV were produced in fs laser ablation. • Nanocrystalline Si and Ge were deposited by using fs laser. • Nanoparticles < 10 nm haven been obtained by fs laser. - Abstract: 150 fs Ti:Sapphire laser pulsed laser deposition of Si and Ge were compared to a nanosecond KrF laser (25 ns). The ablation thresholds for ns lasers were about 2.5 J cm{sup −2} for Si and 2.1 J cm{sup −2} for Ge. The values were about 5–10 times lower when fs laser were used. The power densities were 10{sup 8}–10{sup 9} W cm{sup −2} for ns but 10{sup 12} W cm{sup −2} for fs. By using an ion probe, the ions emission at different fluence were measured where the emitting ions achieving the velocity in the range of 7–40 km s{sup −1} and kinetic energy in the range of 30–200 eV for ns laser. The ion produced by fs laser was measured to be highly energetic, 90–200 km s{sup −1}, 2–10 KeV. Two ion peaks were detected above specific laser fluence for both ns and fs laser ablation. Under fs laser ablation, the films were dominated by nano-sized crystalline particles, drastically different from nanosecond pulsed laser deposition where amorphous films were obtained. The ions characteristics and effects of pulse length on the properties of the deposited films were discussed.

  2. Diffraction characteristics of chirped femtosecond laser pulse by rectangle reflection grating

    Science.gov (United States)

    Liu, Guohua; Xu, Rongrong; Wu, Hanping; Yu, Wenbing

    2012-06-01

    The spectral and temporal intensity distribution expression for the chirped femtosecond laser pulse diffracted by a rectangle reflection grating is derived. The effects of the chirped coefficient on the spatiotemporal and spectral characteristics are theoretically investigated in detail, and a criterion for judging whether or not the diffraction pulse is just split into two independent pulses in the temporal domain is obtained. The results show that the envelope curve of spectral intensity on the diffraction axis is more blue-shift, and its full width at e- 1 maximum is wider for bigger chirped coefficient. The principal maximum on the temporal axis can split into two independent principal maximums for enough height from the upper and the nether reflection surface of the grating. Each principal maximum splits into two smooth pulses, namely one principal pulse and one secondary pulse, and the secondary pulse gradually increases with the increasing of the chirped coefficient; the duration of two principal pulses increases with the increasing of the height of the upper and the nether reflection surface of the grating.

  3. Cavitation dynamics and directional microbubble ejection induced by intense femtosecond laser pulses in liquids

    Science.gov (United States)

    Faccio, D.; Tamošauskas, G.; Rubino, E.; Darginavičius, J.; Papazoglou, D. G.; Tzortzakis, S.; Couairon, A.; Dubietis, A.

    2012-09-01

    We study cavitation dynamics when focusing ring-shaped femtosecond laser beams in water. This focusing geometry reduces detrimental nonlinear beam distortions and enhances energy deposition within the medium, localized at the focal spot. We observe remarkable postcollapse dynamics of elongated cavitation bubbles with high-speed ejection of microbubbles out of the laser focal region. Bubbles are ejected along the laser axis in both directions (away and towards the laser). The initial shape of the cavitation bubble is also seen to either enhance or completely suppress jet formation during collapse. In the absence of jetting, microbubble ejection occurs orthogonal to the laser propagation axis.

  4. Cavitation dynamics and directional microbubble ejection induced by intense femtosecond laser pulses in liquids.

    Science.gov (United States)

    Faccio, D; Tamošauskas, G; Rubino, E; Darginavičius, J; Papazoglou, D G; Tzortzakis, S; Couairon, A; Dubietis, A

    2012-09-01

    We study cavitation dynamics when focusing ring-shaped femtosecond laser beams in water. This focusing geometry reduces detrimental nonlinear beam distortions and enhances energy deposition within the medium, localized at the focal spot. We observe remarkable postcollapse dynamics of elongated cavitation bubbles with high-speed ejection of microbubbles out of the laser focal region. Bubbles are ejected along the laser axis in both directions (away and towards the laser). The initial shape of the cavitation bubble is also seen to either enhance or completely suppress jet formation during collapse. In the absence of jetting, microbubble ejection occurs orthogonal to the laser propagation axis.

  5. Dissociative ionization of ethane with femtosecond pulses of radiation

    Science.gov (United States)

    Boran, Y.; Gutsev, G. L.; Kolomenskii, A. A.; Zhu, F.; Schuessler, A.; Strohaber, J.

    2018-02-01

    We present results of the interaction of ethane with 50 fs pulses of radiation at a wavelength of 800 nm. Ion yields of the parent ion and daughter fragments were measured using a reflectron time-of-flight (TOF) mass spectrometer. The yields of dissociative ionization products were measured as a function of laser intensity and polarization angle. Intensity scans indicate sequential ionization and dissociation. When the field polarization was rotated with respect to the TOF axis, we observed anisotropic ion yields of fragment ions peaked along the TOF axis. Measurements of the fragment {{{C}}}2{{{{H}}}2}2+ reveal the existence of anomalous perpendicular fragmentation. Kinetic energy of the hydrogen ions was measured using linear operation of the TOF and provided information on the underlying mechanisms for formation of H+, {{{{H}}}2}+ and {{{{H}}}3}+. Quantum chemical calculations using GAUSSIAN 09 further investigated the production of {{{{H}}}3}+ and the stability of C2H2+.

  6. Steering dissociation of Br2 molecules with two femtosecond pulses via wave packet interference.

    Science.gov (United States)

    Han, Yong-Chang; Yuan, Kai-Jun; Hu, Wen-Hui; Yan, Tian-Min; Cong, Shu-Lin

    2008-04-07

    The dissociation dynamics of Br2 molecules induced by two femtosecond pump pulses are studied based on the calculation of time-dependent quantum wave packet. Perpendicular transition from X 1Sigma g+ to A 3Pi 1u+ and 1Pi 1u+ and parallel transition from X 1Sigma g+ to B 3Pi 0u+, involving two product channels Br (2P3/2)+Br (2P3/2) and Br (2P3/2)+Br* (2P1/2), respectively, are taken into account. Two pump pulses create dissociating wave packets interfering with each other. By varying laser parameters, the interference of dissociating wave packets can be controlled, and the dissociation probabilities of Br2 molecules on the three excited states can be changed to different degrees. The branching ratio of Br*/(Br+Br*) is calculated as a function of pulse delay time and phase difference.

  7. Generation of air lasing at extended distances by coaxial dual-color femtosecond laser pulses

    Science.gov (United States)

    Li, Helong; Zang, Hongwei; Su, Yue; Fu, Yao; Xu, Huailiang

    2017-12-01

    We present an approach for generation of air lasing at extended distances by coaxial dual-color femtosecond laser pulses. A strong 800 nm pulse prepares the population inversion in {{{N}}}2+ during the filamentation in air, and a weak 400 nm pulse produced coaxially with the 800 nm light by frequency doubling in a BBO crystal seeds the {{{N}}}2+ gain medium, producing strong narrow-band lasing emission at ∼391 nm. We demonstrate that this scheme can overcome the difficulty in spatially overlapping two beams at a far distance, and the lasing emissions at a designed position can be manipulated by dispersion components inserted in the propagation path of the coaxial two-color beam. Our results provide a way for remote generation of air laser for standoff spectroscopy and detection.

  8. 1-MHz high power femtosecond Yb-doped fiber chirped-pulse amplifier

    Science.gov (United States)

    Hu, Zhong-Qi; Yang, Pei-Long; Teng, Hao; Zhu, Jiang-Feng; Wei, Zhi-Yi

    2018-01-01

    A practical femtosecond polarization-maintaining Yb-doped fiber amplifier enabling 153 fs transform-limited pulse duration with 32 μJ pulse energy at 1 MHz repetition rate corresponding to a peak power of 0.21 GW is demonstrated. The laser system based on chirped-pulse amplification (CPA) technique is seeded by a dispersion managed, nonlinear polarization evolution (NPE) mode-locked oscillator with spectrum bandwidth of 31 nm at 1040 nm and amplified by three fiber pre-amplifying stages and a rod type fiber main amplifying stage. The laser works with beam quality of M2 of 1.3 and power stability of 0.63% (root mean square, RMS) over 24 hours will be stable sources for industrial micromachining, medical therapy and scientific research.

  9. Manipulating femtosecond spin-orbit torques with laser pulse sequences to control magnetic memory states and ringing

    Science.gov (United States)

    Lingos, P. C.; Wang, J.; Perakis, I. E.

    2015-05-01

    Femtosecond (fs) coherent control of collective order parameters is important for nonequilibrium phase dynamics in correlated materials. Here, we propose such control of ferromagnetic order based on using nonadiabatic optical manipulation of electron-hole (e -h ) photoexcitations to create fs carrier-spin pulses with controllable direction and time profile. These spin pulses are generated due to the time-reversal symmetry breaking arising from nonperturbative spin-orbit and magnetic exchange couplings of coherent photocarriers. By tuning the nonthermal populations of exchange-split, spin-orbit-coupled semiconductor band states, we can excite fs spin-orbit torques that control complex magnetization pathways between multiple magnetic memory states. We calculate the laser-induced fs magnetic anisotropy in the time domain by using density matrix equations of motion rather than the quasiequilibrium free energy. By comparing to pump-probe experiments, we identify a "sudden" out-of-plane magnetization canting displaying fs magnetic hysteresis, which agrees with switchings measured by the static Hall magnetoresistivity. This fs transverse spin-canting switches direction with magnetic state and laser frequency, which distinguishes it from the longitudinal nonlinear optical and demagnetization effects. We propose that sequences of clockwise or counterclockwise fs spin-orbit torques, photoexcited by shaping two-color laser-pulse sequences analogous to multidimensional nuclear magnetic resonance (NMR) spectroscopy, can be used to timely suppress or enhance magnetic ringing and switching rotation in magnetic memories.

  10. Fast neutron spectrometer with pulse shape discrimination

    International Nuclear Information System (INIS)

    Verbitsky, S.S.

    1978-01-01

    A fast neutron spectrometer with a stilbene single crystal designed to operate at high pulsed count rate has been described. Making use of identification and rejection of events, accompanied by pile-up, allowed to increase permissible count rates by an order of magnitude. The results of energy dependence of signal amplitude and shape relative anisotropy in stilbene in the range 4-10 and 2-8 MeV respectively have been presented. Taking into account anisotropy of the detector-scintillation properties allowed to improve particle discrimination. (Auth.)

  11. Optical fiber link for transmission of 1-nJ femtosecond laser pulses at 1550 nm.

    Science.gov (United States)

    Eichhorn, Finn; Olsson, Rasmus Kjelsmark; Buron, Jonas C D; Grüner-Nielsen, Lars; Pedersen, Jens Engholm; Jepsen, Peter Uhd

    2010-03-29

    We report on numerical and experimental characterization of the performance of a fiber link optimized for the delivery of sub-100-fs laser pulses at 1550 nm over several meters of fiber. We investigate the power handling capacity of the link, and demonstrate all-fiber delivery of 1-nJ pulses over a distance of 5.3 m. The fiber link consists of dispersion-compensating fiber (DCF) and standard single-mode fiber. The optical pulses at different positions in the fiber link are measured using frequency-resolved optical gating (FROG). The results are compared with numerical simulations of the pulse propagation based on the generalized nonlinear Schrödinger equation. The high input power capacity of the fiber link allows the splitting and distribution of femtosecond pulses to an array of fibers with applications in multi-channel fiber-coupled terahertz time-domain spectroscopy and imaging systems. We demonstrate THz pulse generation and detection using a distributed fiber link with 32 channels and 2.6 nJ input pulse energy.

  12. Extension of supercontinuum spectrum generated in photonic crystal fiber by using chirped femtosecond pulses

    Science.gov (United States)

    Vengelis, Julius; Jarutis, Vygandas; Sirutkaitis, Valdas

    2017-08-01

    We present results of experimental and numerical investigation of supercontinuum generation in polarization maintaining photonic crystal fiber (PCF) using chirped femtosecond pulses. The initial unchirped pump pulse source was a mode-locked Yb:KGW laser generating 52 nJ energy 110 fs duration pulses at 1030 nm with 76 MHz repetition rate. The nonlinear medium was a 32 cm long polarization maintaining PCF manufactured by NKT Photonics A/S. We demonstrated the influence of pump pulse chirp on spectral characteristics of supercontinuum. We showed that by chirping pump pulses positively or negatively one can obtain broader supercontinuum spectrum than in case of unchirped pump pulses at the same peak power. Moreover, the extension can be controlled by changing the amount of pump pulse chirp. In our case the supercontinuum spectrum width was extended by up to 115 nm (at maximum chirp value of +10500 fs2 that we could achieve in our setup) compared to the case of unchirped pump at the same peak power.

  13. Beam waist position study for surface modification of polymethyl-methacrylate with femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Caballero-Lucas, F.; Florian, C.; Fernández-Pradas, J.M., E-mail: jmfernandez@ub.edu; Morenza, J.L.; Serra, P.

    2016-06-30

    Highlights: • Surface modification of PMMA with femtosecond laser pulses. • Z-scan reflectance and transmittance study for controlling the sample surface position in the laser beam waist. • Surface modifications with dimensions in the nanometric scale with a 1027 nm wavelength laser. • Extended range of some microns for placing the sample and precise determination of the beam waist position. - Abstract: Femtosecond lasers are versatile tools to process transparent materials. This optical property poses an issue for surface modification. In this case, laser radiation would not be absorbed at the surface unless the beam is just focused there. Otherwise, absorption would take place in the bulk leaving the surface unperturbed. Therefore, strategies to position the material surface at the laser beam waist with high accuracy are essential. We investigated and compared two options to achieve this aim: the use of reflectance data and transmittance measurements across the sample, both obtained during z-scans with pulses from a 1027 nm wavelength laser and 450 fs pulse duration. As the material enters the beam waist region, a reflectance peak is detected while a transmittance drop is observed. With these observations, it is possible to control the position of the sample surface with respect to the beam waist with high resolution and attain pure surface modification. In the case of polymethyl-methacrylate (PMMA), this resolution is 0.6 μm. The results prove that these methods are feasible for submicrometric processing of the surface.

  14. Femtosecond laser pulses for fast 3-D surface profilometry of microelectronic step-structures.

    Science.gov (United States)

    Joo, Woo-Deok; Kim, Seungman; Park, Jiyong; Lee, Keunwoo; Lee, Joohyung; Kim, Seungchul; Kim, Young-Jin; Kim, Seung-Woo

    2013-07-01

    Fast, precise 3-D measurement of discontinuous step-structures fabricated on microelectronic products is essential for quality assurance of semiconductor chips, flat panel displays, and photovoltaic cells. Optical surface profilers of low-coherence interferometry have long been used for the purpose, but the vertical scanning range and speed are limited by the micro-actuators available today. Besides, the lateral field-of-view extendable for a single measurement is restricted by the low spatial coherence of broadband light sources. Here, we cope with the limitations of the conventional low-coherence interferometer by exploiting unique characteristics of femtosecond laser pulses, i.e., low temporal but high spatial coherence. By scanning the pulse repetition rate with direct reference to the Rb atomic clock, step heights of ~69.6 μm are determined with a repeatability of 10.3 nm. The spatial coherence of femtosecond pulses provides a large field-of-view with superior visibility, allowing for a high volume measurement rate of ~24,000 mm3/s.

  15. Manipulation of Squeezed Two-Phonon Bound States using Femtosecond Laser Pulses

    Directory of Open Access Journals (Sweden)

    Nakamura Kazutaka G.

    2013-03-01

    Full Text Available Two-phonon bound states have been excited exclusively in ZnTe(110 via impulsive stimulated second-order Raman scattering, essentially being squeezed states due to phase coherent excitation of two identical components anticorrelated in the wave vector. By using coherent control technique with a pair of femtosecond laser pulses, the manipulation of squeezed states has been demonstrated in which both the amplitude and lifetime of coherent oscillations of squeezed states are modulated, indicating the feasibility to control the quantum noise and the quantum nature of phonon squeezed states, respectively.

  16. Stimulated Brillouin scattering in dispersion-decreasing fiber with ultrahigh-speed femtosecond soliton pulse compression.

    Science.gov (United States)

    Hirooka, Toshihiko; Ono, Shinpei; Hagiuda, Ken-ichi; Nakazawa, Masataka

    2005-02-15

    We report that stimulated Brillouin scattering (SBS) in a dispersion-decreasing fiber (DDF) is particularly disadvantageous with ultrahigh-speed femtosecond soliton compression that exceeds 40 GHz. It is important to note that the increase in the longitudinal mode power of a soliton is proportional to the square of the repetition rate. The SBS threshold is determined by the dispersion-decreasing rate of the DDF, rather than its fiber loss. We suppressed the SBS by applying 30-MHz frequency modulation to a mode-locked fiber laser and successfully obtained a stable 40-GHz, 100-fs pulse train.

  17. Transverse Writing of Multimode Interference Waveguides inside Silica Glass by Femtosecond Laser Pulses

    International Nuclear Information System (INIS)

    Da-Yong, Liu; Yan, Li; Yan-Ping, Dou; Heng-Chang, Guo; Hong, Yang; Qi-Huang, Gong

    2008-01-01

    Multi-mode interference waveguides are fabricated inside silica glass by transverse writing geometry with femtosecond laser pulses. The influences of several writing and reading factors on the output mode are systematically studied. The experimental results of straight waveguides are in good agreement with the simulations by the beam propagation method. By integrating a straight waveguide with a bent waveguide, a 1 × 2 multi-mode splitter is formed and 2 × 3 lobes are observed in the output mode. (fundamental areas of phenomenology (including applications))

  18. Tightly focused femtosecond laser pulse in air: from filamentation to breakdown.

    Science.gov (United States)

    Liu, Xiao-Long; Lu, Xin; Liu, Xun; Xi, Ting-Ting; Liu, Feng; Ma, Jing-Long; Zhang, Jie

    2010-12-06

    The propagation of tightly focused femtosecond laser pulse with numerical aperture of 0.12 in air is investigated experimentally. The formation and evolution of the filament bunch are recorded by time-resolved shadowgraph with laser energy from 2.4 mJ to 47 mJ. The distribution of electron density in breakdown area is retrieved using Nomarski interferometer. It is found that intensity clamping during filamentation effect still play a role even under strong external focusing. The electron density in some interaction zones is higher than 3 × 10(19) cm(-3), which indicates that each air molecule there is ionized.

  19. High-aspect-ratio grooves fabricated in silicon by a single pass of femtosecond laser pulses

    International Nuclear Information System (INIS)

    Ma Yuncan; Shi Haitao; Si Jinhai; Ren Hai; Chen Tao; Chen Feng; Hou Xun

    2012-01-01

    High-aspect-ratio grooves have been fabricated in silicon by a single pass of femtosecond laser pulses in water and ambient air. Scanning electron microscopy and energy dispersive x-ray spectroscopy were employed to image for the morphology of the photoinduced grooves and analyze the chemical composition in the surrounding of the grooves. It was observed that the sidewall of the grooves fabricated in water was much smoother than that in ambient air, and there were homogeneous nano-scale protrusions on the sidewall of the grooves fabricated in water. Meanwhile, oxygen species, which was incorporated into the grooves fabricated in air, was not observed in those in water.

  20. Periodic surface structures on titanium self-organized upon double femtosecond pulse exposures

    Czech Academy of Sciences Publication Activity Database

    Gemini, Laura; Hashida, M.; Miyasaka, Y.; Inoue, S.; Limpouch, J.; Mocek, Tomáš; Sakabe, S.

    2015-01-01

    Roč. 336, May (2015), s. 349-353 ISSN 0169-4332 R&D Projects: GA MŠk ED2.1.00/01.0027; GA MŠk EE2.3.20.0143; GA MŠk(CZ) LG13029; GA MŠk(CZ) LD14089 Grant - others:HILASE(XE) CZ.1.05/2.1.00/01.0027; OP VK 6(XE) CZ.1.07/2.3.00/20.0143 Institutional support: RVO:68378271 Keywords : LIPSS * titanium * femtosecond laser * double pulse irradiations Subject RIV: BH - Optics, Masers, Lasers Impact factor: 3.150, year: 2015

  1. Single-shot femtosecond-pulsed phase-shifting digital holography.

    Science.gov (United States)

    Kakue, Takashi; Itoh, Seiya; Xia, Peng; Tahara, Tatsuki; Awatsuji, Yasuhiro; Nishio, Kenzo; Ura, Shogo; Kubota, Toshihiro; Matoba, Osamu

    2012-08-27

    Parallel phase-shifting digital holography is capable of three-dimensional measurement of a dynamically moving object with a single-shot recording. In this letter, we demonstrated a parallel phase-shifting digital holography using a single femtosecond light pulse whose central wavelength and temporal duration were 800 nm and 96 fs, respectively. As an object, we set spark discharge in atmospheric pressure air induced by applying a high voltage to between two electrodes. The instantaneous change in phase caused by the spark discharge was clearly reconstructed. The reconstructed phase image shows the change of refractive index of air was -3.7 × 10(-4).

  2. Fabrication of micro-optical components using femtosecond oscillator pulses

    Science.gov (United States)

    Rodrigues, Vanessa R. M.; Ramachandran, Hema; Chidangil, Santhosh; Mathur, Deepak

    2017-06-01

    With a penchant for integrated photonics and miniaturization, the fabrication of micron sized optical elements using precision laser pulse management is drawing attention due to the possibility of minimizing tolerances for collateral material damage. The work presented here deals with the design, fabrication and characterization of a range of diffractive optics - gratings, grids and Fresnel zone plates - on transparent and metallic samples. Their low volume, light weight, transmission bandwidth, high damage threshold and flexible design make them suited for replacing conventional refractive optical elements. Our one-step, mask-less, 3-D laser direct writing process is a green fabrication technique which is in stark contrast to currently popular Photo-lithography based micro-structuring. Our method provides scope for modifications on the surface as well as within the bulk of the material. The mechanism involved in the fabrication of these optics on transparent and thin metallic substrates differ from each other. Our studies show that both amplitude and phase versions of micro-structures were achieved successfully with performances bearing 98% accuracy vis-a-vis theoretical expectations.

  3. Coherent population trapping in negatively charged self-assembled quantum dots using a train of femtosecond pulses

    OpenAIRE

    Kumar, Parvendra; Nakajima, Takashi

    2015-01-01

    We demonstrate the coherent population trapping in a single quantum dot and an ensemble of negatively charged quantum dots using a train of femtosecond pulses. Particularly in an ensemble of quantum dots, we show that the detrimental effects due to the inhomogeneous distribution of their properties can be minimized by appropriately choosing the pulse-train parameters and the magnetic-field strength in such a way that the electron-Zeeman splitting is an integer multiple of the pulse repetition...

  4. Pulse Shape Discrimination in the MAJORANA DEMONSTRATOR

    Science.gov (United States)

    Haufe, Christopher; Majorana Collaboration

    2017-09-01

    The MAJORANA DEMONSTRATOR is an experiment constructed to search for neutrinoless double-beta decays in germanium-76 and to demonstrate the feasibility to deploy a large-scale experiment in a phased and modular fashion. It consists of two modular arrays of natural and 76Ge-enriched germanium p-type point contact detectors totaling 44.1 kg, located at the 4850' level of the Sanford Underground Research Facility in Lead, South Dakota, USA. A large effort is underway to analyze the data currently being taken by the DEMONSTRATOR. Key components of this effort are analysis tools that allow for pulse shape discrimination-techniques that significantly reduce background levels in the neutrinoless double-beta decay region of interest. These tools are able to identify and reject multi-site events from Compton scattering as well as events from alpha particle interactions. This work serves as an overview for these analysis tools and highlights the unique advantages that the HPGe p-type point contact detector provides to pulse shape discrimination. This material is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, the Particle Astrophysics and Nuclear Physics Programs of the National Science Foundation, and the Sanford Underground Research Facility.

  5. Photonuclear Contributions to SNS Pulse Shapes

    Energy Technology Data Exchange (ETDEWEB)

    McClanahan, Tucker C. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Iverson, Erik B. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Gallmeier, Franz X. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2017-03-01

    cross sections available and the CEM03 physics model within MCNPX 2.6.0 in the simulation, we are able to estimate the impact of photoneutron production on both overall neutron production and delayed neutron production. We find that a significant number of photon-induced neutrons are produced a few milliseconds after the proton pulse, following prompt gamma emission through the capture of neutrons in the slowing-down and thermalization processes. We name these "slowing-down delayed neutrons" to distinguish them from either "activation-delayed neutrons" or "beta-delayed neutrons." The beta-delayed and activation-delayed neutrons were not part of this study, and will be addressed elsewhere. While these other delayed neutron channels result in the time-independent (constant) production of fast neutrons outside of the prompt pulse, the slowing-down delayed neutrons also a ect the shape of the pulses. Although numerically insignificant in most cases, we describe a set of scenarios related to T0-chopper operation in which the slowing-down delayed neutrons may be important.

  6. Interaction of femtosecond X-ray pulses with periodical multilayer structures

    Energy Technology Data Exchange (ETDEWEB)

    Ksenzov, Dmitry

    2010-07-01

    The VUV Free Electron Laser FLASH operates in soft X-ray range and produces high-intensive pulse trains with few tens femtoseconds duration. The transversely fully coherent beam will open new experiments in solid state physics which can not be studied with present radiation sources. The study of the time dependent response of the multilayer to the X-ray pulse can provide insights into the process of interaction of highly intense FEL radiation with matter. To test the influence of electron excitation on the optical properties of boron carbide, the refractive index of B{sub 4}C was measured near B K-edge by energy-resolved photon-in-photon-out method probing a Bragg reflection from periodical multilayers. The measured data clearly show that the variation of the fine structure of the Kabsorption edges due to the chemical nature of the absorber element. The knowledge obtained from experiments with continuous radiation was used to design the respective experiments with pulse from the FEL. In my thesis, it is proposed that the geometrical setup, where the incident pulse arrives from the FEL under the angle close to the 1st order ML Bragg peak, provides the most valuable information. Preliminary simulation considering form factors of neutral and ionized boron showed that due to ionization, pronounced changes in the reflectivity curve are expected. The proposed scheme can be the powerful tool to study the various processes within the electronic subsystem of the FEL pulse interaction with matter. This type of investigations gives a deep understanding of the nature of the electronic excitation and the recombination at the femtosecond scale. (orig.)

  7. Guiding of Long-Distance Electric Discharges by Combined Femtosecond and Nanosecond Pulses Emitted by Hybrid KrF Laser System

    Science.gov (United States)

    2014-01-30

    laser pulse initiated HV discharge with a time delay of tens nanoseconds – evidently it is developing due to an avalanche -like growth of electron...AFRL-AFOSR-UK-TR-2014-0040 Guiding of long-distance electric discharges by combined femtosecond and nanosecond pulses emitted by...and guiding electric discharge , KrF laser, femtosecond pulse , nanosecond pulse , filamentation, plasma channel, lightning control, laser control of

  8. 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

    2013-01-01

    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. PMID:23478599

  9. High-power femtosecond pulse generation in a passively mode-locked Nd:SrLaAlO4 laser

    Science.gov (United States)

    Liu, Shan-De; Dong, Lu-Lu; Zheng, Li-He; Berkowski, Marek; Su, Liang-Bi; Ren, Ting-Qi; Peng, Yan-Dong; Hou, Jia; Zhang, Bai-Tao; He, Jing-Liang

    2016-07-01

    A high optical quality Nd:SrLaAlO4 (Nd:SLA) crystal was grown using the Czochralski method and showed broad fluorescence spectrum with a full width at half maximum value of 34 nm, which is beneficial for generating femtosecond laser pulses. A stable diode-pumped passively mode-locked femtosecond Nd:SLA laser with 458 fs pulse duration was achieved for the first time at a central wavelength of 1077.9 nm. The average output power of the continuous-wave mode-locked laser was 520 mW and the repetition rate was 78.5 MHz.

  10. Formation of nanograting in fused silica by temporally delayed femtosecond double-pulse irradiation

    Science.gov (United States)

    Wang, Haodong; Song, Juan; Li, Qin; Zeng, Xianglong; Dai, Ye

    2018-04-01

    A 1 kHz femtosecond double-pulse sequence irradiation is used to study the temporal evolution of nanograting in fused silica by controlling the delay times and polarization combinations of two independent beams from a Mach–Zehnder interferometer. A lateral laser-scan experiment with speed at 5 µm s‑1 and each pulse energy of 1 µJ is firstly performed with the delay time from sub-picosecond to 10 ps, and then the written nanostructures are systematically studied under a cross-polarized microscope because the intensity of birefringence signal nearly corresponds to optical retardance and development level of the induced nanograting. The trend shows that the induced nanogratings can continue developing with a decrease of delay time in the case of the linear polarization pulse arriving before. In another vertical laser-scan experiment at the same speed and pulse energy, the morphologies of nanogratings embedded in the lines are characterized by scanning electron microscope after mechanical polishing and chemical etching. The self-organized patterns have a commonly spatial period of 200–300 nm and the orientation is always perpendicular to the polarization of the first laser pulse, and the second pulse in each sequence seems to promote the as-formed nanograting developing further even if the polarized direction is different from the previous pulse. These new findings verify again that a localized memory effect can make positive feedback to reinforce the patterned nanostripes. In that process, the impact ionization from the seed electrons left by the first pulse excitation and the photoionization of self-trapped excitons with lower ionization threshold results in an increase of the re-excited carriers during the second pulse irradiation and the subsequent development of the as-formed nanograting. Our result provides further proofs for understanding the physical mechanism of nanograting strongly connection with the interplay on multiple ionization channels.

  11. Mechanism and experimental study on three-dimensional facula shaping in femtosecond laser micromachining

    Science.gov (United States)

    Pan, Xuetao; Tu, Dawei; Cai, Jianwen

    2015-10-01

    Because of the laser beam waist and diffraction effect of the lens, the focal spot light field in femtosecond laser microprocessing has an ellipsoidal spatial distribution. This leads to the gap between two processing layers increasing along the axial direction, and the distribution density of processing points decreasing along the horizontal direction. This directly reduces the resolution of the microprocessing, and badly affects the machining accuracy and surface quality. We established a mathematical model for three-dimensional (3-D) laser beam shaping based on the Fresnel diffraction theory and designed a kind of four-ring complex amplitude transmittance phase plate by using a global optimization algorithm and genetic algorithm to simultaneously realize transverse and axial 3-D shaping. We numerically showed that the transverse and axial gains of the focal facula after 3-D shaping are 0.77 and 0.68, respectively, where the corresponding peak energy ratio is 0.36, the transverse and axial sidelobe energies are 0.28 and 0.62, respectively, and the defocusing amount is -0.08. We also constructed a confocal/two-photon microscope system to experimentally achieve a better shaping effect in the case of femtosecond laser fabrication at a point on the thin film of a photochromic material.

  12. Reflectance of thin silver film on the glass substrate at the interaction with femtosecond laser pulses

    Science.gov (United States)

    Petrov, Yu V.; Khokhlov, V. A.; Inogamov, N. A.; Khishchenko, K. V.; Anisimov, S. I.

    2016-11-01

    The optical response of thin silver film (of 60 nm thickness) coated on a glass prism (Kretschmann configuration) and heated by the femtosecond laser pulse of small intensity is investigated by the computational modeling. We have calculated the reflectance of p-polarized probe laser beam when it is incident onto the metal film from the glass side. Reflectance is calculated at incidence angles close to the surface plasmon resonance angle. We have considered first 100 ps after the action of femtosecond laser pulse onto the film surface. Changes in thermodynamic state and hydrodynamic motion of film material are described by the system of hydrodynamic equations taking into account different temperatures of electrons and ions (two- temperature state) and consequently two-temperature thermodynamics and kinetics at such early times. These changes define the changes in electron-ion and electron-electron collision frequencies. The collision frequencies of conduction electrons, being calculated in dependence on the density and electron and ion temperatures, allow us to find the Drude part of dielectric permittivity. Together with the interband contribution it gives possibility to calculate reflectance depending on the state of metal surface. It is shown a great importance of electron-electron interactions in the temporal behavior of reflectance at early times of laser-film interaction.

  13. Phototransfection of mouse embryonic stem cells with plasmid DNA using femtosecond laser pulses

    Science.gov (United States)

    Thobakgale, Lebogang; Manoto, Sello Lebohang; Ombinda Lemboumba, Saturnin; Maaza, Malik; Mthunzi-Kufa, Patience

    2017-02-01

    Cellular manipulation by delivery of molecules into cells has been applied extensively in tissue engineering research for medical applications . The different molecular delivery techniques used range from viral and chemical agents to physical and electrical methods. Although successful in most studies, these techniques have inherent difficulties such as toxicity, unwanted genetic mutations and low reproducibility respectively. Literature recognizes pulsed lasers at femtosecond level to be most efficient in photonic interactions with biological material. As of late, laser pulses have been used for drug and DNA delivery into cells via transient optical perforation of the cellular membrane. Thus in this study, we design and construct an optical system coupled to a femtosecond laser for the purpose of phototransfection or insertion of plasmid DNA (pDNA) into cells using lasers. We used fluorescent green protein (pGFP) to transfect mouse embryonic stem cells as our model. Secondly, we applied fluorescence imaging to view the extent of DNA delivery using this method. We also assessed the biocompatibility of our system by performing molecular assays of the cells post irradiation using adenosine triphosphate (ATP) and lactate dehydrogenase (LDH).

  14. Coherent Control of Multiphoton Transitions in the Gas and Condensed Phases with Shaped Ultrashort Pulses

    Energy Technology Data Exchange (ETDEWEB)

    Marcos Dantus

    2008-09-23

    Controlling laser-molecule interactions has become an integral part of developing devices and applications in spectroscopy, microscopy, optical switching, micromachining and photochemistry. Coherent control of multiphoton transitions could bring a significant improvement of these methods. In microscopy, multi-photon transitions are used to activate different contrast agents and suppress background fluorescence; coherent control could generate selective probe excitation. In photochemistry, different dissociative states are accessed through two, three, or more photon transitions; coherent control could be used to select the reaction pathway and therefore the yield-specific products. For micromachining and processing a wide variety of materials, femtosecond lasers are now used routinely. Understanding the interactions between the intense femtosecond pulse and the material could lead to technologically important advances. Pulse shaping could then be used to optimize the desired outcome. The scope of our research program is to develop robust and efficient strategies to control nonlinear laser-matter interactions using ultrashort shaped pulses in gas and condensed phases. Our systematic research has led to significant developments in a number of areas relevant to the AMO Physics group at DOE, among them: generation of ultrashort phase shaped pulses, coherent control and manipulation of quantum mechanical states in gas and condensed phases, behavior of isolated molecules under intense laser fields, behavior of condensed phase matter under intense laser field and implications on micromachining with ultrashort pulses, coherent control of nanoparticles their surface plasmon waves and their nonlinear optical behavior, and observation of coherent Coulomb explosion processes at 10^16 W/cm^2. In all, the research has resulted in 36 publications (five journal covers) and nine invention disclosures, five of which have continued on to patenting

  15. 3D features of modified photostructurable glass-ceramic with infrared femtosecond laser pulses

    International Nuclear Information System (INIS)

    Fernandez-Pradas, J.M.; Serrano, D.; Bosch, S.; Morenza, J.L.; Serra, P.

    2011-01-01

    The exclusive ability of laser radiation to be focused inside transparent materials makes lasers a unique tool to process inner parts of them unreachable with other techniques. Hence, laser direct-write can be used to create 3D structures inside bulk materials. Infrared femtosecond lasers are especially indicated for this purpose because a multiphoton process is usually required for absorption and high resolution can be attained. This work studies the modifications produced by 450 fs laser pulses at 1027 nm wavelength focused inside a photostructurable glass-ceramic (Foturan) at different depths. Irradiated samples were submitted to standard thermal treatment and subsequent soaking in HF solution to form the buried microchannels and thus unveil the modified material. The voxel dimensions of modified material depend on the laser pulse energy and the depth at which the laser is focused. Spherical aberration and self-focusing phenomena are required to explain the observed results.

  16. Femtosecond time-resolved impulsive stimulated Raman spectroscopy using sub-7-fs pulses: Apparatus and applications

    Science.gov (United States)

    Kuramochi, Hikaru; Takeuchi, Satoshi; Tahara, Tahei

    2016-04-01

    We describe details of the setup for time-resolved impulsive stimulated Raman spectroscopy (TR-ISRS). In this method, snapshot molecular vibrational spectra of the photoreaction transients are captured via time-domain Raman probing using ultrashort pulses. Our instrument features transform-limited sub-7-fs pulses to impulsively excite and probe coherent nuclear wavepacket motions, allowing us to observe vibrational fingerprints of transient species from the terahertz to 3000-cm-1 region with high sensitivity. Key optical components for the best spectroscopic performance are discussed. The TR-ISRS measurements for the excited states of diphenylacetylene in cyclohexane are demonstrated, highlighting the capability of our setup to track femtosecond dynamics of all the Raman-active fundamental molecular vibrations.

  17. Femtosecond time-resolved impulsive stimulated Raman spectroscopy using sub-7-fs pulses: Apparatus and applications

    Energy Technology Data Exchange (ETDEWEB)

    Kuramochi, Hikaru [Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198 (Japan); Takeuchi, Satoshi; Tahara, Tahei, E-mail: tahei@riken.jp [Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198 (Japan); Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), 2-1 Hirosawa, Wako 351-0198 (Japan)

    2016-04-15

    We describe details of the setup for time-resolved impulsive stimulated Raman spectroscopy (TR-ISRS). In this method, snapshot molecular vibrational spectra of the photoreaction transients are captured via time-domain Raman probing using ultrashort pulses. Our instrument features transform-limited sub-7-fs pulses to impulsively excite and probe coherent nuclear wavepacket motions, allowing us to observe vibrational fingerprints of transient species from the terahertz to 3000-cm{sup −1} region with high sensitivity. Key optical components for the best spectroscopic performance are discussed. The TR-ISRS measurements for the excited states of diphenylacetylene in cyclohexane are demonstrated, highlighting the capability of our setup to track femtosecond dynamics of all the Raman-active fundamental molecular vibrations.

  18. Direct welding of glass and metal by 1  kHz femtosecond laser pulses.

    Science.gov (United States)

    Zhang, Guodong; Cheng, Guanghua

    2015-10-20

    In the welding process between similar or dissimilar materials, inserting an intermediate layer and pressure assistance are usually thought to be necessary. In this paper, the direct welding between alumina-silicate glass and metal (aluminum, copper, and steel), under exposure from 1 kHz femtosecond laser pulses without any auxiliary processes, is demonstrated. The micron/nanometer-sized metal particles induced by laser ablation were considered to act as the adhesive in the welding process. The welding parameters were optimized by varying the pulse energy and the translation velocity of the sample. The shear joining strength characterized by a shear force testing equipment was as high as 2.34 MPa. This direct bonding technology has potential for applications in medical devices, sensors, and photovoltaic devices.

  19. Gain dynamics of a free-space nitrogen laser pumped by circularly polarized femtosecond laser pulses.

    Science.gov (United States)

    Yao, Jinping; Xie, Hongqiang; Zeng, Bin; Chu, Wei; Li, Guihua; Ni, Jielei; Zhang, Haisu; Jing, Chenrui; Zhang, Chaojin; Xu, Huailiang; Cheng, Ya; Xu, Zhizhan

    2014-08-11

    We experimentally demonstrate ultrafast dynamic of generation of the 337-nm nitrogen laser by injecting an external seed pulse into a femtosecond laser filament pumped by a circularly polarized laser pulse. In the pump-probe scheme, it is revealed that the population inversion between the C(3)Π(u) and B(3)Π(g) states of N(2) for the free-space 337-nm laser is firstly built up on the timescale of several picoseconds, followed by a relatively slow decay on the timescale of tens of picoseconds, depending on the nitrogen gas pressure. By measuring the intensities of 337-nm signal from nitrogen gas mixed with different concentrations of oxygen gas, it is also found that oxygen molecules have a significant quenching effect on the nitrogen laser signal. Our experimental observations agree with the picture of electron-impact excitation.

  20. Efficient optical trapping of CdTe quantum dots by femtosecond laser pulses

    KAUST Repository

    Chiang, Weiyi

    2014-12-11

    The development in optical trapping and manipulation has been showing rapid progress, most of it is in the small particle sizes in nanometer scales, substituting the conventional continuous-wave lasers with high-repetition-rate ultrashort laser pulse train and nonlinear optical effects. Here, we evaluate two-photon absorption in optical trapping of 2.7 nm-sized CdTe quantum dots (QDs) with high-repetition-rate femtosecond pulse train by probing laser intensity dependence of both Rayleigh scattering image and the two-photon-induced luminescence spectrum of the optically trapped QDs. The Rayleigh scattering imaging indicates that the two-photon absorption (TPA) process enhances trapping ability of the QDs. Similarly, a nonlinear increase of the two-photon-induced luminescence with the incident laser intensity fairly indicates the existence of the TPA process.

  1. Interrogation of orbital structure by elliptically polarized intense femtosecond laser pulses

    International Nuclear Information System (INIS)

    Abu-samha, M.; Madsen, L. B.

    2011-01-01

    We solve the three-dimensional time-dependent Schroedinger equation and present investigations of the imprint of the orbital angular node in photoelectron momentum distributions of an aligned atomic p-type orbital following ionization by an intense elliptically polarized laser pulse of femtosecond duration. We investigate the role of light ellipticity and the alignment angle of the major polarization axis of the external field relative to the probed orbital by studying radial and angular momentum distributions, the latter at a fixed narrow interval of final momenta close to the peak of the photoelectron momentum distribution. In general only the angular distributions carry a clear signature of the orbital symmetry. Our study shows that circular polarization gives the most clear imprints of orbital nodes. These findings are insensitive to pulse duration.

  2. Interrogation of orbital structure by elliptically polarized intense femtosecond laser pulses

    DEFF Research Database (Denmark)

    Abu-Samha, Mahmoud; Madsen, Lars Bojer

    2011-01-01

    We solve the three-dimensional time-dependent Schrödinger equation and present investigations of the imprint of the orbital angular node in photoelectron momentum distributions of an aligned atomic p-type orbital following ionization by an intense elliptically polarized laser pulse of femtosecond...... duration. We investigate the role of light ellipticity and the alignment angle of the major polarization axis of the external field relative to the probed orbital by studying radial and angular momentum distributions, the latter at a fixed narrow interval of final momenta close to the peak...... of the photoelectron momentum distribution. In general only the angular distributions carry a clear signature of the orbital symmetry. Our study shows that circular polarization gives the most clear imprints of orbital nodes. These findings are insensitive to pulse duration....

  3. An improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum

    International Nuclear Information System (INIS)

    Zhang, Jinping; Chen, Yuping; Hu, Mengning; Chen, Xianfeng

    2015-01-01

    In this paper, an improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum was proposed and proved in our experiment. Aiming to achieve hole-drilling with a high ratio of depth/entrance diameter in vacuum, this model can predict the depth and radius of the drilled holes precisely when employing different laser parameters. Additionally, for multi-pulse laser ablation, we found that the laser fluence and number of pulses are the dominant parameters and the multi-pulse ablation threshold is much lower than the single-pulse one, which will help to obtain high-quality holes

  4. An improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Jinping; Chen, Yuping, E-mail: ypchen@sjtu.edu.cn; Hu, Mengning; Chen, Xianfeng [State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China)

    2015-02-14

    In this paper, an improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum was proposed and proved in our experiment. Aiming to achieve hole-drilling with a high ratio of depth/entrance diameter in vacuum, this model can predict the depth and radius of the drilled holes precisely when employing different laser parameters. Additionally, for multi-pulse laser ablation, we found that the laser fluence and number of pulses are the dominant parameters and the multi-pulse ablation threshold is much lower than the single-pulse one, which will help to obtain high-quality holes.

  5. Pulse synchronization system for picosecond pulse-pumped OPCPA with femtosecond-level relative timing jitter.

    Science.gov (United States)

    Batysta, František; Antipenkov, Roman; Green, Jonathan T; Naylon, Jack A; Novák, Jakub; Mazanec, Tomáš; Hříbek, Petr; Zervos, Charalampos; Bakule, Pavel; Rus, Bedřich

    2014-12-01

    A simple and compact scheme for synchronization of the pump and signal pulses for short-pulse OPCPA is demonstrated. Relative timing jitter of 17 fs RMS is achieved (1% of the pump pulse duration) and the system remains locked for hours. The scheme uses a balanced optical cross correlator to detect relative delays between the pump and signal pulses and can be operated with just 10's of μJ of pump energy and pJ-level signal energies.

  6. Comparison of two photosensitizers in photodynamic therapy using light pulses in femtosecond regime: an animal study

    Science.gov (United States)

    Grecco, Clóvis; Pratavieira, Sebastião.; Bagnato, Vanderlei; Kurachi, Cristina

    2016-03-01

    Photodynamic therapy is a therapeutic modality for cancer treatment based on the interaction of light with a sensitizer agent and molecular oxygen present into the target cells. The aim of this study is the evaluation of photodynamic therapy using pulsed light source in the femtosecond regime through necrosis induced in healthy rat liver. The induced necrosis profile with CW laser and pulsed laser were evaluated in animal model, which received Photodithazine (chlorine e6 derivative). The light sources used in these studies were a 660 nm CW diode laser and a Ti:Sapphire Regenerative Amplifier laser (1 kHz repetition rate and 100 fs pulse width) associated with an optical parametric amplifier (OPA) to convert to 660 nm. The results were compared with a previous study when was used a hematoporphyrin derivative (Photogem) as a sensitizer. The induced necrosis with Photogen was greater with pulsed laser (2.0 +/- 0.2 mm) in comparison with CW laser (1.0 ± 0.2 mm), while in Photodithazine the induced necrosis with was greater with CW laser (2.9 +/- 0.2 mm) comparing the pulsed laser (2.0 +/- 0.2 mm). These results indicate dependence of PDT mechanisms with photosensitizer and the light regime applied.

  7. Parametric generation and characterization of femtosecond mid-infrared pulses in ZnGeP2.

    Science.gov (United States)

    Wandel, Scott; Lin, Ming-Wei; Yin, Yanchun; Xu, Guibao; Jovanovic, Igor

    2016-03-07

    Ultrafast mid-infrared (IR) coherent radiation plays an important role in strong-field physics, wherein the use of longer wavelengths has reduced the optical intensities needed to drive light-matter interactions by orders of magnitude in comparison to near-IR radiation. Optimizing parametric interactions for generation and characterization of mid-IR pulses is an enabling step for those applications. We report on the production of >50 µJ femtosecond pulses centered at 5 µm in a two-stage optical parametric amplifier (OPA) based on ZnGeP 2 , a high-performance optical material in this spectral region. The OPA is pumped by an ultrafast 2-µm source. Amplified pulses have been characterized by parametric upconversion, enabling the use of standard silicon detectors. A numerical model of the system has been developed and tested to control dispersion, group-velocity mismatch, and off-axis parametric fluorescence. The source architecture is suitable for production of mJ-level mid-IR ultrafast pulses without the use of chirped-pulse amplification, where convenient pumping could be realized directly by mid-IR laser sources based on materials such as Cr:ZnSe or Cr:ZnS.

  8. Tunable pulse-shaping with gated graphene nanoribbons

    DEFF Research Database (Denmark)

    Prokopeva, Ludmila; Emani, Naresh K.; Boltasseva, Alexandra

    2014-01-01

    We propose a pulse-shaper made of gated graphene nanoribbons. Simulations demonstrate tunable control over the shapes of transmitted and reflected pulses using the gating bias. Initial fabrication and characterization of graphene elements is also discussed.......We propose a pulse-shaper made of gated graphene nanoribbons. Simulations demonstrate tunable control over the shapes of transmitted and reflected pulses using the gating bias. Initial fabrication and characterization of graphene elements is also discussed....

  9. Bragg grating photo-inscription in doped microstructured polymer optical fiber by 400 nm femtosecond laser pulses

    DEFF Research Database (Denmark)

    Hu, X.; Woyessa, Getinet; Kinet, D.

    2016-01-01

    In this paper, we report the manufacturing of high-quality endlessly single-mode doped microstructured poly(methyl methacrylate) (PMMA) optical fibers. Bragg gratings are photo-inscribed in such fibers by means of 400 nm femtosecond laser pulses through a 1060-nm-period uniform phase mask...

  10. Pulse shape analysis for γ-ray tracking. Part I: Pulse shape simulation with JASS

    International Nuclear Information System (INIS)

    Schlarb, M.; Gernhaeuser, R.; Klupp, S.; Kruecken, R.

    2011-01-01

    Next-generation γ -ray spectrometers based on highly segmented HPGe detectors are using the recent technique of γ -ray tracking to significantly improve on efficiency and Doppler correction capabilities. A precise reconstruction of the individual interaction locations within the active material is possible through the use of pulse shape analysis (PSA) which, in turn, demands an accurate knowledge of the detector response. We developed JASS, a Java-based simulation software package to generate pulse shapes for the AGATA detectors from physics constraints and basic material parameters. For verifying the simulation experimental data from a coincidence scan with known interaction locations was used. The achieved position resolution, in the order of a few millimeters, is within the requirements of the γ -ray tracking array. (orig.)

  11. Generation of dual-wavelength, synchronized, tunable, high energy, femtosecond laser pulses with nearly perfect gaussian spatial profile

    Science.gov (United States)

    Wang, J.-K.; Siegal, Y.; Lü, C.; Mazur, E.

    1992-07-01

    We use self-phase modulation in a single-mode fiber to produce broadband femtosecond laser pulses. Subsequent amplification through two Bethune cells yields high-energy, tunable, pulses synchronized with the output of an amplified colliding-pulse-modelocked (CPM) laser. We routinely obtain tunable 200 μJ pulses of 42 fs (fwhm) duration with a nearly perfect gaussian spatial profile. Although self-phase modulation in a single-mode fiber is widely used in femtosecond laser systems, amplification of a fiber-generated supercontinuum in a Bethune cell amplifier is a new feature which maintains the high-quality spatial profile while providing high gain. This laser system is particularly well suited for high energy dual-wavelength pump=probe experiments and time-resolved four-wave mixing spectroscopy.

  12. Broadening and Amplification of an Infrared Femtosecond Pulse for Optical Parametric Chirped-Pulse Amplification

    International Nuclear Information System (INIS)

    Wang He-Lin; Yang Ai-Jun; Leng Yu-Xin

    2011-01-01

    A high-average-power diode-pumped narrowband regenerative chirped pulse amplifier is developed using the thin-rod Nd:YAG laser architecture for optical parametric chirped-pulse amplification (OPCPA). The effect of the etalons on the amplified pulse in the regenerative cavity is studied experimentally and theoretically. By inserting glass etalons of thickness 1 mm and 5 mm into the regenerative cavity, the pre-stretching pulse from an Öffner stretcher is further broadened to above 200ps, which matches the amplification windows of the signal pulses in OPCPA and is suitable for use as a pump source in the OPCPA system. The bandwidth of the amplified pulse is 1.5 nm, and an output energy of 2mJ is achieved at a repetition rate of 10Hz. (fundamental areas of phenomenology (including applications))

  13. Ultra-short laser pulse ablation using shear-force feedback: Femtosecond laser induced breakdown spectroscopy feasibility study

    International Nuclear Information System (INIS)

    Samek, Ota; Kurowski, Andre; Kittel, Silke; Kukhlevsky, Sergei; Hergenroeder, Roland

    2005-01-01

    This work reports on a feasibility study of proximity ablation using femtosecond pulses. Ultra-short pulses were launched to a bare tapered optical fiber and delivered to the sample. The tip-sample distance was controlled by means of shear-force feedback. Consequently, ablation craters with submicrometer dimensions were obtained. Potential analytical applications for Laser Induced Breakdown Spectroscopy (LIBS) technique, such as e.g. inclusions in steel or bio cells, are suggested

  14. Dynamic parabolic pulse generation using temporal shaping of wavelength to time mapped pulses.

    Science.gov (United States)

    Nguyen, Dat; Piracha, Mohammad Umar; Mandridis, Dimitrios; Delfyett, Peter J

    2011-06-20

    Self-phase modulation in fiber amplifiers can significantly degrade the quality of compressed pulses in chirped pulse amplification systems. Parabolic pulses with linear frequency chirp are suitable for suppressing nonlinearities, and to achieve high peak power pulses after compression. In this paper, we present an active time domain technique to generate parabolic pulses for chirped pulse amplification applications. Pulses from a mode-locked laser are temporally stretched and launched into an amplitude modulator, where the drive voltage is designed using the spectral shape of the input pulse and the transfer function of the modulator, resulting in the generation of parabolic pulses. Experimental results of pulse shaping with a pulse train from a mode-locked laser are presented, with a residual error of less than 5%. Moreover, an extinction ratio of 27 dB is achieved, which is ideal for chirped pulse amplification applications.

  15. Comparative study of two-photon fluorescent bio-markers at nanosecond and femtosecond pulsed excitation

    Science.gov (United States)

    Peterson, Burl H.; Sarkisov, Sergey S.; Nesterov, V. N.; Curley, Michael J.; Urbas, Augustine; Patel, Darayas N.; Wang, J.-C.

    2007-02-01

    In this study we investigate visible fluorescence of cytotoxic bio-markers (molecular probes) based on the derivatives of piperidone at femtosecond infrared pulsed laser excitation. The subject of this investigation is the origin of the fluorescence. Does it originate from the excited state absorption, which occurs only at slow, nanosecond excitation, or is it due to intrinsic multi-photon absorption? In the past, it has been shown indirectly, through the laser photolysis study, that the contribution of the excited state absorption is minimal for several compounds of such type. The results of direct experiments with an infrared femtosecond fiber laser as an excitation source described here support this hypothesis. The observed dependence of the fluorescence on the pump power indicated the contribution of not only two-photon, but multi-photon routes of excitation. Additionally, it was shown that the spectral features of the fluorescence correlate with the presence of glycine, an amino acid that is one of the building blocks of proteins in a cell. The implication of this result is, in addition to their anticancer action, the compounds can possibly be used for fluorescent diagnostics of cancer and multi-photon fluorescent microscopy of malignant cell cultures using portable infrared fiber lasers as excitation sources.

  16. In vivo micro-lesion of single dendrite with femtosecond laser pulses

    Science.gov (United States)

    Sacconi, L.; Masi, A.; Diana, G.; Buffelli, M.; Pavone, F. S.

    2007-07-01

    Recently, two-photon microscopy has been used for high spatial resolution imaging of the intact neocortex in living rodents. In this work we used near-IR femtosecond laser pulses for a combination of two-photon microscopy and microdissection on fluorescently-labeled neuronal structures in living mice. Three-dimensional reconstructions of dendrites expressing the green fluorescence protein were made in the cortex of GFP-M and YFP-H transgenic mice. Afterwards, single dendrites were laser-dissected irradiating the structure with a high femtosecond laser energy dose. We report that laser dissection can be performed with micrometric precision and without any visible collateral damage of the surrounding neuronal structures. After laser irradiation, one part of the severed dendrite underwent degeneration and disappeared within 5 hours. Using a chronically implanted glass window, we performed long-term imaging in the area of the dissected dendrite. Images of the long-term morphological changes in the neuronal network after dendritic lesioning will be provided. Laser microdissection of selected structures of the neuronal branching in vivo represents a promising tool for neurobiological research.

  17. Femtosecond-laser-induced damage initiation mechanism on metal multilayer dielectric gratings for pulse compression

    Science.gov (United States)

    Huang, Haopeng; Kong, Fanyu; Xia, Zhilin; Jin, Yunxia; Li, Linxin; Wang, Leilei; Chen, Junming; Cui, Yun; Shao, Jianda

    2018-01-01

    The femtosecond-laser-induced damage behaviors of metal multilayer dielectric gratings (MMDG) for pulse compression are explored. The grating ridge of this type of MMDG consists of a layer of HfO2 sandwiched between two SiO2 layers. The initial damage position is on the HfO2 layer of the ridge which opposite to the laser beam direction. A theoretical model is constructed to explain the femtosecond-laser-induced damage initiation mechanism on the MMDG, and the model can simulate the evolution of the electron density in the conduction band and the change of the dielectric constants of HfO2 and SiO2 in the sandwiched grating structure. The dramatic increase in the imaginary part of the dielectric constant of the middle HfO2 layer indicates that it strongly absorbs laser energy, resulting in damage to the MMDG. The experimental results and theoretical calculation agree very well with each other.

  18. Simultaneous spatial and temporal focusing of femtosecond pulses: A new paradigm for material processing and tissue ablation

    Science.gov (United States)

    Block, Erica K.

    Femtosecond lasers are now prolific in many disciplines. While the mechanisms of femtosecond-material interactions are widely understood, femtosecond lasers as industrial and medical tools still have shortcomings. Currently conventional state of the art platforms are unable to support low numerical aperture (NA) beams (that provide large focal volumes and long working distances) without sacrificing axial precision. Furthermore inline (refractive) delivery systems that are necessary for industrial and clinical medical applications are currently hindered by nonlinear effects when delivering femtosecond pulses with tens of microJoule pulse energies and greater. In this thesis Simultaneous Space Time Focusing (SSTF) is presented as a new paradigm to move the field of femtosecond micromachining significantly forward. With this system we have delivered microjoule femtosecond pulses with low numerical aperture geometries (improved compared to standard focusing paradigms. Nonlinear effects that would normally result in focal plane shifts and focal spot distortion are mitigated when SSTF is employed. As a result, it is shown that SSTF will enable surgical implementations that are presently inhibited. Initial ablation experiments of ocular tissue show unprecedented performance with this technique. Implementation of SSTF, in the past, has been overly complicated. Multiple compressors and diffraction gratings resulted in low throughput efficiency. In the second part of this thesis we have focused on significantly streamlining the SSTF design into a flexible, single grating, integrated SSTF/chirped-pulse amplification system with an inline (refractive) delivery system to move towards industrial and clinical medical applications. For the first time this design also allows for variation of the beam aspect ratio of an SSTF beam, and thus the degree of pulse-front tilt at focus, while maintaining a net zero-dispersion system. Accessible variation of pulse front tilt gives full

  19. Generation of quantum beams in large clusters irradiated by Super-Intense, high - contrast femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Faenov, A.Ya.; Pikuz, T.A. [Quantum Beam Science Directorate, Japan Atomic Energy Agency, Kyoto (Japan); Joint Institute for High Temperatures RAS, Moscow (Russian Federation); Fukuda, Y.; Nakamura, T.; Bulanov, S.V.; Hayashi, Y.; Kotaki, H.; Pirozhkov, A.S.; Kawachi, T.; Kando, M. [Quantum Beam Science Directorate, Japan Atomic Energy Agency, Kyoto (Japan); Skobelev, I.Yu.; Fortov, V.E. [Joint Institute for High Temperatures RAS, Moscow (Russian Federation); Chen, L.M.; Zhang, L.; Yan, W.C.; Yuan, D.W.; Mao, J.Y.; Wang, Z.H.; Ma, J.L. [Institute of Physics, Chinese Academy of Sciences, Beijing (China); Kato, Y. [The Graduate School for the Creation of New Photonics Industries, Hamamatsu, Shizuoka (Japan)

    2013-02-15

    A short review of our experimental studies on generation of photon and particle beams in submicron clusters irradiated by intense, high-contrast ({proportional_to} 10{sup 8}-10{sup 10}) femtosecond laser pulses is presented. It is shown that highlyefficient laser-cluster interaction allows creating bright sources of X-ray, high-energy electron and ion beams. The examples of applications of femtosecond-laser-produced cluster plasmas (FLPCP) for X-ray and ion beams radiography are presented. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Low loss depressed cladding waveguide inscribed in YAG:Nd single crystal by femtosecond laser pulses.

    Science.gov (United States)

    Okhrimchuk, Andrey; Mezentsev, Vladimir; Shestakov, Alexander; Bennion, Ian

    2012-02-13

    A depressed cladding waveguide with record low loss of 0.12 dB/cm is inscribed in YAG:Nd(0.3at.%) crystal by femtosecond laser pulses with an elliptical beam waist. The waveguide is formed by a set of parallel tracks which constitute the depressed cladding. It is a key element for compact and efficient CW waveguide laser operating at 1064 nm and pumped by a multimode laser diode. Special attention is paid to mechanical stress resulting from the inscription process. Numerical calculation of mode distribution and propagation loss with the elasto-optical effect taken into account leads to the conclusion that the depressed cladding is a dominating factor in waveguide mode formation, while the mechanical stress only slightly distorts waveguide modes.

  1. Femtosecond pulsed laser ablation in microfluidics for synthesis of photoluminescent ZnSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Chao, E-mail: chaoyangscu@gmail.com [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Feng, Guoying, E-mail: guoing_feng@scu.edu.cn [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Dai, Shenyu, E-mail: 232127079@qq.com [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Wang, Shutong, E-mail: wangshutong.scu@gmail.com [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Li, Guang, E-mail: 632524844@qq.com [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Zhang, Hua [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); Zhou, Shouhuan, E-mail: zhoush@scu.edu.cn [College of Electronics and Information Engineering, Sichuan University, No. 24 South Section 1, 1st Ring Road, Chengdu 610064 (China); North China Research Institute of Electro-Optics, 4 Jiuxianqiao Street, Chaoyang District, Beijing 100015 (China)

    2017-08-31

    Highlights: • A novel method for synthesis and coating of quantum dots by ultrafast laser pulses. • Mild and “green” synthesis method without toxic chemicals. • Enhanced bright green light emission without doped transition metal ions. • Ultrafast laser and coating layer enhanced the emission originated from defects. - Abstract: A simple but new toxic chemical free method, Femtosecond Laser Ablation in Microfluidics (FLAM) was proposed for the first time. ZnSe quantum dots of 4–6 nm were synthesized and with the use of hyperbranched Polyethyleneimine (PEI) as both structural and functional coated layer. These aqueous nanosized micelles consisting of quantum dots exhibit deep defect states emission of bright green light centered at 500 nm. A possible mechanism for the enhanced board band emission was discussed. The properties of toxic matters free and enhanced photoluminescence without doped transition metal ions demonstrate an application potential for biomedical imaging.

  2. Surface-enhanced Raman spectroscopy with Au-nanoparticle substrate fabricated by using femtosecond pulse

    Science.gov (United States)

    Zhang, Wending; Li, Cheng; Gao, Kun; Lu, Fanfan; Liu, Min; Li, Xin; Zhang, Lu; Mao, Dong; Gao, Feng; Huang, Ligang; Mei, Ting; Zhao, Jianlin

    2018-05-01

    Au-nanoparticle (Au-NP) substrates for surface-enhanced Raman spectroscopy (SERS) were fabricated by grid-like scanning a Au-film using a femtosecond pulse. The Au-NPs were directly deposited on the Au-film surface due to the scanning process. The experimentally obtained Au-NPs presented local surface plasmon resonance effect in the visible spectral range, as verified by finite difference time domain simulations and measured reflection spectrum. The SERS experiment using the Au-NP substrates exhibited high activity and excellent substrate reproducibility and stability, and a clearly present Raman spectra of target analytes, e.g. Rhodamine-6G, Rhodamine-B and Malachite green, with concentrations down to 10‑9 M. This work presents an effective approach to producing Au-NP SERS substrates with advantages in activity, reproducibility and stability, which could be used in a wide variety of practical applications for trace amount detection.

  3. Femtosecond pulsed laser ablation in microfluidics for synthesis of photoluminescent ZnSe quantum dots

    International Nuclear Information System (INIS)

    Yang, Chao; Feng, Guoying; Dai, Shenyu; Wang, Shutong; Li, Guang; Zhang, Hua; Zhou, Shouhuan

    2017-01-01

    Highlights: • A novel method for synthesis and coating of quantum dots by ultrafast laser pulses. • Mild and “green” synthesis method without toxic chemicals. • Enhanced bright green light emission without doped transition metal ions. • Ultrafast laser and coating layer enhanced the emission originated from defects. - Abstract: A simple but new toxic chemical free method, Femtosecond Laser Ablation in Microfluidics (FLAM) was proposed for the first time. ZnSe quantum dots of 4–6 nm were synthesized and with the use of hyperbranched Polyethyleneimine (PEI) as both structural and functional coated layer. These aqueous nanosized micelles consisting of quantum dots exhibit deep defect states emission of bright green light centered at 500 nm. A possible mechanism for the enhanced board band emission was discussed. The properties of toxic matters free and enhanced photoluminescence without doped transition metal ions demonstrate an application potential for biomedical imaging.

  4. No effect of femtosecond laser pulses on DNA, protein, M13, or E. coli

    Science.gov (United States)

    Wigle, Jeffrey C.; Holwitt, Eric A.; Noojin, Gary D.; Estlack, Larry E.; Sheldon, Katharine E.; Rockwell, Benjamin A.

    2011-03-01

    We were unable to reproduce published inactivation results, or show any interaction, between 90 femtosecond (fs) pulses of 850 nm or 425 nm laser radiation and buffer/water, DNA, protein, M13 bacteriophage or E. coli. Using agarose electrophoresis and polyacrylamide gel electrophoresis, we examined purified plasmid DNA (pUC19), bovine serum albumin, and DNA and coat proteins extracted from M13 following exposures to irradiances of up to 120 MW/cm2. We measured M13 viability using an assay for plaque-forming ability in soft agar after exposure to the same irradiances used for the protein and DNA experiments. Exposures of up 1 GW/cm2 at 850 nm had no effect on the viability of E. coli as measured by a colony forming assay in soft agar. Peroxynitrite, known to be toxic, to cause single strand breaks in DNA, and fragment proteins in vitro gave positive results in all assays.

  5. Lidar sensing of the atmosphere with gigawatt laser pulses of femtosecond duration

    Energy Technology Data Exchange (ETDEWEB)

    Bukin, O A; Golik, S S; Il' in, A A; Kulchin, Yu N; Lisitsa, V V; Shmirko, K A [Institute for Automation and Control Processes, Far-Eastern Branch, Russian Academy of Sciences, Vladivostok (Russian Federation); Babii, M Yu; Kolesnikov, A V [Far Eastern Federal University, Vladivostok (Russian Federation); Kabanov, A M; Matvienko, G G; Oshlakov, V K [V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, Tomsk (Russian Federation)

    2014-06-30

    We present the results of sensing of the atmosphere in the condition of a transition 'continent – ocean' zone by means of gigawatt femtosecond pulses of the fundamental and second harmonics of a Ti : sapphire laser. In the regime of multi-frequency sensing (supercontinuum from the fundamental harmonic) the emission lines of the first positive system of the nitrogen molecule B{sup 3}Π{sub g} – A{sup 3}Σ{sub u}{sup +} have been recorded, while the sensing using of the second harmonic have revealed the possibility of detecting the lines of Raman scattering of nitrogen (λ = 441 nm). The intensity ratio of the line of Raman scattering of nitrogen and the line of elastic scattering at the wavelength of λ = 400 nm amounts to 5.6 × 10{sup -4}. (extreme light fields and their applications)

  6. Femtosecond laser control of chemical reactions

    CSIR Research Space (South Africa)

    Du Plessis, A

    2010-08-31

    Full Text Available Femtosecond laser control of chemical reactions is made possible through the use of pulse-shaping techniques coupled to a learning algorithm feedback loop – teaching the laser pulse to control the chemical reaction. This can result in controllable...

  7. No effect of femtosecond laser pulses on M13, E. coli, DNA, or protein

    Science.gov (United States)

    Wigle, Jeffrey C.; Holwitt, Eric A.; Estlack, Larry E.; Noojin, Gary D.; Saunders, Katharine E.; Yakovlev, Valdislav V.; Rockwell, Benjamin A.

    2014-01-01

    Data showing what appears to be nonthermal inactivation of M13 bacteriophage (M13), Tobacco mosaic virus, Escherichia coli (E. coli), and Jurkatt T-cells following exposure to 80-fs pulses of laser radiation have been published. Interest in the mechanism led to attempts to reproduce the results for M13 and E. coli. Bacteriophage plaque-forming and bacteria colony-forming assays showed no inactivation of the microorganisms; therefore, model systems were used to see what, if any, damage might be occurring to biologically important molecules. Purified plasmid DNA (pUC19) and bovine serum albumin were exposed to and analyzed by agarose gel electrophoresis (AGE) and polyacrylamide gel electrophoresis (PAGE), respectively, and no effect was found. DNA and coat proteins extracted from laser-exposed M13 and analyzed by AGE or PAGE found no effect. Raman scattering by M13 in phosphate buffered saline was measured to determine if there was any physical interaction between M13 and femtosecond laser pulses, and none was found. Positive controls for the endpoints measured produced the expected results with the relevant assays. Using the published methods, we were unable to reproduce the inactivation results or to show any interaction between ultrashort laser pulses and buffer/water, DNA, protein, M13 bacteriophage, or E. coli.

  8. Steering wave packet dynamics and population transfer between electronic states of the Na2 molecule by femtosecond laser pulses

    International Nuclear Information System (INIS)

    Yuan Kaijun; Sun Zhigang; Cong Shulin; Wang Senming; Yu Jie; Lou Nanquan

    2005-01-01

    An approach used for steering the wave packet dynamics and the population transfer between electronic states of the Na 2 molecule by a pair of femtosecond laser pulses is demonstrated. Four controlling schemes, i.e., four different combinations of time delays (intuitive and counterintuitive sequences) and frequency detunings (positive and negative detunings), are discussed in detail. The light-induced potentials are used to describe the wave packet dynamics and population transfer. The numerical results show that the wave packet excited by femtosecond laser pulses oscillates drastically on 2 1 Π g state with time. The efficiency of controlling population transfer from the X 1 Σ g + to2 1 Π g states of Na 2 is nearly 100% for the schemes of the counterintuitive sequence pulses with positive and negative detunings

  9. [Effect of the pulse shape on electrostimulation of excitable tissues].

    Science.gov (United States)

    Volobuev, A N; Razumov, A N; Romanchuk, P I; Romanchuk, N P

    2010-01-01

    This paper is devoted to the consideration of the mechanisms of electrostimulation of excitable tissues used in remedial medicine. Community of biophysical principles underlying the Weiss-Lapique and Dubois-Reymond laws is emphasized. The action of stimulating pulses on biological tissues and its consequences are analysed with reference to their shape (rectangular, triangular, and exponential). It is shown that the shape of the accommodation curve depends on the shape of stimulating pulses and physiological conditions of the tissue.

  10. Preclinical investigations of articular cartilage ablation with femtosecond and pulsed infrared lasers as an alternative to microfracture surgery

    Science.gov (United States)

    Su, Erica; Sun, Hui; Juhasz, Tibor; Wong, Brian J. F.

    2014-01-01

    Abstract. Microfracture surgery is a bone marrow stimulation technique for treating cartilage defects and injuries in the knee. Current methods rely on surgical skill and instrumentation. This study investigates the potential use of laser technology as an alternate means to create the microfracture holes. Lasers investigated in this study include an erbium:YAG laser (λ=2.94  μm), titanium:sapphire femtosecond laser system (λ=1700  nm), and Nd:glass femtosecond laser (λ=1053  nm). Bovine samples were ablated at fluences of 8 to 18  J/cm2 with the erbium:YAG laser, at a power of 300±15  mW with the titanium:sapphire femtosecond system, and at an energy of 3  μJ/pulse with the Nd:glass laser. Samples were digitally photographed and histological sections were taken for analysis. The erbium:YAG laser is capable of fast and efficient ablation; specimen treated with fluences of 12 and 18  J/cm2 experienced significant amounts of bone removal and minimal carbonization with saline hydration. The femtosecond laser systems successfully removed cartilage but not clinically significant amounts of bone. Precise tissue removal was possible but not to substantial depths due to limitations of the systems. With additional studies and development, the use of femtosecond laser systems to ablate bone may be achieved at clinically valuable ablation rates. PMID:25200394

  11. Multielectron dissociative ionization of methane and formaldehyde molecules with optimally tailored intense femtosecond laser pulses

    Science.gov (United States)

    Irani, E.; Anvari, A.; Sadighi-Bonabi, R.; Monfared, M.

    2017-10-01

    The multielectron dissociative ionization of CH4 and CH2O molecules has been investigated using optimum convolution of different dual tailored short laser pulses. Based on three dimensional molecular dynamics simulations and TDDFT approach, the dissociation probability is enhanced by designing the dual chirped-chirped laser pulses and chirped-ordinary laser pulses for formaldehyde molecule. However, it is interesting to notice that the sensitivity of enhanced dissociation probability into different tailored laser pulses is not significant for methane molecule. In this presented modifications, time variation of bond length, velocity, time dependent electron localization function and evolution of the efficient occupation states are presented to analyze the time evolution of molecular dynamics. This work is proved to be a potential way to reduce the controlling costs with a currently available pulse shaping technology.

  12. Direct time integration of Maxwell's equations in linear dispersive media with absorption for scattering and propagation of femtosecond electromagnetic pulses

    Science.gov (United States)

    Joseph, Rose M.; Hagness, Susan C.; Taflove, Allen

    1991-01-01

    The initial results for femtosecond pulse propagation and scattering interactions for a Lorentz medium obtained by a direct time integration of Maxwell's equations are reported. The computational approach provides reflection coefficients accurate to better than 6 parts in 10,000 over the frequency range of dc to 3 x 10 to the 16th Hz for a single 0.2-fs Gaussian pulse incident upon a Lorentz-medium half-space. New results for Sommerfeld and Brillouin precursors are shown and compared with previous analyses. The present approach is robust and permits 2D and 3D electromagnetic pulse propagation directly from the full-vector Maxwell's equations.

  13. New pulse-shape analysis method with multi-shaping amplifiers

    CERN Document Server

    Sakai, H; Takenaka, Y; Mori, C; Iguchi, T

    1999-01-01

    A novel pulse-shape analysis method that uses similarity to recognize an individual pulse shape is presented in this paper. We obtain four pulse heights by using four linear amplifiers with different shaping time constants. We treat a combination of the four pulse heights as a pattern vector. A similarity of the pulse shape can be obtained by comparison between the pattern vector and a discriminant vector which was given in advance. Each pulse shape is analyzed by using the similarity. The method has been applied for the improvement of characteristics of a CdZnTe semiconductor detector. The characteristics of the energy spectrum of the CdZnTe detector such as the photopeak efficiency or the peak-to-valley ratio are improved after the correction procedure with the similarity.

  14. Formation and fragmentation of quadruply charged molecular ions by intense femtosecond laser pulses.

    Science.gov (United States)

    Yatsuhashi, Tomoyuki; Nakashima, Nobuaki

    2010-07-22

    We investigated the formation and fragmentation of multiply charged molecular ions of several aromatic molecules by intense nonresonant femtosecond laser pulses of 1.4 mum with a 130 fs pulse duration (up to 2 x 10(14) W cm(-2)). Quadruply charged states were produced for 2,3-benzofluorene and triphenylene molecular ion in large abundance, whereas naphthalene and 1,1'-binaphthyl resulted only in up to triply charged molecular ions. The laser wavelength was nonresonant with regard to the electronic transitions of the neutral molecules, and the degree of fragmentation was strongly correlated with the absorption of the singly charged cation radical. Little fragmentation was observed for naphthalene (off-resonant with cation), whereas heavy fragmentation was observed in the case of 1,1'-binaphthyl (resonant with cation). The degree of H(2) (2H) and 2H(2) (4H) elimination from molecular ions increased as the charge states increased in all the molecules examined. A striking difference was found between triply and quadruply charged 2,3-benzofluorene: significant suppression of molecular ions with loss of odd number of hydrogen was observed in the quadruply charged ions. The Coulomb explosion of protons in the quadruply charged state and succeeding fragmentation resulted in the formation of triply charged molecular ions with an odd number of hydrogens. The hydrogen elimination mechanism in the highly charged state is discussed.

  15. 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.

  16. Coherence Properties of Individual Femtosecond Pulses of an X-ray Free-Electron Laser

    Energy Technology Data Exchange (ETDEWEB)

    Vartanyants, I.A.; /DESY /Moscow Phys. Eng. Inst.; Singer, A.; Mancuso, A.P.; Yefanov, O.M.; /DESY; Sakdinawat, A.; Liu, Y.; Bang, E.; /UC, Berkeley; Williams, G.J.; /SLAC; Cadenazzi, G.; Abbey, B.; /Melbourne U.; Sinn, H.; /European XFEL, Hamburg; Attwood, D.; /UC, Berkeley; Nugent, K.A.; /Melbourne U.; Weckert, E.; /DESY; Wang, T.; Zhu, D.; Wu, B.; Graves, C.; Scherz, A.; Turner, J.J.; Schlotter, W.F.; /SLAC /LERMA, Ivry /Zurich, ETH /LBL, Berkeley /ANL, APS /Argonne /SLAC /LLNL, Livermore /Latrobe U. /SLAC /SLAC /European XFEL, Hamburg /SLAC /Hamburg U.

    2012-06-06

    Measurements of the spatial and temporal coherence of single, femtosecond x-ray pulses generated by the first hard x-ray free-electron laser, the Linac Coherent Light Source, are presented. Single-shot measurements were performed at 780 eV x-ray photon energy using apertures containing double pinholes in 'diffract-and-destroy' mode. We determined a coherence length of 17 {micro}m in the vertical direction, which is approximately the size of the focused Linac Coherent Light Source beam in the same direction. The analysis of the diffraction patterns produced by the pinholes with the largest separation yields an estimate of the temporal coherence time of 0.55 fs. We find that the total degree of transverse coherence is 56% and that the x-ray pulses are adequately described by two transverse coherent modes in each direction. This leads us to the conclusion that 78% of the total power is contained in the dominant mode.

  17. Single cell detection using a glass-based optofluidic device fabricated by femtosecond laser pulses.

    Science.gov (United States)

    Kim, Moosung; Hwang, David J; Jeon, Hojeong; Hiromatsu, Kuniaki; Grigoropoulos, Costas P

    2009-01-21

    We demonstrate the fabrication of integrated three-dimensional microchannel and optical waveguide structures inside fused silica for the interrogation and processing of single cells. The microchannels are fabricated by scanning femtosecond laser pulses (523 nm) and subsequent selective wet etching process. Optical waveguides are additionally integrated with the fabricated microchannels by scanning the laser pulse train inside the glass specimen. Single red blood cells (RBC) in diluted human blood inside of the manufactured microchannel were detected by two optical schemes. The first involved sensing the intensity change of waveguide-delivered He-Ne laser light (632.8 nm) induced by the refractive index difference of a cell flowing in the channel. The other approach was via detection of fluorescence emission from dyed RBC excited by Ar laser light (488 nm) delivered by the optical waveguide. The proposed device was tested to detect 23 fluorescent particles per second by increasing the flow rate up to 0.5 microl min(-1). The optical cell detection experiments support potential implementation of a new generation of glass-based optofluidic biochip devices in various single cell treatment processes including laser based cell processing and sensing.

  18. Fixation of bioactive calcium alkali phosphate on Ti6Al4V implant material with femtosecond laser pulses

    International Nuclear Information System (INIS)

    Symietz, Christian; Lehmann, Erhard; Gildenhaar, Renate; Koter, Robert; Berger, Georg; Krueger, Joerg

    2011-01-01

    Bone implants made of metal, often titanium or the titanium alloy Ti6Al4V, need to be surface treated to become bioactive. This enables the formation of a firm and durable connection of the prosthesis with the living bone. We present a new method to uniformly cover Ti6Al4V with a thin layer of ceramics that imitates bone material. These calcium alkali phosphates, called GB14 and Ca10, are applied to the metal by dip coating of metal plates into an aqueous slurry containing the fine ceramic powder. The dried samples are illuminated with the 790 nm radiation of a pulsed femtosecond laser. If the laser fluence is set to a value just below the ablation threshold of the ceramic (ca. 0.4 J/cm 2 ) the 30 fs laser pulses penetrate the partly transparent ceramic layer of 20-40 μm thickness. The remaining laser fluence at the ceramic-metal interface is still high enough to generate a thin metal melt layer leading to the ceramic fixation on the metal. The laser processing step is only possible because Ti6Al4V has a lower ablation threshold (between 0.1 and 0.15 J/cm 2 ) than the ceramic material. After laser treatment in a fluence range between 0.1 and 0.4 J/cm 2 , only the particles in contact with the metal withstand a post-laser treatment (ultrasonic cleaning). The non-irradiated rest of the layer is washed off. In this work, we present results of a successful ceramic fixation extending over larger areas. This is fundamental for future applications of arbitrarily shaped implants.

  19. Pulse shaping amplifier (PSA) for nuclear spectroscopy system

    International Nuclear Information System (INIS)

    Lombigit, L.; Maslina Mohd Ibrahim; Nolida Yusup; Nur Aira Abdul Rahman; Yong, C.F.

    2014-01-01

    Pulse Shaping Amplifier (PSA) is an essential components in nuclear spectroscopy system. This networks have two functions; to shape the output pulse and performs noise filtering. In this paper, we describes procedure for design and development of a pulse shaping amplifier which can be used for nuclear spectroscopy system. This prototype was developed using high performance electronics devices and assembled on a FR4 type printed circuit board. Performance of this prototype was tested by comparing it with an equivalent commercial spectroscopy amplifier (Model SILENA 7611). The test results show that the performance of this prototype is comparable to the commercial spectroscopic amplifier. (author)

  20. Selective bond breakage within the HOD molecule using optimized femtosecond ultraviolet laser pulses

    DEFF Research Database (Denmark)

    Tiwari, Ashwani Kumar; Møller, Klaus Braagaard; Henriksen, Niels Engholm

    2008-01-01

    With the HOD molecule initially in its vibrational ground state, we theoretically analyze the laser-induced control of the OD/OH branching ratio D+OH H+OD in the first absorption band. In the weak-field limit, any form of UV-pulse shaping control leads to a branching ratio larger than similar to 2...

  1. Optical absorption and photocurrent enhancement in semi-insulating gallium arsenide by femtosecond laser pulse surface microstructuring.

    Science.gov (United States)

    Zhao, Zhen-Yu; Song, Zhi-Qiang; Shi, Wang-Zhou; Zhao, Quan-Zhong

    2014-05-19

    We observe an enhancement of optical absorption and photocurrent from semi-insulating gallium arsenide (SI-GaAs) irradiated by femtosecond laser pulses. The SI-GaAs wafer is treated by a regeneratively amplified Ti: Sapphire laser of 120 fs laser pulse at 800 nm wavelength. The laser ablation induced 0.74 μm periodic ripples, and its optical absorption-edge is shifted to a longer wavelength. Meanwhile, the steady photocurrent of irradiated SI-GaAs is found to enhance 50%. The electrical properties of samples are calibrated by van der Pauw method. It is found that femtosecond laser ablation causes a microscale anti-reflection coating surface which enhances the absorption and photoconductivity.

  2. Spin-photo-currents generated by femtosecond laser pulses in a ferrimagnetic GdFeCo/Pt bilayer

    Science.gov (United States)

    Huisman, T. J.; Ciccarelli, C.; Tsukamoto, A.; Mikhaylovskiy, R. V.; Rasing, Th.; Kimel, A. V.

    2017-02-01

    Using THz emission spectroscopy, we detect spin-photo-currents from a ferrimagnetic amorphous alloy GdFeCo to an adjacent Pt capping layer. The currents are generated upon excitation of a GdFeCo/Pt heterostructure with femtosecond laser pulses. It is found that the polarization of the spin-polarized current is determined by magnetic sublattice sensitivity rather than the total magnetization, allowing for spin-polarized current generation when the net magnetization is zero.

  3. Development and applications of femtosecond monolithic Yb-doped fiber chirped-pulse amplifiers

    International Nuclear Information System (INIS)

    Zhu, L.

    2011-01-01

    In the past few years, compact and environmentally stable high-energy ultrashort pulse laser sources have been broadly utilized in many different applications. Fiber lasers offer big practical advantages over bulk solid-state laser systems in terms of flexibility, compactness, reliability, cost effectiveness and turn-key operability. Moreover, thermal effects are dramatically reduced due to the large surface-to-volume ratio of an optical fiber, and good spatial mode quality can be ensured by its waveguiding property. Therefore, a fiber-based laser system is considered to be the preferred laser architecture. The main theme of this thesis is the development of various femtosecond monolithic Yb-doped fiber chirped-pulse-amplification (FCPA) system and their applications. We demonstrate an ultrafast high-energy monolithic Yb-doped FCPA system in which the pulse fidelity is preserved by weakening the nonlinear effects via a substantial level of temporal stretching of the seed pulses and by using highly doped active fibers as amplifying media. The presented monolithic FCPA delivers up to ∼ 25 μJ diffraction-limited pulses that can be recompressed to sub-200 fs duration, and the pulse quality has been confirmed through the second-harmonic-generation (SHG) conversion efficiency of over 52%. Improved dispersion and nonlinearity management schemes of the FCPA system allowing substantial pulse energy scaling in the monolithic format as well as methods for overcoming a series of technological challenges are reported. Three different types of Yb-doped fiber oscillators have been developed and built in the course of this PhD work. First, we compare two oscillator types that are based on the all-normal-dispersion (ANDi) regime and the dispersion-managed (DM) regime. Both of them have been tested as the seed-pulse source of the monolithic Yb-doped FCPA system. Then we introduce another novel design based on higher-order-mode (HOM) dispersion management that competes with a

  4. Regenerative Amplification of Femtosecond Pulses: Design andConstruction of a sub-100fs, muon J Laser System

    Energy Technology Data Exchange (ETDEWEB)

    Schumacher, Andreas B. [Univ. of California, Berkeley, CA (United States)

    1996-10-01

    Femtosecond lasers are a powerful tool for a wealth of applications in physics, chemistry and biology. In most cases, however, their use is fundamentally restricted to a rather narrow spectral range. This thesis deals with the construction and characterization of a femtosecond light source for spectroscopic applications which overcomes that restriction. It is demonstrated how the output of a continuously pumped Ti:sapphire femtosecond oscillator is amplified to the μJ level,while the pulse duration remains below 100 fs. A combination of continuous pumping, acousto-optic switching and Ti:Al2O3 as a gain medium allows amplification at high repetition rates. By focusing the high energy pulses into a sapphire crystal, a broad-band continuum can be generated, extended in wavelengths over several hundred nanometers. To accomplish amplification of three orders of magnitude while maintaining the pulse length, a regenerative multipass amplifier system was built. The thesis describes theoretical design, realization and characterization of the system. Theoretical calculations and preliminary measurements were carried out and allow a critical evaluation of the final performance.

  5. Regenerative amplification of femtosecond pulses: Design and construction of a sub-100fs, {mu}J laser system

    Energy Technology Data Exchange (ETDEWEB)

    Schumacher, A.B. [Universitaet Karlsruhe (Germany). Institut fuer Angewandte Physik]|[Lawrence Berkeley National Lab., CA (United States)

    1996-10-01

    Femtosecond lasers are a powerful tool for a wealth of applications in physics, chemistry and biology. In most cases, however, their use is fundamentally restricted to a rather narrow spectral range. This thesis deals with the construction and characterization of a femtosecond light source for spectroscopic applications which overcomes that restriction. It is demonstrated how the output of a continuously pumped Ti:sapphire femtosecond oscillator is amplified to the {mu}J level, while the pulse duration remains below 100fs. A combination of continuous pumping, acousto-optic switching and Ti:Al{sub 2}O{sub 3} as a gain medium allows amplification at high repetition rates. By focusing the high energy pulses into a sapphire crystal, a broad-band continuum can be generated, extended in wavelengths over several hundred nanometers. To accomplish amplification of three orders of magnitude while maintaining the pulse length, a regenerative multipass amplifier system was built. The thesis describes theoretical design, realization and characterization of the system. Theoretical calculations and preliminary measurements were carried out and allow a critical evaluation of the final performance.

  6. Solvent effect on dynamical TPA and optical limiting of BDMAS molecular media for nanosecond and femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Zhou Yong; Miao Quan; Sun Yuping; Wang Chuankui [College of Physics and Electronics, Shandong Normal University, 250014 Jinan (China); Gel' mukhanov, Faris, E-mail: ckwang@sdnu.edu.cn [Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm (Sweden)

    2011-01-14

    The dynamical two-photon absorption (TPA) cross section as well as optical limiting of a 4,4'-bis(dimethylamino) stilbene (BDMAS) molecular medium for the nanosecond and femtosecond laser pulses is studied. This molecular medium can be described by a cascade three-level model in the visible light regime. Our numerical results show that the BDMAS molecular medium exhibits a strong optical limiting behaviour. The saturation TPA in the femtosecond time domain can be observed, and materials with larger nonlinear absorption cross sections would be much easier to saturate. Due to the contribution of the two-step TPA, the dynamical TPA cross section of BDMAS for nanosecond pulses is about three orders of magnitude larger than that for ultrashort femtosecond pulses. Special attention has been paid to the solvent effects on the optimal limiting performance. With an enhancement of the polarity of solvents, the dynamical optical limiting window becomes broader. In the origin of optical limiting, the dynamical TPA cross section of BDMAS decreases when the polarity of solvents increases, which is in good agreement with the experiment.

  7. Solvent effect on dynamical TPA and optical limiting of BDMAS molecular media for nanosecond and femtosecond laser pulses

    International Nuclear Information System (INIS)

    Zhou Yong; Miao Quan; Sun Yuping; Wang Chuankui; Gel'mukhanov, Faris

    2011-01-01

    The dynamical two-photon absorption (TPA) cross section as well as optical limiting of a 4,4'-bis(dimethylamino) stilbene (BDMAS) molecular medium for the nanosecond and femtosecond laser pulses is studied. This molecular medium can be described by a cascade three-level model in the visible light regime. Our numerical results show that the BDMAS molecular medium exhibits a strong optical limiting behaviour. The saturation TPA in the femtosecond time domain can be observed, and materials with larger nonlinear absorption cross sections would be much easier to saturate. Due to the contribution of the two-step TPA, the dynamical TPA cross section of BDMAS for nanosecond pulses is about three orders of magnitude larger than that for ultrashort femtosecond pulses. Special attention has been paid to the solvent effects on the optimal limiting performance. With an enhancement of the polarity of solvents, the dynamical optical limiting window becomes broader. In the origin of optical limiting, the dynamical TPA cross section of BDMAS decreases when the polarity of solvents increases, which is in good agreement with the experiment.

  8. Shape analysis of pulsed second sound in He II

    International Nuclear Information System (INIS)

    Worthington, T.; Yan, J.; Trefny, J.U.

    1976-01-01

    Second sound in He II has been observed using a heat pulse method. At temperatures where well-developed second sound is observed, the entire pulse shape can be understood if heat sources and geometrical effects are properly taken into account. 4 figures

  9. Efficient atomization of cesium metal in solid helium by low energy (10 $\\mu$J) femtosecond pulses

    OpenAIRE

    Melich, Mathieu; Dupont-Roc, Jacques; Jacquier, Philippe

    2009-01-01

    International audience; Metal atoms in solid and liquid helium-4 have attracted some interest either as a way to keep the atoms in a weakly perturbing matrix, or using them as a probe for the helium host medium. Laser sputtering with nanosecond pulsed lasers is the most often used method for atom production, resulting however in a substantial perturbation of the matrix. We show that a much weaker perturbation can be obtained by using femtosecond laser pulses with energy as low as 10 µJ. As an...

  10. Efficient atomization of cesium metal in solid helium by low energy (10 μJ) femtosecond pulses

    Science.gov (United States)

    Melich, M.; Dupont-Roc, J.; Jacquier, Ph.

    2009-10-01

    Metal atoms in solid and liquid helium-4 have attracted some interest either as a way to keep the atoms in a weakly perturbing matrix, or using them as a probe for the helium host medium. Laser sputtering with nanosecond pulsed lasers is the most often used method for atom production, resulting however in a substantial perturbation of the matrix. We show that a much weaker perturbation can be obtained by using femtosecond laser pulses with energy as low as 10 μJ. As an unexpected benefit, the atomic density produced is much higher.

  11. Metal-like self-organization of periodic nanostructures on silicon and silicon carbide under femtosecond laser pulses

    International Nuclear Information System (INIS)

    Gemini, Laura; Hashida, Masaki; Shimizu, Masahiro; Miyasaka, Yasuhiro; Inoue, Shunsuke; Tokita, Shigeki; Sakabe, Shuji; Limpouch, Jiri; Mocek, Tomas

    2013-01-01

    Periodic structures were generated on Si and SiC surfaces by irradiation with femtosecond laser pulses. Self-organized structures with spatial periodicity of approximately 600 nm appear on silicon and silicon carbide in the laser fluence range just above the ablation threshold and upon irradiation with a large number of pulses. As in the case of metals, the dependence of the spatial periodicity on laser fluence can be explained by the parametric decay of laser light into surface plasma waves. The results show that the proposed model might be universally applicable to any solid state material

  12. Low level alpha activity measurements with pulse shape discrimination

    International Nuclear Information System (INIS)

    Noguchi, Masayasu; Satoh, Kaneaki; Higuchi, Hideo.

    1984-01-01

    Pulse shape discrimination of α and β rays with liquid scintillation counting was investigated for the purpose of low level α activity measurements. Various liquid scintillators for pulse shape discrimination were examined by means of pulse rise time analysis. A new scintillator of low cost and of superior characteristics was found. The figure of merits better than 3.5 in risetime spectrum and the energy resolution better than 9% were obtained for carefully prepared samples. The background counting rate for a sample of 10 ml was reduced to 0.013 cpm/MeV in the range of α ray energy 5 to 7 MeV. (author)

  13. Resonant ablation of single-wall carbon nanotubes by femtosecond laser pulses

    International Nuclear Information System (INIS)

    Arutyunyan, N R; Komlenok, M S; Kononenko, V V; Pashinin, V P; Pozharov, A S; Konov, V I; Obraztsova, E D

    2015-01-01

    The thin 50 nm film of bundled arc-discharge single-wall carbon nanotubes was irradiated by femtosecond laser pulses with wavelengths 675, 1350 and 1745 nm corresponding to the absorption band of metallic nanotubes E 11 M , to the background absorption and to the absorption band of semiconducting nanotubes E 11 S , respectively. The aim was to induce a selective removal of nanotubes of specific type from the bundled material. Similar to conducted thermal heating experiments, the effect of laser irradiation results in suppression of all radial breathing modes in the Raman spectra, with preferential destruction of the metallic nanotubes with diameters less than 1.26 nm and of the semiconducting nanotubes with diameters 1.36 nm. However, the etching rate of different nanotubes depends on the wavelength of the laser irradiation. It is demonstrated that the relative content of nanotubes of different chiralities can be tuned by a resonant laser ablation of undesired nanotube fraction. The preferential etching of the resonant nanotubes has been shown for laser wavelengths 675 nm (E 11 M ) and 1745 nm (E 11 S ). (paper)

  14. Visible to Infrared Diamond Photonics Enabled by Focused Femtosecond Laser Pulses

    Directory of Open Access Journals (Sweden)

    Belén Sotillo

    2017-02-01

    Full Text Available Diamond’s nitrogen-vacancy (NV centers show great promise in sensing applications and quantum computing due to their long electron spin coherence time and because they can be found, manipulated, and read out optically. An important step forward for diamond photonics would be connecting multiple diamond NVs together using optical waveguides. However, the inertness of diamond is a significant hurdle for the fabrication of integrated optics similar to those that revolutionized silicon photonics. In this work, we show the fabrication of optical waveguides in diamond, enabled by focused femtosecond high repetition rate laser pulses. By optimizing the geometry of the waveguide, we obtain single mode waveguides from the visible to the infrared. Additionally, we show the laser writing of individual NV centers within the bulk of diamond. We use µ-Raman spectroscopy to gain better insight on the stress and the refractive index profile of the optical waveguides. Using optically detected magnetic resonance and confocal photoluminescence characterization, high quality NV properties are observed in waveguides formed in various grades of diamond, making them promising for applications such as magnetometry, quantum information systems, and evanescent field sensors.

  15. Surface ablation of inorganic transparent materials using 70W femtosecond pulses at 1MHz (Conference Presentation)

    Science.gov (United States)

    Mishchik, Konstantin; Gaudfrin, Kevin; Audouard, Eric F.; Mottay, Eric P.; Lopez, John

    2017-03-01

    Nowadays processing of transparent materials, such as glass, quartz, sapphire and others, is a subject of high interest for worldwide industry since these materials are widely used for mass markets such as consumer electronics, flat display panels manufacturing, optoelectronics or watchmaking industry. The key issue is to combine high throughput, low residual stress and good processing quality in order to avoid chipping and any post-processing step such as grinding or polishing. Complimentary to non-ablative techniques used for zero-kerf glass cutting, surface ablation of such materials is interesting for engraving, grooving as well as full ablation cutting. Indeed this technique enables to process complex parts including via or blind, open or closed, straight or small radius of curvature patterns. We report on surface ablation experiments on transparent materials using a high average power (70W) and high repetition rate (1 MHz) femtosecond laser. These experiments have been done at 1030nm and 515nm on different inorganic transparent materials, such as regular and strengthened glass, borosilicate glass or sapphire, in order to underline their different ablation behavior. Despite the heat accumulation that occurs above 100 kHz we have reached a good compromise between throughput and processing quality. The effects of fluence, pulse-to-pulse overlap and number of passes are discussed in terms of etch rate, ablation efficiency, optimum fluence, maximum achievable depth, micro cracks formation and residual stresses. These experimental results will be also compared with numerical calculations obtained owing to a simple engineering model based on the two-temperature description of the ultrafast ablation.

  16. Optical shaping of a nano-scale tip by femtosecond laser assisted field evaporation

    Science.gov (United States)

    Di Russo, E.; Houard, J.; Langolff, V.; Moldovan, S.; Rigutti, L.; Deconihout, B.; Blavette, D.; Bogdanowicz, J.; Vella, A.

    2018-04-01

    We have investigated the morphology of a nanotip under femtosecond laser pulse illumination and a high electric field. We show that both the symmetry and the local radius of the tip change with the direction of laser polarization as against the tip axis. The experiments were performed on the very same GaN nanotip by laser-assisted atom probe tomography and electron tomography. This allowed an accurate assessment of the tip features by following the order of evaporation of single atoms from the surface. A change of atom emission sites was observed when a change of the angle between the tip axis and the linearly polarized electric field of the laser was imposed. This enables an optical control of field-evaporation sites. A close optical control of the tip morphology on a scale below 10 nm is thus achievable. Calculations of the field at nanotip apex and absorption maps support the experimental observations. Based on the present study, methods can be developed for reshaping nanotips at the nanometer level. This finding opens perspectives for numerous applications, making use of nanotips as probes or field emitters, and for plasmonic devices.

  17. Pile-up and defective pulse rejection by pulse shape discrimination in surface barrier detectors

    International Nuclear Information System (INIS)

    Sjoeland, K.A.; Kristiansson, P.

    1994-01-01

    A technique to reject pile-up pulses and defective tail pulses from surface barrier detectors by the use of pulse shape discrimination is demonstrated. The electronic implementation of the pulse shape discrimination is based upon the zero crossing technique and for data reduction multiparameter techniques are used. The characteristic τ value for pile-up rejection is shown to be less than 56 ns. Its effect on detection limits from tail reduction in Particle Elastic Scattering Analysis (PESA) and pile-up peak suppression is discussed. ((orig.))

  18. Frequency comb generation using femtosecond pulses and cross-phase modulation in optical fiber at arbitrary center frequencies.

    Science.gov (United States)

    Jones, D J; Diddams, S A; Taubman, M S; Cundiff, S T; Ma, L S; Hall, J L

    2000-03-01

    A technique is presented for generating optical frequency combs centered at arbitrary wavelengths by use of cross-phase modulation (XPM) between a femtosecond pulse train and a cw laser beam by copropagating these signals through an optical fiber. We report results from use of this method to place a 90-MHz frequency comb on an iodine-stabilized Nd:YAG laser at 1064 nm and on a frequency-doubled Nd:YVO(4) laser at 532 nm. XPM is verified to be the comb-generating process, and the width of the frequency comb is measured and compared with theory. The spacing of the frequency comb is compared with the femtosecond source, and a frequency measurement with this comb is demonstrated.

  19. Quantum phase amplification for temporal pulse shaping and super-resolution in remote sensing

    Science.gov (United States)

    Yin, Yanchun

    The use of nonlinear optical interactions to perform nonclassical transformations of electromagnetic field is an area of considerable interest. Quantum phase amplification (QPA) has been previously proposed as a method to perform nonclassical manipulation of coherent light, which can be experimentally realized by use of nonlinear optical mixing processes, of which phase-sensitive three-wave mixing (PSTWM) is one convenient choice. QPA occurs when PSTWM is operated in the photon number deamplification mode, i.e., when the energy is coherently transferred among the low-frequency signal and idler waves and the high-frequency pump wave. The final state is nonclassical, with the field amplitude squeezed and the phase anti-squeezed. In the temporal domain, the use of QPA has been studied to facilitate nonlinear pulse shaping. This novel method directly shapes the temporal electric field amplitude and phase using the PSTWM in a degenerate and collinear configuration, which has been analyzed using a numerical model. Several representative pulse shaping capabilities of this technique have been identified, which can augment the performance of common passive pulse shaping methods operating in the Fourier domain. The analysis indicates that a simple quadratic variation of temporal phase facilitates pulse compression and self-steepening, with features significantly shorter than the original transform-limited pulse. Thus, PSTWM can act as a direct pulse compressor based on the combined effects of phase amplification and group velocity mismatch, even without the subsequent linear phase compensation. Furthermore, it is shown numerically that pulse doublets and pulse trains can be produced at the pump frequency by utilizing the residual linear phase of the signal. Such pulse shaping capabilities are found to be within reach of this technique in common nonlinear optical crystals pumped by pulses available from compact femtosecond chirped-pulse amplification laser systems. The use of

  20. High Intensity Femtosecond XUV Pulse Interactions with Atomic Clusters: Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Ditmire, Todd [Univ. of Texas, Austin, TX (United States). Center for High Energy Density Science

    2016-10-12

    We propose to expand our recent studies on the interactions of intense extreme ultraviolet (XUV) femtosecond pulses with atomic and molecular clusters. The work described follows directly from work performed under BES support for the past grant period. During this period we upgraded the THOR laser at UT Austin by replacing the regenerative amplifier with optical parametric amplification (OPA) using BBO crystals. This increased the contrast of the laser, the total laser energy to ~1.2 J , and decreased the pulse width to below 30 fs. We built a new all reflective XUV harmonic beam line into expanded lab space. This enabled an increase influence by a factor of 25 and an increase in the intensity by a factor of 50. The goal of the program proposed in this renewal is to extend this class of experiments to available higher XUV intensity and a greater range of wavelengths. In particular we plan to perform experiments to confirm our hypothesis about the origin of the high charge states in these exploding clusters, an effect which we ascribe to plasma continuum lowering (ionization potential depression) in a cluster nano-­plasma. To do this we will perform experiments in which XUV pulses of carefully chosen wavelength irradiate clusters composed of only low-Z atoms and clusters with a mixture of this low-­Z atom with higher Z atoms. The latter clusters will exhibit higher electron densities and will serve to lower the ionization potential further than in the clusters composed only of low Z atoms. This should have a significant effect on the charge states produced in the exploding cluster. We will also explore the transition of explosions in these XUV irradiated clusters from hydrodynamic expansion to Coulomb explosion. The work proposed here will explore clusters of a wider range of constituents, including clusters from solids. Experiments on clusters from solids will be enabled by development we performed during the past grant period in which we constructed and

  1. Nonlinear Pulse Shaping in Fibres for Pulse Generation and Optical Processing

    Directory of Open Access Journals (Sweden)

    Sonia Boscolo

    2012-01-01

    Full Text Available The development of new all-optical technologies for data processing and signal manipulation is a field of growing importance with a strong potential for numerous applications in diverse areas of modern science. Nonlinear phenomena occurring in optical fibres have many attractive features and great, but not yet fully explored, potential in signal processing. Here, we review recent progress on the use of fibre nonlinearities for the generation and shaping of optical pulses and on the applications of advanced pulse shapes in all-optical signal processing. Amongst other topics, we will discuss ultrahigh repetition rate pulse sources, the generation of parabolic shaped pulses in active and passive fibres, the generation of pulses with triangular temporal profiles, and coherent supercontinuum sources. The signal processing applications will span optical regeneration, linear distortion compensation, optical decision at the receiver in optical communication systems, spectral and temporal signal doubling, and frequency conversion.

  2. A pulse generator of arbitrary shaped waveform

    International Nuclear Information System (INIS)

    Jiang Jiayou; Chen Zhihao

    2011-01-01

    The three bump magnets in the booster extraction system of SSRF are driven by a signal generator with an external trigger. The signal generator must have three independent and controllable outputs, and both amplitude and make-and-break should be controllable, with current state information being readable. In this paper, we describe a signal generator based on FPGA and DAC boards. It makes use of characteristics of both FPGA flex programmable and rich reconfigurable IO resources. The system has a 16-bit DAC with four outputs, using Matlab to write a GUI based on RS232 protocol for control. It was simulated in Modelsim and tested on board. The results indicate that the system is well designed and all the requirements are met. The arbitrary waveform is writable, and the pulse width and period can be controlled. (authors)

  3. Pulse shape analysis using CsI(Tl) Crystals

    International Nuclear Information System (INIS)

    Silva, J.; Fiori, E.; Loher, B.; Savran, D.; Wirth, R.; Vencelj, M.

    2013-06-01

    The decay time of CsI(Tl) scintillating material consists of more than a single exponential component. The ratio between the intensity of these components varies as a function of the ionizing power of the absorbed particles, such as γ -rays or protons, and the temperature. This property can therefore be used for particle discrimination and for temperature monitoring, using pulse shape analysis. An unsupervised method that uses fuzzy clustering algorithms for particle identification based on pulse shape analysis is presented. The method is applied to discriminate between photon and proton-induced signals in CsI(Tl) scintillator detectors. The first results of a method that uses pulse shape analysis for correcting the temperature-dependent gain effect of the detector are also presented. The method aims at conserving a good energy resolution in a temperature varying environment without the need to measure the temperature of the detector externally (authors)

  4. Selective deactivation of M13 bacteriophage in E. Coli using femtosecond laser pulses

    CSIR Research Space (South Africa)

    Molukanele, P

    2011-09-01

    Full Text Available Potential for the selective deactivation of viruses while leaving the sensitive material such as the host cell unharmed was studied using a femtosecond laser system, and preliminary results are reported....

  5. Reflected pulse damping between charge source and shaping line

    International Nuclear Information System (INIS)

    Bukharov, V.F.; Gerasimov, A.I.; Fedotkin, A.S.

    1987-01-01

    A coaxial device to tranfer electric energy from a pulsed generator to a low-impedance shaping line whose commutation brings about powerful short voltage pulses is described. To damp pulses the internal conductor of the device is enveloped by the element of volumetrically resitant material, and controlled discharge are placed between the external conductor of the device and the element. The device operated efficiency when the radical lines were charged from the Arkadiev-Marx generator during 1 μs up to 500 kV

  6. Comparison of Heat Affected Zone due to nanosecond and femtosecond laser pulses using Transmission Electronic Microscopy

    OpenAIRE

    Le Harzic, Ronan; Huot, Nicolas; Audouard, Eric; Jonin, Christian; Laporte, Pierre; Valette, Stéphane; Fraczkievic, Anna; Fortunier, Roland

    2002-01-01

    International audience; This letter presents a method aimed at quantifying the dimensions of the heat-affected zone ~HAZ!, produced during nanosecond and femtosecond laser–matter interactions. According to this method, 0.1 mm thick Al samples were microdrilled and observed by a transmission electronic microscopy technique. The holes were produced at laser fluences above the ablation threshold in both nanosecond and femtosecond regimes ~i.e., 5 and 2 J/cm2, respectively!. The grain size in the...

  7. Comparative investigations of the spontaneous and stimulated emissions from nitrogen molecules in air with femtosecond laser excitation pulses

    International Nuclear Information System (INIS)

    Li, Ziting; Wang, Zhanshan; Chu, Wei; Zeng, Bin; Yao, Jinping; Li, Guihua; Xie, Hongqiang; Cheng, Ya

    2016-01-01

    We report on experimental investigations on the spontaneous and stimulated emissions from excited nitrogen molecules generated in both linearly and circularly polarized intense laser fields. The spontaneous emission is measured from the side direction of the laser-induced filament whereas the stimulated emission generated by seed amplification is measured in the forward direction of the laser propagation. The comparison between the signal intensities of the spontaneous fluorescence emission and the seed-amplified stimulated emission provides an insight into the population inversion generated in nitrogen molecules with circularly polarized femtosecond laser pulses. (paper)

  8. Mechanism for self-formation of periodic grating structures on a metal surface by a femtosecond laser pulse

    OpenAIRE

    Sakabe, Shuji; Hashida, Masaki; Tokita, Shigeki; Namba, Shin; Okamuro, Kiminori

    2009-01-01

    Periodic grating structures self-formed on a metal surface under the irradiation of a femtosecond laser pulse are characterized by grating spaces which are shorter than the laser wavelength, as well as by dependence on the laser fluence. This Brief Report presents a different interpretation of these features in terms of the process of parametric decay of laser light to surface plasma waves. Depending on the electron density, grating spaces with lengths of 680 nm to as short as 400 nm can be p...

  9. Refractive index modulation of Sb70Te30 phase-change thin films by multiple femtosecond laser pulses

    International Nuclear Information System (INIS)

    Lei, Kai; Wang, Yang; Jiang, Minghui; Wu, Yiqun

    2016-01-01

    In this study, the controllable effective refractive index modulation of Sb 70 Te 30 phase-change thin films between amorphous and crystalline states was achieved experimentally by multiple femtosecond laser pulses. The modulation mechanism was analyzed comprehensively by a spectral ellipsometer measurement, surface morphology observation, and two-temperature model calculations. We numerically demonstrate the application of the optically modulated refractive index of the phase-change thin films in a precisely adjustable color display. These results may provide further insights into ultrafast phase-transition mechanics and are useful in the design of programmable photonic and opto-electrical devices based on phase-change memory materials.

  10. Current pulse shaping of the load current on PTS

    Directory of Open Access Journals (Sweden)

    Minghe Xia

    2016-02-01

    Full Text Available The typical rise time of PTS machine is ∼110 ns with about 10 MA peak current under short pulse mode when all 24 modules discharge simultaneously. By distributing the trigger times of 12 laser beams logically and adjusting the statues of the pulse output switches, longer rise-time pulse can be obtained on the PTS facility. Based on the required pulse shape, whole circuit simulations will be used to calculate the trigger times of each laser triggering gas switch and the status of the pulse output switches. The rise time of the current is determined by the time difference between the first and last trigged laser triggering gas switches. In order to trigger the laser triggering gas switch, sufficient laser power is needed to be sent into the gap of the gas switches. The gas pressure and voltage difference on the two electrodes of the gas switches also affect the triggering of the gas switches, and the voltage added on the gas switch is determined by its transition time. Traditionally the trigger time difference should be less than the transition time of the two neighboring modules. A new simulation model of PTS shows one can break this transition time limits. Series of current pulse shaping experiments have been investigated on the PTS (Primary Test Stand. As results, more than 5 MA peak current were successfully achieved on the load with a rise time of 600 ns. This study and experiments of the pulse shaping on PTS demonstrate the adaptable ability of the PTS for offering different waveform of mega ampere current pulse for different research purpose.

  11. Controllable pulse parameter transcranial magnetic stimulator with enhanced circuit topology and pulse shaping

    Science.gov (United States)

    Peterchev, Angel V.; DʼOstilio, Kevin; Rothwell, John C.; Murphy, David L.

    2014-10-01

    Objective. This work aims at flexible and practical pulse parameter control in transcranial magnetic stimulation (TMS), which is currently very limited in commercial devices. Approach. We present a third generation controllable pulse parameter device (cTMS3) that uses a novel circuit topology with two energy-storage capacitors. It incorporates several implementation and functionality advantages over conventional TMS devices and other devices with advanced pulse shape control. cTMS3 generates lower internal voltage differences and is implemented with transistors with a lower voltage rating than prior cTMS devices. Main results. cTMS3 provides more flexible pulse shaping since the circuit topology allows four coil-voltage levels during a pulse, including approximately zero voltage. The near-zero coil voltage enables snubbing of the ringing at the end of the pulse without the need for a separate active snubber circuit. cTMS3 can generate powerful rapid pulse sequences (\\lt 10 ms inter pulse interval) by increasing the width of each subsequent pulse and utilizing the large capacitor energy storage, allowing the implementation of paradigms such as paired-pulse and quadripulse TMS with a single pulse generation circuit. cTMS3 can also generate theta (50 Hz) burst stimulation with predominantly unidirectional electric field pulses. The cTMS3 device functionality and output strength are illustrated with electrical output measurements as well as a study of the effect of pulse width and polarity on the active motor threshold in ten healthy volunteers. Significance. The cTMS3 features could extend the utility of TMS as a research, diagnostic, and therapeutic tool.

  12. Application of pulse shape discrimination in Si detector for fission ...

    Indian Academy of Sciences (India)

    Pulse shape discrimination (PSD) with totally depleted transmission type Si surface barrier detector in reverse mount has been investigated to identify fission fragments in the presence of elastic background in heavy ion-induced fission reactions by both numerical simulation and experimental studies. The PSD method is ...

  13. A fully integrated 16 channel digitally trimmed pulse shaping amplifier

    Energy Technology Data Exchange (ETDEWEB)

    Hearn, W.E.; Wright, M.E.

    1993-11-01

    A fully integrated CMOS pulse shaping amplifier has been developed at LBL. All frequency dependent networks are included on the chip. Provision is made for tuning to compensate for process variations. The overall architecture and details of the circuitry are discussed. Test results are presented.

  14. A fully integrated 16 channel digitally trimmed pulse shaping amplifier

    International Nuclear Information System (INIS)

    Hearn, W.E.; Wright, M.E.

    1993-11-01

    A fully integrated CMOS pulse shaping amplifier has been developed at LBL. All frequency dependent networks are included on the chip. Provision is made for tuning to compensate for process variations. The overall architecture and details of the circuitry are discussed. Test results are presented

  15. Neutron and Gamma Ray Pulse Shape Discrimination with Polyvinyltoluene

    Energy Technology Data Exchange (ETDEWEB)

    Lintereur, Azaree T.; Ely, James H.; Stave, Jean A.; McDonald, Benjamin S.

    2012-03-01

    The goal of this was research effort was to test the ability of two poly vinyltoluene research samples to produce recordable, distinguishable signals in response to gamma rays and neutrons. Pulse shape discrimination was performed to identify if the signal was generated by a gamma ray or a neutron. A standard figure of merit for pulse shape discrimination was used to quantify the gamma-neutron pulse separation. Measurements were made with gamma and neutron sources with and without shielding. The best figure of merit obtained was 1.77; this figure of merit was achieved with the first sample in response to an un-moderated 252Cf source shielded with 5.08 cm of lead.

  16. Design of nuclear pulse shaped circuit based on proportional counter

    International Nuclear Information System (INIS)

    Song Qianqian; Cheng Yi; Tuo Xianguo

    2011-01-01

    Use the self-developed proportional to sample gas tritium in environment and make the measurement. For this detector, a kind of pulse shape circuit based on second order active low pass filtering circuit realized filtering and shaping nuclear pulse by high-speed operational amplifier, with less stages that has been approved for filter Gaussian wave. Use Multisim 10.0 to simulate the different parameters of the filter circuit. The simulation result was consistent with the theoretical results. The experiments proved the feasibility of this circuit, and at the same time provided a convenient and reliable method for analysis and optimization of the nuclear pulse waveform in order for discriminating by MCA. (authors)

  17. Laser system using ultra-short laser pulses

    Science.gov (United States)

    Dantus, Marcos [Okemos, MI; Lozovoy, Vadim V [Okemos, MI; Comstock, Matthew [Milford, MI

    2009-10-27

    A laser system using ultrashort laser pulses is provided. In another aspect of the present invention, the system includes a laser, pulse shaper and detection device. A further aspect of the present invention employs a femtosecond laser and binary pulse shaping (BPS). Still another aspect of the present invention uses a laser beam pulse, a pulse shaper and a SHG crystal.

  18. On thermophysical effects on the surface of functional nanostructured materials obtained with the application of femtosecond laser pulses

    Science.gov (United States)

    Babenko, D. D.; Dmitriev, A. S.; Makarov, P. G.; Mikhailova, I. A.

    2017-11-01

    In recent years, a great scientific and practical interest is caused by functional energy surfaces, modified for certain technological problems. The urgency of the work is to develop promising technologies for thermal and nuclear power engineering, methods for converting solar energy, cooling low-current and high-current electronics devices, energy storage and transport systems on the basis of studying and developing new ways of creating and modifying the functional surfaces of heat exchange and other devices. Modified functional surfaces must have a number of new mechanical and thermophysical properties, including mechanical strength, a new surface morphology for controlling the processes of wetting and spreading working fluids on them, and have high efficiency from the viewpoint of thermohydrodynamic processes of flow and heat and mass transfer of working fluids to them. Among the various ways of modifying surfaces, recently, the method of surface exposure to femtosecond laser pulses (FLI) has become widespread. The technology of femtosecond laser surface treatment (FLPO) of solid materials has shown high efficiency, reliability, high productivity and a huge variety of modification methods. The paper presents new results on the study of thermophysical phenomena - the wetting and spreading of drops of various liquids, the study of the hysteresis of the contact angle, the study of evaporation and boiling processes on functional energy surfaces modified by femtosecond laser pulses. It is shown that in the majority of cases the presence of regular or stochastic nanostructures on the surface leads to a very strong change in the basic properties of the surface, which makes it possible to use such a technology to quickly and efficiently modify and obtain functional energy surfaces for certain predetermined purposes.

  19. Ionization of one- and three-dimensionally-oriented asymmetric-top molecules by intense circularly polarized femtosecond laser pulses

    DEFF Research Database (Denmark)

    Hansen, Jonas Lerche; Holmegaard, Lotte; Kalhøj, Line

    2011-01-01

    are quantum-state selected using a deflector and three-dimensionally (3D) aligned and oriented adiabatically using an elliptically polarized laser pulse in combination with a static electric field. A characteristic splitting in the molecular frame photoelectron momentum distribution reveals the position......We present a combined experimental and theoretical study on strong-field ionization of a three-dimensionally-oriented asymmetric top molecule, benzonitrile (C7H5N), by circularly polarized, nonresonant femtosecond laser pulses. Prior to the interaction with the strong field, the molecules...... of the nodal planes of the molecular orbitals from which ionization occurs. The experimental results are supported by a theoretical tunneling model that includes and quantifies the splitting in the momentum distribution. The focus of the present article is to understand strong-field ionization from 3D...

  20. Femtosecond pulse with THz repetition frequency based on the coupling between quantum emitters and a plasmonic resonator

    Science.gov (United States)

    Li, Shilei; Ding, Yinxing; Jiao, Rongzhen; Duan, Gaoyan; Yu, Li

    2018-03-01

    Nanoscale pulsed light is highly desirable in nano-integrated optics. In this paper, we obtained femtosecond pulses with THz repetition frequency via the coupling between quantum emitters (QEs) and plasmonic resonators. Our structure consists of a V -groove (VG) plasmonic resonator and a nanowire embedded with two-level QEs. The influences of the incident light intensity and QE number density on the transmission response for this hybrid system are investigated through semiclassical theory and simulation. The results show that the transmission response can be modulated to the pulse form. And the repetition frequency and extinction ratio of the pulses can be controlled by the incident light intensity and QE number density. The reason is that the coupling causes the output power of nanowire to behave as an oscillating form, the oscillating output power in turn causes the field amplitude in the resonator to oscillate over time. A feedback system is formed between the plasmonic resonator and the QEs in the nanowire. This provides a method for generating narrow pulsed lasers with ultrahigh repetition frequencies in plasmonic systems using a continuous wave input, which has potential applications in generating optical clock signals at the nanoscale.

  1. Interactive modeling of scintillation pulses by visual overlay of computed pulse shapes with the raw data

    International Nuclear Information System (INIS)

    Flournoy, J.M.; Lutz, S.S.; Franks, L.A.; Ashford, C.B.; Lyons, P.B.

    1983-01-01

    The modeling technique described was developed to aid in interpretation of the effects of various changes in scintillator formulations on the shape of scintillation pulses. Theoretical pulse shapes were synthesized, the system response function is folded in, and the result is overlaid on the raw data arrays. It has thus been possible to distinguish relatively unambiguously between quenching of the solvent and the solute when various heavy-atom quenchers were added to solutions of a series of substituted terphenyls. The method is found to be valuable in providing basic information about energy transfer steps in a multicomponent scintillator

  2. Measurement and fitting of pulse shapes of moderators at IPNS [Intense Pulsed Neutron Source]: Progress report

    International Nuclear Information System (INIS)

    Bywater, R.L. Jr.; Williams, R.E.; Carpenter, J.M.

    1988-01-01

    We present a progress report on measurements and fitting of pulse shapes for neutrons emerging from one solid and two liquid methane moderators in IPNS. A time-focused crystal spectrometer arrangement was used with a cooled Ge monochromator. Data analysis of one of the liquid methane moderators has shown the need for some generalization of the Ikeda-Carpenter function that worked well for fitting pulse shapes of polyethylene moderators. We describe attempts to model physical insight into the wavelength dependence of function parameters. 5 refs., 7 figs

  3. Testing the energy conservation law in an optical parametric oscillator using phase-controlled femtosecond pulses.

    Science.gov (United States)

    Sun, Jinghua; Gale, Barry J S; Reid, Derryck T

    2007-04-02

    An experimental verification of energy conservation in a parametric oscillator is reported with an optical frequency precision of approximately 200 kHz (< 10(-6) nm). This high precision is made possible by simultaneously measuring the frequency offsets of the pump, signal and idler frequency combs in a singly-resonant femtosecond optical parametric oscillator system.

  4. Jet formation in spallation of metal film from substrate under action of femtosecond laser pulse

    International Nuclear Information System (INIS)

    Inogamov, N. A.; Zhakhovskii, V. V.; Khokhlov, V. A.

    2015-01-01

    It is well known that during ablation by an ultrashort laser pulse, the main contribution to ablation of the substance is determined not by evaporation, but by the thermomechanical spallation of the substance. For identical metals and pulse parameters, the type of spallation is determined by film thickness d f . An important gauge is metal heating depth d T at the two-temperature stage, at which electron temperature is higher than ion temperature. We compare cases with d f < d T (thin film) and d f ≫ d T (bulk target). Radius R L of the spot of heating by an optical laser is the next (after d f ) important geometrical parameter. The morphology of film bulging in cases where d f < d T on the substrate (blistering) changes upon a change in radius R L in the range from diffraction limit R L ∼ λ to high values of R L ≫ λ, where λ ∼ 1 μm is the wavelength of optical laser radiation. When d f < d T , R L ∼ λ, and F abs > F m , gold film deposited on the glass target acquires a cupola-shaped blister with a miniature frozen nanojet in the form of a tip on the circular top of the cupola (F abs and F m are the absorbed energy and the melting threshold of the film per unit surface area of the film). A new physical mechanism leading to the formation of the nanojet is proposed

  5. Evolution of pulse shapes during compressor scans in a CPA system and control of electron acceleration in plasmas

    International Nuclear Information System (INIS)

    Toth, Csaba; Groot, Joeri de; Tilborg, Jeroen van; Geddes, Cameron G.R.; Faure, Jerome; Catravas, Palma; Schroeder, Carl; Shadwick, B.A.; Esarey, Eric; Leemans, Wim

    2002-01-01

    The skewness of the envelope function of 20 - 100 femtosecond Ti:sapphire laser pulses has been controlled by appropriate choice of the higher order special phase coefficients, and used for optimization of a plasma wakefield electron accelerator

  6. Low level alpha activity measurements with pulse shape discrimination

    International Nuclear Information System (INIS)

    Satoh, Kaneaki; Higuchi, Hideo; Kitamura, Kiyoshi; Noguchi, Masayasu.

    1984-01-01

    Liquid scintillation counting of α rays with pulse shape discrimination was applied to the analysis of 226 Ra and 239+240 Pu in environmental samples and of α-emitters in/on a filter paper. The instrument used in this study was either a specially designed detector or a commercial liquid scintillation counter with an automatic sample changer, both of which were connected to the pulse shape discrimination circuit. The background counting rate in α energy region of 5-7 MeV was 0.01 or 0.04 cpm/MeV, respectively. The figure of merit indicating the resolving power for α- and β-particles in time spectrum was found to be 5.7 for the commercial liquid scintillation counter. (author)

  7. Digital pulse shape discrimination of detector data using fuzzy clustering

    International Nuclear Information System (INIS)

    Kumar, Abhinav; Chatterjee, A.; Ramachandran, K.; Shrivastava, A.; Mahata, K.

    2011-01-01

    In accelerator based experiments, data acquisition is done by CAMAC, VME and other systems. The current trend is to digitize the pulse shapes and not just the peak heights of all the input channels, by means of Flash ADCs. In view of the large number of channels involved, this leads to unprecedented data volumes. Therefore, attempts to perform a first level of analysis in real time using algorithms implemented in FPGA have become important. In the present work, digital pulse shape discrimination using fuzzy clustering has been investigated. The attempt has been to devise general purpose PSD Techniques, loosely coupled with the characteristics of detector or particle type, for particle identification. The method is applicable to neutron-gamma discrimination for liquid scintillators and charged particles detected by Si detectors

  8. Robust quantum gates between trapped ions using shaped pulses

    Energy Technology Data Exchange (ETDEWEB)

    Zou, Ping, E-mail: zouping@m.scnu.edu.cn; Zhang, Zhi-Ming, E-mail: zmzhang@scnu.edu.cn

    2015-12-18

    We improve two existing entangling gate schemes between trapped ion qubits immersed in a large linear crystal. Based on the existing two-qubit gate schemes by applying segmented forces on the individually addressed qubits, we present a systematic method to optimize the shapes of the forces to suppress the dominant source of infidelity. The spin-dependent forces in the scheme can be from periodic photon kicks or from continuous optical pulses. The entangling gates are fast, robust, and have high fidelity. They can be used to implement scalable quantum computation and quantum simulation. - Highlights: • We present a systematic method to optimize the shape of the pulses to decouple qubits from intermediary motional modes. • Our optimized scheme can be applied to both the ultrafast gate and fast gate. • Our optimized scheme can suppress the dominant source of infidelity to arbitrary order. • When the number of trapped ions increase, the number of needed segments increases slowly.

  9. Energetic mid-IR femtosecond pulse generation by self-defocusing soliton-induced dispersive waves in a bulk quadratic nonlinear crystal

    DEFF Research Database (Denmark)

    Zhou, Binbin; Guo, Hairun; Bache, Morten

    2015-01-01

    Generating energetic femtosecond mid-IR pulses is crucial for ultrafast spectroscopy, and currently relies on parametric processes that, while efficient, are also complex. Here we experimentally show a simple alternative that uses a single pump wavelength without any pump synchronization...

  10. Ultrashort pulse shaping by optical parametric chirped amplification

    International Nuclear Information System (INIS)

    Nelet, Ambre

    2007-01-01

    The aim of this work is to propose new laser architectures based on optical parametric chirped pulse amplification (OPCPA). Common goals of OPCPA pre-amplifiers are to reach high energy level while maintaining the spectrum width and to adapt geometry of the amplified beam to the high power laser chain optics. We consider OPCPA as a way to control and to sculpt ultrashort pulses. Our first set-up aims at thwarting possible time recovery default between pump and signal pulses, which lower the energy extraction. A regenerative OPCPA, idler resonant, is a way to produce a high-intensity and high-repetition rate train of amplified signal replicas. Our second laser system pre-compensates the spectral gain narrowing by sculpting pulses directly within the OPCPA section, where a temporal shaping of the pump beam permits a spectro-spectral shaping of the amplified signal. Finally, we propose an OPCPA based on spatial coding and uniform amplification of spectral signal components by using a fan-out periodically poled crystal and a zero dispersion line. (author) [fr

  11. Effects of moderate pump and Stokes chirp on chirped-probe pulse femtosecond coherent anti-Stokes Raman scattering thermometry

    KAUST Repository

    Gu, Mingming

    2018-01-08

    The effects of moderate levels of chirp in the pump and Stokes pulses on chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering (CPP fs CARS) were investigated. The frequency chirp in the pump and Stokes pulses was introduced by placing SF11 glass disks with thicknesses of 10 mm or 20 mm in the optical path for these beams. The magnitude of the chirp in the probe beam was much greater and was induced by placing a 30-cm rod of SF10 glass in the beam path. The temperature measurements were performed in hydrogen/air non-premixed flames stabilized on a Hencken burner at equivalence ratios of 0.3, 0.5, 0.7, and 1.0. We performed measurements with no disks in pump and Stokes beam paths, and then with disks of 10 mm and 20 mm placed in both beam paths. The spectrum of the nonresonant background four-wave mixing signal narrowed considerably with increasing pump and Stokes chirp, while the resonant CARS signal was relatively unaffected. Consequently, the interference of the nonresonant background with the resonant CARS signal in the frequency-spread dephasing region of the spectrum was minimized. The increased rate of decay of the resonant CARS signal with increasing temperature was thus readily apparent. We have started to analyze the CPP fs CARS thermometry data and initial results indicate improved accuracy and precision are obtained due to moderate chirp in the pump and Stokes laser pulses.

  12. Laser ablative fabrication of nanocrowns and nanojets on the Cu supported film surface using femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Kuchmizhak, A.A., E-mail: ku4mijak@dvo.ru [School of Natural Sciences, Far Eastern Federal University, 8 Sukhanova Street, Vladivostok 690041 (Russian Federation); Institute of Automation and Control Processes, Far Eastern Branch, Russian Academy of Science, 5 Radio Street, Vladivostok 690041 (Russian Federation); Pavlov, D.V. [Institute of Automation and Control Processes, Far Eastern Branch, Russian Academy of Science, 5 Radio Street, Vladivostok 690041 (Russian Federation); Vitrik, O.B. [School of Natural Sciences, Far Eastern Federal University, 8 Sukhanova Street, Vladivostok 690041 (Russian Federation); Institute of Automation and Control Processes, Far Eastern Branch, Russian Academy of Science, 5 Radio Street, Vladivostok 690041 (Russian Federation); Kulchin, Yu. N. [Institute of Automation and Control Processes, Far Eastern Branch, Russian Academy of Science, 5 Radio Street, Vladivostok 690041 (Russian Federation)

    2015-12-01

    Graphical abstract: - Highlights: • Formation dynamics of the laser-induced nanojets and nanocrowns on the Cu film surface was studied. • The key role of subsurface boiling on the metal film–substrate interface was revealed. • Five-fold plasmon enhancement of the Rh6G photoluminescence signal was demonstrated. • Plasmonic nature of enhancement was proved by measuring of the emission spectra of the Rh6G near the nanocrowns. - Abstract: Formation dynamics of the nanojets and nanocrowns induced on the surface of the Cu supported films of different thickness under the impact of tightly focused femtosecond pulses was studied in detail. We show that the single-shot fs-pulse irradiation of the 120-nm-thick Cu film results in formation of a single nanojet, which splits at increased pulse energy into two and then into a plurality of periodically arranged nanospikes eventually acquiring the form of the so-called nanocrown. The number of nanospike in the nanocrown was found to be linearly dependent on the pulse energy and nanocrown radius. The key role of subsurface boiling occurring on the metal film–substrate interface in the formation process of crown-like nanostructures was revealed by comparing the obtained results with the formation dynamics studied for thinner 60-nm and 20-nm-thick Cu films. In addition, the applicability of the fabricated nanostructures as low-cost substrate for photoluminescence signal enhancement of the organic dyes is also discussed in this paper.

  13. LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Channeling of microwave radiation in a double line containing a plasma filament produced by intense femtosecond laser pulses in air

    Science.gov (United States)

    Bogatov, N. A.; Kuznetsov, A. I.; Smirnov, A. I.; Stepanov, A. N.

    2009-10-01

    The channeling of microwave radiation is demonstrated experimentally in a double line in which a plasma filament produced in air by intense femtosecond laser pulses serves as one of the conductors. It is shown that during the propagation of microwave radiation in this line, ultrashort pulses are formed, their duration monotonically decreasing with increasing the propagation length (down to the value comparable with the microwave field period). These effects can be used for diagnostics of plasma in a filament.

  14. Keratin film ablation for the fabrication of brick and mortar skin structure using femtosecond laser pulses

    Science.gov (United States)

    Haq, Bibi Safia; Khan, Hidayat Ullah; Dou, Yuehua; Alam, Khan; Attaullah, Shehnaz; Zari, Islam

    2015-09-01

    The patterning of thin keratin films has been explored to manufacture model skin surfaces based on the "bricks and mortar" view of the relationship between keratin and lipids. It has been demonstrated that laser light is capable of preparing keratin-based "bricks and mortar" wall structure as in epidermis, the outermost layer of the human skin. "Bricks and mortar" pattern in keratin films has been fabricated using an ArF excimer laser (193 nm wavelength) and femtosecond laser (800 and 400 nm wavelength). Due to the very low ablation threshold of keratin, femtosecond laser systems are practical for laser processing of proteins. These model skin structures are fabricated for the first time that will help to produce potentially effective moisturizing products for the protection of skin from dryness, diseases and wrinkles.

  15. Jet formation in spallation of metal film from substrate under action of femtosecond laser pulse

    Energy Technology Data Exchange (ETDEWEB)

    Inogamov, N. A., E-mail: nailinogamov@googlemail.com [Russian Academy of Sciences, Landau Institute for Theoretical Physics (Russian Federation); Zhakhovskii, V. V. [Dukhov All-Russia Research Institute of Automatics (Russian Federation); Khokhlov, V. A. [Russian Academy of Sciences, Landau Institute for Theoretical Physics (Russian Federation)

    2015-01-15

    It is well known that during ablation by an ultrashort laser pulse, the main contribution to ablation of the substance is determined not by evaporation, but by the thermomechanical spallation of the substance. For identical metals and pulse parameters, the type of spallation is determined by film thickness d{sub f}. An important gauge is metal heating depth d{sub T} at the two-temperature stage, at which electron temperature is higher than ion temperature. We compare cases with d{sub f} < d{sub T} (thin film) and d{sub f} ≫ d{sub T} (bulk target). Radius R{sub L} of the spot of heating by an optical laser is the next (after d{sub f}) important geometrical parameter. The morphology of film bulging in cases where d{sub f} < d{sub T} on the substrate (blistering) changes upon a change in radius R{sub L} in the range from diffraction limit R{sub L} ∼ λ to high values of R{sub L} ≫ λ, where λ ∼ 1 μm is the wavelength of optical laser radiation. When d{sub f} < d{sub T}, R{sub L} ∼ λ, and F{sub abs} > F{sub m}, gold film deposited on the glass target acquires a cupola-shaped blister with a miniature frozen nanojet in the form of a tip on the circular top of the cupola (F{sub abs} and F{sub m} are the absorbed energy and the melting threshold of the film per unit surface area of the film). A new physical mechanism leading to the formation of the nanojet is proposed.

  16. Pulse shapes and surface effects in segmented germanium detectors

    Energy Technology Data Exchange (ETDEWEB)

    Lenz, Daniel

    2010-03-24

    It is well established that at least two neutrinos are massive. The absolute neutrino mass scale and the neutrino hierarchy are still unknown. In addition, it is not known whether the neutrino is a Dirac or a Majorana particle. The GERmanium Detector Array (GERDA) will be used to search for neutrinoless double beta decay of {sup 76}Ge. The discovery of this decay could help to answer the open questions. In the GERDA experiment, germanium detectors enriched in the isotope {sup 76}Ge are used as source and detector at the same time. The experiment is planned in two phases. In the first, phase existing detectors are deployed. In the second phase, additional detectors will be added. These detectors can be segmented. A low background index around the Q value of the decay is important to maximize the sensitivity of the experiment. This can be achieved through anti-coincidences between segments and through pulse shape analysis. The background index due to radioactive decays in the detector strings and the detectors themselves was estimated, using Monte Carlo simulations for a nominal GERDA Phase II array with 18-fold segmented germanium detectors. A pulse shape simulation package was developed for segmented high-purity germanium detectors. The pulse shape simulation was validated with data taken with an 19-fold segmented high-purity germanium detector. The main part of the detector is 18-fold segmented, 6-fold in the azimuthal angle and 3-fold in the height. A 19th segment of 5mm thickness was created on the top surface of the detector. The detector was characterized and events with energy deposited in the top segment were studied in detail. It was found that the metalization close to the end of the detector is very important with respect to the length of the of the pulses observed. In addition indications for n-type and p-type surface channels were found. (orig.)

  17. Comparison Study of Strong-Field Ionization of Molecules and Atoms by Bicircular Two-Color Femtosecond Laser Pulses.

    Science.gov (United States)

    Lin, Kang; Jia, Xinyan; Yu, Zuqing; He, Feng; Ma, Junyang; Li, Hui; Gong, Xiaochun; Song, Qiying; Ji, Qinying; Zhang, Wenbin; Li, Hanxiao; Lu, Peifen; Zeng, Heping; Chen, Jing; Wu, Jian

    2017-11-17

    We experimentally investigate the single and double ionization of N_{2} and O_{2} molecules in bicircular two-color femtosecond laser pulses, and compare with their companion atoms of Ar and Xe with comparable ionization thresholds. Electron recollision assisted enhanced ionization is observed in N_{2} and Ar by controlling the helicity and field ratio between the two colors, whereas the enhanced ionization via the recollision is almost absent in O_{2} and Xe. Our S-matrix simulations clearly reveal the crucial role of the detailed electronic structures of N_{2} and O_{2} on the two-dimensional recollision of the electrons driven by the bicircular two-color laser fields. As compared to Ar, the resonant multiphoton excitation dominates the double ionization of Xe.

  18. Pulse-shape discrimination technique in radioanalytical methods

    International Nuclear Information System (INIS)

    Vacik, J.; Hnatowicz, V.; Cervena, J.; Posta, S.

    1998-01-01

    Several successful techniques have been developed to eliminate unwanted background level in experimental radiation spectra. One of the background-reduction techniques is pulse-shape discrimination (PSD) which is based on the fact that different particles or quanta give rise to different spectrometer response, i.e. to different signal shapes. The shapes can be recognized and analyzed by appropriate electronic circuits which can measure either the rise time or the fall time of the pulses. The PSD technique has been suggested for different particle/background separations (such as n/γ, α/γ, α/proton or αa/electron separations). It has been successfully applied i.e. in separation of (fast) neutrons from intensive gamma background or charged particles from gammas. Recently the principle of the PSD has been applied in the construction of special ORTEC and CANBERRA spectroscopic modules. In this study we have employed the principle of PSD in two different radioanalytical methods developed in the Nuclear Research and Nuclear Physics Institutes in Rez. One of the methods concerns with the determination of uranium by delayed neutron counting (DNC), the second method is known as neutron depth profiling (NDP). An effective elimination of unwanted background signals in measured radiation spectra has been proved. At least two orders of magnitude of background level suppression has been achieved independently of employed PSD circuits. The PSD technique has substantially improved detection limits of the DNC and NDP facilities. (author)

  19. Femtosecond pulsed laser patterning of poly(3,4-ethylene dioxythiophene)-poly(styrenesulfonate) thin films on gold/palladium substrates

    International Nuclear Information System (INIS)

    McDonald, Joel P.; Hendricks, Jeffrey L.; Mistry, Vanita R.; Martin, David C.; Yalisove, Steven M.

    2007-01-01

    Femtosecond pulsed laser damage studies were performed on poly(3,4-ethylene dioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) films of varying thickness on Au/Pd substrates. The femtosecond laser induced damage thresholds of the PEDOT-PSS films were determined (0.007-0.03 J/cm 2 ) and were found to behave similarly to metallic conductors as a function of film thickness. Femtosecond laser patterning of the PEDOT-PSS films was also performed, with minimum wire widths of 1.4 μm produced at speeds of 1 mm/s. Discrete removal of the PEDOT-PSS films from the underlying substrate was also demonstrated, with the film cleared down to the depth of the substrate in linear channels as narrow as 4 μm while maintaining the integrity of the substrate

  20. Broadband Optical Active Waveguides Written by Femtosecond Laser Pulses in Lithium Fluoride

    Science.gov (United States)

    Ismael, Chiamenti; Francesca, Bonfigli; Anderson, S. L. Gomes; Rosa, Maria Montereali; Larissa, N. da Costa; Hypolito, J. Kalinowski

    2014-01-01

    Broadband waveguiding through light-emitting strips directly written in a blank lithium fluoride crystal with a femtosecond laser is reported. Light guiding was observed at several optical wavelengths, from blue, 458 nm, to near-infrared, at 1550 nm. Visible photoluminescence spectra of the optically active F2 and F3+ color centers produced by the fs laser writing process were measured. The wavelength-dependent refractive index increase was estimated to be in the order of 10-3-10-4 in the visible and near-infrared spectral intervals, which is consistent with the stable formation of point defects in LiF.

  1. Pulse-shape discrimination in the IGEX experiment

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez, D.; Morales, J. E-mail: jmorales@posta.unizar.es; Cebrian, S.; Garcia, E.; Irastorza, I.G.; Morales, A.; Ortiz de Solorzano, A.; Puimedon, J.; Sarsa, M.L.; Villar, J.A.; Aalseth, C.E.; Avignone, F.T.; Brodzinski, R.L.; Hensley, W.K.; Miley, H.S.; Reeves, J.H.; Kirpichnikov, I.V.; Vasenko, A.A.; Klimenko, A.A.; Osetrov, S.B.; Smolnikov, A.A.; Vasiliev, S.I.; Pogosov, V.S.; Tamanyan, A.G

    2003-12-11

    The IGEX experiment has been operating enriched germanium detectors in the Canfranc Underground Laboratory (Spain) in a search for the neutrinoless double decay of {sup 76}Ge. The implementation of pulse-shape discrimination techniques to reduce the radioactive background is described in detail. This analysis has been applied to a fraction of the IGEX data, leading to a rejection of {approx}60% of their background, in the region of interest (from 2 to 2.5 MeV), down to {approx}0.09 c/keV kg yr.

  2. Pulse-shape discrimination in the IGEX experiment

    International Nuclear Information System (INIS)

    Gonzalez, D.; Morales, J.; Cebrian, S.; Garcia, E.; Irastorza, I.G.; Morales, A.; Ortiz de Solorzano, A.; Puimedon, J.; Sarsa, M.L.; Villar, J.A.; Aalseth, C.E.; Avignone, F.T.; Brodzinski, R.L.; Hensley, W.K.; Miley, H.S.; Reeves, J.H.; Kirpichnikov, I.V.; Vasenko, A.A.; Klimenko, A.A.; Osetrov, S.B.; Smolnikov, A.A.; Vasiliev, S.I.; Pogosov, V.S.; Tamanyan, A.G.

    2003-01-01

    The IGEX experiment has been operating enriched germanium detectors in the Canfranc Underground Laboratory (Spain) in a search for the neutrinoless double decay of 76 Ge. The implementation of pulse-shape discrimination techniques to reduce the radioactive background is described in detail. This analysis has been applied to a fraction of the IGEX data, leading to a rejection of ∼60% of their background, in the region of interest (from 2 to 2.5 MeV), down to ∼0.09 c/keV kg yr

  3. Numerical simulation of microwave amplification in a plasma channel produced in a gas via multiphoton ionisation by a femtosecond laser pulse

    Energy Technology Data Exchange (ETDEWEB)

    Bogatskaya, A V; Popov, A M [P N Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Volkova, E A [D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

    2014-12-31

    This paper examines the evolution of a nonequilibrium plasma channel produced in xenon by a femtosecond KrF laser pulse. We demonstrate that such a channel can be used to amplify microwave pulses over times of the order of the relaxation time of the photoelectron energy spectrum in xenon. Using the slowly varying amplitude approximation, we analyse the propagation and amplification of an rf pulse in a plasma channel, in particular when the rf field influences the electron energy distribution function in the plasma. (interaction of laser radiation with matter. laser plasma)

  4. Laser alchemy: direct writing of multifunctional components in a glass chip with femtosecond laser pulses

    Science.gov (United States)

    Liao, Yang; Lin, Jintian; Cheng, Ya

    2013-12-01

    Recently, hybrid integration of multifunctional micro-components for creating complex, intelligent micro/nano systems has attracted significant attention. These micro-/nano-systems have important applications in a variety of areas, such as healthcare, environment, communication, national security, and so on. However, fabrication of micro/nano systems incorporated with different functions is still a challenging task, which generally requires fabrication of discrete microcomponents beforehand followed by assembly and packaging procedures. Furthermore, current micro-/nano-fabrication techniques are mainly based on the well-established planar lithographic approach, which suffer from severe issues in producing three dimensional (3D) structures with complex geometries and arbitrary configurations. In recent years, the rapid development of femtosecond laser machining technology has enabled 3D direct fabrication and integration of multifunctional components, such as microfluidics, microoptics, micromechanics, microelectronics, etc., into single substrates. In this invited talk, we present our recent progress in this active area. Particularly, we focus on fabrication of 3D micro- and nanofluidic devices and 3D high-Q microcavities in glass substrates by femtosecond laser direct writing.

  5. Red Shift and Broadening of Backward Harmonic Radiation from Electron Oscillations Driven by Femtosecond Laser Pulse

    International Nuclear Information System (INIS)

    Tian Youwei; Yu Wei; Lu Peixiang; Senecha, Vinod K; Han, Xu; Deng Degang; Li Ruxin; Xu Zhizhan

    2006-01-01

    The characteristics of backward harmonic radiation due to electron oscillations driven by a linearly polarized fs laser pulse are analysed considering a single electron model. The spectral distributions of the electron's backward harmonic radiation are investigated in detail for different parameters of the driver laser pulse. Higher order harmonic radiations are possible for a sufficiently intense driving laser pulse. We have shown that for a realistic pulsed photon beam, the spectrum of the radiation is red shifted as well as broadened because of changes in the longitudinal velocity of the electrons during the laser pulse. These effects are more pronounced at higher laser intensities giving rise to higher order harmonics that eventually leads to a continuous spectrum. Numerical simulations have further shown that by increasing the laser pulse width the broadening of the high harmonic radiations can be controlled

  6. Electron dynamics and optical properties modulation of monolayer MoS{sub 2} by femtosecond laser pulse: a simulation using time-dependent density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Su, Xiaoxing; Jiang, Lan [Beijing Institute of Technology, Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing (China); Wang, Feng [Beijing Institute of Technology, School of Physics, Beijing (China); Su, Gaoshi [Beijing Institute of Technology, School of Mechatronical Engineering, Beijing (China); Qu, Liangti [Beijing Institute of Technology, Key Laboratory of Cluster Science, Ministry of Education, School of Chemistry, Beijing (China); Lu, Yongfeng [University of Nebraska-Lincoln, Department of Electrical Engineering, Lincoln, NE (United States)

    2017-07-15

    In this study, we adopted time-dependent density functional theory to investigate the optical properties of monolayer MoS{sub 2} and the effect of intense few-cycle femtosecond laser pulses on these properties. The electron dynamics of monolayer MoS{sub 2} under few-cycle and multi-cycle laser irradiation were described. The polarization direction of the laser had a marked effect on the energy absorption and electronic excitation of monolayer MoS{sub 2} because of anisotropy. Change in the polarization direction of few-cycle pulse changed the absorbed energy by a factor over 4000. Few-cycle pulse showed a higher sensitivity to the electronic property of material than multi-cycle pulse. The modulation of the dielectric properties of the material was observed on the femtosecond time scale. The negative divergence appeared in the real part of the function at low frequencies and photoinduced blue shift occurred due to Burstein-Moss effect. The irradiation of femtosecond laser caused the dielectric response within the infrared region and introduced anisotropy to the in-plane optical properties. Laser-based engineering of optical properties through controlling transient electron dynamics expands the functionality of MoS{sub 2} and has potential applications in direction-dependent optoelectronic devices. (orig.)

  7. Population Transfer between Two Quantum States by Piecewise Chirping of Femtosecond Pulses: Theory and Experiment

    International Nuclear Information System (INIS)

    Zhdanovich, S.; Shapiro, E. A.; Shapiro, M.; Hepburn, J. W.; Milner, V.

    2008-01-01

    We propose and experimentally demonstrate the method of population transfer by piecewise adiabatic passage between two quantum states. Coherent excitation of a two-level system with a train of ultrashort laser pulses is shown to reproduce the effect of an adiabatic passage, conventionally achieved with a single frequency-chirped pulse. By properly adjusting the amplitudes and phases of the pulses in the excitation pulse train, we achieve complete and robust population transfer to the target state. The piecewise nature of the process suggests a possibility for the selective population transfer in complex quantum systems

  8. Laser Pulse Shaping for Ultrahigh Intensity Compton Scattering*

    Science.gov (United States)

    Troha, A. L.; Le Sage, G. P.; Bennett, C.; Kolner, B. H.; Heritage, J. P.; Hartemann, F. V.; Luhmann, N. C., Jr.

    1996-11-01

    At ultrahigh intensities, where the normalized vector potential associated with the laser wave exceeds unity, the electron axial velocity modulation due to radiation pressure yields nonlinear Compton backscattered spectra. For applications requiring a narrow Doppler upshifted linewidth, such as the future g-g collider or focused X-ray generation, this poses a serious problem. It is shown that temporal laser pulse shaping using holographic (spectral) filtering at the Fourier plane of a chirped pulse laser amplifier, or similar approaches, can alleviate this problem, and that this technique can be scaled to the required multi-TW range. In particular, Compton backscattered spectra are calculated in the case of the optical square pulses similar to those experimentally observed by Weiner et al. Issues such as nonlinear effects, higher-order dispersion, 3D effects and optical noise are also discussed. *Work supported in part by DoD/AFOSR (MURI) F49620-95-1-0253, AFOSR (ATRI) F30602-94-2-001, ARO DAAHO4-95-1-0336 and LLNL/LDRD DoE W-7405-ENG-48

  9. Investigation of the particle size distribution of the ejected material generated during the single femtosecond laser pulse ablation of aluminium

    International Nuclear Information System (INIS)

    Wu, Han; Zhang, Nan; Zhu, Xiaonong

    2014-01-01

    Highlights: • Single 50 fs laser pulse ablation of an aluminium target in vacuum is investigated in our experiments. • Nanoparticles with large radii of several hundred nanometers are observed. • The nanoparticles are most likely from the mechanical tensile stress relaxation. - Abstract: Single femtosecond laser pulses are employed to ablate an aluminium target in vacuum, and the particle size distribution of the ablated material deposited on a mica substrate is examined with atomic force microscopy (AFM). The recorded AFM images show that these particles have a mean radius of several tens of nanometres. It is also determined that the mean radius of these deposited nanoparticles increases when the laser fluence at the aluminium target increases from 0.44 J/cm 2 to 0.63 J/cm 2 . The mechanism of the laser-induced nanoparticle generation is thought to be photomechanical tensile stress relaxation. Raman spectroscopy measurements confirm that the nanoparticles thus produced have the same structure as the bulk aluminium

  10. Design and optimization of fiber optical parametric oscillators for femtosecond pulse generation.

    Science.gov (United States)

    Zhang, Wen Qi; Sharping, Jay E; White, Richard T; Monro, Tanya M; Afshar V, Shahraam

    2010-08-02

    In this paper, we use a genetic algorithm and pulse-propagation analysis to design and optimize optical parametric oscillators based on soft-glass microstructured optical fibers. The maximum parametric gain, phase-match, walk-off between pump (1560 nm) and signal (880 nm) pulses, signal feedback ratio and signal-pump synchronization of the cavity are optimized. Pulse propagation analysis suggests that one can implement a fiber optical parametric oscillator capable of generating approximately 200-fs pulses at 880 nm with 43% peak-power conversion, high output pulse quality (time-bandwidth product approximately 0.43) and a wavelength tuning range that is limited only by the glass transmission windows.

  11. Laboratory transferability of optimally shaped laser pulses for quantum control

    International Nuclear Information System (INIS)

    Moore Tibbetts, Katharine; Xing, Xi; Rabitz, Herschel

    2014-01-01

    Optimal control experiments can readily identify effective shaped laser pulses, or “photonic reagents,” that achieve a wide variety of objectives. An important additional practical desire is for photonic reagent prescriptions to produce good, if not optimal, objective yields when transferred to a different system or laboratory. Building on general experience in chemistry, the hope is that transferred photonic reagent prescriptions may remain functional even though all features of a shaped pulse profile at the sample typically cannot be reproduced exactly. As a specific example, we assess the potential for transferring optimal photonic reagents for the objective of optimizing a ratio of photoproduct ions from a family of halomethanes through three related experiments. First, applying the same set of photonic reagents with systematically varying second- and third-order chirp on both laser systems generated similar shapes of the associated control landscape (i.e., relation between the objective yield and the variables describing the photonic reagents). Second, optimal photonic reagents obtained from the first laser system were found to still produce near optimal yields on the second laser system. Third, transferring a collection of photonic reagents optimized on the first laser system to the second laser system reproduced systematic trends in photoproduct yields upon interaction with the homologous chemical family. These three transfers of photonic reagents are demonstrated to be successful upon paying reasonable attention to overall laser system characteristics. The ability to transfer photonic reagents from one laser system to another is analogous to well-established utilitarian operating procedures with traditional chemical reagents. The practical implications of the present results for experimental quantum control are discussed

  12. Comparative study of ornamental granite cleaning using femtosecond and nanosecond pulsed lasers

    Energy Technology Data Exchange (ETDEWEB)

    Rivas, T., E-mail: trivas@uvigo.es [Dpto. Ingeniería de los Recursos Naturales y Medioambiente. E.T.S. Ingeniería de Minas, Universidad de Vigo, 36200 Vigo Spain (Spain); Lopez, A.J.; Ramil, A. [Centro de Investigaciones Tecnológicas. Campus de Esteiro. Universidad de A Coruña 15403 Ferrol Spain (Spain); Pozo, S. [Dpto. Ingeniería de los Recursos Naturales y Medioambiente. E.T.S. Ingeniería de Minas, Universidad de Vigo, 36200 Vigo Spain (Spain); Fiorucci, M.P. [Centro de Investigaciones Tecnológicas. Campus de Esteiro. Universidad de A Coruña 15403 Ferrol Spain (Spain); Silanes, M.E. López de [Dpto. Ingeniería de los Recursos Naturales y Medioambiente. E.I. Forestales. Universidad de Vigo, Campus Pontevedra. 36005 Pontevedra Spain (Spain); García, A.; Aldana, J. R. Vazquez de; Romero, C.; Moreno, P. [Grupo de Investigación en Microprocesado de Materiales con Laser. Facultad de Ciencias, Universidad de Salamanca, 37008 Salamanca Spain (Spain)

    2013-08-01

    Granite has been widely used as a structural and ornamental element in public works and buildings. In damp climates it is almost permanently humid and its exterior surfaces are consequently biologically colonized and blackened We describe a comparative analysis of the performance of two different laser sources in removing biological crusts from granite surfaces: nanosecond Nd:YVO{sub 4} laser (355 nm) and femtosecond Ti:Sapphire laser at its fundamental wavelength (790 nm) and second harmonic (395 nm). The granite surface was analyzed using scanning electron microscopy, attenuated total reflection – Fourier transform infrared spectroscopy and profilometry, in order to assess the degree of cleaning and to characterize possible morphological and chemical changes caused by the laser sources.

  13. Comparative study of ornamental granite cleaning using femtosecond and nanosecond pulsed lasers

    International Nuclear Information System (INIS)

    Rivas, T.; Lopez, A.J.; Ramil, A.; Pozo, S.; Fiorucci, M.P.; Silanes, M.E. López de; García, A.; Aldana, J. R. Vazquez de; Romero, C.; Moreno, P.

    2013-01-01

    Granite has been widely used as a structural and ornamental element in public works and buildings. In damp climates it is almost permanently humid and its exterior surfaces are consequently biologically colonized and blackened We describe a comparative analysis of the performance of two different laser sources in removing biological crusts from granite surfaces: nanosecond Nd:YVO 4 laser (355 nm) and femtosecond Ti:Sapphire laser at its fundamental wavelength (790 nm) and second harmonic (395 nm). The granite surface was analyzed using scanning electron microscopy, attenuated total reflection – Fourier transform infrared spectroscopy and profilometry, in order to assess the degree of cleaning and to characterize possible morphological and chemical changes caused by the laser sources.

  14. Multi-channel, fiber-based seed pulse distribution system for femtosecond-level synchronized chirped pulse amplifiers.

    Science.gov (United States)

    Horáček, Martin; Indra, Lukáš; Green, Jonathan T; Naylon, Jack A; Tykalewicz, Boguslaw; Novák, Jakub; Batysta, František; Mazanec, Tomáš; Horáček, Jakub; Antipenkov, Roman; Hubka, Zbyněk; Boge, Robert; Bakule, Pavel; Rus, Bedřich

    2017-01-01

    We report on the design and performance of a fiber-based, multi-channel laser amplifier seed pulse distribution system. The device is designed to condition and distribute low energy laser pulses from a mode-locked oscillator to multiple, highly synchronized, high energy amplifiers integrated into a laser beamline. Critical functions such as temporal pulse stretching well beyond 100 ps/nm, pulse picking, and fine control over the pulse delay up to 300 ps are all performed in fiber eliminating the need for bulky and expensive grating stretchers, Pockels cells, and delay lines. These functions are characterized and the system as a whole is demonstrated by seeding two high energy amplifiers in the laser beamline. The design of this system allows for complete computer control of all functions, including tuning of dispersion, and is entirely hands-free. The performance of this device and its subsystems will be relevant to those developing lasers where reliability, size, and cost are key concerns in addition to performance; this includes those developing large-scale laser systems similar to ours and also those developing table-top experiments and commercial systems.

  15. Incubation behaviour in triazenepolymer thin films upon near-infrared femtosecond laser pulse irradiation

    International Nuclear Information System (INIS)

    Bonse, J; Wiggins, S M; Solis, J; Sturm, H; Urech, L; Wokaun, A; Lippert, T

    2007-01-01

    The effects of laser radiation induced by a sequence of ultrashort (130 fs), near-infrared (800 nm) Ti:sapphire laser pulses in ∼1 μm thick triazenepolymer films on glass substrates have been investigated by means of in-situ real-time reflectivity measurements featuring a ps-resolution streak camera and a ns-resolution photodiode set-up. The polymer films show incubation effects when each laser pulse in the sequence has a fluence below the single-pulse damage threshold. Non-damage conditions are maintained for several incubation pulses such that the reflectivity of the film shows a rapid decrease of up to 30% within 1 ns but subsequently recovers to its initial value on a ms timescale. Additional pulses lead to a permanent film damage. The critical number of laser pulses needed to generate a permanent damage of the film has been studied as a function of the laser fluence. Once damage is created, further laser pulses cause a partial removal of the film material from the glass substrate. Scanning force microscopy has been used to characterise ex-situ the irradiated surface areas. Based on these complementary measurements possible incubation mechanisms are discussed

  16. Nonlinear Maxwell's and Schrodinger equations for describing the volumetric interaction of femtosecond laser pulses with transparent solid dielectrics: effect of the boundary conditions

    Czech Academy of Sciences Publication Activity Database

    Zhukov, V.P.; Bulgakova, Nadezhda M.; Fedoruk, M.P.

    2017-01-01

    Roč. 84, č. 7 (2017), s. 439-446 ISSN 1070-9762 R&D Projects: GA MŠk LO1602; GA ČR GA16-12960S Institutional support: RVO:68378271 Keywords : glass * femtosecond laser pulses * Maxwell's and Schrdinger equations Subject RIV: BH - Optics, Masers, Lasers OBOR OECD: Optics (including laser optics and quantum optics) Impact factor: 0.299, year: 2016

  17. Femtosecond laser ablation of silver foil with single and double pulses

    CSIR Research Space (South Africa)

    Roberts, DE

    2009-01-01

    Full Text Available /apsusc r ablation of silver foil with single and double pulses, Appl. Surf. D.E. Roberts et al. / Applied Surface Science xxx (2009) xxx–xxx2 G Model APSUSC-19322; No of Pages 9 pulses used for ablation. While there has been much overlap in the aims... value r ablation of silver foil with single and double pulses, Appl. Surf. ; lon D.E. Roberts et al. / Applied Surface Science xxx (2009) xxx–xxx 3 G Model APSUSC-19322; No of Pages 9 Fig. 1. Surface temperature versus time calculated for double...

  18. Femtosecond laser ablation of silver foil with single and double pulses

    CSIR Research Space (South Africa)

    Roberts, DE

    2009-01-01

    Full Text Available ¼ v2 2 ln E Eth � � (7) so that the waist v at the focus and hence the peak F = 2E/pv2 could be found from the slope of r20 versus ln(E). Absolute values of F were estimated to have an uncertainty of �15%. A Michelson interferometer, with one... was used to check the pulse separation for the Dazzler and the zero crossing of the pulse separation from the Michelson interferometer. 4. Results and discussion The average ablation depth per pulse to penetrate a 50 mm thick Ag foil as a function...

  19. Ultra-short pulse generation in a linear femtosecond fiber laser using a Faraday rotator mirror and semiconductor saturable absorber mirror

    Science.gov (United States)

    Hekmat, M. J.; Gholami, A.; Omoomi, M.; Abdollahi, M.; Bagheri, A.; Normohammadi, H.; Kanani, M.; Ebrahimi, A.

    2018-02-01

    An innovative method for obtaining ultra-short and perfectly stable femtosecond pulses in a linear erbium-doped fiber laser is proposed. A commercial semiconductor saturable absorber mirror and a standard Faraday rotator are used in both sides of the linear fiber optic laser configuration to shorten the pulse duration and suppress undesirable effects on the polarization state. The laser operation is investigated theoretically using a physical model and it is verified using experimental results. The main idea of this research is to apply a Faraday rotator mirror for pulse shortening purposes. For this reason, two types of Er-doped fiber optics with different group velocity dispersion parameters are used to achieve the optimum net group velocity dispersion in the cavity. Output results demonstrate good consistency between theory and experimental results. The output power of the linear oscillator is approximately 45 mW with 135 fs pulses at the 23.5 MHz repetition rate without any pulse compression.

  20. THz field engineering in two-color femtosecond filaments using chirped and delayed laser pulses

    Science.gov (United States)

    Nguyen, A.; González de Alaiza Martínez, P.; Thiele, I.; Skupin, S.; Bergé, L.

    2018-03-01

    We numerically study the influence of chirping and delaying several ionizing two-color light pulses in order to engineer terahertz (THz) wave generation in air. By means of comprehensive 3D simulations, it is shown that two chirped pulses can increase the THz yield when they are separated by a suitable time delay for the same laser energy in focused propagation geometry. To interpret these results, the local current theory is revisited and we propose an easy, accessible all-optical criterion that predicts the laser-to-THz conversion efficiencies given any input laser spectrum. In the filamentation regime, numerical simulations display evidence that a chirped pulse is able to produce more THz radiation due to propagation effects, which maintain the two colors of the laser field more efficiently coupled over long distances. A large delay between two pulses promotes multi-peaked THz spectra as well as conversion efficiencies above 10‑4.

  1. Analysis of pulse-shape discrimination techniques for BC501A using GHz digital signal processing

    International Nuclear Information System (INIS)

    Rooney, B.D.; Dinwiddie, D.R.; Nelson, M.A.; Rawool-Sullivan, Mohini W.

    2001-01-01

    A comparison study of pulse-shape analysis techniques was conducted for a BC501A scintillator using digital signal processing (DSP). In this study, output signals from a preamplifier were input directly into a 1 GHz analog-to-digital converter. The digitized data obtained with this method was post-processed for both pulse-height and pulse-shape information. Several different analysis techniques were evaluated for neutron and gamma-ray pulse-shape discrimination. It was surprising that one of the simplest and fastest techniques resulted in some of the best pulse-shape discrimination results. This technique, referred to here as the Integral Ratio technique, was able to effectively process several thousand detector pulses per second. This paper presents the results and findings of this study for various pulse-shape analysis techniques with digitized detector signals.

  2. Recent developments in plastic scintillators with pulse shape discrimination

    Science.gov (United States)

    Zaitseva, N. P.; Glenn, A. M.; Mabe, A. N.; Carman, M. L.; Hurlbut, C. R.; Inman, J. W.; Payne, S. A.

    2018-05-01

    The paper reports results of studies conducted to improve scintillation performance of plastic scintillators capable of neutron/gamma pulse-shape discrimination (PSD). Compositional modifications made with the polymer matrix improved physical stability, allowing for increased loads of the primary dye that, in combination with selected secondary dyes, provided enhanced PSD especially important for the lower energy ranges. Additional measurements were made with a newly-introduced PSD plastic EJ-276, that replaces the first commercially produced EJ-299. Comparative studies conducted with the new materials and EJ-309 liquids at large scale (up to 10 cm) show that current plastics may provide scintillation and PSD performance sufficient for the replacement of liquid scintillators. Comparison to stilbene single crystals compliments the information about the status of the solid-state materials recently developed for fast neutron detection applications.

  3. Comparison of analog and digital pulse-shape-discrimination systems

    Energy Technology Data Exchange (ETDEWEB)

    Sosa, C.S., E-mail: cssosa@umich.edu; Flaska, M.; Pozzi, S.A.

    2016-08-01

    Pulse shape discrimination (PSD) performance of two optimized PSD systems (one digital and one analog) is compared in this work. One system uses digital charge integration, while the other system uses analog zero crossing. Measurements were conducted with each PSD system using the CAEN V1720 (250 MHz) data acquisition system. An organic-liquid scintillator, coupled to a photo-multiplier tube, was used to detect neutrons and gamma rays from a Cf-252 spontaneous-fission source. The PSD performance of both systems was optimized and quantified using a traditional figure-of-merit (FOM) approach. FOM's were found for three, 300 keVee light-output bins, spanning from 100 to 1000 keVee, and one larger bin from 100 to 1800 keVee. Digital PSD outperformed analog PSD in the lowest light-output bin by approximately 50%, and by 11% for the highest light-output bin.

  4. Pulse shape discrimination in helium-4 scintillation detectors

    Energy Technology Data Exchange (ETDEWEB)

    Kelley, Ryan P., E-mail: rpkelley@ufl.edu; Enqvist, Andreas; Jordan, Kelly A.

    2016-09-11

    Three algorithms were investigated for discriminating between neutrons and gamma rays in a pressurized {sup 4}He gas fast neutron detector: charge comparison, weighted integration, and neutron-gamma model analysis (NGMA). For each algorithm, a comprehensive pulse shape discrimination study was conducted using time-of-flight measurements, receiver operator characteristic curves, figure of merit performance measures, and a comparison of performance between {sup 252}Cf and PuBe mixed neutron/gamma sources. The NGMA method was found to have the best overall performance by both the figure of merit and the receiver operator characteristic curve. The results also illustrated the high gamma rejection efficiency of these detectors, which is desirable in a variety of neutron monitoring applications.

  5. Femtosecond Fiber Lasers Based on Dissipative Processes for Nonlinear Microscopy

    Science.gov (United States)

    Wise, Frank W.

    2012-01-01

    Recent progress in the development of femtosecond-pulse fiber lasers with parameters appropriate for nonlinear microscopy is reviewed. Pulse-shaping in lasers with only normal-dispersion components is briefly described, and the performance of the resulting lasers is summarized. Fiber lasers based on the formation of dissipative solitons now offer performance competitive with that of solid-state lasers, but with the benefits of the fiber medium. Lasers based on self-similar pulse evolution in the gain section of a laser also offer a combination of short pulse duration and high pulse energy that will be attractive for applications in nonlinear bioimaging. PMID:23869163

  6. A pulse-shape discrimination method for improving Gamma-ray spectrometry based on a new digital shaping filter

    Science.gov (United States)

    Qin, Zhang-jian; Chen, Chuan; Luo, Jun-song; Xie, Xing-hong; Ge, Liang-quan; Wu, Qi-fan

    2018-04-01

    It is a usual practice for improving spectrum quality by the mean of designing a good shaping filter to improve signal-noise ratio in development of nuclear spectroscopy. Another method is proposed in the paper based on discriminating pulse-shape and discarding the bad pulse whose shape is distorted as a result of abnormal noise, unusual ballistic deficit or bad pulse pile-up. An Exponentially Decaying Pulse (EDP) generated in nuclear particle detectors can be transformed into a Mexican Hat Wavelet Pulse (MHWP) and the derivation process of the transform is given. After the transform is performed, the baseline drift is removed in the new MHWP. Moreover, the MHWP-shape can be discriminated with the three parameters: the time difference between the two minima of the MHWP, and the two ratios which are from the amplitude of the two minima respectively divided by the amplitude of the maximum in the MHWP. A new type of nuclear spectroscopy was implemented based on the new digital shaping filter and the Gamma-ray spectra were acquired with a variety of pulse-shape discrimination levels. It had manifested that the energy resolution and the peak-Compton ratio were both improved after the pulse-shape discrimination method was used.

  7. Ablation mass features in multi-pulses femtosecond laser ablate molybdenum target

    Science.gov (United States)

    Zhao, Dongye; Gierse, Niels; Wegner, Julian; Pretzler, Georg; Oelmann, Jannis; Brezinsek, Sebastijan; Liang, Yunfeng; Neubauer, Olaf; Rasinski, Marcin; Linsmeier, Christian; Ding, Hongbin

    2018-03-01

    In this study, the ablation mass features related to reflectivity of bulk Molybdenum (Mo) were investigated by a Ti: Sa 6 fs laser pulse at central wavelength 790 nm. The ablated mass removal was determined using Confocal Microscopy (CM) technique. The surface reflectivity was calibrated and measured by a Lambda 950 spectrophotometer as well as a CCD camera during laser ablation. The ablation mass loss per pulse increase with the increasing of laser shots, meanwhile the surface reflectivity decrease. The multi-pulses (100 shots) ablation threshold of Mo was determined to be 0.15 J/cm2. The incubation coefficient was estimated as 0.835. The reflectivity change of the Mo target surface following multi-pulses laser ablation were studied as a function of laser ablation shots at various laser fluences from 1.07 J/cm2 to 36.23 J/cm2. The results of measured reflectivity indicate that surface reflectivity of Mo target has a significant decline in the first 3-laser pulses at the various fluences. These results are important for developing a quantitative analysis model for laser induced ablation and laser induced breakdown spectroscopy for the first wall diagnosis of EAST tokamak.

  8. The effect of the two tailored femtosecond laser pulses in the enhancement of methane dissociation

    International Nuclear Information System (INIS)

    Sadighi-Bonabi, R.; Dehghani, Z.; Irani, E.

    2010-01-01

    Complete text of publication follows. Based on the gradient optimization method a useful approach for dissociation of the methane molecule is introduced. This analytical model produces an optimized two tailored rectangular laser pulses which dissociates the molecular ion CH 4 + with maximum probability of 1. In this approach the field assisted dissociation is used by a semi-classical view. It is assumed that only the selective dissociative bond is in direction of the laser electric field are effective. Saturation is found for dissociation of the mentioned molecular bond, where the first pulse should have higher intensity than the second pulse. In addition to that, the sensitivity of the dissociation probability to the initial bond length and the control of the desired product channel by variation of the laser intensity and its duration of laser field is presented.

  9. Femtosecond pulse-width dependent trapping and directional ejection dynamics of dielectric nanoparticles

    KAUST Repository

    Chiang, Weiyi

    2013-09-19

    We demonstrate that laser pulse duration, which determines its impulsive peak power, is an effective parameter to control the number of optically trapped dielectric nanoparticles, their ejections along the directions perpendicular to polarization vector, and their migration distances from the trapping site. This ability to controllably confine and eject the nanoparticle is explained by pulse width-dependent optical forces exerted on nanoparticles in the trapping site and ratio between the repulsive and attractive forces. We also show that the directional ejections occur only when the number of nanoparticles confined in the trapping site exceeds a definite threshold. We interpret our data by considering the formation of transient assembly of the optically confined nanoparticles, partial ejection of the assembly, and subsequent filling of the trapping site. The understanding of optical trapping and directional ejections by ultrashort laser pulses paves the way to optically controlled manipulation and sorting of nanoparticles. © 2013 American Chemical Society.

  10. Time-resolved structural dynamics of thin metal films heated with femtosecond optical pulses.

    Science.gov (United States)

    Chen, Jie; Chen, Wei-Kan; Tang, Jau; Rentzepis, Peter M

    2011-11-22

    We utilize 100 fs optical pulses to induce ultrafast disorder of 35- to 150-nm thick single Au(111) crystals and observe the subsequent structural evolution using 0.6-ps, 8.04-keV X-ray pulses. Monitoring the picosecond time-dependent modulation of the X-ray diffraction intensity, width, and shift, we have measured directly electron/phonon coupling, phonon/lattice interaction, and a histogram of the lattice disorder evolution, such as lattice breath due to a pressure wave propagating at sonic velocity, lattice melting, and recrystallization, including mosaic formation. Results of theoretical simulations agree and support the experimental data of the lattice/liquid phase transition process. These time-resolved X-ray diffraction data provide a detailed description of all the significant processes induced by ultrafast laser pulses impinging on thin metallic single crystals.

  11. Train of high-power femtosecond pulses: Probe wave in a gas of prepared atoms

    Science.gov (United States)

    Muradyan, Gevorg; Muradyan, Atom Zh.

    2009-09-01

    We present a method for generating a regular train of ultrashort optical pulses in a prepared two-level medium. The train develops from incident monochromatic probe radiation traveling in a medium of atoms, which are in a quantum mechanical superposition of dressed internal states. In the frame of linear theory for the probe radiation, the energy of individual pulses is an exponentially growing function of atom density and of interaction cross section. Pulse repetition rate is determined by the pump field’s generalized Rabi frequency and can be around 1 THz and greater. We also show that the terms, extra to the dipole approximation, endow the gas by a new property: nonsaturating dependence of refractive index on dressing monochromatic field intensity. Contribution of these nonsaturating terms can be compatible with the main dipole approximation term contribution in the wavelength region of about ten micrometers (the range of CO2 laser) or larger.

  12. Improved reproducibility of conical emission from glass under axicon focusing of femtosecond laser pulse

    Science.gov (United States)

    Chekalin, S. V.; Kompanets, V. O.; Kosareva, O. G.; Grigor'evskii, A. V.; Kandidov, V. P.

    2007-06-01

    The supercontinuum conical emission of a 50-fs laser pulse focused into a Κ 108 glass is studied experimentally and numerically. It is found that, as the pulse energy was increased from 2 to 30 uj, the continuous picture of conical emission decomposed into speckles upon focusing with a lens and split into narrow rings upon focusing with an axicon. Preserving of distinct interference picture under more than 1000 shots exposure evidences in favor of much more stable positioning of microfilament in the case of axicon.

  13. Spot size and pulse number dependence of femtosecond laser ablation thresholds of silicon and stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Armbruster, Oskar; Naghilou, Aida [University of Vienna, Department of Physical Chemistry, Währinger Straße 42, A-1090 Vienna (Austria); Kitzler, Markus [TU Wien, Photonics Institute, Gusshausstraße 27-29, A-1040 Vienna (Austria); Kautek, Wolfgang, E-mail: wolfgang.kautek@univie.ac.at [University of Vienna, Department of Physical Chemistry, Währinger Straße 42, A-1090 Vienna (Austria)

    2017-02-28

    Highlights: • Influence of laser spot size and pulse number on the ablation of solids. • An extended defect model describes the dependence of the threshold fluence on the basis of high and low density defects. • Successfully applied to silicon and stainless steel. - Abstract: Laser spot size and pulse number are two major parameters influencing the ablation of solids. The extended defect model describes the dependence of the threshold fluence on the basis of high and low density defects. This model was successfully applied to silicon and stainless steel. It is demonstrated that heat accumulation cannot describe the experimental results.

  14. The application of pulse shape discrimination in NE 213 to neutron spectrometry

    International Nuclear Information System (INIS)

    Perkins, L.J.; Scott, M.C.

    1979-01-01

    The use of a zero-crossing pulse shape discrimination technique to distinguish protons from alpha particles in NE 213 is described, and a theoretical analysis is performed to predict the zero crossing characteristics. It is shown that, irrespective of the particular method of pulse shape discrimination employed, the pulse shape at low energies no longer uniquely determines the particle type for electrons, protons, alpha particles or 12 C nuclei, and the general limitations of pulse shape discrimination in NE 213 are deduced. The use of an alpha discrimination technique is then discribed, enabling neutron spectra to be unfolded from the measured detector response using a differential code. (orig.)

  15. The temperature dependence of pulse shape discrimination with NE213 scintillation counters

    International Nuclear Information System (INIS)

    Galloway, R.B.; Sharaf, J.M.

    1984-01-01

    The temperature dependence of the pulse shape discrimination between neutrons and gamma rays has been investigated for two scintillation counters using NE213 liquid scintillator. One counter used the zero cross-over timing technique of pulse shape discrimination and showed no significant temperature dependence over the range 35 to -8 0 C. The other used the space charge saturation technique of pulse shape discrimination and showed a marked temperature dependence. The findings are compared with previously published contradictory results. The influence of temperature on the gain of the detectors is found to be more important than the influence on the pulse shape discrimination. (orig.)

  16. FY 1999 report on the results of the R and D of femtosecond technology. Development of ultra-short pulse optoelectronics technology; 1999 nendo femutobyo technology no kenkyu kaihatsu seika hokokusho. Chotan pulse hikari electronics gijutsu kaihatsu

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2000-03-01

    The paper described the FY 1999 results of the R and D of femtosecond technology. For the purpose of creating new industrial basement technology which supports the highly information-oriented society in the 21st century, the ultra-high speed electronics technology is indispensable which is beyond speed limits of the existing electronics technology and has new functionality. The ultra-high speed electronics basement technology is established through the R and D of the technology to control the state of light and electronics in the femtosecond time domain (10{sup -15} - 10{sup -12} second). Themes of the R and D are technology to generate/transmit femtosecond optical pulse, technology for control/distribution, and ultra-short pulse optoelectronics common basement technology. In FY 1999, a lot of results were obtained in the following: generation of the pulse train highly repeated at 500GHz in semiconductor laser; 139km transmission of 250fs optical pulse; switching movement at ultra-high speed of 150fs-1.2ps in transition among subbands of GaN base and Sb base materials; DEMUXA movement toward 160-10Gb/s in Mach-Zehnder type optical switch. (NEDO)

  17. Solitonic supercontinuum of femtosecond mid-IR pulses in W-type index tellurite fibers with two zero dispersion wavelengths

    Directory of Open Access Journals (Sweden)

    S. Kedenburg

    2016-11-01

    Full Text Available We present a detailed experimental parameter study on mid-IR supercontinuum generation in W-type index tellurite fibers, which reveals how the core diameter, pump wavelength, fiber length, and pump power dramatically influence the spectral broadening. As pump source, we use femtosecond mid-IR pulses from a post-amplified optical parametric oscillator tunable between 1.7 μm and 4.1 μm at 43 MHz repetition rate. We are able to generate red-shifted dispersive waves up to a wavelength of 5.1 μm by pumping a tellurite fiber in the anomalous dispersion regime between its two zero dispersion wavelengths. Distinctive soliton dynamics can be identified as the main broadening mechanism resulting in a maximum spectral width of over 2000 nm with output powers of up to 160 mW. We experimentally demonstrated that efficient spectral broadening with considerably improved power proportion in the important first atmospheric transmission window between 3 and 5 μm can be achieved in robust W-type tellurite fibers pumped at long wavelengths by ultra-fast lasers.

  18. Revealing silent vibration modes of nanomaterials by detecting anti-Stokes hyper-Raman scattering with femtosecond laser pulses.

    Science.gov (United States)

    Zeng, Jianhua; Chen, Lei; Dai, Qiaofeng; Lan, Sheng; Tie, Shaolong

    2016-01-21

    We proposed a scheme in which normal Raman scattering is coupled with hyper-Raman scattering for generating a strong anti-Stokes hyper-Raman scattering in nanomaterials by using femtosecond laser pulses. The proposal was experimentally demonstrated by using a single-layer MoS2 on a SiO2/Si substrate, a 17 nm-thick MoS2 on an Au/SiO2 substrate and a 9 nm-thick MoS2 on a SiO2-SnO2/Ag/SiO2 substrate which were confirmed to be highly efficient for second harmonic generation. A strong anti-Stokes hyper-Raman scattering was also observed in other nanomaterials possessing large second-order susceptibilities, such as silicon quantum dots self-assembled into "coffee" rings and tubular Cu-doped ZnO nanorods. In all the cases, many Raman inactive vibration modes were clearly revealed in the anti-Stokes hyper-Raman scattering. Apart from the strong anti-Stokes hyper-Raman scattering, Stokes hyper-Raman scattering with small Raman shifts was detected during the ablation process of thick MoS2 layers. It was also observed by slightly defocusing the excitation light. The detection of anti-Stokes hyper-Raman scattering may serve as a new technique for studying the Raman inactive vibration modes in nanomaterials.

  19. Effect of an electric field on air filament decay at the trail of an intense femtosecond laser pulse.

    Science.gov (United States)

    Bodrov, Sergey; Aleksandrov, Nickolay; Tsarev, Maxim; Murzanev, Alexey; Kochetov, Igor; Stepanov, Andrey

    2013-05-01

    Air plasma density decay in a filament produced by an intense femtosecond laser pulse in an external electric field was investigated experimentally and theoretically. It was demonstrated by means of the terahertz scattering technique that the rate of plasma decay decreases with increasing electric field. At the electric field of 7 kV/cm the lifetime of plasma with the density above 10(16) cm(-3) was prolonged from 0.5 ns to 1 ns. Numerical simulation of electron density decay and electron temperature evolution was performed, taking into consideration dissociative and three-body electron-ion recombination as well as formation of complex positive ions. The simulation showed that under the electric field the electron temperature evolves nonmonotonically and passes through a minimum due to varying contribution of electron-ion collisions to electron heating in the field. The rate of three-body electron recombination with O(2)(+) ions of 2×10(-19)(300/T(e))(9/2) cm(6)/s was found from the experimental measurements at electron temperatures in the 0.25-0.4 eV range and electron densities in the 10(15)-10(17) cm(-3) range.

  20. Measurements of sound velocity in iron-nickel alloys by femtosecond laser pulses in a diamond anvil cell

    Science.gov (United States)

    Wakamatsu, Tatsuya; Ohta, Kenji; Yagi, Takashi; Hirose, Kei; Ohishi, Yasuo

    2018-01-01

    By comparing the seismic wave velocity profile in the Earth with laboratory data of the sound velocity of iron alloys, we can infer the chemical composition of materials in the Earth's core. The sound velocity of pure iron (Fe) has been sufficiently measured using various techniques, while experimental study on the sound velocity of iron-nickel (Fe-Ni) alloys is limited. Here, we measured longitudinal wave velocities of hexagonal-close-packed (hcp) structured Fe up to 29 GPa, Fe-5 wt% Ni, and Fe-15 wt% Ni up to 64 GPa via a combination of the femtosecond pulse laser pump-probe technique and a diamond anvil cell at room temperature condition. We found that the effect of Ni on the sound velocity of an Fe-based alloy is weaker than that determined by previous experimental study. In addition, we obtained the parameters of Birch's law to be V P = 1146(57)ρ - 3638(567) for Fe-5 wt% Ni and V P = 1141(45)ρ- 3808(446) for Fe-15 wt% Ni, respectively, where V P is longitudinal wave velocity (m/s) and ρ is density (g/cm3).

  1. Femtosecond Laser Filamentation

    CERN Document Server

    Chin, See Leang

    2010-01-01

    Femtosecond Laser Filamentation gives a comprehensive review of the physics of propagation of intense femtosecond laser pulses in optical media (principally air) and the applications and challenges of this new technique. This book presents the modern understanding of the physics of femtosecond laser pulse propagation, including unusual new effects such as the self-transformation of the pulse into a white light laser pulse, intensity clamping, the physics of multiple filamentation and competition, and how filaments’ ability to melt glass leads to wave guide writing. The potential applications of laser filamentation in atmospheric sensing and the generation of other electromagnetic pulses from the UV to the radio frequency are treated, together with possible future challenges in the excitation of super-excited states of molecules. Exciting new phenomena such as filament induced ultrafast birefringence and the excitation of molecular rotational wave packets and their multiple revivals in air (gases) will also ...

  2. Phototransfection of mouse embryonic stem cells with plasmid DNA using femtosecond laser pulses

    CSIR Research Space (South Africa)

    Thobakgale, Setumo L

    2017-02-01

    Full Text Available efficient in photonic interactions with biological material. As of late, laser pulses have been used for drug and DNA delivery into cells via transient optical perforation of the cellular membrane. Thus in this study, we design and construct an optical...

  3. Nanostructure formation upon femtosecond ablation from silicon: Effect of double pulses

    Science.gov (United States)

    Reif, Juergen; Varlamova, Olga; Bounhalli, Mourad; Muth, Marco; Arguirov, Tzanimir

    2012-09-01

    To study the dynamics of laser-ablation induced structure formation (LIPPS), silicon was irradiated by (above-threshold) pulse pairs with a variable time-lag between 100 fs and a few picoseconds. With increasing pulse-to-pulse delay we find a significant change in ablated-area morphology: the central range of the irradiated spot becomes less and less depressed whereas a surrounding ring structure exhibits increasingly coarser modulation, typical for strong irradiation, where the ripples are characterized by an alternation between elevation above and depression below the unaffected surface level. At the spot center the ablation depth decreases with increasing pulse separation, showing only structures usually observed for weak irradiation. Micro-Raman spectroscopy of the modified areas indicates an unexpectedly high, almost mono-dispersed, abundance of confined nanostructures. The results clearly seem to rule out structure formation by any interference-induced modulated ablation. Instead, they support the model of self-organized structure formation upon the creation of a thermally unstable, "soft" state of the target after laser impact.

  4. A method for ultrashort electron pulse-shape measurement using coherent synchrotron radiation

    International Nuclear Information System (INIS)

    Geloni, G.; Yurkov, M.V.

    2003-03-01

    In this paper we discuss a method for nondestructive measurements of the longitudinal profile of sub-picosecond electron bunches for X-ray free electron lasers (XFELs). The method is based on the detection of the coherent synchrotron radiation (CSR) spectrum produced by a bunch passing a dipole magnet system. This work also contains a systematic treatment of synchrotron radiation theory which lies at the basis of CSR. Standard theory of synchrotron radiation uses several approximations whose applicability limits are often forgotten: here we present a systematic discussion about these assumptions. Properties of coherent synchrotron radiation from an electron moving along an arc of a circle are then derived and discussed. We describe also an effective and practical diagnostic technique based on the utilization of an electromagnetic undulator to record the energy of the coherent radiation pulse into the central cone. This measurement must be repeated many times with different undulator resonant frequencies in order to reconstruct the modulus of the bunch form-factor. The retrieval of the bunch profile function from these data is performed by means of deconvolution techniques: for the present work we take advantage of a constrained deconvolution method. We illustrate with numerical examples the potential of the proposed method for electron beam diagnostics at the TESLA test facility (TTF) accelerator. Here we choose, for emphasis, experiments aimed at the measure of the strongly non-Gaussian electron bunch profile in the TTF femtosecond-mode operation. We demonstrate that a tandem combination of a picosecond streak camera and a CSR spectrometer can be used to extract shape information from electron bunches with a narrow leading peak and a long tail. (orig.)

  5. Laser beam welding of titanium nitride coated titanium using pulse-shaping

    Directory of Open Access Journals (Sweden)

    Milton Sergio Fernandes de Lima

    2005-09-01

    Full Text Available A new welding method which allows the assembly of two titanium nitride coated titanium parts is proposed. The welding procedure utilizes the possibility for pulse-shaping in order to change the energy distribution profile during the laser pulse. The pulse-shaping is composed of three elements: a a short high power pulse for partial ablation at the surface; b a long pulse for thermal penetration; and c a quenching slope for enhanced weldability. The combination of these three elements produces crack-free welds. The weld microstructure is changed in comparison to normal welding, i.e. with a rectangular pulse, as the nitrogen and the microhardness are more homogenously distributed in the weld under pulse-shaping conditions. This laser pulse dissolves the TiN layer and allows nitrogen to diffuse into the melt pool, also contributing to an enhanced weldability by providing suitable thermal conditions.

  6. XUV-laser induced ablation of PMMA with nano-, pico-, and femtosecond pulses

    Czech Academy of Sciences Publication Activity Database

    Juha, Libor; Bittner, Michal; Chvostová, Dagmar; Létal, V.; Krása, Josef; Otčenášek, Zdeněk; Kozlová, Michaela; Polan, Jiří; Präg R., Ansgar; Rus, Bedřich; Stupka, Michal; Krzywinski, J.; Andrejczuk, A.; Pelka, J. B.; Sobierajski, R.; Ryc, L.; Feldhaus, J.; Boody, F. P.; Grisham, M. E.; Vaschenko, G. O.; Menoni, C.S.; Rocca, J.J.

    144-147, - (2005), s. 929-932 ISSN 0368-2048 R&D Projects: GA MŠk(CZ) 1P04LA235; GA MŠk(CZ) LN00A100 Institutional research plan: CEZ:AV0Z10100523 Keywords : XUV lasers * soft x-ray lasers * ablation * pulse duration effects * wavelength effects * poly(methyl methacrylate) * PMMA Subject RIV: BH - Optics, Masers, Lasers Impact factor: 1.183, year: 2005

  7. Investigation of visible emission induced by infrared femtosecond pulses in erbium-doped YVO{sub 4} and LuVO{sub 4} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Ryba-Romanowski, Witold; Macalik, Bogusław; Strzęp, Adam; Lisiecki, Radosław, E-mail: R.Lisiecki@int.pan.wroc.pl; Solarz, Piotr; Kowalski, Robert M.

    2013-12-15

    Illumination of single crystal samples of erbium-doped YVO{sub 4} and LuVO{sub 4} by infrared femtosecond pulses brings about an intense green luminescence assigned to the {sup 4}S{sub 3/2} - {sup 4}I{sub 15/2} transition of Er{sup 3+} ions. When lowering the sample temperature an additional broad band in the blue related to the VO{sub 4}{sup 3−} emission appears and next grows steadily. It has been observed that the variation of wavelength of incident infrared femtosecond pulses in the region 800 nm–1600 nm affects weakly the intensity of both the blue and green luminescence bands. Analysis of luminescence dynamics made it possible to reveal that upon infrared excitation the rise time of the {sup 4}S{sub 3/2} luminescence is longer by a factor of four, roughly as compared to that recorded upon direct excitation into high energy levels of Er{sup 3+}. Observed temperature dependence of up-converted blue and green luminescence implies that the energy transfer from vanadate groups cannot be considered as a main mechanism involved in the excitation erbium ions. It has been supposed that erbium ions are likely to be excited by energy transfer from free electrons created in the conduction band of the host by multiphoton excitation and /or by non-resonant multi-step ETU process involving absorption of infrared light in multiphonon side bands of electronic transitions. Creation of free electrons has been corroborated by changes of electrical conductivity of crystals induced by an illumination with infrared femtosecond pulses. -- Highlights: • Processes of interaction of ultrashort light pulses with pure and rare earth-doped vanadate crystals are considered. • Effect and mechanism of excitation of up-converted visible luminescence initiated by infrared femtosecond pulses are examined. • The unlike phenomena was observed in relation to excitation with nanosecond or longer lasting light pulses. • The energy transfer from free electrons to erbium ions is concluded.

  8. Initiation and channelling of a microwave discharge by a plasma filament created in atmospheric air by an intense femtosecond laser pulse

    International Nuclear Information System (INIS)

    Bodrov, S B; Kulagin, D I; Malkov, Yu A; Murzanev, A A; Smirnov, A I; Stepanov, A N

    2012-01-01

    We study the initiation of a pulsed microwave discharge in atmospheric air by a plasma channel induced by intense femtosecond laser pulses. It is shown that the electric field threshold for the initiated discharge is lowered compared with the self-discharge by about a factor of two, from 25 to 12 kV cm -1 . Channelling of the atmospheric-pressure microwave discharge in the direction of the plasma filament has been detected. The time of existence of the initiated discharge plasma was determined by the duration of the microwave pulse and amounted to 1-2 µs for the maximum electron density estimated as about 4 × 10 15 cm -3 . The developed theory of propagation of the microwave radiation along the plasma channel created by a femtosecond laser pulse predicts that the relatively low conductivity of the plasma and its rapid decay limit the characteristic scale of decay of the microwave fields confined by the plasma channel to a few centimetres. (paper)

  9. Pulse shape discrimination performance of inverted coaxial Ge detectors

    Science.gov (United States)

    Domula, A.; Hult, M.; Kermaïdic, Y.; Marissens, G.; Schwingenheuer, B.; Wester, T.; Zuber, K.

    2018-05-01

    We report on the characterization of two inverted coaxial Ge detectors in the context of being employed in future 76Ge neutrinoless double beta (0 νββ) decay experiments. It is an advantage that such detectors can be produced with bigger Ge mass as compared to the planar Broad Energy Ge (BEGe) or p-type Point Contact (PPC) detectors that are currently used in the GERDA and MAJORANA DEMONSTRATOR 0 νββ decay experiments respectively. This will result in a lower background for the search of 0 νββ decay due to a reduction of detector surface to volume ratio, cables, electronics and holders which are dominating nearby radioactive sources. The measured resolution near the 76Ge Q-value at 2039 keV is 2.3 keV FWHM and their pulse-shape discrimination of background events are similar to BEGe and PPC detectors. It is concluded that this type of Ge-detector is suitable for usage in 76Ge 0 νββ decay experiments.

  10. Radiation drive with a composite laser pulse shape

    International Nuclear Information System (INIS)

    Cobble, James A.; Tubbs, David L.; Hoffman, Nelson M.; Swift, Damian C.; Tierney, Thomas

    2004-01-01

    The objective is to develop a 6-ns Hohlraum environment on Omega for Be anisotropy studies. In particular, they are seeking an environment for Be isotropy studies with enough growth times to assess the suitability of Be for NIF ignition capsules. In 20 shots to date, we have: (1) synchronized 2 laser pulse shapes at Omega to obtain a smooth halfraum drive for ∼6 ns; (2) characterized the drive with Dante (∼180 eV peak); (3) obtained high quality VISAR data (using a mirror); (4) measured ejected Be sample velocity; (5) made the first estimates of Au migration to the axis of the vacuum halfraum; and (6) collected the first face-on x-ray images of sinusoidally perturbed Be samples. The immediate objective is to qualify a target for the Be studies. To that end, we hope: (1) to explore alternate foot drives; (2) optimize the radiography; and (3) to field and characterize gas-filled targets within the next 6 months.

  11. Control of cis-stilbene photochemistry using shaped ultraviolet pulses.

    Science.gov (United States)

    Greenfield, M; McGrane, S D; Moore, D S

    2009-03-19

    We demonstrate product branching control of the photoisomerization and cyclization reactions of cis-stilbene dissolved in n-hexane. An acousto-optical modulator-based pulse shaper was used at 266 nm, in a shaped pump-supercontinuum probe technique, to enhance and suppress the relative yields of the cis- to trans-stilbene isomerization as well as the cis-stilbene to 4a,4b-dihydrophenanthrene cyclization. Global, local, and single variable optimization control schemes were all successful at controlling stilbene's excited-state intramolecular rearrangements. The presence of multiphoton transitions was determined to be crucial in changing the yield under the experimental conditions employed. We have mapped experimental conditions in which multiphoton absorption was successful in controlling photoproduct branching ratios in stilbene, illustrated that the intensity dependence of the product yields can provide details of reactive channel branching ratios of higher excited-states, and shown that under the experimental conditions employed (150 fs laser) intensity control was the only mechanism available to the optimal control methods employed that could affect reaction yields.

  12. Pulse shape analysis for germanium detectors used in DM searches

    Energy Technology Data Exchange (ETDEWEB)

    Sagdeev, I.R. (Department of Physics, University of South Carolina, Columbia, SC 29208 (United States)); Drukier, A.K. (Department of Physics, University of South Carolina, Columbia, SC 29208 (United States)); Welsh, D.J. (Department of Physics, University of South Carolina, Columbia, SC 29208 (United States)); Klimenko, A.A. (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312 (Russian Federation)); Osetrov, S.B. (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312 (Russian Federation)); Smolnikov, A.A. (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312 (Russian Federation))

    1994-05-01

    Progress in Ge detector technology has resulted in ultralow backgrounds of less than 0.3 countskeV[sup -1]kg[sup -1]d[sup -1] at energies between 6 and 9keV and from 12 to 20keV. Between 4 and 6keV it is less than 2 countskeV[sup -1]kg[sup -1]d[sup -1]. Coupled with good energy resolution, 0.4keV FWHM at 10keV, this allows searches for DM particles with m[>=]qslant8GeV/c[sup 2].Electromagnetic interference (EMI) and acoustical pick-up are the main sources of background in the best Ge detectors. A PC-based on-line pulse shape analysis system is presented which permits rejection of large fraction of the EMI/acoustical background. The hardware uses a low cost, commercially available digital storage oscilloscope (DSO). The software consists of about 40000 lines of code in Pascal and assembly language. We tested this system using a low radioactive background Ge-system at the Baksan observatory. For low energy events (<100keV) this system permits improvement in the background by about 20-30%. ((orig.))

  13. Pulse Shape Discrimination in the LUX Dark Matter Experiment

    Science.gov (United States)

    Khaitan, Dev Ashish; LUX Collaboration

    2017-09-01

    The Large Underground Xenon (LUX) experiment is a dual-phase xenon time projection chamber (TPC), with an active mass of approx. 250 kg, located in the Sanford Underground Research Facility in Lead, South Dakota, USA. The experiment searches for Weakly Interacting Massive Particles (WIMPs), a leading candidate for the dark matter content of the universe. It is expected that their interaction will be nuclear recoils (NR) and must be distinguished from background due to gamma rays and beta decays which will create electron recoil (ER) interactions. Typically, this is accomplished using the ratio of collected ionization charge to scintillation light. We present a new analysis of LUX calibration data that studies the time structure of liquid xenon scintillation in an attempt to improve ER/NR discrimination using Pulse Shape Discrimination (PSD). Using an advanced photon counting and timing algorithm, we reconstruct the detection time of photons and optimize a prompt fraction discriminator to distinguish between ER and NR interactions. We quantify how this discriminator performs and demonstrate how it can be used, in conjunction with the charge-to-light ratio, to improve the overall discrimination in LUX. This work was partially supported by the U.S. Department of Energy (DOE) under Award Number DE-SC0006605.

  14. Experimental results of laser wakefield acceleration using a femtosecond terawatt laser pulse

    International Nuclear Information System (INIS)

    Kando, Masaki; Ahn, Hyeyoung; Dewa, Hideki

    1999-01-01

    Laser wakefield acceleration (LWA) experiments have been carried out in an underdense plasma driven by a 2 TW, 90 fs laser pulse synchronized with a 17 MeV RF linac electron injector at 10 Hz. Around optimum plasma densities for LWA, we have observed electrons accelerated to 35 MeV. Wakefield excitation has been confirmed by measuring the electron density oscillation with a frequency domain interferometer. At plasma densities higher than the optimum density, we have also observed high energy electrons over 100 MeV up to 200 MeV. (author)

  15. K-α emission form medium and high-Z materials irradiated by femtosecond laser pulses

    International Nuclear Information System (INIS)

    Limpouch, J.; Klimo, O.; Zhavoronkov, N.; Andreev, A.A.

    2006-01-01

    Complete test of publication follows. Fast electrons are created at the target surface during the interaction of high intensity ultra short laser pulses with solids. Fast electrons penetrate deep into the target where they generate K-α and Bremsstrahlung radiation. Generated high brightness K-α pulses offer the prospect of creating a cheap and compact X-ray source, posing a promising alternative to synchrotron radiation, e.g. in medical application and in material science. With an increase in laser intensity, efficient X-ray emission in the multi-keV range with pulse duration shorter than few picoseconds is expected. This short incoherent but monochromatic X-ray emission synchronized with laser pulses may be used for time-resolved measurements. Acceleration of fast electrons, their transport and K-α photon generation and emission from the target surface in both forward and backward directions are studied here numerically. The results are compared to recent experiments studying K-α emission from the front and rear surface of copper foil targets of various thicknesses and for various parameters of the laser plasma interaction. One-dimensional PIC simulations coupled with 3D time-resolved Monte Carlo simulations show that account of ionization processes and of density profile formed by laser ASE emission is essential for reliable explanation of experimental data. While sub-relativistic intensities are optimum for laser energy transformation into K-α emission for medium-Z targets, relativistic laser intensities have to be used for hard X-ray generation in high-Z materials. The cross-section for K-α shell ionization of high-Z elements by electrons increases or remains approximately constant within a factor of two at relativistic electron energies up to electron energies in the 100-MeV range. Moreover, the splitting ratio of K-α photon emission to Auger electron emission is favorable for high-Z materials, and thus efficient K-α emission is possible. In our

  16. Coherent terahertz emission from ferromagnetic films excited by femtosecond laser pulses

    International Nuclear Information System (INIS)

    Beaurepaire, E.; Turner, G.M.; Harrel, S.M.; Beard, M.C.; Bigot, J.-Y.; Schmuttenmaer, C.A.

    2004-01-01

    It is shown that the laser induced ultrafast demagnetization of ferromagnetic films results in the emission of a terahertz electromagnetic pulse. This emission has been detected from Ni films using free-space electro-optic sampling. The radiated electric field E(t) is explained by Maxwell equations (radiation from a time dependent magnetic dipole), and is expected to be proportional to the second time derivative of the magnetization d 2 M/dt 2 , as measured in the far field. This technique opens appealing perspectives in the context of measuring and understanding the ultrafast spin dynamics as well as the interaction of electrons (both charge and spin) with electromagnetic fields

  17. Study of light-induced processes in lithium niobate crystals with femtosecond light pulses; Untersuchung lichtinduzierter Prozesse in Lithiumniobat-Kristallen mit Femtosekunden-Lichtpulsen

    Energy Technology Data Exchange (ETDEWEB)

    Beyer, O.

    2005-12-15

    For the realization of many applications with LiNbO{sub 3} a deeper understanding of nonlinear processes for high light intensities and the charge-carrier dynamics on short time scales is necessary. For the study in this thesis femtosecond pulses with a lifetime of {tau}{approx}200 fs are applied. By pump pulses ({lambda}{sub p}=388 nm) absorption changes are caused, which are detected time-resolvedly by probe pulses ({lambda}{sub r}=776 nm) respectively continuous light ({lambda}{sub r}=785 nm). For the absorption centers absorption cross sections of {sigma}{sub YY}{approx}9.2 x 10{sup -22} m{sup 2} for ordinarily {sigma}{sub Z}Z{approx}6.0 x 10{sup -22} m{sup 2} for extraordinarily polarized light of the wavelength {lambda}{sub r}=776 nm result.Polarization and wavelength dependence as well as the comparison with nanosecond pulses suggest that the absorption centers are small polarons, which exist already 400 fs after the excitation of the charge carriers. At holographic pump probe studies, which are sensitive both for absorption and for refractive-index changes, gratings with two pump pulses are generated and read out by one pump pulse. The time dependence of the diffraction efficiency of the transient grating in LiNbO{sub 3} exhibits first a symmetric maximum, the time width of which is compatible with the expectations from model calculations. Thereafter the diffraction efficiency decreases to a constant value in the picosecond range and decreases further on the nanosecond time scale. By illumination of iron-doped lithium niobate crystals with 1.5 {mu}m femtosecond pulses permanent refractive-index changes in the range {delta}n{approx}10{sup -3} ({lambda}=633 nm) are generated.

  18. Second-order shaped pulsed for solid-state quantum computation

    Energy Technology Data Exchange (ETDEWEB)

    Sengupta, Pinaki [Los Alamos National Laboratory

    2008-01-01

    We present the construction and detailed analysis of highly optimized self-refocusing pulse shapes for several rotation angles. We characterize the constructed pulses by the coefficients appearing in the Magnus expansion up to second order. This allows a semianalytical analysis of the performance of the constructed shapes in sequences and composite pulses by computing the corresponding leading-order error operators. Higher orders can be analyzed with the numerical technique suggested by us previously. We illustrate the technique by analyzing several composite pulses designed to protect against pulse amplitude errors, and on decoupling sequences for potentially long chains of qubits with on-site and nearest-neighbor couplings.

  19. Femtosecond stimulated Raman spectroscopy as a tool to detect molecular vibrations in ground and excited electronic states

    Energy Technology Data Exchange (ETDEWEB)

    Gelin, Maxim F.; Domcke, Wolfgang [Department of Chemistry, Technische Universität München, D-85747 Garching (Germany); Rao, B. Jayachander [Departamento de Química and Centro de Química, Universidade de Coimbra, 3004-535 Coimbra (Portugal)

    2016-05-14

    We give a detailed theoretical analysis of the simplest variant of femtosecond stimulated Raman spectroscopy, where a picosecond Raman pump pulse and a femtosecond Raman probe pulse are applied resonantly to a chromophore in thermal equilibrium in the ground electronic state. We demonstrate that this technique is capable of the detection of dephasing-free Raman-like lines revealing vibrational modes not only in the electronic ground state but also in the excited electronic state of the chromophore. The analytical results obtained with simplifying assumptions for the shape of the laser pulses are substantiated by numerical simulations with realistic laser pulses, employing the equation-of-motion phase-matching approach.

  20. Circular photocurrent in Ag/Pd resistive films upon excitation by femtosecond laser pulses

    Science.gov (United States)

    Mikheev, G. M.; Saushin, A. S.; Vanyukov, V. V.; Mikheev, K. G.; Svirko, Yu. P.

    2016-11-01

    This paper presents the results of the experimental investigation of the generation of nanosecond photocurrent pulses in silver-palladium (Ag/Pd) resistive films under excitation by laser pulses with a duration of 120 fs at a wavelength of 795 nm. The photocurrent was detected in the direction perpendicular to the plane of incidence of the laser beam on the film. The 20-μm-thick films under investigation were a porous polycrystalline material consisting predominantly of nanocrystallites of the palladium oxide PdO and the Ag-Pd solid solution. The direction of the photocurrent observed in the films depends on the sign of the circular polarization of the incident radiation. It was found that the observed photocurrent depends on the angle of incidence in accordance with the odd law and consists of the circular and linear contributions, which are dependent on and independent of the sign of the circular polarization, respectively. It was shown that the circular photocurrent is significantly higher than the linear photocurrent. It was established that, for both the circular and linear polarizations, the photocurrent is directly proportional to the power of the excitation radiation. For the linearly polarized laser radiation, the photocurrent depends on the polarization angle in accordance with the odd law. The regularities revealed are consistent with the mechanism of the generation of transverse photocurrent with the photon drag effect.

  1. Femtosecond laser materials processing

    International Nuclear Information System (INIS)

    Stuart, B.C.

    1997-01-01

    The use femtosecond pulses for materials processing results in very precise cutting and drilling with high efficiency. Energy deposited in the electrons is not coupled into the bulk during the pulse, resulting in negligible shock or thermal loading to adjacent areas

  2. Silicon structuring by etching with liquid chlorine and fluorine precursors using femtosecond laser pulses

    International Nuclear Information System (INIS)

    Radu, C.; Simion, S.; Zamfirescu, M.; Ulmeanu, M.; Enculescu, M.; Radoiu, M.

    2011-01-01

    The aim of this study is to investigate the micrometer and submicrometer scale structuring of silicon by liquid chlorine and fluorine precursors with 200 fs laser pulses working at both fundamental (775 nm) and frequency doubled (387 nm) wavelengths. The silicon surface was irradiated at normal incidence by immersing the Si (111) substrates in a glass container filled with liquid chlorine (CCl 4 ) and fluorine (C 2 Cl 3 F 3 ) precursors. We report that silicon surfaces develop an array of spikes with single step irradiation processes at 775 nm and equally at 387 nm. When irradiating the Si surface with 400 pulses at 330 mJ/cm 2 laser fluence and a 775 nm wavelength, the average height of the formed Si spikes in the case of fluorine precursors is 4.2 μm, with a full width at half maximum of 890 nm. At the same irradiation wavelength chlorine precursors develop Si spikes 4 μm in height and with a full width at half maximum of 2.3 μm with irradiation of 700 pulses at 560 mJ/cm 2 laser fluence. Well ordered areas of submicrometer spikes with an average height of about 500 nm and a width of 300 nm have been created by irradiation at 387 nm by chlorine precursors, whereas the fluorine precursors fabricate spikes with an average height of 700 nm and a width of about 200 nm. Atomic force microscopy and scanning electron microscopy of the surface show that the formation of the micrometer and sub-micrometer spikes involves a combination of capillary waves on the molten silicon surface and laser-induced etching of silicon, at both 775 nm and 387 nm wavelength irradiation. The energy-dispersive x-ray measurements indicate the presence of chlorine and fluorine precursors on the structured surface. The fluorine precursors create a more ordered area of Si spikes at both micrometer and sub-micrometer scales. The potential use of patterned Si substrates with gradient topography as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell

  3. Interaction of doughnut-shaped laser pulses with glasses

    Czech Academy of Sciences Publication Activity Database

    Zhukov, V.P.; Rubenchik, A.M.; Fedoruk, M.P.; Bulgakova, Nadezhda M.

    2017-01-01

    Roč. 34, č. 2 (2017), s. 463-471 ISSN 0740-3224 R&D Projects: GA MŠk LO1602; GA MŠk EF15_003/0000445; GA MŠk LM2015086 Grant - others:OP VVV - BIATRI(XE) CZ.02.1.01/0.0/0.0/15_003/0000445 Institutional support: RVO:68378271 Keywords : femtosecond-laser * transparent materials * wave-guides * photonic devices * fused-silica * dielectrics * media * filamentation * fabrication * ionization Subject RIV: BH - Optics, Masers, Lasers OBOR OECD: Optics (including laser optics and quantum optics) Impact factor: 1.843, year: 2016

  4. Comment on ''Generation of Electromagnetic Pulses from Plasma Channels Induced by Femtosecond Light Strings''

    International Nuclear Information System (INIS)

    Shvets, Gennady; Kaganovich, Igor; Startsev, Edward

    2002-01-01

    In a recent Letter, Cheng et al. calculated/predicted several new effects: that (a) fraction of the short laser pulse momentum can be imparted to plasma electrons via collisional damping of the laser, thereby exciting a long-lived (longer than an oscillation period) plasma wave, which (b) gives rise to a spatially uniform dipole moment of a plasma, which (c) emits far-field narrow-band radiation at the plasma frequency omega subscript ''p'' over the recombination time of the plasma. We claim that the calculation of the effect (a) is in error and the predicted effects (b,c) do not occur as described. In fact, predicted narrow-band emission at omega subscript ''p'' would not occur even if the momentum transfer and the dipole excitation were calculated correctly

  5. Fibre-Bragg-grating writing in single-mode optical fibres by UV femtosecond pulses

    International Nuclear Information System (INIS)

    Zagorul'ko, K A; Kryukov, P G; Dianov, Evgenii M; Dragomir, A; Nikogosyan, D N

    2003-01-01

    Fibre-Bragg-grating writing in single-mode optical fibres by the phase-mask method using 220-fs, 264-nm UV pulses of intensity 31 - 77 GW cm -2 is reported for the first time. The achieved degree of modulation of the photoinduced refractive index was 1.9 x 10 -3 in an H 2 -loaded SMF-28 telecommunication fibre and 1.1 x 10 -3 in a H 2 -free Nufern GF1 fibre. The dependence of the induced refractive index on the intensity for the same irradiation fluences in the case of the H 2 -loaded SMF-28 fibre shows that the refractive index is induced due to nonlinear absorption. (letters)

  6. Stealth dicing of sapphire wafers with near infra-red femtosecond pulses

    Science.gov (United States)

    Yadav, Amit; Kbashi, Hani; Kolpakov, Stanislav; Gordon, Neil; Zhou, Kaiming; Rafailov, Edik U.

    2017-05-01

    The quality of the reflecting faces after dicing is critical for the fabrication of efficient and stable laser diodes emitting in the green-violet region. However, high-quality faces can be difficult to achieve for devices grown on a sapphire substrate as this material is difficult to cleave cleanly. We have therefore investigated a technology known as "stealth dicing". The technology uses a pulsed laser to damage a plane of material inside of the wafer due to multi-photon absorption instead of cutting through the wafer surface. If the damage is induced in a line of stress points, the sample can then be cleaved easily along the damaged plane to leave a high-quality surface. The use of this technique also reduces thermal damage and debris.

  7. Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses

    Directory of Open Access Journals (Sweden)

    Rebecca Boll

    2016-07-01

    Full Text Available Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I21+. The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse.

  8. Thermal response of a dental tissue induced by femtosecond laser pulses.

    Science.gov (United States)

    Chang, K P; Tsai, T W; Huang, K Y; Huang, C H; Wang, S Y; Cheng, C W; Chen, J K; Tzou, D Y

    2013-09-20

    This paper reports a theoretical and experimental study for thermal transport in a thin slice of human tooth induced by a 120 fs, 800 nm pulse laser at a repetition rate of 1 kHz. The surface reflectivity of enamel and the convection heat transfer coefficient were determined using an inverse heat transfer analysis. Instead of a fully three-dimensional modeling, two simplified two-dimensional (2D) planar and axisymmetric heat conduction models were proposed to simulate the temperature fields. The temperature responses obtained from the 2D planar and axisymmetric model agree well with the experimental measurements. On the other hand, the one-dimensional (1D) result significantly differs from the 2D axisymmetric one, suggesting that care should be taken when a 1D thermal model is considered for estimating temperature response.

  9. Characterization of nanoparticle mediated laser transfection by femtosecond laser pulses for applications in molecular medicine.

    Science.gov (United States)

    Schomaker, Markus; Heinemann, Dag; Kalies, Stefan; Willenbrock, Saskia; Wagner, Siegfried; Nolte, Ingo; Ripken, Tammo; Murua Escobar, Hugo; Meyer, Heiko; Heisterkamp, Alexander

    2015-02-03

    In molecular medicine, the manipulation of cells is prerequisite to evaluate genes as therapeutic targets or to transfect cells to develop cell therapeutic strategies. To achieve these purposes it is essential that given transfection techniques are capable of handling high cell numbers in reasonable time spans. To fulfill this demand, an alternative nanoparticle mediated laser transfection method is presented herein. The fs-laser excitation of cell-adhered gold nanoparticles evokes localized membrane permeabilization and enables an inflow of extracellular molecules into cells. The parameters for an efficient and gentle cell manipulation are evaluated in detail. Efficiencies of 90% with a cell viability of 93% were achieved for siRNA transfection. The proof for a molecular medical approach is demonstrated by highly efficient knock down of the oncogene HMGA2 in a rapidly proliferating prostate carcinoma in vitro model using siRNA. Additionally, investigations concerning the initial perforation mechanism are conducted. Next to theoretical simulations, the laser induced effects are experimentally investigated by spectrometric and microscopic analysis. The results indicate that near field effects are the initial mechanism of membrane permeabilization. This methodical approach combined with an automated setup, allows a high throughput targeting of several 100,000 cells within seconds, providing an excellent tool for in vitro applications in molecular medicine. NIR fs lasers are characterized by specific advantages when compared to lasers employing longer (ps/ns) pulses in the visible regime. The NIR fs pulses generate low thermal impact while allowing high penetration depths into tissue. Therefore fs lasers could be used for prospective in vivo applications.

  10. Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

    DEFF Research Database (Denmark)

    Canton, Sophie E.; Kjær, Kasper S.; Vankó, György

    2015-01-01

    Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectrosc...

  11. Impact of initial pulse shape on the nonlinear spectral compression in optical fibre

    Science.gov (United States)

    Boscolo, Sonia; Chaussard, Frederic; Andresen, Esben; Rigneault, Hervé; Finot, Christophe

    2018-02-01

    We theoretically study the effects of the temporal intensity profile of the initial pulse on the nonlinear propagation spectral compression process arising from nonlinear propagation in an optical fibre. Various linearly chirped input pulse profiles are considered, and their dynamics is explained with the aid of time-frequency representations. While initially parabolic-shaped pulses show enhanced spectral compression compared to Gaussian pulses, no significant spectral narrowing occurs when initially super-Gaussian pulses are used. Triangular pulses lead to a spectral interference phenomenon similar to the Fresnel bi-prism experiment.

  12. TDDFT investigation of excitation of water tetramer under femtosecond laser pulse irradiation

    Science.gov (United States)

    Wang, Zhiping; Xu, Xuefen; Zhang, Fengshou; Qian, Chaoyi

    2018-04-01

    We study the static properties of water tetramer in ground state, the optical absorption spectra and ultrafast nonadiabatic dynamical response of water tetramer to short and intense laser pulses with different intensities by a real-space, real-time implementation of time-dependent density functional theory coupled to molecular dynamics (TDDFT-MD) nonadiabatically. The calculated results are in good agreement with available values in literature. Four typical irradiated scenarios of water tetramer in laser field, which are “normal vibration,” “break and reorganization,” “fragmentation and new formation” and “pure fragmentation”, are explored by discussing the ionization, the bond lengths of OH bonds and hydrogen bonds and the kinetic energy of ions. The dynamic simulation shows that the reaction channel of water tetramer can really be controlled by choosing appropriate laser parameters referring to the optical absorption spectra and hydrogen ions play an important role in the reaction channel. Furthermore, it is found that the laser intensity affects the kinetic energy of ejected protons more than that of the remaining fragments and all dynamic processes are somehow directly related to the velocity of departing protons.

  13. Proton acceleration in two-species targets irradiated by an ultra-intense femtosecond laser pulse

    Science.gov (United States)

    Domański, J.; Badziak, J.; Jabłoński, S.

    2018-01-01

    This paper presents results of two-dimensional particle-in-cell simulations of proton acceleration at the interactions of a 130 fs, linearly polarized laser pulse of intensity from the range 1021 –1023 W/cm2, predicted for the ELI (Extreme Light Infrastructure) lasers, with thin hydrocarbon (CH) or hydride (ErH3) targets. It is shown that for the targets of the areal density σ > 0.1 mg/cm2 and laser intensities below 1022 W/cm2 a higher efficiency of proton acceleration is achieved for hydride targets. However for the highest, ultra-relativistic laser intensities (~ 1023 W/cm2) considerably higher proton energies and proton beam intensities are achieved for thin (σ ≤ 0.1 mg/cm2) CH targets. In this case, at short distances from the irradiated CH target ( 1021 W/cm2 and > 1012 A/cm2, respectively, which are much higher than those attainable in conventional accelerators. Such proton beams can open the door for new areas of research in nuclear physics and high energy-density physics as well as can be useful for materials research.

  14. Hadronic vs. electromagnetic pulse shape discrimination in CsI(Tl) for high energy physics experiments

    Science.gov (United States)

    Longo, S.; Roney, J. M.

    2018-03-01

    Pulse shape discrimination using CsI(Tl) scintillators to perform neutral hadron particle identification is explored with emphasis towards application at high energy electron-positron collider experiments. Through the analysis of the pulse shape differences between scintillation pulses from photon and hadronic energy deposits using neutron and proton data collected at TRIUMF, it is shown that the pulse shape variations observed for hadrons can be modelled using a third scintillation component for CsI(Tl), in addition to the standard fast and slow components. Techniques for computing the hadronic pulse amplitudes and shape variations are developed and it is shown that the intensity of the additional scintillation component can be computed from the ionization energy loss of the interacting particles. These pulse modelling and simulation methods are integrated with GEANT4 simulation libraries and the predicted pulse shape for CsI(Tl) crystals in a 5 × 5 array of 5 × 5 × 30 cm3 crystals is studied for hadronic showers from 0.5 and 1 GeV/c KL0 and neutron particles. Using a crystal level and cluster level approach for photon vs. hadron cluster separation we demonstrate proof-of-concept for neutral hadron detection using CsI(Tl) pulse shape discrimination in high energy electron-positron collider experiments.

  15. 2-Dimension pulse shape discriminator for phoswich detector based on FPGA

    International Nuclear Information System (INIS)

    Ji Jianfeng; Liu Congzhan; Zhang Zhi

    2011-01-01

    It improves the data acquire system for the pulse signal based on digital front-rear pulse shape discrimination system. It adds pulse width information into the pulse's data package. Base on this, we divide the pulse event process into two process, on line coast process and offline accurate process: the online process sets a big threshold, just save the data of the event below this threshold; the offline process uses the acquired data, get the pulse amplitude and pulse width, and then according the spectrum's real shape, set the accurate threshold. this design resolves the problem that the detector's decay time change with the temperature; at the same time, it can correct the system's distortion when the input signal at small amplitude, improves the discrimination system's accuracy. (authors)

  16. Analytical optimal pulse shapes obtained with the aid of genetic algorithms

    International Nuclear Information System (INIS)

    Guerrero, Rubén D.; Arango, Carlos A.; Reyes, Andrés

    2015-01-01

    We propose a methodology to design optimal pulses for achieving quantum optimal control on molecular systems. Our approach constrains pulse shapes to linear combinations of a fixed number of experimentally relevant pulse functions. Quantum optimal control is obtained by maximizing a multi-target fitness function using genetic algorithms. As a first application of the methodology, we generated an optimal pulse that successfully maximized the yield on a selected dissociation channel of a diatomic molecule. Our pulse is obtained as a linear combination of linearly chirped pulse functions. Data recorded along the evolution of the genetic algorithm contained important information regarding the interplay between radiative and diabatic processes. We performed a principal component analysis on these data to retrieve the most relevant processes along the optimal path. Our proposed methodology could be useful for performing quantum optimal control on more complex systems by employing a wider variety of pulse shape functions

  17. Analytical optimal pulse shapes obtained with the aid of genetic algorithms

    Energy Technology Data Exchange (ETDEWEB)

    Guerrero, Rubén D., E-mail: rdguerrerom@unal.edu.co [Department of Physics, Universidad Nacional de Colombia, Bogota (Colombia); Arango, Carlos A. [Department of Chemical Sciences, Universidad Icesi, Cali (Colombia); Reyes, Andrés [Department of Chemistry, Universidad Nacional de Colombia, Bogota (Colombia)

    2015-09-28

    We propose a methodology to design optimal pulses for achieving quantum optimal control on molecular systems. Our approach constrains pulse shapes to linear combinations of a fixed number of experimentally relevant pulse functions. Quantum optimal control is obtained by maximizing a multi-target fitness function using genetic algorithms. As a first application of the methodology, we generated an optimal pulse that successfully maximized the yield on a selected dissociation channel of a diatomic molecule. Our pulse is obtained as a linear combination of linearly chirped pulse functions. Data recorded along the evolution of the genetic algorithm contained important information regarding the interplay between radiative and diabatic processes. We performed a principal component analysis on these data to retrieve the most relevant processes along the optimal path. Our proposed methodology could be useful for performing quantum optimal control on more complex systems by employing a wider variety of pulse shape functions.

  18. Femtosecond laser spectroscopy

    CERN Document Server

    Hannaford, Peter

    2005-01-01

    As concepts and methodologies have evolved over the past two decades, the realm of ultrafast science has become vast and exciting and has impacted many areas of chemistry, biology and physics, and other fields such as materials science, electrical engineering, and optical communication. The field has recently exploded with the announcement of a series of remarkable new developments and advances. This volume surveys this recent growth in eleven chapters written by leading international researchers in the field. It includes sections on femtosecond optical frequency combs, soft x-ray femtosecond laser sources, and attosecond laser sources. In addition, the contributors address real-time spectroscopy of molecular vibrations with sub-5-fs pulses and multidimensional femtosecond coherent spectroscopies for studying molecular and electron dynamics. Novel methods for measuring and characterizing ultrashort laser pulses and ultrashort pulses of light are also described. The topics covered are revolutionizing the field...

  19. Mono-Cycle Photonics and Optical Scanning Tunneling Microscopy Route to Femtosecond Ångstrom Technology

    CERN Document Server

    Yamashita, Mikio; Morita, Ryuji

    2005-01-01

    "Mono-Cycle Photonics and Optical Scanning Tunneling Microscopy" deals with both the ultrashort laser-pulse technology in the few- to mono-cycle region and the laser-surface-controlled scanning-tunneling microscopy (STM) extending into the spatiotemporal extreme technology. The former covers the theory of nonlinear pulse propagation beyond the slowly-varing-envelope approximation, the generation and active chirp compensation of ultrabroadband optical pulses, the amplitude and phase characterization of few- to mono-cycle pulses, and the feedback field control for the mono-cycle-like pulse generation. In addition, the wavelength-multiplex shaping of ultrabroadband pulse is described. The latter covers the CW-laser-excitation STM, the femtosecond-time-resolved STM and atomic-level surface phenomena controlled by femtosecond pulses.

  20. Femtosecond lasers for countermeasure applications

    NARCIS (Netherlands)

    Franssen, G.C.; Schleijpen, H.M.A.; Heuvel, J.C. van den; Buersing, H.; Eberle, B.; Walter, D.

    2009-01-01

    In recent years, much advance in the field of high-power femtosecond laser technology has been made. The high pulse power of femtosecond laser systems leads to various interesting phenomena, such as a very high power density and the formation of a plasma in the propagation medium, which is usually

  1. The shaped pulses control and operation on the SG-III prototype facility

    Science.gov (United States)

    Ping, Li; Wei, Wang; Sai, Jin; Wanqing, Huang; Wenyi, Wang; Jingqin, Su; Runchang, Zhao

    2018-04-01

    The laser driven inertial confined fusion experiments require careful temporal shape control of the laser pulse. Two approaches are introduced to improve the accuracy and efficiency of the close loop feedback system for long term operation in TIL; the first one is a statistical model to analyze the variation of the parameters obtained from previous shots, the other is a matrix algorithm proposed to relate the electrical signal and the impulse amplitudes. With the model and algorithm applied in the pulse shaping in TIL, a variety of shaped pulses were produced with a 10% precision in half an hour for almost three years under different circumstance.

  2. Improvement of SOI microdosimeter performance using pulse shape discrimination techniques

    International Nuclear Information System (INIS)

    Cornelius, I.

    2002-01-01

    Full text: Microdosimetry is used to study the radiobiological properties of densely ionising radiations encountered in hadron therapy and space environments by measuring energy deposition in microscopic volumes. The creation of a solid state microdosimeter to replace the traditional tissue equivalent proportional counter is a topic of ongoing research. The Centre for Medical Radiation Physics has been investigating a technique using microscopic arrays of reverse biased pn junctions to measure the linear energy transfer of ions. A prototype silicon-on-insulator (SOI) microdosimeter was developed and measurements were conducted at boron neutron capture therapy, proton therapy, and fast neutron therapy facilities. Previous studies have shown the current microdosimeter possesses a poorly defined sensitive volume, a consequence of charge collection events being measured for ion strikes outside the pn junction via the diffusion of charge carriers. As a result, the amount of charge collected by the microdosimeter following an ion strike has a strong dependence on the location of the strike on the device and the angle of incidence of the ion. The aim of this work was to investigate the use of pulse shape discrimination (PSD) techniques to preclude the acquisition of events resulting from ion strikes outside the depletion region of the pn junction. Experiments were carried out using the Heavy Ion Microprobe (HIMP) at the Australian Nuclear Science and Technology Organisation, Lucas Heights, Australia. The HIMP was used to measure the charge collection time as a function of ion strike location on the microdosimeter array. As expected, the charge collection time was seen to increase monotonically as the distance of the ion strike from the junction increased. The charge collection time corresponding to ion strikes within the junction was determined. Through use of suitable electronics it was possible to gate the charge collection signal based on simultaneous measurements of

  3. Mechanism of equivalent electric dipole oscillation for high-order harmonic generation from grating-structured solid-surface by femtosecond laser pulse

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yang; Song, Hai-Ying; Liu, H.Y.; Liu, Shi-Bing, E-mail: sbliu@bjut.edu.cn

    2017-07-12

    Highlights: • Proposed a valid mechanism of high harmonic generation by laser grating target interaction: oscillation of equivalent electric dipole (OEED). • Found that there also exist harmonic emission at large emission angle but not just near-surface direction as the former researches had pointed out. • Show the process of the formation and motion of electron bunches at the grating-target surface irradiating with femtosecond laser pulse. - Abstract: We theoretically study high-order harmonic generation (HHG) from relativistically driven overdense plasma targets with rectangularly grating-structured surfaces by femtosecond laser pulses. Our particle-in-cell (PIC) simulations show that, under the conditions of low laser intensity and plasma density, the harmonics emit principally along small angles deviating from the target surface. Further investigation of the surface electron dynamics reveals that the electron bunches are formed by the interaction between the laser field and the target surface, giving rise to the oscillation of equivalent electric-dipole (OEED), which enhances specific harmonic orders. Our work helps understand the mechanism of harmonic emissions from grating targets and the distinction from the planar harmonic scheme.

  4. All-fiber femtosecond laser providing 9 nJ, 50 MHz pulses at 1650 nm for three-photon microscopy

    Science.gov (United States)

    Cadroas, P.; Abdeladim, L.; Kotov, L.; Likhachev, M.; Lipatov, D.; Gaponov, D.; Hideur, A.; Tang, M.; Livet, J.; Supatto, W.; Beaurepaire, E.; Février, S.

    2017-06-01

    The spectral window lying between 1.6 and 1.7 μm is interesting for in-depth multiphoton microscopy of intact tissues due to reduced scattering and absorption in this wavelength range. However, wide adoption of this excitation range will rely on the availability of robust and cost-effective high peak power pulsed lasers operating at these wavelengths. In this communication, we report on a monolithically integrated high repetition rate (50 MHz) all-fiber femtosecond laser based on a soliton self-frequency shift providing 9 nJ, 75 fs pulses at 1650 nm. We illustrate its potential for biological microscopy by recording three-photon-excited fluorescence and third-harmonic generation images of mouse nervous tissue and developing Drosophila embryos labeled with a red fluorescent protein.

  5. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Effect of nonlinear light scattering in air on ablation of materials produced by femtosecond laser pulses

    Science.gov (United States)

    Klimentov, Sergei M.; Kononenko, Taras V.; Pivovarov, Pavel A.; Konov, Vitalii I.; Prokhorov, A. M.; Breitling, D.; Dausinger, F.

    2002-05-01

    Nonlinear light scattering appearing upon air breakdown induced by high-power ultrashort pulses (110 — 5200 fs) from a Ti:Al2O3 laser is studied. As a result of forward scattering, the beam profile is severely deformed, which is accompanied by spectral conversion of the incident radiation to a series of shorter-wavelength peaks extending into the visible spectral range. Measurements are made of the thresholds and the scattered radiation energy, which amounts to 75% of the incident energy. The effect of scattering on the material ablation in air is investigated. The obtained data offer an explanation for the experimentally observed paradoxical morphology of the channels ablated by high-power femtosecond pulses.

  6. Decay of coherent acoustic phonons generated by femtosecond pulsed optical excitation and injected in a Wannier-Stark superlattice (Conference Presentation)

    Science.gov (United States)

    Kent, Anthony J.; Poyser, Caroline L.; Akimov, Andrey V.; York, William; Henini, Mohamed; Campion, Richard P.

    2017-02-01

    In the past decade, sound amplification by the stimulated emission of (acoustic phonon) radiation (saser) devices for generating coherent terahertz (THz) acoustic waves have been demonstrated [1 - 3]. The devices exploit the electron-phonon interactions in periodic semiconductor nanostructures known as superlattices (SLs) to amplify acoustic phonons. In addition, the particular acoustic properties of SLs can be exploited to make mirrors and cavities for THz phonons. Thus SLs can provide the two essential elements of a saser: the acoustic gain medium and the acoustic cavity. In this presentation I will describe experimental studies of the THz phonon dynamics in a weakly-coupled GaAs/AlAs saser SL, which is DC electrically biased into the Wannier-Stark regime. Picoseconds-duration pulses of coherent THz acoustic phonons were generated using pump light pulses from a femtosecond laser and injected into the SL device. These phonon pulses seeded the saser cavity modes at about 220 and 440 GHz, which were amplified within the device. The phonons were detected using two methods: reflection of femtosecond probe light pulses, in a conventional pump-probe arrangement, and through the transient electrical response of the device itself. When the DC bias conditions for saser were achieved in the device, the amplitude and lifetime of the seeded modes were both increased, analogous to the threshold and spectral line narrowing effects seen in laser devices. [1] R P Beardsley et al., Phys. Rev. Lett. 104, 085501 (2010). [2] W Maryam et al., Nature Communications 4:2184 (2013). [3] K Shinokita et al., Phys. Rev. Lett. 116, 075504 (2016).

  7. Pulse-shape discrimination in radioanalytical methods. Part I. Delayed fission neutron counting

    International Nuclear Information System (INIS)

    Posta, S.; Vacik, J.; Hnatowicz, V.; Cervena, J.

    1999-01-01

    In this study the principle of pulse shape discrimination (PSD) has been employed in delayed fission neutron counting (DNC) method. Effective elimination of unwanted gamma background signals in measured radiation spectra has been proved. (author)

  8. Proposal and design of phase-modulated fiber gratings in transmission for pulse shaping.

    Science.gov (United States)

    Preciado, Miguel A; Shu, Xuewen; Sugden, Kate

    2013-01-01

    An approach to pulse shaping using a phase-modulated fiber Bragg grating (FBG) in transmission is proposed and designed. We show that phase-modulated FBGs can provide transmission responses suitable for pulse shaping applications, offering important technological feasibility benefits, since the coupling strength remains basically uniform in the grating. Moreover, this approach retains the substantial advantages of FBGs in transmission, such as optimum energy efficiency, no requirement for an optical circulator, and robustness against fabrication errors.

  9. Time and Frequency Localized Pulse Shape for Resolution Enhancement in STFT-BOTDR

    Directory of Open Access Journals (Sweden)

    Linqing Luo

    2016-01-01

    Full Text Available Short-Time Fourier Transform-Brillouin Optical Time-Domain Reflectometry (STFT-BOTDR implements STFT over the full frequency spectrum to measure the distributed temperature and strain along the optic fiber, providing new research advances in dynamic distributed sensing. The spatial and frequency resolution of the dynamic sensing are limited by the Signal to Noise Ratio (SNR and the Time-Frequency (T-F localization of the input pulse shape. T-F localization is fundamentally important for the communication system, which suppresses interchannel interference (ICI and intersymbol interference (ISI to improve the transmission quality in multicarrier modulation (MCM. This paper demonstrates that the T-F localized input pulse shape can enhance the SNR and the spatial and frequency resolution in STFT-BOTDR. Simulation and experiments of T-F localized different pulses shapes are conducted to compare the limitation of the system resolution. The result indicates that rectangular pulse should be selected to optimize the spatial resolution and Lorentzian pulse could be chosen to optimize the frequency resolution, while Gaussian shape pulse can be used in general applications for its balanced performance in both spatial and frequency resolution. Meanwhile, T-F localization is proved to be useful in the pulse shape selection for system resolution optimization.

  10. Fiscal 1998 R and D report on femtosecond technology (ultra-short pulse optoelectronics technology); 1998 nendo femuto byo technology no kenkyu kaihatsu (chotan pulse hikari electronics gijutsu kaihatsu) seika hokokusho

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1999-03-01

    This report reports the result of the fiscal 1998 R and D on femtosecond technology supported by NEDO. For creation of industrial basic technologies supporting the advanced information society in the 21st century, ultra-high speed electronics technology including new functions beyond the speed limit of conventional electronics technologies is indispensable. From such viewpoint, this R and D aims at establishment of the basic technology necessary for ultra- high speed electronics technology through R and D of technology controlling conditions of beams and electrons in a femtosecond (10{sup -15}-10{sup -12} seconds) region. In fiscal 1998, this project first succeeded in fabrication of a prototype pulse compressor by using semiconductors, and developed a new pulse compressing method by using fibers to generate ultra-short pulse of 38fs. By developing new materials for intersubband transition where ultra-high speed responses can be expected, optical absorption by intersubband transition was first confirmed at optical communication wavelength. The main result for every theme is reported and explained. (NEDO)

  11. Plasma shape control by pulsed solenoid on laser ion source

    Science.gov (United States)

    Sekine, M.; Ikeda, S.; Romanelli, M.; Kumaki, M.; Fuwa, Y.; Kanesue, T.; Hayashizaki, N.; Lambiase, R.; Okamura, M.

    2015-09-01

    A Laser ion source (LIS) provides high current heavy ion beams with a very simple mechanical structure. Plasma is produced by a pulsed laser ablation of a solid state target and ions are extracted by an electric field. However, it was difficult to manipulate the beam parameters of a LIS, since the plasma condition could only be adjusted by the laser irradiation condition. To enhance flexibility of LIS operation, we employed a pulsed solenoid in the plasma drift section and investigated the effect of the solenoid field on singly charged iron beams. The experimentally obtained current profile was satisfactorily controlled by the pulsed magnetic field. This approach may also be useful to reduce beam emittance of a LIS.

  12. Plasma shape control by pulsed solenoid on laser ion source

    International Nuclear Information System (INIS)

    Sekine, M.; Ikeda, S.; Romanelli, M.; Kumaki, M.; Fuwa, Y.; Kanesue, T.; Hayashizaki, N.; Lambiase, R.; Okamura, M.

    2015-01-01

    A Laser ion source (LIS) provides high current heavy ion beams with a very simple mechanical structure. Plasma is produced by a pulsed laser ablation of a solid state target and ions are extracted by an electric field. However, it was difficult to manipulate the beam parameters of a LIS, since the plasma condition could only be adjusted by the laser irradiation condition. To enhance flexibility of LIS operation, we employed a pulsed solenoid in the plasma drift section and investigated the effect of the solenoid field on singly charged iron beams. The experimentally obtained current profile was satisfactorily controlled by the pulsed magnetic field. This approach may also be useful to reduce beam emittance of a LIS

  13. Preparation of Monolayer MoS2 Quantum Dots using Temporally Shaped Femtosecond Laser Ablation of Bulk MoS2 Targets in Water

    OpenAIRE

    Li, Bo; Jiang, Lan; Li, Xin; Ran, Peng; Zuo, Pei; Wang, Andong; Qu, Liangti; Zhao, Yang; Cheng, Zhihua; Lu, Yongfeng

    2017-01-01

    Zero-dimensional MoS2 quantum dots (QDs) possess distinct physical and chemical properties, which have garnered them considerable attention and facilitates their use in a broad range of applications. In this study, we prepared monolayer MoS2 QDs using temporally shaped femtosecond laser ablation of bulk MoS2 targets in water. The morphology, crystal structures, chemical, and optical properties of the MoS2 QDs were characterized by transmission electron microscopy, X-ray diffraction, Raman spe...

  14. Pulse shape discrimination with silicon detectors using charge and current-sensitive preamplifiers

    Energy Technology Data Exchange (ETDEWEB)

    Hamrita, H.; Rauly, E.; Blumenfeld, Y.; Borderie, B.; Chabot, M.; Edelbruck, P.; Lavergne, L.; Le Bris, J.; Le Neindre, N.; Richard, A.; Rivet, M.F.; Scarpaci, J.A.; Barbey, S.; Becheva, E.; Bzyl, F.R.; D' Esesquelles, P.; Galichet, E.; Lalu, G.; Martinet, G.; Pierre, S. [Institut de Physique Nucleaire, IN2P3-CNRS, 91 - Orsay (France); Legou, Th.; Tillier, J.; Bocage, F.; Bougault, R.; Carniol, B.; Cussol, D.; Etasse, D.; Grevy, S.; Lopez, O.; Tamain, B.; Vient, E. [Caen Univ., LPC, IN2P3-CNRS, ENSI, 14 - Caen (France); Galichet, E. [Conservatoire National des Arts et Metier, 75 - Paris (France); Guinet, D.; Lautesse, Ph. [Villeurbanne Univ., Institut de Physique Nucleaire, IN2P3-CNRS, 69 (France); Lanzalone, G. [Catania Univ., INFN, Laboratori Nazionali del Sud and Dipartimento di Fisica e Astronomia, (Italy); Politi, G. [Catania Univ., INFN, Sezione di Catania and Dipartimento di Fisica e Astronomia (Italy); Rosato, E. [Napoli, Univ., Dipt. di Scienze Fisiche e Sezione INFN (Italy)

    2003-07-01

    For the first time shapes of current pulses from light charged particles and carbon ions are presented. Capabilities for pulse shape discrimination techniques are demonstrated. In this work, charge and current-sensitive preamplifier prototypes for nuclear structure and dynamics experiments have been developed and tested with the aim of improving PSD (pulse shape discrimination) method by studying in detail current signal shapes from particles and ions over a large energy range. Note that current signal shapes have been recently used in atomic cluster studies to identify partitions of carbon cluster fragmentation. The paper is organized as follows. Section 2 is devoted to characterization of preamplifiers. In section 3, results of on beam tests will be presented, discussed and compared to a simple simulation.

  15. Comparative study of the dissociative ionization of 1,1,1-trichloroethane using nanosecond and femtosecond laser pulses

    CSIR Research Space (South Africa)

    Du Plessis, A

    2010-03-01

    Full Text Available the fragmentation pattern, while at high femtosecond intensities large changes are observed in relative ion peak sizes. The total ionization yield and fragmentation ratios are presented for a range of wavelengths and intensities, and compared to the changes observed...

  16. Research on spectrum broadening covering visible light of a fiber femtosecond optical frequency comb for absolute frequency measurement

    Science.gov (United States)

    Xing, Shuai; Wu, Tengfei; Li, Shuyi; Xia, Chuanqing; Han, Jibo; Zhang, Lei; Zhao, Chunbo

    2018-03-01

    As a bridge connecting microwave frequency and optical frequency, femtosecond laser has important significance in optical frequency measurement. Compared with the traditional Ti-sapphire femtosecond optical frequency comb, with the advantages of compact structure, strong anti-interference ability and low cost, the fiber femtosecond optical frequency comb has a wider application prospect. An experiment of spectrum broadening in a highly nonlinear photonic crystal fiber pumped by an Er-fiber mode-locked femtosecond laser is studied in this paper. Based on optical amplification and frequency doubling, the central wavelength of the output spectrum is 780nm and the average power is 232mW. With the femtosecond pulses coupled into two different photonic crystal fibers, the coverage of visible spectrum is up to 500nm-960nm. The spectral shape and width can be optimized by changing the polarization state for satisfying the requirments of different optical frequencies measurement.

  17. Electron pulse shaping in the FELIX RF accelerator

    NARCIS (Netherlands)

    Weits, H. H.; van der Geer, C. A. J.; Oepts, D.; van der Meer, A. F. G.

    1999-01-01

    The FELIX free-electron laser uses short pulses of relativistic electrons produced by an RF accelerator. The design target for the duration of these electron bunches was around 3 ps. In experiments we observed that the bunches emit coherently enhanced spontaneous emission (CSE) when they travel

  18. Influence of amplification on pulse shaping for coherent control applications

    CSIR Research Space (South Africa)

    Du Plessis, A

    2011-07-01

    Full Text Available irradiation by near transform limited pulses, using time of flight mass spectroscopy and confirmed by gas chromatography. This product is confirmed to only be formed when H2 is also present in the reaction cell. There is also evidence for C-H and C-C bond...

  19. Photon polarization in Compton scattering: pulse shape effects

    International Nuclear Information System (INIS)

    Boca, M; Stoica, C; Dumitriu, A; Florescu, V

    2015-01-01

    We study in the framework of quantum electrodynamics the scattering of a plane wave electromagnetic field on free electrons in the low intensity limit. We derive analytic formulas describing the polarization properties of the emitted photons. We discuss and illustrate with a numerical example the effects of the electromagnetic pulse duration on their polarization

  20. The Trichel pulse corona in N2 + CCl2F2 mixtures: the shape of pulses

    International Nuclear Information System (INIS)

    Vagnerova, L.; Dindosova, D.; Skalny, J.D.

    1998-01-01

    The formation of regular Trichel pulses in electronegative gaseous mixtures is studied experimentally, with emphasis on the consequences of different electron attachment mechanisms in the used gas mixtures on the behavior of the discharge. Negative ions are believed to be responsible for excitation of the Trichel pulses. The experimental data presented in the paper give evidence that the origin of the negative ions does not play any substantial role in the formation of the initial part of the Trichel pulses. (J.U.)

  1. Simulation of neutrons and gamma pulse signal and research on the pulse shape discrimination technology

    International Nuclear Information System (INIS)

    Zuo Guangxia; He Bin; Xu Peng; Qiu Xiaolin; Ma Wenyan; Li Sufen

    2012-01-01

    In neutrons detection, it is important to discriminate the neutron signals from the gamma-ray background. In this article, simulation of neutrons and gamma pulse signals is developed based on the LabVIEW platform. Two digital algorithms of the charge comparison method and the pulse duration time method are realized using 10000 simulation signals. Experimental results show that neutron and gamma pulse signals can be discriminated by the two methods, and the pulse duration time method is better than the charge comparison method. (authors)

  2. Generation, shaping, compression, characterization and application of intense ultrashort laser pulses

    CERN Document Server

    Cheng, Z

    2001-01-01

    Recently, the development of intense ultrashort laser pulses has attracted much interest because of their significant applications in many fields of science and technology. This thesis contributes to the generation, shaping, compression, characterization and application of intense ultrashort laser pulses as follows: 1. Laser pulses of 17.5-fs with a peak power of 0.1-TW at 1-kHz repetition rate have been generated by a compact single-stage ten-pass Ti:sapphire amplifier system with a high-order-dispersion-mirror compensator and a spectral shaping for the first time. The experimental results are in reasonable agreement with numerical calculations. 2. The first experimental study on arbitrary shaping of intense ultrashort pulses has been conducted in a kHz amplifier system capable of generating 27 fs pulses by using an acousto-optic programmable dispersive filter (AOPDF). 17-fs transform-limited pulses have been achieved and arbitrary shaping of these 17-fs pulses has been demonstrated both in the temporal and ...

  3. Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

    DEFF Research Database (Denmark)

    Canton, Sophie E.; Kjær, Kasper S.; Vankó, György

    2015-01-01

    Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectrosc...... states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined....... as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Experimental and theoretical results establish that mediation through electronically excited molecular...

  4. Femtosecond pulse laser-induced self-organized nanostructures on the surface of ZnO crystal

    International Nuclear Information System (INIS)

    Zhong Minjian; Guo Guanglei; Yang Junyi; Ma Ninghua; Ye Guo; Ma Hongliang; Guo Xiaodong; Li Ruxin

    2008-01-01

    This paper reports self-organized nanostructures observed on the surface of ZnO crystal after irradiation by a focused beam of a femtosecond Ti:sapphire laser with a repetition rate of 250 kHz. For a linearly polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was promoted. The period of self-organization structures is about 180 nm. The grating orientation is adjusted by the laser polarization direction. A long range Bragg-like grating is formed by moving the sample at a speed of 10 μm/s. For a circularly polarized laser beam, uniform spherical nanoparticles were formed as a result of Coulomb explosion during the interaction of near-infrared laser with ZnO crystal

  5. Shaping and timing gradient pulses to reduce MRI acoustic noise

    NARCIS (Netherlands)

    Segbers, Marcel; Sierra, Carlos V. Rizzo; Duifhuis, Hendrikus; Hoogduin, Johannes M.

    A method to reduce the acoustic noise generated by gradient systems in MRI has been recently proposed; such a method is based on the linear response theory. Since the physical cause of MRI acoustic noise is the time derivative of the gradient current, a common trapezoid current shape produces an

  6. Pulse Shape Analysis and Discrimination for Silicon-Photomultipliers in Helium-4 Gas Scintillation Neutron Detector

    Science.gov (United States)

    Barker, Cathleen; Zhu, Ting; Rolison, Lucas; Kiff, Scott; Jordan, Kelly; Enqvist, Andreas

    2018-01-01

    Using natural helium (helium-4), the Arktis 180-bar pressurized gas scintillator is capable of detecting and distinguishing fast neutrons and gammas. The detector has a unique design of three optically separated segments in which 12 silicon-photomultiplier (SiPM) pairs are positioned equilaterally across the detector to allow for them to be fully immersed in the helium-4 gas volume; consequently, no additional optical interfaces are necessary. The SiPM signals were amplified, shaped, and readout by an analog board; a 250 MHz, 14-bit digitizer was used to examine the output pulses from each SiPMpair channel. The SiPM over-voltage had to be adjusted in order to reduce pulse clipping and negative overshoot, which was observed for events with high scintillation production. Pulse shaped discrimination (PSD) was conducted by evaluating three different parameters: time over threshold (TOT), pulse amplitude, and pulse integral. In order to differentiate high and low energy events, a 30ns gate window was implemented to group pulses from two SiPM channels or more for the calculation of TOT. It was demonstrated that pulses from a single SiPM channel within the 30ns window corresponded to low-energy gamma events while groups of pulses from two-channels or more were most likely neutron events. Due to gamma pulses having lower pulse amplitude, the percentage of measured gamma also depends on the threshold value in TOT calculations. Similarly, the threshold values were varied for the optimal PSD methods of using pulse amplitude and pulse area parameters. Helium-4 detectors equipped with SiPMs are excellent for in-the-field radiation measurement of nuclear spent fuel casks. With optimized PSD methods, the goal of developing a fuel cask content monitoring and inspection system based on these helium-4 detectors will be achieved.

  7. Performance scaling via passive pulse shaping in cavity-enhanced optical parametric chirped-pulse amplification.

    Science.gov (United States)

    Siddiqui, Aleem M; Moses, Jeffrey; Hong, Kyung-Han; Lai, Chien-Jen; Kärtner, Franz X

    2010-06-15

    We show that an enhancement cavity seeded at the full repetition rate of the pump laser can automatically reshape small-signal gain across the interacting pulses in an optical parametric chirped-pulse amplifier for close-to-optimal operation, significantly increasing both the gain bandwidth and the conversion efficiency, in addition to boosting gain for high-repetition-rate amplification. Applied to a degenerate amplifier, the technique can provide an octave-spanning gain bandwidth.

  8. Shaping the Spontaneous Emission Pulse from a Superconducting Qubit

    Science.gov (United States)

    Srinivasan, Srikanth; Liu, Yanbing; Zhang, Gengyan; Yu, Terri; Gambetta, Jay; Girvin, Steven; Houck, Andrew

    2013-03-01

    We report on measurements of spontaneous emission in a circuit quantum electrodynamics system. A superconducting qubit with tunable coupling to a coplanar waveguide cavity is operated in a regime where the qubit relaxation time, and consequently the spontaneous emission rate, is dominated by the interaction strength. This fast control knob on the coupling strength is used to shape the emitted single photon's wavepacket. The independent control over the coupling allows the dressed qubit frequency to remain truly constant during the emission. The wavepacket shape becomes important in experiments where quantum information needs to be transported between various nodes in a quantum network. The transfer can happen with a very high fidelity if the wavepacket is time-symmetric, since emission by the source and absorption by the destination become time reversed processes. Authors would like to thank IARPA for their generous support.

  9. Investigation of novel shape-controlled linearly and circularly polarized attosecond pulse sources

    International Nuclear Information System (INIS)

    Tóth, György; Tibai, Zoltán; Nagy-Csiha, Zsuzsanna; Márton, Zsuzsanna; Almási, Gábor; Hebling, János

    2016-01-01

    In this article, we investigate the temporal shape of one- or few-cycle, 20–180 nm central wavelength attosecond pulses that are produced in a scheme based on coherent undulator radiation. It is demonstrated, that the carrier–envelope phase (CEP) of the radiated electric field can be chosen arbitrarily by shaping the magnetic field of the radiator undulator appropriately. It is shown that the temporal shape and the spectrum of the generated electric field are influenced by the spatial shape and amplitude of the magnetic field of the radiator undulator for different central wavelength pulses, while both are practically independent of the energy of the initial electron bunch. Shape distortions at high K undulator parameters are also discussed.

  10. Formation of periodic mesoscale structures arranged in a circular symmetry at the silicon surface exposed to radiation of a single femtosecond laser pulse

    International Nuclear Information System (INIS)

    Romashevskiy, S.A.; Ashitkov, S.I.; Ovchinnikov, A.V.; Kondratenko, P.S.; Agranat, M.B.

    2016-01-01

    Graphical abstract: - Highlights: • Single pulse irradiation of silicon gave rise to the periodic mesoscale structures. • The number of the periodic structures depends on the incident laser fluence. • The theory of periodically modulated absorption of laser energy is proposed. - Abstract: The periodic mesoscale structures arranged in a circular symmetry were found at the silicon surface exposed to radiation of the single femtosecond laser pulse with a Gaussian intensity profile in the ambient air conditions. These peculiar structures have the appearance of the protrusions of ∼10 nm height and of ∼600 nm width (at a FWHM) separately located inside the ablated region with a period of the incident laser wavelength. It was found that their position at the surface corresponds to the specified laser intensity slightly above the ablation threshold. The number of the formed periodic structures varies with the fluence of the incident laser pulse and in our experiments it was found to have changed from one to eleven. We suppose that formation of these mesoscale structures is caused by heating of a microscale volume to the strongly defined temperature. The theoretical model was proposed to explain the obtained data. It assumes that the interference of incident laser radiation with laser-induced surface electromagnetic waves results in generation of periodic distribution of electron temperature. Thus formation of the periodic structures at the specified laser intensity is attributed to periodically modulated absorption of laser energy at a focal laser spot.

  11. Laser pulse shape design for laser-indirect-driven quasi-isentropic compression experiments

    Science.gov (United States)

    Xue, Quanxi; Jiang, Shaoen; Wang, Zhebin; Wang, Feng; Zhao, Xueqing; Ding, Yongkun

    2018-02-01

    Laser pulse shape design is a key work in the design of indirect-laser-driven experiments, especially for long pulse laser driven quasi-isentropic compression experiments. A method for designing such a laser pulse shape is given here. What's more, application experiments were performed, and the results of a typical shot are presented. At last of this article, the details of the application of the method are discussed, such as the equation parameter choice, radiation ablation pressure expression, and approximations in the method. The application shows that the method can provide reliable descriptions of the energy distribution in a hohlraum target; thus, it can be used in the design of long-pulse laser driven quasi-isentropic compression experiments and even other indirect-laser-driven experiments.

  12. Nanosecond and femtosecond ablation of La0.6Ca0.4CoO3: a comparison between plume dynamics and composition of the films

    DEFF Research Database (Denmark)

    Canulescu, Stela; Papadopoulou, E.; Anglos, D.

    2011-01-01

    Thin films of La0.6Ca0.4CoO3 were grown by pulsed laser ablation with nanosecond and femtosecond pulses. The films deposited with femtosecond pulses (248 nm, 500 fs pulse duration) exhibit a higher surface roughness and deficiency in the cobalt content compared to the films deposited with nanosec......Thin films of La0.6Ca0.4CoO3 were grown by pulsed laser ablation with nanosecond and femtosecond pulses. The films deposited with femtosecond pulses (248 nm, 500 fs pulse duration) exhibit a higher surface roughness and deficiency in the cobalt content compared to the films deposited...... and in a background pressure of 60 Pa of oxygen. The ns-induced plume in vacuum exhibits a spherical shape, while for femtosecond ablation the plume is more elongated along the expansion direction, but with similar velocities for ns and fs laser ablation. In the case of ablation in the background gas similar...

  13. The optimal input optical pulse shape for the self-phase modulation based chirp generator

    Science.gov (United States)

    Zachinyaev, Yuriy; Rumyantsev, Konstantin

    2018-04-01

    The work is aimed to obtain the optimal shape of the input optical pulse for the proper functioning of the self-phase modulation based chirp generator allowing to achieve high values of chirp frequency deviation. During the research, the structure of the device based on self-phase modulation effect using has been analyzed. The influence of the input optical pulse shape of the transmitting optical module on the chirp frequency deviation has been studied. The relationship between the frequency deviation of the generated chirp and frequency linearity for the three options for implementation of the pulse shape has been also estimated. The results of research are related to the development of the theory of radio processors based on fiber-optic structures and can be used in radars, secure communications, geolocation and tomography.

  14. Shaping the output pulse of a linear-transformer-driver module

    Directory of Open Access Journals (Sweden)

    W. A. Stygar

    2009-03-01

    Full Text Available We demonstrate that a wide variety of current-pulse shapes can be generated using a linear-transformer-driver (LTD module that drives an internal water-insulated transmission line. The shapes are produced by varying the timing and initial charge voltage of each of the module’s cavities. The LTD-driven accelerator architecture outlined in [Phys. Rev. ST Accel. Beams 10, 030401 (2007PRABFM1098-440210.1103/PhysRevSTAB.10.030401] provides additional pulse-shaping flexibility by allowing the modules that drive the accelerator to be triggered at different times. The module output pulses would be combined and symmetrized by water-insulated radial-transmission-line impedance transformers [Phys. Rev. ST Accel. Beams 11, 030401 (2008PRABFM1098-440210.1103/PhysRevSTAB.11.030401].

  15. Tests on a digital neutron-gamma pulse shape discriminator with NE213

    International Nuclear Information System (INIS)

    Bell, Z.W.

    1981-01-01

    A technique using charge sensitive analog-to-digital converters to do neutron-gamma pulse shape discrimination is reported. The converters are gated by short (135 ns) pulses so as to reduce pile-up and the timing is such that the slow and total light output from the scintillator are measured. Preliminary tests indicate that the system performs reasonably well but poorer than some reported analog systems employing gated integrators or cross-over techniques. (orig.)

  16. Study and Characterization of Subharmonic Emissions by Using Shaped Ultrasonic Driving Pulse

    Science.gov (United States)

    Masotti, L.; Biagi, E.; Breschi, L.; Vannacci, E.

    Subharmonic emissions from Ultrasound Contrast Agents (UCAs) were studied by a Pulse Inversion method in order to assess the feasibility of implementation of this technique to subharmonic imaging. Interesting results concerning the dependence of the subharmonic emission with respect to initial pulse shape are presented. The experimentation was performed also by varying the acoustic pressure and concentration of the contrast agent (SonoVue®)

  17. Multidimensional spectroscopy with a single broadband phase-shaped laser pulse

    International Nuclear Information System (INIS)

    Glenn, Rachel; Mukamel, Shaul

    2014-01-01

    We calculate the frequency-dispersed nonlinear transmission signal of a phase-shaped visible pulse to fourth order in the field. Two phase profiles, a phase-step and phase-pulse, are considered. Two dimensional signals obtained by varying the detected frequency and phase parameters are presented for a three electronic band model system. We demonstrate how two-photon and stimulated Raman resonances can be manipulated by the phase profile and sign, and selected quantum pathways can be suppressed

  18. Wilcoxon signed-rank-based technique for the pulse-shape analysis of HPGe detectors

    Energy Technology Data Exchange (ETDEWEB)

    Martín, S., E-mail: sergiomr@usal.es; Quintana, B.; Barrientos, D.

    2016-07-01

    The characterization of the electric response of segmented-contact high-purity germanium detectors requires scanning systems capable of accurately associating each pulse with the position of the interaction that generated it. This process requires an algorithm sensitive to changes above the electronic noise in the pulse shapes produced at different positions, depending on the resolution of the Ge crystal. In this work, a pulse-shape comparison technique based on the Wilcoxon signed-rank test has been developed. It provides a method to distinguish pulses coming from different interaction points in the germanium crystal. Therefore, this technique is a necessary step for building a reliable pulse-shape database that can be used later for the determination of the position of interaction for γ-ray tracking spectrometry devices such as AGATA, GRETA or GERDA. The method was validated by comparison with a χ{sup 2} test using simulated and experimental pulses corresponding to a Broad Energy germanium detector (BEGe).

  19. Pulse shaping and energy storage capabilities of angularly multiplexed KrF laser fusion drivers

    Science.gov (United States)

    Lehmberg, R. H.; Giuliani, J. L.; Schmitt, A. J.

    2009-07-01

    This paper describes a rep-rated multibeam KrF laser driver design for the 500kJ Inertial Fusion test Facility (FTF) recently proposed by NRL, then models its optical pulse shaping capabilities using the ORESTES laser kinetics code. It describes a stable and reliable iteration technique for calculating the required precompensated input pulse shape that will achieve the desired output shape, even when the amplifiers are heavily saturated. It also describes how this precompensation technique could be experimentally implemented in real time on a reprated laser system. The simulations show that this multibeam system can achieve a high fidelity pulse shaping capability, even for a high gain shock ignition pulse whose final spike requires output intensities much higher than the ˜4MW/cm2 saturation levels associated with quasi-cw operation; i.e., they show that KrF can act as a storage medium even for pulsewidths of ˜1ns. For the chosen pulse, which gives a predicted fusion energy gain of ˜120, the simulations predict the FTF can deliver a total on-target energy of 428kJ, a peak spike power of 385TW, and amplified spontaneous emission prepulse contrast ratios IASE/Ilaser.

  20. Spatio-temporal shaping of photocathode laser pulses for linear electron accelerators

    Science.gov (United States)

    Mironov, S. Yu; Andrianov, A. V.; Gacheva, E. I.; Zelenogorskii, V. V.; Potemkin, A. K.; Khazanov, E. A.; Boonpornprasert, P.; Gross, M.; Good, J.; Isaev, I.; Kalantaryan, D.; Kozak, T.; Krasilnikov, M.; Qian, H.; Li, X.; Lishilin, O.; Melkumyan, D.; Oppelt, A.; Renier, Y.; Rublack, T.; Felber, M.; Huck, H.; Chen, Y.; Stephan, F.

    2017-10-01

    Methods for the spatio-temporal shaping of photocathode laser pulses for generating high brightness electron beams in modern linear accelerators are discussed. The possibility of forming triangular laser pulses and quasi-ellipsoidal structures is analyzed. The proposed setup for generating shaped laser pulses was realised at the Institute of Applied Physics (IAP) of the Russian Academy of Sciences (RAS). Currently, a prototype of the pulse-shaping laser system is installed at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). Preliminary experiments on electron beam generation using ultraviolet laser pulses from this system were carried out at PITZ, in which electron bunches with a 0.5-nC charge and a transverse normalized emittance of 1.1 mm mrad were obtained. A new scheme for the three-dimensional shaping of laser beams using a volume Bragg profiled grating is proposed at IAP RAS and is currently being tested for further electron beam generation experiments at the PITZ photoinjector.

  1. Systematic study of high-order harmonic optimal control by temporal pulse shaping of laser pulses

    International Nuclear Information System (INIS)

    Boyko, O.; Valentin, C.; Mercier, B.; Coquelet, Ch.; Pascal, V.; Papalazarou, E.; Rey, G.; Balcou, Ph.

    2007-01-01

    We explore experimentally and numerically the physics underlying the optimization of high-order harmonic generation by intense laser pulses, whose temporal profile is tailored by a learning genetic algorithm. Based on a large set of optimization data obtained under different generation parameters, we show that the algorithm converges toward a class of very special profiles on the leading edge of the pulse. The behavior of the harmonic signal is then compared with theoretical simulations based on the time-dependent Schroedinger equation, allowing one to identify separately the role of microscopic and macroscopic phenomena in the temporal dynamics of high-harmonic generation and optimization

  2. A Novel Ring Shaped Photodiode for Reflectance Pulse Oximetry in Wireless Applications

    DEFF Research Database (Denmark)

    Duun, Sune; Haahr, Rasmus Grønbek; Birkelund, Karen

    2007-01-01

    We present a pulse oximeter for use in home-care applications in a sticking patch with integrated electronics. The core in the pulse oximeter is a large ring shaped backside silicon pn photodiode placed around a Ledtronics dual LED with wavelengths of 660 nm and 940 nm. The concentric photodiode...... photodiode has an inner-outer radius of 3.29 -4.07 mm and an area of 18 mm2 , however, photodiodes with ring center radii ranging from 2.8 -4.9 mm have been fabricated. Using the pulse oxymetry sensor photoplethysmograms clearly showing the cardiovascular cycle are recorded. An on-chip integrated Au...

  3. Rejecting escape events in large volume Ge detectors by a pulse shape selection procedure

    Energy Technology Data Exchange (ETDEWEB)

    Del Zoppo, A. (Istituto Nazionale di Fisica Nucleare - Laboratorio Nazionale del Sud, Catania (Italy)); Agodi, C. (Istituto Nazionale di Fisica Nucleare - Laboratorio Nazionale del Sud, Catania (Italy)); Alba, R. (Istituto Nazionale di Fisica Nucleare - Laboratorio Nazionale del Sud, Catania (Italy)); Bellia, G. (Istituto Nazionale di Fisica Nucleare - Laboratorio Nazionale del Sud, Catania (Italy) Dipartimento di Fisica dell' Universita, Catania (Italy)); Coniglione, R. (Istituto Nazionale di Fisica Nucleare - Laboratorio Nazionale del Sud, Catania (Italy)); Loukachine, K. (Istituto Nazionale di Fisica Nucleare - Laboratorio Nazionale del Sud, Catania (Italy)); Maiolino, C. (Istituto Nazionale di Fisica Nucleare - Laboratorio Nazionale del Sud, Catania (Italy)); Migneco, E. (Istituto Nazionale di Fisica Nucleare - Laboratorio Nazionale del Sud, Catania (Italy) Dipartimento di Fisica dell' Universita, Catania (Italy)); Piattelli, P. (Istituto Nazionale di Fisica Nucleare - Labora

    1993-10-01

    The dependence of the response to [gamma]-rays of a large volume Ge detector on the interval width of a selected initial rise pulse slope is investigated. The number of escape events associated with a small pulse slope is found to be greater than the corresponding number of full energy events. An escape event rejection procedure based on the observed correlation between energy deposition and pulse shape is discussed. Such a procedure seems particularly suited for the design of highly granular large volume Ge detector arrays. (orig.)

  4. Rejecting escape events in large volume Ge detectors by a pulse shape selection procedure

    International Nuclear Information System (INIS)

    Del Zoppo, A.; Agodi, C.; Alba, R.; Bellia, G.; Coniglione, R.; Loukachine, K.; Maiolino, C.; Migneco, E.; Piattelli, P.; Santonocito, D.; Sapienza, P.

    1993-01-01

    The dependence of the response to γ-rays of a large volume Ge detector on the interval width of a selected initial rise pulse slope is investigated. The number of escape events associated with a small pulse slope is found to be greater than the corresponding number of full energy events. An escape event rejection procedure based on the observed correlation between energy deposition and pulse shape is discussed. Such a procedure seems particularly suited for the design of highly granular large volume Ge detector arrays. (orig.)

  5. Modeling the Pulse Signal by Wave-Shape Function and Analyzing by Synchrosqueezing Transform.

    Directory of Open Access Journals (Sweden)

    Hau-Tieng Wu

    Full Text Available We apply the recently developed adaptive non-harmonic model based on the wave-shape function, as well as the time-frequency analysis tool called synchrosqueezing transform (SST to model and analyze oscillatory physiological signals. To demonstrate how the model and algorithm work, we apply them to study the pulse wave signal. By extracting features called the spectral pulse signature, and based on functional regression, we characterize the hemodynamics from the radial pulse wave signals recorded by the sphygmomanometer. Analysis results suggest the potential of the proposed signal processing approach to extract health-related hemodynamics features.

  6. Femtosecond damage resistance of femtosecond multilayer and hybrid mirrors.

    Science.gov (United States)

    Csajbók, Viktória; Szikszai, Lőrinc; Nagy, Benedek J; Dombi, Péter

    2016-08-01

    Improving the laser-induced damage threshold of optical components is a basic endeavor in femtosecond technology. By testing more than 30 different femtosecond mirrors with 42 fs laser pulses at 1 kHz repetition rate, we found that a combination of high-bandgap dielectric materials and improved design and coating techniques enable femtosecond multilayer damage thresholds exceeding 2  J/cm2 in some cases. A significant ×2.5 improvement in damage resistance can also be achieved for hybrid Ag-multilayer mirrors exhibiting more than 1  J/cm2 threshold with a clear anticorrelation between damage resistance and peak field strength in the stack. Slight dependence on femtosecond pulse length and substantial decrease for high (megahertz) repetition rates are also observed.

  7. Design of one-dimensional optical pulse-shaping filters by time-domain topology optimization

    DEFF Research Database (Denmark)

    Yang, Lirong; Lavrinenko, Andrei; Hvam, Jørn Märcher

    2009-01-01

    Time-domain topology optimization is used here to design optical pulse-shaping filters in Si/SiO2 thin-film systems. A novel envelope objective function as well as explicit penalization are used to adapt the optimization method to this unique class of design problems.......Time-domain topology optimization is used here to design optical pulse-shaping filters in Si/SiO2 thin-film systems. A novel envelope objective function as well as explicit penalization are used to adapt the optimization method to this unique class of design problems....

  8. A nonlinearity-tolerant frequency domain root M-shaped pulse for coherent optical communication systems.

    Science.gov (United States)

    Xu, Xian; Zhuge, Qunbi; Châtelain, Benoît; Morsy-Osman, Mohamed; Chagnon, Mathieu; Qiu, Meng; Plant, David V

    2013-12-30

    A new intersymbol interference (ISI)-free nonlinearity-tolerant frequency domain root M-shaped pulse (RMP) is derived for dispersion unmanaged coherent optical transmission systems. Beginning with the relationship between pulse shaping and intra-channel nonlinearity effects, we derive closed-form expressions for the proposed pulse. Experimental demonstrations reveal that by employing the proposed pulse at a roll-off factor of 1, the maximum transmission reach of a single-channel 56 Gb/s polarization-division-multiplexed quadrature phase-shift keying (PDM-QPSK) system can be extended by 33% and 17%, when compared to systems using a root raised cosine (RRC) pulse and a root optimized pulse (ROP), respectively. For a single-channel 128 Gb/s polarization-division-multiplexed 16-quadrature amplitude modulation (PDM-16QAM) system, the reach can be extended by 44% and 18%, respectively. Reach increases of 30% and 13% are also observed for a dense wavelength-division multiplexing (DWDM) 504 Gb/s PDM-QPSK transmission system. The tolerance to narrow filtering effect for the three pulses is experimentally studied as well.

  9. Shaping light with MOEMS

    Science.gov (United States)

    Noell, W.; Weber, S.; Masson, J.; Extermann, J.; Bonacina, L.; Bich, A.; Bitterli, R.; Herzig, H. P.; Kiselev, D.; Scharf, T.; Voelkel, R.; Weible, K. J.; Wolf, J.-P.; de Rooij, N. F.

    2011-03-01

    Shaping light with microtechnology components has been possible for many years. The Texas Instruments digital micromirror device (DMD) and all types of adaptive optics systems are very sophisticated tools, well established and widely used. Here we present, however, two very dedicated systems, where one is an extremely simple MEMS-based tunable diffuser, while the second device is complex micromirror array with new capabilities for femtosecond laser pulse shaping. Showing the two systems right next to each other demonstrates the vast options and versatility of MOEMS for shaping light in the space and time domain.

  10. Pulse-shape Discrimination in Organic Scintillators Using the Rising Edge

    International Nuclear Information System (INIS)

    Jones, A.; Joyce, M.J.

    2013-06-01

    The possibility of discriminating between neutrons and γ rays on the basis of differences in the rising edge of corresponding pulses from organic scintillation detectors is described. It has long been known that radiation type can be discerned on the basis of subtle differences in pulse shape from a variety of detection materials, but discrimination in fast organic scintillators has long been reliant on the separation in decay face of the pulse. This can constrain pulse-shape discrimination techniques to follow after the peak amplitude of the event and they can thus be more susceptible to the effects of pile up. Furthermore, discrimination in the decay face places a fundamental limit on the time relative to the evolution of the event when discrimination can be performed and thus this can be a significant constraint on the event processing rate for high pulse-rate applications. In this paper the correspondence between established mathematical models of organic pulse shape and real events in the rising edge part of the event is investigated, and the potential for rise-time based pulse-shape discrimination in mixed-field data from organic scintillators is explored. Special nuclear materials (SNM) are of particular interest to security surveillance and based on active interrogation. Active interrogation involves neutrons hitting a material that is fissile, and detecting the emitted γ rays and neutrons to try and classify materials. Faster, more efficient and more transportable devices are being sought to help in the prevention of illicit transport of nuclear materials. SNM are difficult to detect due to high-flux γ emissions, and very low neutron signatures (authors)

  11. Fiscal 1997 report under consignment from NEDO on the R and D of femto-second technology (development of ultra short pulse optoelectronics technology); 1997 nendo Shin energy Sangyo Gijutsu Sogo Kaihatsu Kiko itaku femto gyo technology no kenkyu kaihatsu (chotan pulse ko electronics gijutsu kaihatsu) seika hokokusho

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-03-01

    Very high speed electronics technology is indispensable for the creation of industrial base technology which supports high grade informatizing in the 21st century. The state of light and electronics is controlled in the femto-second time domain. As to the development of femto-second light pulse generation/transmission technology, mode synchronous semiconductor laser was manufactured using the strain quantum well structure aiming at heightening profit, and the repeated frequency, 166GHz, was achieved. Relating to the pulse compression element, exciton photonic band was newly designed. A technology of coding was also studied. As to the development of technology of femto-second light pulse control/distribution, shortening of the wavelength down to 1.5{mu}m and a possibility of femto-second domain high speed response were indicated by the combined double quantum well structure. The quantitative measurement of spin relaxation characteristics was successfully made. By the Mach-Zehnder light switch, obtained was the world`s fastest light switching characteristic. To realize the femto-second class very high speed element, conditions were grasped on the crystal growth of Sb based ultra thin films operating in the 1.5{mu}m zone by studying the quantum well using transition among sub-bands. 242 refs., 280 figs., 12 tabs.

  12. Low-cost cavity-dumped femtosecond Cr:LiSAF laser producing >100 nJ pulses.

    Science.gov (United States)

    Demirbas, Umit; Hong, Kyung-Han; Fujimoto, James G; Sennaroglu, Alphan; Kärtner, Franz X

    2010-02-15

    We report a low-cost cavity-dumped Cr:colquiriite laser for generating enhanced pulse energies. Four single-mode laser diodes were used to pump a Cr:LiSAF laser, which was mode locked with a semiconductor saturable absorber mirror. Cavity dumping at 10 kHz repetition rate, the laser generated approximately 120 fs pulses at approximately 825 nm, with 112 nJ pulse energies and approximately 0.93 MW of peak power, using only approximately 600 mW of incident pump power. At higher dumping rates of up to 1 MHz, reduced pulse energies of 62 nJ could be generated. Two-photon absorption in the saturable absorber mirror limits pulse durations, while Q-switching instabilities limit pulse energy extraction.

  13. Low Group Delay Dispersion Optical Coating for Broad Bandwidth High Reflection at 45° Incidence, P Polarization of Femtosecond Pulses with 900 nm Center Wavelength

    Directory of Open Access Journals (Sweden)

    John C. Bellum

    2016-03-01

    Full Text Available We describe an optical coating design suitable for broad bandwidth high reflection (BBHR at 45° angle of incidence (AOI, P polarization (Ppol of femtosecond (fs laser pulses whose wavelengths range from 800 to 1000 nm. Our design process is guided by quarter-wave HR coating properties. The design must afford low group delay dispersion (GDD for reflected light over the broad, 200 nm bandwidth in order to minimize temporal broadening of the fs pulses due to dispersive alteration of relative phases between their frequency components. The design should also be favorable to high laser-induced damage threshold (LIDT. We base the coating on TiO2/SiO2 layer pairs produced by means of e-beam evaporation with ion-assisted deposition, and use OptiLayer Thin Film Software to explore designs starting with TiO2/SiO2 layers having thicknesses in a reverse chirped arrangement. This approach led to a design with R > 99% from 800 to 1000 nm and GDD < 20 fs2 from 843 to 949 nm (45° AOI, Ppol. The design’s GDD behaves in a smooth way, suitable for GDD compensation techniques, and its electric field intensities show promise for high LIDTs. Reflectivity and GDD measurements for the initial test coating indicate good performance of the BBHR design. Subsequent coating runs with improved process calibration produced two coatings whose HR bands satisfactorily meet the design goals. For the sake of completeness, we summarize our previously reported transmission spectra and LIDT test results with 800 ps, 8 ps and 675 fs pulses for these two coatings, and present a table of the LIDT results we have for all of our TiO2/SiO2 BBHR coatings, showing the trends with test laser pulse duration from the ns to sub-ps regimes.

  14. Monolithic stabilized Yb-fiber All-PM laser directly delivering nJ-level femtosecond pulses

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Liu, Xiaomin; Lægsgaard, Jesper

    2008-01-01

    We present a monolithic, self-starting, all-PM, stabilized Yb-fiber laser, pulse-compressed in a hollow-core PM photonic crystal fiber, providing the 370 fs pulses of 4 nJ energy with high mode quality.......We present a monolithic, self-starting, all-PM, stabilized Yb-fiber laser, pulse-compressed in a hollow-core PM photonic crystal fiber, providing the 370 fs pulses of 4 nJ energy with high mode quality....

  15. Revealing the second harmonic generation in a femtosecond laser-driven cluster-based plasma by analyzing shapes of Ar XVII spectral lines.

    Science.gov (United States)

    Oks, Eugene; Dalimier, Elisabeth; Faenov, Anatoly; Pikuz, Tatiana; Fukuda, Yuji; Andreev, Alexander; Koga, James; Sakaki, Hironao; Kotaki, Hideyuki; Pirozhkov, Alexander; Hayashi, Yukio; Skobelev, Igor; Pikuz, Sergei; Kawachi, Tetsuya; Kando, Masaki; Kondo, Kiminori; Zhidkov, Alexei; Kodama, Ryosuke

    2015-12-14

    We present experiments dealing with a femtosecond laser-driven cluster-based plasma, where by analyzing the nonlinear phenomenon of satellites of spectral lines of Ar XVII, we revealed the nonlinear phenomenon of the generation of the second harmonic of the laser frequency. For performing this analysis we developed new results in the theory of satellites of spectral lines. From such lineshape analysis we found, in particular, that the efficiency of converting the short (40 fs) intense (3x10¹⁸ W/cm²) incident laser light into the second harmonic was 2%. This result is in the excellent agreement with the 2-Dimensional Particle-In-Cell (2D PIC) simulation that we also performed. There is also an order of magnitude agreement between the thresholds for the SHG found from the line shape analysis and from the 2D PIC simulations.

  16. Proposal to generate 10 TW level femtosecond X-ray pulses from a baseline undulator in conventional SASE regime at the European XFEL

    Energy Technology Data Exchange (ETDEWEB)

    Serkez, Svitozar; Kocharyan, Vitali; Saldin, Evgeni; Zagorodnov, Igor [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Geloni, Gianluca [European XFEL GmbH, Hamburg (Germany)

    2013-08-15

    Output characteristics of the European XFEL have been previously studied assuming an operation point at 5 kA peak current. In this paper we explore the possibility to go well beyond such nominal peak current level. In order to illustrate the potential of the European XFEL accelerator complex we consider a bunch with 0.25 nC charge, compressed up to a peak current of 45 kA. An advantage of operating at such high peak current is the increase of the X-ray output peak power without any modification to the baseline design. Based on start-to-end simulations, we demonstrate that such high peak current, combined with undulator tapering, allows one to achieve up to a 100-fold increase in a peak power in the conventional SASE regime, compared to the nominal mode of operation. In particular, we find that 10 TW-power level, femtosecond x-ray pulses can be generated in the photon energy range between 3 keV and 5 keV, which is optimal for single biomolecule imaging. Our simulations are based on the exploitation of all the 21 cells foreseen for the SASE3 undulator beamline, and indicate that one can achieve diffraction to the desired resolution with 15 mJ (corresponding to about 3.10{sup 13} photons) in pulses of about 3 fs, in the case of a 100 nm focus at the photon energy of 3.5 keV.

  17. Proposal to generate 10 TW level femtosecond X-ray pulses from a baseline undulator in conventional SASE regime at the European XFEL

    International Nuclear Information System (INIS)

    Serkez, Svitozar; Kocharyan, Vitali; Saldin, Evgeni; Zagorodnov, Igor; Geloni, Gianluca

    2013-08-01

    Output characteristics of the European XFEL have been previously studied assuming an operation point at 5 kA peak current. In this paper we explore the possibility to go well beyond such nominal peak current level. In order to illustrate the potential of the European XFEL accelerator complex we consider a bunch with 0.25 nC charge, compressed up to a peak current of 45 kA. An advantage of operating at such high peak current is the increase of the X-ray output peak power without any modification to the baseline design. Based on start-to-end simulations, we demonstrate that such high peak current, combined with undulator tapering, allows one to achieve up to a 100-fold increase in a peak power in the conventional SASE regime, compared to the nominal mode of operation. In particular, we find that 10 TW-power level, femtosecond x-ray pulses can be generated in the photon energy range between 3 keV and 5 keV, which is optimal for single biomolecule imaging. Our simulations are based on the exploitation of all the 21 cells foreseen for the SASE3 undulator beamline, and indicate that one can achieve diffraction to the desired resolution with 15 mJ (corresponding to about 3.10 13 photons) in pulses of about 3 fs, in the case of a 100 nm focus at the photon energy of 3.5 keV.

  18. Interstellar scattering effect on pulsar mean pulse shape and apparent angular size: stochastic ray trajectory method

    International Nuclear Information System (INIS)

    Bocharov, A.A.

    1988-01-01

    The extension of stochastic ray-trajectory method - a specific approach to the analysis of radio wave scattering in the interstellar medium - is presented. This method enables one to obtain different characteristics of scattered radiation, connected with mean pulse shape. It allows one to complete very simple and efficient programs for numerical calculation of these characteristics

  19. A survey of pulse shape options for a revised plastic ablator ignition design

    International Nuclear Information System (INIS)

    Clark, D. S.; Milovich, J. L.; Hinkel, D. E.; Salmonson, J. D.; Peterson, J. L.; Berzak Hopkins, L. F.; Eder, D. C.; Haan, S. W.; Jones, O. S.; Marinak, M. M.; Robey, H. F.; Smalyuk, V. A.; Weber, C. R.

    2014-01-01

    Recent experimental results using the “high foot” pulse shape for inertial confinement fusion ignition experiments on the National Ignition Facility (NIF) [Moses et al., Phys. Plasmas 16, 041006 (2009)] have shown encouraging progress compared to earlier “low foot” experiments. These results strongly suggest that controlling ablation front instability growth can significantly improve implosion performance even in the presence of persistent, large, low-mode distortions. Simultaneously, hydrodynamic growth radiography experiments have confirmed that ablation front instability growth is being modeled fairly well in NIF experiments. It is timely then to combine these two results and ask how current ignition pulse shapes could be modified to improve one-dimensional implosion performance while maintaining the stability properties demonstrated with the high foot. This paper presents such a survey of pulse shapes intermediate between the low and high foot extremes in search of an intermediate foot optimum. Of the design space surveyed, it is found that a higher picket version of the low foot pulse shape shows the most promise for improved compression without loss of stability

  20. Pulse shape optimization for electron-positron production in rotating fields

    Science.gov (United States)

    Fillion-Gourdeau, François; Hebenstreit, Florian; Gagnon, Denis; MacLean, Steve

    2017-07-01

    We optimize the pulse shape and polarization of time-dependent electric fields to maximize the production of electron-positron pairs via strong field quantum electrodynamics processes. The pulse is parametrized in Fourier space by a B -spline polynomial basis, which results in a relatively low-dimensional parameter space while still allowing for a large number of electric field modes. The optimization is performed by using a parallel implementation of the differential evolution, one of the most efficient metaheuristic algorithms. The computational performance of the numerical method and the results on pair production are compared with a local multistart optimization algorithm. These techniques allow us to determine the pulse shape and field polarization that maximize the number of produced pairs in computationally accessible regimes.

  1. Simultaneous SU(2) rotations on multiple quantum dot exciton qubits using a single shaped pulse

    Science.gov (United States)

    Mathew, Reuble; Yang, Hong Yi Shi; Hall, Kimberley C.

    2015-10-01

    Recent experimental demonstration of a parallel (π ,2 π ) single qubit rotation on excitons in two distant quantum dots [Nano Lett. 13, 4666 (2013), 10.1021/nl4018176] is extended in numerical simulations to the design of pulses for more general quantum state control, demonstrating the feasibility of full SU(2) rotations of each exciton qubit. Our results show that simultaneous high-fidelity quantum control is achievable within the experimentally accessible parameter space for commercial Fourier-domain pulse shaping systems. The identification of a threshold of distinguishability for the two quantum dots (QDs) for achieving high-fidelity parallel rotations, corresponding to a difference in transition energies of ˜0.25 meV , points to the possibility of controlling more than 10 QDs with a single shaped optical pulse.

  2. Characterization of liquid scintillation detector (BC-501A) and digital pulse shape discrimination (DPSD) system

    Energy Technology Data Exchange (ETDEWEB)

    Lombigit, L., E-mail: lojius@nm.gov.my; Yussup, N., E-mail: nolida@nm.gov.my; Ibrahim, Maslina Mohd; Rahman, Nur Aira Abd; Rawi, M. Z. M. [Instrumentation Group, Malaysian Nuclear Agency, Bangi, 43000 Kajang, Selangor (Malaysia)

    2015-04-29

    A digital n/γ pulse shape discrimination (PSD) system is currently under development at Instrumentation and Automation Centre, Malaysian Nuclear Agency. This system aims at simultaneous detection of fast neutron and gamma ray in mixed radiations environment. This work reports the system characterization performed on the liquid scintillation detector (BC-501A) and digital pulse shape discrimination (DPSD) system. The characterization involves measurement of electron light output from the BC-501A detector and energy channels calibration of the pulse height spectra acquired with DPSD system using set of photon reference sources. The main goal of this experiment is to calibrate the ADC channel of our DPSD system, characterized the BC-501 detector and find the position of Compton edge which later could be used as threshold for the n/γ PSD experiment. The detector resolution however is worse as compared to other published data but it is expected as our detector has a smaller active volume.

  3. All-fiber high-power monolithic femtosecond laser at 1.59 µm with 63-fs pulse width

    Science.gov (United States)

    Hekmat, M. J.; Omoomi, M.; Gholami, A.; Yazdabadi, A. Bagheri; Abdollahi, M.; Hamidnejad, E.; Ebrahimi, A.; Normohamadi, H.

    2018-01-01

    In this research, by adopting an alternative novel approach to ultra-short giant pulse generation which basically originated from difficulties with traditional employed methods, an optimized Er/Yb co-doped double-clad fiber amplifier is applied to boost output average power of single-mode output pulses to a high level of 2-W at 1.59-µm central wavelength. Output pulses of approximately 63-fs pulse width at 52-MHz repetition rate are obtained in an all-fiber monolithic laser configuration. The idea of employing parabolic pulse amplification for stretching output pulses together with high-power pulse amplification using Er/Yb co-doped active fibers for compressing and boosting output average power plays crucial role in obtaining desired results. The proposed configuration enjoys massive advantages over previously reported literature which make it well-suited for high-power precision applications such as medical surgery. Detailed dynamics of pulse stretching and compressing in active fibers with different GVD parameters are numerically and experimentally investigated.

  4. Creating large second-order optical nonlinearity in optical waveguides written by femtosecond laser pulses in boro-aluminosilicate glass

    Science.gov (United States)

    An, Hong-Lin; Arriola, Alexander; Gross, Simon; Fuerbach, Alexander; Withford, Michael J.; Fleming, Simon

    2014-01-01

    The thermal poling technique was applied to optical waveguides embedded in a commercial boro-aluminosilicate glass, resulting in high levels of induced second-order optical nonlinearity. The waveguides were fabricated using the femtosecond laser direct-write technique, and thermally poled samples were characterized with second harmonic optical microscopy to reveal the distribution profile of the induced nonlinearity. It was found that, in contrast to fused silica, the presence of waveguides in boro-aluminosilicate glass led to an enhancement of the creation of the second-order nonlinearity, which is larger in the laser written waveguiding regions when compared to the un-modified substrate. The magnitude of the nonlinear coefficient d33 achieved in the core of the laser-written waveguides, up to 0.2 pm/V, was comparable to that in thermally poled fused silica, enabling the realization of compact integrated electro-optic devices in boro-aluminosilicate glasses.

  5. Bragg gratings inscription in step-index PMMA optical fiber by femtosecond laser pulses at 400 nm

    Science.gov (United States)

    Hu, X.; Kinet, D.; Chah, K.; Mégret, P.; Caucheteur, C.

    2016-05-01

    In this paper, we report photo-inscription of uniform Bragg gratings in trans-4-stilbenemethanol-doped photosensitive step-index polymer optical fiber. Gratings were produced at ~1575 nm by the phase mask technique with a femtosecond laser emitting at 400 nm with different average optical powers (8 mW, 13 mW and 20 mW). The grating growth dynamics in transmission were monitored during the manufacturing process, showing that the grating grows faster with higher power. Using 20 mW laser beam power, the reflectivity reaches 94 % (8 dB transmission loss) in 70 seconds. Finally, the gratings were characterized in temperature in the range 20 - 45 °C. The thermal sensitivity has been computed equal to - 86.6 pm/°C.

  6. Distortions in frequency spectra of signals associated with sampling-pulse shapes

    International Nuclear Information System (INIS)

    Njau, E.C.

    1983-04-01

    A method developed earlier by the author [IC/82/44; IC/82/45] is used to investigate distortions introduced into frequency spectra of signals by the shapes of the sampling pulses involved. Conditions are established under which the use of trapezoid or exponentially-edged pulses to digitize signals can make the frequency spectra of the resultant data samples devoid of the main features of the signals. This observation does not, however, apply in any way to cosinusoidally-edged pulses or to pulses with cosine-squared edges. Since parts of the Earth's surface and atmosphere receive direct solar energy in discrete samples (i.e. only from sunrise to sunset) we have extended the technique and attempted to develop a theory that explains the observed solar terrestrial relationships. A very good agreement is obtained between the theory and previous long-term and short-term observations. (author)

  7. Detection of coincident radiations in a single transducer by pulse shape analysis

    Science.gov (United States)

    Warburton, William K [Menlo Park, CA

    2008-03-11

    Pulse shape analysis determines if two radiations are in coincidence. A transducer is provided that, when it absorbs the first radiation produces an output pulse that is characterized by a shorter time constant and whose area is nominally proportional to the energy of the absorbed first radiation and, when it absorbs the second radiation produces an output pulse that is characterized by a longer time constant and whose area is nominally proportional to the energy of the absorbed second radiation. When radiation is absorbed, the output pulse is detected and two integrals are formed, the first over a time period representative of the first time constant and the second over a time period representative of the second time constant. The values of the two integrals are examined to determine whether the first radiation, the second radiation, or both were absorbed in the transducer, the latter condition defining a coincident event.

  8. Fiscal 1998 R and D report on femtosecond technology (power generation facility monitoring system using high- intensity X-ray pulse); 1998 nendo femuto byo technology no kenkyu kaihatsu (kokido X senb pulse riyo hatsuden shisetsu monitoring system no kenkyu kaihatsu) seika hokokusho

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1999-03-01

    This report reports the fiscal 1998 R and D result of Femtosecond Technology Research Association (FESTA) supported by NEDO. For creation of industrial basic technologies supporting the advanced information society in the 21st century, ultra-high speed electronics technology including new functions beyond the speed limit of conventional electronics technologies is indispensable. From such viewpoint, this R and D aims at establishment of the basic technology controlling conditions of beams and electrons in a femtosecond (10{sup -15}-10{sup -12} seconds) region. In development of the titled system, this R and D aims at generation of high-intensity X-ray pulse by interaction between femtosecond light pulse and high-density electron beam pulse, and development of measurement technology (non- stop inspection) of high-speed moving objects using such X- ray pulse. In fiscal 1998, this project succeeded in time stabilization of laser oscillators at a 100fs level and generation of low-emittance electron beam pulse through development of ultra-short pulse synchronization, laser stabilization and electron beam pulse generation technologies. (NEDO)

  9. Generation of ring-shaped beams by a graded-index plasma lens

    Science.gov (United States)

    Tan, Chao; Fu, Xiquan; Deng, Yangbao

    2013-12-01

    We experimentally demonstrate the generation of ring-shaped beams using a plasma channel with Gaussian profile. The plasma channel is produced when an intense femtosecond pulse propagates in carbon disulfide. The refractive index of the plasma is similar to that of a graded-index lens. Due to the existence of critical plasma density, the beam from the He-Ne laser cannot pass through the center region of the plasma and is refracted in the periphery. The dark spot size of the ring-shaped beams can be controlled easily by a femtosecond pulse. We also show the propagation of ring-shaped beams in free space.

  10. Multiplexed two-photon microscopy of dynamic biological samples with shaped broadband pulses.

    Science.gov (United States)

    Pillai, Rajesh S; Boudoux, Caroline; Labroille, Guillaume; Olivier, Nicolas; Veilleux, Israel; Farge, Emmanuel; Joffre, Manuel; Beaurepaire, Emmanuel

    2009-07-20

    Coherent control can be used to selectively enhance or cancel concurrent multiphoton processes, and has been suggested as a means to achieve nonlinear microscopy of multiple signals. Here we report multiplexed two-photon imaging in vivo with fast pixel rates and micrometer resolution. We control broadband laser pulses with a shaping scheme combining diffraction on an optically-addressed spatial light modulator and a scanning mirror allowing to switch between programmable shapes at kiloHertz rates. Using coherent control of the two-photon excited fluorescence, it was possible to perform selective microscopy of GFP and endogenous fluorescence in developing Drosophila embryos. This study establishes that broadband pulse shaping is a viable means for achieving multiplexed nonlinear imaging of biological tissues.

  11. Coherent control of atoms and diatomic molecules with shaped ultrashort pulses

    International Nuclear Information System (INIS)

    Degert, J.

    2002-12-01

    This thesis deals with the theoretical and experimental study of coherent control of atomic and molecular systems with shaped pulses. At first, we present several experiments of control of coherent transients in rubidium. These transients appear when a two-level system is excited by a perturbative chirped pulse, and are characterized by oscillations in the excited state population. For a strong chirp, we show that a phase step in the spectrum modifies the phase of the oscillations. Then, by direct analogy with Fresnel zone lens, we conceive a chirped pulse with a highly modulated amplitude, allowing to suppress destructive contributions to the population transfer. In a second set of experiments, we focus on quantum path interferences in two-photon transitions excited by linearly chirped pulses. Owing to the broad bandwidth of ultrashort pulses, sequential and direct excitation paths contribute to the excited state population. Oscillations resulting from interferences between these two paths are observed in atomic sodium. Moreover, we show that they are observable whatever the sign of chirp. Theoretically, we study the control of the predissociation of a benchmark diatomic molecule: NaI. Predissociation leads to matter wave interferences in the fragments distribution. First, we show that a suitably chosen probe pulse allows the observation of theses interferences. Next, using a sequence of control pulse inducing electronic transition, we demonstrate the possibility to manipulate fragment energy distribution. (author)

  12. Development of high sensitivity 4H-SiC detectors for fission neutron pulse shape measurements

    Science.gov (United States)

    Wu, Jian; Jiang, Yong; Li, Meng; Zeng, Lina; Li, Junjie; Gao, Hui; Zou, Dehui; Bai, Zhongxiong; Ye, Cenming; Liang, Wenfeng; Dai, Shaofeng; Lu, Yi; Rong, Ru; Du, Jinfeng; Fan, Xiaoqiang

    2017-08-01

    4H-silicon carbide (4H-SiC) detectors are well suited for measurements of fission neutron pulse shape for their compact size, excellent radiation resistance, and hydrogen free composition. The aim of this study is to improve the 4H-SiC detector's sensitivity to fission neutron pulses. 4H-SiC detectors with varied epilayer thicknesses are fabricated and then tested in the pulsed neutron field of the Chinese Fast Burst Reactor II (CFBR II). The sensitivity of the 4H-SiC detector to the CFBR II neutron pulse is increased by 139.8%, with the enlargement of epilayer thickness from 20 μm to 120 μm. By employing the proton-recoil method, the sensitivity of the 4H-SiC detector to the CFBR II neutron pulse is further increased by 11.6%. With enhanced sensitivity to fission neutron pulses, 4H-SiC detectors are promising devices for high intensity neutron pulse measurements.

  13. Selective fabrication of p-type and n-type thermoelectric micropatterns by the reduction of CuO/NiO mixed nanoparticles using femtosecond laser pulses

    Science.gov (United States)

    Mizoshiri, Mizue; Hata, Seiichi

    2018-01-01

    p-type and n-type thermoelectric micropatterns were selectively fabricated via the reduction and reoxidation of CuO/NiO mixed nanoparticles using femtosecond laser pulses. The micropatterns were formed by raster scanning focused femtosecond laser pulses on a solution film containing CuO and NiO nanoparticles, ethylene glycol, and polyvinylpyrrolidone, followed by the removal of the non-irradiated nanoparticles. Cu-Ni was generated by reductive sintering of the CuO/NiO mixed nanoparticles at laser scanning speeds ranging from 5 to 20 mm/s and a laser fluence of 0.055 J/cm2. In contrast, intense peaks corresponding to Cu2O and NiO were observed in the X-ray diffraction spectrum of the micropattern formed at a scanning speed of 1 mm/s, indicating that Cu2O and NiO were generated via the reoxidation of the reduced metals. The Seebeck coefficients of the micropatterns formed at a fluence of 0.055 J/cm2 and scanning speeds of 5-20 mm/s were between - 32 and - 16 µV/K, whereas that of the micropattern formed at a fluence of 0.055 J/cm2 and scanning speed of 1 mm/s was 250 µV/K. These results suggest that the Seebeck coefficient depends on the generated n-type Cu-Ni and p-type Cu2O and NiO phases. A thermoelectric couple was fabricated by selectively fabricating p-type and n-type thermoelectric elements. The thermoelectric couple exhibited a thermoelectric voltage of 0.25 mV/K when a temperature gradient was applied between its hot and cold sides. The generated voltage was nearly consistent with the estimated voltage based on the Seebeck coefficient. The developed process for selective fabrication is expected to be useful for the direct writing of thermoelectric-type sensors.

  14. Parameter studies on the effect of pulse shape on the dynamic plastic deformation of a hexagon

    International Nuclear Information System (INIS)

    Youngdahl, C.K.

    1973-10-01

    Results of a parameter study on the dynamic plastic response of a hexagonal subassembly duct subjected to an internal pressure pulse of arbitrary shape are presented. Plastic distortion of the cross section and large-deformation geometric effects that result in redistribution of the internal forces between bending and membrane stresses in the hexagon wall are included in the analytical model. Correlation procedures are established for relating permanent plastic deformation to simple properties of the pressure pulse, for both the small- and large-deformation ranges. Characteristic response times are determined, and the dynamic load factor for large-deformation plastic response is computed

  15. A technique based on pulse shape comparison for linearizing compressed signals

    CERN Document Server

    Cattaneo, P W

    2002-01-01

    A nuclear electronics system designed to perform high precision energy measurement on a large dynamic range through high speed sampling of the output might be impossible to match to an adequate ADC. A solution consists in compressing the signal before digitization and linearizing it after with a look-up table, encoding the inverse of the compression function. This look-up table can be constructed using test pulses, the smallest of which is in the linear part and the largest spans the whole dynamic range. Reconstructing these pulse shapes and requiring them to be omothetic generates the look-up table providing a minimal distortion in the RMS sense.

  16. In-Fiber Subpicosecond Pulse Shaping for Nonlinear Optical Telecommunication Data Processing at 640 Gbit/s

    DEFF Research Database (Denmark)

    Azaña, J.; Oxenløwe, Leif Katsuo; Palushani, Evarist

    2012-01-01

    We review recent work on all-fiber (long-period fiber grating) devices for optical pulse shaping, particularly flat-top pulse generation, down to the subpicosecond range and their application for nonlinear switching (demultiplexing) of optical time-division multiplexed (OTDM) data signals in fiber......-like gating pulses). Long-period fiber grating pulse shapers with reduced polarization dependence are fabricated and successfully used for polarization-independent 640-to-10 Gbit/s demultiplexing experiments....

  17. Monolithic all-PM femtosecond Yb-fiber laser stabilized with a narrow-band fiber Bragg grating and pulse-compressed in a hollow-core photonic crystal fiber

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Liu, Xiaomin; Lægsgaard, Jesper

    2008-01-01

    We report on an environmentally stable self-starting monolithic (i.e. without any free-space coupling) all-polarization-maintaining (PM) femtosecond Yb-fiber laser, stabilized against Q-switching by a narrow-band fiber Bragg grating and modelocked using a semiconductor saturable absorber mirror....... The laser output is compressed in a spliced-on hollow-core PM photonic crystal fiber, thus providing direct end-of-the-fiber delivery of pulses of around 370 fs duration and 4 nJ energy with high mode quality. Tuning the pump power of the end amplifier of the laser allows for the control of output pulse...

  18. Study of time-domain digital pulse shaping algorithms for nuclear signals

    International Nuclear Information System (INIS)

    Zhou Jianbin; Tuo Xianguo; Zhu Xing; Liu Yi; Zhou Wei; Lei Jiarong

    2012-01-01

    With the development on high-speed integrated circuit, fast high resolution sampling ADC and digital signal processors are replacing analog shaping amplifier circuit. This paper firstly presents the numerical analysis and simulation on R-C shaping circuit model and C-R shaping circuit model. Mathematic models are established based on 1 st order digital differential method and Kirchhoff Current Law in time domain, and a simulation and error evaluation experiment on an ideal digital signal are carried out with Excel VBA. A digital shaping test for a semiconductor X-ray detector in real time is also presented. Then a numerical analysis for Sallen-Key(S-K) low-pass filter circuit model is implemented based on the analysis of digital R-C and digital C-R shaping methods. By applying the 2 nd order non-homogeneous differential equation,the authors implement a digital Gaussian filter model for a standard exponential-decaying signal and a nuclear pulse signal. Finally, computer simulations and experimental tests are carried out and the results show the possibility of the digital pulse processing algorithms. (authors)

  19. System for determining the type of nuclear radiation from detector output pulse shape

    Science.gov (United States)

    Miller, William H.; Berliner, Ronald R.

    1994-01-01

    A radiation detection system determines the type of nuclear radiation received in a detector by producing a correlation value representative of the statistical cross correlation between the shape of the detector signal and pulse shape data previously stored in memory and characteristic of respective types of radiation. The correlation value is indicative of the type of radiation. The energy of the radiation is determined from the detector signal and is used to produce a spectrum of radiation energies according to radiation type for indicating the nature of the material producing the radiation.

  20. Research of photonic-assisted triangular-shaped pulses generation based on quadrupling RF modulation

    Science.gov (United States)

    Yuan, Jin; Ning, Ti-gang; Li, Jing; Li, Yue-qin; Chen, Hong-yao; Zhang, Chan

    2015-05-01

    We propose an approach to generate optical triangular-shaped pulse train with tunable repetition rate using quadrupling radio frequency (RF) modulation and optical grating dispersion-induced power fading. In this work, a piece of chirped fiber Bragg grating (FBG) is employed as the dispersive media to remove the undesired 8th harmonic in optical intensity. Thus, the generated harmonics of optical intensity can be corresponding to the first two Fourier components of typical periodic triangular pulses. This work also analyzes the impacts of the extinction ratio and the bias voltage drift on the harmonic distortion suppression ratio. After that, the value of the extinction ratio and the range of the bias voltage drift can be obtained. The advantage of this proposal is that it can generate high order frequency-multiplexed optical pulses train which can be applied in all optical signal processing and other fields.

  1. Design of FIR digital filters for pulse shaping and channel equalization using time-domain optimization

    Science.gov (United States)

    Houts, R. C.; Vaughn, G. L.

    1974-01-01

    Three algorithms are developed for designing finite impulse response digital filters to be used for pulse shaping and channel equalization. The first is the Minimax algorithm which uses linear programming to design a frequency-sampling filter with a pulse shape that approximates the specification in a minimax sense. Design examples are included which accurately approximate a specified impulse response with a maximum error of 0.03 using only six resonators. The second algorithm is an extension of the Minimax algorithm to design preset equalizers for channels with known impulse responses. Both transversal and frequency-sampling equalizer structures are designed to produce a minimax approximation of a specified channel output waveform. Examples of these designs are compared as to the accuracy of the approximation, the resultant intersymbol interference (ISI), and the required transmitted energy. While the transversal designs are slightly more accurate, the frequency-sampling designs using six resonators have smaller ISI and energy values.

  2. Alpha/beta pulse shape discrimination in plastic scintillation using commercial scintillation detectors

    International Nuclear Information System (INIS)

    Bagan, H.; Tarancon, A.; Rauret, G.; Garcia, J.F.

    2010-01-01

    Activity determination in different types of samples is a current need in many different fields. Simultaneously analysing alpha and beta emitters is now a routine option when using liquid scintillation (LS) and pulse shape discrimination. However, LS has an important drawback, the generation of mixed waste. Recently, several studies have shown the capability of plastic scintillation (PS) as an alternative to LS, but no research has been carried out to determine its capability for alpha/beta discrimination. The objective of this study was to evaluate the capability of PS to discriminate alpha/beta emitters on the basis of pulse shape analysis (PSA). The results obtained show that PS pulses had lower energy than LS pulses. As a consequence, a lower detection efficiency, a shift to lower energies and a better discrimination of beta and a worst discrimination of alpha disintegrations was observed for PS. Colour quenching also produced a decrease in the energy of the particles, as well as the effects described above. It is clear that in PS, the discrimination capability was correlated with the energy of the particles detected. Taking into account the discrimination capabilities of PS, a protocol for the measurement and the calculation of alpha and beta activities in mixtures using PS and commercial scintillation detectors has been proposed. The new protocol was applied to the quantification of spiked river water samples containing a pair of radionuclides ( 3 H- 241 Am or 90 Sr/ 90 Y- 241 Am) in different activity proportions. The relative errors in all determinations were lower than 7%. These results demonstrate the capability of PS to discriminate alpha/beta emitters on the basis of pulse shape and to quantify mixtures without generating mixed waste.

  3. Ex vivo evaluation of femtosecond pulse laser incision of urinary tract tissue in a liquid environment: implications for endoscopic treatment of benign ureteral strictures.

    Science.gov (United States)

    Liang, Jun-Hao; Kang, Jian; Pan, Yu-Long; Zhang, Liang; Qi, Jun

    2011-08-01

    The femtosecond (FS) pulse laser incises soft tissues with minimal peripheral damage and is a promising cutting tool for ureteroscopic endoureterotomy of benign ureteral strictures. To evaluate the feasibility of applying the FS laser to ureteroscopic endoureterotomy. A commercial Ti:Sapphire regenerative amplifier system (Coherent, RegA 9050, USA) was used in this study. Normal saline, 5% glucose solution, 4% mannitol solution, distilled water, and a 1% (v/v) suspension of whole blood with each of these solutions were tested for their attenuation rate (AR) of the FS laser's power. Bladder specimens from Sprague-Dawley (SD) rats were used as a surrogate model. The laser incised slots of 2 mm in length at bladder samples using three power grades (5×, 10×, and 20× the threshold power) combined with five effective pulse rates (40, 20, 10, 5, and 2.5 kHz), both in air and in normal saline. After samples were processed with standard hematoxylin-eosin staining procedures, the incision depth and collateral damage range were determined microscopically. The ARs of blood suspensions with each of the three isosmotic solutions were significantly higher than the other five solutions (P laser's cutting depth and the collateral damage were increased with the laser power or power density but the collateral damages were less than 100 µm. Microbubble formation was detected in the liquid environments tested and influenced the effective laser power. Endoscopic application of the FS laser is feasible. Microbubble formation with the laser incision, however, may influence cutting effects. Proposed methods to address these issues include increasing the irrigation rate, using distilled water as irrigation or using gas insufflation instead of irrigation. It is necessary to evaluate these methods, as well as the long-term biologic response to laser incision, on living animal models in endoscopic settings before use on humans. Copyright © 2011 Wiley-Liss, Inc.

  4. Single-pass waveguide amplifiers in Er-Yb doped zinc polyphosphate glass fabricated with femtosecond laser pulses

    NARCIS (Netherlands)

    Fletcher, L.B.; Witcher, J.J.; Troy, N.; Brow, R.K.; Krol, D.M.

    2012-01-01

    We have investigated the direct fabrication of subsurface waveguide amplifiers in Er-Yb zinc polyphosphate glass by utilizing the relationship between the initial glass composition and the resulting changes to the network structure after modification by fs laser pulses. Waveguides, exhibiting

  5. Bayesian signal processing of pulse shapes for background rejection in the Majorana Demonstrator

    Science.gov (United States)

    Shanks, Benjamin; Majorana Collaboration

    2015-10-01

    The Majorana Demonstrator uses high purity germanium (HPGe) detectors in the p-type point contact (PPC) geometry to search for neutrinoless double-beta decay (0 νββ) in 76Ge. Due to the unique electric potential created within the PPC geometry, the detailed pulse shape depends on the number of energy depositions contained within a given event. Pulse shape analysis (PSA) techniques can be used to estimate the number of separate depositions which combine to form a single pulse. This information can be used to discriminate between 0 νββ candidate events, which deposit energy at a single detector site, and gamma ray background, which can scatter and deposit energy in multiple locations. The problem of determining whether a pulse is single- or multi-site is well suited to Bayesian classifiers. Once trained via supervised machine learning, these algorithms can perform nonlinear cuts against multi-site events using the estimated probability function as a discriminator. The Bayesian approach can also be naturally extended to incorporate a model of the physical process responsible for signal generation within the detector. Presented here is an overview of the Bayesian classifier developed for use on the Demonstrator. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, the Particle Astrophysics Program of the National Science Foundation, and the Sanford Underground Research Facility.

  6. Triple pulse shape discrimination and capture-gated spectroscopy in a composite heterogeneous scintillator

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, M., E-mail: mksharma@umich.edu [University of Michigan, Ann Arbor, MI 48109 (United States); Nattress, J. [University of Michigan, Ann Arbor, MI 48109 (United States); Wilhelm, K. [Pennsylvania State University, University Park, PA 16802 (United States); Jovanovic, I. [University of Michigan, Ann Arbor, MI 48109 (United States)

    2017-06-11

    We demonstrate an all-solid-state design for a composite heterogeneous scintillation detector sensitive to interactions with high-energy photons (gammas), fast neutrons, and thermal neutrons. The scintillator exhibits triple pulse shape discrimination, effectively separating electron recoils, fast neutron recoils, and neutron captures. This is accomplished by combining the properties of two distinct scintillators, whereby a 51-mm diameter, 51-mm tall cylinder of pulse shape discriminating plastic is wrapped by a 320-µm thick sheet of {sup 6}LiF:ZnS(Ag), optically coupling the scintillators to each other and to the photomultiplier tube. In this way, the sensitivity to neutron captures is achieved without the need to load the plastic scintillator with a capture agent. We demonstrate a figure of merit of up to 1.2 for fast neutrons/gammas and 5.7 for thermal neutrons/gammas. Intrinsic capture efficiency is found to be 0.46±0.05% and is in good agreement with simulation, while gamma rejection was 10{sup −6} with respect to the capture region and 10{sup −4} with respect to the recoil region using a 300 keVee threshold. Finally, we show an improvement in capture-gated neutron spectroscopy by rejecting accidental gamma coincidences using pulse shape discrimination in the plastic scintillator.

  7. Triple pulse shape discrimination and capture-gated spectroscopy in a composite heterogeneous scintillator

    Science.gov (United States)

    Sharma, M.; Nattress, J.; Wilhelm, K.; Jovanovic, I.

    2017-06-01

    We demonstrate an all-solid-state design for a composite heterogeneous scintillation detector sensitive to interactions with high-energy photons (gammas), fast neutrons, and thermal neutrons. The scintillator exhibits triple pulse shape discrimination, effectively separating electron recoils, fast neutron recoils, and neutron captures. This is accomplished by combining the properties of two distinct scintillators, whereby a 51-mm diameter, 51-mm tall cylinder of pulse shape discriminating plastic is wrapped by a 320-μm thick sheet of 6LiF:ZnS(Ag), optically coupling the scintillators to each other and to the photomultiplier tube. In this way, the sensitivity to neutron captures is achieved without the need to load the plastic scintillator with a capture agent. We demonstrate a figure of merit of up to 1.2 for fast neutrons/gammas and 5.7 for thermal neutrons/gammas. Intrinsic capture efficiency is found to be 0.46±0.05% and is in good agreement with simulation, while gamma rejection was 10-6 with respect to the capture region and 10-4 with respect to the recoil region using a 300 keVee threshold. Finally, we show an improvement in capture-gated neutron spectroscopy by rejecting accidental gamma coincidences using pulse shape discrimination in the plastic scintillator.

  8. Photoisomerization among ring-open merocyanines. I. Reaction dynamics and wave-packet oscillations induced by tunable femtosecond pulses

    Science.gov (United States)

    Ruetzel, Stefan; Diekmann, Meike; Nuernberger, Patrick; Walter, Christof; Engels, Bernd; Brixner, Tobias

    2014-06-01

    Upon ultraviolet excitation, photochromic spiropyran compounds can be converted by a ring-opening reaction into merocyanine molecules, which in turn can form several isomers differing by cis and trans configurations in the methine bridge. Whereas the spiropyran-merocyanine conversion reaction of the nitro-substituted indolinobenzopyran 6-nitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] (6-nitro BIPS) has been studied extensively in theory and experiments, little is known about photoisomerization among the merocyanine isomers. In this article, we employ femtosecond transient absorption spectroscopy with variable excitation wavelengths to investigate the excited-state dynamics of the merocyanine in acetonitrile at room temperature, where exclusively the trans-trans-cis (TTC) and trans-trans-trans (TTT) isomers contribute. No photochemical ring-closure pathways exist for the two isomers. Instead, we found that (18±4)% of excited TTC isomers undergo an ultrafast excited-state cis→trans photoisomerization to TTT within 200 fs, while the excited-state lifetime of TTC molecules that do not isomerize is 35 ps. No photoisomerization was detected for the TTT isomer, which relaxes to the ground state with a lifetime of roughly 160 ps. Moreover, signal oscillations at 170 cm-1 and 360 cm-1 were observed, which can be ascribed to excited-state wave-packet dynamics occurring in the course of the TTC→TTT isomerization. The results of high-level time-dependent density functional theory in conjunction with polarizable continuum models are presented in the subsequent article [C. Walter, S. Ruetzel, M. Diekmann, P. Nuernberger, T. Brixner, and B. Engels, J. Chem. Phys. 140, 224311 (2014)].

  9. A comparison of two methods of pulse-shape discrimination for alpha-gamma separation with trans-stilbene

    International Nuclear Information System (INIS)

    Shani, G.; Cojocaru, M.

    1977-01-01

    A method for measurement of low level alpha particles in high level gamma background is investigated. Because of its pulse-shape-discrimination properties and being a solid scintillator, trans-stilbene seems to be the proper scintillator, for this purpose. The investigation was done by measuring the effect of different gamma background level (from very low to very high) on constant alpha count rate. Two different pulse-shape-discrimination systems were used and compared. The Ortec system measures the pulse fall time and supplies a corresponding pulse height and the Elscint system checks whether the pulse is what is expected to be the gamma pulse, or is a longer pulse. Both systems yielded good results and were found to be adequate for alpha-gamma separation with trans-stilbene. (Auth.)

  10. Femtosecond coherent pulses in the keV range from inner-shell transitions pumped by a betatron source

    Energy Technology Data Exchange (ETDEWEB)

    Ribiere, M.; Jacquemot, S. [Univ Paris 06, CEA, Ecole Polytech, Lab Utilisat Lasers Intenses, F-91128 Palaiseau (France); Ribiere, M.; Sebban, S.; Corde, S.; Phuoc, K.T.; Valentin, C.; Gautier, J.; Zeitoun, P.; Lambert, G.; Tissandier, F.; Rousse, A. [Ecole Polytech, CNRS, UMR 7639, ENSTA ParisTech, Lab Opt Appl, F-91761 Palaiseau (France); Jacquemot, S. [CEA Bruyeres-le-Chatel, DIF 91 (France)

    2010-07-01

    We present a new method to generate ultra-short X-ray laser pulses by using the recently demonstrated laser-driven betatron source to photo-pump inner-shell transitions. The proposed compact set-up will then open the route to a wide range of applications. The betatron spectrum and ion-population kinetics are modeled and the temporal evolution of the gain coefficient for the K-{alpha} transitions is assessed. Using measured values of divergence, duration, and number of photons per pulse of the betatron source as input parameters, local gain values close to 60 cm{sup -1} are calculated for nitrogen at 3.2 nm. Significant gain values are also numerically obtained at shorter wavelengths (for neon at 1.5 nm) when the betatron energy distribution is optimized as suggested by recent laser wakefield electron acceleration experiments. (authors)

  11. Confined longitudinal acoustic phonon modes in free-standing Si membranes coherently excited by femtosecond laser pulses

    OpenAIRE

    Hudert, Florian; Bruchhausen, Axel; Issenmann, Daniel; Schecker, Olivier; Waitz, Reimar; Erbe, Artur; Scheer, Elke; Dekorsy, Thomas; Mlayah, Adnen; Huntzinger, Jean-Roch

    2009-01-01

    In this Rapid Communication we report the first time-resolved measurements of confined acoustic phonon modes in free-standing Si membranes excited by fs laser pulses. Pump-probe experiments using asynchronous optical sampling reveal the impulsive excitation of discrete acoustic modes up to the 19th harmonic order for membranes of two different thicknesses. The modulation of the membrane thickness is measured with fm resolution. The experimental results are compared with a theoretical model in...

  12. The Influence of Vesicle Shape and Medium Conductivity on Possible Electrofusion under a Pulsed Electric Field.

    Science.gov (United States)

    Liu, Linying; Mao, Zheng; Zhang, Jianhua; Liu, Na; Liu, Qing Huo

    2016-01-01

    The effects of electric field on lipid membrane and cells have been extensively studied in the last decades. The phenomena of electroporation and electrofusion are of particular interest due to their wide use in cell biology and biotechnology. However, numerical studies on the electrofusion of cells (or vesicles) with different deformed shapes are still rare. Vesicle, being of cell size, can be treated as a simple model of cell to investigate the behaviors of cell in electric field. Based on the finite element method, we investigate the effect of vesicle shape on electrofusion of contact vesicles in various medium conditions. The transmembrane voltage (TMV) and pore density induced by a pulsed field are examined to analyze the possibility of vesicle fusion. In two different medium conditions, the prolate shape is observed to have selective electroporation at the contact area of vesicles when the exterior conductivity is smaller than the interior one; selective electroporation is more inclined to be found at the poles of the oblate vesicles when the exterior conductivity is larger than the interior one. Furthermore, we find that when the exterior conductivity is lower than the internal conductivity, the pulse can induce a selective electroporation at the contact area between two vesicles regardless of the vesicle shape. Both of these two findings have important practical applications in guiding electrofusion experiments.

  13. Development of a high power femtosecond laser

    CSIR Research Space (South Africa)

    Neethling, PH

    2010-10-01

    Full Text Available the pulses from the Coherent Mira/BMI amplified femtosecond laser at the LRI. Ideally the OPCPA stage should be pumped by a 100 ? 300 ps laser with tens of mJ pulse energy, matching the stretched pulse duration. This laser will be developed by the CSIR...

  14. A 16-channel real-time digital processor for pulse-shape discrimination in multiplicity assay

    International Nuclear Information System (INIS)

    Joyce, Malcolm J.; Aspinall, M.D.; Cave, F.D.; Lavietes, A.

    2013-06-01

    In recent years, real-time neutron/γ-ray pulse-shape discrimination has become feasible for use with scintillator-based detectors that respond extremely quickly, on the order of 25 ns in terms of pulse width, and their application to a variety of nuclear material assays has been reported. For the in-situ analysis of nuclear materials, measurements are often based on the multiplicity assessment of spontaneous fission events. An example of this is the 240 Pu eff assessment stemming from long-established techniques developed for 3 He-based neutron coincidence counters when 3 He was abundant and cheap. However, such measurements when using scintillator detectors can be plagued by low detection efficiencies and low orders of coincidence (often limited to triples) if the number of detectors in use is similarly limited to 3-4 detectors. Conversely, an array of >10 detector modules arranged to optimize efficiency and multiplicity sensitivity, shifts the emphasis in terms of performance requirement to the real-time digital analyzer and, critically, to the scope remaining in the temporal processing window of these systems. In this paper we report on the design, development and commissioning of a bespoke, 16-channel real-time pulse-shape discrimination analyzer specified for the materials assay challenge summarized above. The analyzer incorporates 16 dedicated and independent high-voltage supplies along with 16 independent digital processing channels offering pulse-shape discrimination at a rate of 3 x 10 6 events per second. These functions are configured from a dedicated graphical user interface, and all settings can be adjusted on-the-fly with the analyzer effectively configured one-time-only (where desired) for subsequent plug-and-play connection, for example to a fuel bundle organic scintillation detector array. (authors)

  15. Single-pass waveguide amplifiers in Er-Yb doped zinc polyphosphate glass fabricated with femtosecond laser pulses.

    Science.gov (United States)

    Fletcher, Luke B; Witcher, Jon J; Troy, Neil; Brow, Richard K; Krol, Denise M

    2012-04-01

    We have investigated the direct fabrication of subsurface waveguide amplifiers in Er-Yb zinc polyphosphate glass by utilizing the relationship between the initial glass composition and the resulting changes to the network structure after modification by fs laser pulses. Waveguides, exhibiting internal gain of 1 dB/cm at 1.53 μm when pumped with 500 mW at 976 nm, were directly fabricated using a regenerative amplified Ti:sapphire 1 kHz, 180 fs laser system. Optical properties as well as insertion losses and internal gain are reported.

  16. Control of HOD photodissociation dynamics via bond-selective infrared multiphoton excitation and a femtosecond ultraviolet laser pulse

    DEFF Research Database (Denmark)

    Amstrup, Bjarne; Henriksen, Niels Engholm

    1992-01-01

    moment, excites the molecule to a dissociative electronic state. We consider the HOD molecule which is ideal due to the local mode structure of the vibrational states. It is shown that selective and localized bond stretching can be created in simple laser fields. When such a nonstationary vibrating HOD...... molecule is photodissociated with a short laser pulse (~5 fs) complete selectivity between the channels H+OD and D+OH is observed over the entire absorption band covering these channels. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....

  17. Effect of prepulse on fast electron lateral transport at the target surface irradiated by intense femtosecond laser pulses

    International Nuclear Information System (INIS)

    Lin, X. X.; Li, Y. T.; Liu, B. C.; Liu, F.; Du, F.; Wang, S. J.; Lu, X.; Chen, L. M.; Zhang, L.; Liu, X.; Wang, J.; Liu, F.; Liu, X. L.; Wang, Z. H.; Ma, J. L.; Wei, Z. Y.; Zhang, J.

    2010-01-01

    The effects of preplasma on lateral fast electron transport at front target surface, irradiated by ultraintense (>10 18 W/cm 2 ) laser pulses, are investigated by Kα imaging technique. A large annular Kα halo with a diameter of ∼560 μm surrounding a central spot is observed. A specially designed steplike target is used to identify the possible mechanisms. It is believed that the halos are mainly generated by the lateral diffusion of fast electrons due to the electrostatic and magnetic fields in the preplasma. This is illustrated by simulated electron trajectories using a numerical model.

  18. Neutron-gamma discrimination based on pulse shape discrimination in a Ce:LiCaAlF6 scintillator

    International Nuclear Information System (INIS)

    Yamazaki, Atsushi; Watanabe, Kenichi; Uritani, Akira; Iguchi, Tetsuo; Kawaguchi, Noriaki; Yanagida, Takayuki; Fujimoto, Yutaka; Yokota, Yuui; Kamada, Kei; Fukuda, Kentaro; Suyama, Toshihisa; Yoshikawa, Akira

    2011-01-01

    We demonstrate neutron-gamma discrimination based on a pulse shape discrimination method in a Ce:LiCAF scintillator. We have tried neutron-gamma discrimination using a difference in the pulse shape or the decay time of the scintillation light pulse. The decay time is converted into the rise time through an integrating circuit. A 252 Cf enclosed in a polyethylene container is used as the source of thermal neutrons and prompt gamma-rays. Obvious separation of neutron and gamma-ray events is achieved using the information of the rise time of the scintillation light pulse. In the separated neutron spectrum, the gamma-ray events are effectively suppressed with little loss of neutron events. The pulse shape discrimination is confirmed to be useful to detect neutrons with the Ce:LiCAF scintillator under an intense high-energy gamma-ray condition.

  19. Neutron-gamma discrimination based on pulse shape discrimination in a Ce:LiCaAlF{sub 6} scintillator

    Energy Technology Data Exchange (ETDEWEB)

    Yamazaki, Atsushi, E-mail: a-yamazaki@nucl.nagoya-u.ac.jp [Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University (Japan); Watanabe, Kenichi; Uritani, Akira [Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University (Japan); Iguchi, Tetsuo [Department of Quantum Engineering, Graduate School of Engineering, Nagoya University (Japan); Kawaguchi, Noriaki [Tokuyama Corporation (Japan); Yanagida, Takayuki; Fujimoto, Yutaka; Yokota, Yuui; Kamada, Kei [Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University (Japan); Fukuda, Kentaro; Suyama, Toshihisa [Tokuyama Corporation (Japan); Yoshikawa, Akira [Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University (Japan); New Industry Creation Hatchery Center (NICHe), Tohoku University (Japan)

    2011-10-01

    We demonstrate neutron-gamma discrimination based on a pulse shape discrimination method in a Ce:LiCAF scintillator. We have tried neutron-gamma discrimination using a difference in the pulse shape or the decay time of the scintillation light pulse. The decay time is converted into the rise time through an integrating circuit. A {sup 252}Cf enclosed in a polyethylene container is used as the source of thermal neutrons and prompt gamma-rays. Obvious separation of neutron and gamma-ray events is achieved using the information of the rise time of the scintillation light pulse. In the separated neutron spectrum, the gamma-ray events are effectively suppressed with little loss of neutron events. The pulse shape discrimination is confirmed to be useful to detect neutrons with the Ce:LiCAF scintillator under an intense high-energy gamma-ray condition.

  20. Gamma–neutron imaging system utilizing pulse shape discrimination with CLYC

    International Nuclear Information System (INIS)

    Whitney, Chad M.; Soundara-Pandian, Lakshmi; Johnson, Erik B.; Vogel, Sam; Vinci, Bob; Squillante, Michael; Glodo, Jarek; Christian, James F.

    2015-01-01

    Recently, RMD has investigated the use of CLYC (Cs 2 LiYCl 6 :Ce), a new and emerging scintillation material, in a gamma–neutron coded aperture imaging system based on RMD's commercial RadCam TM instrument. CLYC offers efficient thermal neutron detection, fast neutron detection capabilities, excellent pulse shape discrimination (PSD), and gamma-ray energy resolution as good as 4% at 662 keV. PSD improves the isolation of higher energy gammas from thermal neutron interactions (>3 MeV electron equivalent peak), compared to conventional pulse height techniques. The scintillation emission time in CLYC provides the basis for PSD; where neutron interactions result in a slower emission rise and decay components while gamma interactions result in a faster emission components. By creating a population plot based on the ratio of the decay tail compared to the total integral amplitude (PSD ratio), discrimination of gammas, thermal neutrons, and fast neutrons is possible. Previously, we characterized the CLYC-based RadCam system for imaging gammas and neutrons using a layered W-Cd coded aperture mask and employing only pulse height discrimination. In this paper, we present the latest results which investigate gamma-neutron imaging capabilities using PSD. An FPGA system is used to acquire the CLYC–PSPMT last dynode signals, determine a PSD ratio for each event, and compare it to a calibrated PSD cutoff. Each event is assigned either a gamma (low) or neutron (high) flag signal which is then correlated with the imaging information for each event. - Highlights: • The latest results are presented for our CLYC RadCam-2 system which investigate gamma–neutron imaging using pulse shape discrimination. • CLYC RadCam-2 system successfully discriminates gammas, thermal neutrons, and fast neutrons by employing a fully integrated, FPGA-based PSD system. • Imaging of our 252 Cf source was possible using both pulse height and pulse shape discrimination with CLYC. • Imaging

  1. Gamma–neutron imaging system utilizing pulse shape discrimination with CLYC

    Energy Technology Data Exchange (ETDEWEB)

    Whitney, Chad M., E-mail: cwhitney@rmdinc.com; Soundara-Pandian, Lakshmi; Johnson, Erik B.; Vogel, Sam; Vinci, Bob; Squillante, Michael; Glodo, Jarek; Christian, James F.

    2015-06-01

    Recently, RMD has investigated the use of CLYC (Cs{sub 2}LiYCl{sub 6}:Ce), a new and emerging scintillation material, in a gamma–neutron coded aperture imaging system based on RMD's commercial RadCam{sup TM} instrument. CLYC offers efficient thermal neutron detection, fast neutron detection capabilities, excellent pulse shape discrimination (PSD), and gamma-ray energy resolution as good as 4% at 662 keV. PSD improves the isolation of higher energy gammas from thermal neutron interactions (>3 MeV electron equivalent peak), compared to conventional pulse height techniques. The scintillation emission time in CLYC provides the basis for PSD; where neutron interactions result in a slower emission rise and decay components while gamma interactions result in a faster emission components. By creating a population plot based on the ratio of the decay tail compared to the total integral amplitude (PSD ratio), discrimination of gammas, thermal neutrons, and fast neutrons is possible. Previously, we characterized the CLYC-based RadCam system for imaging gammas and neutrons using a layered W-Cd coded aperture mask and employing only pulse height discrimination. In this paper, we present the latest results which investigate gamma-neutron imaging capabilities using PSD. An FPGA system is used to acquire the CLYC–PSPMT last dynode signals, determine a PSD ratio for each event, and compare it to a calibrated PSD cutoff. Each event is assigned either a gamma (low) or neutron (high) flag signal which is then correlated with the imaging information for each event. - Highlights: • The latest results are presented for our CLYC RadCam-2 system which investigate gamma–neutron imaging using pulse shape discrimination. • CLYC RadCam-2 system successfully discriminates gammas, thermal neutrons, and fast neutrons by employing a fully integrated, FPGA-based PSD system. • Imaging of our {sup 252}Cf source was possible using both pulse height and pulse shape discrimination with

  2. Shape-dependent magnetic properties of Co nanostructure arrays synthesized by pulsed laser melting

    Energy Technology Data Exchange (ETDEWEB)

    Shirato, N. [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Sherrill, S. [Department of Materials Science and Engineering, Georgia Institute of Technology, GA 30332 (United States); Gangopadhyay, A.K. [Department of Physics and Institute of Materials Science and Engineering, Washington University in St. Louis, St. Louis, MO 63132 (United States); Kalyanaraman, R., E-mail: ramki@utk.edu [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Sustainable Energy Education and Research Center (SEERC), University of Tennessee, Knoxville, TN 37996 (United States); Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN 37996 (United States)

    2016-06-01

    One dimensional (1D) magnetic nanowires show unique magnetic behaviors, such as large coercivity and high remanence, in comparison to the bulk and thin film materials. Here, planar arrays of Co nanowires, nanorods and nanoparticles were fabricated from thin Co films by a nanosecond pulsed laser interference irradiation technique. Magnetic force microscopy (MFM) and surface magneto-optic Kerr effect (SMOKE) techniques were used to study the individual and average magnetic properties of the nanostructures. Magnetic domain orientation was found to depend on the in-plane aspect ratio of the nanostructure. The magnetic orientation was out-of-plane for in-plane aspect ratio ranging from 1 to 1.4 and transitioned to an in-plane orientation for aspect ratios greater than 1.4 (such as in nanorods and nanowires). Our results also showed that polycrystalline Co nanowires showed much higher coercivity and remanence as compared to bulk and thin film materials, as well as shapes with smaller aspect ratio. This result was attributed mainly to the shape anisotropy. This study demonstrated that nanosecond pulsed laser synthesis is capable of fabricating various nanostructures in a simple, robust and rapid manner and SMOKE is a reliable technique to rapidly characterize such magnetic nanostructures. - Highlights: • Pulsed laser synthesis of Co nanostructures with different aspect ratio was demonstrated. • The magnetic properties of these nanostructures were characterized. • The magnetic orientation was found to depend on the aspect ratio.

  3. Spectrum library concept and pulse shape analysis in liquid scintillation counting

    Energy Technology Data Exchange (ETDEWEB)

    Kaihola, L. [Wallac Oy, Turku (Finland)

    1997-03-01

    Wallac introduced in 1990 a new absolute liquid scintillation counting (LSC) method, Digital Overlay Technique (DOT) to correct for quench. This method allows quantization of multilabel samples by referring to library spectra which are generated against chemical and color quench indices at the factory. The libraries can further be expanded to any beta emitter by user with a method called fine tuning, which can be carried out even with a single sample. Spectrum libraries are created over the whole spectrum range of the radionuclide and allow automatic identification of a single label beta emitting radionuclide, called Easy Count method. Another improvement in LSC is commercial introduction of Pulse Shape Analysis (PSA) in 1986 by Wallac. This method recognizes alpha particle decay by pulse shape and leads to excellent sensitivity in alpha counting because most of the background signal in LSC comprises of short or beta like pulses. PSA detects alpha events in the presence of high excess of beta activity over alphas, up to a ratio 100000 to 1. (orig.)

  4. Pulse Shaping for High Capacity Impulse Radio Ultra-Wideband Wireless Links Under the Russian Spectral Emission Mask

    DEFF Research Database (Denmark)

    Grakhova, Elizaveta P.; Rommel, Simon; Jurado-Navas, Antonio

    2016-01-01

    Two pulse shapes for IR-UWB transmission under the Russian spectral emission mask are proposed and their potential experimentally demonstrated. Pulses based on the hyperbolic secant square function and the frequency B-spline wavelet are shown to enable transmission of 1.25 Gbit/s signals, reachin...

  5. Pulse Shaping for High Capacity Impulse Radio Ultra-Wideband Wireless Links Under the Russian Spectral Emission Mask

    DEFF Research Database (Denmark)

    Grakhova, Elizaveta P.; Rommel, Simon; Jurado-Navas, Antonio

    2016-01-01

    Two pulse shapes for IR-UWB transmission under the Russian spectral emission mask are proposed and their potential experimentally demonstrated. Pulses based on the hyperbolic secant square function and the frequency B-spline wavelet are shown to enable transmission of 1.25 Gbit/s signals, reaching...

  6. Surface treatment of screw shaped titanium dental implants by high intensity laser pulses

    Science.gov (United States)

    Pető, G.; Karacs, A.; Pászti, Z.; Guczi, L.; Divinyi, T.; Joób, A.

    2002-01-01

    Machined and Al 2O 3 blasted surfaces of screw shaped Ti dental implants were irradiated by 30 ns pulses of Nd:glass laser at 1064 nm wavelength with 0.5-3 J pulse energy. The laser treatment increased the temperature of the Ti surface well above the melting temperature. The resulting ablation of some surface layers was followed by a very rapid solidification. These thermal processes strongly modified the original morphology of the surface and removed the contaminations. The new morphology was characterized by features mostly in ten micron and partly in submicron ranges. The surface composition was the same as the bulk titanium without any segregation. Animal experiments demonstrated that this surface treatment seems to be promising for the improvement of the osseointegration of dental implants.

  7. Theoretical estimation of nonlinear optical force on dielectric spherical particles of arbitrary size under femtosecond pulsed excitation

    Science.gov (United States)

    Devi, Anita; De, Arijit K.

    2017-08-01

    Experimental evidence indicates that high-repetition-rate ultrafast pulsed excitation is more efficient in optical trapping of dielectric nanoparticles as compared with continuous-wave excitation at the same average power. The physics behind the different nature of force under these two excitation conditions remained deceptive until quite recently when it was theoretically explained, in the dipole limit, as a combined effect of (1) repetitive instantaneous momentum transfer and (2) optical Kerr nonlinearity. The role of optical Kerr effect was theoretically studied for larger dielectric spherical particles, in the ray optics limit, also. However, a theoretical underpinning is yet to be established as to whether the effect of optical nonlinearity is omnipresent across different particle sizes, which we investigate here. Using localized approximation of generalized Lorenz-Mie theory, we theoretically analyze the nature of force (and potential) and provide a detailed comparative discussion between this generalized scattering formulation with dipole scattering formulation for dielectric nanoparticles.

  8. Infrared emissivity studies of melting thresholds and structural changes of aluminium and copper samples heated by femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Hallo, L; Riou, O; Stenz, C; Tikhonchuk, V T [Centre Lasers Intenses et Applications, UMR 5107 CNRS-Universite Bordeaux 1-CEA, Universite Bordeaux 1, 351 Cours de la Liberation, 33405 Talence Cedex (France)

    2006-12-21

    We propose a new method for studies of laser-induced heating and melting of metallic foils. The method is based on time-integrated measurements of the surface infrared thermal emission. The experimental data are compared with a model where two equations describe the evolution of electron and lattice temperatures and the emissivity is found from the Drude model with the temperature-dependent electron collision frequency. A good agreement between the experimental data and the model is found for the aluminium samples. It is less satisfactory for the copper, but a signature of phase melting can also be pointed out. A multi-pulse laser irradiation study indicates significant changes in the surface emittance, related to preheating, oxidation and/or chemical modification of the copper sample. The proposed method is relatively simple and complementary to the pump-probe technique.

  9. Pattern dynamics and filamentation of femtosecond terawatt laser pulses in air including the higher-order Kerr effects.

    Science.gov (United States)

    Huang, T W; Zhou, C T; He, X T

    2013-05-01

    Plasma defocusing and higher-order Kerr effects on multiple filamentation and pattern formation of ultrashort laser pulse propagation in air are investigated. Linear analyses and numerical results show that these two saturable nonlinear effects can destroy the coherent evolution of the laser field, and small-scale spatial turbulent structures rapidly appear. For the two-dimensional case, numerical simulations show that blow-up-like solutions, spatial chaos, and pseudorecurrence can appear at higher laser intensities if only plasma defocusing is included. These complex patterns result from the stochastic evolution of the higher- or shorter-wavelength modes of the laser light spectrum. From the viewpoint of nonlinear dynamics, filamentation can be attributed to the modulational instability of these spatial incoherent localized structures. Furthermore, filament patterns associated with multiphoton ionization of the air molecules with and without higher-order Kerr effects are compared.

  10. Tailoring the laser pulse shape to improve the quality of the self-injected electron beam in laser wakefield acceleration

    International Nuclear Information System (INIS)

    Upadhyay, Ajay K.; Samant, Sushil A.; Krishnagopal, S.

    2013-01-01

    In laser wakefield acceleration, tailoring the shape of the laser pulse is one way of influencing the laser-plasma interaction and, therefore, of improving the quality of the self-injected electron beam in the bubble regime. Using three-dimensional particle-in-cell simulations, the evolution dynamics of the laser pulse and the quality of the self-injected beam, for a Gaussian pulse, a positive skew pulse (i.e., one with sharp rise and slow fall), and a negative skew pulse (i.e., one with a slow rise and sharp fall) are studied. It is observed that with a negative skew laser pulse there is a substantial improvement in the emittance (by around a factor of two), and a modest improvement in the energy-spread, compared to Gaussian as well as positive skew pulses. However, the injected charge is less in the negative skew pulse compared to the other two. It is also found that there is an optimal propagation distance that gives the best beam quality; beyond this distance, though the energy increases, the beam quality deteriorates, but this deterioration is least for the negative skew pulse. Thus, the negative skew pulse gives an improvement in terms of beam quality (emittance and energy spread) over what one can get with a Gaussian or positive skew pulse. In part, this is because of the lesser injected charge, and the strong suppression of continuous injection for the negative skew pulse.

  11. MeV surface fast electron emission from femtosecond laser pulses interacting with planar and nanowire targets

    Science.gov (United States)

    Tian, Ye; Liu, Jiansheng; Wang, Wentao; Wang, Cheng; Lu, Xiaoming; Leng, Yuxin; Liang, Xiaoyan; Li, Ruxin; Xu, Zhizhan

    2014-07-01

    The mechanics of generating MeV target surface fast electrons (SFEs) is investigated using a 5 J, 50 fs laser pulse focused on a Cu planar and nanowire target. The energy spectrum and spatial angular distribution of fast electrons emitted from the planar target are determined and compared with those from the nanowire target. When the laser intensity reaches 1 × 1019 W cm-2, the coupling from the laser to 1-3 MeV electrons reaches 1.1% on the planar target at a 45° incidence angle, while the number of SFEs generated from the nanowire target is about 10% of those from the planar target. The two-dimensional particle-in-cell simulation results reproduce the electron emission characteristics and reveal a strong continuous surface magnetic field on the surface of the planar target as compared with the discrete magnetic field on the nanowire target which decreases SFEs. A high, hot electron temperature in the forward direction at 556keV is achieved for the nanowire structure capable of guiding and confining fast electrons along the wire direction, compared with 178keV for the planar target.

  12. Photoinduced electric currents in ring-shaped molecules by circularly polarized laser pulses

    International Nuclear Information System (INIS)

    Nobusada, Katsuyuki; Yabana, Kazuhiro

    2007-01-01

    We have theoretically demonstrated that circularly polarized laser pulses induce electric currents and magnetic moments in ring-shaped molecules Na 10 and benzene. The time-dependent adiabatic local density approximation is employed for this purpose, solving the time-dependent Kohn-Sham equation in real space and real time. It has been found that the electric currents are induced efficiently and persist continuously even after the laser pulses were switched off provided the frequency of the applied laser pulse is in tune with the excitation energy of the electronic excited state with the dipole strength for each molecular system. The electric currents are definitely revealed to be a second-order nonlinear optical response to the magnitude of the electric field. The magnetic dipole moments inevitably accompany the ring currents, so that the molecules are magnetized. The production of the electric currents and the magnetic moments in the present procedure is found to be much more efficient than that utilizing static magnetic fields

  13. The Shape of an Auxin Pulse, and What It Tells Us about the Transport Mechanism.

    Directory of Open Access Journals (Sweden)

    Graeme Mitchison

    2015-10-01

    Full Text Available Auxin underlies many processes in plant development and physiology, and this makes it of prime importance to understand its movements through plant tissues. In stems and coleoptiles, classic experiments showed that the peak region of a pulse of radio-labelled auxin moves at a roughly constant velocity down a stem or coleoptile segment. As the pulse moves it becomes broader, at a roughly constant rate. It is shown here that this 'spreading rate' is larger than can be accounted for by a single channel model, but can be explained by coupling of channels with differing polar transport rates. An extreme case is where strongly polar channels are coupled to completely apolar channels, in which case auxin in the apolar part is 'dragged along' by the polar part in a somewhat diffuse distribution. The behaviour of this model is explored, together with others that can account for the experimentally observed spreading rates. It is also shown that saturation of carriers involved in lateral transport can explain the characteristic shape of pulses that result from uptake of large amounts of auxin.

  14. Fast neutron flux analyzer with real-time digital pulse shape discrimination

    Energy Technology Data Exchange (ETDEWEB)

    Ivanova, A.A., E-mail: a.a.ivanova@inp.nsk.su [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Zubarev, P.V. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Novosibirsk State Technical University, 630092 Novosibirsk (Russian Federation); Ivanenko, S.V. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Khilchenko, A.D. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Novosibirsk State Technical University, 630092 Novosibirsk (Russian Federation); Kotelnikov, A.I. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Polosatkin, S.V. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Novosibirsk State Technical University, 630092 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation); Puryga, E.A.; Shvyrev, V.G. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Novosibirsk State Technical University, 630092 Novosibirsk (Russian Federation); Sulyaev, Yu.S. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation)

    2016-08-11

    Investigation of subthermonuclear plasma confinement and heating in magnetic fusion devices such as GOL–3 and GDT at the Budker Institute (Novosibirsk, Russia) requires sophisticated equipment for neutron-, gamma- diagnostics and upgrading data acquisition systems with online data processing. Measurement of fast neutron flux with stilbene scintillation detectors raised the problem of discrimination of the neutrons (n) from background cosmic particles (muons) and neutron-induced gamma rays (γ). This paper describes a fast neutron flux analyzer with real-time digital pulse-shape discrimination (DPSD) algorithm FPGA-implemented for the GOL–3 and GDT devices. This analyzer was tested and calibrated with the help of {sup 137}Cs and {sup 252}Cf radiation sources. The Figures of Merit (FOM) calculated for different energy cuts are presented. - Highlights: • Electronic equipment for measurement of fast neutron flux with stilbene scintillator is presented. • FPGA-implemented digital pulse-shape discrimination algorithm by charge comparison method is shown. • Calibration of analyzer was carried out with {sup 137}Cs and {sup 252}Cf. • Figures of Merit (FOM) values for energy cuts from 1/8 Cs to 2 Cs are from 1.264 to 2.34 respectively.

  15. Magnetically driven isentropic compression to multimegabar pressures using shaped current pulses on the Z accelerator

    International Nuclear Information System (INIS)

    Davis, Jean-Paul; Deeney, Christopher; Knudson, Marcus D.; Lemke, Raymond W.; Pointon, Timothy D.; Bliss, David E.

    2005-01-01

    A technique has previously been developed on the Z accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] to generate ramped compression waves in condensed matter for equation-of-state studies [C. A. Hall, J. R. Asay, M. D. Knudson, W. A. Stygar, R. B. Spielman, T. D. Pointon, D. B. Reisman, A. Toor, and R. C. Cauble, Rev. Sci. Instrum. 72, 3587 (2001)] by using the Lorentz force to push on solid electrodes rather than to drive a Z pinch. This technique has now been extended to multimegabar pressures by shaping the current pulse on Z to significantly increase the sample thickness through which the compression wave can propagate without forming a shock. Shockless, free-surface velocity measurements from multiple sample thicknesses on a single experiment can be analyzed using a backward integration technique [D. B. Hayes, C. A. Hall, J. R. Asay, and M. D. Knudson, J. Appl. Phys. 94, 2331 (2003)] to extract an isentropic loading curve. At very high pressures, the accuracy of this method is dominated by relative uncertainty in the transit time between two thicknesses. This paper discusses in some detail the issues involved with accurate measurement of a multimegabar isentrope, including experiment design trade-offs and mechanics of pulse shaping on Z

  16. Electroluminescence pulse shape and electron diffusion in liquid argon measured in a dual-phase TPC

    Energy Technology Data Exchange (ETDEWEB)

    Agnes, P.; et al.

    2018-02-05

    We report the measurement of the longitudinal diffusion constant in liquid argon with the DarkSide-50 dual-phase time projection chamber. The measurement is performed at drift electric fields of 100 V/cm, 150 V/cm, and 200 V/cm using high statistics $^{39}$Ar decays from atmospheric argon. We derive an expression to describe the pulse shape of the electroluminescence signal (S2) in dual-phase TPCs. The derived S2 pulse shape is fit to events from the uppermost portion of the TPC in order to characterize the radial dependence of the signal. The results are provided as inputs to the measurement of the longitudinal diffusion constant DL, which we find to be (4.12 $\\pm$ 0.04) cm$^2$/s for a selection of 140keV electron recoil events in 200V/cm drift field and 2.8kV/cm extraction field. To study the systematics of our measurement we examine datasets of varying event energy, field strength, and detector volume yielding a weighted average value for the diffusion constant of (4.09 $\\pm$ 0.09) cm$^2$ /s. The measured longitudinal diffusion constant is observed to have an energy dependence, and within the studied energy range the result is systematically lower than other results in the literature.

  17. Femtosecond near-infrared laser pulses elicit generation of reactive oxygen species in mammalian cells leading to apoptosis-like death.

    Science.gov (United States)

    Tirlapur, U K; König, K; Peuckert, C; Krieg, R; Halbhuber, K J

    2001-02-01

    Two-photon excitation-based near-infrared (NIR) laser scanning microscopy is currently emerging as a new and versatile alternative to conventional confocal laser scanning microscopy, particularly for vital cell imaging in life sciences. Although this innovative microscopy has several advantages such as highly localized excitation, higher penetration depth, reduced photobleaching and photodamage, and improved signal to noise ratio, it has, however, recently been evidenced that high-power NIR laser irradiation can drastically inhibit cell division and induce cell death. In the present study we have investigated the cellular responses of unlabeled rat kangaroo kidney epithelium (PtK2) cells to NIR femtosecond laser irradiation. We demonstrate that NIR 170-fs laser pulses operating at 80-MHz pulse repetition frequency and at mean power of > or = 7 mW evoke generation of reactive oxygen species (ROS) such as H2O2 that can be visualized in situ by standard in vivo cytochemical analysis using Ni-3,3'-diaminobenzidine (Ni-DAB) as well as with a recently developed fluorescent probe Jenchrom px blue. The formation of the Ni-DAB reaction product as well as that of Jenchrom was relatively more pronounced when irradiated cells were incubated in alkaline solution (pH 8) than in those incubated in acidic solution (pH 6), suggesting peroxisomal localization of these reaction products. Two-photon time-lapse imaging of the internalization of the cell impermeate fluorescent dye propidium iodide revealed that the integrity of the plasma membrane of NIR irradiated cells is drastically compromised. Visualization of the nuclei with DNA-specific fluorescent probes such as 4',6-diamidino-2-phenylindole 24 h postirradiation further provided tangible evidence that the nuclei of these cells undergo several deformations and eventual fragmentation. That these NIR irradiated cells die by apoptosis has been established by in situ detection of DNA strand breaks using the terminal deoxynucleotidyl

  18. Optimization of the integration time of pulse shape analysis for dual-layer GSO detector with different amount of Ce

    International Nuclear Information System (INIS)

    Yamamoto, Seiichi

    2008-01-01

    For a multi-layer depth-of-interaction (DOI) detector using different decay times, pulse shape analysis based on two different integration times is often used to distinguish scintillators in DOI direction. This method measures a partial integration and a full integration, and calculates the ratio of these two to obtain the pulse shape distribution. The full integration time is usually set to integrate full width of the scintillation pulse. However, the optimum partial integration time is not obvious for obtaining the best separation of the pulse shape distribution. To make it clear, a theoretical analysis and experiments were conducted for pulse shape analysis by changing the partial integration time using a scintillation detector of GSOs with different amount of Ce. A scintillation detector with 1-in. round photomultiplier tube (PMT) optically coupled GSO of 1.5 mol% (decay time: 35 ns) and that of 0.5 mol% (decay time: 60 ns) was used for the experiments. The signal from PMT was digitally integrated with partial (50-150 ns) and full (160 ns) integration times and ratio of these two was calculated to obtain the pulse shape distribution. In the theoretical analysis, partial integration time of 50 ns showed largest distance between two peaks of the pulse shape distribution. In the experiments, it showed maximum at 70-80 ns of partial integration time. The peak to valley ratio showed the maximum at 120-130 ns. Because the separation of two peaks is determined by the peak to valley ratio, we conclude the optimum partial integration time for these combinations of GSOs is around 120-130 ns, relatively longer than the expected value

  19. Simulation and real-time analysis of pulse shapes from segmented HPGe-detectors

    Energy Technology Data Exchange (ETDEWEB)

    Schlarb, Michael Christian

    2009-11-17

    The capabilities of future HPGe arrays consisting of highly segmented detectors, like AGATA will depend heavily on the performance of {gamma}-ray tracking. The most crucial component in the whole concept is the pulse shape analysis (PSA). The working principle of PSA is to compare the experimental signal shape with signals available from a basis set with known interaction locations. The efficiency of the tracking algorithm hinges on the ability of the PSA to reconstruct the interaction locations accurately, especially for multiple {gamma}-interactions. Given the size of the arrays the PSA algorithm must be run in a real-time environment. A prerequisite to a successful PSA is an accurate knowledge of the detectors response. Making a full coincidence scan of a single AGATA detector, however takes between two and three months, which is too long to produce an experimental signal basis for all detector elements. A straight forward possibility is to use a precise simulation of the detector and to provide a basis of simulated signals. For this purpose the Java Agata Signal Simulation (JASS) was developed in the course of this thesis. The geometry of the detector is given with numerical precision and models describing the anisotropic mobilities of the charge carriers in germanium were taken from the literature. The pulse shapes of the transient and net-charge signals are calculated using weighting potentials on a finite grid. Special care was taken that the interpolation routine not only reproduces the weighting potentials precisely in the highly varying areas of the segment boundaries but also that its performance is independent of the location within the detector. Finally data from a coincidence scan and a pencil beam experiment were used to verify JASS. The experimental signals are reproduced accurately by the simulation. Pulse Shape Analysis (PSA) reconstructs the positions of the individual interactions and the corresponding energy deposits within the detector. This

  20. Numerical investigations of signal-spectrum shaping based on conformal profile theory in optical parametric chirped pulse amplification

    Science.gov (United States)

    Li, Wenqi; Yu, Lianghong; Peng, Chun; Liang, Xiaoyan

    2017-11-01

    We proposed a theoretical description and numerical model of signal-spectrum shaping based on conformal profile theory and the three-dimensional coupling wave equations for improving the performance of optical parametric chirped pulse amplification (OPCPA). Using our model, we executed quantitative simulations of signal-spectrum shaping and compared the differences of spatiotemporal amplification characteristics between a shaped signal-spectrum and Gaussian signal-spectrum of an OPCPA based on LiB3O5 near 800 nm. By comparison, we found that the conversion efficiency from pump to signal can be dramatically boosted via signal-spectrum shaping. Meanwhile the amplified-spectrum profile, as well as the Fourier-limited pulse, can be improved significantly. We also found that the spatial spot profiles, for injecting a shaped signal or a Gaussian signal in OPCPA, are nearly the same before the saturation regime and at the maximum conversion efficiency or output energy.

  1. All-fiber femtosecond Cherenkov source

    Directory of Open Access Journals (Sweden)

    Tu H.

    2013-03-01

    Full Text Available An all-fiber femtosecond Cherenkov radiation source is demonstrated for the first time, to the best of our knowledge. Using a stable monolithic femtosecond Ybdoped fiber laser as the pump source, and the combination of photonic crystal fibers as the wave-conversion medium, we have generated tunable Cherenkov radiation at visible wavelengths 580 – 630 nm, with pulse duration of sub-160 fs, and the 3 dB spectral bandwidth not exceeding 36 nm. Such femtosecond source can find applications in practical biophotonics such as bio-imaging and microscopy.

  2. All-fiber femtosecond Cherenkov source

    DEFF Research Database (Denmark)

    Liu, Xiaomin; Lægsgaard, Jesper; Møller, Uffe Visbech

    2013-01-01

    An all-fiber femtosecond Cherenkov radiation source is demonstrated for the first time, to the best of our knowledge. Using a stable monolithic femtosecond Ybdoped fiber laser as the pump source, and the combination of photonic crystal fibers as the wave-conversion medium, we have generated tunable...... Cherenkov radiation at visible wavelengths 580 - 630 nm, with pulse duration of sub-160 fs, and the 3 dB spectral bandwidth not exceeding 36 nm. Such femtosecond source can find applications in practical biophotonics such as bio-imaging and microscopy....

  3. Femtosecond Optics: Advanced Devices and Ultrafast Phenomena

    Science.gov (United States)

    2007-05-31

    stability, the drift of the resonance frequency caused by temperature variations as well as drift in the PZT bias offset were minimal and a manual ...with a femtosecond laser," Optics Letters 21(21): 1729-31 (1996). [4] D. Homoelle, S. Wielandy, A. L. Gaeta, N. F. Borrelli , and C. Smith, "Infrared...Streltsov and N. F. Borrelli , "Fabrication and analysis of a directional coupler written in glass by nanojoule femtosecond laser pulses," Optics

  4. A photonic-assisted periodic triangular-shaped pulses generator based on FWM effect in an SOA

    Science.gov (United States)

    Yuan, Jin; Ning, Tigang; Li, Jing; Chen, Hongyao; Li, Yueqin; Zhang, Chan

    2016-12-01

    We propose a photonic-assisted triangular-shaped pulse train generator based on four-wave mixing effect (FWM) in a semiconductor optical amplifier (SOA). A dual-parallel Mach-Zehnder operated at quadrupling RF modulation is employed to generate two primary sidebands (±2nd) in spectrum of the triangular-shaped pulse. Then the FWM effect leads to generation of two new frequency components. By setting the modulation index and bias current of the SOA properly, the generated harmonics of optical intensity can be corresponding to the Fourier components of typical periodic triangular pulses. Finally, a triangular pulse train with tunable repetition rate can be obtained. Numerical simulations have been taken to evaluate the impact of several key parameters to make the scheme more practical.

  5. Charged particle identification including Pions by pulse-shape discrimination with an NE213 liquid scintillator

    International Nuclear Information System (INIS)

    Nakamoto, T.; Ishibashi, K.; Matsufuji, N.; Shigyo, N.; Maehata, K.

    1995-01-01

    Particles emitted from spallation reactions induced by protons having GeV energies were measured with an NE213 liquid scintillator, 12.7 cm in diameter and 12.7 cm thick. The pulse-shape discrimination (PSD) was carried out for charged particle identification by the two-gate integration method. Pions having energies up to 60 MeV were clearly discriminated from protons and electrons. On the contrary, pions with higher energies could not be identified since they escaped from the detector. The advantage of PSD for charged particle identification is that there is no requirement for a ΔE detector in the measurements. copyright 1995 American Institute of Physics

  6. Application of neural networks to digital pulse shape analysis for an array of silicon strip detectors

    Energy Technology Data Exchange (ETDEWEB)

    Flores, J.L. [Dpto de Ingeniería Eléctrica y Térmica, Universidad de Huelva (Spain); Martel, I. [Dpto de Física Aplicada, Universidad de Huelva (Spain); CERN, ISOLDE, CH 1211 Geneva, 23 (Switzerland); Jiménez, R. [Dpto de Ingeniería Electrónica, Sist. Informáticos y Automática, Universidad de Huelva (Spain); Galán, J., E-mail: jgalan@diesia.uhu.es [Dpto de Ingeniería Electrónica, Sist. Informáticos y Automática, Universidad de Huelva (Spain); Salmerón, P. [Dpto de Ingeniería Eléctrica y Térmica, Universidad de Huelva (Spain)

    2016-09-11

    The new generation of nuclear physics detectors that used to study nuclear reactions is considering the use of digital pulse shape analysis techniques (DPSA) to obtain the (A,Z) values of the reaction products impinging in solid state detectors. This technique can be an important tool for selecting the relevant reaction channels at the HYDE (HYbrid DEtector ball array) silicon array foreseen for the Low Energy Branch of the FAIR facility (Darmstadt, Germany). In this work we study the feasibility of using artificial neural networks (ANNs) for particle identification with silicon detectors. Multilayer Perceptron networks were trained and tested with recent experimental data, showing excellent identification capabilities with signals of several isotopes ranging from {sup 12}C up to {sup 84}Kr, yielding higher discrimination rates than any other previously reported.

  7. Fast neutron flux analyzer with real-time digital pulse shape discrimination

    Science.gov (United States)

    Ivanova, A. A.; Zubarev, P. V.; Ivanenko, S. V.; Khilchenko, A. D.; Kotelnikov, A. I.; Polosatkin, S. V.; Puryga, E. A.; Shvyrev, V. G.; Sulyaev, Yu. S.

    2016-08-01

    Investigation of subthermonuclear plasma confinement and heating in magnetic fusion devices such as GOL-3 and GDT at the Budker Institute (Novosibirsk, Russia) requires sophisticated equipment for neutron-, gamma- diagnostics and upgrading data acquisition systems with online data processing. Measurement of fast neutron flux with stilbene scintillation detectors raised the problem of discrimination of the neutrons (n) from background cosmic particles (muons) and neutron-induced gamma rays (γ). This paper describes a fast neutron flux analyzer with real-time digital pulse-shape discrimination (DPSD) algorithm FPGA-implemented for the GOL-3 and GDT devices. This analyzer was tested and calibrated with the help of 137Cs and 252Cf radiation sources. The Figures of Merit (FOM) calculated for different energy cuts are presented.

  8. Fast-Neutron Spectrometry Using a 3He Ionization Chamber and Digital Pulse Shape Analysis

    Energy Technology Data Exchange (ETDEWEB)

    D. L. Chichester; J. T. Johnson; E. H. Seabury

    2010-05-01

    Digital pulse shape analysis (dPSA) has been used with a Cuttler-Shalev type 3He proportional counter to measure the fast neutron spectra of bare 252Cf and 241AmBe neutron sources. Measurements have also been made to determine the attenuated fast neutron spectra of 252Cf shielded by several materials including water, graphite, liquid nitrogen, magnesium, and tungsten. Rise-time dPSA has been employed using the common rise-time approach for analyzing n +3He ? 1H + 3H ionization events and a new approach has been developed to improve the fidelity of these measurements. Simulations have been performed for the different experimental arrangements and are compared, demonstrating general agreement between the dPSA processed fast neutron spectra and predictions.

  9. Statistical and Machine-Learning Classifier Framework to Improve Pulse Shape Discrimination System Design

    Energy Technology Data Exchange (ETDEWEB)

    Wurtz, R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Kaplan, A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-10-28

    Pulse shape discrimination (PSD) is a variety of statistical classifier. Fully-­realized statistical classifiers rely on a comprehensive set of tools for designing, building, and implementing. PSD advances rely on improvements to the implemented algorithm. PSD advances can be improved by using conventional statistical classifier or machine learning methods. This paper provides the reader with a glossary of classifier-­building elements and their functions in a fully-­designed and operational classifier framework that can be used to discover opportunities for improving PSD classifier projects. This paper recommends reporting the PSD classifier’s receiver operating characteristic (ROC) curve and its behavior at a gamma rejection rate (GRR) relevant for realistic applications.

  10. Digital pulse shape discrimination between fast neutrons and gamma rays with para-terphenyl scintillator

    Science.gov (United States)

    Chepurnov, A. S.; Kirsanov, M. A.; Klenin, A. A.; Klimanov, S. G.; Kubankin, A. S.

    2017-12-01

    In the presented work, we investigated several digital methods of a discrimination signals from fast neutrons and gamma quanta. The experimental setup consists of a Pu-Be neutron source, a scintillation detector with an organic para-terphenyl monocrystal, and a digitizer (CAEN DT5730, 500 MS/s). Mixed waveform sequences were stored and then separated by pulse shape. Four methods were used for signals separation. Comparison of the traditional and the new methods of Figure of Merit (FOM) calculation is given. FOM = 1.5 was obtained in our setup for the minimum threshold value. A scintillation detector with a para-terphenyl crystal was used to measure neutron yield in the neutron generator with carbon nanotubes.

  11. 2 micron femtosecond fiber laser

    Science.gov (United States)

    Liu, Jian; Wan, Peng; Yang, Lihmei

    2014-07-29

    Methods and systems for generating femtosecond fiber laser pulses are disclose, including generating a signal laser pulse from a seed laser oscillator; using a first amplifier stage comprising an input and an output, wherein the signal laser pulse is coupled into the input of the first stage amplifier and the output of the first amplifier stage emits an amplified and stretched signal laser pulse; using an amplifier chain comprising an input and an output, wherein the amplified and stretched signal laser pulse from the output of the first amplifier stage is coupled into the input of the amplifier chain and the output of the amplifier chain emits a further amplified, stretched signal laser pulse. Other embodiments are described and claimed.

  12. Optimizing Atom Probe Analysis with Synchronous Laser Pulsing and Voltage Pulsing.

    Science.gov (United States)

    Zhao, Lu; Normand, Antoine; Houard, Jonathan; Blum, Ivan; Delaroche, Fabien; Latry, Olivier; Ravelo, Blaise; Vurpillot, Francois

    2017-04-01

    Atom probe has been developed for investigating materials at the atomic scale and in three dimensions by using either high-voltage (HV) pulses or laser pulses to trigger the field evaporation of surface atoms. In this paper, we propose an atom probe setup with pulsed evaporation achieved by simultaneous application of both methods. This provides a simple way to improve mass resolution without degrading the intrinsic spatial resolution of the instrument. The basic principle of this setup is the combination of both modes, but with a precise control of the delay (at a femtosecond timescale) between voltage and laser pulses. A home-made voltage pulse generator and an air-to-vacuum transmission system are discussed. The shape of the HV pulse presented at the sample apex is experimentally measured. Optimizing the delay between the voltage and the laser pulse improves the mass spectrum quality.

  13. Gamma-neutron imaging system utilizing pulse shape discrimination with CLYC

    Science.gov (United States)

    Whitney, Chad M.; Soundara-Pandian, Lakshmi; Johnson, Erik B.; Vogel, Sam; Vinci, Bob; Squillante, Michael; Glodo, Jarek; Christian, James F.

    2015-06-01

    Recently, RMD has investigated the use of CLYC (Cs2LiYCl6:Ce), a new and emerging scintillation material, in a gamma-neutron coded aperture imaging system based on RMD's commercial RadCamTM instrument. CLYC offers efficient thermal neutron detection, fast neutron detection capabilities, excellent pulse shape discrimination (PSD), and gamma-ray energy resolution as good as 4% at 662 keV. PSD improves the isolation of higher energy gammas from thermal neutron interactions (>3 MeV electron equivalent peak), compared to conventional pulse height techniques. The scintillation emission time in CLYC provides the basis for PSD; where neutron interactions result in a slower emission rise and decay components while gamma interactions result in a faster emission components. By creating a population plot based on the ratio of the decay tail compared to the total integral amplitude (PSD ratio), discrimination of gammas, thermal neutrons, and fast neutrons is possible. Previously, we characterized the CLYC-based RadCam system for imaging gammas and neutrons using a layered W-Cd coded aperture mask and employing only pulse height discrimination. In this paper, we present the latest results which investigate gamma-neutron imaging capabilities using PSD. An FPGA system is used to acquire the CLYC-PSPMT last dynode signals, determine a PSD ratio for each event, and compare it to a calibrated PSD cutoff. Each event is assigned either a gamma (low) or neutron (high) flag signal which is then correlated with the imaging information for each event.

  14. Optimal design of waveform digitisers for both energy resolution and pulse shape discrimination

    Science.gov (United States)

    Cang, Jirong; Xue, Tao; Zeng, Ming; Zeng, Zhi; Ma, Hao; Cheng, Jianping; Liu, Yinong

    2018-04-01

    Fast digitisers and digital pulse processing have been widely used for spectral application and pulse shape discrimination (PSD) owing to their advantages in terms of compactness, higher trigger rates, offline analysis, etc. Meanwhile, the noise of readout electronics is usually trivial for organic, plastic, or liquid scintillator with PSD ability because of their poor intrinsic energy resolution. However, LaBr3(Ce) has been widely used for its excellent energy resolution and has been proven to have PSD ability for alpha/gamma particles. Therefore, designing a digital acquisition system for such scintillators as LaBr3(Ce) with both optimal energy resolution and promising PSD ability is worthwhile. Several experimental research studies about the choice of digitiser properties for liquid scintillators have already been conducted in terms of the sampling rate and vertical resolution. Quantitative analysis on the influence of waveform digitisers, that is, fast amplifier (optional), sampling rates, and vertical resolution, on both applications is still lacking. The present paper provides quantitative analysis of these factors and, hence, general rules about the optimal design of digitisers for both energy resolution and PSD application according to the noise analysis of time-variant gated charge integration.

  15. Pulse shape discrimination of plastic scintillator EJ 299-33 with radioactive sources

    Science.gov (United States)

    Pagano, E. V.; Chatterjee, M. B.; De Filippo, E.; Russotto, P.; Auditore, L.; Cardella, G.; Geraci, E.; Gnoffo, B.; Guazzoni, C.; Lanzalone, G.; De Luca, S.; Maiolino, C.; Martorana, N. S.; Pagano, A.; Papa, M.; Parsani, T.; Pirrone, S.; Politi, G.; Porto, F.; Quattrocchi, L.; Rizzo, F.; Trifirò, A.; Trimarchi, M.

    2018-05-01

    The present study has been carried out in order to investigate about the possibility of using EJ 299-33 scintillator in a multi-detector array to detect neutrons along with light charged particles. In a reaction induced by stable and exotic heavy-ions beams, where copious production of neutrons and other light charged particles occurs, discrimination with low identification threshold of these particles are of great importance. In view of this, EJ 299-33 scintillator having dimension of 3 cm × 3 cm × 3 cm backed by a photomultiplier tube was tested and used under vacuum to detect neutrons, gamma-rays and alpha particles emitted by radioactive sources. Anode pulses from the photomultiplier tube were digitized through GET electronics, recorded and stored in a data acquisition system for the purpose of an off-line analysis. The measurements, under vacuum and low background conditions, show good pulse shape discrimination properties characterized by low identification threshold for neutrons, gamma-rays and alpha particles. The Figures of Merit for neutron-gamma and alpha particles-gamma discriminations have been evaluated together with the energy resolution for gamma-ray and alpha particles.

  16. Energy calibration of CsI(Tl) scintillator in pulse-shape identification technique

    CERN Document Server

    Avdeichikov, V; Golubev, P; Jakobsson, B; Colonna, N

    2003-01-01

    A batch of 16 CsI(Tl) scintillator crystals, supplied by the Bicron Company, has been studied with respect to precise energy calibration in pulse-shape identification technique. The light corresponding to pulse integration within the time interval 1.6-4.5 mu s (long gate) and 0.0-4.5 mu s (extra-long gate) exhibits a power law relation, L(E,Z,A)=a1(Z,A)E sup a sup 2 sup ( sup Z sup , sup A sup ) , for sup 1 sup , sup 2 sup , sup 3 H isotopes in the measured energy range 5-150 MeV. For the time interval 0.0-0.60 mu s (short gate), a significant deviation from the power law relation is observed, for energy greater than approx 30 MeV. The character of the a2(p)-a2(d) and a2(p)-a2(t) correlations for protons, deuterons and tritons, reveals 3 types of crystals in the batch. These subbatches differ in the value of the extracted parameter a2 for protons, and in the value of the spread of a2 for deuterons and tritons. This may be explained by the difference in the energy dependence of the fast decay time component an...

  17. Neutron-Gamma Pulse Shape Discrimination With Ne-213 Liquid Scintillator By Using Digital Signal Processing Combined With Similarity Method

    International Nuclear Information System (INIS)

    Mardiyanto

    2008-01-01

    Neutron-Gamma Pulse Shape Discrimination with a NE-213 Liquid Scintillator by Using Digital Signal Processing Combined with Similarity Method. Measurement of mixed neutron-gamma radiation is difficult because a nuclear detector is usually sensitive to both radiations. A new attempt of neutron-gamma pulse shape discrimination for a NE-213 liquid scintillator is presented by using digital signal processing combined with an off-line similarity method. The output pulse shapes are digitized with a high speed digital oscilloscope. The n-γ discrimination is done by calculating the index of each pulse shape, which is determined by the similarity method, and then fusing it with its corresponding pulse height. Preliminary results demonstrate good separation of neutron and gamma-ray signals from a NE-213 scintillator with a simple digital system. The results were better than those with a conventional rise time method. Figure of Merit is used to determine the quality of discrimination. The figure of merit of the discrimination using digital signal processing combined with off-line similarity method are 1.9; 1.7; 1.1; 1.1; and 0.8; on the other hand by using conventional method the rise time are 0.9; 0.9; 0.9; 0.7; and 0.4 for the equivalent electron energy of 800; 278; 139; 69; and 30 keV. (author)

  18. Dynamic feedback circuits function as a switch for shaping a maturation-inducing steroid pulse in Drosophila

    DEFF Research Database (Denmark)

    Møller, Morten Erik; Danielsen, Erik Thomas; Herder, Rachel

    2013-01-01

    Steroid hormones trigger the onset of sexual maturation in animals by initiating genetic response programs that are determined by steroid pulse frequency, amplitude and duration. Although steroid pulses coordinate growth and timing of maturation during development, the mechanisms generating...... these pulses are not known. Here we show that the ecdysone steroid pulse that drives the juvenile-adult transition in Drosophila is determined by feedback circuits in the prothoracic gland (PG), the major steroid-producing tissue of insect larvae. These circuits coordinate the activation and repression...... of hormone synthesis, the two key parameters determining pulse shape (amplitude and duration). We show that ecdysone has a positive-feedback effect on the PG, rapidly amplifying its own synthesis to trigger pupariation as the onset of maturation. During the prepupal stage, a negative-feedback signal ensures...

  19. Serial Femtosecond Crystallography Opens New Avenues for Structural Biology

    Science.gov (United States)

    Coe, Jesse; Fromme, Petra

    2016-01-01

    Free electron lasers (FELs) provide X-ray pulses in the femtosecond time domain with up to 1012 higher photon flux than synchrotrons and open new avenues for the determination of difficult to crystallize proteins, like large complexes and human membrane proteins. While the X-ray pulses are so strong that they destroy any solid material, the crystals diffract before they are destroyed. The most successful application of FELs for biology has been the method of serial femtosecond crystallography (SFX) where nano or microcrystals are delivered to the FEL beam in a stream of their mother liquid at room temperature, which ensures the replenishment of the sample before the next X-ray pulse arrives. New injector technology allows also for the delivery of crystal in lipidic cubic phases or agarose, which reduces the sample amounts for an SFX data set by two orders of magnitude. Time-resolved SFX also allows for analysis of the dynamics of biomolecules, the proof of principle being recently shown for light-induced reactions in photosystem II and photoactive yellow protein. An SFX data sets consist of thousands of single crystal snapshots in random orientations, which can be analyzed now “on the fly” by data analysis programs specifically developed for SFX, but de-novo phasing is still a challenge, that might be overcome by two-color experiments or phasing by shape transforms. PMID:26786767

  20. Diode-pumped, single frequency Nd:YLF laser for 60-beam OMEGA laser pulse-shaping system

    International Nuclear Information System (INIS)

    Okishev, A.V.; Seka, W.

    1997-01-01

    The operational conditions of the OMEGA pulse-shaping system require an extremely reliable and low-maintenance master oscillator. The authors have developed a diode-pumped, single-frequency, pulsed Nd:YLF laser for this application. The laser generates Q-switched pulses of ∼160-ns duration and ∼10-microJ energy content at the 1,053-nm wavelength with low amplitude fluctuations (<0.6% rms) and low temporal jitter (<7 ns rms). Amplitude and frequency feedback stabilization systems have been used for high long-term amplitude and frequency stability