Sample records for er-doped ultrashort pulse

  1. All-polarization-maintaining Er-doped ultrashort-pulse fiber laser using carbon nanotube saturable absorber.

    Nishizawa, N; Seno, Y; Sumimura, K; Sakakibara, Y; Itoga, E; Kataura, H; Itoh, K


    We present an all-polarization-maintaining Er-doped ultrashort-pulse fiber laser using a single-wall carbon nanotube polyimide nanocomposite saturable absorber. The maximum average power for single-pulse operation is 4.8 mW, and the repetition frequency is 41.3 MHz. Self-start and stable mode-locking operation is achieved. The RF amplitude noise is also examined and it is confirmed that the noise figure is as low as that of a solid-state laser. Using a polarization-maintaining anomalous dispersive fiber, a 314 fs output pulse is compressed to 107 fs via higher-order soliton compression. The peak power of the compressed pulse is up to 1.1 kW.

  2. Ultrashort Laser Pulse Phenomena

    Diels, Jean-Claude


    Ultrashort Laser Pulse Phenomena, 2e serves as an introduction to the phenomena of ultra short laser pulses and describes how this technology can be used to examine problems in areas such as electromagnetism, optics, and quantum mechanics. Ultrashort Laser Pulse Phenomena combines theoretical backgrounds and experimental techniques and will serve as a manual on designing and constructing femtosecond (""faster than electronics"") systems or experiments from scratch. Beyond the simple optical system, the various sources of ultrashort pulses are presented, again with emphasis on the basic

  3. Ultrashort-pulse laser calligraphy

    Yang, Weijia; Kazansky, Peter G. [Optoelectronics Research Centre, University of Southampton, SO17 1BJ (United Kingdom); Shimotsuma, Yasuhiko; Sakakura, Masaaki; Miura, Kiyotaka; Hirao, Kazuyuki [Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan)


    Control of structural modifications inside silica glass by changing the front tilt of an ultrashort pulse is demonstrated, achieving a calligraphic style of laser writing. The phenomena of anisotropic bubble formation at the boundary of an irradiated region and modification transition from microscopic bubbles formation to self-assembled form birefringence are observed, and the physical mechanisms are discussed. The results provide the comprehensive evidence that the light beam with centrosymmetric intensity distribution can produce noncentrosymmetric material modifications.

  4. Ultrashort-pulse laser calligraphy

    Yang, Weijia; Kazansky, Peter G.; Shimotsuma, Yasuhiko; Sakakura, Masaaki; Miura, Kiyotaka; Hirao, Kazuyuki


    Control of structural modifications inside silica glass by changing the front tilt of an ultrashort pulse is demonstrated, achieving a calligraphic style of laser writing. The phenomena of anisotropic bubble formation at the boundary of an irradiated region and modification transition from microscopic bubbles formation to self-assembled form birefringence are observed, and the physical mechanisms are discussed. The results provide the comprehensive evidence that the light beam with centrosymmetric intensity distribution can produce noncentrosymmetric material modifications.

  5. Black phosphorus saturable absorber for ultrashort pulse generation

    Sotor, J., E-mail:; Sobon, G.; Abramski, K. M. [Laser and Fiber Electronics Group, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, Wroclaw 50-370 (Poland); Macherzynski, W.; Paletko, P. [Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, Wroclaw 50-372 (Poland)


    Low-dimensional materials, due to their unique and versatile properties, are very interesting for numerous applications in electronics and optoelectronics. Recently rediscovered black phosphorus, with a graphite-like layered structure, can be effectively exfoliated up to the single atomic layer called phosphorene. Contrary to graphene, it possesses a direct band gap controllable by the number of stacked atomic layers. For those reasons, black phosphorus is now intensively investigated and can complement or replace graphene in various photonics and electronics applications. Here, we demonstrate that black phosphorus can serve as a broadband saturable absorber and can be used for ultrashort optical pulse generation. The mechanically exfoliated ∼300 nm thick layers of black phosphorus were transferred onto the fiber core, and under pulsed excitation at 1560 nm wavelength, its transmission increases by 4.6%. We have demonstrated that the saturable absorption of black phosphorus is polarization sensitive. The fabricated device was used to mode-lock an Er-doped fiber laser. The generated optical solitons with the 10.2 nm bandwidth and 272 fs duration were centered at 1550 nm. The obtained results unambiguously show that black phosphorus can be effectively used for ultrashort pulse generation with performances similar or even better than currently used graphene or carbon nanotubes. This application of black phosphorus proves its great potential to future practical use in photonics.

  6. Pulse shape distortion in a 2-stage all-fiber Er-doped amplifier

    Michalska, M.; Mamajek, M.


    The issue of temporal pulse distortion occurring during amplification process in a 2-stage, fiber amplifier, operating in the eye-safe spectral region, is discussed. The amplifier was built in a Master Oscillator Power Amplifier (MOPA) configuration and seeded by a distributed feedback (DFB) laser providing nanosecond pulses at a repetition rate of 20 kHz. It operated at a wavelength of 1549.13 nm and generated over 200 mW of output power with a slope efficiency of up to 28%. The comparison between the calculated and measured results on saturation-induced pulse shape deformation, for ~300-ns pulses, is presented. The analyzed pulse shapes embraced rectangle, Gaussian, triangle and "M" letter.

  7. Up to 400 GHz burst-mode pulse generation from a hybrid harmonic mode-locked Er-doped fibre laser

    Wang, Sheng-Min; Lai, Yinchieh


    By inserting a birefringence filter with FSR  =  100 GHz inside a hybrid mode-locked Er-doped fibre laser, we successfully generate ps to sub-ps optical burst pulses with the intra-burst pulse rate up to 400 GHz. Multiplication of the intra-burst pulse rate is attributed to a new effect analogous to rational harmonic mode-locking, which occurs due to the relative alignment of the cavity harmonic frequencies, the external phase modulation induced frequencies, and the filter-selected frequencies.

  8. Ultrashort Laser Pulses in Biology and Medicine

    Braun, Markus; Zinth, Wolfgang


    Sources of ultrashort laser pulses are nowadays commercially available and have entered many areas of research and development. This book gives an overview of biological and medical applications of these laser pulses. The briefness of these laser pulses permits the tracing of the fastest processes in photo-active bio-systems, which is one focus of the book. The other focus is applications that rely on the high peak intensity of ultrashort laser pulses. Examples covered span non-linear imaging techniques, optical tomography, and laser surgery.

  9. Pulsed Laser Deposition of Er doped tellurite films on large area

    Bouazaoui, M [Laboratoire PhLAM, UMR 8523, Groupe Photonique, Universite des Sciences et Technologies de Lille, 59655 Villeneuve d' Ascq Cedex (France); Capoen, B [Laboratoire PhLAM, UMR 8523, Groupe Photonique, Universite des Sciences et Technologies de Lille, 59655 Villeneuve d' Ascq Cedex (France); Caricato, A P [L3 group, Dipartimento di Fisica, Lecce, Via Arnesano, 73100 Lecce (Italy); Chiasera, A [CNR-IFN, CSMFO group, via Sommarive 14, 38100 Povo-Trento (Italy); Fazzi, A [L3 group, Dipartimento di Fisica, Lecce, Via Arnesano, 73100 Lecce (Italy); Ferrari, M [CNR-IFN, CSMFO group, via Sommarive 14, 38100 Povo-Trento (Italy); Leggieri, G [L3 group, Dipartimento di Fisica, Lecce, Via Arnesano, 73100 Lecce (Italy); Martino, M [L3 group, Dipartimento di Fisica, Lecce, Via Arnesano, 73100 Lecce (Italy); Mattarelli, M [Physics Department, CSMFO group, via Sommarive 14, 38100 Povo-Trento (Italy); Montagna, M [Physics Department, CSMFO group, via Sommarive 14, 38100 Povo-Trento (Italy); Romano, F [L3 group, Dipartimento di Fisica, Lecce, Via Arnesano, 73100 Lecce (Italy); Tunno, T [L3 group, Dipartimento di Fisica, Lecce, Via Arnesano, 73100 Lecce (Italy); Turrel, S [Universite des Sciences et Technologies de Lille, Laboratoire de Spectrochimie Infrarouge et Raman, LASIR - UMR 8516 du CNRS - Bat C5 - 59655 - Villeneuve d' Ascq cedex (France); Vishnubhatla, K [Physics Department, CSMFO group, via Sommarive 14, 38100 Povo-Trento (Italy)


    Thin films of Er{sup 3+}-doped tungsten tellurite glass have been prepared by the pulsed laser deposition technique using an ArF excimer laser. The depositions were performed at different O{sub 2} pressure (5, 10 Pa) and at different substrate temperatures (RT, 100deg. C and 200deg. C). The composition and the optical properties of the deposited films, such as transmission, dispersion curves of refraction index and extinction coefficient, and film thickness were studied for the different deposition parameters. Transparent films at the highest substrate temperature were obtained only for a higher oxygen pressure with respect to the RT conditions.

  10. High energy, 1572.3 nm pulses for CO2 LIDAR from a polarization-maintaining, very-large-mode-area, Er-doped fiber amplifier.

    Nicholson, J W; DeSantolo, A; Yan, M F; Wisk, P; Mangan, B; Puc, G; Yu, A W; Stephen, M A


    We demonstrate the first polarization-maintaining, very-large-mode-area, Er-doped fiber amplifier with ~1100 μm2 effective area. The amplifier is core pumped by a Raman fiber laser and is used to generate single-frequency, one-microsecond, pulses with pulse energy of 541 μJ, peak power of 700 W, M2 of 1.1, and polarization extinction > 20 dB. The amplifier operates at 1572.3 nm, a wavelength useful for trace atmospheric CO2 detection.

  11. Intense ultrashort terahertz pulses: generation and applications

    Hoffmann, Matthias C [Max Planck Research Department for Structural Dynamics, University of Hamburg, CFEL, 22607 Hamburg (Germany); Fueloep, Jozsef Andras, E-mail:, E-mail: [Department of Experimental Physics, University of Pecs, Ifjusag u. 6, 7624 Pecs (Hungary)


    Ultrashort terahertz pulses derived from femtosecond table-top sources have become a valuable tool for time-resolved spectroscopy during the last two decades. Until recently, the pulse energies and field strengths of these pulses have been generally too low to allow for the use as pump pulses or the study of nonlinear effects in the terahertz range. In this review article we will describe methods of generation of intense single cycle terahertz pulses with emphasis on optical rectification using the tilted-pulse-front pumping technique. We will also discuss some applications of these intense pulses in the emerging field of nonlinear terahertz spectroscopy. (topical review)

  12. Ultrashort X-ray pulse science

    Chin, Alan Hap [Univ. of California, Berkeley, CA (US). Dept. of Physics; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)


    A variety of phenomena involves atomic motion on the femtosecond time-scale. These phenomena have been studied using ultrashort optical pulses, which indirectly probe atomic positions through changes in optical properties. Because x-rays can more directly probe atomic positions, ultrashort x-ray pulses are better suited for the study of ultrafast structural dynamics. One approach towards generating ultrashort x-ray pulses is by 90° Thomson scattering between terawatt laser pulses and relativistic electrons. Using this technique, the author generated ~ 300 fs, 30 keV (0.4 Å) x-ray pulses. These x-ray pulses are absolutely synchronized with ultrashort laser pulses, allowing femtosecond optical pump/x-ray probe experiments to be performed. Using the right-angle Thomson scattering x-ray source, the author performed time-resolved x-ray diffraction studies of laser-perturbated InSb. These experiments revealed a delayed onset of lattice expansion. This delay is due to the energy relaxation from a dense electron-hole plasma to the lattice. The dense electron-hole plasma first undergoes Auger recombination, which reduces the carrier concentration while maintaining energy content. Longitudinal-optic (LO) phonon emission then couples energy to the lattice. LO phonon decay into acoustic phonons, and acoustic phonon propagation then causes the growth of a thermally expanded layer. Source characterization is instrumental in utilizing ultrashort x-ray pulses in time-resolved x-ray spectroscopies. By measurement of the electron beam diameter at the generation point, the pulse duration of the Thomson scattered x-rays is determined. Analysis of the Thomson scattered x-ray beam properties also provides a novel means of electron bunch characterization. Although the pulse duration is inferred for the Thomson scattering x-ray source, direct measurement is required for other x-ray pulse sources. A method based on the laser-assisted photoelectric effect (LAPE) has been demonstrated as a

  13. Ultrashort X-ray pulse science

    Chin, Alan Hap [Univ. of California, Berkeley, CA (US). Dept. of Physics; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)


    A variety of phenomena involves atomic motion on the femtosecond time-scale. These phenomena have been studied using ultrashort optical pulses, which indirectly probe atomic positions through changes in optical properties. Because x-rays can more directly probe atomic positions, ultrashort x-ray pulses are better suited for the study of ultrafast structural dynamics. One approach towards generating ultrashort x-ray pulses is by 90{sup o} Thomson scattering between terawatt laser pulses and relativistic electrons. Using this technique, the author generated {approx} 300 fs, 30 keV (0.4 {angstrom}) x-ray pulses. These x-ray pulses are absolutely synchronized with ultrashort laser pulses, allowing femtosecond optical pump/x-ray probe experiments to be performed. Using the right-angle Thomson scattering x-ray source, the author performed time-resolved x-ray diffraction studies of laser-perturbated InSb. These experiments revealed a delayed onset of lattice expansion. This delay is due to the energy relaxation from a dense electron-hole plasma to the lattice. The dense electron-hole plasma first undergoes Auger recombination, which reduces the carrier concentration while maintaining energy content. Longitudinal-optic (LO) phonon emission then couples energy to the lattice. LO phonon decay into acoustic phonons, and acoustic phonon propagation then causes the growth of a thermally expanded layer. Source characterization is instrumental in utilizing ultrashort x-ray pulses in time-resolved x-ray spectroscopies. By measurement of the electron beam diameter at the generation point, the pulse duration of the Thomson scattered x-rays is determined. Analysis of the Thomson scattered x-ray beam properties also provides a novel means of electron bunch characterization. Although the pulse duration is inferred for the Thomson scattering x-ray source, direct measurement is required for other x-ray pulse sources. A method based on the laser-assisted photoelectric effect (LAPE) has

  14. Propagation of ultrashort pulsed beams in dispersive media

    刘志军; 吕百达


    Starting from the Rayleigh diffraction integral, the propagation equation of ultrashort pulsed beams in dispersive media is derived without making the paraxial approximation and slowly varying envelope approximation (SVEA). The spatiotemporal properties of ultrashort pulsed beams in dispersive media, such as spectrum redshifting, narrowing and pulse distortion are illustrated with pulsed Gaussian beams. It is stressed that the "antibeam" behaviour of ultrashort pulsed beams can be avoided, if a suitable truncation function is chosen.

  15. Neuromuscular disruption with ultrashort electrical pulses

    Pakhomov, Andrei; Kolb, Juergen F.; Joshi, Ravindra P.; Schoenbach, Karl H.; Dayton, Thomas; Comeaux, James; Ashmore, John; Beason, Charles


    Experimental studies on single cells have shown that application of pulsed voltages, with submicrosecond pulse duration and an electric field on the order of 10 kV/cm, causes sudden alterations in the intracellular free calcium concentration, followed by immobilization of the cell. In order to examine electrical stimulation and incapacitation with such ultrashort pulses, experiments on anesthetized rats have been performed. The effect of single, 450 nanosecond monopolar pulses have been compared with that of single pulses with multi-microsecond duration (TASER pulses). Two conditions were explored: 1. the ability to elicit a muscle twitch, and, 2. the ability to suppress voluntary movement by using nanosecond pulses. The second condition is relevant for neuromuscular incapacitation. The preliminary results indicate that for stimulation microsecond pulses are advantageous over nanosecond pulses, whereas for incapacitation, the opposite seems to apply. The stimulation effects seem to scale with electrical charge, whereas the disruption effects don't follow a simple scaling law. The increase in intensity (time of incapacitation) for a given pulse duration, is increasing with electrical energy, but is more efficient for nanosecond than for microsecond pulses. This indicates different cellular mechanisms for incapacitation, most likely subcellular processes, which have been shown to become increasingly important when the pulse duration is shortened into the nanosecond range. If further studies can confirm these initial results, consequences of reduced pulse duration are a reduction in weight and volume of the pulse delivery system, and likely, because of the lower required energy for neuromuscular incapacitation, reduced safety risks.

  16. Magnetization reversal in ultrashort magnetic field pulses

    Bauer, M; Fassbender, J; Hillebrands, B


    We report the switching properties of a thin magnetic film subject to an ultrashort, laterally localized magnetic field pulse, obtained by numerical investigations. The magnetization distribution in the film is calculated on a grid assuming Stoner-like coherent rotation within the grid square size. Perpendicularly and in-plane magnetized films exhibit a magnetization reversal due to a 4 ps magnetic field pulse. Outside the central region the pulse duration is short compared to the precession period. In this area the evolution of the magnetization during the field pulse does not depend strongly on magnetic damping and/or pulse shape. However, the final magnetization distribution is affected by the magnetic damping. Although the pulse duration is short compared to the precession period, the time needed for the relaxation of the magnetization to the equilibrium state is rather large. The influence of the different magnetic anisotropy contributions and the magnetic damping parameter enters into the magnetization ...

  17. Fabrication and photoluminescence of Er-doped ZnO thin films on SiO2/Si substrate by pulsed laser deposition

    GU Xiuquan; ZHU Liping; YE Zhizhen; HE Haiping; ZHAO Binghui


    Er doped ZnO thin films were grown on Si substrates using SiO2 buffer layer by pulsed laser deposition (PLD) method.The obtained films crystallize well and show high c-axis orientation.The Er content was evidently detected by the energy dispersive X-ray spectroscopy (EDS).Upon annealing in O2 ambience at different temperatures, the films show different photoluminescence properties at 1.54 μm.The samples annealed at 700 and 850 ℃ show intense photoluminescence peaks which enhance with the annealing temperature, while no obvious luminescence peaks are observed for the as-grown samples or annealed at 500 ℃.The possible mechanism was discussed.

  18. Molecular wakes for ultrashort laser pulses


    The molecular wake-assisted interaction between two collinear femotosecond laser pulses is investigated in air,which leads to the generation of a controllable 1.8 mJ super-continuum pulse with an elongated self-guided channel due to the cross-phase modulation of the impulsively aligned diatomic molecules in air. For two parallel launched femtosecond laser pulses with a certain spatial separation,controllable attraction and repulsion of the pulses are observed due to the counter-balance among molecular wakes,Kerr and plasma effects,where the molecular wakes show a longer interaction distance than the others to control the propagation of the intense ultrashort laser pulses.

  19. Nanoplasmonic generation of ultrashort EUV pulses

    Choi, Joonhee; Lee, Dong-Hyub; Han, Seunghwoi; Park, In-Yong; Kim, Seungchul; Kim, Seung-Woo


    Ultrashort extreme-ultraviolet (EUV) light pulses are an important tool for time-resolved pump-probe spectroscopy to investigate the ultrafast dynamics of electrons in atoms and molecules. Among several methods available to generate ultrashort EUV light pulses, the nonlinear frequency upconversion process of high-harmonic generation (HHG) draws attention as it is capable of producing coherent EUV pulses with precise control of burst timing with respect to the driving near-infrared (NIR) femtosecond laser. In this report, we present and discuss our recent experimental data obtained by the plasmon-driven HHG method that generate EUV radiation by means of plasmonic nano-focusing of NIR femtosecond pulses. For experiment, metallic waveguides having a tapered hole of funnel shape inside were fabricated by adopting the focused-ion-beam process on a micro-cantilever substrate. The plasmonic field formed within the funnelwaveguides being coupled with the incident femtosecond pulse permitted intensity enhancement by a factor of ~350, which creates a hot spot of sub-wavelength size with intensities strong enough for HHG. Experimental results showed that with injection of noble gases into the funnel-waveguides, EUV radiation is generated up to wavelengths of 32 nm and 29.6 nm from Ar and Ne gas atoms, respectively. Further, it was observed that lower-order EUV harmonics are cut off in the HHG spectra by the tiny exit aperture of the funnel-waveguide.

  20. Dynamics of a Dispersion-Managed Passively Mode-Locked Er-Doped Fiber Laser Using Single Wall Carbon Nanotubes

    Norihiko Nishizawa


    Full Text Available We investigated the dynamics of a dispersion-managed, passively mode-locked, ultrashort-pulse, Er-doped fiber laser using a single-wall carbon nanotube (SWNT device. A numerical model was constructed for analysis of the SWNT fiber laser. The initial process of passive mode-locking, the characteristics of the output pulse, and the dynamics inside the cavity were investigated numerically for soliton, dissipative-soliton, and stretched-pulse mode-locking conditions. The dependencies on the total dispersion and recovery time of the SWNTs were also examined. Numerical results showed similar behavior to experimental results.

  1. Ceramic dentures manufactured with ultrashort laser pulses

    Werelius, Kristian; Weigl, Paul


    Conventional manufacturing of individual ceramic dental prosthesis implies a handmade metallic framework, which is then veneered with ceramic layers. In order to manufacture all-ceramic dental prosthesis a CAD/CAM system is necessary due to the three dimensional shaping of high strength ceramics. Most CAD/CAM systems presently grind blocks of ceramic after the construction process in order to create the prosthesis. Using high-strength ceramics, such as Hot Isostatic Pressed (HIP)-zirconia, this is limited to copings. Anatomically shaped fixed dentures have a sculptured surface with small details, which can't be created by existing grinding tools. This procedure is also time consuming and subject to significant loss in mechanical strength and thus reduced survival rate once inserted. Ultra-short laser pulses offer a possibility in machining highly complex sculptured surfaces out of high-strength ceramic with negligible damage to the surface and bulk of the ceramic. In order to determine efficiency, quality and damage, several laser ablation parameters such as pulse duration, pulse energy and ablation strategies were studied. The maximum ablation rate was found using 400 fs at high pulse energies. High pulse energies such as 200μJ were used with low damage in mechanical strength compared to grinding. Due to the limitation of available laser systems in pulse repetition rates and power, the use of special ablation strategies provide a possibility to manufacture fully ceramic dental prosthesis efficiently.

  2. Ultra-short pulse laser proton acceleration

    Zeil, Karl; Kraft, Stephan; Bussmann, Michael; Cowan, Thomas; Kluge, Thomas; Metzkes, Josefine; Richter, Tom; Schramm, Ulrich [Forschungszentrum Dresden-Rossendorf, Dresden (Germany)


    We present a systematic investigation of ultra-short pulse laser acceleration of protons yielding unprecedented maximum proton energies of 17 MeV using the Ti:Sapphire lased high power laser of 100 TW Draco at the Research Centre Dresden-Rossendorf. For plain few micron thick foil targets a linear scaling of the maximum proton energy with laser power is observed and attributed to the short acceleration period close to the target rear surface. Although excellent laser pulse contrast was available slight deformations of the target rear were found to lead to a predictable shift of the direction of the energetic proton emission away from target normal towards the laser direction. The change of the emission characteristics are compared to analytical modelling and 2D PIC simulations.

  3. Generation And Measurement Of High Contrast Ultrashort Intense Laser Pulses

    Konoplev, O A


    In this thesis, the generation and measurement of high contrast, intense, ultrashort pulses have been studied. Various factors affecting the contrast and pulse shape of ultrashort light pulses from a chirped pulse amplification (CPA) laser system are identified. The level of contrast resulting from influence of these factors is estimated. Methods for improving and controlling the pulse shape and increasing the contrast are discussed. Ultrahigh contrast, 1-ps pulses were generated from a CPA system with no temporal structure up to eleven orders of magnitude. This is eight orders of magnitude higher contrast than the original pulse. This contrast boost was achieved using two techniques. One is the optical pulse cleaning based on the nonlinear birefringence of the chirping fiber and applied to the pulses before amplification. The other is the fast saturable absorber. The fast saturable absorber was placed after amplification and compression of the pulse. The measurements of high-contrast, ultrashort pulse with h...

  4. Laser system using ultra-short laser pulses

    Dantus, Marcos; Lozovoy, Vadim V.; Comstock, Matthew


    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.

  5. Interaction of ultrashort electromagnetic pulses with matter

    Astapenko, Valeriy


    The book is devoted to the theory describing the interaction of  ultra-short electromagnetic pulses (USP) with matter, including both classical and quantum cases. This theme is a hot topic in modern physics because of the great achievements in generating USP. Special attention is given to the peculiarities of UPS-matter interaction. One of the important items of this book is the derivation and applications of a new formula which describes the total photo-process probability under the action of USP in the framework of perturbation theory. Strong field-matter interaction is also considered with the use of the Bloch formalism in a two-level approximation for UPS with variable characteristics.  

  6. Dislocation structure produced by an ultrashort shock pulse

    Matsuda, Tomoki, E-mail:; Hirose, Akio [Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); Sano, Tomokazu [Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); JST, CREST, Suita, Osaka 565-0871 (Japan); Arakawa, Kazuto [JST, CREST, Suita, Osaka 565-0871 (Japan); Department of Material Science, Interdisciplinary Faculty of Science and Engineering, Shimane University, Matsue, Shimane 690-8504 (Japan)


    We found an ultrashort shock pulse driven by a femtosecond laser pulse on iron generates a different dislocation structure than the shock process which is on the nanosecond timescale. The ultrashort shock pulse produces a highly dense dislocation structure that varies by depth. According to transmission electron microscopy, dislocations away from the surface produce microbands via a network structure similar to a long shock process, but unlike a long shock process dislocations near the surface have limited intersections. Considering the dislocation motion during the shock process, the structure near the surface is attributed to the ultrashort shock duration. This approach using an ultrashort shock pulse will lead to understanding the whole process off shock deformation by clarifying the early stage.

  7. Measurement of ultrashort pulses with a non-instantaneous nonlinearity

    DeLong, K.W.; Ladera, C.L.; Trebino, R. [Sandia National Labs., Livermore, CA (United States); Kohler, B.; Wilson, K.R. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Chemistry


    We show how non-instantaneous nonlinearities can be used to characterize an ultrashort pulse in an extension of the Frequency-Resolved Optical Gating technique. We demonstrate this principle using the Raman effect in fused silica.

  8. Ultrashort pulse laser technology laser sources and applications

    Schrempel, Frank; Dausinger, Friedrich


    Ultrashort laser pulses with durations in the femtosecond range up to a few picoseconds provide a unique method for precise materials processing or medical applications. Paired with the recent developments in ultrashort pulse lasers, this technology is finding its way into various application fields. The book gives a comprehensive overview of the principles and applications of ultrashort pulse lasers, especially applied to medicine and production technology. Recent advances in laser technology are discussed in detail. This covers the development of reliable and cheap low power laser sources as well as high average power ultrashort pulse lasers for large scale manufacturing. The fundamentals of laser-matter-interaction as well as processing strategies and the required system technology are discussed for these laser sources with respect to precise materials processing. Finally, different applications within medicine, measurement technology or materials processing are highlighted.

  9. Ultrashort-pulse lasers based on the Sagnac interferometer

    Bezrodnyi, V.I.; Prokhorenko, V.I.; Tikhonov, E.A.; Shpak, M.T.; Iatskiv, D.IA.


    Results of experimental studies carried out on passively mode-locked and synchronously pumped ultrashort-pulse lasers with cavities based on the Sagnac interferometer are reported. It is shown that the use of the interferometer makes it possible to substantially improve the principal parameters of the ultrashort-pulse laser, such as repeatability, stability, spatial-angular characteristics, and the frequency tuning range. In particular, results are presented for YAG:Nd(3+) and dye lasers with Sagnac interferometers. 10 references.

  10. Effect of Orbital Angular Momentum on Nondiffracting Ultrashort Optical Pulses.

    Ornigotti, Marco; Conti, Claudio; Szameit, Alexander


    We introduce a new class of nondiffracting optical pulses possessing orbital angular momentum. By generalizing the X-wave solution of the Maxwell equation, we discover the coupling between angular momentum and the temporal degrees of freedom of ultrashort pulses. The spatial twist of propagation invariant light pulse turns out to be directly related to the number of optical cycles. Our results may trigger the development of novel multilevel classical and quantum transmission channels free of dispersion and diffraction. They may also find application in the manipulation of nanostructured objects by ultrashort pulses and for novel approaches to the spatiotemporal measurements in ultrafast photonics.

  11. Thin film surface processing by ultrashort laser pulses (USLP)

    Scorticati, D.; Skolski, J.Z.P.; Römer, Gerardus Richardus, Bernardus, Engelina; Huis in 't Veld, Bert; Workum, M.; Theelen, M.; Zeman, M.; Wehrspohn, R.; Gombert, A.


    In this work, we studied the feasibility of surface texturing of thin molybdenum layers on a borosilicate glass substrate with Ultra-Short Laser Pulses (USLP). Large areas of regular diffraction gratings were produced consisting of Laserinduced periodic surface structures (LIPSS). A short pulsed las

  12. Thin film surface processing by ultrashort laser pulses (USLP)

    Scorticati, D.; Skolski, J.Z.P.; Romer, G.R.B.E.; Huis in 't Veld, A.J.; Workum, M.J.; Theelen, M.J.; Zeman, M.


    In this work, we studied the feasibility of surface texturing of thin molybdenum layers on a borosilicate glass substrate with Ultra-Short Laser Pulses (USLP). Large areas of regular diffraction gratings were produced consisting of Laserinduced periodic surface structures (LIPSS). A short pulsed las

  13. Nanopore formation in neuroblastoma cells following ultrashort electric pulse exposure

    Roth, Caleb C.; Payne, Jason A.; Wilmink, Gerald J.; Ibey, Bennett L.


    Ultrashort or nanosecond electrical pulses (USEP) cause repairable damage to the plasma membranes of cells through formation of nanopores. These nanopores are able to pass small ions such as sodium, calcium, and potassium, but remain impermeable to larger molecules like trypan blue and propidium iodide. What remains uncertain is whether generation of nanopores by ultrashort electrical pulses can inhibit action potentials in excitable cells. In this paper, we explored the sensitivity of excitable cells to USEP using Calcium Green AM 1 ester fluorescence to measure calcium uptake indicative of nanopore formation in the plasma membrane. We determined the threshold for nanopore formation in neuroblastoma cells for three pulse parameters (amplitude, pulse width, and pulse number). Measurement of such thresholds will guide future studies to determine if USEP can inhibit action potentials without causing irreversible membrane damage.

  14. Theory and simulation of ultra-short pulse laser interactions

    More, R.; Walling, R.; Price, D.; Guethlein, G.; Stewart, R.; Libby, S.; Graziani, F.; Levatin, J. [Lawrence Livermore National Lab., Livermore, CA (United States)


    This paper describes recent Livermore work aimed at building computational tools to describe ultra-short pulse laser plasmas. We discuss calculations of laser absorption, atomic data for high-charge ions, and a new idea for linear-response treatment of non-equilibrium phenomena near LTE. (author)

  15. Melting of copper surface by ultrashort laser pulses

    Oboňa, J.V.; Ocelík, V.; Hosson, J.T.M. de; Skolski, J.Z.P.; Mitko, V.S.; Römer, G.R.B.E.; Huis in 't Veld, A.J.


    The main advantage of ultrashort laser pulses in manufacturing technology is their very high removal rate of material and high quality of microstructures with the smallest dimensions at 1 μm level. The accuracy is mainly due to an almost absence of thermal diffusion into bulk material. In this paper

  16. Surface melting of copper by ultrashort laser pulses

    Oboňa, J.V.; Ocelík, V.; De Hosson, J.T.M.; Skolski, J.Z.P.; Mitko, V.S.; Römer, G.R.B.E.; Huis in 't Veld, A.J.


    The main advantage of ultrashort laser pulses in manufacturing technology is their very high removal rate of material and high quality of microstructures with the smallest dimensions at 1 μm level. The accuracy is mainly due to an almost absence of thermal diffusion into bulk material. In this paper

  17. Surface melting of copper by ultrashort laser pulses

    Oboňa, J.V.; Ocelík, V.; De Hosson, J.T.M.; Skolski, J.Z.P.; Mitko, V.S.; Römer, G.R.B.E.; Huis in 't Veld, A.J.


    The main advantage of ultrashort laser pulses in manufacturing technology is their very high removal rate of material and high quality of microstructures with the smallest dimensions at 1 μm level. The accuracy is mainly due to an almost absence of thermal diffusion into bulk material. In this paper

  18. Ultrashort pulse laser microsurgery system with plasma luminescence feedback control

    Kim, B.M.; Feit, M.D.; Rubenchik, A.M.; Gold, D.M.; Darrow, C.B.; Da Silva, L.B.


    Plasma luminescence spectroscopy was used for precise ablation of bone tissue during ultrashort pulse laser (USPL) micro-spinal surgery. Strong contrast of the luminescence spectra between bone marrow and spinal cord provided the real time feedback control so that only bone tissue can be selectively ablated while preserving the spinal cord.

  19. Vectorial diffraction of extreme ultraviolet light and ultrashort light pulses

    Nugrowati, A.M.


    In this thesis, we present applications in optics involving the diffraction theory of light for two advanced technologies. We have used a rigorous vectorial diffraction method to model: (i) the imaging of mask structures in extreme ultraviolet lithography, and (ii) ultrashort pulse propagation thro

  20. Ultra-short pulsed laser engineered metal-glass nanocomposites

    Stalmashonak, Andrei; Abdolvand, Amin


    Glasses containing metallic nanoparticles exhibit very promising linear and nonlinear optical properties, mainly due to the surface plasmon resonances (SPRs) of the nanoparticles. The spectral position in the visible and near-infrared range and polarization dependence of the SPR are characteristically determined by the nanoparticles’ shapes. The focus of Ultra-Short Pulsed Laser Engineered Metal-Glass Nanocomposites is the interaction of intense ultra-short laser pulses with glass containing silver nanoparticles embedded in soda-lime glass, and nanostructural modifications in metal-glass nanocomposites induced by such laser pulses. In order to provide a comprehensive physical picture of the processes leading to laser-induced persistent shape transformation of the nanoparticles, series of experimental results investigating the dependences of laser assisted shape modifications of nanoparticles with laser pulse intensity, excitation wavelength, temperature are considered. In addition, the resulting local opti...

  1. Describing spatiotemporal couplings in ultrashort pulses using coupling coefficients

    Zeng Shu-Guang; Dan You-Quan; Zhang Bin; Sun Nian-Chun; Sui Zhan


    Three coupling coefficients are defined to describe spatiotemporal coupling in ultrashort pulses.With these coupling coefficients,the first-order spatiotemporal couplings of Gaussian pulse and beam are described analytically.Also,the first-order and the second-order spatiotemporal couplings caused by angular dispersion elements are studied using these coupling coefficients.It can be shown that these coupling coefficients are dimensionless and normalized,and readily indicate the severity of spatiotemporal coupling.

  2. Numerical simulation of copper ablation by ultrashort laser pulses

    Ding, PengJi; Li, YuHong


    Using a modified self-consistent one-dimensional hydrodynamic lagrangian fluid code, laser ablation of solid copper by ultrashort laser pulses in vacuum was simulated to study fundamental mechanisms and to provide a guide for drilling periodic microholes or microgratings on the metal surface. The simulated laser ablation threshold is a approximate constancy in femtosecond regime and increases as the square root of pulse duration in picosecond regime. The ablation depth as a function of pulse duration shows four different regimes and a minimum for a pulse duration of ~ 12ps for various laser fluences. The influence of laser-induced plasma shielding on ablation depth is also studied.

  3. Measuring ultrashort pulses using frequency-resolved optical gating

    Trebino, R. [Sandia National Laboratories, Livermore, CA (United States)


    The purpose of this program is the development of techniques for the measurement of ultrafast events important in gas-phase combustion chemistry. Specifically, goals of this program include the development of fundamental concepts and spectroscopic techniques that will augment the information currently available with ultrafast laser techniques. Of equal importance is the development of technology for ultrafast spectroscopy. For example, methods for the production and measurement of ultrashort pulses at wavelengths important for these studies is an important goal. Because the specific vibrational motion excited in a molecule depends sensitively on the intensity, I(t), and the phase, {psi}(t), of the ultrashort pulse used to excite the motion, it is critical to measure both of these quantities for an individual pulse. Unfortunately, this has remained an unsolved problem for many years. Fortunately, this year, the authors present a technique that achieves this goal.

  4. Ultrashort Optical Pulse Propagation in terms of Analytic Signal

    Sh. Amiranashvili


    Full Text Available We demonstrate that ultrashort optical pulses propagating in a nonlinear dispersive medium are naturally described through incorporation of analytic signal for the electric field. To this end a second-order nonlinear wave equation is first simplified using a unidirectional approximation. Then the analytic signal is introduced, and all nonresonant nonlinear terms are eliminated. The derived propagation equation accounts for arbitrary dispersion, resonant four-wave mixing processes, weak absorption, and arbitrary pulse duration. The model applies to the complex electric field and is independent of the slowly varying envelope approximation. Still the derived propagation equation posses universal structure of the generalized nonlinear Schrödinger equation (NSE. In particular, it can be solved numerically with only small changes of the standard split-step solver or more complicated spectral algorithms for NSE. We present exemplary numerical solutions describing supercontinuum generation with an ultrashort optical pulse.

  5. Cavity Optical Pulse Extraction: ultra-short pulse generation as seeded Hawking radiation.

    Eilenberger, Falk; Kabakova, Irina V; de Sterke, C Martijn; Eggleton, Benjamin J; Pertsch, Thomas


    We show that light trapped in an optical cavity can be extracted from that cavity in an ultrashort burst by means of a trigger pulse. We find a simple analytic description of this process and show that while the extracted pulse inherits its pulse length from that of the trigger pulse, its wavelength can be completely different. Cavity Optical Pulse Extraction is thus well suited for the development of ultrashort laser sources in new wavelength ranges. We discuss similarities between this process and the generation of Hawking radiation at the optical analogue of an event horizon with extremely high Hawking temperature. Our analytic predictions are confirmed by thorough numerical simulations.

  6. Coherent ultrashort pulse generation from incoherent light by pulse trapping in birefringent fibers.

    Shiraki, Eiji; Nishizawa, Norihiko


    We investigated the nonlinear fiber phenomena of pulse trapping and amplification between incoherent light and an ultrashort soliton pulse in birefringent fibers both experimentally and numerically. Using the phenomena in a 1.4 km-long low-birefringence fiber, a coherent, nearly transform-limited, sech2-shaped, ultrashort pulse was generated from incoherent light from a super-luminescent diode. The average pulse energy and pulse width were 121 pJ and 640 fs, respectively. The estimated gain of this system was as large as 62 dB.

  7. Filamentation of ultrashort laser pulses of different wavelengths in argon



    We investigate the filaments formed by the ultrashort laser pulses with different wavelengths of 400 nm, 586 nm and 800 nm propagating in argon. Numerical results show that, when the input power or the ratio of the input power to the critical power is given, the pulse with 400 nm wavelength has the largest on-axis intensity, as well as the narrowest filament and the most stable beam radius. These results indicate that the pulse with shorter wavelength is more suitable for the long-range propagation in argon.

  8. Regularization of an autoconvolution problem in ultrashort laser pulse characterization

    Gerth, Daniel; Birkholz, Simon; Koke, Sebastian; Steinmeyer, Günter


    An ill-posed inverse problem of autoconvolution type is investigated. This inverse problem occurs in nonlinear optics in the context of ultrashort laser pulse characterization. The novelty of the mathematical model consists in a physically required extension of the deautoconvolution problem beyond the classical case usually discussed in literature: (i) For measurements of ultrashort laser pulses with the self-diffraction SPIDER method, a stable approximate solution of an autocovolution equation with a complex-valued kernel function is needed. (ii) The considered scenario requires complex functions both, in the solution and the rhs of the integral equation. Since, however, noisy data are available not only for amplitude and phase functions of the rhs, but also for the amplitude of the solution, the stable approximate reconstruction of the associated smooth phase function represents the main goal of the paper. An iterative regularization approach is described that is specifically adapted to the physical situati...

  9. Optical feedback signal for ultrashort laser pulse ablation of tissue

    Kim, B.-M.; Feit, M.D.; Rubenchik, A.M.; Mammini, B.M.; Da Silva, L.B.


    An optical feedback system for controlled precise tissue ablation is discussed. Our setup includes an ultrashort pulse laser (USPL), and a diagnostic system using analysis of either tissue fluorescence or plasma emission luminescence. Current research is focused on discriminating hard and soft tissues such as bone and spinal cord during surgery using either technique. Our experimental observations exhibit considerable spectroscopic contrast between hard and soft tissue, and both techniques offer promise for a practical diagnostic system.

  10. Modeling the early ionization of dielectrics by ultrashort laser pulses

    Bourgeade, Antoine; Mézel, Candice; Saut, Olivier


    International audience; In this paper, we present a model for propagation of intense and ultrashort laser pulses ionizing dielectrics. We consider early ion- ization so that this process is sufficiently weak to avoid requiring a complete description of the ionization process (e.g. the use of ki- netic equations which are very expensive from a computational point of view). As the intensity of the field is small, one photon ioniza- tion is neglected. Ionization may only occur through multi-phot...

  11. Generalized projection retrieval of dispersion scans for ultrashort pulse characterization

    Miranda, Miguel; Guo, Chen; Harth, Anne; Louisy, Maite; Neoricic, Lana; L'Huillier, Anne; Arnold, Cord L


    We present a retrieval algorithm based on generalized projections for ultrashort pulse characterization using dispersion scan (d-scan). The new algorithm is tested on several simulated cases and in two different experimental cases in the few-cycle regime. The proposed algorithm is much faster and leads to a drastic reduction of retrieval times, but performs less robust in the retrieval of noisy d-scan traces compared to the standard algorithm.

  12. Generator of ultrashort megavolt voltage pulses

    Zheltov, K A; Shalimanov, V F


    Paper describes approx 3 ns duration and > 1 MW amplitude voltage pulse generator under high-ohmic (approx 450 Ohm) load. Generator comprises pulse transformer with magnetized core, as well as, resonance tuned circuit of high-voltage solenoid and accumulating spaces of a shaping line containing, moreover, spark gap to switch charge in transmitting line. Paper contains the results of voltage measuring in generator basic units

  13. Ultrashort Pulse (USP) Laser-Matter Interactions


    unlimited 2D electron wavepacket quantum simulation Source: Luis Plaja, U Salamanca 31 Direct Frequency Comb Spectroscopy in the Extreme...intensity short pulse laser interacting with structured targets yields an enhancement in the number and energy of hot electron. • Monte Carlo

  14. Modulated coupled nanowires for ultrashort pulses

    Solntsev, Alexander S


    We predict analytically and confirm with numerical simulations that inter-mode dispersion in nanowire waveguide arrays can be tailored through periodic waveguide bending, facilitating flexible spatio-temporal reshaping without break-up of femtosecond pulses. This approach allows simulta- neous and independent control of temporal dispersion and spatial diffraction that are often strongly connected in nanophotonic structures.

  15. Using ultra-short pulses to determine particle size and density distributions

    Lee, Christopher James; van der Slot, Petrus J.M.; Boller, Klaus J.


    We analyze the time dependent response of strongly scattering media (SSM) to ultra-short pulses of light. A random walk technique is used to model the optical scattering of ultra-short pulses of light propagating through media with random shapes and various packing densities. The pulse spreading was




    Harmonic emission was studied from a plasma produced by ultrashort laser pulses. Unlike the harmonics from plasmas created by long (ns) laser pulses, the 3/2 harmonic emission was not observed in the interaction between plasmas and ultrashort laser pulses. A simple model is proposed to explain this phenomenon.

  17. Optical soliton communication using ultra-short pulses

    Sadegh Amiri, Iraj


    This brief analyzes the characteristics of a microring resonator (MRR) to perform communication using ultra-short soliton pulses. The raising of nonlinear refractive indices, coupling coefficients and radius of the single microring resonator leads to decrease in input power and round trips wherein the bifurcation occurs. As a result, bifurcation or chaos behaviors are seen at lower input power of 44 W, where the nonlinear refractive index is n2=3.2×10−20 m2/W. Using a decimal convertor system, these ultra-short signals can be converted into quantum information. Results show that multi solitons with FWHM and FSR of 10 pm and 600 pm can be generated respectively. The multi optical soliton with FWHM and FSR of 325 pm and 880 nm can be incorporated with a time division multiple access (TDMA) system wherein the transportation of quantum information is performed.

  18. High power parallel ultrashort pulse laser processing

    Gillner, Arnold; Gretzki, Patrick; Büsing, Lasse


    The class of ultra-short-pulse (USP) laser sources are used, whenever high precession and high quality material processing is demanded. These laser sources deliver pulse duration in the range of ps to fs and are characterized with high peak intensities leading to a direct vaporization of the material with a minimum thermal damage. With the availability of industrial laser source with an average power of up to 1000W, the main challenge consist of the effective energy distribution and disposition. Using lasers with high repetition rates in the MHz region can cause thermal issues like overheating, melt production and low ablation quality. In this paper, we will discuss different approaches for multibeam processing for utilization of high pulse energies. The combination of diffractive optics and conventional galvometer scanner can be used for high throughput laser ablation, but are limited in the optical qualities. We will show which applications can benefit from this hybrid optic and which improvements in productivity are expected. In addition, the optical limitations of the system will be compiled, in order to evaluate the suitability of this approach for any given application.

  19. Extending ultra-short pulse laser texturing over large area

    Mincuzzi, G., E-mail:; Gemini, L.; Faucon, M.; Kling, R.


    Highlights: • We carried out metal surface texturing (Ripples, micro grooves, Spikes) using a high power, high repetition rate, industrial, Ultra-short pulses laser. • Extremely Fast processing is shown (Laser Scan speed as high as 90 m/s) with a polygon scanner head. • Stainless steel surface blackening with Ultra-short pulses laser has been obtained with unprecedented scanspeed. • Full SEM surface characterization was carried out for all the different structures obtained. • Reflectance measurements were carried out to characterize surface reflectance. - Abstract: Surface texturing by Ultra-Short Pulses Laser (UPL) for industrial applications passes through the use of both fast beam scanning systems and high repetition rate, high average power P, UPL. Nevertheless unwanted thermal effects are expected when P exceeds some tens of W. An interesting strategy for a reliable heat management would consists in texturing with a low fluence values (slightly higher than the ablation threshold) and utilising a Polygon Scanner Heads delivering laser pulses with unrepeated speed. Here we show for the first time that with relatively low fluence it is possible over stainless steel, to obtain surface texturing by utilising a 2 MHz femtosecond laser jointly with a polygonal scanner head in a relatively low fluence regime (0.11 J cm{sup −2}). Different surface textures (Ripples, micro grooves and spikes) can be obtained varying the scan speed from 90 m s{sup −1} to 25 m s{sup −1}. In particular, spikes formation process has been shown and optimised at 25 m s{sup −1} and a full morphology characterization by SEM has been carried out. Reflectance measurements with integrating sphere are presented to compare reference surface with high scan rate textures. In the best case we show a black surface with reflectance value < 5%.

  20. Generation of high harmonics and attosecond pulses with ultrashort laser pulse filaments and conical waves

    A Couairon; A Lotti; D Faccio; P Di Trapani; D S Steingrube; E Schulz; T Binhammer; U Morgner; M Kovacev; M B Gaarde


    Results illustrating the nonlinear dynamics of ultrashort laser pulse filamentation in gases are presented, with particular emphasis on the filament properties useful for developing attosecond light sources. Two aspects of ultrashort pulse filaments are specifically discussed: (i) numerical simulation results on pulse self-compression by filamentation in a gas cell filled with noble gas. Measurements of high harmonics generated by the pulse extracted from the filament allows for the detection of intensity spikes and subcycle pulses generated within the filament. (ii) Simulation results on the spontaneous formation of conical wavepackets during filamentation in gases, which in turn can be used as efficient driving pulses for the generation of high harmonics and isolated attosecond pulses.

  1. Investigation of Early Plasma Evolution Induced by Ultrashort Laser Pulses

    Hu, Wenqian; Shin, Yung C.; King, Galen B.


    Early plasma is generated owing to high intensity laser irradiation of target and the subsequent target material ionization. Its dynamics plays a significant role in laser-material interaction, especially in the air environment1-11. Early plasma evolution has been captured through pump-probe shadowgraphy1-3 and interferometry1,4-7. However, the studied time frames and applied laser parameter ranges are limited. For example, direct examinations of plasma front locations and electron number densities within a delay time of 100 picosecond (ps) with respect to the laser pulse peak are still very few, especially for the ultrashort pulse of a duration around 100 femtosecond (fs) and a low power density around 1014 W/cm2. Early plasma generated under these conditions has only been captured recently with high temporal and spatial resolutions12. The detailed setup strategy and procedures of this high precision measurement will be illustrated in this paper. The rationale of the measurement is optical pump-probe shadowgraphy: one ultrashort laser pulse is split to a pump pulse and a probe pulse, while the delay time between them can be adjusted by changing their beam path lengths. The pump pulse ablates the target and generates the early plasma, and the probe pulse propagates through the plasma region and detects the non-uniformity of electron number density. In addition, animations are generated using the calculated results from the simulation model of Ref. 12 to illustrate the plasma formation and evolution with a very high resolution (0.04 ~ 1 ps). Both the experimental method and the simulation method can be applied to a broad range of time frames and laser parameters. These methods can be used to examine the early plasma generated not only from metals, but also from semiconductors and insulators. PMID:22806170

  2. Selective laser melting of copper using ultrashort laser pulses

    Kaden, Lisa; Matthäus, Gabor; Ullsperger, Tobias; Engelhardt, Hannes; Rettenmayr, Markus; Tünnermann, Andreas; Nolte, Stefan


    Within the field of laser-assisted additive manufacturing, the application of ultrashort pulse lasers for selective laser melting came into focus recently. In contrast to conventional lasers, these systems provide extremely high peak power at ultrashort interaction times and offer the potential to control the thermal impact at the vicinity of the processed region by tailoring the pulse repetition rate. Consequently, materials with extremely high melting points such as tungsten or special composites such as AlSi40 can be processed. In this paper, we present the selective laser melting of copper using 500 fs laser pulses at MHz repetition rates emitted at a center wavelength of about 1030 nm. To identify an appropriate processing window, a detailed parameter study was performed. We demonstrate the fabrication of bulk copper parts as well as the realization of thin-wall structures featuring thicknesses below 100 {μ }m. With respect to the extraordinary high thermal conductivity of copper which in general prevents the additive manufacturing of elements with micrometer resolution, this work demonstrates the potential for sophisticated copper products that can be applied in a wide field of applications extending from microelectronics functionality to complex cooling structures.

  3. Plasma lenses for ultrashort multi-petawatt laser pulses

    Palastro, J P; Hafizi, B; Johnson, L A; Penano, J; Hubbard, R F; Helle, M; Kaganovich, D


    An ideal plasma lens can provide the focusing power of a small f-number, solid-state focusing optic at a fraction of the diameter. An ideal plasma lens, however, relies on a steady-state, linear laser pulse-plasma interaction. Ultrashort multi-petawatt (MPW) pulses possess broad bandwidths and extreme intensities, and, as a result, their interaction with the plasma lens is neither steady state nor linear. Here we examine nonlinear and time-dependent modifications to plasma lens focusing, and show that these result in chromatic and phase aberrations and amplitude distortion. We find that a plasma lens can provide enhanced focusing for 30 fs pulses with peak power up to ~1 PW. The performance degrades through the MPW regime, until finally a focusing penalty is incurred at ~10 PW.

  4. Ultrashort Laser Pulse Heating of Nanoparticles: Comparison of Theoretical Approaches

    Renat R. Letfullin


    Full Text Available The interaction between nanoparticles and ultrashort laser pulses holds great interest in laser nanomedicine, introducing such possibilities as selective cell targeting to create highly localized cell damage. Two models are studied to describe the laser pulse interaction with nanoparticles in the femtosecond, picosecond, and nanosecond regimes. The first is a two-temperature model using two coupled diffusion equations: one describing the heat conduction of electrons, and the other that of the lattice. The second model is a one-temperature model utilizing a heat diffusion equation for the phonon subsystem and applying a uniform heating approximation throughout the particle volume. A comparison of the two modeling strategies shows that the two-temperature model gives a good approximation for the femtosecond mode, but fails to accurately describe the laser heating for longer pulses. On the contrary, the simpler one-temperature model provides an adequate description of the laser heating of nanoparticles in the femtosecond, picosecond, and nanosecond modes.

  5. The envelope Hamiltonian for electron interaction with ultrashort pulses

    Toyota, Koudai; Rost, Jan M


    For ultrashort VUV pulses with a pulse length comparable to the orbital time of the bound electrons they couple to we propose a simplified envelope Hamiltonian. It is based on the Kramers-Henneberger representation in connection with a Floquet expansion of the strong-field dynamics but keeps the time dependence of the pulse envelope explicit. Thereby, the envelope Hamiltonian captures the essence of the physics, -- light-induced shifts of bound states, single-photon absorption, and non-adiabatic electronic transitions. It delivers quantitatively accurate ionization dynamics and allows for physical insight into the processes occurring. Its minimal requirements for construction in terms of laser parameters make it ideally suited for a large class of atomic and molecular problems.

  6. Generation of powerful ultrashort electromagnetic pulses based on superradiance

    Ginzburg, N S; Novozhilova, Y V; Sergeev, A S; Phelps, A D R; Cross, A W; Wiggins, S M; Ronald, K; Shpak, V G; Yalandin, M I; Shunailov, S A; Ulmaskulov, M R


    Experimental results of the observation of superradiation from intense, subnanosecond electron bunches moving through a periodic waveguide and interacting with a backward propagating TM sub 0 sub 1 wave are presented. The ultra-short microwave pulses in Ka, W, and G band were generated with repetition frequencies of up to 25 Hz. Observation of RF breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, leads to an estimate of the peak power as high as 60-120 MW for the 300-400 ps pulses at 38 GHz. The initial observation of 75 GHz 10-15 MW radiation pulses with duration less than 150 ps, and of 150 GHz microwave spikes with a risetime of 75ps are also reported. Comparison with simulations is discussed as well.

  7. Experimental energy-density flux characterization of ultrashort laser pulse filaments.

    Faccio, Daniele; Lotti, Antonio; Matijosius, Aidas; Bragheri, Francesca; Degiorgio, Vittorio; Couairon, Arnaud; Di Trapani, Paolo


    Visualization of the energy density flux gives a unique insight into the propagation properties of complex ultrashort pulses. This analysis, formerly relegated to numerical investigations, is here shown to be an invaluable experimental diagnostic tool. By retrieving the spatio-temporal amplitude and phase we experimentally obtain the energy density flux within complex ultrashort pulses generated by filamentation in a nonlinear Kerr medium.

  8. Laser-Material Interaction of Powerful Ultrashort Laser Pulses

    Komashko, A


    Laser-material interaction of powerful (up to a terawatt) ultrashort (several picoseconds or shorter) laser pulses and laser-induced effects were investigated theoretically in this dissertation. Since the ultrashort laser pulse (USLP) duration time is much smaller than the characteristic time of the hydrodynamic expansion and thermal diffusion, the interaction occurs at a solid-like material density with most of the light energy absorbed in a thin surface layer. Powerful USLP creates hot, high-pressure plasma, which is quickly ejected without significant energy diffusion into the bulk of the material, Thus collateral damage is reduced. These and other features make USLPs attractive for a variety of applications. The purpose of this dissertation was development of the physical models and numerical tools for improvement of our understanding of the process and as an aid in optimization of the USLP applications. The study is concentrated on two types of materials - simple metals (materials like aluminum or copper) and wide-bandgap dielectrics (fused silica, water). First, key physical phenomena of the ultrashort light interaction with metals and the models needed to describe it are presented. Then, employing one-dimensional plasma hydrodynamics code enhanced with models for laser energy deposition and material properties at low and moderate temperatures, light absorption was self-consistently simulated as a function of laser wavelength, pulse energy and length, angle of incidence and polarization. Next, material response on time scales much longer than the pulse duration was studied using the hydrocode and analytical models. These studies include examination of evolution of the pressure pulses, effects of the shock waves, material ablation and removal and three-dimensional dynamics of the ablation plume. Investigation of the interaction with wide-bandgap dielectrics was stimulated by the experimental studies of the USLP surface ablation of water (water is a model of

  9. Measurement of Ultra-Short Solitary Electromagnetic Pulses

    Eva Gescheidtova


    Full Text Available In connection with the events of the last few years and with the increased number of terrorist activities, the problem of identification and measurement of electromagnetic weapons or other systems impact occurred. Among these are also microwave sources, which can reach extensive peak power of up to Pmax = 100 MW. Solitary, in some cases several times repeated, impulses lasting from tp E <1, 60>ns, cause the destruction of semiconductor junctions. These days we can find scarcely no human activity, where semiconductor structures are not used. The problem of security support of the air traffic, transportation, computer nets, banks, national strategic data canter’s, and other applications crops up. Several types of system protection from the ultra-short electromagnetic pulses present itself, passive and active protection. The analysis of the possible measuring methods, convenient for the identification and measurement of the ultra-short solitary electromagnetic pulses in presented in this paper; some of the methods were chosen and used for practical measurement. This work is part of Research object MSM262200022 "Research of microelectronic systems".

  10. Measurement of Ultra-Short Single-Photon Pulse Duration with Two-Photon Interference

    LV Fan; SUN Fang-Wen; ZOU Chang-Ling; HAN Zheng-Fu; GUO Guang-Can


    We proposed a protocol of measuring the duration of ultra-short single-photon pulse with two-photon interference.The pulse duration can be obtained from the width of the visibility of two-photon Hong-Ou-Mandel interference or the indistinguishability of the two photons. Moreover, the shape of a single-photon pulse can be measured with ultra-short single-photon pulses through the two-photon interference.%@@ We proposed a protocol of measuring the duration of ultra-short single-photon pulse with two-photon interference.The pulse duration can be obtained from the width of the visibility of two-photon Hong-Ou-Mandel interference or the indistinguishability of the two photons.Moreover, the shape of a single-photon pulse can be measured with ultra-short single-photon pulses through the two-photon interference.

  11. Production of color centers in PMMA by ultrashort laser pulses

    Elgul Samad, Ricardo, E-mail: [Instituto de Pesquisas Energeticas e Nucleares, IPEN-CNEN/SP, Av. Prof. Lineu Prestes 2242, Cidade universitaria 05508-000, Sao Paulo, SP (Brazil); Coronato Courrol, Lilia [Departamento de Ciencias Exatas e da Terra, UNIFESP, Diadema, SP (Brazil); Benevolo Lugao, Ademar; Zanardi Freitas, Anderson de; Dias Vieira, Nilson [Instituto de Pesquisas Energeticas e Nucleares, IPEN-CNEN/SP, Av. Prof. Lineu Prestes 2242, Cidade universitaria 05508-000, Sao Paulo, SP (Brazil)


    We report here the creation of color centers in commercial, transparent PMMA samples by ultrashort pulses from a Ti:Sapphire laser emitting at 800 nm, with spatial control. Although the 800 nm photon energy is not sufficient to ionize the polymer, the centers are created following a multiphotonic absorption that causes the ionization. We propose that the free electrons quivering motion on the pulse electric field displaces atoms from its equilibrium positions, creating free radicals and double bonds that coalesce into color centers. The absorption and emission spectra of the centers were measured, but a dose-like curve could not be built due to the presence of damages created along with the centers that scatter the excitation and emission lights due to the commercial sample's poor optical quality.

  12. High extinction amplitude modulation in ultrashort pulse shaping

    Lin, Yen-Wei


    We explored the issues related to the resolution and the modulation extinction when filtering the spectrum of a UV femtosecond laser with a standard ultrashort pulse shaper. We have learned that a higher pulse shaping resolution often requires a larger working beam size or a higher density grating for greater dispersion. However, these approaches also introduce more optical errors and degrade the extinction. In this work, we examined specifics of each component to determine the best configuration of our spectral filtering setup. As a proof-of-concept demonstration, we utilized elements available as standard products and achieved 100 GHz filtering resolution with high extinction at the UV-A wavelength, which is superb in this wavelength range. The high extinction spectral filtering is especially important while modifying a broadband laser for the optical control of molecule's internal state.

  13. Droplet deformation and fragmentation by ultra-short laser pulses

    Krivokorytov, M S; Sidelnikov, Yu V; Krivtsun, V M; Medvedev, V V; Kompanets, V O; Lash, A A; Koshelev, K N


    We report on the experimental studies of the deformation and fragmentation of liquid metal droplets by picosecond and subpicosecond laser pulses. The experiments were performed with laser irradiance varying in 10E13-10E15 W/cm^2 range. The observed evolution of the droplet shape upon the impact dramatically differs from the previously reported for nanosecond laser pulses. Instead of flattening the droplet undergoes rapid asymmetric expansion and transforms into a complex shape which can be interpreted as two conjunct spheroid shells and finally fragments. We explain the described hydrodynamic response to the ultra-short impact as a result of the propagation of the laser-induced convergent shockwave through the volume of droplet.

  14. Nonlinear scattering in hard tissue studied with ultrashort laser pulses

    Eichler, J. [Technische Fachhochschule Berlin, Univ. of Applied Sciences (Germany); Kim, B.M. [Yonsei Univ., Wonjoo, Kangwon-Do (Korea)


    The back-scattered spectrum of ultrashort laser pulses (800 nm, 0.2 ps) was studied in human dental and other hard tissues in vitro below the ablation threshold. Frequency doubled radiation (SHG), frequency tripled radiation and two-photon fluorescence were detected. The relative yield for these processes was measured for various pulse energies. The dependence of the SHG signal on probe thickness was determined in forward and back scattering geometry. SHG is sensitive to linear polarization of the incident laser radiation. SHG in human teeth was studied in vitro showing larger signals in dentin than in cementum and enamel. In carious areas no SHG signal could be detected. Possible applications of higher harmonic radiation for diagnostics and microscopy are discussed. (orig.)

  15. Ionization of molecular hydrogen in ultrashort intense laser pulses

    Vanne, Yulian V.


    A novel ab initio numerical approach is developed and applied that solves the time-dependent Schroedinger equation describing two-electron diatomic molecules (e.g. molecular hydrogen) exposed to an intense ultrashort laser pulse. The method is based on the fixed-nuclei and the non-relativistic dipole approximations and aims to accurately describe both correlated electrons in full dimensionality. The method is applicable for a wide range of the laser pulse parameters and is able to describe both few-photon and many-photon single ionization processes, also in a non-perturbative regime. A key advantage of the method is its ability to treat the strong-field response of the molecules with arbitrary orientation of the molecular axis with respect to the linear-polarized laser field. Thus, this work reports on the first successful orientation-dependent analysis of the multiphoton ionization of H{sub 2} performed by means of a full-dimensional numerical treatment. Besides the investigation of few-photon regime, an extensive numerical study of the ionization by ultrashort frequency-doubled Ti:sapphire laser pulses (400 nm) is presented. Performing a series of calculations for different internuclear separations, the total ionization yields of H{sub 2} and D{sub 2} in their ground vibrational states are obtained for both parallel and perpendicular orientations. A series of calculations for 800 nm laser pulses are used to test a popular simple interference model. Besides the discussion of the ab initio numerical method, this work considers different aspects related to the application of the strong-field approximation (SFA) for investigation of a strong-field response of an atomic and molecular system. Thus, a deep analysis of the gauge problem of SFA is performed and the quasistatic limit of the velocity-gauge SFA ionization rates is derived. The applications of the length-gauge SFA are examined and a recently proposed generalized Keldysh theory is criticized. (orig.)

  16. Plasma mediated ablation of biological tissues with ultrashort laser pulses

    Oraevsky, A.A. [Lawrence Livermore National Lab., CA (United States)]|[Rice Univ., Houston, TX (United States). Dept. of Electrical Engineering; DaSilva, L.B.; Feit, M.D. [Lawrence Livermore National Lab., CA (United States)] [and others


    Plasma mediated ablation of collagen gels and porcine cornea was studied at various laser pulse durations in the range from 350 fs to 1 ns at 1,053 nm wavelength. A time resolved stress detection technique was employed to measure transient stress profiles and amplitudes. Optical microscopy was used to characterize ablation craters qualitatively, while a wide band acoustic transducer helped to quantify tissue mechanical response and the ablation threshold. The ablation threshold was measured as a function of laser pulse duration and linear absorption coefficient. For nanosecond pulses the ablation threshold was found to have a strong dependence on the linear absorption coefficient of the material. As the pulse length decreased into the subpicosecond regime the ablation threshold became insensitive to the linear absorption coefficient. The ablation efficiency was found to be insensitive to both the laser pulse duration and the linear absorption coefficient. High quality ablation craters with no thermal or mechanical damage to surrounding material were obtained with 350 fs laser pulses. The mechanism of optical breakdown at the tissue surface was theoretically investigated. In the nanosecond regime, optical breakdown proceeds as an electron collisional avalanche ionization initiated by thermal seed electrons. These seed electrons are created by heating of the tissue by linear absorption. In the ultrashort pulse range, optical breakdown is initiated by the multiphoton ionization of the irradiated medium (6 photons in case of tissue irradiated at 1,053 nm wavelength), and becomes less sensitive to the linear absorption coefficient. The energy deposition profile is insensitive to both the laser pulse duration and the linear absorption coefficient.

  17. Hamiltonian structure of propagation equations for ultrashort optical pulses

    Amiranashvili, Sh.; Demircan, A.


    A Hamiltonian framework is developed for a sequence of ultrashort optical pulses propagating in a nonlinear dispersive medium. To this end a second-order nonlinear wave equation for the electric field is transformed into a first-order propagation equation for a suitably defined complex electric field. The Hamiltonian formulation is then introduced in terms of normal variables, i.e., classical complex fields referring to the quantum creation and annihilation operators. The derived z-propagated Hamiltonian accounts for forward and backward waves, arbitrary medium dispersion, and four-wave mixing processes. As a simple application we obtain integrals of motion for the pulse propagation. The integrals reflect time-averaged fluxes of energy, momentum, and photons transferred by the pulse. Furthermore, pulses in the form of stationary nonlinear waves are considered. They yield extremal values of the momentum flux for a given energy flux. Simplified propagation equations are obtained by reduction of the Hamiltonian. In particular, the complex electric field reduces to an analytic signal for the unidirectional propagation. Solutions of the full bidirectional model are numerically compared to the predictions of the simplified equation for the analytic signal and to the so-called forward Maxwell equation. The numerics is effectively tested by examining the conservation laws.

  18. Ultrashort-pulse laser excitation and damage of dielectric materials

    Haahr-Lillevang, Lasse; Balling, Peter


    Ultrashort-pulse laser excitation of dielectrics is an intricate problem due to the strong coupling between the rapidly changing material properties and the light. In the present paper, details of a model based on a multiple-rate-equation description of the conduction band are provided. The model...... is verified by comparison with recent experimental measurements of the transient optical properties in combination with ablation-depth determinations. The excitation process from the first creation of conduction-band electrons at low intensities to the formation of a highly-excited plasma and associated...... material fragmentation is explained by the model. For quartz samples, the optical properties are strongly influenced by self-trapped excitons, and the associated additions to the model are described....

  19. Analytical study of ultra-short pulse reflectometry

    Bruskin, L.G. [Japan Atomic Energy Research Institute, Naka Fusion Research Establishment, Mukoyama, Nakamachi, Naka-gun, Ibaraki-ken (Japan)]. E-mail:; Mase, A.; Yamamoto, A.; Kogi, Y. [Kyushu University, Advanced Science and Technology Center for Cooperative Research, Fukuoka-ken, Kasuga (Japan)


    The results of an analytical treatment of the time-dependent 2D full-wave equation are presented here for the case of ultra-short pulse (USP) reflectometry. We consider several models of the plasma geometry, namely linear and nonlinear slab models, as well as a 2D plasma density profile with cylindrical symmetry. The latter model is more realistic when compared to the 1D stratified plasma models previously employed in all the analytical, and most numerical, treatments, since the plasma in fusion toroidal devices, mirror machines and plasma processing chambers can often be considered axially symmetric on the scale relevant to microwave reflectometry. Based on the results of analytical modelling, a signal record analysis method of profile reconstruction is proposed. The method has the advantage of using raw signal records instead of poorly localized frequency modes, which makes it robust for the profile measurements using USP reflectometry. (author)

  20. Precision resection of intestine using ultrashort laser pulses

    Beck, Rainer J.; Gora, Wojciech S.; Jayne, David; Hand, Duncan P.; Shephard, Jonathan D.


    Endoscopic resection of early colorectal neoplasms typically employs electrocautery tools, which lack precision and run the risk of full thickness thermal injury to the bowel wall with subsequent perforation. We present a means of endoluminal colonic ablation using picosecond laser pulses as a potential alternative to mitigate these limitations. High intensity ultrashort laser pulses enable nonlinear absorption processes, plasma generation, and as a consequence a predominantly non-thermal ablation regimen. Robust process parameters for the laser resection are demonstrated using fresh ex vivo pig intestine samples. Square cavities with comparable thickness to early colorectal neoplasms are removed for a wavelength of 1030 nm and 515 nm using a picosecond laser system. The corresponding histology sections exhibit in both cases only minimal collateral damage to the surrounding tissue. The ablation depth can be controlled precisely by means of the pulse energy. Overall, the application of ultrafast lasers for the resection of intestine enables significantly improved precision and reduced thermal damage to the surrounding tissue compared to conventional electrocautery.

  1. Spectrum-Induced Changes in Non-Paraxial Property of Ultrashort Pulsed Beam

    陆大全; 胡巍; 杨振军; 郑一周


    A spatiotemporal non-paraxial correction to the paraxial solution of ultrashort pulsed beam is obtained by using the Fourier transform and the Taylor expansion. By studying the propagation of an isodiffracting pulsed Gaussian beam with different pulse shapes, we find that there are spectrum-induced changes in the non-paraxial propagation of the pulsed beam. We analyse the influence of pulse spectrum on the non-paraxial property of the ultrashort pulsed beam and explain it base on the paraxial approximation condition.

  2. Effect of noise on Frequency-Resolved Optical Gating measurements of ultrashort pulses

    Fittinghoff, D.N.; DeLong, K.W.; Ladera, C.L.; Trebino, R.


    We study the effects of noise in Frequency-Resolved Optical Gating measurements of ultrashort pulses. We quantify the measurement accuracy in the presence of additive, muliplicative, and quantization noise, and discuss filtering and pre-processing of the data.

  3. Ultra-Short Pulse Tracking by Using Wavelength Dispersion for a Short-Time Optical Buffer

    Tsuyoshi; Konishi; Hideaki; Furukawa; Kousuke; Asano; Kazuyoshi; Itoh


    To synchronize a control signal with a packet signal in response to changing timing jitter, we investigate ultra-short pulse tracking by using wavelength dispersion for a short-time optical buffer in an optical router.

  4. Sharp photonic Crystal Defect Modes and Their Response to Ultrashort Optical Pulses

    Kyozo; Kanamoto; Sheng; Lan; Naoki; Ikeda; Yoshimasa; Sugimoto; Kiyoshi; Asakawa; Hiroshi; Ishikawa


    Single photonic crystal defects based on an air-bridge structure were fabricated. We obtained sharp defect modes with quality factors higher than 600 and observed their response to ultrashort optical pulses by utilizing two-photon absorption.

  5. Double Clad Er-doped Fiber Amplifier

    FU Yong-jun; MAO Xiang-qiao; WEI Huai; LI jian


    Presented is a theoretical study of double-clad Er-doped fiber power amplifier(EDFA). Two kinds of double clad fibers(DCF) with rectangular and "flower" inner clad shapes are studied, and these fibers have different coupling constants and propagation losses. We calculate the effective pump power absorption ratio along the fiber with different coupling constants from the first cladding to the doped core and with different propagation losses for the power in the inner cladding. Then the gains of the double clad Er-doped fiber amplifiers versus fiber lengths are calculated using the EDFA model based on propagation and rate equations of a homogeneous, two-level medium.

  6. Analysis of ultra-short pulse shaping with programmable amplitude and phase masks

    Shanhong You; Weidong Shao; Wenfeng Cai; Honglong Cao; M. Kavehrad


    @@ Specified ultra-short pulse waveforms could be synthesized with high-resolution zero-dispersion pulse shaping system.The system and parameters are analyzed and discussed.The pulse shaping system with optimized parameters could resolve the frequency components of ultra-broad bandwidth pulse and prevent the spatial shaping of individual frequency components.The specified waveforms, Meyer wavelet and square root raised cosine pulses, are generated with programmable amplitude and phase masks.%Specified ultra-short pulse waveforms could be synthesized with high-resolution zero-dispersion pulse shaping system. The system and parameters are analyzed and discussed. The pulse shaping system with optimized parameters could resolve the frequency components of ultra-broad bandwidth pulse and prevent the spatial shaping of individual frequency components. The specified waveforms, Meyer wavelet and square root raised cosine pulses, are generated with programmable amplitude and phase masks.

  7. Investigation of ultrashort-pulsed laser on dental hard tissue

    Uchizono, Takeyuki; Awazu, Kunio; Igarashi, Akihiro; Kato, Junji; Hirai, Yoshito


    Ultrashort-pulsed laser (USPL) can ablate various materials with precious less thermal effect. In laser dentistry, to solve the problem that were the generation of crack and carbonized layer by irradiating with conventional laser such as Er:YAG and CO II laser, USPL has been studied to ablate dental hard tissues by several researchers. We investigated the effectiveness of ablation on dental hard tissues by USPL. In this study, Ti:sapphire laser as USPL was used. The laser parameter had the pulse duration of 130 fsec, 800nm wavelength, 1KHz of repetition rate and the average power density of 90~360W/cm2. Bovine root dentin plates and crown enamel plates were irradiated with USPL at 1mm/sec using moving stage. The irradiated samples were analyzed by SEM, EDX, FTIR and roughness meter. In all irradiated samples, the cavity margin and wall were sharp and steep, extremely. In irradiated dentin samples, the surface showed the opened dentin tubules and no smear layer. The Ca/P ratio by EDX measurement and the optical spectrum by FTIR measurement had no change on comparison irradiated samples and non-irradiated samples. These results confirmed that USPL could ablate dental hard tissue, precisely and non-thermally. In addition, the ablation depths of samples were 10μm, 20μm, and 60μm at 90 W/cm2, 180 W/cm2, and 360 W/cm2, approximately. Therefore, ablation depth by USPL depends on the average power density. USPL has the possibility that can control the precision and non-thermal ablation with depth direction by adjusting the irradiated average power density.

  8. Ultra-short pulsed ytterbium-doped fiber laser and amplifier

    Guanglei Ding; Xin Zhao; Yishan Wang; Wei Zhao; Guofu Chen


    @@ This paper investigates a high power all fiber ultrashort pulse laser system. This system consists of a modelocking laser oscillator, a multi-stage amplifier, a pulse selector, and a paired grating pulse compressor.With pulse energy of 12 μJ at repetition rate of 30 kHz, the laser at center wavelength of 1.05 μm was obtained. Pulse width of 525 fs was achieved after the grating pair compressor.

  9. Selective Alignment of D2 Induced by Two Ultrashort Laser Pulses

    Zeng-qiang Yang; Zhi-rong Guo; Gui-xian Ge


    The dynamics of molecular rotational wave packets of D2 induced by ultrashort laser pulses was investigated numerically by solving the time-dependent Schrodinger equation. Results show that an ultrashort pulse can manipulate a coherent rotational wave packet of D2 se-lectively. In the calculation, a first laser pulse was used to create a coherent rotational wave packet from an initial thermal ensemble of D2 at the temperature of 300 K. The second laser pulse was used to manipulate the rotational wave packet selectively around the first quarter and the three quarters revival. The alignment parameter and its Fourier transform amplitude both illustrate that the relative populations of even and odd rotational states in the final rotational wave packet of D2 can be manipulated by precisely selecting the time delay between the first and the second ultrashort pulse.

  10. Optical and electrical properties of SnO2 thin films after ultra-short pulsed laser annealing

    Scorticati, D.; Illiberi, A.; Römer, G.R.B.E.; Bor, T.C.; Ogieglo, W.; Klein Gunnewiek, M.; Lenferink, A.; Otto, C.; Skolski, J.Z.P.; Grob, F.; Lange, de D.F.; Huis in 't Veld, A.J.; Reutzel, Edward W.


    Ultra-short pulsed laser sources, with pulse durations in the ps and fs regime, are commonly exploited for cold ablation. However, operating ultra-short pulsed laser sources at fluence levels well below the ablation threshold allows for fast and selective thermal processing. The latter is especially

  11. Optical and electrical properties of SnO2 thin films after ultra-short pulsed laser annealing

    Scorticati, D.; Illiberi, A.; Römer, G.R.B.E.; Bor, T.; Ogieglo, W.; Klein Gunnewiek, M.; Lenferink, A.; Otto, C.; Skolski, J.Z.P.; Grob, F.; de Lange, D.F.; Huis in 't Veld, A.J.; Reutzel, Edward W.


    Ultra-short pulsed laser sources, with pulse durations in the ps and fs regime, are commonly exploited for cold ablation. However, operating ultra-short pulsed laser sources at fluence levels well below the ablation threshold allows for fast and selective thermal processing. The latter is especially

  12. Novel oral applications of ultra-short laser pulses

    Wieger, V.; Wernisch, J.; Wintner, E.


    In the past decades, many efforts have been made to replace mechanical tools in oral applications by various laser systems. The reasons therefore are manifold: i) Friction causes high temperatures damaging adjacent tissue. ii) Smear layers and rough surfaces are produced. iii) Size and shape of traditional tools are often unsuitable for geometrically complicated incisions and for minimum invasive treatment. iv) Mechanical damage of the remaining tissue occurs. v) Online diagnosis for feedback is not available. Different laser systems in the µs and sub-&mrgs-pulse regime, among them Erbium lasers, have been tested in the hope to overcome the mentioned drawbacks and, to some extent, they represent the current state of the art with respect to commercial and hence practical application. In the present work the applicability of scanned ultrashort pulse lasers (USPLs) for biological hard tissue as well as dental restoration material removal was tested. It is shown that cavities with features superior to mechanically treated or Erbium laser ablated cavities can be generated if appropriate scan algorithms and optimum laser parameters are matched. Smooth cavity rims, no microcracks, melting or carbonisation and precise geometry are the advantages of scanned USLP ablation. For bone treatment better healing conditions are expected as the natural structure remains unaffected by the preparation procedure. The novelty of this work is represented by a comprehensive compilation of various experimental results intended to assess the performance of USPLs. In this context, various pulse durations in the picosecond and femtosecond regime were applied to dental and bone tissue as well as dental restoration materials which is considered to be indispensable for a complete assessment. Parameters like ablation rates describing the efficiency of the ablation process, and ablation thresholds were determined - some of them for the first time - and compared to the corresponding Erbium

  13. Collapse of ultrashort spatiotemporal pulses described by the cubic generalized Kadomtsev-Petviashvili equation

    Leblond, Hervé; Mihalache, Dumitru; 10.1103/PHYSREVA.81.033824


    By using a reductive perturbation method, we derive from Maxwell-Bloch equations a cubic generalized Kadomtsev-Petviashvili equation for ultrashort spatiotemporal optical pulse propagation in cubic (Kerr-like) media without the use of the slowly varying envelope approximation. We calculate the collapse threshold for the propagation of few-cycle spatiotemporal pulses described by the generic cubic generalized Kadomtsev-Petviashvili equation by a direct numerical method and compare it to analytic results based on a rigorous virial theorem. Besides, typical evolution of the spectrum (integrated over the transverse spatial coordinate) is given and a strongly asymmetric spectral broadening of ultrashort spatiotemporal pulses during collapse is evidenced.

  14. Canonical and Singular Propagation of Ultrashort Pulses in a Nonlinear Medium

    Karl Glasner; Miroslav Kolesik; Moloney, Jerome V.; Newell, Alan C.


    We examine the two types of singular behaviors of ultrashort pulses in a nonlinear medium, pulse steepening if the weak longitudinal dispersion is normal and collapse if it is anomalous. Connections with analogous behaviors of wave packets of almost monochromatic waves in strongly dispersive media are discussed.

  15. Time evolution of the diffraction pattern of an ultrashort laser pulse.

    Lefrancois, M; Pereira, S


    An analytical expression for the time evolution of the diffraction pattern of an ultrashort laser pulse passing through a circular aperture is obtained in the Fresnel regime. The diffraction is not constant in time as the pulse travels through the aperture. This may have implications in experiments involving fast dynamics. Examples of the evolution of the diffraction pattern are given.

  16. Thin film surface processing by UltraShort Laser Pulses (USLP)

    Scorticati, D.; Skolski, J.Z.P.; Römer, G.R.B.E.; Huis in 't Veld, A.J.; Workum, M.; Theelen, M.J.; Zeman, M.


    In this work, we studied the feasibility of surface texturing of thin molybdenum layers on a borosilicate glass substrate with Ultra-Short Laser Pulses (USLP). Large areas of regular diffraction gratings were produced consisting of Laserinduced periodic surface structures (LIPSS). A short pulsed las

  17. Dual wavelength laser damage mechanisms in the ultra-short pulse regime

    Gyamfi, Mark; Costella, Marion; Willemsen, Thomas; Jürgens, Peter; Mende, Mathias; Jensen, Lars; Ristau, Detlev


    New ultrashort pulse laser systems exhibit an ever increasing performance which includes shorter pulses and higher pulse energies. Optical components used in these systems are facing increasing requirements regarding their durability, and therefore understanding of the damage mechanism is crucial. In the ultra-short pulse regime electron ionization processes control the damage mechanisms. For the single wavelength, single pulse regime the Keldysh [1] and the Drude model [2] allow a quantitative description of these ionization processes. However, in this model, the electrical field is restricted to a single wavelength, and therefore it cannot be applied in the case of irradiation with two pulses at different wavelengths. As frequency conversion is becoming more common in ultra-short pulse applications, further research is needed in this field to predict the damage resistance of optical components. We investigate the damage behavior of high reflective mirrors made of different metal oxide materials under simultaneous exposure to ultra-short pulses at the wavelengths 387.5 nm and 775 nm, respectively.

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

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


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

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

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


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

  20. Ablation enhancement of silicon by ultrashort double-pulse laser ablation

    Zhao, Xin; Shin, Yung C. [Center for Laser-Based Manufacturing, School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)


    In this study, the ultrashort double-pulse ablation of silicon is investigated. An atomistic simulation model is developed to analyze the underlying physics. It is revealed that the double-pulse ablation could significantly increase the ablation rate of silicon, compared with the single pulse ablation with the same total pulse energy, which is totally different from the case of metals. In the long pulse delay range (over 1 ps), the enhancement is caused by the metallic transition of melted silicon with the corresponding absorption efficiency. At ultrashort pulse delay (below 1 ps), the enhancement is due to the electron excitation by the first pulse. The enhancement only occurs at low and moderate laser fluence. The ablation is suppressed at high fluence due to the strong plasma shielding effect.

  1. (3+1)-dimensional nonlinear propagation equation for ultrashort pulsed beam in left-handed material

    Hu Yong-Hua; Fu Xi-Quan; Wen Shuang-Chun; Su Wen-Hua; Fan Dian-Yuan


    In this paper a comprehensive framework for treating the nonlinear propagation of ultrashort pulse in metamaterial with dispersive dielectric susceptibility and magnetic permeability is presented. Under the slowly-evolving-wave approximation, a generalized (3+1)-dimensional wave equation first order in the propagation coordinate and suitable for both right-handed material (RHM) and left-handed material (LHM) is derived. By the commonly used Drude dispersive model for LHM, a (3+1)-dimensional nonlinear Schr(o)dinger equation describing ultrashort pulsed beam propagation in LHM is obtained, and its difference from that for conventional RHM is discussed. Particularly, the self-steeping effect of ultrashort pulse is found to be anomalous in LHM.

  2. All-optical histology using two photon laser scanning microscopy and ablation with ultrashort pulses

    Tsai, Philbert S.

    This dissertation discusses the use of ultrashort laser pulses to image and manipulate tissue for the purpose of three-dimensional histological reconstruction of extended brain structures. Two photon laser scanning microscopy (TPLSM) and ultrashort pulsed laser ablation are used to provide in situ three-dimensional imaging through thick preparations of fixed tissue. Surface regions of fixed tissue are first imaged using TPLSM. The imaged regions are then removed by ablation with amplified, ultrashort laser pulses, thereby exposing a previously underlying tissue region for imaging. This process of imaging and ablation proceeds iteratively until the desired tissue volume has been processed. First, the principles, design, and construction of a two photon laser scanning microscope are discussed, followed by a discussion of the physical mechanisms of tissue ablation with ultrashort laser pulses. The compatibility of tissue ablation using ultrashort pulses with subsequent histological analysis, particularly with fluorescent microscopy, is evaluated. Tissue ablation with ultrashort laser pulses is found to produce ablated tissue surfaces that are smooth to within a micrometer. Intrinsic fluorescence as well as immunoreactivity are found to be resilient to the ablation process. The all-optical histological technique is demonstrated on brain tissue from rats and mice, including tissue from embryonic mouse as early at E15. The ablation process is shown to preserve both macroscopic and microscopic structures within tissue. To facilitate the all-optical histological analysis of neuronal vasculature and its relative distribution to surrounding neuronal tissue, a fluorescent gel perfusion technique is developed that provides a temperature-stabilized fluorescent label of the neuronal vasculature. The use of immunohistochemistry to label specific cell populations throughout an 800 micrometer-thick tissue section is demonstrated. Additionally, the immersion of fixed tissue in high

  3. Measurement of ultrashort-pulse cross-polarization scattering in a tandem mirror

    Kogi, Yuichiro; Mase, Atsushi [Advanced Science and Technology Center for Cooperative Research, Kyushu University, Kasuga, Fukuoka (Japan); Hojo, Hitoshi; Itakura, Akiyoshi; Ichimura, Makoto; Yatsu, Kiyoshi [Plasma Research Center, Tsukuba Univ., Tsukuba, Ibaraki (Japan)


    Cross-polarization scattering (CPS) diagnostics using ultrashort pulse microwaves is applied to the GAMMA 10 tandem mirror for the measurement of internal magnetic fluctuations. The CPS process uses the mode conversion effect of electromagnetic waves by means of magnetic fluctuations in a plasma. The mode contamination of antennas and multiple reflections from the vacuum vessel make the CPS measurement difficult since they easily mask the CPS signal. By using polarizers and performing time-of-flight measurement on the ultrashort pulse, the spurious electromagnetic waves are eliminated and the identification of the CPS process is successful. (author)

  4. Parallel simulation for the ultra-short laser pulses' propagation in air

    Ma, Cunliang


    A parallel 2D+1 split-step Fourier method with Crank-Nicholson scheme running on multi-core shared memory architectures is developed to study the propagation of ultra-short high-intensity laser pulses in air. The parallel method achieves a near linear speed-up with results for the efficiency of more than 95% on a 24-core machine. This method is of great potential application in studying the long-distance propagation of the ultra-short high intensity laser pulses.

  5. High-Quality Ultrashort Pulse Generation Utilizing a Self-Phase Modulation-Based Reshaper


    An ultrashort 10-GHz pulse generation scheme was successfully demonstrated using a bulk material InGaAsP electroabsorption modulator to generate the seed pulse. A self-phase modulation-based reshaper was used after the adiabatic soliton compression in a comb-like dispersion profiled fiber. Experiments and simulations confirm that the reshaper effectively removes the pulse pedestal and improves the pulse extinction ratio. As a result, the 10-GHz pulse had no pedestal, a high extinction ratio, and a pulse width of only 1.4 ps.

  6. Directional release of the stored ultrashort light pulses from a tunable Bragg-grating microcavity.

    Fu, Shenhe; Deng, Zhigui; Li, Zhen; Zhu, Siqi; Zhang, Peixiong; Yin, Hao; Li, Yongyao; Chen, Zhenqiang


    We demonstrate numerically the ability for directionally releasing the stored ultrashort light pulse from a microcavity by means of two-pulse nonlinear interaction in a cascading Bragg grating structure. The setting is built by a chirped grating segment which is linked through a uniform segment, including a tunable microcavity located at the junction between the two components. Our simulations show that stable trapping of an ultrashort light pulse can be achieved in the setting. The stored light pulse in a microcavity can be possibly released, by nonlinearly interacting with the lateral incident control pulse. Importantly, by breaking the symmetry of potential cavity, the stably trapped light pulse can be successfully released from the microcavity to the expected direction. Owing to the induced optical nonlinearity, the released ultrashort light pulses could preserve their shapes, propagating in a form of Bragg grating solitons through the uniform component, which is in contrast to the extensively studied light pulse trappings in photonic crystal cavities which operate at the linear regime.

  7. Influence of spatiotemporal coupling on the capture-and-acceleration-scenario vacuum electron acceleration by ultrashort pulsed laser beam

    Lu Da-Quan; Qian Lie-Jia; Li Yong-Zhong; Fan Dian-Yuan


    This paper investigates the properties of the ultrashort pulsed beam aimed to the capture-and-acceleration-scenario(CAS) vacuum electron acceleration. The result shows that the spatiotemporal distribution of the phase velocity, the longitudinal component of the electric field and the acceleration quality factor are qualitatively similar to that of the continuous-wave Gaussian beam, and are slightly influenced by the spatiotemporal coupling of the ultrashort pulsed beam. When the pulse is compressed to an ultrashort one in which the pulse duration TFWHM < 5T0, the variation of the maximum net energy gain due to the carrier-envelope phase is a crucial disadvantage in the CAS acceleration process.

  8. Characterization of phase and contrast of high peak power, ultrashort laser pulses

    Sagisaka, Akito; Aoyama, Makoto; Matsuoka, Sinichi; Akahane, Yutaka; Nakano, Fumihiko; Yamakawa, Koichi [Advanced Photon Research Center, Kansai Research Establishment, Japan Atomic Energy Research Inst., Kizu, Kyoto (Japan)


    We fully characterize a high-peak power, ultrashort laser pulse in a Ti:sapphire chirped-pulse amplification laser system. The phase and contrast of the 20 fs pulse are determined by using frequency-resolved optical gating and high dynamic range cross-correlation techniques. The result of the phase measurement of the pulse indicate that the predominant phase distortion is quartic. The measured contrast of the pulse is of the order of 10{sup -6} limited by amplified spontaneous emission coming from the amplifiers. (author)

  9. Annealing of SnO2 thin films by ultra-short laser pulses

    Scorticati, D.; Illiberi, A.; Bor, Teunis Cornelis; Eijt, S.W.H.; Schut, H.; Römer, Gerardus Richardus, Bernardus, Engelina; de Lange, D.F.; Huis in 't Veld, Bert


    Post-deposition annealing by ultra-short laser pulses can modify the optical properties of SnO2 thin films by means of thermal processing. Industrial grade SnO2 films exhibited improved optical properties after picosecond laser irradiation, at the expense of a slightly increased sheet resistance

  10. Ultrashort pulsed laser treatment inactivates viruses by inhibiting viral replication and transcription in the host nucleus.

    Tsen, Shaw-Wei D; Chapa, Travis; Beatty, Wandy; Xu, Baogang; Tsen, Kong-Thon; Achilefu, Samuel


    Ultrashort pulsed laser irradiation is a new method for virus reduction in pharmaceuticals and blood products. Current evidence suggests that ultrashort pulsed laser irradiation inactivates viruses through an impulsive stimulated Raman scattering process, resulting in aggregation of viral capsid proteins. However, the specific functional defect(s) in viruses inactivated in this manner have not been demonstrated. This information is critical for the optimization and the extension of this treatment platform to other applications. Toward this goal, we investigated whether viral internalization, replication, or gene expression in cells were altered by ultrashort pulsed laser irradiation. Murine Cytomegalovirus (MCMV), an enveloped DNA virus, was used as a model virus. Using electron and fluorescence microscopy, we found that laser-treated MCMV virions successfully internalized in cells, as evidenced by the detection of intracellular virions, which was confirmed by the detection of intracellular viral DNA via PCR. Although the viral DNA itself remained polymerase-amplifiable after laser treatment, no viral replication or gene expression was observed in cells infected with laser-treated virus. These results, along with evidence from previous studies, support a model whereby the laser treatment stabilizes the capsid, which inhibits capsid uncoating within cells. By targeting the mechanical properties of viral capsids, ultrashort pulsed laser treatment represents a unique potential strategy to overcome viral mutational escape, with implications for combatting emerging or drug-resistant pathogens.

  11. Thermal processing of thin films using ultra-short laser pulses: applied to photovoltaic materials

    Scorticati, D.


    In this thesis a novel approach to raise the thermal selectivity of superficial heat treatments, exploiting ultra-short laser pulses, is proposed and studied. That is, the effective applicability of ultrafast lasers for selective heat treatments is proven by increasing the performance of different

  12. Plasma-enhanced Chemical Vapor Deposition of Aluminum Oxide Using Ultrashort Precursor Injection Pulses

    Dingemans, G.; M. C. M. van de Sanden,; Kessels, W. M. M.


    An alternative plasma-enhanced chemical vapor deposition (PECVD) method is developed and applied for the deposition of high-quality aluminum oxide (AlOx) films. The PECVD method combines a continuous plasma with ultrashort precursor injection pulses. We demonstrate that the modulation of the precurs

  13. On the surface topography of ultrashort laser pulse treated steel surfaces

    Obona, J. Vincenc; Ocelik, V.; Skolski, J. Z. P.; Mitko, V. S.; Romer, G. R. B. E.; in't Veld, A. J. Huis; De Hosson, J. Th M.; Römer, G.R.B.E.; Huis in’t Veld, A.J.


    This paper concentrates on observations of the surface topography by scanning electron microscopy (SEM) on alloyed and stainless steels samples treated by ultrashort laser pulses with duration of 210 fs and 6.7 ps. Globular-like and jet-like objects were found depending on the various levels of the

  14. Experimental studies of axial magnetic fields generated in ultrashort-pulse laser-plasma interaction

    李玉同; 张杰; 陈黎明; 赵理曾; 夏江帆; 魏志义; 江文勉


    The quasistatic axial magnetic fields in plasmas produced by ultrashort laser pulses were measured by measuring the Faraday rotation angle of the backscattered emission. The spatial distribution of the axial magnetic field was obtained with a peak value as high as 170 Tesla. Theory suggests that the axial magnetic field is generated by dynamo effect in laser-plasma interaction.

  15. Annealing of SnO2 thin films by ultra-short laser pulses

    Scorticati, D.; Illiberi, A.; Bor, T.; Eijt, S.W.H.; Schut, H.; Römer, G.R.B.E.; Lange, D.F. de; Huis In't Veld, A.J.


    Post-deposition annealing by ultra-short laser pulses can modify the optical properties of SnO2 thin films by means of thermal processing. Industrial grade SnO2 films exhibited improved optical properties after picosecond laser irradiation, at the expense of a slightly increased sheet resistance [Pr

  16. A new method and instrument for accurately measuring interval between ultrashort pulses

    Zhonggang Ji; Yuxin Leng; Yunpei Deng; Bin Tang; Haihe Lu; Ruxin Li; Zhizhan Xu


    @@ Using second-order autocorrelation conception, a novel method and instrument for accurately measuring interval between two linearly polarized ultrashort pulses with real time were presented. The experiment demonstrated that the measuring method and instrument were simple and accurate (the measurement error < 5 fs). During measuring, there was no moving element resulting in dynamic measurement error.

  17. Generation, shaping, compression, characterization and application of intense ultrashort laser pulses

    Cheng, Z


    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 ...

  18. Interaction of ultrashort laser pulses and silicon solar cells under short circuit conditions

    Mundus, M.; Giesecke, J. A.; Fischer, P.; Hohl-Ebinger, J.; Warta, W.


    Ultrashort pulse lasers are promising tools for numerous measurement purposes. Among other benefits their high peak powers allow for efficient generation of wavelengths in broad spectral ranges and at spectral powers that are orders of magnitude higher than in conventional light sources. Very recently this has been exploited for the establishment of sophisticated measurement facilities for electrical characterization of photovoltaic (PV) devices. As the high peak powers of ultrashort pulses promote nonlinear optical effects they might also give rise to nonlinear interactions with the devices under test that possibly manipulate the measurement outcome. In this paper, we present a comprehensive theoretical and experimental study of the nonlinearities affecting short circuit current (ISC) measurements of silicon (Si) solar cells. We derive a set of coupled differential equations describing the radiation-device interaction and discuss the nonlinearities incorporated in those. By a semi-analytical approach introducing a quasi-steady-state approximation and integrating a Green's function we solve the system of equations and obtain simulated ISC values. We validate the theoretical model by ISC ratios obtained from a double ring resonator setup capable for reproducible generation of various ultrashort pulse trains. Finally, we apply the model to conduct the most prominent comparison of ISC generated by ultrashort pulses versus continuous illumination. We conclude by the important finding that the nonlinearities induced by ultrashort pulses are negligible for the most common ISC measurements. However, we also find that more specialized measurements (e.g., of concentrating PV or Si-multijunction devices as well as highly localized electrical characterizations) will be biased by two-photon-absorption distorting the ISC measurement.

  19. LIGHT SOURCE: Terahertz emission in tenuous gases irradiated by ultrashort laser pulses

    Wang, Wei-Min; Sheng, Zheng-Ming; Wit, Hui-Chun; Chen, Min; Li, Chun; Zhang, Jie; Mima, K.


    Mechanism of terahertz (THz) pulse generation in gases irradiated by ultrashort laser pulses is investigated theoretically. Quasi-static transverse currents produced by laser field ionization of gases and the longitudinal modulation in formed plasmas are responsible for the THz emission at the electron plasma frequency, as demonstrated by particle-in-cell simulations including field ionization. The THz field amplitude scaling with the laser amplitude within a large range is also discussed.

  20. Ultrashort Intense Pulse Propagator Applications: Light Strings, Higher Harmonic Generation and Extreme NLO


    A. Lotti, M. Kolesik, J. V. Moloney, “Analogue gravity and ultrashort laser pulse filamentation”, Europhysics Letters 89, 34004 (2010) Jinjie Liu...followed the same scenario, or if the propagation distance matters. Such was the motivation of our work published recently in Physical Review Letters ...filaments in a high-power pulse determined by the linear “preparation” of the beam? In our previous work published in Physical Review Letters , we

  1. Frequency-resolved optical gating measurement of ultrashort pulses by using single nanowire

    Yu, Jiaxin; Liao, Feng; Gu, Fuxing; Zeng, Heping


    The use of ultrashort pulses for fundamental studies and applications has been increasing rapidly in the past decades. Along with the development of ultrashort lasers, exploring new pulse diagnositic approaches with higher signal-to-noise ratio have attracted great scientific and technological interests. In this work, we demonstrate a simple technique of ultrashort pulses characterization with a single semiconductor nanowire. By performing a frequency-resolved optical gating method with a ZnO nanowire coupled to tapered optical microfibers, the phase and amplitude of a pulse series are extracted. The generated signals from the transverse frequency conversion process can be spatially distinguished from the input, so the signal-to-noise ratio is improved and permits lower energy pulses to be identified. Besides, since the nanometer scale of the nonlinear medium provides relaxed phase-matching constraints, a measurement of 300-nm-wide supercontinuum pulses is achieved. This system is highly compatible with standard optical fiber systems, and shows a great potential for applications such as on-chip optical communication.

  2. Frequency-resolved optical gating measurement of ultrashort pulses by using single nanowire

    Yu, Jiaxin; Liao, Feng; Gu, Fuxing; Zeng, Heping


    The use of ultrashort pulses for fundamental studies and applications has been increasing rapidly in the past decades. Along with the development of ultrashort lasers, exploring new pulse diagnositic approaches with higher signal-to-noise ratio have attracted great scientific and technological interests. In this work, we demonstrate a simple technique of ultrashort pulses characterization with a single semiconductor nanowire. By performing a frequency-resolved optical gating method with a ZnO nanowire coupled to tapered optical microfibers, the phase and amplitude of a pulse series are extracted. The generated signals from the transverse frequency conversion process can be spatially distinguished from the input, so the signal-to-noise ratio is improved and permits lower energy pulses to be identified. Besides, since the nanometer scale of the nonlinear medium provides relaxed phase-matching constraints, a measurement of 300-nm-wide supercontinuum pulses is achieved. This system is highly compatible with standard optical fiber systems, and shows a great potential for applications such as on-chip optical communication. PMID:27609521

  3. Prompt pre-thermal laser ion sheath acceleration with ultra-short laser pulses

    Zeil, Karl; Bussmann, Michael; Cowan, Thomas; Kluge, Thomas; Kraft, Stephan; Metzkes, Josefine; Schramm, Ulrich [Helmholtz-Zentrum Dresden-Rossendorf (Germany)


    Recent laser-ion acceleration experiments performed at the 150 TW Draco laser in Dresden, Germany, have demonstrated the importance of a precise understanding of the electron dynamics in solids on an ultra-short time scale. For example, with ultra-short laser pulses a description based purely on the evolution of a thermal electron ensemble, as in standard TNSA models, is not sufficient anymore. Rather, non-thermal effects during the ultra-short intra-pulse phase of laser-electron interaction in solids become important for the acceleration of ions when the laser pulse duration is in the order of only a few tens of femtoseconds. While the established maximum ion energy scaling in the TNSA regime goes with the square root of the laser intensity, for such ultra short pulse durations the maximum ion energy is found to scale linear with laser intensity, motivating the interest in such laser systems. Investigating the influence of laser pulse contrast, laser polarization and laser incidence angle on the proton maximum energy and angular distribution, we present recent advances in the description of the laser interaction with solids, focusing on the implications of intra-pulse non-thermal phenomena on the ion acceleration.

  4. Design and fabrication of hollow-core photonic crystal fibers for high-power ultrashort pulse transportation and pulse compression.

    Wang, Y Y; Peng, Xiang; Alharbi, M; Dutin, C Fourcade; Bradley, T D; Gérôme, F; Mielke, Michael; Booth, Timothy; Benabid, F


    We report on the recent design and fabrication of kagome-type hollow-core photonic crystal fibers for the purpose of high-power ultrashort pulse transportation. The fabricated seven-cell three-ring hypocycloid-shaped large core fiber exhibits an up-to-date lowest attenuation (among all kagome fibers) of 40 dB/km over a broadband transmission centered at 1500 nm. We show that the large core size, low attenuation, broadband transmission, single-mode guidance, and low dispersion make it an ideal host for high-power laser beam transportation. By filling the fiber with helium gas, a 74 μJ, 850 fs, and 40 kHz repetition rate ultrashort pulse at 1550 nm has been faithfully delivered at the fiber output with little propagation pulse distortion. Compression of a 105 μJ laser pulse from 850 fs down to 300 fs has been achieved by operating the fiber in ambient air.

  5. Characterization of a High Efficiency, Ultrashort Pulse Shaper Incorporating a Reflective 4096-Element Spatial Light Modulator.

    Field, Jeffrey J; Planchon, Thomas A; Amir, Wafa; Durfee, Charles G; Squier, Jeff A


    We demonstrate pulse shaping via arbitrary phase modulation with a reflective, 1×4096 element, liquid crystal spatial light modulator (SLM). The unique construction of this device provides a very high efficiency when the device is used for phase modulation only in a prism based pulse shaper, namely 85%. We also present a single shot characterization of the SLM in the spatial domain and a single shot characterization of the pulse shaper in the spectral domain. These characterization methods provide a detailed picture of how the SLM modifies the spectral phase of an ultrashort pulse.

  6. Ultrashort hard x-ray pulses generated by 90 degrees Thomson scattering

    Chin, A.H. [Univ. of California, Berkeley, CA (United States); Schoenlein, R.W.; Glover, T.E. [Ernest Orlando Lawrence Berkeley National Lab., CA (United States)] [and others


    Ultrashort x-ray pulses permit observation of fast structural dynamics in a variety of condensed matter systems. The authors have generated 300 femtosecond, 30 keV x-ray pulses by 90 degrees Thomson scattering between femtosecond laser pulses and relativistic electrons. The x-ray and laser pulses are synchronized on a femtosecond time scale, an important prerequisite for ultrafast pump-probe spectroscopy. Analysis of the x-ray beam properties also allows for electron bunch characterization on a femtosecond time scale.

  7. Intense ultrashort pulse generation using the JAERI far-infrared free electron laser

    Nagai, R; Nishimori, N; Kikuzawa, N; Sawamura, M; Minehara, E J


    An intense ultrashort optical pulse has been quasi-continuously generated using a superconducting RF linac-based free-electron laser at a wavelength of 22.5 mu m. The pulse shape and width are measured by second-order optical autocorrelation with a birefringent Te crystal. At synchronism of the optical resonator, the pulse shape is a smooth single pulse with an FWHM width of 255 fs and energy of 74 mu J. A train of subpulses is developed by increasing the desynchronism of the optical resonator. The measured results are in good agreement with numerical simulation.

  8. Propagation of an ultrashort electromagnetic pulse in solid-state plasma

    Astapenko, V A


    The change of the shape of an ultrashort electromagnetic pulse in its propagation in solid-state plasma was calculated in the linear approximation. A case of solid-state silver plasma and of a "Mexican hat" wavelet pulse was considered. The dielectric permittivity of the medium was calculated in the Drude model. Strong dispersion spreading of a pulse at distances of the order of several microns was shown, and the comparison of evolution of the pulse shape for different center frequencies was carried out.

  9. High-gain Yb:YAG amplifier for ultrashort pulse laser at high-average power

    Vetrovec, John; Copeland, Drew A.; Litt, Amardeep S.; Du, Detao


    We report on a Yb:YAG laser amplifier for ultrashort pulse applications at kW-class average power. The laser uses two large-aperture, disk-type gain elements fabricated from composite ceramic YAG material, and a multi-pass extraction architecture to obtain high gain in a chirped-pulse amplification system. The disks are edge-pumped, thus allowing for reduced doping of host material with laser ions, which translates to lower lasing threshold and lower heat dissipation in the Yb:YAG material. The latter makes it possible to amplify a near diffraction-limited seed without significant thermo-optical distortions. This work presents results of testing the laser amplifier with relay optics configured for energy extraction with up to 40 passes through the disks. Applications for the ultrashort pulse laser amplifier include producing laser-induced plasma channel, laser material ablation, and laser acceleration of atomic particles.

  10. High-gain multipassed Yb:YAG amplifier for ultrashort pulse laser

    Vetrovec, John; Copeland, Drew A.; Litt, Amardeep S.; Du, Detao


    We report on a Yb:YAG laser amplifier for ultrashort pulse applications at kW-class average power. The laser uses two large-aperture, disk-type gain elements fabricated from composite ceramic YAG material, and a multi-pass extraction architecture to obtain high gain in a chirped-pulse amplification system. The disks are edge-pumped, thus allowing for reduced doping of the host material with laser ions, which translates to lower lasing threshold and lower heat dissipation in the Yb:YAG material. The latter makes it possible to amplify a near diffraction-limited seed without significant thermo-optical distortions. This work presents results of testing the laser amplifier with relay optics and passive polarization switching configured for energy extraction with up to 40 passes through the disks. Applications for the ultrashort pulse laser amplifier include producing a laser-induced plasma channel, laser material ablation, and laser acceleration of atomic particles.

  11. A study of ultrafast electron diffusion kinetics in ultrashort-pulse laser ablation of metals

    Yang Jian-Jun; Liu Wei-Wei; Zhu Xiao-Nong


    Temperature dependence of the electron diffusion in metallic targets, where the electron-electron collision is the dominant process, is investigated with the help of an extended two-temperature model. In sharp contrast to the low electron temperature case, where only the electron-phonon collisions are commonly considered, the electron diffusion process underlying the high electron temperatures evolves dramatically different in both temporal and spatial domains.Calculated results of the ablation yield at different pulse durations are presented for a copper plate impinged by ultrashort laser pulses with energy fluences ranging from 0.1 J/cm2 to 10 J/cm2. The excellent agreement between the simulation results and the experimental data indicates the significant role of electron-electron collisions in material ablations using intense ultrashort laser pulses.

  12. Non-dissociative and dissociative ionization of a CO+ beam in intense ultrashort laser pulses

    Gaire, B.; Ablikim, U.; Zohrabi, M.; Roland, S.; Carnes, K. D.; Ben-Itzhak, I.


    We have investigated the ionization of CO+ beams in intense ultrashort laser pulses. With the recent upgrades to our coincidence three-dimensional momentum imaging method we are able to measure both non-dissociative and dissociative ionization of the molecular-ion beam targets. Using CO+ as an example, we have found that non-dissociative ionization (leading to the metastable dication CO2+) involves a direct transition, i.e. the molecule is ionized with little or no internuclear distance stretch. Dissociative ionization (C+ + O+) occurs both directly and indirectly, stretching first and then ionizing. Our results show that the yield of dissociative ionization is higher than that of non-dissociative ionization and can be manipulated with the laser pulse duration by suppressing the indirect ionization path using ultrashort pulses (Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

  13. Sub-10 nm near-field localization by plasmonic metal nanoaperture arrays with ultrashort light pulses.

    Lee, Hongki; Kim, Chulhong; Kim, Donghyun


    Near-field localization by ultrashort femtosecond light pulses has been investigated using simple geometrical nanoapertures. The apertures employ circular, rhombic, and triangular shapes to localize the distribution of surface plasmon. To understand the geometrical effect on the localization, aperture length and period of the nanoapertures were varied. Aperture length was shown to affect the performance more than aperture period due mainly to intra-aperture coupling of near-fields. Triangular apertures provided the strongest spatial localization below 10 nm in size as well as the highest enhancement of field intensity by more than 7000 times compared to the incident light pulse. Use of ultrashort pulses was found to allow much stronger light localization than with continuous-wave light. The results can be used for super-localization sensing and imaging applications where spatially localized fields can break through the limits in achieving improved sensitivity and resolution.

  14. The Ultrashort laser pulses in water that violates the Lambert-Beer Law

    Byeon, Joong; Kattawar, George; Naveira, Lucas; Sokolov, Alexei


    Recent experiments have opened the possibility that by using ultrashort Laser Pulse in H2O, it may be possible to propagate light (signal) over much further distance than predicted by the familiar Beer-Lambert Law. To explain it, the complete femtosecond-width pulse propagation process will be modeled and simulated by FDTD method in visible frequency range. We will show how the FDTD method can be used to accuately model the propagation of Ultrashort pulses in water. We will also show the development of the both the Sommerfeld and Brillouin optical precursors. We will, for the first time, use the actual absorption spectrum of water in these calculations and compare the results with experimental data.

  15. Vibrational predissociation of methylnitrite using phase-locked ultrashort laser pulses

    Dateo, Christopher E.; Metiu, Horia


    We solve numerically the time-dependent Schroedinger equation to study the behavior of a molecule interacting with two phase-locked ultrashort laser pulses. The 2D model used in the calculations mimics the properties of the CH3ONO molecule. The two pulses are identical except for their relative phase and are tuned to excite an upper electronic state of the molecule. After excitation the molecule predissociates, and we calculate the dependence of the NO yield and of the NO vibrational population on the delay time between the pulses.

  16. Underwater acoustic wave generation by filamentation of terawatt ultrashort laser pulses

    Jukna, Vytautas; Milián, Carles; Brelet, Yohann; Carbonnel, Jérôme; André, Yves-Bernard; Guillermin, Régine; Sessarego, Jean-Pierre; Fattaccioli, Dominique; Mysyrowicz, André; Couairon, Arnaud; Houard, Aurélien


    Acoustic signals generated by filamentation of ultrashort TW laser pulses in water are characterized experimentally. Measurements reveal a strong influence of input pulse duration on the shape and intensity of the acoustic wave. Numerical simulations of the laser pulse nonlinear propagation and the subsequent water hydrodynamics and acoustic wave generation show that the strong acoustic emission is related to the mechanism of superfilamention in water. The elongated shape of the plasma volume where energy is deposited drives the far-field profile of the acoustic signal, which takes the form of a radially directed pressure wave with a single oscillation and a very broad spectrum.

  17. Temporal Behaviour of Harmonics from One-Dimensional H2+ in an UltrashortLaser Pulse

    屈卫星; 李儒新; 徐至展; 夏宇兴; 甘明龙


    With the method of wavelet transform, we consider the temporal behaviour of high-order harmonic generationfrom one-dimensional H2+ exposed to an ultrashort laser pulse with a duration of tens of femtoseconds. The results, which are calculated by numerically solving the corresponding time-dependent Schrodinger equation with the split-operator method in the non-Born-Oppenheimer approach, show that: (1) the high-order harmonics in the cut-off range emitted as a train of pulses have better coherence than those in the plateau; (2) the harmonics are emitted early in time when the intensity of the laser pulse increases.

  18. Simultaneous analytical characterisation of two ultrashort laser pulses using spectrally resolved interferometric correlations

    Amat-Roldan, Ivan; Artigas, David; Cormack, Iain G.; Loza-Alvarez, Pablo


    In this paper we discuss in detail the underlying theory of a novel method that allows the characterizing of ultrashort laser pulses to be achieved in an analytical way. MEFISTO, (measuring the electric field by interferometric spectral trace observation) is based on a Fourier analysis of the information contained in a spectrally resolved interferometric correlation and can be applied to both situations: the characterization of an unknown pulse (MEFISTO) or to the simultaneous characterization of two different unknowns pulses (Blind-MEFISTO). The theoretical development and experimental practical implications are discussed in both situations.

  19. Modulation of ionization on laser frequency in ultra-short pulse intense laser-gas-target

    Hu Qiang-Lin; Liu Shi-Bing


    Based on the dispersion relation of intense laser pulse propagating in gradually ionized plasma, this paper discusses the frequency modulation induced by ionization of an ultra-short intense laser pulse interacting with a gas target.The relationship between the frequency modulation and the ionization rate, the plasmas frequency variation, and the polarization of atoms (ions) is analysed. The numerical results indicate that, at high frequency, the polarization of atoms (ions) plays a more important role than plasma frequency variation in modulating the laser frequency, and the laser frequency variation is different at different positions of the laser pulse.

  20. Stimulated recombination of antiproton and positron with ultra-short ultra-high intensity laser pulse

    Ryabinina, M V


    Ionization of hydrogen atom in the field of high-intense ultra-short femto-second laser pulse recently became the subject of comprehensive theoretical approaches. On the other hand, there exists experimental evidence that short electric pulses can effectively stimulate electron-proton (as well as antiproton-positron) recombination to high-level (Rydberg) state. In this paper we present the results of the theoretical estimations of antiproton-positron recombination cross-section in cold mixed plasmas in traps in the conditions of ATHENA/ATRAP experiments in CERN under the action of sub-fs laser pulse with TW intensity. (2 refs).

  1. Experimental Research of Fast Proton Generation From Ultra-short Intense Laser Pulses Interaction With Different Thickness Al Foils

    LAN; Xiao-fei; LU; Jian-xin; HUANG; Yong-sheng; WANG; Lei-jian; XI; Xiao-feng; TANG; Xiu-zhang


    <正>With the development of laser technology, the generation of fast ions by the interaction of ultra-short ultra-intense laser pulses with matters has recently been attracting considerable attention, especially for acceleration of proton. Before performing experiment, we calibrated the CR39 detector using standard proton beams from conventional accelerator. In the field of proton acceleration driven by ultra-short ultra-intense laser pulses,

  2. Polarization sensitive anisotropic structuring of silicon by ultrashort light pulses

    Zhang, Jingyu; Drevinskas, Rokas, E-mail:; Beresna, Martynas; Kazansky, Peter G. [Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ (United Kingdom)


    Imprinting of anisotropic structures on the silicon surface by double pulse femtosecond laser irradiation is demonstrated. The origin of the polarization-induced anisotropy is explained in terms of interaction of linearly polarized second pulse with the wavelength-sized symmetric crater-shaped structure generated by the linearly polarized first pulse. A wavefront sensor is fabricated by imprinting an array of micro-craters. Polarization controlled anisotropy of the structures can be also explored for data storage applications.

  3. Plasma Membrane Permeabilization by Trains of Ultrashort Electric Pulses


    REFERENCES 1. Beebe, S.J., et al., Nanosecond Pulsed Electric Field (nsPEF) Effects on Cells and Tissues: Apoptosis Induction and Tumor Growth Inhibition...nanosecond pulsed electric field Bioelectromagnetics, 2007. 28: p. 655-663. 13. Gowrishankar, T.R. and J.C. Weaver, Electrical behavior and pore... electric field (nsPEF). Bioelectromagnetics, 2007. 28: p. 655- 663. 19. Nuccitelli, R., et al., A new pulsed electric field therapy for melanoma disrupts

  4. Evolution of optical force on two-level atom by ultrashort time-domain dark hollow Gaussian pulse

    Cao, Xiaochao; Wang, Zhaoying; Lin, Qiang


    Based on the analytical expression of the ultrashort time-domain dark hollow Gaussian (TDHG) pulse, the optical force on two-level atoms induced by a TDHG pulse is calculated in this paper. The phenomena of focusing or defocusing of the light force is numerical analyzed for different detuning, various duration time, and different order of the ultrashort pulse. The transverse optical force can change from a focusing force to a defocusing force depending on the spatial-temporal coupling effect as the TDHG pulses propagating in free space. Our results also show that the initial phase of the TDHG pulse can significantly changes the envelope of the optical force.

  5. Modification of transparent materials with ultrashort laser pulses: What is energetically and mechanically meaningful?

    Bulgakova, Nadezhda M., E-mail: [HiLASE Centre, Institute of Physics ASCR, Za Radnicí 828, 25241 Dolní Břežany (Czech Republic); Institute of Thermophysics SB RAS, 1 Lavrentyev Ave., 630090 Novosibirsk (Russian Federation); Zhukov, Vladimir P. [Institute of Computational Technologies SB RAS, 6 Lavrentyev Ave., 630090 Novosibirsk (Russian Federation); Novosibirsk State Technical University, 20 Karl Marx Ave., 630073, Novosibirsk (Russian Federation); Sonina, Svetlana V. [Novosibirsk State University, 1 Koptuga Ave., 630090 Novosibirsk (Russian Federation); Meshcheryakov, Yuri P. [Design and Technology Branch of Lavrentyev Institute of Hydrodynamics SB RAS, Tereshkovoi street 29, 630090 Novosibirsk (Russian Federation)


    A comprehensive analysis of laser-induced modification of bulk glass by single ultrashort laser pulses is presented which is based on combination of optical Maxwell-based modeling with thermoelastoplastic simulations of post-irradiation behavior of matter. A controversial question on free electron density generated inside bulk glass by ultrashort laser pulses in modification regimes is addressed on energy balance grounds. Spatiotemporal dynamics of laser beam propagation in fused silica have been elucidated for the regimes used for direct laser writing in bulk glass. 3D thermoelastoplastic modeling of material relocation dynamics under laser-induced stresses has been performed up to the microsecond timescale when all motions in the material decay. The final modification structure is found to be imprinted into material matrix already at sub-nanosecond timescale. Modeling results agree well with available experimental data on laser light transmission through the sample and the final modification structure.

  6. Ablation of a nanostructured metal surface by ultrashort X-ray pulses

    Rosandi, Yudi, E-mail: [Department of Physics, Universitas Padjadjaran, Jatinangor, Sumedang 45363 (Indonesia); Fachbereich Physik und Forschungszentrum OPTIMAS, Universität Kaiserslautern, Erwin-Schrödinger-Straße, D-67663 Kaiserslautern (Germany); Urbassek, Herbert M., E-mail: [Fachbereich Physik und Forschungszentrum OPTIMAS, Universität Kaiserslautern, Erwin-Schrödinger-Straße, D-67663 Kaiserslautern (Germany)


    Using molecular-dynamics simulation, we study the interaction of an ultrashort X-ray pulse with an Al surface. The surface has a periodic grating structure consisting of alternating ridges of height 80 nm and width 80 nm, separated by trenches of width 160 nm. After irradiation with an ultrashort (0.2 ps) X-ray pulse with a fluence above the ablation threshold we observe that the ridges first disintegrate into a foamy mixture of melt and gas bubbles, which grow faster than those in the trenches. Due to the interference of tensile pressure build-up below the ridges and the trenches, the material does not spall. At the concave edges, jets are emitted with velocities of around 1000 m/s, which may ultimately lead to the creation of finer surface structures.

  7. Ultrashort x-ray pulse generation by electron beam slicing in storage rings

    A. He


    Full Text Available We propose a new method to generate ultrashort x-ray pulses using focused short low energy (∼20  MeV electron bunches to create short slices of electrons from the circulating electron bunches in a synchrotron radiation storage ring. When a low energy electron bunch crosses from the top of a high energy storage ring electron bunch, its Coulomb force will kick a short slice from the core of the storage ring electron bunch. The separated slices, when passing through an undulator, will radiate ultrashort x-ray pulses at about 160 fs. We discuss the advantages, challenges, and provide data which confirm the feasibility of this new method.

  8. Modification of transparent materials with ultrashort laser pulses: What is energetically and mechanically meaningful?

    Bulgakova, Nadezhda M.; Zhukov, Vladimir P.; Sonina, Svetlana V.; Meshcheryakov, Yuri P.


    A comprehensive analysis of laser-induced modification of bulk glass by single ultrashort laser pulses is presented which is based on combination of optical Maxwell-based modeling with thermoelastoplastic simulations of post-irradiation behavior of matter. A controversial question on free electron density generated inside bulk glass by ultrashort laser pulses in modification regimes is addressed on energy balance grounds. Spatiotemporal dynamics of laser beam propagation in fused silica have been elucidated for the regimes used for direct laser writing in bulk glass. 3D thermoelastoplastic modeling of material relocation dynamics under laser-induced stresses has been performed up to the microsecond timescale when all motions in the material decay. The final modification structure is found to be imprinted into material matrix already at sub-nanosecond timescale. Modeling results agree well with available experimental data on laser light transmission through the sample and the final modification structure.

  9. The Role of Initial Phase in an Ultrashort Pulse

    WANG Yingsong; XU Zhizhan


    The form E(t)= f(t)sin(ωt+φ) is often adopted to describe a laser pulse in the simulation of the physical process of laser interaction with matters. In the present paper, the validity of this expression and found it skeptical to model a pulse with the width less than a single optical cycle.

  10. Axisymmetric modeling of ultrashort-pulse laser interactions with thin metal film

    E. Majchrzak


    Full Text Available The hyperbolic two-temperature model is used in order to describe the heat propagation in metal film subjected to an ultrashort-pulse laser heating. An axisymmetric heat soureceewith Gaussian temporeal and spatial distributions has been taken into account. At the stage of numerical computations the finite difference method is used. In the final part of the paper the examples of computations are shown.

  11. Nonperturbative Approach to the Description of Molecular Excitation by Ultrashort Laser Pulses

    Biryukov А.А.


    Full Text Available We study the problem of excitation of molecules by an ultrashort laser pulse sequence by the use of path-integral approach in energy states space. Using numerical calculations of path-integral we evaluate laser field parameters at which there are quantum resonances in rotational dynamics of dinitrogen isotopes. So we describe recent experimental results [Phys. Rev. Lett. 109, 043003 (2012] theoretically.

  12. High energy electron generation by the 15 mJ ultrashort pulse laser

    Takano, K; Hotta, E; Nemoto, K [Department of Energy Sciences Tokyo Institute of Technology 4259 Nagatsuta-cho Midori-ku Yokohama 226-8502 (Japan); Nayuki, T; Oishi, Y; Fujii, T; Zhidkov, A [Central Research Institute of Electric Power Industry 2-6-1 Nagasaka, Yokosuka, Kanagawa, 240-0196 (Japan); Todoriki, M; Hasegawa, S [University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8654 (Japan)], E-mail:


    We propose a small size high energy X-ray source utilizing ultrashort pulse lasers, and a new scheme for generating quasi-monoenergetic electrons. In this paper, we developed a compact laser electron generator and performed experiment that generated energetic electrons over 1 MeV electrons with only 15 mJ laser energy. The temperatures of emitted electrons were measured to be 0.2 MeV and 0.25 MeV without and with prepulse, respectively.

  13. Prospects for a Novel Ultrashort Pulsed Laser Technology for Pathogen Inactivation


    Virus (HAV), Encephalomyocarditis Virus (EMCV), Tobacco Mosaic Virus (TMV) and M13 bacteriophage, as well as bacteria such as E. coli, Salmonella spp ...5 M13 bacteriophage Non-enveloped, single-stranded DNA 10 5 Escherichia coli Gram negative 10 4 Salmonella typhi Gram negative 10 5...Inactivation of bacteria by ultrashort pulsed lasers We take Salmonella typhimurium as an example. To obtain insight into the inactivation mechanisms

  14. Maxwell-Bloch Equations Modeling of Ultrashort Optical Pulse Propagation in Semiconductor Materials

    Goorjian, Peter M.; Agrawal, Govind, P.


    An algorithm has been developed that solves the semiconductor Maxwell-Bloch equations, without making the standard slowly-varying envelope (SVEA) and rotating-wave (RWA) approximations. It is applied to study the propagation of ultrashort pulses in semiconductor materials. The results include many-body effects due to the Coulomb interaction among the charge carriers as well as the nonlinear effects resulting from spectral hole-burning.

  15. Phase retrieval and time-frequency methods in the measurement of ultrashort laser pulses

    DeLong, K.W.; Fittinghoff, D.N.; Ladera, C.L.; Trebino, R.


    Recently several techniques have become available to measure the time- (or frequency-) dependent intensity and phase of ultrashort laser pulses. One of these, Frequency-Resolved Optical Gating (FROG), is rigorous and has achieved single-laser-shot operation. FROG combines the concepts of time-frequency analysis in the form of spectrogram generation (in order to create a two-dimensional problem), and uses a phase-retrieval-based algorithm to invert the experimental data to yield the intensity and phase of the laboratory laser pulse. In FROG it is easy to generate a spectrogram of the unknown signal, and inversion of the spectrogram to recover the signal is the main goal. Because the temporal width of a femtosecond laser pulse is much shorter than anything achievable by electronics, FROG uses the pulse to measure itself. In FROG, the laser pulse is split into two replicas of itself by a partially reflecting beamsplitter, and the two replicas interact with each other in a medium with an instantaneous nonlinear-optical response. This interaction generates a signal field that is then frequency-resolved using a spectrometer. The spectrum of the signal field is measured for all relevant values of the temporal delay between the two pulses. Here, the authors employ FROG and FROG related techniques to measure the time-dependent intensity and phase of an ultrashort laser pulse.

  16. Diffraction of Ultrashort Pulse on a Nanoscale Conductive Cone

    Golovinski, P A; Manuylovich, E S


    Surface plasmon polariton is collective oscillation of the free electrons at metal dielectric interface. As a wave phenomenon, surface plasmon polaritons can be focused using appropriate excitation geometry of metallic structures. We theoretically demonstrate the possibility of controlling nanoscale short pulse superfocusing based on the generation of radially polarized surface plasmon polariton mode of conical metallic tip. Numerical simulation for femtosecond pulse propagation along a silver nano-needle is discussed. The spatial distribution for a near field strongly depends on a linear chirp of the laser pulse which can partially compensate the wave dispersion. Field distribution is calculated for different chirp values, opening angles and distances. For a pulse with a negative chirp, pulse duration becomes shorter with amplification ~40.

  17. Ramsey-comb spectroscopy with intense ultrashort laser pulses

    Morgenweg, Jonas; Eikema, Kjeld S E


    Optical frequency combs based on mode-locked lasers have revolutionised the field of metrology and precision spectroscopy by providing precisely calibrated optical frequencies and coherent pulse trains. Amplification of the pulsed output from these lasers is very desirable, as nonlinear processes can then be employed to cover a much wider range of transitions and wavelengths for ultra-high precision, direct frequency comb spectroscopy. Therefore full repetition rate laser amplifiers and enhancement resonators have been employed to produce up to microjoule-level pulse energies. Here we show that the full frequency comb accuracy and resolution can be obtained by using only two frequency comb pulses amplified to the millijoule pulse energy level, orders of magnitude more energetic than what has previously been possible. The novel properties of this approach, such as cancellation of optical light-shift effects, is demonstrated on weak two-photon transitions in atomic rubidium and caesium, thereby improving the fr...

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

    Xin Fu; Hongming Zhang; Meng Yan; Minyu Yao


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

  19. Application of the G'/G Expansion Method in Ultrashort Pulses in Nonlinear Optical Fibers

    Jiang Xing-Fang


    Full Text Available With the increasing input power in optical fibers, the dispersion problem is becoming a severe restriction on wavelength division multiplexing (WDM. With the aid of solitons, in which the shape and speed can remain constant during propagation, it is expected that the transmission of nonlinear ultrashort pulses in optical fibers can effectively control the dispersion. The propagation of a nonlinear ultrashort laser pulse in an optical fiber, which fits the high-order nonlinear Schrödinger equation (NLSE, has been solved using the G'/G expansion method. Group velocity dispersion, self-phase modulation, the fourth-order dispersion, and the fifth-order nonlinearity of the high-order NLSE were taken into consideration. A series of solutions has been obtained such as the solitary wave solutions of kink, inverse kink, the tangent trigonometric function, and the cotangent trigonometric function. The results have shown that the G'/G expansion method is an effective way to obtain the exact solutions for the high-order NLSE, and it provides a theoretical basis for the transmission of ultrashort pulses in nonlinear optical fibers.

  20. Next generation ultrashort pulse lasers: Terawatts to Petawatts

    Barty, C.P.; Gordon, C.L. III; Korn, G.; Lemoff, B.E.; Raksi, F.; Rose-Petruck, C.; Squier, J.; Wilson, K.R.; Yakovlev, V.V.; Yamakawa, K. [University of California, San Diego, Urey Hall, Mail Code 0339, La Jolla, California 92093-0339 (United States)


    Techniques for the control of femtosecond resolution phase and amplitude distortions during the amplification of 10-fs optical pulses to joule-level energies are discussed. {copyright} {ital 1996 American Institute of Physics.}

  1. Ultrashort pulse laser processing of hard tissue, dental restoration materials, and biocompatibles

    Yousif, A.; Strassl, M.; Beer, F.; Verhagen, L.; Wittschier, M.; Wintner, E.


    During the last few years, ultra-short laser pulses have proven their potential for application in medical tissue treatment in many ways. In hard tissue ablation, their aptitude for material ablation with negligible collateral damage provides many advantages. Especially teeth representing an anatomically and physiologically very special region with less blood circulation and lower healing rates than other tissues require most careful treatment. Hence, overheating of the pulp and induction of microcracks are some of the most problematic issues in dental preparation. Up till now it was shown by many authors that the application of picosecond or femtosecond pulses allows to perform ablation with very low damaging potential also fitting to the physiological requirements indicated. Beside the short interaction time with the irradiated matter, scanning of the ultra-short pulse trains turned out to be crucial for ablating cavities of the required quality. One main reason for this can be seen in the fact that during scanning the time period between two subsequent pulses incident on the same spot is so much extended that no heat accumulation effects occur and each pulse can be treated as a first one with respect to its local impact. Extension of this advantageous technique to biocompatible materials, i.e. in this case dental restoration materials and titanium plasma-sprayed implants, is just a matter of consequence. Recently published results on composites fit well with earlier data on dental hard tissue. In case of plaque which has to be removed from implants, it turns out that removal of at least the calcified version is harder than tissue removal. Therefore, besides ultra-short lasers, also Diode and Neodymium lasers, in cw and pulsed modes, have been studied with respect to plaque removal and sterilization. The temperature increase during laser exposure has been experimentally evaluated in parallel.

  2. High-Order Temporal Corrected Fields of Ultra-Short Laser Pulses and Laser-Driven Acceleration

    XIE Yong-Jie; HUO Yu-Kun; KONG Qing; WANG Ping-Xiao; CHEN Zhao; LIU Jing-Ru


    @@ Up to third-order temporal correction in terms of a small dimensionless temporal parameter ε = 1/(ω0t0) (ω0 =ck0 the central oscillatory frequency, t0 the pulse duration of half period), the field expressions of ultra-short focused laser pulses are explicitly presented. To evaluate the correction efficacy, electric amplitudes of zeroth-order and higher-order corrected fields are compared for different pulse durations. Furthermore, electron interaction with ultra-short laser pulses is simulated using both the zeroth-order and higher-order corrected field equations.

  3. Hot electrons generated by ultra-short pulse laser interacting with solid targets

    陈黎明; 张杰; 李玉同; 梁天骄; 王龙; 魏志义; 江文勉


    Hot electrons produced by ultra-short pulse laser interacting with solid targets were studied systematically. When 800 nm, 8 × 1015 W/cm2 laser pulses interacted with solid targets, hot electron e-mission was found to be collimated in certain directions and the angular distribution of hot electrons depended on the energy absorption. The angular divergence of outgoing hot electrons was inversely proportional to the hot electron energy. The energy spectrum of hot electrons was found to be in a bi-Maxwellian distribution and the maximum energy was over 500 keV.

  4. Hot electrons generated by ultra-short pulse laser interacting with solid targets


    Hot electrons produced by ultra-short pulse laser interacting with solid targets were studied systematically. When 800 nm, 8×1015 W/cm2 laser pulses interacted with solid targets, hot electron emission was found to be collimated in certain directions and the angular distribution of hot electrons depended on the energy absorption. The angular divergence of outgoing hot electrons was inversely proportional to the hot electron energy. The energy spectrum of hot electrons was found to be in a bi-Maxwellian distribution and the maximum energy was over 500 keV.

  5. Ultra-short pulse reconstruction software in high power laser system

    Galletti, M. [Physics Department of the University and INFN, Pisa (Italy); Galimberti, M. [Central Laser Facility, Rutherford Appleton Laboratory, Didcot (United Kingdom); Giulietti, D. [Physics Department of the University and INFN, Pisa (Italy)


    An ultra-short pulse reconstruction software, validated through a set of experimental measurements on the front-end of the Vulcan laser at the RAL Central Laser Facility is presented. The measurements were acquired in Target Area Petawatt of the Vulcan laser, both using a conventional autocorrelation technique and the GRENOUILLE technique in order to compare the results. The FWHM of the laser pulses considered came out to be comparable for the two techniques. In this experimental campaign for the first time a technique different from the autocorrelation one has been used for a PW class laser as Vulcan.

  6. Role of pre-pulses in the interaction of intense, ultrashort lasers with structured surfaces

    Rajeev, P.P.; Kahaly, S.; Bagchi, S.; Bose, S.; Kiran, P.P.; Ayyub, P.; Ravindra Kumar, G. [Tata Institute of Fundamental Research, Mumbai (India)


    We examine enhanced hard X-ray emission (20 - 200 keV) from plasmas produced on nano-particles coated optically polished copper surface under different prepulse conditions. We observe that enhancement reduces with increasing prepulse intensity. The dynamics of the process is seen to be in the picosecond regime. We attribute this to pre-plasma formation on nano-particles and subsequent modification/destruction of the nano-structure layer before the arrival of the main pulse. It is suggested that high-contrast ultrashort pulses are essential for nano-particles to function as yield enhancer. (authors)

  7. Single-step electropolymerization patterning of a polypyrrole nanowire by ultra-short pulses via an AFM cantilever

    Nam, Kihwan; Lee, Gyudo; Jung, Huihun; Kim, Chi Hyun; Seo, Jongbum; Yoon, Dae Sung; Lee, Sang Woo; Kwon, Taeyun [Department of Biomedical Engineering, Yonsei University, Wonju, 220-710 (Korea, Republic of); Park, Jinsung, E-mail:, E-mail: [Department of Mechanical Engineering, Korea University, Seoul, 136-701 (Korea, Republic of)


    Conducting polymers (CPs) have attracted a great deal of attention due to their unique properties; these properties are useful in implementing various functional devices, such as memory, and chemical and biological sensors. In particular, the nanopatterning of CPs is a key technology that will accelerate the adoption of CPs in fabricating nanoscaled multifunctional devices. This paper presents an innovative technique for forming polypyrrole nanowire (PPy-NW) patterns, without any additional pretreatment on the gold surface, using atomic force microscopy (AFM) and ultra-short pulse voltage. Applying the ultra-short pulse voltage to the AFM tip has the following advantage: since the electrochemical current is extremely localized around the tip, the successful formation of CP nanowires results. This is because the pulse width is much shorter than the resistor-capacitor (RC) time constant of the equivalent electrochemical circuit of our experimental set-up. This paper provides systematic results regarding the dimensional variation of the PPy-NW patterns produced by varying the electrical conditions of the ultra-short pulse, such as the pulse amplitude, width, and frequency. The results show that use of an ultra-short pulse is essential in fabricating PPy-NW patterns. Additionally, an ultra-short pulse offers excellent pattern controllability for both width (353 nm {approx} 3.37 {mu}m) and height (2.0 {approx} 88.3 nm).

  8. Medical applications of ultra-short pulse lasers

    Kim, B M; Marion, J E


    The medical applications for ultra short pulse lasers (USPLs) and their associated commercial potential are reviewed. Short pulse lasers offer the surgeon the possibility of precision cutting or disruption of tissue with virtually no thermal or mechanical damage to the surrounding areas. Therefore the USPL offers potential improvement to numerous existing medical procedures. Secondly, when USPLs are combined with advanced tissue diagnostics, there are possibilities for tissue-selective precision ablation that may allow for new surgeries that cannot at present be performed. Here we briefly review the advantages of short pulse lasers, examine the potential markets both from an investment community perspective, and from the view. of the technology provider. Finally nominal performance and cost requirements for the lasers, delivery systems and diagnostics and the present state of development will be addressed.

  9. Phase Sensitive Amplifier Based on Ultrashort Pump Pulses

    Gershikov, Alexander


    We demonstrate a narrow band phase sensitive amplifier in the pump degenerate configuration which employs ps pump pulses. Control of the amplifier bandwidth is achieved via changes of the pump spectral width. A phase sensitive gain between -6 and 6 decibels, with an overall system gain of 28dB was demonstrated.

  10. Ultra-short pulsed millimeter-wave laser

    Wilson, Thomas


    High peak power pulses of 1.22-mm wavelength radiation have recently been obtained from a novel cavity-dumped far-infrared optically-pumped laser^1. Smooth reproducible pulses with the following characteristics have been routinely obtained: peak power=25-kW, pulsewidth (FWHM)=5-ns, repetition rate=10 pps. (This compares favorably to typical far-infrared, cavity-dumped output - 11-kW, 30-ns, 1 pps - available from the University of California - Santa Barbara Free Electron Laser). The pumping laser is a grating-tuned, hybrid TEA CO2 laser providing 1J / pulse at the 9P32 transition. The far-infrared gain medium is isotopic (C^13) methyl flouride. Experiments are underway for using the novel source to resonantly excite coherent pulses of 250-GHz longitudinal acoustic phonons in silicon doping superlattices. ^1 Thomas E. Wilson, "Modeling the high-speed switching of far-infrared radiation by photoionization in a semiconductor", Phys. Rev. B 59 (20), 12996 (1999).

  11. Analysis of confocal microscopy under ultrashort light-pulse illumination

    Kempe, M.; Rudolph, W. (Univ. of New Mexico, Albuquerque (United States))


    The resolution of confocal laser scanning microscopes is analyzed if they are used in measurements that are to combine high spatial and high temporal resoltuion. A generalized Fourier-optical treatment is developed in which the system characteristics contain all necessary information regarding the optical arrangement and the illuminating light pulses. Coherent and incoherent imaging are considered in detail. 10 refs., 8 figs.

  12. Oral applications of ultra-short laser pulses: a new approach for gentle and painless treatment?

    Yousif, A.; Strassl, M.; Wieger, V.; Zoppel, S.; Wintner, E.


    In dental hard tissue ablation, ultra-short laser pulses have proven sufficiently their potential for material ablation with negligible collateral damage providing many advantages. The absence of microcracks and the possibility to avoid overheating of the pulp during dental cavity preparation may be among the most important issues, the latter opening up an avenue for potential painless treatment. Beside the evident short interaction time of laser radiation with the irradiated tissue, scanning of the ultra-short pulse trains turned out to be crucial for ablating cavities of required quality and shape. Additionally, such a technique allows to treat larger areas like the ones dentists are used to work with, i.e. ~ 1 mm Ø.In this paper, an overview of different scanning methods together with the algorithms used and an assessment of their applicability is presented. A variety of pulse durations from ~100 fs up to several ps has been used by numerous authors over the last approximately ten years. Having employed 330 fs pulses, we present the corresponding ablation thresholds for dental hard tissue (enamel, dentine; human and bovine), for a number of dental restoration materials, as well as for different types of bovine bone. Dental implants frequently have to be cleaned from plaque being deposited around their necks in areas where the gums have already retreated. A preliminary investigation is presented on the applicability of ultra-short pulses with mentioned duration for the gentle cleaning of titanium implants focusing on the preservation of the special plasma-sprayed biocompatible implant surface.

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

    Marcos Dantus


    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

  14. Electron rescattering at metal nanotips induced by ultrashort laser pulses

    Wachter, G.; Lemell, C.; Burgdörfer, J.


    We theoretically investigate the interaction of moderate intensity near-infrared few cycle laser pulses with nano-scale metal tips. Local field enhancement in a nanometric region around the tip apex triggers coherent electron emission on the nanometer length and femtosecond time scale. The quantum dynamics at the surface are simulated with time-dependent density functional theory (TDDFT) and interpreted based on the simple man's model. We investigate the dependence of the emitted electron spectra on the laser wavelength.

  15. Analysis of shot noise in the detection of ultrashort optical pulse trains

    Quinlan, Franklyn; Jiang, Haifeng; Diddams, Scott A


    We present a frequency domain model of shot noise in the photodetection of ultrashort optical pulse trains using a time-varying analysis. Shot noise-limited photocurrent power spectral densities, signal-to-noise expressions, and shot noise spectral correlations are derived that explicitly include the finite response of the photodetector. It is shown that the strength of the spectral correlations in the shot noise depends on the optical pulse width, and that these correlations can create orders-of-magnitude imbalance between the shot noise-limited amplitude and phase noise of photonically generated microwave carriers. It is also shown that only by accounting for spectral correlations can shot noise be equated with the fundamental quantum limit in the detection of optical pulse-to-pulse timing jitter.

  16. A broadly tunable autocorrelator for ultra-short, ultra-high power infrared optical pulses

    Szarmes, E.B.; Madey, J.M.J. [Duke Univ., Durham, NC (United States)


    We describe the design of a crossed-beam, optical autocorrelator that uses an uncoated, birefringent beamsplitter to split a linearly polarized incident pulse into two orthogonally polarized pulses, and a Type II, SHG crystal to generate the intensity autocorrelation function. The uncoated beamsplitter accommodates extremely broad tunability while precluding any temporal distortion of ultrashort optical pulses at the dielectric interface, and the specific design provides efficient operation between 1 {mu}m and 4 {mu}m. Furthermore, the use of Type II SHG completely eliminates any single-beam doubling, so the autocorrelator can be operated at very shallow crossed-beam angles without generating a background pedestal. The autocorrelator has been constructed and installed in the Mark III laboratory at Duke University as a broadband diagnostic for ongoing compression experiments on the chirped-pulse FEL.

  17. Wear-reducing Surface Functionalization of Implant Materials Using Ultrashort Laser Pulses

    Oldorf, P.; Peters, R.; Reichel, S.; Schulz, A.-P.; Wendlandt, R.

    The aim of the project called "EndoLas" is the development of a reproducible and reliable method for a functionalization of articulating surfaces on hip joint endoprostheses due to a reduction of abrasion and wear by the generation of micro structures using ultrashort laser pulses. On the one hand, the microstructures shall ensure the capture of abraded particles, which cause third-body wear and thereby increase aseptic loosening. On the other hand, the structures shall improve or maintain the tribologically important lubricating film. Thereby, the cavities serve as a reservoir for the body's own synovial fluid. The dry friction, which promotes abrasion and is a part of the mixed friction in the joint, shall therefore be reduced. In experimental setups it was shown, that the abrasive wear can be reduced significantly due to micro-structuring the articulating implant surfaces. To shape the fine and deterministic cavities on the surfaces, an ultra-short pulsed laser, which is integrated in a high-precision, 5-axes micro-machining system, was used. The laser system, based on an Yb:YAG thin-disk regenerative amplifier, has an average output power of 50 W at the fundamental wavelength of 1030 nm, a maximum repetition rate of 400 kHz and a pulse duration of 6 ps. Due to this, a maximum pulse energy of 125 μJ is achievable. Furthermore external second and third harmonic generation enables the usage of wavelengths in the green and violet spectral range.

  18. Characterization of fiber ultrashort pulse delivery for nonlinear endomicroscopy.

    Ibrahim, A; Poulon, F; Habert, R; Lefort, C; Kudlinski, A; Haidar, D Abi


    In this work, we present a detailed characterization of a small-core double-clad photonic crystal fiber, dedicated and approved for in vivo nonlinear imaging endomicroscopy. A numerical and experimental study has been performed to characterize the excitation and collection efficiencies through a 5 m-long optical fiber, including the pulse duration and spectral shape. This was first done without any distal optics, and then the performances of the system were studied by using two kinds of GRIN lenses at the fiber output. These results are compared to published data using commercial double clad fibers and GRIN lenses.

  19. Heat transport in metals irradiated by ultrashort laser pulses

    Kanavin, Andrei P.; Afanasiev, Yuri V.; Chichkov, Boris N.; Isakov, Vladimir A.; Smetanin, Igor V.


    Different regimes of heat propagation in metals irradiated by subpicosecond laser pulses are studied on the basis of two-temperature diffusion model. New analytical solutions for the heat conduction equation, corresponding to the different temperature dependences of the electron thermal conductivity (formula available n paper), are found. It is shown that in case of a strong electron-lattice nonequilibrium, the heat penetration depth grows linearly with time, lT varies direct as t, in opposite to the ordinary diffusionlike behavior, lT varies direct as t1/2. Moreover, the heat propagation velocity decreases with increasing laser fluence.

  20. Measurement and compensation schemes for the pulse front distortion of ultra-intensity ultra-short laser pulses

    Wu, Fenxiang; Xu, Yi; Yu, Linpeng; Yang, Xiaojun; Li, Wenkai; Lu, Jun; Leng, Yuxin


    Pulse front distortion (PFD) is mainly induced by the chromatic aberration in femtosecond high-peak power laser systems, and it can temporally distort the pulse in the focus and therefore decrease the peak intensity. A novel measurement scheme is proposed to directly measure the PFD of ultra-intensity ultra-short laser pulses, which can work not only without any extra struggle for the desired reference pulse, but also largely reduce the size of the required optical elements in measurement. The measured PFD in an experimental 200TW/27fs laser system is in good agreement with the calculated result, which demonstrates the validity and feasibility of this method effectively. In addition, a simple compensation scheme based on the combination of concave lens and parabolic lens is also designed and proposed to correct the PFD. Based on the theoretical calculation, the PFD of above experimental laser system can almost be completely corrected by using this compensator with proper parameters.

  1. Near and intermediate fields of an ultrashort pulse transmitted through Young’s double-slit experiment

    Nugrowati, A.M.; Pereira, S.F.; Van de Nes, A.S.


    We present a systematic study of the transmitted field of an ultrashort pulse through Young’s double slit. We show how the spatial-temporal distribution of the field in the near and intermediate zone is affected by the input polarization state of the pulse. The analysis has been separated to study t

  2. Near and intermediate fields of an ultrashort pulse transmitted through Young’s double-slit experiment

    Nugrowati, A.M.; Pereira, S.F.; Van de Nes, A.S.


    We present a systematic study of the transmitted field of an ultrashort pulse through Young’s double slit. We show how the spatial-temporal distribution of the field in the near and intermediate zone is affected by the input polarization state of the pulse. The analysis has been separated to study

  3. Limits of applicability of a two-temperature model under nonuniform heating of metal by an ultrashort laser pulse

    Polyakov, D. S.; Yakovlev, E. B.


    The heating of metals (silver and aluminium) by ultrashort laser pulses is analysed proceeding from a spatially nonuniform kinetic equation for the electron distribution function. The electron subsystem thermalisation is estimated in a wide range of absorbed pulse energy density. The limits of applicability are determined for the two-temperature model.

  4. Applications of ultra-short pulsed laser ablation: thin films deposition and fs/ns dual-pulse laser-induced breakdown spectroscopy

    Teghil, R; De Bonis, A; Galasso, A [Dipartimento di Chimica, Universita della Basilicata, Via N. Sauro 85, 85100 Potenza (Italy); Santagata, A; Albano, G; Villani, P; Spera, D; Parisi, G P [CNR-IMIP, Unita di Potenza, Via S. Loja, 85050 Tito Scalo (Italy)], E-mail:


    In this paper, we report a survey of two of the large number of possible practical applications of the laser ablation performed by an ultra-short pulse laser, namely pulsed laser deposition (PLD) and fs/ns dual-pulse laser-induced breakdown spectroscopy (DP-LIBS). These applications differ from those using just longer pulsed lasers as a consequence of the distinctive characteristics of the plasma produced by ultra-short laser beams. The most important feature of this plasma is the large presence of particles with nanometric size which plays a fundamental role in both applications.

  5. Electron rescattering at metal nanotips induced by ultrashort laser pulses

    Wachter, Georg; Burgdörfer, Joachim; Schenk, Markus; Krüger, Michael; Hommelhoff, Peter


    We report on the first investigation of plateau and cut-off structures in photoelectron spectra from nano-scale metal tips interacting with few-cycle near-infrared laser pulses. These hallmarks of electron rescattering, well-known from atom-laser interaction in the strong-field regime, appear at remarkably low laser intensities with nominal Keldysh parameters of the order of $\\gtrsim 10$. Quantum and quasi-classical simulations reveal that a large field enhancement near the tip and the increased backscattering probability at a solid-state target play a key role. Plateau electrons are by an order of magnitude more abundant than in comparable atomic spectra, reflecting the high density of target atoms at the surface. The position of the cut-off serves as an in-situ probe for the locally enhanced electric field at the tip apex.

  6. Interaction of ultra-short laser pulses with CIGS and CZTSe thin films

    Gečys, P.; Markauskas, E.; Dudutis, J.; Račiukaitis, G.


    The thin-film solar cell technologies based on complex quaternary chalcopyrite and kesterite materials are becoming more attractive due to their potential for low production costs and optimal spectral performance. As in all thin-film technologies, high efficiency of small cells might be maintained with the transition to larger areas when small segments are interconnected in series to reduce photocurrent and related ohmic losses in thin films. Interconnect formation is based on the three scribing steps, and the use of a laser is here crucial for performance of the device. We present our simulation and experimental results on the ablation process investigations in complex CuIn1- x Ga x Se2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTSe) cell's films using ultra-short pulsed infrared (~1 μm) lasers which can be applied to the damage-free front-side scribing processes. Two types of processes were investigated—direct laser ablation of ZnO:Al/CIGS films with a variable pulse duration of a femtosecond laser and the laser-induced material removal with a picosecond laser in the ZnO:Al/CZTSe structure. It has been found that the pulse energy and the number of laser pulses have a significantly stronger effect on the ablation quality in ZnO:Al/CIGS thin films rather than the laser pulse duration. For the thin-film scribing applications, it is very important to carefully select the processing parameters and use of ultra-short femtosecond pulses does not have a significant advantage compared to picosecond laser pulses. Investigations with the ZnO:Al/CZTSe thin films showed that process of the absorber layer removal was triggered by a micro-explosive effect induced by high pressure of sublimated material due to a rapid temperature increase at the molybdenum-CZTSe interface.

  7. Interaction of ultrashort pulses with molecules and solids: Physics and applications

    S Venugopal Rao


    The interaction of ultrashort laser pulses with molecules and solids is an extremely complex area of science research encompassing the fields of physics, chemistry, and materials science. The physics of interaction has been fairly understood over the last couple of decades and, consequently, several applications have been envisaged from these interactions in the fields of photonics, lithography, biomedicine, sensing, telecommunications etc. In the present article we describe three different components of interaction of ultrashort pulses with matter: (1) with liquid molecules/thin films wherein we present the results from our studies of optical nonlinearities predominantly using picosecond and femtosecond pulses, (2) with molecules/solids wherein plasma generated from the surface was studied for applications in understanding the molecular dynamics and towards identifying high-energy molecules and (3) within the bulk and on the surface of solids (e.g. glasses, bulk polymers and metals) resulting in micro- and nanostructures. Different applications resulting from such interactions in photonics and microfluidics are presented and discussed.

  8. Micro drilling using deformable mirror for beam shaping of ultra-short laser pulses

    Smarra, Marco; Strube, Anja; Dickmann, Klaus


    Using ultra-short laser pulses for micro structuring or drilling applications reduces the thermal influence to the surrounding material. The best achievable beam profile equals a Gaussian beam. Drilling with this beam profile results in cylindrical holes. To vary the shape of the holes, the beam can either be scanned or - for single pulse and percussion drilling - manipulated by masks or lenses. A high flexible method for beam shaping can be realized by using a deformable mirror. This mirror contains a piezo-electric ceramic, which can be deformed by an electric potential. By separating the ceramic into independent controllable segments, the shape of the surface can be varied individually. Due to the closed surface of the mirror, there is no loss of intensity due to diffraction. The mirror deformation is controlled by Zernike polynomials and results e.g. in a lens behavior. In this study a deformable mirror was used to generate e.g. slits in thin steel foils by percussion drilling using ultra-short laser pulses. The influence of the cylindrical deformation to the laser beam and the resulting geometry of the generated holes was studied. It was demonstrated that due to the high update rate up to 150 Hz the mirror surface can be varied in each scan cycle, which results in a high flexible drilling process.

  9. Ultra-short laser pulses in dentistry: a solution toward painless dental treatment?

    Wieger, V.; Yousif, A.; Strassl, M.; Wintner, E.


    Within the last years, modern ultra-short pulse lasers have successfully proven their potential for application in medical tissue treatment in many respects. In dentistry, overheating of the pulp and induction of micro cracks are usually among the most problematic issues which can be solved in this way. An additional benefit can be seen in the possibility of plasma emission spectroscopy as a means of feedback. Up till now it was shown by many authors that the application of picosecond or femtosecond pulses allows to perform ablation with very low damaging potential also fitting to the special physiological requirements. Beside the short interaction time with the irradiated biological matter, lateral scanning of ultra-short pulses following optimized algorithms turned out to be crucial for ablating cavities with the required quality and size, a finding which we also believe to be valid for dental restoration materials. Additionally, out of practical reasons, scanning is necessary to treat larger volumes than just the focal spots typically having dimensions on the order of more than 1 mm 3, thereby allowing to realize an "optical drill".

  10. Heat-induced structure formation in metal films generated by single ultrashort laser pulses

    Koch, Jürgen; Unger, Claudia; Chichkov, Boris N.


    Ultrashort pulsed lasers are increasingly used in micromachining applications. Their short pulse lengths lead to well defined thresholds for the onset of material ablation and to the formation of only very small heat affected zones, which can be practically neglected in the majority of cases. Structure sizes down to the sub-micron range are possible in almost all materials - including heat sensitive materials. Ultrashort pulse laser ablation - even though called "cold ablation" - in fact is a heat driven process. Ablation takes place after a strong and fast temperature increase carrying away most of the heat with the ablated particles. This type of heat convection is not possible when reducing the laser fluence slightly below the ablation threshold. In this case temperature decreases slower giving rise to heat-induced material deformations and melt dynamics. After cooling down protruding structures can remain - ablation-free laser surface structuring is possible. Structure formation is boosted on thin metal films and offers best reproducibility and broadest processing windows for metals with high ductility and weak electron phonon coupling strength. All approaches to understand the process formation are currently based only on images of the final structures. The pump-probe imaging investigations presented here lead to a better process understanding.

  11. Prospects for a novel ultrashort pulsed laser technology for pathogen inactivation

    Tsen Shaw-Wei D


    Full Text Available Abstract The threat of emerging pathogens and microbial drug resistance has spurred tremendous efforts to develop new and more effective antimicrobial strategies. Recently, a novel ultrashort pulsed (USP laser technology has been developed that enables efficient and chemical-free inactivation of a wide spectrum of viral and bacterial pathogens. Such a technology circumvents the need to introduce potentially toxic chemicals and could permit safe and environmentally friendly pathogen reduction, with a multitude of possible applications including the sterilization of pharmaceuticals and blood products, and the generation of attenuated or inactivated vaccines.

  12. Spatio-temporal light springs: extended encoding of orbital angular momentum in ultrashort pulses.

    Pariente, G; Quéré, F


    We introduce a new class of spatio-temporally coupled ultrashort laser beams, which are obtained by superimposing Laguerre-Gauss beams whose azimuthal mode index is correlated to their frequency. These beams are characterized by helical structures for their phase and intensity profiles, which both encode the orbital angular momentum carried by the light. They can easily be engineered in the optical range, and are naturally produced at shorter wavelengths when attosecond pulses are generated by intense femtosecond Laguerre-Gauss laser beams. These spatio-temporal "light springs" will allow for the transfer of the orbital angular momentum to matter by stimulated Raman scattering.

  13. Printed organic smart devices characterized by ultra-short laser pulses

    Pastorelli, Francesco

    Resume: In this study, we demonstrate that nonlinear optical microscopy is a promising technique to characterize organic printed electronics. Using ultrashort laser pulses we stimulate two-photon absorption in a roll coated polymer semiconductor and map the resulting two-photon induced...... propose that the TPPL is a good indicator to map and monitor the charge carrier density and the molecular packing of the printed polymer material. Importantly, simple calculations based on the signal levels, suggest that this technique can be extended to the real time mapping of the polymer semiconductor...... film, even during the printing process, in which the high printing speed poses the need for equally high acquisition rates....

  14. Experimental and Analytical Investigation of Cemented Tungsten Carbide Ultra-Short Pulse Laser Ablation

    Urbina, J. P. Calderón; Daniel, C.; Emmelmann, C.

    Ultra-short pulse laser processing of hard materials, such as cemented tungsten carbide, requires an accurate and agile experimental and analytical investigation to obtain adequate information and setting parameters to maximize ablation rate. Therefore, this study presents a systematic approach which, first, experimentally searches for the variables with the most significant influence on the objective using a design of experiments method; and second, analyzes by means of existing ablation theory the interaction of the material and laser taking into account the Beer-Lambert law and incubation effect.Therefore, this places a basis for future analytical-experimental validation of the examined material.

  15. Heat accumulation in ultra-short pulsed scanning laser ablation of metals.

    Bauer, Franziska; Michalowski, Andreas; Kiedrowski, Thomas; Nolte, Stefan


    High average laser powers can have a serious adverse impact on the ablation quality in ultra-short pulsed laser material processing of metals. With respect to the scanning speed, a sharp transition between a smooth, reflective and an uneven, dark ablated surface is observed. Investigating the influence of the sample temperature, it is experimentally shown that this effect stems from heat accumulation. In a numerical heat flow simulation, the critical scanning speed indicating the change in ablation quality is determined in good agreement with the experimental data.

  16. In situ imaging of hole shape evolution in ultrashort pulse laser drilling.

    Döring, Sven; Richter, Sören; Nolte, Stefan; Tünnermann, Andreas


    For the first time, in situ the hole shape evolution during ultrashort pulse laser drilling in semiconductor material is imaged. The trans-illumination of the sample at a wavelength of 1.06 µm is projected onto a standard CCD camera during the ablation, providing an image of the contour of the ablated structure perpendicular to the irradiation for drilling. This demonstrated technique enables a direct, high resolution investigation of the temporal evolution of the drilling process in the depth of the material without complex sample preparation or post processing.

  17. A novel generation scheme of ultra-short pulse trains with multiple wavelengths

    Su, Yulong; Hu, Hui; Feng, Huan; Li, Lu; Han, Biao; Wen, Yu; Wang, Yishan; Si, Jinhai; Xie, Xiaoping; Wang, Weiqiang


    We demonstrate a novel scheme based on active mode locking combined with four-wave mixing (FWM) to generate ultra-short pulse trains at high repetition rate with multiple wavelengths for applications in various fields. The obtained six wavelengths display high uniformity both in temporal and frequency domain. Pulses at each wavelength are mode locked with pulse duration of 44.37 ps, signal-to-noise ratio (SNR) of 47.89 dB, root-mean-square (RMS) timing jitter of 552.7 fs, and the time-bandwidth product of 0.68 at repetition rate of 1 GHz. The experimental results show this scheme has promising usage in optical communications, optical networks, and fiber sensing.

  18. Energy Squeeze of Ultrashort Light Pulse by Kerr Nonlinear Photonic Crystals

    LIU Ye; ZHOU Fei; ZHANG Dao-Zhong; LI Zhi-Yuan


    Self-phase modulation can efficiently shape the spectrum of an optical pulse propagating along an optical material with Kerr nonlinearity. In this work we show that a one-dimensional Kerr nonlinear photonic crystal can impose anomalous spectrum modulation to a high-power ultrashort light pulse. The spectrum component at the photonic band gap edge can be one order of magnitude enhanced in addition to the ordinary spectrum broadening due to self-phase modulation. The enhancement is strictly pinned at the band gap edge by changing the sample length, the intensity or central wavelength of the incident pulse. The phenomenon is attributed to band gap induced enhancement of light-matter interaction.

  19. Microcavity design for low threshold polariton condensation with ultrashort optical pulse excitation

    Poellmann, C; Galopin, E; Lemaître, A; Amo, A; Bloch, J; Huber, R; Ménard, J -M


    We present a microcavity structure with a shifted photonic stop-band to enable efficient non-resonant injection of a polariton condensate with spectrally broad femtosecond pulses. The concept is demonstrated theoretically and confirmed experimentally for a planar GaAs/AlGaAs multilayer heterostructure pumped with ultrashort near-infrared pulses while photoluminescence is collected to monitor the optically injected polariton density. As the excitation wavelength is scanned, a regime of polariton condensation can be reached in our structure at a consistently lower fluence threshold than in a state-of-the-art conventional microcavity. Our microcavity design improves the polariton injection efficiency by a factor of 4, as compared to a conventional microcavity design, when broad excitation pulses are centered at a wavelength of 740 nm. Most remarkably, this improvement factor reaches 270 when the excitation wavelength is centered at 750 nm.

  20. Temporal and Spectral Resolved Measurement of Soft X-ray From Ultrashort Pulse Laser Produced Plasma

    W.Theobald; L.Veisz; H.Schwoerer; R.Sauerbrey; X.Z.Tang


    Ultrashort laser pulse produced plasmas are powerful sources of incoherent XUV/soft X-ray radiation and have important applications range from microscopy to lithography. Adding a prepulse is one possible way to enhance soft X-ray emission. The experiment is performed on the Jena 10 TW laser system in IOQ, Germany. The main purpose is to measure the time-resolved soft X-ray spectrum, and study how a prepulse play an important role and enhance the X-ray emission as well as and pulse duration. We clarified the temporal behavior of X-ray emission from quartz plasma produced by intensive femtosecond 800 nm laser pulse, and obtained a quantitative pictures of the

  1. Robust signatures of quantum radiation reaction in focused ultrashort laser pulses.

    Li, Jian-Xing; Hatsagortsyan, Karen Z; Keitel, Christoph H


    Radiation-reaction effects in the interaction of an electron bunch with a superstrong focused ultrashort laser pulse are investigated in the quantum radiation-dominated regime. The angle-resolved Compton scattering spectra are calculated in laser pulses of variable duration using a semiclassical description for the radiation-dominated dynamics and a full quantum treatment for the emitted radiation. In dependence of the laser-pulse duration we find signatures of quantum radiation reaction in the radiation spectra, which are characteristic for the focused laser beam and visible in the qualitative behavior of both the angular spread and the spectral bandwidth of the radiation spectra. The signatures are robust with respect to the variation of the electron and laser-beam parameters in a large range. Qualitatively, they differ fully from those in the classical radiation-reaction regime and are measurable with presently available laser technology.

  2. An Experimental Study of Ultrashort Pulsed Ytterbium-Doped Fibre Laser and Amplifier

    YANG Ling-Zhen; XIONG Hong-Jun; CHEN Guo-Fu; WANG Yi-Shan; ZHAO Wei; CHENG Zhao


    @@ We report the generation of ultrashort pulses in ytterbium-doped fibre oscillator emitting around 1.05μm at a repetition rate of 17.6MHz. A diode laser with single silica fibre at 976nm pumps the ytterbium fibre laser, the aH-fibre picosecond pulsed oscillator has excellent stability and compact size, and freedom from misalignment. After amplifying, pulse energy of 3.4 nj and an average power of 60 mW are obtained. The compression is obtained with a grating pair out of the cavity. The compressor produces 307fs with the peak power 5.47kW. A practical fibre-based source with good performance is thus demonstrated.

  3. Carrier-envelope phase effects for a dipolar molecule interacting with ultrashort laser pulse

    Zhao Ke; Li Hong-Yu; Liu Ji-Cai; Wang Chuan-Kui


    In this paper the phase-dependent features of ultrashort laser pulse resonant propagation in a two-level dipolar molecule are demonstrated by solving full Maxwell-Bloch equations. The electronic properties of dipolar molecule 4-trans-[p-(N, N-Di-n-butylamino)-p -stilbenylvinyl] pyridine (DBASVP) molecule, one-dimensional asymmetric organic molecule, is calculated by density functional theory at ab initio level. The numerical results show that the carrier propagation and the spectrum evolution of the pulse are sensitive to its initial phase and the phase sensitivity is more obvious for larger area pulse. The phase-dependent feature is more evident in dipolar molecule because the permanent dipole moment makes the nonlinear effects stronger.

  4. Complex {PT}-symmetric extensions of the nonlinear ultra-short light pulse model

    Yan, Zhenya


    The short pulse equation u_{xt}=u+\\frac{1}{2}(u^2u_x)_x is PT symmetric, which arises in nonlinear optics for the ultra-short pulse case. We present a family of new complex PT-symmetric extensions of the short pulse equation, i[(iu_x)^{\\sigma }]_t=au+bu^m+ic[u^n(iu_x)^{\\epsilon }]_x \\,\\, (\\sigma ,\\, \\epsilon ,\\,a,\\,b,\\,c,\\,m,\\,n \\in {R}), based on the complex PT-symmetric extension principle. Some properties of these equations with some chosen parameters are studied including the Hamiltonian structures and exact solutions such as solitary wave solutions, doubly periodic wave solutions and compacton solutions. Our results may be useful to understand complex PT-symmetric nonlinear physical models. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Quantum physics with non-Hermitian operators’.

  5. Nonlinear Dynamics of Ultrashort Long-Range Surface Plasmon Polariton Pulses in Gold Strip Waveguides

    Lysenko, Oleg; Bache, Morten; Olivier, Nicolas


    We study experimentally and theoretically nonlinear propagation of ultrashort long-range surface plasmon polaritons in gold strip waveguides. The nonlinear absorption of the plasmonic modes in the waveguides is measured with femtosecond pulses revealing a strong dependence of the third......-order nonlinear susceptibility of the gold core on the pulse duration and layer thickness. A comprehensive model for the pulse duration dependence of the third-order nonlinear susceptibility is developed on the basis of the nonlinear Schrödinger equation for plasmonic mode propagation in the waveguides....... The model accounts for the intrinsic delayed (noninstantaneous) nonlinearity of free electrons of gold as well as the thickness of the gold film and is experimentally verified. The obtained results are important for the development of active plasmonic and nanophotonic components....

  6. Extraction of enhanced, ultrashort laser pulses from a passive 10-MHz stack-and-dump cavity

    Breitkopf, Sven; Wunderlich, Stefano; Eidam, Tino; Shestaev, Evgeny; Holzberger, Simon; Gottschall, Thomas; Carstens, Henning; Tünnermann, Andreas; Pupeza, Ioachim; Limpert, Jens


    Periodic dumping of ultrashort laser pulses from a passive multi-MHz repetition-rate enhancement cavity is a promising route towards multi-kHz repetition-rate pulses with Joule-level energies at an unparalleled average power. Here, we demonstrate this so-called stack-and-dump scheme with a 30-m-long cavity. Using an acousto-optic modulator, we extract pulses of 0.16 mJ at 30-kHz repetition rate, corresponding to 65 stacked input pulses, representing an improvement in three orders of magnitude over previously extracted pulse energies. The ten times longer cavity affords three essential benefits over former approaches. First, the time between subsequent pulses is increased to 100 ns, relaxing the requirements on the switch. Second, it allows for the stacking of strongly stretched pulses (here from 800 fs to 1.5 ns), thus mitigating nonlinear effects in the cavity optics. Third, the choice of a long cavity offers increased design flexibility with regard to thermal robustness, which will be crucial for future power scaling. The herein presented results constitute a necessary step towards stack-and-dump systems providing access to unprecedented laser parameter regimes.

  7. High-energy ultra-short pulse thin-disk lasers: new developments and applications

    Michel, Knut; Klingebiel, Sandro; Schultze, Marcel; Tesseit, Catherine Y.; Bessing, Robert; Häfner, Matthias; Prinz, Stefan; Sutter, Dirk; Metzger, Thomas


    We report on the latest developments at TRUMPF Scientific Lasers in the field of ultra-short pulse lasers with highest output energies and powers. All systems are based on the mature and industrialized thin-disk technology of TRUMPF. Thin Yb:YAG disks provide a reliable and efficient solution for power and energy scaling to Joule- and kW-class picosecond laser systems. Due to its efficient one dimensional heat removal, the thin-disk exhibits low distortions and thermal lensing even when pumped under extremely high pump power densities of 10kW/cm². Currently TRUMPF Scientific Lasers develops regenerative amplifiers with highest average powers, optical parametric amplifiers and synchronization schemes. The first few-ps kHz multi-mJ thin-disk regenerative amplifier based on the TRUMPF thindisk technology was developed at the LMU Munich in 20081. Since the average power and energy have continuously been increased, reaching more than 300W (10kHz repetition rate) and 200mJ (1kHz repetition rate) at pulse durations below 2ps. First experiments have shown that the current thin-disk technology supports ultra-short pulse laser solutions >1kW of average power. Based on few-picosecond thin-disk regenerative amplifiers few-cycle optical parametric chirped pulse amplifiers (OPCPA) can be realized. These systems have proven to be the only method for scaling few-cycle pulses to the multi-mJ energy level. OPA based few-cycle systems will allow for many applications such as attosecond spectroscopy, THz spectroscopy and imaging, laser wake field acceleration, table-top few-fs accelerators and laser-driven coherent X-ray undulator sources. Furthermore, high-energy picosecond sources can directly be used for a variety of applications such as X-ray generation or in atmospheric research.

  8. Fast Prototyping of Sensorized Cell Culture Chips and Microfluidic Systems with Ultrashort Laser Pulses

    Sebastian M. Bonk


    Full Text Available We developed a confined microfluidic cell culture system with a bottom plate made of a microscopic slide with planar platinum sensors for the measurement of acidification, oxygen consumption, and cell adhesion. The slides were commercial slides with indium tin oxide (ITO plating or were prepared from platinum sputtering (100 nm onto a 10-nm titanium adhesion layer. Direct processing of the sensor structures (approximately three minutes per chip by an ultrashort pulse laser facilitated the production of the prototypes. pH-sensitive areas were produced by the sputtering of 60-nm Si3N4 through a simple mask made from a circuit board material. The system body and polydimethylsiloxane (PDMS molding forms for the microfluidic structures were manufactured by micromilling using a printed circuit board (PCB milling machine for circuit boards. The microfluidic structure was finally imprinted in PDMS. Our approach avoided the use of photolithographic techniques and enabled fast and cost-efficient prototyping of the systems. Alternatively, the direct production of metallic, ceramic or polymeric molding tools was tested. The use of ultrashort pulse lasers improved the precision of the structures and avoided any contact of the final structures with toxic chemicals and possible adverse effects for the cell culture in lab-on-a-chip systems.

  9. Fabrication of Nb/Pb structures through ultrashort pulsed laser deposition

    Gontad, Francisco; Lorusso, Antonella, E-mail:; Perrone, Alessio [Dipartimento di Matematica e Fisica “E. De Giorgi,” Università del Salento and Istituto Nazionale di Fisica Nucleare, 73100 Lecce (Italy); Klini, Argyro; Fotakis, Costas [Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology-Hellas (FORTH), 100 N. Plastira St., GR 70013 Heraklion, Crete (Greece); Broitman, Esteban [Thin Film Physics Division, IFM, Linköping University, 581-83 Linköping (Sweden)


    This work reports the fabrication of Nb/Pb structures with an application as photocathode devices. The use of relatively low energy densities for the ablation of Nb with ultrashort pulses favors the reduction of droplets during the growth of the film. However, the use of laser fluences in this ablation regime results in a consequent reduction in the average deposition rate. On the other hand, despite the low deposition rate, the films present a superior adherence to the substrate and an excellent coverage of the irregular substrate surface, avoiding the appearance of voids or discontinuities on the film surface. Moreover, the low energy densities used for the ablation favor the growth of nanocrystalline films with a similar crystalline structure to the bulk material. Therefore, the use of low ablation energy densities with ultrashort pulses for the deposition of the Nb thin films allows the growth of very adherent and nanocrystalline films with adequate properties for the fabrication of Nb/Pb structures to be included in superconducting radiofrequency cavities.

  10. Modifying molecular scattering from rough solid surfaces using ultrashort laser pulses

    Khodorkovsky, Yuri; Averbukh, Ilya Sh


    We consider solid surface scattering of molecules that were subject to strong non-resonant ultrashort laser pulses just before hitting the surface. The pulses modify the rotational states of the molecules, causing their field free alignment, or a rotation with a preferred sense. We show that field-free laser-induced molecular alignment leads to correlations between the scattering angle and the sense of rotation of the scattered molecules. Moreover, by controlling the sense of laser induced unidirectional molecular rotation, one may affect the scattering angle of the molecules. This provides a new means for separation of mixtures of molecules (such as isotopes and nuclear-spin isomers) by laser controlled surface scattering.

  11. Hydrodynamic model for ultra-short pulse ablation of hard dental tissue

    London, R.A.; Bailey, D.S.; Young, D.A.; Alley, W.E.; Feit, M.D.; Rubenchik, A.M. [Lawrence Livermore National Lab., CA (United States); Neev, J. [Beckman Laser Inst., Irvine, CA (United States)


    A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 fsec and intensity greater than 10{sup 12} W/cm{sup 2} are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.

  12. Crack-free conditions in welding of glass by ultrashort laser pulse.

    Miyamoto, Isamu; Cvecek, Kristian; Schmidt, Michael


    The spatial distribution of the laser energy absorbed by nonlinear absorption process in bulk glass w(z) is determined and thermal cycles due to the successive ultrashort laser pulse (USLP) is simulated using w(z) based on the transient thermal conduction model. The thermal stress produced in internal melting of bulk glass by USLP is qualitatively analyzed based on a simple thermal stress model, and crack-free conditions are studied in glass having large coefficient of thermal expansion. In heating process, cracks are prevented when the laser pulse impinges into glass with temperatures higher than the softening temperature of glass. In cooling process, shrinkage stress is suppressed to prevent cracks, because the embedded molten pool produced by nonlinear absorption process behaves like an elastic body under the compressive stress field unlike the case of CW-laser welding where the molten pool having a free surface produced by linear absorption process is plastically deformed under the compressive stress field.

  13. Magnetic resonance imaging of the Achilles tendon using ultrashort TE (UTE) pulse sequences

    Robson, M.D.; Benjamin, M.; Gishen, P.; Bydder, G.M. E-mail:


    AIM: To assess the potential value of imaging the Achilles tendon with ultrashort echo time (UTE) pulse sequences. MATERIALS AND METHODS: Four normal controls and four patients with chronic Achilles tendinopathy were examined in the sagittal and transverse planes. Three of the patients were examined before and after intravenous gadodiamide. RESULTS: The fascicular pattern was clearly demonstrated within the tendon and detail of the three distinct fibrocartilaginous components of an 'enthesis organ' was well seen. T2* measurements showed two short T2* components. Increase in long T2 components with reduction in short T2 components was seen in tendinopathy. Contrast enhancement was much more extensive than with conventional sequences in two cases of tendinopathy but in a third case, there was a region of reduced enhancement. CONCLUSION: UTE pulse sequences provide anatomical detail not apparent with conventional sequences, demonstrate differences in T2* and show patterns of both increased and decreased enhancement in tendinopathy.

  14. Shock wave acceleration of protons in inhomogeneous plasma interacting with ultrashort intense laser pulses

    Lecz, Zs. [ELI-ALPS, ELI-HU Nkft., Szeged (Hungary); Andreev, A. [ELI-ALPS, ELI-HU Nkft., Szeged (Hungary); Max-Born Institute, Berlin (Germany)


    The acceleration of protons, triggered by solitary waves in expanded solid targets is investigated using particle-in-cell simulations. The near-critical density plasma is irradiated by ultrashort high power laser pulses, which generate the solitary wave. The transformation of this soliton into a shock wave during propagation in plasma with exponentially decreasing density profile is described analytically, which allows to obtain a scaling law for the proton energy. The high quality proton bunch with small energy spread is produced by reflection from the shock-front. According to the 2D simulations, the mechanism is stable only if the laser pulse duration is shorter than the characteristic development time of the parasitic Weibel instability.

  15. Electron-lattice kinetics of metals heated by ultrashort laser pulses

    Falkovsky, L. A.; Mishchenko, E. G.


    We propose a kinetic model of transient nonequilibrium phenomena in metals exposed to ultrashort laser pulses when heated electrons affect the lattice through direct electron-phonon interaction. This model describes the destruction of a metal under intense laser pumping. We derive the system of equations for the metal, which consists of hot electrons and a cold lattice. Hot electrons are described with the help of the Boltzmann equation and equation of thermoconductivity. We use the equations of motion for lattice displacements with the electron force included. The lattice deformation is estimated immediately after the laser pulse up to the time of electron temperature relaxation. An estimate shows that the ablation regime can be achieved.

  16. Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses.

    Taira, Y; Toyokawa, H; Kuroda, R; Yamamoto, N; Adachi, M; Tanaka, S; Katoh, M


    High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90° collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF2 scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF2 scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured.

  17. Industrial grade fiber-coupled laser systems delivering ultrashort high-power pulses for micromachining

    Pricking, Sebastian; Welp, Petra; Overbuschmann, Johannes; Nutsch, Sebastian; Gebs, Raphael; Fleischhaker, Robert; Kleinbauer, Jochen; Wolf, Martin; Budnicki, Aleksander; Sutter, Dirk H.; Killi, Alexander; Mielke, Michael


    We report on an industrial fiber-delivered laser system producing ultra-short pulses in the range of a few picoseconds down to a few hundred femtoseconds with high average power suitable for high-precision micromachining. The delivery fiber is a hollow-core photonic crystal fiber with a Kagomé shaped lattice and a hypocycloid core wall enabling the guiding of laser radiation over several meters with exceptionally low losses and preservation of high beam quality (M2laser head providing a compact footprint without the need for external boxes. The laser head is carefully designed regarding its thermo-mechanical properties to allow a highly reliable coupling stability. The exchangeable delivery fiber is packaged using Trumpf's well established LLK-D connectors which offer a very high mechanical precision, the possibility to add water cooling, as well as full featured safety functions. The fiber is hermetically sealed and protected by a robust but flexible shield providing bend protection and break detection. We show the linear and nonlinear optical properties of the transported laser radiation and discuss its feasibility for pulse compression. Measurements are supported by simulation of pulse propagation by solving the nonlinear Schrödinger equation implementing the split-step Fourier method. In addition, mode properties are measured and confirmed by finite element method simulations. The presented industrial laser system offers the known advantages of ultra-short pulses combined with the flexibility of fiber delivery yielding a versatile tool perfectly suitable for all kinds of industrial micromachining applications.

  18. Increasing efficiency of two-photon excited fluorescence and second harmonic generation using ultrashort pulses

    Tang, Shuo; Krasieva, Tatiana B.; Chen, Zhongping; Tempea, Gabriel; Tromberg, Bruce J.


    Multiphoton microscopy (MPM) has become an important tool for high-resolution and non-invasive imaging in biological tissues. However, the efficiencies of two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) are relatively low because of their nonlinear nature. Therefore, it is critical to optimize laser parameters for most efficient excitation of MPM. Reducing the pulse duration can increase the peak intensity of excitation and thus potentially increase the excitation efficiency. In this paper, a multiphoton microscopy system using a 12 fs Ti:Sapphire laser is reported. With adjustable dispersion pre-compensation, the pulse duration at the sample location can be varied from 400 fs to sub-20 fs. The efficiencies of TPEF and SHG are studied for the various pulse durations, respectively. Both TPEF and SHG are found to increase proportionally to the inverse of the pulse duration for the entire tested range. To transmit most of the SHG and TPEF signals, the spectral transmission widow of the detection optics needs to be carefully considered. Limitation from phase-matching in SHG generation is not significant because the effective interaction length for SHG is less than 10 μm at the focal depth of the objectives. These results are important in improving MPM excitation efficiency using ultrashort pulses. MPM images from human artery wall are also demonstrated.

  19. High-throughput machining using high average power ultrashort pulse lasers and ultrafast polygon scanner

    Schille, Joerg; Schneider, Lutz; Streek, André; Kloetzer, Sascha; Loeschner, Udo


    In this paper, high-throughput ultrashort pulse laser machining is investigated on various industrial grade metals (Aluminium, Copper, Stainless steel) and Al2O3 ceramic at unprecedented processing speeds. This is achieved by using a high pulse repetition frequency picosecond laser with maximum average output power of 270 W in conjunction with a unique, in-house developed two-axis polygon scanner. Initially, different concepts of polygon scanners are engineered and tested to find out the optimal architecture for ultrafast and precision laser beam scanning. Remarkable 1,000 m/s scan speed is achieved on the substrate, and thanks to the resulting low pulse overlap, thermal accumulation and plasma absorption effects are avoided at up to 20 MHz pulse repetition frequencies. In order to identify optimum processing conditions for efficient high-average power laser machining, the depths of cavities produced under varied parameter settings are analyzed and, from the results obtained, the characteristic removal values are specified. The maximum removal rate is achieved as high as 27.8 mm3/min for Aluminium, 21.4 mm3/min for Copper, 15.3 mm3/min for Stainless steel and 129.1 mm3/min for Al2O3 when full available laser power is irradiated at optimum pulse repetition frequency.

  20. Internal modification of glass by ultrashort laser pulse and its application to microwelding

    Miyamoto, Isamu; Cvecek, Kristian; Okamoto, Yasuhiro; Schmidt, Michael


    Internal modification process of glass by ultrashort laser pulse (USLP) and its applications to microwelding of glass are presented. A simulation model is developed, which can determine intensity distribution of absorbed laser energy, nonlinear absorptivity and temperature distribution at different pulse repetition rates and pulse energies in internal modification of bulk glass with fs- and ps-laser pulses from experimental modified structure. The formation process of the dual-structured internal modification is clarified, which consists of a teardrop-shaped inner structure and an elliptical outer structure, corresponding to the laser-absorbing region and heat-affected molten region, respectively. Nonlinear absorptivity at high pulse repetition rates increases due to the increase in the thermally excited free electron density for avalanche ionization. USLP enables crack-free welding of glass because the shrinkage stress is suppressed by producing embedded molten pool by nonlinear absorption process, in contrast to conventional continuous wave laser welding where cracks cannot be avoided due to shrinkage stress produced in cooling process. Microwelding techniques of glass by USLP have been developed to join glass/glass and Si/glass using optically contacted sample pairs. The strength of the weld joint as high as that of base material is obtained without pre- and post-heating in glass/glass welding. In Si/glass welding, excellent joint performances competitive with anodic bonding in terms of joint strength and process throughput have been attained.

  1. Carrier Envelope Phase Controlled High-Order Harmonic Generation in Ultrashort Laser Pulse

    WANG Bing-Bing; CHEN Jing; LIU Jie; LI Xiao-Feng; FU Pan-Ming


    @@ We investigate the carrier envelope phase (CEP) effects on high-order harmonic generation (HHG) in ultrashort pulses with the pulse duration 2.5fs when the laser intensity is high enough so that the initial state is ionized effectively during the laser pulse but remains about 20% population at the end of the laser pulse. We find that the ionization process of the initial state is very sensitive to the CEP during the laser pulse. The ionization process of the initial state determines the continuum state population and hence influences dramatically the weights of the classical trajectories that contribute to HHG. In such a case we can not predict the cutoff and the structure of the harmonic spectrum only by the number and the kinetic energy of the classical trajectories. The harmonic spectrum exhibits abundant characters for different CEP cases. As a result, we can control the cutoff frequency and the plateau structure of the harmonic spectrum with CEP by controlling the time behaviour of the ionization of the initial state.

  2. Generating a New Higher-Dimensional Ultra-Short Pulse System: Lie-Algebra Valued Connection and Hidden Structural Symmetries

    Hermann T. Tchokouansi; Victor K. Kuetche; Abbagari Souleymanou; Thomas B. Bouetou; Timoleon C. Kofane


    We carry out the hidden structural symmetries embedded within a system comprising ultra-short pulses which propagate in optical nonlinear media. Based upon the Wahlquist Estabrook approach, we construct the Lie-algebra valued connections associated to the previous symmetries while deriving their corresponding Lax-pairs, which are particularly useful in soliton theory. In the wake of previous results, we extend the above prolongation scheme to higher-dimensional systems from which a new (2 + l)-dimensional ultra-short pulse equation is unveiled along with its inverse scattering formulation, the application of which are straightforward in nonlinear optics where an additional propagating dimension deserves some attention.%We carry out the hidden structural symmetries embedded within a system comprising ultra-short pulses which propagate in optical nonlinear media.Based upon the Wahlquist Estabrook approach,we construct the Liealgebra valued connections associated to the previous symmetries while deriving their corresponding Lax-pairs,which are particularly useful in soliton theory.In the wake of previous results,we extend the above prolongation scheme to higher-dimensional systems from which a new (2+ 1)-dimensional ultra-short pulse equation is unveiled along with its inverse scattering formulation,the application of which are straightforward in nonlinear optics where an additional propagating dimension deserves some attention.

  3. Absolute phase control of spectra effects in a two-level medium driven by two-color ultrashort laser pulses

    Xia Keyu [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Graduate University of Chinese Academy of Sciences (China); Niu Yueping [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Graduate University of Chinese Academy of Sciences (China); Li Chunfang [Department of Physics, Shanghai University, Shanghai 200436 (China); Gong Shangqing [CCAST (World Laboratory), PO Box 8730, Beijing 100080 (China) and State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China)]. E-mail:


    Using a {omega}-3{omega} combination scenario, we investigate the absolute phase control of the spectra effects for ultrashort laser pulses propagating in a two-level medium. It is found that the higher spectral components can be controlled by the absolute phases. In particular, different absolute phase combinations can lead to the buildup or split of the even harmonics.

  4. Reflectivity of plasmas created by high-intensity, ultra-short laser pulses

    Gold, D.M.


    Experiments were performed to characterize the creation and evolution of high-temperature (T{sub e}{approximately}100eV), high-density (n{sub e}>10{sup 22}cm{sup {minus}3}) plasmas created with intense ({approximately}10{sup 12}-10{sup 16}W/cm{sup 2}), ultra-short (130fs) laser pulses. The principle diagnostic was plasma reflectivity at optical wavelengths (614nm). An array of target materials (Al, Au, Si, SiO{sub 2}) with widely differing electronic properties tested plasma behavior over a large set of initial states. Time-integrated plasma reflectivity was measured as a function of laser intensity. Space- and time-resolved reflectivity, transmission and scatter were measured with a spatial resolution of {approximately}3{mu}m and a temporal resolution of 130fs. An amplified, mode-locked dye laser system was designed to produce {approximately}3.5mJ, {approximately}130fs laser pulses to create and nonintrusively probe the plasmas. Laser prepulse was carefully controlled to suppress preionization and give unambiguous, high-density plasma results. In metals (Al and Au), it is shown analytically that linear and nonlinear inverse Bremsstrahlung absorption, resonance absorption, and vacuum heating explain time-integrated reflectivity at intensities near 10{sup 16}W/cm{sup 2}. In the insulator, SiO{sub 2}, a non-equilibrium plasma reflectivity model using tunneling ionization, Helmholtz equations, and Drude conductivity agrees with time-integrated reflectivity measurements. Moreover, a comparison of ionization and Saha equilibration rates shows that plasma formed by intense, ultra-short pulses can exist with a transient, non-equilibrium distribution of ionization states. All targets are shown to approach a common reflectivity at intensities {approximately}10{sup 16}W/cm{sup 2}, indicating a material-independent state insensitive to atomic or solid-state details.

  5. Complete optical absorption of ultrashort pulses by plasmons in nanostructured graphene (Conference Presentation)

    Martínez Saavedra, José Ramón; Cerullo, Giulio; Pruneri, Valerio; Wall, Simon; García de Abajo, Javier


    The peculiar electronic structure of graphene results in a large optoelectronic response that holds great potential for technology. For example, this material exhibits a nearly constant absorption 2.3% over a broad spectral range [1], which can be electrically modulated in the mid-IR by injecting attainable densities of charge carriers. When doped, graphene can sustain plasmons that radically modify its optical response, enabling complete optical absorption for suitably designed patterns [2]. Graphene nanoribbons constitute one of the simplest geometrical patterns that one can produce. They have been extensively studied and their plasmons accurately explained with simple models [3]. When heated to a large electronic temperature, graphene behaves nearly as if is was highly doped, also giving rise to plasmon modes [4]. In this work, we study the possibility of using ultrashort light pulses together with the natural electronic relaxation mechanisms in graphene nanoribbons as a way to tune their optical response. We first discuss the optically induced plasmons of individual nanoribbons when illuminated with ultrashort pulses and then analyze the evolution of the plasmon frequency as a function of the delay between pump and probe. We study the redshift of these plasmons with increasing delay due to electron relaxation. We also investigate the optical response of the ribbon exposed to a train of optical pulses. We further discuss ribbon arrays illuminated from the substrate under total internal reflection conditions, for which we predict complete absorption for a suitable choice of geometrical and illumination parameters. References [1] F. H. L. Koppens, D. E. Chang, and F. J. García de Abajo, Nano Letters 11, 3370-3377 (2011) [2] S. Thongrattanasiri, F. H. L. Koppens, and F. J. García de Abajo, Phys. Rev. Lett. 108, 047401 (2012) [3] I. Silveiro, J. M. Plaza Ortega, and F. J. García de Abajo, Light: Science and Applications 4, e241 (2015) [4] F. J. García de Abajo

  6. Electron-phonon nonequilibrium during ultrashort pulsed laser heating of metals

    Smith, Andrew Neil


    Ultrashort pulsed lasers have repeatedly been demonstrated as an effective tool for the observation of transport properties on atomistic time and length scales. Accordingly, the number of applications of these types of lasers as diagnostic tools is rapidly increasing. To effectively use these tools, precise knowledge of the energy deposition mechanism is absolutely necessary. The accepted model for ultrashort pulsed laser heating is the ``Two Temperature Model'' which assumes equilibrium electron and phonon distributions that are not in equilibrium with each other. Recently the applicability of the ``Two Temperature Model'' has received some scrutiny for very low and very high intensity application. This model gave rise to the electron-phonon coupling factor, which, when combined with the temperature difference between the two systems, represents the rate of energy transfer for small perturbations in temperature. However, numerous applications use moderate to high intensity ultrashort pulses, which create far more than small perturbations in temperature. In this investigation the temperature dependence of the electron-phonon coupling factor, electron heat capacity, and thermal conductivity are examined for significant changes in the electron temperature. Experimental results are presented for transient thermoreflectance data taken at moderate fluences. A significant discrepancy is apparent between the two temperature model and the experimental data taken on Au. This problem was originally thought to arise from increased electron- phonon coupling for moderate changes in the electron temperature. Investigation into the temperature dependence of the electron-phonon coupling factor did not support this hypothesis. It was discovered that the discrepancy was due to a nonlinear relationship between changes in the electron temperature and changes in reflectance. The incident probe energy used when taking the experimental data was 1.5 eV, which is significantly less than

  7. Influence of the pulse duration and the experimental approach onto the specific removal rate for ultra-short pulses

    Jaeggi, B.; Neuenschwander, B.; Remund, S.; Kramer, T.


    To be competitive in industrial applications the throughput is a key factor in laser micro machining using ultra-short pulsed laser systems. Both, ps and fs laser systems are suitable for industrial applications. Therefore one has to choose the right pulse duration for highest ablation efficiency. As shown in earlier publications the efficiency of the ablation process can be described by the specific removal rate, which has a maximum value at an optimum fluence. But its value often bases on a calculation using the threshold fluence and energy penetration depth deduced by measuring the depth of ablated cavities machined with different fluences and number of pulses. But this calculated specific removal rate often differs from the one deduced from ablated squares as recently shown in literature. Further an unexpected drop of the specific removal rate was reported for stainless steel when the pulse duration was reduced from 900 fs to 400 fs. Thus the influence of the pulse duration in the fs and low ps regime onto the specific removal rate is investigated with different methods for industrial relevant materials

  8. Unexpected Behavior on Nonlinear Tunneling of Chirped Ultrashort Soliton Pulse in Non-Kerr Media with Raman Effect

    Rajan, M. S. Mani


    In this manuscript, the ultrashort soliton pulse propagation through nonlinear tunneling in cubic quintic media is investigated. The effect of chirping on propagation characteristics of the soliton pulse is analytically investigated using similarity transformation. In particular, we investigate the propagation dynamics of ultrashort soliton pulse through dispersion barrier for both chirp and chirp-free soliton. By investigating the obtained soliton solution, we found that chirping has strong influence on soliton dynamics such as pulse compression with amplification. These two important dynamics of chirped soliton in cubic quintic media open new possibilities to improve the solitonic communication system. Moreover, we surprisingly observe that a dispersion well is formed for the chirped case whereas a barrier is formed for the chirp-free case, which has certain applications in the construction of logic gate devices to achieve ultrafast switching.

  9. Radiation from high-intensity ultrashort-laser-pulse and gas-jet magnetized plasma interaction.

    Dorranian, Davoud; Starodubtsev, Mikhail; Kawakami, Hiromichi; Ito, Hiroaki; Yugami, Noboru; Nishida, Yasushi


    Using a gas-jet flow, via the interaction between an ultrashort high-intensity laser pulse and plasma in the presence of a perpendicular external dc magnetic field, the short pulse radiation from a magnetized plasma wakefield has been observed. Different nozzles are used in order to generate different densities and gas profiles. The neutral density of the gas-jet flow measured with a Mach-Zehnder interferometer is found to be proportional to back pressure of the gas jet in the range of 1 to 8 atm. Strength of the applied dc magnetic field varies from 0 to 8 kG at the interaction region. The frequency of the emitted radiation with the pulse width of 200 ps (detection limit) is in the millimeter wave range. Polarization and spatial distributions of the experimental data are measured to be in good agreement with the theory based on the V(p)xB radiation scheme, where V(p) is the phase velocity of the electron plasma wave and B is the steady magnetic field intensity. Characteristics of the radiation are extensively studied as a function of plasma density and magnetic field strength. These experiments should contribute to the development of a new kind of millimeter wavelength radiation source that is tunable in frequency, pulse duration, and intensity.

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

    Samek, Ota [ISAS-Institute for Analytical Sciences, Bunsen-Kirchhoff Str.11, 44139 Dortmund (Germany)]. E-mail:; Kurowski, Andre [ISAS-Institute for Analytical Sciences, Bunsen-Kirchhoff Str.11, 44139 Dortmund (Germany); Kittel, Silke [ISAS-Institute for Analytical Sciences, Bunsen-Kirchhoff Str.11, 44139 Dortmund (Germany); Kukhlevsky, Sergei [Institute of Physics, University of Pecs, Ifjusag u. 6, Pecs 7624 (Hungary); Hergenroeder, Roland [ISAS-Institute for Analytical Sciences, Bunsen-Kirchhoff Str.11, 44139 Dortmund (Germany)


    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.

  11. Blistering of film from substrate after action of ultrashort laser pulse

    Inogamov, N. A.; Zhakhovsky, V. V.; Khokhlov, V. A.; Kuchmizhak, A. A.; Kudryashov, S. I.


    The goal of the paper is to explain experimental results concerning film blistering. Tightly focused diffraction limited ultrashort optical laser pulse illuminates a small spot at a surface of a thin metal film mounted upon a dielectric or semiconductor support (substrate). Film mechanically separates from substrate and form a cupola like bump in a rather narrow range of absorbed fluences. Below this range deformations inside the spot are negligible. While above the range the hole remains in a film in the irradiated spot. The paper presents physical model starting from absorption and two-temperature state and including, first, description of conductive redistribution of absorbed heat, melting, hydrodynamics of strong three-dimensional deformations of a moving film, and, second, freezing of molten metal.

  12. How to optimize ultrashort pulse laser interaction with glass surfaces in cutting regimes?

    Bulgakova, Nadezhda M., E-mail: [HiLASE Centre, Institute of Physics ASCR, Za Radnicí 828, 25241 Dolní Břežany (Czech Republic); Institute of Thermophysics SB RAS, 1 Lavrentyev Ave., Novosibirsk 630090 (Russian Federation); Zhukov, Vladimir P. [Institute of Computational Technologies SB RAS, 6 Lavrentyev Ave., 630090 Novosibirsk (Russian Federation); Novosibirsk State Technical University, 20 Karl Marx Ave., 630073 Novosibirsk (Russian Federation); Collins, Adam R. [NCLA, NUI Galway, Galway (Ireland); Rostohar, Danijela; Derrien, Thibault J.-Y.; Mocek, Tomáš [HiLASE Centre, Institute of Physics ASCR, Za Radnicí 828, 25241 Dolní Břežany (Czech Republic)


    Highlights: • The factors influencing laser micromachining of transparent materials are analyzed. • Important role of ambient gas in laser processing is shown by numerical simulations. • The large potential of bi-wavelength laser processing is demonstrated. - Abstract: The interaction of short and ultrashort pulse laser radiation with glass materials is addressed. Particular attention is paid to regimes which are important in industrial applications such as laser cutting, drilling, functionalization of material surfaces, etc. Different factors influencing the ablation efficiency and quality are summarized and their importance is illustrated experimentally. The effects of ambient gas ionization in front of the irradiated target are also analyzed. A possibility to enhance laser coupling with transparent solids by bi-wavelength irradiation is discussed.

  13. Space-selective growth of frequency-conversion crystals in glasses with ultrashort infrared laser pulses.

    Miura, K; Qiu, J; Mitsuyu, T; Hirao, K


    We report on space-selective growth of a second-harmonic-generation beta-BaB(2)O(4) (BBO) crystal inside a BaO-Al(2)O(3)-B(2)O(3) glass sample at the focal point of an 800-nm femtosecond laser beam. A spherical heated region was formed during the focused laser irradiation through observation with an optical microscope. We moved the heated region by changing the position of the focal point of the laser beam relative to the glass sample. We grew BBO crystal continuously in the glass sample by adjusting the moving speed of the heated zone. Our results demonstrate that functional crystals can be formed three dimensionally in glasses by use of a nonresonant ultrashort pulsed laser.

  14. Reconstruction method of X-mode ultrashort-pulse reflectometry in LHD

    Yokota, Y; Uchino, K [Graduate School of Engineering Sciences, Kyushu University, Kasuga 816-8580 (Japan); Mase, A [Art Science and Technology Center for Cooperative Research, Kyushu University, Kasuga 816-8580 (Japan); Kogi, Y [Fukuoka Institute of Technology, Fukuoka 811-0295 (Japan); Tokuzawa, T; Kawahata, K; Nagayama, Y [National Institute for Fusion Science, Toki 509-5292 (Japan); Hojo, H, E-mail: [Plasma Research Center, University of Tsukuba, Tsukuba 305-8577 (Japan)


    Reflectometry is considered to be one of the key diagnostics to measure density profiles and density fluctuations of fusion oriented plasmas. When an electromagnetic wave is launched into a plasma, the wave is reflected at the corresponding cutoff layer of the ordinary (O) mode or the extraordinary (X) mode. Reflectometry measures the time of flight (TOF) or group delay of the reflected wave. We have applied ultrashort-pulse reflectometry (USPR) to Large Helical Device (LHD) at National Institute for Fusion Science (NIFS). The highspatial analysis method called signal record analysis (SRA) is utilized to reconstruct the density profiles from the TOF signal. Also, it is noted that the remote control system using super science information network (super-SINET) has been introduced to the present USPR system. This remote system is exclusive, and it seems to be quite effective for collaborating experiment of large devices such as ITER.

  15. Theoretical analysis of supercontinuum and colored conical emission produced during ultrashort laser pulse interaction with gases

    Semak, V V


    We use a conceptually new approach to theoretical modeling of self-focusing in which we integrated diffractive and geometrical optics in order to explain and predict emission of white light and colored rings observed in ultrashort laser pulse interaction. In our approach laser beam propagation is described by blending solution of linear Maxwell's equation and a correction term that represents nonlinear field perturbation expressed in terms of paraxial ray-optics (eikonal) equation. No attempt is made to create appearance of exhaustive treatment via use of complex mathematical models. Rather, emphasis is placed on elegance of the formulations leading to fundamental understanding of underlying physics and, eventually, to an accurate practical numerical model capable of simulating white light generation and conical emission of colored rings produced around the filament.

  16. Classical Dynamics of Harmonic Generation of the Hydrogen Molecular Ion Interacting with Ultrashort Intense Laser Pulses

    LI Chao-Hong; DUAN Yi-Wu; Wing-Ki Liu; Jian-Min Yuan


    Within Born-Oppenheimer approximation, by using the classical trajectory theory, a description for the high order harmonic generation of the hydrogen molecular ion interacting with ultrashort laser pulses has been pre sented. The Coulomb singularities have been remedied by the regularization. The action-angle variables have been used to generate the initial inversion symmetry microcanonical distribution. Within a proper intensity range, a harmonic plateau with only odd harmonics appears. For a larger intensity, because of the existence of chaos, the harmonic spectra become noisier. For a large enough intensity, the ionization takes place and the harmonics disappear. So the chaos causes the noises, the ionization suppresses the harmonic generation, and the onset of the ionization follows the onset of chaos.

  17. Crystallographic orientation and induced potential effects in photoelectron emission from metal surfaces by ultrashort laser pulses

    Rubiano, C A Rios; Mitnik, D M; Silkin, V M; Gravielle, M S


    The influence of the crystallographic orientation of a typical metal surface, like aluminum, on electron emission spectra produced by grazing incidence of ultrashort laser pulses is investigated by using the band-structure-based-Volkov (BSB-V) approximation. The present version of the BSB-V approach includes not only a realistic description of the surface interaction, accounting for band structure effects, but also effects due to the induced potential that originates from the collective response of valence-band electrons to the external electromagnetic field. The model is applied to evaluate differential electron emission probabilities from the valence band of Al(100) and Al(111). For both crystallographic orientations, the contribution of partially occupied surface electronic states and the influence of the induced potential are separately analyzed as a function of the laser carrier frequency. We found that the induced potential strongly affects photoelectron emission distributions, opening a window to scrut...

  18. Propagation of an ultrashort, intense laser pulse in a relativistic plasma

    Ritchie, B.; Decker, C.D. [Lawrence Livermore National Lab., CA (United States)


    A Maxwell-relativistic fluid model is developed for the propagation of an ultrashort, intense laser pulse through an underdense plasma. The separability of plasma and optical frequencies ({omega}{sub p} and {omega} respectively) for small {omega}{sub p}/{omega} is not assumed; thus the validity of multiple-scales theory (MST) can be tested. The theory is valid when {omega}{sub p}/{omega} is of order unity or for cases in which {omega}{sub p}/{omega} {much_lt} 1 but strongly relativistic motion causes higher-order plasma harmonics to be generated which overlap the region of the first-order laser harmonic, such that MST would not expected to be valid although its principal validity criterion {omega}{sub p}/{omega} {much_lt} 1 holds.

  19. Upconversion chirped pulse amplification of ultrashort pulses using a multimode Tm:ZBLAN fiber

    Yang, L.M.; Sosnowski, T.; Stock, M.L.; Norris, T.B.; Squier, J.; Mourou, G. [Univ. of Michigan, Ann Arbor, MI (United States). Center for Ultrafast Optical Science; Dennis, M.L.; Duling, I.N. III [Naval Research Lab., Washington, DC (United States)


    Microjoule pulse energies are achieved from a single stage upconversion fiber amplifier for the first time in this demonstration of chirped pulse amplification using a multimode TM:ZBLAN fiber. A Ti:sapphire laser system provides the seed pulse for the upconversion fiber amplifier which produces subpicosecond pulse trains with energies as great as 16 {micro}J at repetition rate of 4.4 kHz. The compressed, pulse peak power is more than 1 MW, and the pulse is characterized both temporally and spatially.

  20. Charge and spin dynamics driven by ultrashort extreme broadband pulses: A theory perspective

    Moskalenko, Andrey S.; Zhu, Zhen-Gang; Berakdar, Jamal


    This article gives an overview on recent theoretical progress in controlling the charge and spin dynamics in low-dimensional electronic systems by means of ultrashort and ultrabroadband electromagnetic pulses. A particular focus is put on sub-cycle and single-cycle pulses and their utilization for coherent control. The discussion is mostly limited to cases where the pulse duration is shorter than the characteristic time scales associated with the involved spectral features of the excitations. The relevant current theoretical knowledge is presented in a coherent, pedagogic manner. We work out that the pulse action amounts in essence to a quantum map between the quantum states of the system at an appropriately chosen time moment during the pulse. The influence of a particular pulse shape on the post-pulse dynamics is reduced to several integral parameters entering the expression for the quantum map. The validity range of this reduction scheme for different strengths of the driving fields is established and discussed for particular nanostructures. Acting with a periodic pulse sequence, it is shown how the system can be steered to and largely maintained in predefined states. The conditions for this nonequilibrium sustainability are worked out by means of geometric phases, which are identified as the appropriate quantities to indicate quasistationarity of periodically driven quantum systems. Demonstrations are presented for the control of the charge, spin, and valley degrees of freedom in nanostructures on picosecond and subpicosecond time scales. The theory is illustrated with several applications to one-dimensional semiconductor quantum wires and superlattices, double quantum dots, semiconductor and graphene quantum rings. In the case of a periodic pulsed driving the influence of the relaxation and decoherence processes is included by utilizing the density matrix approach. The integrated and time-dependent spectra of the light emitted from the driven system deliver

  1. Optical field ionization of atoms and ions using ultrashort laser pulses

    Fittinghoff, D.N.


    This dissertation research is an investigation of the strong optical field ionization of atoms and ions by 120-fs, 614-run laser pulses and 130-fs, 800-nm laser pulses. The experiments have shown ionization that is enhanced above the predictions of sequential tunneling models for He{sup +2}, Ne{sup +2} and Ar{sup +2}. The ion yields for He{sup +l}, Ne{sup +l} and Ar{sup +l} agree well with the theoretical predictions of optical tunneling models. Investigation of the polarization dependence of the ionization indicates that the enhancements are consistent with a nonsequential ionization mechanism in which the linearly polarized field drives the electron wavefunction back toward the ion core and causes double ionization through inelastic e-2e scattering. These investigations have initiated a number of other studies by other groups and are of current scientific interest in the fields of high-irradiance laser-matter interactions and production of high-density plasmas. This work involved: (1) Understanding the characteristic nature of the ion yields produced by tunneling ionization through investigation of analytic solutions for tunneling at optical frequencies. (2) Extensive characterization of the pulses produced by 614-nm and 800-ran ultrashort pulse lasers. Absolute calibration of the irradiance scale produced shows the practicality of the inverse problem--measuring peak laser irradiance using ion yields. (3) Measuring the ion yields for three noble gases using linear, circular and elliptical polarizations of laser pulses at 614-nm and 800-nm. The measurements are some of the first measurements for pulse widths as low as 120-fs.

  2. Human dermis separation via ultra-short pulsed laser plasma-mediated ablation

    Huang Huan; Guo Zhixiong, E-mail: guo@jove.rutgers.ed [Department of Mechanical and Aerospace Engineering, Rutgers, State University of New Jersey, Piscataway, NJ 08854 (United States)


    In vitro layer separation of human dermal tissues via laser plasma-mediated ablation was successfully conducted for the first time. The ablation of wet dermis was generated using a 900 fs ultra-short pulsed laser with the wavelength centred at 1552 nm. The ablation and separation results were imaged and measured by scanning electron microscopy. The dermis ablation threshold was determined as 9.65 {+-} 1.21 J cm{sup -2} and the incubation factor was found as 0.46 {+-} 0.03. Histological examinations were performed to find proper laser parameters for dermis ablation and separation with minimal thermal damage. No thermal damage was found in the single line ablation results when the pulse overlap rate was not over 5 pulses {mu}m{sup -1}. Even in the multi-line ablation, thermal damage was insignificant and the lateral damage zone was generally within 5 {mu}m in the results with 100 continuously repeated line scans. The separation of a whole piece of wet dermal tissue into two thin layers was presented. Several separation tests with different layer thicknesses from 200 to 600 {mu}m were completed. The unevenness of the separated layers was generally under 10%. The cohesion and morphology of the separated tissue layers were not altered.

  3. Phonon-assisted nonlinear optical processes in ultrashort-pulse pumped optical parametric amplifiers

    Isaienko, Oleksandr; Robel, István


    Optically active phonon modes in ferroelectrics such as potassium titanyl phosphate (KTP) and potassium titanyl arsenate (KTA) in the ~7-20 THz range play an important role in applications of these materials in Raman lasing and terahertz wave generation. Previous studies with picosecond pulse excitation demonstrated that the interaction of pump pulses with phonons can lead to efficient stimulated Raman scattering (SRS) accompanying optical parametric oscillation or amplification processes (OPO/OPA), and to efficient polariton-phonon scattering. In this work, we investigate the behavior of infrared OPAs employing KTP or KTA crystals when pumped with ~800-nm ultrashort pulses of duration comparable to the oscillation period of the optical phonons. We demonstrate that under conditions of coherent impulsive Raman excitation of the phonons, when the effective χ(2) nonlinearity cannot be considered instantaneous, the parametrically amplified waves (most notably, signal) undergo significant spectral modulations leading to an overall redshift of the OPA output. The pump intensity dependence of the redshifted OPA output, the temporal evolution of the parametric gain, as well as the pump spectral modulations suggest the presence of coupling between the nonlinear optical polarizations PNL of the impulsively excited phonons and those of parametrically amplified waves.

  4. Stimulated Raman scattering in hydrogen by ultrashort laser pulse in the keV regime

    Bachau, H.; Dondera, M.


    This letter addresses the problem of stimulated Raman excitation of a hydrogen atom submitted to an ultrashort and intense laser pulse in the keV regime. The pulse central frequency ω of 55 a.u. (about 1.5 keV) is in the weakly relativistic regime, ω ≤ c/a0 (c is the speed of light in vacuum and a 0 the Bohr radius) and the pulse duration is τ ≈ 18.85 a.u. (about 456 attoseconds). We solve the corresponding time-dependent Schrödinger equation (TDSE) using a spectral approach, retardation (or nondipole) effects are included up to O(1/c) , breaking the conservation of the magnetic quantum number m and forcing the resolution of the TDSE in a three-dimensional space. Due to the laser bandwidth, which is of the order of the ionization potential of hydrogen, stimulated Raman scattering populates nlm excited states (n and l are the principal and azimuthal quantum numbers, respectively). The populations of these excited states are calculated and analyzed in terms of l and m quantum numbers, this showing the contributions of the retardation effects and their relative importance.

  5. Study on Ultra-Short Laser Pulse Ablation of Metals by Molecular Dynamics Simulation

    LIU Xuan; WANG Yang; ZHAO Li-jie


    The dynamical progresses involved in ultra-short laser pulse ablation of face-centered cubic metals under stress confinement condition are described completely using molecular dynamics method. The laser beam absorption and thermal energy turning into kinetics energy of atoms are taken into account to give a detailed picture of laser metal interaction. Superheating phenomenon is observed, and the phase change from solid to liquid is characterized by a destroyed atom configuration and a decreased number density. The steep velocity gradients are found in the systems of Cu and Ni after pulse in consequence of located heating and exponential decrease of fluences following the Lambert-Beer expression. The shock wave velocities are predicted to be about 5000m/s in Cu and 7200m/s in Ni. The higher ablation rates are obtained from simulations compared with experimental data as a result of a well-defined crystalline surface irradiated by a single pulse. Simulation results show that the main mechanisms of ablation are evaporation and thermoelastic stress due to located heating.

  6. Reconstruction of edge density profiles on Large Helical Device using ultrashort-pulse reflectometry.

    Yokota, Yuya; Mase, Atsushi; Kogi, Yuichiro; Tokuzawa, Tokihiko; Kawahata, Kazuo; Nagayama, Yoshio; Hojo, Hitoshi


    Reflectometry has been expected to be one of the key diagnostics to measure density profiles. We have applied an ultrashort-pulse reflectometry (USPR) system to Large Helical Device in the National Institute for Fusion Science. Wide frequency band system is required to obtain wide density profile since an incident wave is reflected at the density layer corresponding to its cutoff frequency. The reflectometry utilizes an impulse with less than 30 ps pulse width as a source. Since the bandwidth of an impulse has an inverse relation to the pulse width, we can cover the frequency range of micro- to millimeter waves (18-40 GHz) with a single source. The density profiles can be reconstructed by collecting time-of-flight (TOF) signals for each frequency component of an impulse reflected from the corresponding cutoff layer. We utilize the signal record analysis (SRA) method to reconstruct the density profiles from the TOF signal. The effectiveness of the SRA method for the profile reconstruction is confirmed by a simulation study of the USPR using a finite-difference time domain method.

  7. Adaptive Bessel-autocorrelation of ultrashort pulses with phase-only spatial light modulators

    Huferath-von Luepke, Silke; Bock, Martin; Grunwald, Ruediger


    Recently, we proposed a new approach of a noncollinear correlation technique for ultrashort-pulsed coherent optical signals which was referred to as Bessel-autocorrelator (BAC). The BAC-principle combines the advantages of Bessellike nondiffracting beams like stable propagation, angular robustness and self-reconstruction with the principle of temporal autocorrelation. In comparison to other phase-sensitive measuring techniques, autocorrelation is most straightforward and time-effective because of non-iterative data processing. The analysis of nonlinearly converted fringe patterns of pulsed Bessel-like beams reveals their temporal signature from details of fringe envelopes. By splitting the beams with axicon arrays into multiple sub-beams, transversal resolution is approximated. Here we report on adaptive implementations of BACs with improved phase resolution realized by phase-only liquid-crystal-on-silicon spatial light modulators (LCoS-SLMs). Programming microaxicon phase functions in gray value maps enables for a flexible variation of phase and geometry. Experiments on the diagnostics of few-cycle pulses emitted by a mode-locked Ti:sapphire laser oscillator at wavelengths around 800 nm with 2D-BAC and angular tuned BAC were performed. All-optical phase shift BAC and fringe free BAC approaches are discussed.

  8. The interaction of intense ultrashort laser pulses with cryogenic He jets

    Shihab, M; Redmer, R


    We study the interaction of intense ultrashort laser pulses with cryogenic He jets using 2d/3v relativistic Particle-in-Cell simulations (XOOPIC). Of particular interest are laser intensities $(10^{15}-10^{20})$ W/cm$^2$, pulse lengths $\\le 100$ fs, and the frequency regime $\\sim 800$ nm for which the jets are initially transparent and subsequently not homogeneously ionized. Pulses $\\ge 10^{16}$ W/cm$^2$ are found to drive ionization along the jet and outside the laser spot, the ionization-front propagates along the jet at a fraction of the speed of light. Within the ionized region, there is a highly transient field, which may be interpreted as two-surface wave decay and as a result of the charge-neutralizing disturbance at the jet-vacuum interface. The ionized region has solid-like densities and temperatures of few to hundreds of eV, i.e., warm and hot dense matter regimes. Such extreme conditions are relevant for high-energy densities as found, e.g., in shock-wave experiments and inertial confinement fusion...

  9. Quasi-classical model of dynamic molecular structure and non-destructive wavepacket manipulation by ultrashort laser pulses

    Bryan, W A; King, R B; Nemeth, G R A J; Greenwood, J B; Williams, I D; Newell, W R


    A quasi-classical model (QCM) of molecular dynamics in intense femtosecond laser fields has been developed, and applied to a study of the effect of an ultrashort `control' pulse on the vibrational motion of a deuterium molecular ion in its ground electronic state. A nonadiabatic treatment accounts for the initial ionization-induced vibrational population caused by an ultrashort `pump' pulse. In the QCM, the nuclei move classically on the molecular potential as it is distorted by the laser-induced Stark shift and transition dipole. The nuclei then adjust to the modified potential, non-destructively shifting the vibrational population and relative phase. This shift has been studied as a function of control pulse parameters. Excellent agreement is observed with predictions of time-dependent quantum simulations, lending confidence to the validity of the model and permitting new observations to be made. The applicability of the QCM to more complex multi-potential energy surface molecules (where a quantum treatment...

  10. Material processing with ultra-short pulse lasers working in 2μm wavelength range

    Voisiat, B.; Gaponov, D.; Gečys, P.; Lavoute, L.; Silva, M.; Hideur, A.; Ducros, N.; Račiukaitis, G.


    New wavelengths of laser radiation are of interest for material processing. Results of application of the all-fiber ultrashort pulsed laser emitting in 2 µm range, manufactured by Novae, are presented. Average output power was 4.35 W in a single-spatial-mode beam centered at the 1950 nm wavelength. Pulses duration was 40 ps, and laser operated at 4.2 MHz pulse repetition rate. This performance corresponded to 25 kW of pulse peak power and almost 1 µJ in pulse energy. Material processing was performed using three different focusing lenses (100, 30 and 18 mm) and mechanical stages for the workpiece translation. 2 µm laser radiation is strongly absorbed by some polymers. Swelling of PMMA surface was observed for scanning speed above 5 mm/s using the average power of 3.45 W focused with the 30 mm lens. When scanning speed was reduced below 4 mm/s, ablation of PMMA took place. The swelling of PMMA is a consequence of its melting due to absorbed laser power. Therefore, experiments on butt welding of PMMA and overlapping welding of PMMA with other polymers were performed. Stable joint was achieved for the butt welding of two PMMA blocks with thickness of 5 mm. The laser was used to cut a Kapton film on a paper carrier with the same set-up as previous. The cut width depended on the cutting speed and focusing optics. A perfect cut with a width of 11 µm was achieved at the translation speed of 60 mm/s.

  11. Modeling of ablation threshold dependence on pulse duration for dielectrics with ultrashort pulsed laser

    Sun, Mingying; Zhu, Jianqiang; Lin, Zunqi


    We present a numerical model of plasma formation in ultrafast laser ablation on the dielectrics surface. Ablation threshold dependence on pulse duration is predicted with the model and the numerical results for water agrees well with the experimental data for pulse duration from 140 fs to 10 ps. Influences of parameters and approximations of photo- and avalanche-ionization on the ablation threshold prediction are analyzed in detail for various pulse lengths. The calculated ablation threshold is strongly dependent on electron collision time for all the pulse durations. The complete photoionization model is preferred for pulses shorter than 1 ps rather than the multiphoton ionization approximations. The transition time of inverse bremsstrahlung absorption needs to be considered when pulses are shorter than 5 ps and it can also ensure the avalanche ionization (AI) coefficient consistent with that in multiple rate equations (MREs) for pulses shorter than 300 fs. The threshold electron density for AI is only crucial for longer pulses. It is reasonable to ignore the recombination loss for pulses shorter than 100 fs. In addition to thermal transport and hydrodynamics, neglecting the threshold density for AI and recombination could also contribute to the disagreements between the numerical and the experimental results for longer pulses.

  12. Development of Ultrashort Pulse Lasers and Their Applications to Ultrafast Spectroscopy in the Visible and NIR Ranges

    Kobayashi, Takayoshi


    The use of ultrafast spectroscopy to gain detailed information about nonlinear processes can disclose the key physical mechanisms in the processes. The information promises to be a useful means to enhance the necessary nonlinearity for optical devices such as optical switches and optical manipulations of quantum states. Our group has generated stable visible to near-infrared laser pulses with a sub-5-fs duration using a non-collinear optical parametric amplifier. We also developed a detection system composed of 128 lock-in detectors, which provides an indispensable means of obtaining ultrafast nonlinear responses simultaneously in a very broad spectral range. The developed ultrashort pulse laser is used to study the electronic relaxation and molecular vibration dynamics in molecular systems through the interaction of the ultrashort pulses with the systems. Ultrashort pulses can stimulate Raman scattering in a molecular system. Observed time-resolved spectrum was analyzed to separate the electronic and vibrational contributions to the transient difference absorbance. The probe wavelength dependence of the vibrational amplitude is explained in terms of the coupling between the two pairing components among the pump field, Stokes field, anti-Stokes field, and coherent vibrational coordinates.

  13. Towards radiation pressure acceleration of protons using linearly polarized ultrashort petawatt laser pulses

    Kim, I Jong; Kim, Chul Min; Kim, Hyung Taek; Sung, Jae Hee; Lee, Seong Ku; Yu, Tae Jun; Choi, Il Woo; Lee, Chang-Lyoul; Nam, Kee Hwan; Nickles, Peter V; Jeong, Tae Moon; Lee, Jongmin


    Particle acceleration using ultraintense, ultrashort laser pulses is one of the most attractive topics in relativistic laser-plasma research. We report proton/ion acceleration in the intensity range of 5x1019 W/cm2 to 3.3x1020 W/cm2 by irradiating linearly polarized, 30-fs, 1-PW laser pulses on 10- to 100-nm-thick polymer targets. The proton energy scaling with respect to the intensity and target thickness was examined. The experiments demonstrated, for the first time with linearly polarized light, a transition from the target normal sheath acceleration to radiation pressure acceleration and showed a maximum proton energy of 45 MeV when a 10-nm-thick target was irradiated by a laser intensity of 3.3x1020 W/cm2. The experimental results were further supported by two- and three-dimensional particle-in-cell simulations. Based on the deduced proton energy scaling, proton beams having an energy of ~ 200 MeV should be feasible at a laser intensity of 1.5x1021 W/cm2.

  14. Optically induced mode conversion in graded-index fibers using ultra-short laser pulses

    Hellwig, Tim; Fallnich, Carsten


    We propose the use of graded-index few-mode fibers for mode-conversion by long-period gratings (LPG) transiently written by ultrashort laser pulses using the optical Kerr effect. The mode inter- action is studied by numerically solving the multi-mode coupled nonlinear Schroedinger equations. We present highly efficient conversion of the LP 01 - into the LP 11 -mode preserving the pulse shape in contrast to previous results in step-index fibers. Furthermore, mode conversion using different wavelengths for inducing and probing the LPG is shown. Due to the flat phase-matching curve of the examined modes in the graded-index fiber, mode-conversion can be observed for probe center wavelengths of 1100nm up to 1800nm with a write beam centered around 1030nm. Therefore, a complete separation of the probe from the write beam should be possible as well as the application of optically induced guided mode conversion for all optical modulation across a broad wavelength range.

  15. Self-phase modulation of an ultra-short laser pulse from laser breakdown plasma

    Zhang, Yongsheng; Yan, Lixin; Zheng, Guoxin; Wang, Lijun; Liu, Jingru


    The detailed dynamic of an atom in a laser field with strength comparable to the atomic electric field is rich in physics and potential applications. Laser-breakdown plasma-induced spectral shifting in supersonic rare gases jet has been investigated with a sub-picosecond KrF excimer laser focused to peak intensity in the region of 10 15W/cm2. A 1.4mm diameter gas jet target was used in the experiment to minimize the refraction of the laser beam and thus a well-defined focused region was obtained. The typical quasi-periodic spectral shifting structures for helium and argon have been measured at various gas densities. For gas densities below 1x10 20cm -3,both spectral red-shift and blue-shift were observed, indicating the gas is partially ionized, in contrast to the predominantly blue shifted as the gas densities grows high and fully ionized. Compared to the other ultra-short pulse measurement methods, qualitative information about the pulse can be deduced by observing their spectrum after interacting with rare gas.

  16. Development of ultra-short high voltage pulse technology using magnetic pulse compression

    Cha, Byung Heon; Kim, S. G.; Nam, S. M.; Lee, B. C.; Lee, S. M.; Jeong, Y. U.; Cho, S. O.; Jin, J. T.; Choi, H. L


    The control circuit for high voltage switches, the saturable inductor for magnetic assist, and the magnetic pulse compression circuit were designed, constructed, and tested. The core materials of saturable inductors in magnetic pulse compression circuit were amorphous metal and ferrite and total compression stages were 3. By the test, in high repetition rate, high pulse compression were certified. As a result of this test, it became possible to increase life-time of thyratrons and to replace thyratrons by solid-state semiconductor switches. (author). 16 refs., 16 tabs.

  17. Autler- Townes Splitting in Photoelectron Spectrum of Three-Level Li2 Molecule in Ultrashort Pulse Laser Fields

    HU Wen-Hui; YUAN Kai-Jun; HAN Yong-Chang; Shu Chuang-Cun; CONG Shu-Lin


    The Autler-Townes (AT) splitting in femtosecond photoelectron spectrum of three-level Lii molecules is theoretically investigated using time-dependent quantum wave packet method. With proper femtosecond laser pulses, three peaks of the AT splitting can be observed in the photoelectron spectrum. The AT splitting stems from rapid Rabi oscillation caused by intense ultrashort laser pluses. The effects of laser parameters on the molecular ionization dynamics are also discussed.

  18. BRIEF COMMUNICATIONS: Influence of intracavity stimulated Raman scattering on self-modulation of a ring laser emitting ultrashort pulses

    Yashkir, Yu N.; Yashkir, O. V.


    An investigation is made of the generation of ultrashort pulses in a ring laser in the presence of intracavity nonlinear losses due to stimulated Raman scattering. A numerical analysis of the attractors of the problem is used in a study of typical lasing regimes: stable, unstable regular, and unstable irregular (optical turbulence). A change in the nonlinearity parameter reveals also "intermittence" regions. An analysis is made of the influence of feedback provided by the Stokes radiation on the localization of an instability region.

  19. Long Wavelength Electromagnetic Light Bullets Generated by a 10.6 micron CO2 Ultrashort Pulsed Source


    GRANT NUMBER FA9550-15-1-0272 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Dr . Jerome V. Moloney, Professor of Optical Sciences University of> Subject: Final Report to Dr . Arje Nachman Contract/Grant Title: Long Wavelength Electromagnetic Light Bullets Generated by a 10.6...kilometer ranges. Our in- house ultrashort pulse simulation tool was used to provide basic research support for studying atmospheric propagation of a

  20. Generation of time-dependent ultra-short optical pulse trains in the presence of self-steepening effect

    Zhong Xian-Qiong; Xiang An-Ping


    Starting from the extended nonlinear Schrodinger equation in which the self-steepening effect is included, the evolution and the splitting processes of continuous optical wave whose amplitude is perturbed into time related ultra-short optical pulse trains in an optical fibre are numerically simulated by adopting the split-step Fourier algorithm. The results show that the self-steepening effect can cause the characteristic of the pulse trains to vary with time, which is different from the self-steepening-free case where the generated pulse trains consist of single pulses which are identical in width, intensity, and interval, namely when pulses move a certain distance, they turn into the pulse trains within a certain time range. Moreover, each single pulse may split into several sub-pulses. And as timc gocs on, the number of the sub-pulses will decrease gradually and the pulse width and the pulse intcnsity will change too. With the increase of the self-steepening parameter, the distance needed to generate time-dependent pulse trains will shorten. In addition, for a large self-steepening parameter and at the distance where more sub-pulses appear, the corresponding frequency spectra of pulse trains are also wider.

  1. The interaction of intense ultrashort laser pulses with cryogenic He planar jets

    Shihab, M.; Bornath, Th; Redmer, R.


    We study the interaction of intense ultrashort laser pulses with cryogenic He planar jets, i.e., slabs, using 2D3V relativistic particle-in-cell simulations. Of particular interest are laser intensities ({10}15{--}{10}20) W cm‑2, pulse lengths ≤100 fs, and the wave length regime ∼800 nm for which the slabs are initially transparent and subsequently inhomogeneously ionized. Pulses ≥slant {10}16 W cm‑2 are found to drive ionization along the slab and outside the laser spot, the ionization front propagates along the slab at a considerable fraction of the speed of light. Within the ionized region, there is a highly transient field which is a result of the charge-neutralizing disturbance at the slab-vacuum interface and which may be interpreted in terms of a two-surface-wave decay. The ionized region is predicted to reach solid-like densities and temperatures of few to hundreds of eV, i.e., it belongs to warm and hot dense matter regimes. Such extreme conditions are relevant for high-energy densities as found, e.g., in shock-wave experiments and inertial confinement fusion studies. The temporal evolution of the ionization is studied considering theoretically a pump–probe x-ray Thomson scattering scheme. We observe plasmon and non-collective modes that are generated in the slab, and their amplitude is proportional to the ionized volume. Our theoretical findings could be tested at free-electron laser facilities such as FLASH and the European XFEL (Hamburg) and the LCLS (Stanford).

  2. Stimulated Raman scattering of an ultrashort XUV radiation pulse by a hydrogen atom

    Dondera, Mihai; Florescu, Viorica; Bachau, Henri


    We consider the hydrogen atom H (1 s ) exposed to an ultrashort laser pulse with a central frequency ω0 ranging from several hundreds of eV to 1.5 keV (≈55 a.u.) and a peak intensity of 3.51 ×1016W /cm2 . We study the excitation of the atom by stimulated Raman scattering, a process involving pairs of frequencies (ω1,ω2 ). These frequencies are non-negligible components of the pulse Fourier transform and they satisfy the condition Eg+ℏ ω1=Eb+ℏ ω2,Eg and Eb≡En being the ground-state and the excited-state energy, respectively. The numerical results obtained by integrating the time-dependent Schrödinger equation (TDSE) are compared with calculations in lowest order perturbation theory (LOPT). In LOPT we consider, in the second order of PT, the contribution of the term A .P in the dipole approximation and, in first order of PT, the expression of A2 taken for first-order retardation effects. (A denotes the vector potential of the field and P is the momentum operator.) We focus on the Raman excitation of bound states with principal quantum numbers n up to n =13 . The evaluation in perturbation theory of the A .P contribution to 1 s -n s and 1 s -n d transition probabilities uses analytic expressions of the corresponding Kramers-Heisenberg matrix elements. At fixed pulse duration τ =6 π a.u. (≈0.48 fs), we find that the retardation effects play an important role at high frequencies: they progressively diminish as the frequency decreases until the contribution of A .P dominates over the A2 contribution for ω0 values of a few a.u. We also study the dependence of the Raman process on the pulse duration for several values of ω0. In the case ω0=13 a .u .(≈354 eV ) where dipole and nondipole contributions are of the same order of magnitude, we present the Raman excitation probability as a function of the pulse duration for excited n s ,n p , and n d states.

  3. Fabrication of amorphous micro-ring arrays in crystalline silicon using ultrashort laser pulses

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


    We demonstrate a simple way to fabricate amorphous micro-rings in crystalline silicon using direct laser writing. This method is based on the fact that the phase of a thin surface layer can be changed into the amorphous phase by irradiation with a few ultrashort laser pulses (800 nm wavelength and 100 fs duration). Surface-depressed amorphous rings with a central crystalline disk can be fabricated without the need for beam shaping, featuring attractive optical, topographical, and electrical properties. The underlying formation mechanism and phase change pathway have been investigated by means of fs-resolved microscopy, identifying fluence-dependent melting and solidification dynamics of the material as the responsible mechanism. We demonstrate that the lateral dimensions of the rings can be scaled and that the rings can be stitched together, forming extended arrays of structures not limited to annular shapes. This technique and the resulting structures may find applications in a variety of fields such as optics, nanoelectronics, and mechatronics.

  4. Understanding the beam self-cleaning behavior of ultrashort laser pulse filamentation

    LIU WeiWei; See Leang Chin


    In this paper we report a recent study on the beam self-cleaning behavior occurred during the ultrashort laser pulse filamentation process. The propagation of a Gaussian beam with distorted beam profile is numerically simulated based on the nonlinear wave equation. Our results demonstrate that when the power is not too high so that multiple filaments are not yet induced, the intensity perturbation contained in the initial beam profile could be treated as high order spatial modes superpositioning on a fundamental mode. Then the self-focusing of the laser beam acts as a spatial filter. It focuses the fundamental mode toward the propagation axis, and produces a fundamental mode profile at the self-focus. While the strong diffraction of higher order modes could not be counteracted by the self-focusing. Therefore their propagation is mainly governed by the divergence without destroying the high profile quality at the self-focal region. These lead to the observation of beam profile self-cleaning behavior.

  5. Understanding the beam self-cleaning behavior of ultrashort laser pulse filamentation

    See; Leang; Chin


    In this paper we report a recent study on the beam self-cleaning behavior occurred during the ultrashort laser pulse filamentation process. The propagation of a Gaussian beam with distorted beam profile is numerically simulated based on the nonlinear wave equation. Our results demonstrate that when the power is not too high so that multiple filaments are not yet induced, the intensity perturbation con-tained in the initial beam profile could be treated as high order spatial modes su-perpositioning on a fundamental mode. Then the self-focusing of the laser beam acts as a spatial filter. It focuses the fundamental mode toward the propagation axis, and produces a fundamental mode profile at the self-focus. While the strong diffraction of higher order modes could not be counteracted by the self-focusing. Therefore their propagation is mainly governed by the divergence without de-stroying the high profile quality at the self-focal region. These lead to the observa-tion of beam profile self-cleaning behavior.

  6. Chemical-free inactivated whole influenza virus vaccine prepared by ultrashort pulsed laser treatment

    Tsen, Shaw-Wei David; Donthi, Nisha; La, Victor; Hsieh, Wen-Han; Li, Yen-Der; Knoff, Jayne; Chen, Alexander; Wu, Tzyy-Choou; Hung, Chien-Fu; Achilefu, Samuel; Tsen, Kong-Thon


    There is an urgent need for rapid methods to develop vaccines in response to emerging viral pathogens. Whole inactivated virus (WIV) vaccines represent an ideal strategy for this purpose; however, a universal method for producing safe and immunogenic inactivated vaccines is lacking. Conventional pathogen inactivation methods such as formalin, heat, ultraviolet light, and gamma rays cause structural alterations in vaccines that lead to reduced neutralizing antibody specificity, and in some cases, disastrous T helper type 2-mediated immune pathology. We have evaluated the potential of a visible ultrashort pulsed (USP) laser method to generate safe and immunogenic WIV vaccines without adjuvants. Specifically, we demonstrate that vaccination of mice with laser-inactivated H1N1 influenza virus at about a 10-fold lower dose than that required using conventional formalin-inactivated influenza vaccines results in protection against lethal H1N1 challenge in mice. The virus, inactivated by the USP laser irradiation, has been shown to retain its surface protein structure through hemagglutination assay. Unlike conventional inactivation methods, laser treatment did not generate carbonyl groups in protein, thereby reducing the risk of adverse vaccine-elicited T helper type 2 responses. Therefore, USP laser treatment is an attractive potential strategy to generate WIV vaccines with greater potency and safety than vaccines produced by current inactivation techniques.

  7. Experimental study on the development of a micro-drilling cycle using ultrashort laser pulses

    Romoli, L.; Vallini, R.


    Microholes for the production of high precision devices were obtained by ultrashort pulsed laser machining of martensitic stainless steels. A micro-drilling cycle based on the sequence of a drilling through phase, an enlargement and finishing phase is proposed in order to solve the trade-off between process time and quality of the ablated surfaces without making use of complex design of experiments. The three phases were studied taking into account the evolution of the microhole shape as a function of the main process parameters (number of passes per phase, incidence angle and radius of the beam trajectory respect to the hole's axis). Experiments testified that the drilling strategy was able to produce cylindrical holes with diameter of 180±2 μm on a 350 μm thick plate in total absence of burrs and debris within a drilling time of 3.75 s. Repeatability tests showed a process capability of nearly 99%. SEM inspection of the inner surface of the microholes showed the presence of elongated and periodic ripples whose size and inclination can be controlled adjusting the incidence angle of the beam over the tapered surface before the ultimate finishing phase.

  8. Generation of Ultrashort Optical Pulses from Chromium - Forsterite and Chromium-Doped Yttrium Aluminum Garnet Tunable Solid-State Lasers.

    Sennaroglu, Alphan

    In this thesis, experimental results of ultrashort pulse generation from the Cr:forsterite and Cr:YAG laser systems are presented. Ultrashort pulses from these coherent light sources are potentially important in such technological applications as fiber-optic communications, time-resolved spectroscopy of narrow-bandgap semiconductors, and medical imaging of tissues. Additive-pulse mode-locked operation of a Cr:forsterite laser was first pursued. By using a single-mode optical fiber for pulse shaping, 150-fs pulses were produced at 1.23 μm with 60 mW of average output power. However, pulse-train instabilities, cryogenic operation, and the overall complexity of the experimental setup hindered ready commercialization of this ultrashort pulse source. Regeneratively initiated self-mode-locked operation of the same laser system was then investigated. Regenerative initiation, where synchronization of the rf signal driving the modulator and the pulse repetition rate obviated the need for stringent cavity-length control, gave rise to the formation of a very stable, uninterrupted train of femtosecond pulses. Nearly transform-limited, 48-fs pulses, tunable from 1.21 to 1.27 mum, were produced with useful output powers of 360 mW at 1.23 mum. By employing the high-peak-power pulses generated from the Cr:forsterite laser in external second harmonic generation experiments, red pulses of 116 fs duration, tunable in the wavelength range from 605 to 635 nm, were obtained with power conversion efficiencies approaching 10%. In the next set of experiments, the continuous -wave (cw) power performance of a Cr:YAG laser was characterized as a function of various operating laser parameters. As high as 1.9 W of useful cw output power was obtained at 1.45 μm with a 2% transmitting output coupler when the gain medium was thermoelectrically cooled at 3 ^circC, significantly exceeding the results previously reported in the literature. Self -mode-locked operation of this laser system was also

  9. Two-dimensional angular energy spectrum of electrons accelerated by the ultra-short relativistic laser pulse

    Borovskiy, A. V. [Department of Computer Science and Cybernetics, Baikal State University of Economics and Law, 11 Lenin Street, Irkutsk 664003 (Russian Federation); Galkin, A. L. [Coherent and Nonlinear Optics Department, A.M. Prokhorov General Physics Institute of the RAS, 38 Vavilov Street, Moscow 119991 (Russian Federation); Department of Physics of MBF, Pirogov Russian National Research Medical University, 1 Ostrovitianov Street, Moscow 117997 (Russian Federation); Kalashnikov, M. P., E-mail: [Max-Born-Institute for Nonlinear Optics and Short-Time Spectroscopy, 2a Max-Born-Strasse, Berlin 12489 (Germany)


    The new method of calculating energy spectra of accelerated electrons, based on the parameterization by their initial coordinates, is proposed. The energy spectra of electrons accelerated by Gaussian ultra-short relativistic laser pulse at a selected angle to the axis of the optical system focusing the laser pulse in a low density gas are theoretically calculated. The two-peak structure of the electron energy spectrum is obtained. Discussed are the reasons for its appearance as well as an applicability of other models of the laser field.

  10. Controlling magnetism by ultrashort laser pulses: from fundamentals to nanoscale engineering

    Bossini, D.; Rasing, Th.


    From the discovery of sub-picosecond demagnetization over a decade ago [1] to the recent demonstration of magnetization reversal by a single 40 femtosecond laser pulse [2], the manipulation of spins by ultra-short laser pulses has become a fundamentally challenging topic with a potentially high impact for future spintronics, data storage and manipulation and quantum computation [3]. It was realized that the femtosecond laser induced all-optical switching (AOS) as observed in ferrimagnets exploits the laser induced strongly non-equilibrium dynamics and the antiferromagnetic exchange interaction between their sublattices [4-6]. This opens the way to engineer new magnetic materials for AOS [7,8], though for real applications nanoscale control of inhomogeneities appears to be relevant [9]. Besides the intruiging technological implications of these observations, they broadened remarkably the frontiers of our fundamental knowledge of magnetic phenomena. The laser driven out-of-equilibrium states cannot be described in term of the well-established thermodynamical approach, which is based on the concepts of equilibrium and adiabatic transformations. Theoretical efforts, although in their infancy, have already demonstrated [5,6] that light-induced spin dynamics on the (sub)-picosecond time scale results in phenomena utterly forbidden in a thermodynamical framework. Another challenge is how to bring the optical manipulation of magnetic media to the required nanoscale. This is clearly a key element for the perspectives in terms of magnetic recording. In addition, it would allow to explore a novel regime of spin dynamics, since the investigation of magnets on the femtosecond time-scale and the nanometer length-scale simultaneously is unexplored. One experimental approach which may be successful makes use of wave-shaping techniques [10]. Recent results with engineered hybrid magnetic materials and nanofocusing via a plasmonic antenna showed the practical potential of AOS: the

  11. Generation of ultrashort pulses with minimum duration of 90\\ {\\text{fs}} in a hybrid mode-locked erbium-doped all-fibre ring laser

    Dvoretskiy, D. A.; Sazonkin, S. G.; Voropaev, V. S.; Negin, M. A.; Leonov, S. O.; Pnev, A. B.; Karasik, V. E.; Denisov, L. K.; Krylov, A. A.; Davydov, V. A.; Obraztsova, E. D.


    Regimes of ultrashort pulse generation in an erbium-doped all-fibre ring laser with hybrid mode locking based on single-wall carbon - boron nitride nanotubes and the nonlinear Kerr effect in fibre waveguides are studied. Stable dechirped ultrashort pulses are obtained with a duration of ˜ 90 {\\text{fs}}, a repetition rate of ˜ 42.2 {\\text{MHz}}, and an average output power of ˜ 16.7 {\\text{mW}}, which corresponds to a pulse energy of ˜ 0.4 {\\text{nJ}} and a peak laser power of ˜ 4.4 {\\text{kW}}.

  12. Large net-normal dispersion Er-doped fibre laser mode-locked with a nonlinear amplifying loop mirror

    Bowen, Patrick; Broderick, Neil G R


    We report on an environmentally stable, all-PM-fibre, Er-doped, mode-locked laser with a central wavelength of 1550 nm. Significantly, the laser possesses large net-normal dispersion such that its dynamics are comparable to that of an all-normal dispersion fibre laser at 1 {\\mu}m with an analogous architecture. The laser is mode-locked with a nonlinear amplifying loop mirror to produce pulses that are externally compressible to 500 fs. Experimental results are in good agreement with numerical simulations.

  13. Magnetic resonance imaging of the normal pituitary gland using ultrashort TE (UTE) pulse sequences (REV 1.0)

    Portman, Olivia; Flemming, Stephen; Cox, Jeremy P.D.; Johnston, Desmond G. [Imperial College Faculty of Medicine, St Mary' s Hospital, Endocrinology and Metabolic Medicine, London (United Kingdom); Bydder, Graeme M. [University of California, San Diego, Department of Radiology, San Diego, CA (United States)


    The purpose of this study was to examine the normal pituitary gland in male subjects with ultrashort echo time (TE) pulse sequences, describe its appearance and measure its signal intensity before and after contrast enhancement. Eleven male volunteers (mean age 57.1 years; range 36-81 years) were examined with a fat-suppressed ultrashort TE (= 0.08 ms) pulse sequence. The studies were repeated after the administration of intravenous gadodiamide. The MR scans were examined for gland morphology and signal intensity before and after enhancement. Endocrinological evaluation included baseline pituitary function tests and a glucagon stimulatory test to assess pituitary cortisol and growth hormone reserve. High signal intensity was observed in the anterior pituitary relative to the brain in nine of the 11 subjects. These regions involved the whole of the anterior pituitary in three subjects, were localised to one side in two examples and were seen inferiorly in three subjects. Signal intensities relative to the brain increased with age, with a peak around the sixth or seventh decade and decreasing thereafter. Overall, the pituitary function tests were considered to be within normal limits and did not correlate with pituitary gland signal intensity. The anterior pituitary shows increased signal intensity in normal subjects when examined with T{sub 1}-weighted ultrashort TE pulse sequences. The cause of this increased intensity is unknown, but fibrosis and iron deposition are possible candidates. The variation in signal intensity with age followed the temporal pattern of iron content observed at post mortem. No relationship with endocrine status was observed. (orig.)

  14. Nonlinear dynamics of high-power ultrashort laser pulses: exaflop computations on a laboratory computer station and subcycle light bullets

    Voronin, A. A.; Zheltikov, A. M.


    The propagation of high-power ultrashort light pulses involves intricate nonlinear spatio-temporal dynamics where various spectral-temporal field transformation effects are strongly coupled to the beam dynamics, which, in turn, varies from the leading to the trailing edge of the pulse. Analysis of this nonlinear dynamics, accompanied by spatial instabilities, beam breakup into multiple filaments, and unique phenomena leading to the generation of extremely short optical field waveforms, is equivalent in its computational complexity to a simulation of the time evolution of a few billion-dimensional physical system. Such an analysis requires exaflops of computational operations and is usually performed on high-performance supercomputers. Here, we present methods of physical modeling and numerical analysis that allow problems of this class to be solved on a laboratory computer boosted by a cluster of graphic accelerators. Exaflop computations performed with the application of these methods reveal new unique phenomena in the spatio-temporal dynamics of high-power ultrashort laser pulses. We demonstrate that unprecedentedly short light bullets can be generated as a part of that dynamics, providing optical field localization in both space and time through a delicate balance between dispersion and nonlinearity with simultaneous suppression of diffraction-induced beam divergence due to the joint effect of Kerr and ionization nonlinearities.

  15. Ab initio time-dependent method to study the hydrogen molecule exposed to intense ultrashort laser pulses

    Sanz-Vicario, J.L. [Departamento de Quimica, C-IX, Universidad Autonoma de Madrid, 28049-Madrid (Spain); Sede de Investigacion Universitaria (SIU). Instituto de Fisica, Universidad de Antioquia, Medellin (Colombia)], E-mail:; Palacios, A. [Departamento de Quimica, C-IX, Universidad Autonoma de Madrid, 28049-Madrid (Spain); Cardona, J.C. [Sede de Investigacion Universitaria (SIU). Instituto de Fisica, Universidad de Antioquia, Medellin (Colombia); Bachau, H. [Centre des Lasers Intenses et Applications, UMR 5107 du CNRS-Universite bordeaux I-CEA, Universite Bordeaux I, 33405 Talence Cedex (France); Martin, F. [Departamento de Quimica, C-IX, Universidad Autonoma de Madrid, 28049-Madrid (Spain)


    An ab initio non-perturbative time dependent method to describe ionization of molecular systems by ultrashort (femtosecond) laser pulses has been developed. The method allows one to describe competing processes such as non dissociative ionization, dissociative ionization and dissociation into neutrals, including the possibility of autoionization. In this work we assess the validity of the method by applying it to different physical situations and by comparing with results previously obtained within stationary perturbation theory. In particular, it is shown that inclusion of the nuclear motion is essential to describe H{sub 2} resonance enhanced multiphoton ionization and interferences mediated by H{sub 2} autoionizing states.

  16. Soft-x-ray imaging from an ultrashort-pulse laser-produced plasma using a multilayer coated optic

    Norby, J. R.; van Woerkom, L. D.


    Measurements are presented of soft-x-ray images from a plasma produced by a high-intensity ultrashort-pulse laser. For the intensity range of 1015-1016 W / cm2 the soft-x-ray source appears to follow the spatial profile of the driving laser. A curved multilayer coated optic is used to collect 13.5-nm light and form a magnified image of the plasma. Knife-edge scans have been performed in the image plane and show a geometrically limited spot size of 280 mu m.

  17. Interband photorefractive effect in beta-BBO crystal due to multiphoton excitation by intense ultrashort optical pulses.

    Xu, Shixiang; Cai, Hua; Zeng, Heping


    This paper presents the first experimental observation of interband photo- refractive (PR) effects in beta-BBO crystal due to multiphoton excitation with intense ultrashort pulses. In order to fully characterize the PR effects, a sensitive intracavity scheme is developed to magnify the dynamics of nonlinear lenses induced by the PR effects. The reproducible PR phenomena depend strongly on the power, wavelength, and spatial intensity profile of the intense laser pulses and the electro-optic coefficient of the optical materials. Its response time is from tens of seconds to several minutes. The results may be very helpful for us to find a solution to overcome the deleterious influence of multiphoton induced photo-charges on nonlinear optical frequency conversions, e.g. optical parametric chirped pulse amplification.

  18. Role of coherent resonant nonlinear processes in the ultrashort KrF laser pulse propagation and filamentation in air

    Smetanin, I.V.; Levchenko, A.O.; Shutov, A.V.; Ustinovskii, N.N. [P.N. Lebedev Physical Institute of Russian Academy of Sciences, 53 Leninskii pr., 119991 Moscow (Russian Federation); Zvorykin, V.D. [P.N. Lebedev Physical Institute of Russian Academy of Sciences, 53 Leninskii pr., 119991 Moscow (Russian Federation); National Research Nuclear University “MEPhI”, 31 Kashirskoe sh., 115409 Moscow (Russian Federation)


    Recent experiments on multiple filamentation of sub-picosecond terawatt-level KrF laser pulse in air and multi-photon ionization of air revealed an extremely low electron density in filaments, which is out of the conventional filamentation model considering Kerr self-focusing and plasma de-focusing. We propose here the coherent resonant scattering and ionization processes at the pulse durations significantly less than the polarization relaxation time to be possible explanation of the observed filamentation peculiarities. Namely, we argue that the plasma production results from the resonance enhanced (2+1)-photon ionization of the oxygen molecules through the two-photon excitation of the 3s metastable Rydberg state. Coherent Raman self-scattering at rotational transitions of nitrogen molecules provides self-induced focusing of the ultrashort UV laser pulse and filament formation.

  19. On the feasibility of nanocrystal imaging using intense and ultrashort 1.5 {\\AA} X-ray pulses

    Caleman, C; Maia, F R N C; Ortiz, C; Parak, F G; Hajdu, J; van der Spoel, D; Chapman, H N; Timneanu, N


    Structural studies of biological macromolecules are severely limited by radiation damage. Traditional crystallography curbs the effects of damage by spreading damage over many copies of the molecule of interest. X-ray lasers, such as the recently built LINAC Coherent Light Source (LCLS), offer an additional opportunity for limiting damage by out-running damage processes with ultrashort and very intense X-ray pulses. Such pulses may allow the imaging of single molecules, clusters or nanoparticles, but coherent flash imaging will also open up new avenues for structural studies on nano- and micro-crystalline substances. This paper addresses the theoretical potentials and limitations of nanocrystallography with extremely intense coherent X-ray pulses. We use urea nanocrystals as a model for generic biological substances and simulate primary and secondary ionization dynamics in the crystalline sample. Our results establish conditions for ultrafast nanocrystallography diffraction experiments as a function of fluenc...

  20. Electron acceleration in vacuum by a linearly-polarized ultra-short tightly-focused THz pulse

    Salamin, Yousef I.


    The analytic expressions for the electric and magnetic fields of an ultra-short, tightly-focused, linearly-polarized laser pulse propagating in vacuum, derived elsewhere (Salamin, 2015) [13] to lowest-order of a truncated power-series expansion from vector and scalar potentials, are employed here for single electron acceleration calculations by THz radiation. It is shown that, while currently available THz peak powers cannot accelerate electrons appreciably, yet they result in substantial energy gradients. The field equations are used to show that an electron can be accelerated, in vacuum, from rest to 4.83 MeV by interaction with a single THz pulse of 1 TW power. Similarly, a 1 GW power pulse focused to sub-wavelength waist radius at focus is shown to accelerate the electron from rest to 5.76 keV.

  1. Analytical performances of laser-induced micro-plasma of Al samples with single and double ultrashort pulses in air and with Ar-jet: A comparative study

    Semerok, A., E-mail: [CEA Saclay, DEN/DPC/SEARS/LISL, 91191 Gif-sur-Yvette (France); Dutouquet, C. [CEA Saclay, DEN/DPC/SEARS/LISL, 91191 Gif-sur-Yvette (France); INERIS/DRC/CARA/NOVA, F-60550 Verneuil En Halatte (France)


    Ultrashort pulse laser microablation coupled with optical emission spectroscopy was under study to obtain several micro-LIBS analytical features (shot-to-shot reproducibility, spectral line intensity and lifetime, calibration curves, detection limits). Laser microablation of Al matrix samples with known Cu- and Mg-concentrations was performed by single and double pulses of 50 fs and 1 ps pulse duration in air and with Ar-jet. The micro-LIBS analytical features obtained under different experimental conditions were characterized and compared. The highest shot-to-shot reproducibility and gain in plasma spectral line intensity were obtained with double pulses with Ar-jet for both 50 fs and 1 ps pulse durations. The best calibration curves were obtained with 1 ps pulse duration with Ar-jet. Micro-LIBS with ultrashort double pulses may find its effective application for surface elemental microcartography. - Highlights: • Analytical performances of micro-LIBS with ultrashort double pulses were studied. • The maximal line intensity gain of 20 was obtained with double pulses and Ar-jet. • LIBS gain was obtained without additional ablation of a sample by the second pulse. • LIBS properties were almost the same for both 50 fs and 1 ps pulses. • The micro-LIBS detection limit was around 35 ppm.

  2. Ultrashort Generation Regimes in the All-Fiber Kerr Mode-Locked Erbium-Doped Fiber Ring Laser for Terahertz Pulsed Spectroscopy

    V. S. Voropaev


    Full Text Available Many femtosecond engineering applications require for a stable generation of ultrashort pulses. Thus, in the terahertz pulsed spectroscopy a measurement error in the refractive index is strongly dependent on the pulse duration stability with allowable variation of few femtoseconds. The aim of this work is to study the ultrashort pulses (USP regimes stability in the all – fiber erbium doped ring laser with Kerr mode-locking. The study was conducted at several different values of the total resonator intra-cavity dispersion. Three laser schemes with the intra-cavity dispersion values from -1.232 ps2 to +0.008 ps2 have been studied. In the experiment there were two regimes of generation observed: the stretched pulse generation and ordinary soliton generation. Main attention is focused on the stability of regimes under study. The most stable regime was that of the stretched pulse generation with a spectrum form of sech2 , possible pulse duration of 490 fs at least, repetition rate of 2.9 MHz, and average output power of 17 mW. It is worth noting, that obtained regimes had characteristics suitable for the successful use in the terahertz pulsed spectroscopy. The results may be useful in the following areas of science and technology: a high-precision spectroscopy, optical frequency standards, super-continuum generation, and terahertz pulsed spectroscopy. The future system development is expected to stabilize duration and repetition rate of the obtained regime of ultra-short pulse generation.


    D. S. Ivanov


    Full Text Available Subject of Study. The mechanism of surface restructuring by ultrashort laser pulses involves a lot of fast, non-equilibrium, and interrelated processes while the solid is in a transient state. As a result, the analysis of the experimental data cannot cover all the mechanisms of nanostructuring. We present a direct comparison of a simulation and experimental results of surface nanomodification induced by a single laser pulse. Method. The experimental results were obtained by using a mask projection setup with a laser wavelength equal to 248 nm and a pulse length equal to 1.6 ps. This setup is used to produce an intensity grating on a gold surface with a sinusoidal shape and a period of 500 nm. The formed structures were analyzed by a scanning and transmission electron microscope, respectively. Then a hybrid atomistic-continuum model capable of capturing the essential mechanisms responsible for the nanostructuring process was used for modeling the interaction of the laser pulse with a thick gold target. Main Results. A good agreement between simulation and experimental data justifies the proposed approach as a powerful tool revealing the physics behind the nanostructuring process at a gold surface and providing a microscopic insight into the dynamics of the structuring processes of metals in general. The presented model, therefore, is an important step towards a new computational tool in predicting materials response to an ultrashort laser pulse on the atomic scale and properties of the modified surfaces. Practical Relevance. This detailed understanding of the dynamics of the process will pave the way towards pre-designed topologies for functionalized surfaces on the nano- and micro-scales.

  4. Process optimization in high-average-power ultrashort pulse laser microfabrication: how laser process parameters influence efficiency, throughput and quality

    Schille, Joerg; Schneider, Lutz; Loeschner, Udo


    In this paper, laser processing of technical grade stainless steel and copper using high-average-power ultrashort pulse lasers is studied in order to gain deeper insight into material removal for microfabrication. A high-pulse repetition frequency picosecond and femtosecond laser is used in conjunction with high-performance galvanometer scanners and an in-house developed two-axis polygon scanner system. By varying the processing parameters such as wavelength, pulse length, fluence and repetition rate, cavities of standardized geometry are fabricated and analyzed. From the depths of the cavities produced, the ablation rate and removal efficiency are estimated. In addition, the quality of the cavities is evaluated by means of scanning electron microscope micrographs or rather surface roughness measurements. From the results obtained, the influence of the machining parameters on material removal and machining quality is discussed. In addition, it is shown that both material removal rate and quality increase by using femtosecond compared to picosecond laser pulses. On stainless steel, a maximum throughput of 6.81 mm3/min is achieved with 32 W femtosecond laser powers; if using 187 W picosecond laser powers, the maximum is 15.04 mm3/min, respectively. On copper, the maximum throughputs are 6.1 mm3/min and 21.4 mm3/min, obtained with 32 W femtosecond and 187 W picosecond laser powers. The findings indicate that ultrashort pulses in the mid-fluence regime yield most efficient material removal. In conclusion, from the results of this analysis, a range of optimum processing parameters are derived feasible to enhance machining efficiency, throughput and quality in high-rate micromachining. The work carried out here clearly opens the way to significant industrial applications.

  5. Ultrashort pulse laser patterning of indium tin oxide thin films on glass by uniform diffractive beam patterns

    Kuang Zheng, E-mail: [Laser Group, School of Engineering, University of Liverpool, Brownlow Street, Liverpool L69 3GQ (United Kingdom); Perrie, Walter; Liu Dun; Fitzsimons, Paul; Edwardson, Stuart P.; Fearon, Eamonn; Dearden, Geoff; Watkins, Ken G. [Laser Group, School of Engineering, University of Liverpool, Brownlow Street, Liverpool L69 3GQ (United Kingdom)


    In the last decade, indium tin oxide (ITO) has been most commonly employed to create transparent conducting oxides (TCOs) thin films for many industrial applications. It is usually necessary to pattern ITO thin films to create functional structures for specific applications. Direct-write micro-patterning of ITO thin films by ultra-short pulse lasers has demonstrated high quality without requiring multiple processing stations, compared with conventional patterning technologies (e.g. wet-etch lithography). However, the processing efficiency and throughput with a single beam can be insufficient because of the high level of attenuation needed for the output to meet the required 'thermal-free' parameters. In this paper, high throughput surface direct micro-structuring of ITO on glass is demonstrated by parallel processing using diffractive multiple ultrashort pulse laser beams ({lambda} = 1064 nm, {tau}p = 10 ps). By avoiding periodic and symmetrical geometry design, the diffractive multiple beam pattern generated by a spatial light modulator has high uniformity (the energy variation between each diffractive beam is <9%). The ITO thin film is removed by laser ablation of 25 identical beams at the same time without any damage to the glass substrate. Additionally, by synchronizing a scanning galvanometer, the processing demonstrates high flexibility to generate various surface patterns.

  6. Novel D-shaped fiber fabrication method for saturable absorber application in the generation of ultra-short pulses

    Ahmad, H.; Safaei, R.; Rezayi, M.; Amiri, I. S.


    A cost-efficient, time-saving and effective technique for the fabrication of D-shaped fibers is presented, to provide a platform with a strong evanescent field to be used as a saturable absorber (SA). This technique provides flexibility by removing the required portion of the fiber, and a small polished length which offers a unique opportunity to deposit SA on its surface by simply submerging it in the SA solution without high losses. A compact fiber laser utilizing a graphene oxide coating on a fabricated D-shaped fiber as an SA capable of generating ultrashort pulses is designed and verified. We report the generation of ultrafast pulses as short as 227 fs with a 34.7 MHz repetition rate, having a 3 dB bandwidth of 14 nm at the 1570 nm center wavelength.

  7. Synthesis, Characterization, and Photocatalysis of ZnO and Er-Doped ZnO

    Yu, Kai-sheng; Shi, Jian-ying; Zhang, Zai-Li; Liang, Yong-Mei; LIU Wei


    ZnO and Er-doped ZnO with different molar ratios of Er/Zn were prepared using the homogeneous precipitation method. The photocatalysts prepared were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), UV-vis spectroscopy, and photoluminescence spectroscopy. The results showed that the Er-doped ZnO displayed characteristic wurtzite-type peaks in the XRD spectra. The Er-doped ZnO absorbed much more light than ZnO in the ultraviolet region...

  8. New theoretical approaches to atomic and molecular dynamics triggered by ultrashort light pulses on the atto- to picosecond time scale

    Pabst, Stefan Ulf


    The concept of atoms as the building blocks of matter has existed for over 3000 years. A revolution in the understanding and the description of atoms and molecules has occurred in the last century with the birth of quantum mechanics. After the electronic structure was understood, interest in studying the dynamics of electrons, atoms, and molecules increased. However, time-resolved investigations of these ultrafast processes were not possible until recently. The typical time scale of atomic and molecular processes is in the picosecond to attosecond realm. Tremendous technological progress in recent years makes it possible to generate light pulses on these time scales. With such ultrashort pulses, atomic and molecular dynamics can be triggered, watched, and controlled. Simultaneously, the need rises for theoretical models describing the underlying mechanisms. This doctoral thesis focuses on the development of theoretical models which can be used to study the dynamical behavior of electrons, atoms, and molecules in the presence of ultrashort light pulses. Several examples are discussed illustrating how light pulses can trigger and control electronic, atomic, and molecular motions. In the first part of this work, I focus on the rotational motion of asymmetric molecules, which happens on picosecond and femtosecond time scales. Here, the aim is to align all three axes of the molecule as well as possible. To investigate theoretically alignment dynamics, I developed a program that can describe alignment motion ranging from the impulsive to the adiabatic regime. The asymmetric molecule SO{sub 2} is taken as an example to discuss strategies of optimizing 3D alignment without the presence of an external field (i.e., field-free alignment). Field-free alignment is particularly advantageous because subsequent experiments on the aligned molecule are not perturbed by the aligning light pulse. Wellaligned molecules in the gas phase are suitable for diffraction experiments. From the

  9. Effect of gas heating on the generation of an ultrashort avalanche electron beam in the pulse-periodic regime

    Baksht, E. Kh.; Burachenko, A. G.; Lomaev, M. I.; Sorokin, D. A.; Tarasenko, V. F.


    The generation of an ultrashort avalanche electron beam (UAEB) in nitrogen in the pulse-periodic regime is investigated. The gas temperature in the discharge gap of the atmospheric-pressure nitrogen is measured from the intensity distribution of unresolved rotational transitions ( C 3Π u , v' = 0) → ( B 3Π g , v″ = 0) in the nitrogen molecule for an excitation pulse repetition rate of 2 kHz. It is shown that an increase in the UAEB current amplitude in the pulse-periodic regime is due to gas heating by a series of previous pulses, which leads to an increase in the reduced electric field strength as a result of a decrease in the gas density in the zone of the discharge formation. It is found that in the pulse-periodic regime and the formation of the diffuse discharge, the number of electrons in the beam increases by several times for a nitrogen pressure of 9 × 103 Pa. The dependences of the number of electrons in the UAEB on the time of operation of the generator are considered.

  10. Enhanced magnetodielectric and multiferroic properties of Er-doped bismuth ferrite nanoparticles

    Mukherjee, A.; Banerjee, M. [Department of Physics, National Institute of Technology, Durgapur 713209 (India); Basu, S., E-mail: [Department of Physics, National Institute of Technology, Durgapur 713209 (India); Mukadam, M.D.; Yusuf, S.M. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Pal, M. [CSIR-Central Glass & Ceramic Research Institute, Kolkata 700032 (India)


    An enhancement in multiferroic properties has been achieved for chemically prepared BFO nanoparticles by doping with erbium (Er). XRD along with electron microscopy study reveals the phase purity and nanocrystalline nature of BFO. Enhancement of both the magnetic moment and resistivity is observed by virtue of Er doping. The observed enhanced magnetic moment is considered to be associated with smaller crystallite whereas increase of resistivity may be attributed to a decrease of oxygen vacancies. Doping also display an improvement of leakage behaviour and dielectric constant in nanocrystalline BFO, reflected in well-developed P-E loop. In addition, large enhancement in magnetodielectric coefficient is observed because of Er doping. Therefore, the results provide interesting approaches to improve the multiferroic properties of BFO, which has great implication towards its applications. - Highlights: • Synthesis of pure Er-doped BFO nanoparticles by chemical route. • Large increase in magnetic moment and resistivity due to Er doping. • Er doping produce well developed P-E loop and enhance polarization. • Drastic increase in dielectric constant as well as magnetodielectric coefficient observes because of Er doping.

  11. High-throughput machining using a high-average power ultrashort pulse laser and high-speed polygon scanner

    Schille, Joerg; Schneider, Lutz; Streek, André; Kloetzer, Sascha; Loeschner, Udo


    High-throughput ultrashort pulse laser machining is investigated on various industrial grade metals (aluminum, copper, and stainless steel) and Al2O3 ceramic at unprecedented processing speeds. This is achieved by using a high-average power picosecond laser in conjunction with a unique, in-house developed polygon mirror-based biaxial scanning system. Therefore, different concepts of polygon scanners are engineered and tested to find the best architecture for high-speed and precision laser beam scanning. In order to identify the optimum conditions for efficient processing when using high-average laser powers, the depths of cavities made in the samples by varying the processing parameter settings are analyzed and, from the results obtained, the characteristic removal values are specified. For overlapping pulses of optimum fluence, the removal rate is as high as 27.8 mm3/min for aluminum, 21.4 mm3/min for copper, 15.3 mm3/min for stainless steel, and 129.1 mm3/min for Al2O3, when a laser beam of 187 W average laser powers irradiates. On stainless steel, it is demonstrated that the removal rate increases to 23.3 mm3/min when the laser beam is very fast moving. This is thanks to the low pulse overlap as achieved with 800 m/s beam deflection speed; thus, laser beam shielding can be avoided even when irradiating high-repetitive 20-MHz pulses.

  12. Sub-wavelength ripples in fused silica after irradiation of the solid/liquid interface with ultrashort laser pulses.

    Böhme, R; Vass, C; Hopp, B; Zimmer, K


    Laser-induced backside wet etching (LIBWE) is performed using ultrashort 248 nm laser pulses with a pulse duration of 600 fs to obtain sub-wavelength laser-induced periodic surface structures (LIPSS) on the back surface of fused silica which is in contact with a 0.5 mol l(-1) solution of pyrene in toluene. The LIPSS are strictly one-dimensional patterns, oriented parallel to the polarization of the laser radiation, and have a constant period of about 140 nm at all applied laser fluences (0.33-0.84 J cm(-2)) and pulse numbers (50-1000 pulses). The LIPSS amplitude varies due to the inhomogeneous fluence in the laser spot. The LIPSS are examined with scanning electron microscopy (SEM) and atomic force microscopy (AFM). Their power spectral density (PSD) distribution is analysed at a measured area of 10 µm × 10 µm. The good agreement of the measured and calculated LIPSS periods strongly supports a mechanism based on the interference of surface-scattered and incident waves.

  13. Application of the ultrashort pulses in bovine dental enamel; Aplicacao de pulsos ultracurtos em esmalte dental bovino

    Todescan, Carla de Rago


    The interaction of lasers with the hard structures of the teeth, has found the excess of heat as a problem for its utilization. This study analyzes, in vitro, the interaction of the ultrashort pulse laser of Ti:safire (830 nm) with the bovine dental enamel. The system consisted in one main oscillator integrated with an amplifier (CPA). The pulses extracted before the temporal compression inside the amplifier had 30 ps, 1000 Hz and {approx}1 mJ. The pulses extracted after the compression had 60 fs, 1000 Hz and {approx}0,7 mJ. The M{sup 2} was 1,3, the focal lens 2,5 cm, the focal distance 29,7 and a computerized translation stage x,y,z. We evaluated the amount of tissue removed per pulse,the resulting cavities and the surrounding tissues not irradiated, under OM and SEM. The fluency was the major factor for differentiating the two regimens studied, therefore, the intensity was not so important as we expected in this process. We found: one ablation region in 'cat tongue', one ablation length, one fluency {approx}0,7 J/cm{sup 2} for 30 ps and {approx}0,5 J/cm{sup 2} for 60 fs (50% of high speed burr), smooth edge for 30 ps and high precision of the sharp edge cut of submicrometric order for 60 fs. (author)

  14. Various Kinds Waves and Solitons Interaction Solutions of Boussinesq Equation Describing Ultrashort Pulse in Quadratic Nonlinear Medium

    Guo, Bang-Xing; Gao, Zhan-Jie; Lin, Ji


    The consistent tanh expansion (CTE) method is applied to the (2+1)-dimensional Boussinesq equation which describes the propagation of ultrashort pulse in quadratic nonlinear medium. The interaction solutions are explicitly given, such as the bright soliton-periodic wave interaction solution, variational amplitude periodic wave solution, and kink-periodic wave interaction solution. We also obtain the bright soliton solution, kind bright soliton solution, double well dark soliton solution and kink-bright soliton interaction solution by using Painlevé truncated expansion method. And we investigate interactive properties of solitons and periodic waves. Supported by the National Natural Science Foundation of Zhejiang Province under Grant No. LZ15A050001 and the National Natural Science Foundation of China under Grant No. 11675164

  15. A Sensitive Scheme to Observe Weak Photo-Refraction Effects in Some Nonlinear Optical Crystals Pumped by Ultrashort Optical Pulses

    XU Shi-Xiang; GAO Yan-Xia; CAI Hua; LI Jing-Zhen


    We present a sensitive scheme, for the first time to our knowledge, to observe photo-refraction (PR) effects in some nonlinear optical crystals, e.g.β-BBO, LBO and BIBO, pumped by an intense ultrashort laser pulse chain. These quite weak effects are "amplified" by sensitive cw intracavity loss modulation. Our results show that they are repeatable and are dependent on pumping power and wavelength, and their response time ranges from tens of seconds to several minutes. The recorded dynamical transitions between the self-focusing to the self-defocusing (or vice versa) induced by the PR effect may be critically important for us to give more insight into the stability of some cascade nonlinear frequency conversions, e.g. multi-stage optical parametric amplifiers.

  16. The new methods of treatment for age-related macular degeneration using the ultra-short pulsed laser

    Iwamoto, Yumiko; Awazu, Kunio; Suzuki, Sachiko; Ohshima, Tetsuro; Sawa, Miki; Sakaguchi, Hirokazu; Tano, Yasuo; Ohji, Masahito


    The non-invasive methods of treatments have been studying for the improvement of quality of life (QOL) of patients undergoing treatment. A photodynamic therapy (PDT) is one of the non-invasive treatments. PDT is the methods of treatment using combination of a laser and a photosensitizer. PDT has few risks for patients. Furthermore, PDT enables function preservation of a disease part. PDT has been used for early cancer till now, but in late years it is applied for age-related macular degeneration (AMD). AMD is one of the causes of vision loss in older people. However, PDT for AMD does not produce the best improvement in visual acuity. The skin photosensivity by an absorption characteristic of a photosensitizer is avoided. We examined new PDT using combination of an ultra-short pulsed laser and indocyanine green (ICG).

  17. Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse

    Liu Ji-Cai; Wang Chun-Xin; Gel'mukhanov Faris; Wang Chuan-Kui


    This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultrashort laser pulse by solving numerically the full-wave Maxwell-Bloeh equations.The 4,4'-bis(dimethylamino) stilbene molecule is used as the model molecule because of its strong two-photon absorption property.The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence.The propagation effects on the evolution of the cooperative radiations are also taken into account.The cooperative radiations are enhanced for large number density of the molecule,while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions.The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance.

  18. Time delay and excitation mode induced tunable red/near-infrared to green emission ratio of Er doped BiOCl

    Avram, Daniel; Florea, Mihaela; Tiseanu, Ion; Tiseanu, Carmen


    Herein, we report on the emission color tunability of Er doped BiOCl measured under up—conversion as well as x-ray excitation modes. The dependence of red (670 nm) to green emission (543 nm) ratio on Er concentration (1 and 5%), excitation wavelength into different (656.4, 802 and 976 nm) or across single Er absorption levels (965 ÷ 990 nm) and delay after the laser pulse (0.001 ÷ 1 ms) is discussed in terms of ground state absorption/excited state absorption and energy transfer up-conversion mechanisms. A first example of extended Er x-ray emission measured in the range of 500 to 1700 nm shows comparable emission intensities corresponding to 543 nm and 1500 nm based transitions. The present results together with our earlier report on the upconversion emission of Er doped BiOCl excited at 1500 nm, suggest that Er doped BiOCl may be considered an attractive system for optical and x-ray imaging applications.

  19. Effect of ultrashort pulsed laser on bond strength of Y-TZP zirconia ceramic to tooth surfaces.

    Unal, Server Mutluay; Nigiz, Remzi; Polat, Zelal Seyfioglu; Usumez, Aslıhan


    There is limited knowledge about the effects of ultrashort pulsed laser on zirconia ceramic surfaces. The aim of this study was to evaluate the effects of ytterbium (Yb)-doped fiber laser and other surface treatment methods -namely, sandblasting with 110 µm aluminum oxide or 30 µm silica-coated alumina on shear bond strength (SBS) of zirconia to tooth surface. A total of 128 zirconium oxide disks were made by using CAD-CAM technology. Disk surfaces were sandblasted with Al2O3 particles or silica-coated alumina or irradiated with Yb-doped fiber based nanosecond pulsed laser at 85W output power at 25 kHz. Disks were luted to dentin using two different resin cement. SBS of each specimen was measured. Results were statistically analyzed using two-way analysis of variance (ANOVA) and Bonferroni and Dunnett tests (p<0.005). Highest bond strength was obtained when zirconia surface was pretreated with Yb-doped fiber-based nanosecond pulsed laser regardless of the resin cement used.

  20. Time-dependent H-like and He-like Al lines produced by ultra-short pulse laser

    Kato, Takako; Kato, Masatoshi [National Inst. for Fusion Science, Nagoya (Japan); Shepherd, R.; Young, B.; More, R.; Osterheld, Al


    We have performed numerical modeling of time-resolved x-ray spectra from thin foil targets heated by the LLNL Ultra-short pulse (USP) laser. The targets were aluminum foils of thickness ranging from 250 A to 1250 A, heated with 120 fsec pulses of 400 nm light from the USP laser. The laser energy was approximately 0.2 Joules, focused to a 3 micron spot size for a peak intensity near 2 x 10{sup 19} W/cm{sup 2}. Ly{alpha} and He{alpha} lines were recorded using a 900 fsec x-ray streak camera. We calculate the effective ionization, recombination and emission rate coefficients including density effects for H-like and He-like aluminum ions using a collisional radiative model. We calculate time-dependent ion abundances using these effective ionization and recombination rate coefficients. The time-dependent electron temperature and density used in the calculation are based on an analytical model for the hydrodynamic expansion of the target foils. During the laser pulse the target is ionized. After the laser heating stops, the plasma begins to recombine. Using the calculated time dependent ion abundances and the effective emission rate coefficients, we calculate the time dependent Ly{alpha} and He{alpha} lines. The calculations reproduce the main qualitative features of the experimental spectra. (author)

  1. Ultrashort-Pulse Lasers Treating the Crystalline Lens: Will They Cause Vision-Threatening Cataract? (An American Ophthalmological Society Thesis)

    Krueger, Ronald R.; Uy, Harvey; McDonald, Jared; Edwards, Keith


    Purpose: To demonstrate that ultrashort-pulse laser treatment in the crystalline lens does not form a focal, progressive, or vision-threatening cataract. Methods: An Nd:vanadate picosecond laser (10 ps) with prototype delivery system was used. Primates: 11 rhesus monkey eyes were prospectively treated at the University of Wisconsin (energy 25–45 μJ/pulse and 2.0–11.3M pulses per lens). Analysis of lens clarity and fundus imaging was assessed postoperatively for up to 4½ years (5 eyes). Humans: 80 presbyopic patients were prospectively treated in one eye at the Asian Eye Institute in the Philippines (energy 10 μJ/pulse and 0.45–1.45M pulses per lens). Analysis of lens clarity, best-corrected visual acuity, and subjective symptoms was performed at 1 month, prior to elective lens extraction. Results: Bubbles were immediately seen, with resolution within the first 24 to 48 hours. Afterwards, the laser pattern could be seen with faint, noncoalescing, pinpoint micro-opacities in both primate and human eyes. In primates, long-term follow-up at 4½ years showed no focal or progressive cataract, except in 2 eyes with preexisting cataract. In humans, 70% reported acceptable or better distance vision and no or mild symptoms. Meanwhile, >70% without sparing (0 and 0.5 mm radius) lost 2 or more lines, and most reported poor or severe vision and symptoms. Conclusions: Focal, progressive, and vision-threatening cataracts can be avoided by lowering the laser energy, avoiding prior cataract, and sparing the center of the lens. PMID:23818739

  2. Generating ultra-short energetic pulses with cascaded soliton compression in lithium niobate crystals

    Zhou, Binbin; Bache, Morten; Chong, A.;


    By launching energetic femtosecond pulses in a lithium niobate crystal, the phase mismatched second-harmonic generation process compresses the 50 fs input pulse at 1250 nm to 30 fs through a soliton effect.......By launching energetic femtosecond pulses in a lithium niobate crystal, the phase mismatched second-harmonic generation process compresses the 50 fs input pulse at 1250 nm to 30 fs through a soliton effect....

  3. Controllable delay of ultrashort pulses in a quantum dot optical amplifier

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


    Optical and electrical tuning of the propagation time of 170 fs pulses in a quantum dot semiconductor amplifier at room temperature is demonstrated. Both pulse slowdown and advancement is possible and we achieve fractional delays (delay divided with pulse duration) of up to 40%. The results...

  4. Ultrashort optical pulse generation from a chromium(4)- doped yttrium aluminium garnet tunable solid-state laser

    Chang, Yongmao


    In this thesis, experimental results of ultrashort pulse generation from Cr4+-doped yttrium aluminium garnet (YAG) laser system are presented. The Cr4+:YAG crystal is a vibronically broadened solid state laser gain medium, which lases at room temperature from 1.34 to 1.58 μm and can be pumped by a Nd:YAG laser at 1.06 μm. Ultrashort pulses from this coherent light source are potentially important in technology applications such as ultrafast fiber-optic communications and time-resolved spectroscopy of narrow- bandgap, semiconductors. It is a practical alternative to more conventional cryogenic colour center lasers at this wavelength such as NaCl:OH- or complex optical parametric oscillators synchronously pumped by a Ti:sapphire laser. The cw power performance of a Cr4+:YAG laser was characterized and several unique properties were identified. A broad tuning range of 210 nm, i.e., from 1345 to 1557 nm, was demonstrated by means of one set of mirrors with useful cw output power of as high as 730 mW at 1.46 μm (with a Nd:YAG pump power of 6.5 W). The lasing action was found to be strongly influenced by the temperature of the crystal and the combined effects of thermal lensing and saturable absorption of the pump beam. The excited-state absorption (ESA) at the pump and lasing wavelengths were investigated both experimentally and theoretically. ESA at the lasing wavelength occurs for the transition from the state 3B2(3T2) to 3E(3T1(F)), while the pump ESA comes from the transition from 3A2(3T2 ) to 3E(3T1(P)). The emission ESA cross sections for the free-running modes were estimated from the laser efficiency data by taking into account the pump and cavity parameters. Ultrashort pulse generation with a Cr4+:YAG laser was investigated using passive mode-locking with a semiconductor quantum well saturable absorber. Self-starting of the laser system was demonstrated using a strained GaInAs/InAlAs saturable Bragg reflector (SBR) with a single prism for dispersion

  5. Effect of Lorentz local field correction on propagation of ultrashort laser pulse in one-dimensional para-nitroaniline (PNA)molecules

    Zhou Yong; Miao Quan; Wang Chuan-Kui


    This paper investigates the effect of Lorentz local field correction(LFC)on the propagation of ultrashort laser pulses in a para-nitroaniline molecular medium under resonant and nonresonant conditions by solving numerically the full-wave Maxwell-Bloch equations beyond slowly-varying envelope approximation and rotating-wave approximation.The effect of the LFC is considerably obvious when pulses with large areas propagate in the dense molecular medium.In the case of resonance, the group velocity of the sub-pulses split from the incident pulse along propagation is severely decreased by the LFC, especially for the latest sub-pulse. However, in the case of nonresonance, the influence of the LFC on the temporal evolution of the pulse is less obvious and lacks homogeneity with an increase in incident pulse area, propagation distance and molecular density.

  6. Pondermotive acceleration of electrons to GeV energies by a tightly focused ultra-short ultra-intense laser pulse

    Tian, Youwei; Yu, Wei; Lu, Peixiang; He, Feng; Xu, Han


    Laser-driven pondermotive acceleration of electrons in vacuum has been considered using computer simulations. It is demonstrated that a low-energy free electron can be violently accelerated to final kinetic energy of GeV by a tightly focused ultra-short ultra-intense laser pulse. Suitable conditions that are crucial for this phenomenon to occur have been investigated. It is shown that selection of appropriate initial conditions like relative time delay between electron and the laser pulse, electron's incident angle and momentum, laser pulse duration and its focal spot size play important roles in the efficient acceleration scheme.

  7. Optical control of filamentation-induced damage to DNA by intense, ultrashort, near-infrared laser pulses

    Dharmadhikari, J. A.; Dharmadhikari, A. K.; Kasuba, K. C.; Bharambe, H.; D’Souza, J. S.; Rathod, K. D.; Mathur, D.


    We report on damage to DNA in an aqueous medium induced by ultrashort pulses of intense laser light of 800 nm wavelength. Focusing of such pulses, using lenses of various focal lengths, induces plasma formation within the aqueous medium. Such plasma can have a spatial extent that is far in excess of the Rayleigh range. In the case of water, the resulting ionization and dissociation gives rise to in situ generation of low-energy electrons and OH-radicals. Interactions of these with plasmid DNA produce nicks in the DNA backbone: single strand breaks (SSBs) are induced as are, at higher laser intensities, double strand breaks (DSBs). Under physiological conditions, the latter are not readily amenable to repair. Systematic quantification of SSBs and DSBs at different values of incident laser energy and under different external focusing conditions reveals that damage occurs in two distinct regimes. Numerical aperture is the experimental handle that delineates the two regimes, permitting simple optical control over the extent of DNA damage.

  8. Precise ablation of dental hard tissues with ultra-short pulsed lasers. Preliminary exploratory investigation on adequate laser parameters.

    Bello-Silva, Marina Stella; Wehner, Martin; Eduardo, Carlos de Paula; Lampert, Friedrich; Poprawe, Reinhart; Hermans, Martin; Esteves-Oliveira, Marcella


    This study aimed to evaluate the possibility of introducing ultra-short pulsed lasers (USPL) in restorative dentistry by maintaining the well-known benefits of lasers for caries removal, but also overcoming disadvantages, such as thermal damage of irradiated substrate. USPL ablation of dental hard tissues was investigated in two phases. Phase 1--different wavelengths (355, 532, 1,045, and 1,064 nm), pulse durations (picoseconds and femtoseconds) and irradiation parameters (scanning speed, output power, and pulse repetition rate) were assessed for enamel and dentin. Ablation rate was determined, and the temperature increase measured in real time. Phase 2--the most favorable laser parameters were evaluated to correlate temperature increase to ablation rate and ablation efficiency. The influence of cooling methods (air, air-water spray) on ablation process was further analyzed. All parameters tested provided precise and selective tissue ablation. For all lasers, faster scanning speeds resulted in better interaction and reduced temperature increase. The most adequate results were observed for the 1064-nm ps-laser and the 1045-nm fs-laser. Forced cooling caused moderate changes in temperature increase, but reduced ablation, being considered unnecessary during irradiation with USPL. For dentin, the correlation between temperature increase and ablation efficiency was satisfactory for both pulse durations, while for enamel, the best correlation was observed for fs-laser, independently of the power used. USPL may be suitable for cavity preparation in dentin and enamel, since effective ablation and low temperature increase were observed. If adequate laser parameters are selected, this technique seems to be promising for promoting the laser-assisted, minimally invasive approach.

  9. Evolution of hole shape and size during short and ultrashort pulse laser deep drilling.

    Döring, Sven; Szilagyi, John; Richter, Sören; Zimmermann, Felix; Richardson, Martin; Tünnermann, Andreas; Nolte, Stefan


    A detailed study of the influence of the pulse duration, from the femtosecond to the nanosecond regime, on the evolution of the hole shape and depth during percussion drilling in silicon is presented. Real-time backlight imaging of the hole development is obtained for holes up to 2 mm deep with aspect ratios extending to 25:1. For low pulse energies, the hole-shape and drilling characteristics are similar for femtosecond, picoseconds and nanosecond regimes. At higher pulse energies, ns-pulses exhibit slower average drilling rates but eventually reach greater final depths. The shape of these holes is however dominated by branching and large internal cavities. For ps-pulses, a cylindrical shape is maintained with frequent small bulges on the side-walls. In contrast, fs-pulses cause only a limited number of imperfections on a tapered hole shape.

  10. Effects of spectral linewidth of ultrashort pulses on the spa-tiotemporal distribution of diffraction fields


    The spatiotemporal characteristics of electromagnetic pulses with ultrabroad spectral bandwidth in the far field are analyzed by using classical scalar diffraction theory. The effects of the ratio of the frequency width to the central frequency on the diffraction spatial distribution are discussed. It is concluded that the diffraction spatial dis-tribution of the pulsed radiation gets narrower than a mono-chromatic wave when the frequency width of the pulse is comparable to or larger than its central frequency.

  11. Normal Auger processes with ultrashort x-ray pulses in neon

    Sullivan, Raymond; Jia, Junteng; Vázquez-Mayagoitia, Álvaro; Picón, Antonio


    Modern x-ray sources enable the production of coherent x-ray pulses with a pulse duration in the same order as the characteristic lifetimes of core-hole states of atoms and molecules. These pulses enable the manipulation of the core-hole population during Auger-decay processes, modifying the line shape of the electron spectra. In this work, we present a theoretical model to study those effects in neon. We identify effects in the Auger-electron-photoelectron coincidence spectrum due to the duration and intensity of the pulses. The normal Auger line shape is recovered in Auger-electron spectra integrated over all photoelectron energies.

  12. Measurement of Hot Electron Spectrum During the Interaction of Ultrashort Pulse UV Laser With Solid Target

    LIYe-jun; SHANYu-sheng; ZHANGJi; ZHANGHai-feng; TANGXiu-zhang; WANGLei-jian


    The hot electron spectrum was measured using electron magnetic spectrometer through the irradiation of solid Cu target by an intense, UV (248 nm) femtosecond (440 fs) laser pulse with free pre-pulse, and the intensity of laser is 1017 W/cm2. We find the electron spectrum presents two temperatures Maxwellian distribution.

  13. Proceedings of the first JAERI-Kansai international workshop on ultrashort-pulse ultrahigh-power lasers and simulation for laser-plasma interactions



    Records of the First JAERI-Kansai International Workshop, which focused on the subject of `Ultrashort-Pulse Ultrahigh-Power Lasers and Simulation for Laser-Plasma Interactions`, are contained in this issue. The First JAERI-Kansai International Workshop was held as Joint ICFA/JAERI-Kansai International Workshop `97 with International Committee for Future Accelerators (ICFA). This report consists of 24 contributed papers. (J.P.N.)

  14. Design and Fabrication of an Er-Doped Silica Optical Fiber with Six Photosensitive Subcores

    LI Jian; WANG Jing; LIU Peng; LU Shao-Hua; MAO Xiang-Qiao; JIANG Wei-Wei; NING Ti-Gang; JIAN Shui-Sheng


    A type of multi-core Er-doped photosensitive silica optical fiber (MC-EDPF) is proposed and fabricated, in which a high consistency Er-doped core is surrounded by six high consistency Ge-doped cores. The multi-core design can overcome the difficulties encountered in the design and fabrication of single-core EDPFs through a modified chemical vapor deposition method combined with solution doping technology, and there is a conflict between high consistency Er doping and high consistency Ge doping. The absorption of MC-EDPFs achieved 15.876dB/m at 1550nm and 10dB/m at 980hm. The reflectivity of the fiber Bragg gratings (FBGs) written directly on the MC-EDPFs is as much as 96.84%.

  15. Ultrashort-pulse laser irradiation of metal films: the effect of a double-peak laser pulse

    Rosandi, Yudi [Universitaet Kaiserslautern, Fachbereich Physik und Forschungszentrum OPTIMAS, Kaiserslautern (Germany); Universitas Padjadjaran, Department of Physics, Sumedang (Indonesia); Urbassek, Herbert M. [Universitaet Kaiserslautern, Fachbereich Physik und Forschungszentrum OPTIMAS, Kaiserslautern (Germany)


    Using molecular-dynamics simulation coupled to a homogeneous model for the electron gas, we study the response of an Al thin film on short-pulse laser irradiation. Laser pulses are considered to have a double-peak structure consisting of two Gaussian pulses; the time delay between the two pulses is varied. The temporal dependence of the energy transfer from the electronic system to the lattice is considered in detail. The effect on the temperature and pressure inside the material, as well as on melting, void nucleation and spallation (ablation) are studied. (orig.)

  16. Ultrashort-pulse generation in a YAG:Nd(3+) laser in a scheme with colliding pulses

    Prokhorenko, V.I.; Tikhonov, E.A.; Iatskiv, D.IA.; Bushmakin, E.N.


    The time, energy, and statistical characteristics of a picosecond mode-locked YAG:Nd(3+) laser with colliding pulses are studied. Under these conditions, no additional pulse shortening occurs as compared to a laser utilizing an absorber which is in contact with the nontransmitting mirror. However, this mode of operation is characterized by a greater reproducibility of the emitted pulse duration. A direct recording of the duration and the spectrum is used. It is shown that spectrally limited pulses are emitted only when the cell with a saturable absorber (dye No. 3274) is located in the center of the antiresonant reflector. 11 references.

  17. Filamentation of ultrashort laser pulses in silica glass and KDP crystal: A comparative study

    Rolle, Jérémie; Duchateau, Guillaume; Skupin, Stefan


    Ionizing 800-nm femtosecond laser pulses propagating in silica glass and in potassium dihydrogen phosphate (KDP) crystal are investigated by means of a unidirectional pulse propagation code. Filamentation in fused silica is compared with the self-channeling of light in KDP accounting for the presence of defect states and electron-hole dynamics. In KDP, laser pulses produce intense filaments with higher clamping intensities up to 200 TW/cm$^2$ and longer plasma channels with electron densities above $10^{16}$ cm$^{-3}$. Despite these differences, the propagation dynamics in silica and KDP are almost identical at equivalent ratios of input power over the critical power for self-focusing.

  18. Temporal transformation of periodic incoherent ultrashort light pulses by chirped fiber gratings.

    Zalvidea, Dobryna; Duchowicz, Ricardo; Sicre, Enrique E


    The analogy between free-space propagation of optical beams and light-pulse reflection from linearly chirped fiber gratings is used to analyze the Lau effect in the temporal domain. The coherence conditions that are satisfied in the spatial domain for obtaining, at certain fixed locations, periodic fringes patterns are reformulated for guided light propagation. In this analogy, spatial periodic irradiance distributions are transformed in periodic sequences of light pulses. An optical setup is proposed to produce sharp pulse trains, with minimal distortion effects, that have repetition frequencies that are different from those associated with the input periodic optical signal. Some numerical results are given to illustrate this approach.

  19. Stimulated Raman scattering of light absorbing media excited by ultrashort laser pulses

    Marchevskiy, F. N.; Strizhevskiy, V. L.; Feshchenko, V. P.


    The fluctuation-dissipation theory of spontaneous and stimulated vibration Raman scattering is worked out taking into account the dissipation losses at frequencies of laser pump and scattering radiation. General expressions are found, which describe the absolute intensities and shape, energy and duration of scattered pulses in terms of the parameters of the medium and the the input laser pulses. The general regularities are analyzed in detail. Conditions are found for the realization of spontaneous or stimulated Raman scattering and its dependence on absorption, pulse duration and other parameters of the problem.

  20. Production of ultrashort FEL XUV pulses via a reverse undulator taper

    Fawley, W. M.


    We adapt the "reverse taper" scheme presented by Saldin et al. (Phys. Rev. ST Accel. Beams 9 (2006) 050702) for attosecond pulse production to the XUV/soft-X-ray regime. We find that GW-level pulses of a few femtosecond duration or shorter can be produced using electron beams of quite moderate parameters and undulators of 20-m length or shorter. The output pulse is significantly shifted in wavelength relative to the main background which permits a further increase in contrast ratio via simple monochromatization. Moreover, the output pulse has a natural wavelength chirp that allows further temporal compression, if wanted. Both positive and negative chirps can be produced depending upon the sign of the undulator taper.

  1. Precise measurement of the micron-scale spot of ultrashort laser pulse based on film scanning

    Fengtie Wu; Jianrong Zhang; Yunbin Chen; Dongdong Guo


    @@ A novel and precise micron-scale nanosecond laser spot measurement based on film-scanning method is presented. The method can be used to measure the spot size, beam profile, and intensity distribution of the pulse.

  2. Coherent population transfer in molecules coupled with a dissipative environment by an intense ultrashort chirped pulse

    Fainberg, B. D.; Gorbunov, V. A.


    We have studied the intense chirped pulse excitation of a molecule coupled with a dissipative environment taking into account electronic coherence effects. We considered a two-state electronic system with relaxation treated as a diffusion on electronic potential energy surfaces. This relaxation model enables us to trace continuously the transition from a coherent population transfer to incoherent one. An inhomogeneously broadened system with frozen nuclear motion is invoked to model a purely coherent transfer. We show that the type of population transfer (coherent or incoherent) strongly depends on the pulse chirp, its sign, and the detunings of the exciting pulse carrier frequency with respect to the frequency of the Franck-Condon transition. For positive chirped pulses and moderate detunings, relaxation does not hinder a coherent population transfer. Moreover, under these conditions the relaxation favors more efficient population transfer with respect to the "coherent" system with frozen nuclear motion.

  3. Selective Ablation of thin Nickel-chromium-alloy Films Using Ultrashort Pulsed Laser

    Pabst, Linda; Ebert, Robby; Exner, Horst

    The selective ablation of 100nm thin Nickel-Chromium-alloy films on glass substrate was investigated using femtosecond laser pulses (λ=1030nm, τp=170 fs, Ep,max=7μJ). The influence of the processing parameters such as fluence, pulse number and pulse repetition rate on the ablation process was examined. Single and multiple pulses ablation thresholds of the Nickel-Chromium-alloy film were determined and the incubation coefficient calculated. Optical and electron microscopy were employed to characterize the patterned area. As a result, different irradiation morphologies were observed, dependent from the processing parameters. A processing window for film side ablation of the Nickel-Chromium-alloy film without damaging the underlying glass substrate was found, however, the edge of the ablation craters were covered with laser induced periodic surface structures (LIPSS).

  4. On the interaction of the ultrashort laser pulses with human brain matter

    Marciak-Kozlowska, J


    In this paper the modified Schrodinger equation for attosecond laser pulses interaction with "atoms" of human brain . i.e. neurons is developed and solved. Considering that the mass of the human neuron is of the order of Planck mass =10-5 g the model equation for Planck masses is applied to the laser pulse neuron interaction. Key words: Modified Schr\\"odinger Equation, Planck particles, neurons

  5. Harmonizing HeLa cell cytoskeleton behavior by multi-Ti oxide phased nanostructure synthesized through ultrashort pulsed laser.

    Chinnakkannu Vijayakumar, Chandramouli; Venkatakrishnan, Krishnan; Tan, Bo


    Knowledge about cancer cell behavior on heterogeneous nanostructures is relevant for developing a distinct biomaterial that can actuate cancer cells. In this manuscript, we have demonstrated a harmonized approach of forming multi Ti-oxide phases in a nanostructure (MTOP nanostructure) for its unique cancer cell controlling behavior.Conventionally, single phases of TiO2 are used for targeted therapy and as drug carrier systems.In this research, we have shown a biomaterial that can control HeLa cells diligently using a combination of TiO, Ti3O and TiO2 phases when compared to fibroblast (NIH3T3) cells.MTOP-nanostructures are generated by varying the ionization energy in the vapor plume of the ultrashort pulse laser; this interaction with the material allows accurate tuning and composition of phases within the nanostructure. In addition, the lattice spacing of MTOP-nanostructures was analyzed as shown by HR-TEM investigations. An FESEM investigation of MTOP-nanostructures revealed a greater reduction of HeLa cells relative to fibroblast cells. Altered cell adhesion was followed by modulation of HeLa cell architecture with a significant reduction of actin stress fibers.The intricate combination of MTOP-nanostructures renders a biomaterial that can precisely alter HeLa cell but not fibroblast cell behavior, filling a void in the research for a biomaterial to modulate cancer cell behavior.

  6. Enhancing ablation efficiency in micro structuring using a deformable mirror for beam shaping of ultra-short laser pulses

    Smarra, M.; Dickmann, K.


    Using ultra-short laser pulses for the generation of microstructures results in a high flexible tool for free form geometries in the micro range. Increasing laser power and repetition rates increase as well the demand of high flexible and efficient process strategies. To increase the ablation efficiency the optimal fluency can be determined, which is a material specific value. By varying the beam shape, the ablation efficiency can be enhanced. In this study a deformable mirror was used to vary the beam shape. This mirror is built by combining a piezo-electric ceramic and a mirror substrate. The ceramic is divided into several segments, which can be controlled independently. This results in a high flexible deformable mirror which influences the beam shape and can be used to vary the spot size or generate line geometries. The ablation efficiency and roughness of small generated cavities were analyzed in this study as well as the dimensions of the cavity. This can be used to optimize process strategies to combine high volume ablation and fine detail generation.

  7. Harmonizing HeLa cell cytoskeleton behavior by multi-Ti oxide phased nanostructure synthesized through ultrashort pulsed laser

    Chinnakkannu Vijayakumar, Chandramouli; Venkatakrishnan, Krishnan; Tan, Bo


    Knowledge about cancer cell behavior on heterogeneous nanostructures is relevant for developing a distinct biomaterial that can actuate cancer cells. In this manuscript, we have demonstrated a harmonized approach of forming multi Ti-oxide phases in a nanostructure (MTOP nanostructure) for its unique cancer cell controlling behavior.Conventionally, single phases of TiO2 are used for targeted therapy and as drug carrier systems.In this research, we have shown a biomaterial that can control HeLa cells diligently using a combination of TiO, Ti3O and TiO2 phases when compared to fibroblast (NIH3T3) cells.MTOP-nanostructures are generated by varying the ionization energy in the vapor plume of the ultrashort pulse laser; this interaction with the material allows accurate tuning and composition of phases within the nanostructure. In addition, the lattice spacing of MTOP-nanostructures was analyzed as shown by HR-TEM investigations. An FESEM investigation of MTOP-nanostructures revealed a greater reduction of HeLa cells relative to fibroblast cells. Altered cell adhesion was followed by modulation of HeLa cell architecture with a significant reduction of actin stress fibers.The intricate combination of MTOP-nanostructures renders a biomaterial that can precisely alter HeLa cell but not fibroblast cell behavior, filling a void in the research for a biomaterial to modulate cancer cell behavior.

  8. Ultrashort pulses-driven dynamics of blisters in Au-coated gratings

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


    Au-coated gratings (ACGs) for chirped pulse compression were irradiated using 800 ± 35 nm multiple laser pulses with duration of 30 fs. The laser-induced damage threshold (LIDT) of Au-coated gratings decreases from 0.35 J/cm2 to 0.10 J/cm2 with the increased pulse shots. The near threshold damage feature of Au-coated gratings at different pulses shows blisters. It is indicated that the gradually increased blister height with increasing multiple pulses on ACGs is caused by the accumulation effect. The damage morphologies combine with simulated results indicate that the damage of the ACGs can be attributed to the pinholes at the base of grating pillars and the separation of gold coating and photoresist gratings caused by the photoresist absorbed the incident laser energy. Therefore, we consider the damage threshold can be enhanced by optimizing coating deposition technology to reduce pinholes density and increase the adhesion between the gold and the photoresist.

  9. Study of ultra-high gradient wakefield excitation by intense ultrashort laser pulses in plasma

    Kotaki, H


    We investigate a mechanism of nonlinear phenomena in laser-plasma interaction, a laser wakefield excited by intense laser pulses, and the possibility of generating an intense bright electron source by an intense laser pulse. We need to understand and further employ some of these phenomena for our purposes. We measure self-focusing, filamentation, and the anomalous blueshift of the laser pulse. The ionization of gas with the self-focusing causes a broad continuous spectrum with blueshift. The normal blueshift depends on the laser intensity and the plasma density. We, however, have found different phenomenon. The laser spectrum shifts to fixed wavelength independent of the laser power and gas pressure above some critical power. We call the phenomenon 'anomalous blueshift'. The results are explained by the formation of filaments. An intense laser pulse can excite a laser wakefield in plasma. The coherent wakefield excited by 2 TW, 50 fs laser pulses in a gas-jet plasma around 10 sup 1 sup 8 cm sup - sup 3 is mea...

  10. Generation of "gigantic" ultra-short microwave pulses based on passive mode-locking effect in electron oscillators with saturable absorber in the feedback loop

    Ginzburg, N. S.; Denisov, G. G.; Vilkov, M. N.; Zotova, I. V.; Sergeev, A. S.


    A periodic train of powerful ultrashort microwave pulses can be generated in electron oscillators with a non-linear saturable absorber installed in the feedback loop. This method of pulse formation resembles the passive mode-locking widely used in laser physics. Nevertheless, there is a specific feature in the mechanism of pulse amplification when consecutive energy extraction from different fractions of a stationary electron beam takes place due to pulse slippage over the beam caused by the difference between the wave group velocity and the electron axial velocity. As a result, the peak power of generated "gigantic" pulses can exceed not only the level of steady-state generation but also, in the optimal case, the power of the driving electron beam.

  11. Effect of intense, ultrashort laser pulses on DNA plasmids in their native state: strand breakages induced by {\\it in-situ} electrons and radicals

    D'Souza, J S; Dharmadhikari, A K; Rao, B J; Mathur, D


    Single strand breaks are induced in DNA plasmids, pBR322 and pUC19, in aqueous media exposed to strong fields generated using ultrashort laser pulses (820 nm wavelength, 45 fs pulse duration, 1 kHz repetition rate) at intensities of 1-12 TW cm$^{-2}$. The strong fields generate, {\\it in situ}, electrons and radicals that induce transformation of supercoiled DNA into relaxed DNA, the extent of which is quantified. Introduction of electron and radical scavengers inhibits DNA damage; results indicate that OH radicals are the primary (but not sole) cause of DNA damage.

  12. Coherent manipulation of four-level double lambda-like atomic system by a train of ultra-short few-cycle-optical pulses

    Kumar, Pawan


    We have demonstrated that near complete coherence can be achieved in a four level double lambda-like systems using a train of ultra-short optical pulses. The effect of the Doppler broadening has been analyzed and a scheme has been proposed for establishing high and uniform coherence across different velocity groups in the atomic ensemble. We have also presented a novel scheme of excitation using chirped pulses and shown that in addition to generating coherence in the system it is possible to alter the translational states of the atoms.

  13. Two-phase zirconium boride thin film obtained by ultra-short pulsed laser ablation of a ZrB{sub 12} target

    De Bonis, A., E-mail: [Dipartimento di Scienze, Università della Basilicata, Viale dell’Ateneo Lucano, 10 -85100 Potenza (Italy); Istituto di Metodologie Inorganiche e dei Plasmi, Consiglio Nazionale delle Ricerche, U.O.S. di Potenza, C.da Santa Loja, 85010 Tito Scalo, Potenza (Italy); Santagata, A. [Istituto di Metodologie Inorganiche e dei Plasmi, Consiglio Nazionale delle Ricerche, U.O.S. di Potenza, C.da Santa Loja, 85010 Tito Scalo, Potenza (Italy); Rau, J.V. [Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Via del Fosso del Cavaliere 100, 00133 Rome (Italy); Latini, A. [Università di Roma “La Sapienza”, Dipartimento di Chimica, Piazzale Aldo Moro, 5 -00185 Rome (Italy); Mori, T. [National Institute for Materials Science (NIMS) WPI Materials Nanoarchitectonics Center (MANA), Namiki 1-1, Tsukuba 305-0044 (Japan); Medici, L. [Istituto di Metodologie per le Analisi Ambientali, Consiglio Nazionale delle Ricerche, U.O.S. di Potenza, C.da Santa Loja, 85010 Tito Scalo, Potenza (Italy); Teghil, R. [Dipartimento di Scienze, Università della Basilicata, Viale dell’Ateneo Lucano, 10 -85100 Potenza (Italy)


    Two-phase zirconium boride thin films have been obtained by ultra-short pulsed laser ablation (PLA) of a zirconium dodecaboride (ZrB{sub 12}) target performed in vacuum. The ablation source was a frequency doubled (λ = 527 nm) Nd:glass laser with a pulse duration of 250 fs. Laser induced plasma has been studied by ICCD imaging and time and space resolved optical emission spectroscopy (OES), whereas the deposited films have been characterized by atomic force microscopy, scanning electron microscopy, X-Ray diffraction and micro-Raman spectroscopy. The film morphology and composition have been interpreted on the basis of the laser ablation mechanism.

  14. Hydrodynamics driven by ultrashort laser pulse: simulations and the optical pump—X-ray probe experiment

    Inogamov, N. A.; Zhakhovsky, V. V.; Hasegawa, N.; Nishikino, M.; Yamagiwa, M.; Ishino, M.; Agranat, M. B.; Ashitkov, S. I.; Faenov, A. Ya.; Khokhlov, V. A.; Ilnitsky, D. K.; Petrov, Yu. V.; Migdal, K. P.; Pikuz, T. A.; Takayoshi, S.; Eyama, T.; Kakimoto, N.; Tomita, T.; Baba, M.; Minami, Y.; Suemoto, T.; Kawachi, T.


    Spatial structures of ablative mass flow produced by femtosecond laser pulses are studied. In experiments with a gold film, the Ti:sapp laser pulse having a focal size of 100 microns on a target was used, while a soft X-ray probe pulse was utilized for diagnostics. The experimental data are compared with simulated mass flows obtained by two-temperature hydrodynamics and molecular dynamics methods. Simulation shows evolution of a thin surface layer pressurized after electron-ion thermalization, which leads to melting, cavitation and formation of spallation liquid layer. The calculated asymptotic surface velocity of this layer as a function of fluence is in reasonably good agreement with experimental data.

  15. Electron Acceleration and the Propagation of Ultrashort High-Intensity Laser Pulses in Plasmas

    Wang, Xiaofang; Krishnan, Mohan; Saleh, Ned; Wang, Haiwen; Umstadter, Donald


    Reported are interactions of high-intensity laser pulses ({lambda}=810 nm and I{<=}3x10{sup 18} W /cm{sup 2} ) with plasmas in a new parameter regime, in which the pulse duration ({tau}=29 fs ) corresponds to 0.6-2.6 plasma periods. Relativistic filamentation is observed to cause laser-beam breakup and scattering of the beam out of the vacuum propagation angle. A beam of megaelectronvolt electrons with divergence angle as small as 1 degree sign is generated in the forward direction, which is correlated to the growth of the relativistic filamentation. Raman scattering, however, is found to be much less than previous long-pulse results. (c) 2000 The American Physical Society.

  16. An ultrashort-pulse reconstruction software: GROG, applied to the FLAME laser system

    Galletti, Mario


    The GRENOUILLE traces of FLAME Probe line pulses (60mJ, 10mJ after compression, 70fs, 1cm FWHM, 10Hz) were acquired in the FLAME Front End Area (FFEA) at the Laboratori Nazionali di Frascati (LNF), Instituto Nazionale di Fisica Nucleare (INFN). The complete characterization of the laser pulse parameters was made using a new algorithm: GRenouille/FrOG (GROG). A characterization with a commercial algorithm, QUICKFrog, was also made. The temporal and spectral parameters came out to be in great agreement for the two kinds of algorithms. In this experimental campaign the Probe line of FLAME has been completely characterized and it has been showed how GROG, the developed algorithm, works as well as QuickFrog algorithm with this type of pulse class.

  17. Fragmentation dynamics of liquid-metal droplets under ultra-short laser pulses

    Basko, M. M.; Krivokorytov, M. S.; Vinokhodov, A. Yu; Sidelnikov, Yu V.; Krivtsun, V. M.; Medvedev, V. V.; Kim, D. A.; Kompanets, V. O.; Lash, A. A.; Koshelev, K. N.


    We present the measurements and theoretical analysis of the deformation and fragmentation of spherical liquid-metal drops by picosecond and subpicosecond laser pulses. In the experiments, 60 μm droplets of Sn-In alloy were irradiated by Ti:Sa laser pulses with a peak energy fluence of  ˜100 J cm-2. The observed evolution of the droplet shape dramatically differs from that previously reported for nanosecond pulses. Invoking 2D hydrodynamic simulations, we explain how, due to the specifics of matter dynamics in the liquid-vapor phase coexistence region, a liquid droplet is transformed into a characteristic acorn-like expanding shell with two inner cavities. High sensitivity of the measured shell parameters to the details of the equation of state and metastable dynamics suggests that such experiments offer new possibilities in exploration of thermophysical properties of metals in the region of liquid-vapor phase transition.

  18. Non-Linear Compton Scattering of Ultrashort and Ultraintense Laser Pulses

    Seipt, D


    The scattering of temporally shaped intense laser pulses off electrons is discussed by means of manifestly covariant quantum electrodynamics. We employ a framework based on Volkov states with a time dependent laser envelope in light-cone coordinates within the Furry picture. An expression for the cross section is constructed, which is independent of the considered pulse shape and pulse length. A broad distribution of scatted photons with a rich pattern of subpeaks like that obtained in Thomson scattering is found. These broad peaks may overlap at sufficiently high laser intensity, rendering inappropriate the notion of individual harmonics. The limit of monochromatic plane waves as well as the classical limit of Thomson scattering are discussed. As a main result, a scaling law is presented connecting the Thomson limit with the general result for arbitrary kinematics. In the overlapping regions of the spectral density, the classical and quantum calculations give different results, even in the Thomson limit. Thu...

  19. Study of ultra-high gradient wakefield excitation by intense ultrashort laser pulses in plasma

    Kotaki, Hideyuki; Kando, Masaki; Oketa, Takatsugu; Masuda, Shinichi; Koga, James K.; Kondo, Shuji; Kanazawa, Shuhei; Yokoyama, Takashi; Matoba, Toru; Nakajima, Kazuhisa


    We investigate a laser wakefield excited by intense laser pulses, and the possibility of generating an intense bright electron source by an intense laser pulse. The coherent wakefield excited by 2 TW, 50 fs laser pulses in a gas-jet plasma around 1018 cm-3 is measured with a time-resolved frequency domain interferometer (FDI). The results show an accelerating wakefield excitation of 20 GeV/m with good coherency. This is the first time-resolved measurement of laser wakefield excitation in a gas-jet plasma. The experimental results agree with the simulation results and linear theory. The pump-probe interferometer system of FDI will be modified to the optical injection system as a relativistic electron beam injector. In 1D particle in cell simulation we obtain results of high quality intense electron beam generation.

  20. Indirect versus direct photoionization with ultrashort pulses: interferences and time-resolved bond-length changes

    Gräfe, S.; Engel, V.


    The photoionization of NaI molecules with femtosecond laser pulses leads to photoelectron distributions which vary with the delay between a pump- and a probe-pulse. If the vibrational wave packet as prepared in the pump-transition is located in a region where the bonding character is ionic, the photoelectron, due to its localization on the iodine atom, may be ejected directly or be scattered from the Na + ion. This leads to structures in the photoelectron spectrum which, in turn, reflect temporal bond-length changes.

  1. Development of high resolution Michelson interferometer for stable phase-locked ultrashort pulse pair generation.

    Okada, Takumi; Komori, Kazuhiro; Goshima, Keishiro; Yamauchi, Shohgo; Morohashi, Isao; Sugaya, Takeyoshi; Ogura, Mutsuo; Tsurumachi, Noriaki


    We developed a high resolution Michelson interferometer with a two-frequency He-Ne laser positioning system in order to stabilize the relative phase of a pulse pair. The control resolution corresponded to a 12 as time resolution or a phase of 1.5 degrees at 900 nm. This high resolution Michelson interferometer can generate a phase-locked pulse pair either with a specific relative phase such as 0 or pi radians or with an arbitrary phase. Coherent control of an InAs self-assembled quantum dot was demonstrated using the high resolution Michelson interferometer with a microspectroscopy system.

  2. Mechanisms of amplification of ultrashort electromagnetic pulses in gyrotron traveling wave tube with helically corrugated waveguide

    Ginzburg, N. S.; Zotova, I. V.; Sergeev, A. S.; Zaslavsky, V. Yu.; Zheleznov, I. V.; Samsonov, S. V.; Mishakin, S. V.


    A time-domain self consistent theory of a gyrotron traveling wave tube with a helically corrugated operating waveguide has been developed. Based on this model, the process of short pulse amplification was studied in regimes of grazing and intersection of the dispersion curves of the electromagnetic wave and the electron beam. In the first case, the possibility of amplification without pulse form distortion was demonstrated for the pulse spectrum width of the order of the gain bandwidth. In the second case, when the electrons' axial velocity was smaller than the wave's group velocity, it was shown that the slippage of the incident signal with respect to the electron beam provides feeding of the signal by "fresh" electrons without initial modulation. As a result, the amplitude of the output pulse can exceed the amplitude of its saturated value for the case of the grazing regime, and, for optimal parameters, the peak output power can be even larger than the kinetic power of the electron beam.

  3. Ultra-Short Optical Pulse Generation with Single-Layer Graphene

    Lee, C -C; Bunch, J S; Schibli, T R


    Pulses as short as 260 fs have been generated in a diode-pumped low-gain Er:Yb:glass laser by exploiting the nonlinear optical response of single-layer graphene. The application of this novel material to solid-state bulk lasers opens up a way to compact and robust lasers with ultrahigh repetition rates.

  4. Rate equations for nitrogen molecules in ultrashort and intense x-ray pulses

    Liu, Ji-Cai; Cederbaum, Lorenz S; Cryan, James P; Glownia, James M; Schafer, Kenneth J; Buth, Christian


    We study theoretically the molecular dynamics of nitrogen molecules (N$_2$) exposed to x rays at a wavelength of 1.1 nm (1100 eV photon energy) from the Linac Coherent Light Source (LCLS) free electron laser. Molecular rate equations are derived to describe the intertwined photoionization, decay, and dissociation processes occurring for N2 in intense and ultrafast x rays from LCLS. This model complements our earlier phenomenological approaches, the single-atom, symmetric-sharing, and fragmentation-matrix models of J. Chem. Phys. $\\mathbf{136}$, 214310 (2012). Our rate-equations are used to obtain the effective pulse energy at the sample and the time scale for the dissociation of the metastable dication N$_2^{2+}$. This leads to a very good agreement between the theoretically and experimentally obtained ion yields and, consequently, the average charge states. The effective pulse energy is found to decrease with shortening pulse duration. This variation in the effective pulse energy together with a change in th...

  5. Mechanisms of amplification of ultrashort electromagnetic pulses in gyrotron traveling wave tube with helically corrugated waveguide

    Ginzburg, N. S., E-mail:; Zaslavsky, V. Yu. [Institute of Applied Physics of the Russian Academy of Sciences, 46 Ul' yanov Str., 603950 Nizhny Novgorod (Russian Federation); Nizhny Novgorod State University, 23 Gagarin Ave., 603950 Nizhny Novgorod (Russian Federation); Zotova, I. V.; Sergeev, A. S.; Zheleznov, I. V.; Samsonov, S. V.; Mishakin, S. V. [Institute of Applied Physics of the Russian Academy of Sciences, 46 Ul' yanov Str., 603950 Nizhny Novgorod (Russian Federation)


    A time-domain self consistent theory of a gyrotron traveling wave tube with a helically corrugated operating waveguide has been developed. Based on this model, the process of short pulse amplification was studied in regimes of grazing and intersection of the dispersion curves of the electromagnetic wave and the electron beam. In the first case, the possibility of amplification without pulse form distortion was demonstrated for the pulse spectrum width of the order of the gain bandwidth. In the second case, when the electrons' axial velocity was smaller than the wave's group velocity, it was shown that the slippage of the incident signal with respect to the electron beam provides feeding of the signal by “fresh” electrons without initial modulation. As a result, the amplitude of the output pulse can exceed the amplitude of its saturated value for the case of the grazing regime, and, for optimal parameters, the peak output power can be even larger than the kinetic power of the electron beam.

  6. First-principles simulation for strong and ultra-short laser pulse propagation in dielectrics

    Yabana, K.


    We develop a computational approach for interaction between strong laser pulse and dielectrics based on time-dependent density functional theory (TDDFT). In this approach, a key ingredient is a solver to simulate electron dynamics in a unit cell of solids under a time-varying electric field that is a time-dependent extension of the static band calculation. This calculation can be regarded as a constitutive relation, providing macroscopic electric current for a given electric field applied to the medium. Combining the solver with Maxwell equations for electromagnetic fields of the laser pulse, we describe propagation of laser pulses in dielectrics without any empirical parameters. An important output from the coupled Maxwell+TDDFT simulation is the energy transfer from the laser pulse to electrons in the medium. We have found an abrupt increase of the energy transfer at certain laser intensity close to damage threshold. We also estimate damage threshold by comparing the transferred energy with melting and cohesive energies. It shows reasonable agreement with measurements.

  7. Novel extraction algorithm for amplitude and phase measurement of ultrashort optical pulses via spectral phase interferometry

    Pasquazi, Alessia; Azana, Jose; Moss, David J; Morandotti, Roberto


    We present a novel extraction algorithm for spectral phase interferometry for direct field reconstruction (SPIDER) for the so-called X-SPIDER configuration. Our approach largely extends the measurable time windows of pulses without requiring any modification to the experimental X-SPIDER set-up.

  8. Fibre amplifier based on an ytterbium-doped active tapered fibre for the generation of megawatt peak power ultrashort optical pulses

    Koptev, M Yu; Anashkina, E A; Lipatov, D S; Andrianov, A V; Muravyev, S V; Kim, A V [Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod (Russian Federation); Bobkov, K K; Likhachev, M E; Levchenko, A E; Aleshkina, S S; Semjonov, S L; Denisov, A N; Bubnov, M M [Fiber Optics Research Center, Russian Academy of Sciences, Moscow (Russian Federation); Laptev, A Yu; Gur' yanov, A N [G.G.Devyatykh Institute of Chemistry of High-Purity Substances, Russian Academy of Sciences, Nizhnii Novgorod (Russian Federation)


    We report a new ytterbium-doped active tapered fibre used in the output amplifier stage of a fibre laser system for the generation of megawatt peak power ultrashort pulses in the microjoule energy range. The tapered fibre is single-mode at its input end (core and cladding diameters of 10 and 80 μm) and multimode at its output end (diameters of 45 and 430 μm), but ultrashort pulses are amplified in a quasi-single-mode regime. Using a hybrid Er/Yb fibre system comprising an erbium master oscillator and amplifier at a wavelength near 1.5 μm, a nonlinear wavelength converter to the 1 μm range and a three-stage ytterbium-doped fibre amplifier, we obtained pulses of 1 μJ energy and 7 ps duration, which were then compressed by a grating-pair dispersion compressor with 60% efficiency to a 130 fs duration, approaching the transform-limited pulse duration. The present experimental data agree well with numerical simulation results for pulse amplification in the threestage amplifier. (extreme light fields and their applications)

  9. Synthesis of Er-doped Lu2O3 nanoparticles and transparent ceramics

    Serivalsatit, K.; Wasanapiarnpong, T.; Kucera, C.; Ballato, J.


    Transparent rare earth-doped Lu2O3 ceramics have received much attention for use in solid-state scintillator and laser applications. The fabrication of these ceramics, however, requires ultrafine and uniform powders as precursors. Presented here is the synthesis of Er-doped Lu2O3 nanopowders by a solution precipitation method using Er-doped lutetium sulfate solution and hexamethylenetetramine as a precipitant and the fabrication of Er-doped Lu2O3 transparent ceramics from these nanopowders. The precipitated precursors were calcined at 1100 °C for 4 h in order to convert the precursors into Lu2O3 nanoparticles with an average particle size of 60 nm. Thermal decomposition and phase evolution of the precursors were studied by simultaneous thermal analysis (STA), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Er-doped Lu2O3 transparent ceramics were fabricated from these nanopowders using vacuum sintering followed by hot isostatic pressing at 1700 °C for 8 h. The transparent ceramics exhibit an optical transmittance of 78% at a wavelength of 1.55 μm.

  10. Er-doped concentric-cores optical fiber for simultaneous amplification and compensation of positive dispersion

    Pramod R. Watekar; M. L. N. Goswami; H. N. Acharya; J. C. Biswas; B. P. Pal


    The Er-doped concentric-cores dispersion compensating fiber (EDDCF) has been demonstrated. The rare earth has been doped as a ring around the inner core. We have obtained 14-dB gain at 1550 nm (using the optical fiber network where amplification as well as negative dispersion are necessary.

  11. Controlled modification of biomolecules by ultrashort laser pulses in polar liquids

    Gruzdev, Vitaly; Korkin, Dmitry; Mooney, Brian P.


    Targeted chemical modification of peptides and proteins by laser pulses in a biologically relevant environment, i.e. aqueous solvent at room temperature, allows for accurate control of biological processes. However, the traditional laser methods of control of chemical reactions are applicable only...... to a small class of photosensitive biomolecules because of strong and ultrafast perturbations from biomolecule-solvent interactions. Here, we report excitation of harmonics of vibration modes of solvent molecules by femtosecond laser pulses to produce controlled chemical modifications of non......-photosensitive peptides and proteins in polar liquids under room conditions. The principal modifications included lysine formylation and methionine sulfoxidation both of which occur with nearly 100% yield under atmospheric conditions. That modification occurred only if the laser irradiance exceeded certain threshold...

  12. Asymptotically one-dimensional dynamics of high-peak-power ultrashort laser pulses

    Voronin, A. A.; Zheltikov, A. M.


    Laser fields with peak powers P well above the critical power of self-focusing P cr are intrinsically unstable with respect to modulation instabilities, breaking up into multiple filaments as a part of a quintessentially three-dimensional nonlinear beam dynamics. Here, however, we show that—even for P \\gg P cr—the spatiotemporal field evolution can stay effectively one-dimensional. In this regime, observed as an asymptotic case of large diffraction lengths, the laser field can undergo a rich diversity of pulse transformation scenarios, including, most notably, pulse self-compression to subcycle field waveforms with very high peak powers, while remaining decoupled, within a limited propagation length, from beam dynamics.

  13. Ultra-short pulsed laser ablation of silicon nitride layers: Investigation near threshold fluence

    Heinrich, Gerrit, E-mail: [CIS Forschungsinstititut für Mikrosensorik und Photovoltaik GmbH, Konrad-Zuse-Straße 14, Erfurt 99099 (Germany); Technische Universität Ilmenau, Institut für Physik, Weimarer Str. 32, Ilmenau 98693 (Germany); Wollgarten, Markus [Helmholtz Zentrum Berlin für Materialien und Energie GmbH, Bereich Solarenergieforschung, Institut für Technologie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Bähr, Mario; Lawerenz, Alexander [CIS Forschungsinstititut für Mikrosensorik und Photovoltaik GmbH, Konrad-Zuse-Straße 14, Erfurt 99099 (Germany)


    In this work, silicon nitride (SiN{sub x}) layers, deposited on a planar silicon wafer are locally irradiated by ultra short laser pulses with fluences near the threshold fluence. The irradiated areas are investigated by SEM and TEM in order to analyze the laser influence to silicon and to the SiN{sub x} layer. Thereby, a lift-off process is observed for this SiN{sub x} layer. The silicon absorbs the laser pulse energy. For low fluences, crystalline silicon is disordered below the SiN{sub x} layer. For high fluences, silicon evaporates below the SiN{sub x} layer and bulge the SiN{sub x} layer. If the pressure within the bulge is high enough, the SiN{sub x} layer will break down due to high mechanical stress.

  14. Application of ultrashort laser pulses for timing characterization of silicon photomultipliers

    Popova, E. V.; Buzhan, P. Zh; Stifutkin, A. A.; Ilyin, A. L.; Mavritskii, O. B.; Egorov, A. N.; Nastulyavichius, A. A.


    The application of femtosecond laser irradiation for the investigation of Geiger discharge process in silicon photomultiplier (SiPM) is discussed. It is shown experimentally that sub-picosecond pulses of laser beam focused to micron spot sizes allow studying the dynamics of Geiger discharge process in single cell of silicon photomultiplier. These studies are aimed at identifying the factors limiting the timing resolution of this class of devices.

  15. Method and apparatus for improving the quality and efficiency of ultrashort-pulse laser machining

    Stuart, Brent C.; Nguyen, Hoang T.; Perry, Michael D.


    A method and apparatus for improving the quality and efficiency of machining of materials with laser pulse durations shorter than 100 picoseconds by orienting and maintaining the polarization of the laser light such that the electric field vector is perpendicular relative to the edges of the material being processed. Its use is any machining operation requiring remote delivery and/or high precision with minimal collateral dames.

  16. Hybrid mode-locked ultrashort-pulse erbium-doped fiber laser

    Lazarev, Vladimir A.; Sazonkin, Stanislav S.; Pniov, Alexey B.; Tsapenko, Konstantin P.; Krylov, Alexander A.; Obraztsova, Elena D.


    One of the implementations of fs-laser with CNT-film for mode-locking is considered. Scheme of single-pulse, self-starting, stable mode-locked laser generation by appropriate polarization controllers adjustment is suggested. The mechanism of cavity length stabilization for a femtosecond fiber laser based on the pump source modulation is considered. Bandwidth of the feedback frequency stabilization system based on pump source modulation method is defined.

  17. The wavelength dependence of gold nanorod-mediated optical breakdown during infrared ultrashort pulses

    Davletshin, Yevgeniy R.; Kumaradas, J. Carl [Department of Physics, Ryerson University, Toronto, ON (Canada)


    This paper investigates the wavelength dependence of the threshold of gold nanorod-mediated optical breakdown during picosecond and femtosecond near infrared optical pulses. It was found that the wavelength dependence in the picosecond regime is governed solely by the changes of a nanorod's optical properties. On the other hand, the optical breakdown threshold during femtosecond pulse exposure falls within one of two regimes. When the ratio of the maximum electric field from the outside to the inside of the nanorod is less then 7 (the absorption regime) the seed electrons are initiated by photo-thermal emission, and the wavelength dependence in the threshold of optical breakdown is the result of optical properties of the nanoparticle. When the ratio is greater than 7 (the near-field regime) more seed electrons are initiated by multiphoton ionization, and the wavelength dependence of the threshold of optical breakdown results from a combination of nanorod's optical properties and transitions in the order of multiphoton ionization. The findings of this study can guide the design of nanoparticle based optical breakdown applications. This analysis also deepens the understanding of nanoparticle-mediated laser induced breakdown for picosecond and femtosecond pulses at near infrared wavelengths. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Control of photoassociation reaction F+H→HF with ultrashort laser pulse


    The laser-induced vibrational state-selectivity of product HF in photoassociation reaction H+F→HF is theoretically investigated by using the time-dependent quantum wave packet method. The population transfer process from the continuum state down to the bound vibrational states can be controlled by the driving laser. The effects of laser pulse parameters and the initial momentum of the two collision atoms on the vibrational population of the product HF are discussed in detail. Photodissociation accompanied with the photoassociation process is also described.

  19. Solitons in Stimulated Raman Scattering: Generation and Control of Ultrashort Optical Pulses.


    State, and ZIP Code) P. 0. Box 12211 Fairfield, IA 52556 Research Triangle Park, NC 27709-2211 Ba. NAME OF FUNDING/SPONSORING 6b. OFFICE SYMBOL 9...and ZiP Code) 10. SOURCE OF FUNDING NUMBERS P. 0. Box 12211 PROGRAM PROJECT TASK IWORK UNIT Research Triangle Park, NC 27709-2211 ELEMENT NO. NO. NO...Lowdermilk, "Self-nduced gain an loss modulation in coherent, transient Raman pulse propagation", Phys. Rev. A14, 1472-1474 (1976); V.I. Karpman

  20. Decoration of silica nanowires with gold nanoparticles through ultra-short pulsed laser deposition

    Gontad, F.; Caricato, A. P.; Cesaria, M.; Resta, V.; Taurino, A.; Colombelli, A.; Leo, C.; Klini, A.; Manousaki, A.; Convertino, A.; Rella, R.; Martino, M.; Perrone, A.


    The ablation of a metal target at laser energy densities in the range of 1-10 TW/cm2 leads to the generation of nanoparticles (NP) of the ablated material. This aspect is of particular interest if the immobilization of NPs on three-dimensional (3D) substrates is necessary as for example in sensing applications. In this work the deposition of Au NP by irradiation of a Au bulk target with a sub-picosecond laser beam (500 fs; 248 nm; 10 Hz) on 2D (silica and Si(100)) and 3D substrates (silica nanowire forests) is reported for different number of laser pulses (500, 1000, 1500, 2000, 2500). A uniform coverage of small Au NPs (with a diameter of few nm) on both kinds of substrates has been obtained using a suitable number of laser pulses. The presence of spherical droplets, with a diameter ranging from tens of nm up to few μm was also detected on the substrate surface and their presence can be explained by the weak electron-phonon coupling of Au. The optical characterization of the samples on 2D and 3D substrates evidenced the surface plasmon resonance peak characteristic of the Au NPs although further improvements of the size-distribution are necessary for future applications in sensing devices.

  1. Bilayer Bismuth Selenide nanoplatelets based saturable absorber for ultra-short pulse generation (Invited)

    Xu, Yanhua; Xie, Hanhan; Jiang, Guobao; Miao, Lili; Wang, Ke; Tang, Siying; Yu, Xuefeng; Zhang, Han; Bao, Qiaoliang


    Based on an efficient and bottom-up synthesis technique, Bismuth Selenide (Bi2Se3) nanoplatelets with uniform morphology and average thickness down to 3-7 nm had been fabricated. Its nonlinear absorption property under high power excitation had been well characterized by our Z-scan measurement system at different illumination wavelengths, and we found that the as-fabricated bi-layer Bi2Se3 nanoplatelets show unique nonlinear optical responses, that is, with a saturable optical intensity of 32 GW/cm2 (resp. 3.7 MW/cm2) and a modulation depth of 88% (resp. 36%) at 800 nm (resp. 1565 nm). By implementing its saturable absorption property, we designed an optical saturable absorber device based on bilayer Bi2Se3 nanoplatelets through deposited them onto the end-facet of optical fiber. The as-fabricated optical saturable absorber device allows for the generation of mode-locking pulses at 1571 nm with pulse duration of 579 fs and a repetition rate of 12.54 MHz at a pump power of 160 mW. The method on fabricating ultrathin Bi2Se3 nanoplatelets may pave a new way to massive production of large-area topological insulator thin films that can be used in two-dimensional layered materials related photonics device.

  2. Ultrashort Pulsed Laser Ablation of Magnesium Diboride: Plasma Characterization and Thin Films Deposition

    Angela De Bonis


    Full Text Available A MgB2 target has been ablated by Nd:glass laser with a pulse duration of 250 fs. The plasma produced by the laser-target interaction, showing two temporal separated emissions, has been characterized by time and space resolved optical emission spectroscopy and ICCD fast imaging. The films, deposited on silicon substrates and formed by the coalescence of particles with nanometric size, have been analyzed by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, micro-Raman spectroscopy, and X-ray diffraction. The first steps of the films growth have been studied by Transmission Electron Microscopy. The films deposition has been studied by varying the substrate temperature from 25 to 500°C and the best results have been obtained at room temperature.

  3. An ultrashort pulse ultra-violet radiation undulator source driven by a laser plasma wakefield accelerator

    Anania, M. P. [SUPA, Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); INFN, Laboratori Nazionali di Frascati, I-00044 Frascati (Italy); Brunetti, E.; Wiggins, S. M.; Grant, D. W.; Welsh, G. H.; Issac, R. C.; Cipiccia, S.; Shanks, R. P.; Manahan, G. G.; Aniculaesei, C.; Jaroszynski, D. A., E-mail: [SUPA, Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Geer, S. B. van der; Loos, M. J. de [Pulsar Physics, Burghstraat 47, 5614 BC Eindhoven (Netherlands); Poole, M. W.; Shepherd, B. J. A.; Clarke, J. A. [ASTeC, STFC, Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Gillespie, W. A. [SUPA, School of Engineering, Physics and Mathematics, University of Dundee, Dundee DD1 4HN (United Kingdom); MacLeod, A. M. [School of Computing and Creative Technologies, University of Abertay Dundee, Dundee DD1 1HG (United Kingdom)


    Narrow band undulator radiation tuneable over the wavelength range of 150–260 nm has been produced by short electron bunches from a 2 mm long laser plasma wakefield accelerator based on a 20 TW femtosecond laser system. The number of photons measured is up to 9 × 10{sup 6} per shot for a 100 period undulator, with a mean peak brilliance of 1 × 10{sup 18} photons/s/mrad{sup 2}/mm{sup 2}/0.1% bandwidth. Simulations estimate that the driving electron bunch r.m.s. duration is as short as 3 fs when the electron beam has energy of 120–130 MeV with the radiation pulse duration in the range of 50–100 fs.

  4. Monte Carlo study of impact ionization in InSb induced by intense ultrashort terahertz pulses

    Asmontas, S.; Raguotis, R.; Bumeliene, S. [Center for Physical Sciences and Technology, Vilnius (Lithuania)


    The electron impact ionization dynamic has been investigated by Monte Carlo method in n-type InSb under the action of single-cycle pulses with 1 ps duration. The threshold electric field of impact ionization has been estimated to be about 8 kV/cm at 80 K. The number of generated carriers increases rapidly with increasing of electric field strength over threshold, and at 100 kV/cm, normalized electron concentration reaches 14. It is found that impact ionization process is dominant energy loss mechanism for hot carriers with energy larger than threshold energy of impact ionization. The results of calculations are compared with available experimental data. The agreement between theoretical calculations and experimental results was obtained. (orig.)

  5. Ultrashort pulse laser micro-welding of cyclo-olefin copolymers

    Roth, Gian-Luca; Rung, Stefan; Hellmann, Ralf


    We report on the joining of transparent thermoplastic polymers using infrared femtosecond laser pulses. Due to nonlinear absorption, the developed micro-welding process for cyclo-olefin copolymers does not require any intermediate absorbing layers or any surface pre-processing of the welding partners. In view of an optimized and stable micro-welding process, the influence of the welding speed and focal position on both, the quality and shear force strength are investigated. We highlight that welding seam widths of down to 65 μm are feasible for welding speeds of up to 75 mm/s. However, a variation of the welding speed affects the required focal position for a successful joining process. The shear force strength of the welding seam is determined to 37 MPa, which corresponds to 64% of the shear strength of the bulk material and is not affected by the welding speed.

  6. Spin Flips versus Spin Transport in Nonthermal Electrons Excited by Ultrashort Optical Pulses in Transition Metals

    Shokeen, V.; Sanchez Piaia, M.; Bigot, J.-Y.; Müller, T.; Elliott, P.; Dewhurst, J. K.; Sharma, S.; Gross, E. K. U.


    A joint theoretical and experimental investigation is performed to understand the underlying physics of laser-induced demagnetization in Ni and Co films with varying thicknesses excited by 10 fs optical pulses. Experimentally, the dynamics of spins is studied by determining the time-dependent amplitude of the Voigt vector, retrieved from a full set of magnetic and nonmagnetic quantities performed on both sides of films, with absolute time reference. Theoretically, ab initio calculations are performed using time-dependent density functional theory. Overall, we demonstrate that spin-orbit induced spin flips are the most significant contributors with superdiffusive spin transport, which assumes only that the transport of majority spins without spin flips induced by scattering does not apply in Ni. In Co it plays a significant role during the first ˜20 fs only. Our study highlights the material dependent nature of the demagnetization during the process of thermalization of nonequilibrium spins.

  7. Carbonyl Vibrational Wave Packet Circulation in Mn$_2$(CO)$_{10}$ Driven by Ultrashort Polarized Laser Pulses

    Abdel-Latif, Mahmoud K


    The excitation of the degenerate $E_1$ carbonyl stretching vibrations in dimanganese decacarbonyl is shown to trigger wave packet circulation in the subspace of these two modes. On the time scale of about 5 picoseconds intramolecular anharmonic couplings do not cause appreciable disturbance, even under conditions where the two $E_1$ modes are excited by up to about two vibrational quanta each. The compactness of the circulating wave packet is shown to depend strongly on the excitation conditions such as pulse duration and field strength. Numerical results for the solution of the seven-dimensional vibrational Schr\\"odinger equation are obtained for a density functional theory based potential energy surface and using the multi-configuration time-dependent Hartree method.

  8. Soliton compression to ultra-short pulses using cascaded quadratic nonlinearities in silica photonic crystal fibers

    Bache, Morten; Lægsgaard, Jesper; Bang, Ole;


    We investigate the possibility of using poled silica photonic crystal fibers for self-defocusing soliton compression with cascaded quadratic nonlinearities. Such a configuration has promise due to the desirable possibility of reducing the group-velocity mismatch. However, this unfortunately leads...... nonlinearity, and show that compression of nJ pulses to few-cycle duration is possible in such a fiber. A small amount of group-velocity mismatch optimizes the compression.......We investigate the possibility of using poled silica photonic crystal fibers for self-defocusing soliton compression with cascaded quadratic nonlinearities. Such a configuration has promise due to the desirable possibility of reducing the group-velocity mismatch. However, this unfortunately leads...

  9. Histological observation on dental hard tissue irradiated by ultrashort-pulsed laser

    Uchizono, Takeyuki; Awazu, Kunio; Igarashi, Akihiro; Kato, Junji; Hirai, Yoshito


    In the field of dentistry, effectiveness of USPL irradiation is researched because USPL has less thermal side effect to dental hard tissue. In this paper, we observed morphological change and optical change of dental hard tissue irradiated by USPL for discussing the safety and effectiveness of USPL irradiation to dental hard tissues. Irradiated samples were crown enamel and root dentin of bovine teeth. Lasers were Ti:sapphire laser, which had pulse duration (P d)of 130 fsec and pulse repetition rate (f) of 1kHz and wavelength (l) of 800nm, free electron laser (FEL), which had P d of 15 μsec and f of 10Hz and wavelength of 9.6μm, and Er:YAG laser, which had P d of 250 μsec and f of 10Hz and wavelength of 2.94μm. After laser irradiation, the sample surfaces and cross sections were examined with SEM and EDX. The optical change of samples was observed using FTIR. In SEM, the samples irradiated by USPL had sharp and accurate ablation with no crack and no carbonization. But, in FEL and Er:YAG laser, the samples has rough ablation with crack and carbonization. It was cleared that the P/Ca ratio of samples irradiated by USPL had same value as non-irradiated samples. There was no change in the IR absorption spectrum between samples irradiated by USPL and non-irradiated sample. But, they of samples irradiated by FEL and Er:YAG laser, however, had difference value as non-irradiated samples. These results showed that USPL might be effective to ablate dental hard tissue without thermal damage.

  10. Particle characteristics of different materials after ultra-short pulsed laser (USPL) irradiation

    Meister, Joerg; Schelle, Florian; Kowalczyk, Philip; Frentzen, Matthias


    The exposition of nanoparticles caused by laser application in dental health care is an open discussion. Based on the fact that nanoparticles can penetrate through the mucosa, the knowledge about particle characteristics after irradiation with an USPL is of high importance. Therefore, the aim of this study was to investigate the particle characteristics, especially the size of the ablated debris after USPL irradiation. The irradiation was carried out with an USP Nd:YVO4 laser with a center wavelength of 1064 nm. Based on the pulse duration of 8 ps and a pulse repetition rate of 500 kHz the laser emits an average power of 9 W. The materials investigated were dental tissues and dental restorative materials (composite and amalgam), ceramic and different metals (gold and aluminium). The samples were irradiated with a power density in the order of 300 GW/cm2 at distances of 5, 10, 15, and 20 mm. The debris was collected on an object plate. SEM pictures were used for analysis of the ablation debris. Depending on the irradiated material, we observed different kinds of structures: vitreous, flocculent, and pellet-like. The mean particle sizes were 10 x 10 up to 30 x 30 μm2. In addition, a cluster of ablated matter (nanometer range) distributed over the whole irradiated area was found. With increasing distances the cluster structure reduced from multi-layer to mono-layer clusters. Particle sizes in the micrometer and nanometer range were found after irradiation with an USPL. The nanoparticles create a cluster structure which is influenced by increasing distances.

  11. Spectral splitting of high order harmonics of ionizing gases irradiated with ultrashort intense laser pulses


    [1]Chang Zenghu,Rundquist,A.,Wang Haiwen et al.,Generation of coherent soft X-rays a 2.7 nm using high harmonics,Phys.Rev.Lett.,1997,79(16): 2967-2970.[2]Schnurer,M.,Spielmann,Ch.,Wobrauschek, al.,Coherent 0.5 keV X-ray emission from Helium driven by a sub-10-fs laser,Phys.Rev.Lett.,1998,80(15): 3236-3239.[3]Corkum,P.B.,Plasma perspective on strong-field multiphoton ionization,Phys.Rev.Lett.,1993,71(13): 1994-1997.[4]Lewenstein,M.,Balcou,Ph., al.,Theory of high-harmonic generation by low frequency laser fields,Phys.Rev.A,1994,49(3): 2117-2132.[5]Li,X.F.,L'Huillier,A.L.,Ferray, al.,Multiple-harmonic generation in rare gases at high laser intensity,Phys.Rev.A,1989,39(11): 5751-5761.[6]L'Huillier,A.,Schafer,K.J.,Kulander,K.C.,Theoretical aspects of intense field harmonic generation,J.Phys.B,1991,24(),3315-3341.[7]L'Huillier,A.,Balcou,Ph.,Candel, al.,Calculation of high-order harmonic-generation processin Xeon at 1064 nm,Phys.Rev.A,1992,46(5): 2778-2790.[8]Balcou,Ph.,L'Huillier,A.,Phase-matching effects in strong-field harmonics generation,Phys.Rev.A,1993,47(2): 1447-1459.[9]Race,S.C.,Burnett,K.,Detailed simulation of plasma-induced spectral blueshifting,Phys.Rev.A,1992,46(2): 1084-1090.[10]Wood,W.M.,Siders,C.W.,Downer,M.C.,Measurement of femtosecond ionization dynamics of atmosphere density gases by spectral blueshifting ,Phys.Rev.Lett.,1991,67(25): 3523-3526.[11]Le Blanc S.P.,Sauerbrey,R.,Rae, al.,Spectral blue shifting of a femtosecond laser pulse propagating through a high-pressure gas,J.Opt.Soc.Am.B,1993,10(10): 1801-1809.[12]Le Blanc,S.P.,Sauerbrey,R.,Spectral,temporal,and spatial characteristics of plasma-induced spectral blue shifting and its application to femtosecond pulse measurement,J.Opt.Soc.Am.B,1996,[13](1): 72-88.13.Burnett,N.H.,Corkum,P.B.,Cold-plasma production for recombination extreme-ultraviolet lasers by optical-field-induced ionization,J.Opt.Soc.Am.B,1989,6(6): 1195

  12. Two- and three-body fragmentation of CO 2 + induced by intense ultrashort laser pulses

    Rajput, Jyoti; Ablikim, U.; Zohrabi, M.; Jochim, Bethany; Berry, Ben; Carnes, K. D.; Esry, B. D.; Ben-Itzhak, I.


    We have studied the fragmentation dynamics of a CO2+molecular-ion beam in the strong-field regime using >= 32 fs laser pulses (about 795 nm and 1x 1016 W/ cm2) . A coincidence three-dimensional momentum imaging method was used to measure all ionic and neutral fragments formed during this multiphoton process. The angular distributions for the dominant two-body fragmentation channels CO+ + O, CO2+ + O and CO+ + O+ show two features, one predominantly aligned with the polarization axis and the other close to isotropic. The angular distributions for the three-body channels C+ + O+ + O and C+ + O+ + O+, populated via dissociative ionization, show the polarization axis lying preferentially in the molecular plane. We will discuss the kinetic energy release, angular distributions and relative production probability of the observed two- and three-body fragmentation channels. This work was supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy. BJ was also supported by DOE-SCGF (DE-AC05- 06OR23100).

  13. Precise ablation milling with ultrashort pulsed Nd:YAG lasers by optical and acoustical process control

    Schulze, Volker; Weber, Patricia


    Laser ablation milling with ultra short pulsed Nd:YAG lasers enables micro structuring in nearly all kinds of solid materials like metals, ceramics and polymers. A precise machining result with high surface quality requires a defined ablation process. Problems arise through the scatter in the resulting ablation depth of the laser beam machining process where material is removed in layers. Since the ablated volume may change due to varying absorption properties in single layers and inhomogeneities in the material, the focal plane might deviate from the surface of the work piece when the next layer is machined. Thus the focal plane has to be adjusted after each layer. A newly developed optical and acoustical process control enables an in-process adjustment of the focal plane that leads to defined process conditions and thus to better ablation results. The optical process control is realized by assistance of a confocal white light sensor. It enables an automated work piece orientation before machining and an inline ablation depth monitoring. The optical device can be integrated for an online or offline process control. Both variants will be presented and discussed. A further approach for adjustment of the focal plane is the acoustical process control. Acoustic emissions are detected while laser beam machining. A signal analysis of the airborne sound spectrum emitted by the process enables conclusions about the focal position of the laser beam. Based on this correlation an acoustic focus positioning is built up. The focal plane can then be adjusted automatically before ablation.

  14. Dynamics of laser ablation at the early stage during and after ultrashort pulse

    Ilnitsky, D. K.; Khokhlov, V. A.; Zhakhovsky, V. V.; Petrov, Yu V.; Migdal, K. P.; Inogamov, N. A.


    Study of material flow in two-temperature states is needed for a fundamental understanding the physics of femtosecond laser ablation. To explore phenomena at a very early stage of laser action on a metallic target our in-house two-temperature hydrodynamics code is used here. The early stage covers duration of laser pulse with next first few picoseconds. We draw attention to the difference in behavior at this stage between the cases: (i) of an ultrathin film (thickness of order of skin depth d skin or less), (ii) thin films (thickness of a film is 4-7 of d skin for gold), and (iii) bulk targets (more than 10d skin for gold). We demonstrate that these differences follow from a competition among conductive cooling of laser excited electrons in a skin layer, electron-ion coupling, and hydrodynamics of unloading caused by excess of pressure of excited free electrons. Conductive cooling of the skin needs a heat sink, which is performed by the cold material outside the skin. Such sink is unavailable in the ultrathin films.

  15. Highlighting the DNA damage response with ultrashort laser pulses in the near infrared and kinetic modeling

    Elisa eFerrando-May


    Full Text Available Our understanding of the mechanisms governing the response to DNA damage in higher eucaryotes crucially depends on our ability to dissect the temporal and spatial organization of the cellular machinery responsible for maintaining genomic integrity. To achieve this goal, we need experimental tools to inflict DNA lesions with high spatial precision at pre-defined locations, and to visualize the ensuing reactions with adequate temporal resolution. Near-infrared femtosecond laser pulses focused through high-aperture objective lenses of advanced scanning microscopes offer the advantage of inducing DNA damage in a 3D-confined volume of subnuclear dimensions. This high spatial resolution results from the highly nonlinear nature of the excitation process. Here we review recent progress based on the increasing availability of widely tunable and user-friendly technology of ultrafast lasers in the near infrared. We present a critical evaluation of this approach for DNA microdamage as compared to the currently prevalent use of UV or VIS laser irradiation, the latter in combination with photosensitizers. Current and future applications in the field of DNA repair and DNA-damage dependent chromatin dynamics are outlined. Finally, we discuss the requirement for proper simulation and quantitative modeling. We focus in particular on approaches to measure the effect of DNA damage on the mobility of nuclear proteins and consider the pros and cons of frequently used analysis models for FRAP and photoactivation and their applicability to nonlinear photoperturbation experiments.

  16. Characterization of ultrashort pulses by time-frequency conversion and temporal magnification based on four-wave mixing at 1  μm.

    Qiao, Zhi; Pan, Xue; Wang, Xiaochao; Huang, Tingrui; Zhang, Peng; Fan, Wei; Li, Xuechun; Lin, Zunqi


    In order to characterize ultrashort pulses in real time at 1 μm wavelength, a temporal imaging structure based on the four-wave mixing effect in highly nonlinear fibers is implemented and analyzed both theoretically and experimentally. It is found that both time-frequency transfer and the temporal magnification process can be realized approximately in one structure. The pulse widths of the signal laser measured by the time-frequency transfer and the temporal magnification process are 3.2 ps and 3.1 ps, respectively, which are nearly the same and are in agreement with the result of the autocorrelator. The temporal magnification factor is 33, and the temporal resolution is 380 fs. The method based on the temporal magnification process is inherently real time and single shot, which makes it suitable for applications in the measurement of high-power ultrashort pulses. The four-wave mixing time lens promises future applications in the characterization of the single-shot high-power short laser.

  17. An electrohydrodynamics model for non-equilibrium electron and phonon transport in metal films after ultra-short pulse laser heating

    Zhou, Jun; Li, Nianbei; Yang, Ronggui


    The electrons and phonons in metal films after ultra-short pulse laser heating are in highly non-equilibrium states not only between the electrons and the phonons but also within the electrons. An electrohydrodynamics model consisting of the balance equations of electron density, energy density of electrons, and energy density of phonons is derived from the coupled non-equilibrium electron and phonon Boltzmann transport equations to study the nonlinear thermal transport by considering the electron density fluctuation and the transient electric current in metal films, after ultra-short pulse laser heating. The temperature evolution is calculated by the coupled electron and phonon Boltzmann transport equations, the electrohydrodynamics model derived in this work, and the two-temperature model. Different laser pulse durations, film thicknesses, and laser fluences are considered. We find that the two-temperature model overestimates the electron temperature at the front surface of the film and underestimates the damage threshold when the nonlinear thermal transport of electrons is important. The electrohydrodynamics model proposed in this work could be a more accurate prediction tool to study the non-equilibrium electron and phonon transport process than the two-temperature model and it is much easier to be solved than the Boltzmann transport equations.

  18. Withdrawal of Chinese Physics Letters 26 (2009) 114209 "A Sensitive Scheme to Observe Weak Photo-Refraction Effects in Some Nonlinear Optical Crystals Pumped by Ultrashort Optical Pulses"

    XU Shi-Xiang


    @@ This paper has been retracted because Fig.2 is copied from an earlier paper, "Interband photorefrac- tive effect in β-BBO crystal due to multiphoton exci- tation by intense ultrashort optical pulses" by Shix- iang Xu et al., which appeared in Optics Express 15 (2007) 10576, and its Figs.3 and 4 also present simi- lar data as in Figs.3 and 4 of the same Optics Express paper though they are measured at a different pump- ing power.This paper includes the first meaningful measurements of the photorefractive effect in BIBO and LBO crystals by intense ultrashort optical pulses, the first explanation of the phase-matching effect on the measurement of the photorefractive effect in BBO crystal and the reduction of pumping beam intensity of the second harmonic generator in the experimental setup to mitigate the effect of the nonlinear instability on our measurements.However, I admit, the Chinese Physics Letter paper contains serious replication with- out proper citation.%This paper has been retracted because Fig. 2 is copied from an earlier paper, "Interband photorefrac-tive effect in /3-BBO crystal due to multiphoton excitation by intense ultrashort optical pulses" by Shix-iang Xu et al, which appeared in Optics Express 15 (2007) 10576, and its Figs. 3 and 4 also present similar data as in Figs. 3 and 4 of the same Optics Express paper though they are measured at a different pumping power. This paper includes the first meaningful measurements of the photorefractive effect in BIBO and LBO crystals by intense ultrashort optical pulses, the first explanation of the phase-matching effect on the measurement of the photorefractive effect in BBO crystal and the reduction of pumping beam intensityof the second harmonic generator in the experimental setup to mitigate the effect of the nonlinear instability on our measurements. However, I admit, the Chinese Physics Letter paper contains serious replication without proper citation.I am so sorry for my faults and nescience. I alone

  19. Conversion of recoilless gamma-radiation into a periodic sequence of ultrashort pulses in a set of dispersive and absorptive resonant media

    Radeonychev, Y V; Vagizov, F G; Shakhmuratov, R N; Kocharovskaya, Olga


    An efficient technique to produce a periodic sequence of ultrashort pulses of recoilless gamma-radiation via its transmission through the optically thick vibrating resonant absorber was demonstrated recently [Nature, 508, 80 (2014)]. In this work we extend the theoretical analysis to the case of a set of multiple absorbers. We consider an analytical model describing the control of spectral content of a frequency modulated gamma-radiation by selective correction of amplitudes and initial phases of some spectral components, using, respectively, the resonant absorption or dispersion of nuclei. On the basis of the analytical solutions we determine the ultimate possibilities of the proposed technique.

  20. Generation of trains of ultrashort microwave pulses by two coupled helical gyro-TWTs operating in regimes of amplification and nonlinear absorption

    Ginzburg, N. S.; Denisov, G. G.; Vilkov, M. N.; Sergeev, A. S.; Zotova, I. V.; Samsonov, S. V.; Mishakin, S. V.


    Based on a time-domain model, we demonstrate that a periodic train of powerful ultrashort microwave pulses can be generated in an electron oscillator consisting of two coupled helically corrugated gyrotron travelling wave tubes (gyro-TWTs) operating in regimes of amplification and saturable absorption, respectively. The mechanism of pulse formation in such an oscillator is based on the effect of passive mode-locking widely used in laser physics. Saturable absorption can be implemented in a gyro-TWT in the Kompfner dip regime by a proper matching of the guiding magnetic field. According to simulations with the parameters of an experimentally realized Ka-band gyro-TWT, the peak power of generated pulses with a duration of 200 ps can achieve 400 kW.

  1. Dynamics of the spectral behaviour of an ultrashort laser pulse in an argon-gas-filled capillary discharge-preformed plasma channel

    Sakai S.


    Full Text Available We have reported the argon plasma waveguide produced in an alumina (Al2O3 capillary discharge and used to guide ultrashort laser pulses at intensities of the order of 1016  W/cm2. A one-dimensional magnetohydrodynamic (MHD code was used to evaluate the average degree of ionization of Ar in the preformed plasma channel. The spectrum of the propagated laser pulse in the Ar plasma waveguide was not modified and was well reproduced by a particle-in-cell (PIC simulation under initial ion charge state of Ar3+ in the preformed plasma waveguide. The optimum timing for the laser pulse injection was around 150 ns after initiation of a discharge with a peak current of 200 A.

  2. Soft x-ray generation in gases with an ultrashort pulse laser

    Ditmire, Todd Raymond [Univ. of California, Davis, CA (United States)


    An experimental investigation of soft x-ray production resulting from the interaction of intense near infra-red laser radiation with gases is presented in this thesis. Specifically, soft x-ray generation through high order harmonic generation or exploiting intense inverse bremsstrahlung heating is examined. Most of these studies are conducted with femtosecond, terawatt class Cr:LiSrAlF6 (LiSAF) laser, though results derived from studies with other laser systems are presented as well. The majority of this work is devoted to experimental investigations, however, theoretical and computational models are developed to interpret the data. These studies are motivated by the possibility of utilizing the physics of intense laser/matter interactions as a potential compact source of bright x-rays. Consequently, the thrust of many of the experiments conducted is aimed at characterizing the x-rays produced for possible use in applications. In general, the studies of this manuscript fall into three categories. First, a unique 130 fs, 8 TW laser that is based on chirped pulse amplification, is described, and its performance is evaluated. The generation of x-rays through high order harmonics is then discussed with emphasis on characterizing and optimizing harmonic generation. Finally, the generation of strong, incoherent x-ray radiation by the intense irradiation of large (>1,000 atom) clusters in gas jets, is explored. The physics of laser energy absorption by clusters illuminated with intensities of 1015 to 1017 W/cm2 is considered in detail. X-ray spectroscopy of the hot plasmas that result from the irradiation of the clusters is conducted, and energy transport and kinetics issues in these plasmas are discussed.

  3. Photoionization of monocrystalline CVD diamond irradiated with ultrashort intense laser pulse

    Lagomarsino, Stefano; Sciortino, Silvio; Obreshkov, Boyan; Apostolova, Tzveta; Corsi, Chiara; Bellini, Marco; Berdermann, Eleni; Schmidt, Christian J.


    Direct laser writing of conductive paths in synthetic diamond is of interest for implementation in radiation detection and clinical dosimetry. Unraveling the microscopic processes involved in laser irradiation of diamond below and close to the graphitization threshold under the same conditions as the experimental procedure used to produce three-dimensional devices is necessary to tune the laser parameters to optimal results. To this purpose a transient currents technique has been used to measure laser-induced current signals in monocrystalline diamond detectors in a wide range of laser intensities and at different bias voltages. The current transients vs time and the overall charge collected have been compared with theoretical simulations of the carrier dynamics along the duration and after the conclusion of the 30 fs laser pulse. The generated charge has been derived from the collected charge by evaluation of the lifetime of the carriers. The plasma volume has also been evaluated by measuring the modified region. The theoretical simulation has been implemented in the framework of the empirical pseudopotential method extended to include time-dependent couplings of valence electrons to the radiation field. The simulation, in the low-intensity regime, I ˜1 TW /cm2 , predicts substantial deviation from the traditional multiphoton ionization, due to nonperturbative effects involving electrons from degenerate valence bands. For strong field with intensity of about 50 TW /cm2, nonadiabatic effects of electron-hole pair excitation become prominent with high carrier densities eventually causing the optical breakdown of diamond. The comparison of theoretical prediction with experimental data of laser-generated charge vs laser energy density yields a good quantitative agreement over six orders of magnitude. At the highest intensities the change of slope in the trend is explained taking into account the dependence of the optical parameters and the carrier mobility on plasma

  4. Coherent control of atoms and diatomic molecules with shaped ultrashort pulses; Manipulation coherente d'atomes et de molecules diatomiques avec des impulsions mises en forme

    Degert, J


    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)

  5. Er-doped fiber ring laser gyroscopes operating in continuous waves

    Jingren Qian; Jue Su; Xuxu Wang; Bing Zhu


    A direction related polarizer was inserted into a ring laser cavity to eliminate one of the two eigen-modes as well as spatial hole burning of the gain medium in a bidirectional Er-doped fiber ring laser. Thus, a fiber ring laser gyroscope (FRLG) operating in continuous wave was demonstrated. A beat signal of over 30-dB noise was observed and a good inear relation between the beat frequency shift and cavity rotation rate was obtained.

  6. Yb{sup 3+}:Sr{sub 3}Y{sub 2}(BO{sub 3}){sub 4}: A potential ultrashort pulse laser crystal

    Sun, Shijia; Xu, Jinlong [Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002 (China); Wei, Qi [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Lou, Fei [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Huang, Yisheng; Yuan, Feifei; Zhang, Lizhen [Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002 (China); Lin, Zhoubin, E-mail: [Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002 (China); He, Jingliang [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Wang, Guofu [Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002 (China)


    Highlights: • A Yb{sup 3+}:Sr{sub 3}Y{sub 2}(BO{sub 3}){sub 4} crystal was grown successfully by Czochralski method. • The crystal has wide absorption and emission bandwidth. • 3.47 W continuous wave laser output with a slope efficiency of 29% was obtained. • The results show that the crystal is a promising ultrashort pulse laser material. - Abstract: A Yb{sup 3+}:Sr{sub 3}Y{sub 2}(BO{sub 3}){sub 4} crystal was grown successfully by the Czochralski method. The polarized spectral properties and continuous wave laser output of this crystal were investigated in detail. The crystal has larger absorption and emission cross sections compared with many mature Yb{sup 3+}-doped borate crystals. The full width at half maximum of the emission bands around 1023 nm are 69 nm (E//a), 61 nm (E//b) and 65 nm (E//c). 3.47 W continuous wave laser output with a slope efficiency of 29% and an optical conversion efficiency of 24% was obtained. The results reveal that Yb{sup 3+}:Sr{sub 3}Y{sub 2}(BO{sub 3}){sub 4} crystal is an excellent candidate for ultrashort pulse laser crystal.

  7. Degradation of optical properties of a film-type single-wall carbon nanotubes saturable absorber (SWNT-SA) with an Er-doped all-fiber laser.

    Ryu, Sung Yoon; Kim, Kyung-Soo; Kim, Jungwon; Kim, Soohyun


    Single-wall carbon nanotubes (SWNTs) are promising materials for saturable absorbers (SAs) in mode-locked lasers. However it has been widely recognized that the degradation of optical properties of film-type SWNTs used in femtosecond mode-locked lasers limits the achievable long-term stability of such lasers. In this paper, we study the degradation of optical properties of SWNT-SA fabricated as sandwich type using HiPCO SWNTs with an Er-doped all-fiber laser. The thresholds of laser pump power are examined to avoid the damage of the SWNT-SA. Based on the proposed analysis, it is shown that all-fiber laser pulses of 300 fs pulse width, 3.85 mW average output power, 211.7 MW/cm² peak intensity and 69.9 MHz repetition rate can be reliably generated without any significant damage to the SWNT-SA film.

  8. Quantification of a propagating spin-wave packet created by an ultrashort laser pulse in a thin film of a magnetic metal

    Iihama, S.; Sasaki, Y.; Sugihara, A.; Kamimaki, A.; Ando, Y.; Mizukami, S.


    Coherent spin-wave generation by focused ultrashort laser pulse irradiation was investigated for a permalloy thin film at micrometer scale using an all-optical space- and time-resolved magneto-optical Kerr effect microscope. The spin-wave packet propagating perpendicular to the magnetization direction was clearly observed; however, that propagating parallel to the magnetization direction was not observed. The propagation length, group velocity, center frequency, and packet width of the observed spin-wave packet were evaluated and quantitatively explained in terms of the propagation of a magnetostatic spin wave driven by the ultrafast change of an out-of-plane demagnetization field induced by the focused-pulse laser.

  9. Efficient photo-dissociation of CH{sub 4} and H{sub 2}CO molecules with optimized ultra-short laser pulses

    Rasti, S.; Irani, E.; Sadighi-Bonabi, R., E-mail: [Department of Physics, Sharif University of Technology, P.O. Box 11365-9567, Tehran (Iran, Islamic Republic of)


    The fragmentation dynamics of CH{sub 4} and H{sub 2}CO molecules have been studied with ultra-short pulses at laser intensityof up to 10{sup 15}Wcm{sup −2}. Three dimensional molecular dynamics calculations for finding the optimized laser pulses are presented based on time-dependent density functional theory and quantum optimal control theory. A comparison of the results for orientation dependence in the ionization process shows that the electron distribution for CH{sub 4} is more isotropic than H{sub 2}CO molecule. Total conversion yields of up to 70% at an orientation angle of 30{sup o} for CH{sub 4} and 65% at 90{sup 0} for H{sub 2}CO are achieved which lead to enhancement of dissociation probability.

  10. Photoluminescence in Er-doped V{sub 2}O{sub 5} and Er-doped CdV{sub 2}O{sub 6}

    González-Rivera, Y.A.; Cervantes-Juárez, E.; Aquino-Meneses, L. [Benemérita Universidad Autónoma de Puebla. Postgrado en Física Aplicada. Facultad de Ciencias Físico-Matemáticas, Av. San Claudio y Av. 18 sur, Col. San Manuel Ciudad Universitaria, Puebla Pue. C. P. 72570 (Mexico); Lozada-Morales, R., E-mail: [Benemérita Universidad Autónoma de Puebla. Postgrado en Física Aplicada. Facultad de Ciencias Físico-Matemáticas, Av. San Claudio y Av. 18 sur, Col. San Manuel Ciudad Universitaria, Puebla Pue. C. P. 72570 (Mexico); Jiménez-Sandoval, S. [Centro de Investigación y de Estudios Avanzados del IPN, Unidad Querétaro, Apartado Postal 1-798, Querétaro, Qro. 76001 (Mexico); Rubio-Rosas, E.; Agustín-Serrano, R.; Cerna, C. de la; Reyes-Cervantes, E. [Centro Universitario de Vinculación y transferencia de Tecnología, Prol. De la 24 Sur y Av. San Claudio, Col. San Manuel, Puebla (Mexico); Zelaya Angel, O.; Tomas, S.A. [Departamento de Física, Centro de Investigación y de Estudios Avanzados, P.O. Box 14-740, México 07360, D.F. (Mexico); Rodriguez-Melgarejo, F. [Centro de Investigación y de Estudios Avanzados del IPN, Unidad Querétaro, Apartado Postal 1-798, Querétaro, Qro. 76001 (Mexico); and others


    A group of samples from the CdO–V{sub 2}O{sub 5} binary system, particularly with high V{sub 2}O{sub 5} content, doped with Er{sup 3+} were prepared. The set of samples was fabricated using the conventional melt-quenching method. Depending on the proportion of the used reactants, the existence of V{sub 2}O{sub 5} and of CdV{sub 2}O{sub 6} was identified from X-ray diffraction measurements and Raman spectroscopy. Depending on the relative concentrations of CdO and V{sub 2}O{sub 5}, different types of morphologies for each sample were found in a scanning electron microscope. Their chemical composition was measured from energy dispersive spectroscopy in the same instrument. An effective Er-doping of the order of 1.0±0.35 at% was found for each sample. From optical absorption data, the composition dependent optical band gap was determined with values between 1.94 and 2.29 eV. Finally, photoluminescence experiments showed, in the samples with the highest V{sub 2}O{sub 5} content, wide bands associated to oxygen vacancies. For the rest of the samples emissions from electronic transitions of Er{sup 3+} ions were detected. - Highlights: • PL ascribed to oxygen vacancies in Er-doped V{sub 2}O{sub 5} was observed. • PL of electronic transitions of Er{sup 3+} which is immersed in CdV{sub 2}O{sub 6} was found. • Some of those electronic transitions present sharp and narrow emissions. • An E{sub g} in the 1.94–2.29 range for this batch of samples was determined.

  11. Effects of in-pulse transverse relaxation in 3D ultrashort echo time sequences: analytical derivation, comparison to numerical simulation and experimental application at 3T.

    Springer, Fabian; Steidle, Günter; Martirosian, Petros; Claussen, Claus D; Schick, Fritz


    The introduction of ultrashort-echo-time-(UTE)-sequences to clinical whole-body MR scanners has opened up the field of MR characterization of materials or tissues with extremely fast signal decay. If the transverse relaxation time is in the range of the RF-pulse duration, approximation of the RF-pulse by an instantaneous rotation applied at the middle of the RF-pulse and immediately followed by free relaxation will lead to a distinctly underestimated echo signal. Thus, the regular Ernst equation is not adequate to correctly describe steady state signal under those conditions. The paper presents an analytically derived modified Ernst equation, which correctly describes in-pulse relaxation of transverse magnetization under typical conditions: The equation is valid for rectangular excitation pulses, usually applied in 3D UTE sequences. Longitudinal relaxation time of the specimen must be clearly longer than RF-pulse duration, which is fulfilled for tendons and bony structures as well as many solid materials. Under these conditions, the proposed modified Ernst equation enables adequate and relatively simple calculation of the magnetization of materials or tissues. Analytically derived data are compared to numerical results obtained by using an established Runge-Kutta-algorithm based on the Bloch equations. Validity of the new approach was also tested by systematical measurements of a solid polymeric material on a 3T whole-body MR scanner. Thus, the presented modified Ernst equation provides a suitable basis for T1 measurements, even in tissues with T2 values as short as the RF-pulse duration: independent of RF-pulse duration, the 'variable flip angle method' led to consistent results of longitudinal relaxation time T1, if the T2 relaxation time of the material of interest is known as well.

  12. Experimental characterization of the inner surface in micro-drilling of spray holes: A comparison between ultrashort pulsed laser and EDM

    Romoli, L.; Rashed, C. A. A.; Fiaschi, M.


    In this research, the inner surface characteristics of micro-drilled holes of fuel injector nozzles were analyzed by Shear Force Microscopy (SHFM). The surface texture was characterized by maximum peak-to-valley distance and periodicity whose dimensions were related to the adopted energy. 180 µm diameter holes were drilled using ultrashort pulsed laser process using pulse energies within the range of 10-50 µJ. Laser ablated surfaces in the tested energy range offer a smooth texture with a peculiar periodic structure with a variation in height between 60 and 90 nm and almost constant periodicity. The Scanning Electron Microscopy (SEM) photograph of the Laser Induced Periodic Surface Structure (LIPSS) showed the co-existence of Low Spatial Frequency LIPSS (LSFL) and High Spatial Frequency LIPSS (HSFL). A comparative analysis was carried out between the highest laser pulse energy in the tested range energy laser drilling which enables the shortest machining time and micro-Electrical Discharge Machining (µ-EDM). On the contrary, results showed that surfaces obtained by electro-erosion are characterized by a random distribution of craters with a total excursion up to 1.5 µm with a periodicity of 10 µm. The mean-squared surface roughness (Rq) derived from the scanned maps ranges between 220 and 560 nm for µ-EDM, and between 50 and 100 nm for fs-pulses laser drilling.

  13. Comparison of Er-doped sol-gel glasses with various hosts

    Xiang, Qing; Zhou, Yan; Lam, Yee Loy; Ooi, Boon Siew; Chan, Yuen Chuen; Kam, Chan Hin


    Using the sol-gel process, we prepared three groups of Er-doped glasses, namely, Er-doped Si02-A101.5 (SAB) glass, Er-doped Si02-Ti02-A101.5 (STAE) glass, and Er-doped Si02-Ge02-Al01.5 (SGAE) glass. Various erbium concentration and different host composition under the same processing condition have been studied in order to optimize the material composition to get the strongest fluorescence emission for each material system. It has been found that for SAE glass, the strongest fluorescence emission is obtained when the mole ratio of the three constituent oxides is lOOSiO2 : 20A101.5 2ErO1.5. For the STAE material system, the best composition ratio for the strongest fluorescence emission is 93 Si02 : 7TiO2: 20A101.5 : lErO1.5, whereas the value for SGAE glass is 9OSiO2:lOGeO2 : 2OAlO1.5: 1ErO1.5. But the relative lifetimes were obtained with the recipe lOOSiO2:10A101.5:1ErO1.5 for SAE series, 90 Si02:lOGeO2:1OAlO1.5: 1ErO1.5 for STAE group and 93 Si02:7Ti02:20A101.5:1ErO1.5 for STAE group. Using these recipes, three 20-layer (up to 2.5 μm) crack-free films have been deposited on silica-on-silicon (SOS) substrates with multiple spin-coating and rapid thermal annealing (RTA). Only the STAE film and the SGAE film are found to guide light. The experimental results show that STAB glasses have higher hydrophilicity than SGAE glasses and SGAE glasses has lower crystallization temperature than STAE glasses. The fact that these waveguiding films emit relatively strong fluorescence around the wavelength of 1.55 μm implies that such planar waveguides are potential candidates from which integrated optical waveguide amplifiers and lasers operating at the third optical fiber communication window can be fabricated.

  14. Crystal growth and scintillation properties of Er-doped Lu{sub 3}Al{sub 5}O{sub 12} single crystals

    Sugiyama, Makoto, E-mail: [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Fujimoto, Yutaka [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Yanagida, Takayuki [New Industry Creation Hatchery Center (NICHe), Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8579 (Japan); Totsuka, Daisuke [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Nihon Kessho Kogaku Co. Ltd., 810-5 Nobe-cho Tatebayashi Gunma (Japan); Kurosawa, Shunsuke; Futami, Yoshisuke; Yokota, Yuui; Chani, Valery [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Yoshikawa, Akira [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); New Industry Creation Hatchery Center (NICHe), Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8579 (Japan)


    Er-doped Lu{sub 3}Al{sub 5}O{sub 12} (Er:LuAG) single crystalline scintillators with different Er concentrations of 0.1, 0.5, 1, and 3% were grown by the micro-pulling-down ({mu}-PD) method. The grown crystals were composed of single-phase material, as demonstrated by powder X-ray diffraction (XRD). The radioluminescence spectra measured under {sup 241}Am {alpha}-ray excitation indicated host emission at approximately 350 nm and Er{sup 3+} 4f-4f emissions. According to the pulse height spectra recorded under {gamma}-ray irradiation, the 0.5% Er:LuAG exhibited the highest peak channel among the samples. The {gamma}-ray excited decay time profiles were well fitted by the two-component exponential approximation (0.8 {mu}s and 6-10 {mu}s).

  15. Effects of Pumping Sizes on THz Radiation Based on Ultrashort Light Pulse Optical Rectification for High Spatial Resolution T-Ray Imaging

    XU Shi-Xiang; DAI Xiao-Ming; YANG Xiao-Hua; LI Jing-Zhen


    @@ We present our experimental studies on the effects of the pumping sizes on THz radiation based on ultrashort light pulse optical rectification for high spatial resolution T-Ray imaging.Our experiments show that high spatial resolution T-ray imaging requires both thin THz emitter and sample, and rigorous tolerance of the gap between the sample and the emitter, as well as small pumping size which usually much smaller compared with THz wavelength.Such a small pumping size results in dramatic decrease of the THz wave power, which originates from strong diffraction of THz wave, the depolarization of the focused tightly pumping beam, the spatial filtering of the emitter exit-surface, and the strong phase-mismatching between the pumping and the high spatial Fourier components of the THz signal, rather than two-photon absorption.

  16. Ultra-short laser-accelerated proton pulses have similar DNA-damaging effectiveness but produce less immediate nitroxidative stress than conventional proton beams

    Raschke, S.; Spickermann, S.; Toncian, T.; Swantusch, M.; Boeker, J.; Giesen, U.; Iliakis, G.; Willi, O.; Boege, F.


    Ultra-short proton pulses originating from laser-plasma accelerators can provide instantaneous dose rates at least 107-fold in excess of conventional, continuous proton beams. The impact of such extremely high proton dose rates on A549 human lung cancer cells was compared with conventionally accelerated protons and 90 keV X-rays. Between 0.2 and 2 Gy, the yield of DNA double strand breaks (foci of phosphorylated histone H2AX) was not significantly different between the two proton sources or proton irradiation and X-rays. Protein nitroxidation after 1 h judged by 3-nitrotyrosine generation was 2.5 and 5-fold higher in response to conventionally accelerated protons compared to laser-driven protons and X-rays, respectively. This difference was significant (p DNA damaging potential as conventional proton beams, while inducing less immediate nitroxidative stress, which probably entails a distinct therapeutic potential.

  17. Influence of the matrix properties on the performances of Er-doped Si nanoclusters light emitting devices

    Irrera, Alessia; Iacona, Fabio; Franzò, Giorgia; Miritello, Maria; Lo Savio, Roberto; Castagna, Maria Eloisa; Coffa, Salvatore; Priolo, Francesco


    We investigated the properties of light emitting devices whose active layer consists of Er-doped Si nanoclusters (nc) generated by thermal annealing of Er-doped SiOx layers prepared by magnetron cosputtering. Differently from a widely used technique such as plasma enhanced chemical vapor deposition, sputtering allows to synthesize Er-doped Si nc embedded in an almost stoichiometric oxide matrix, so as to deeply influence the electroluminescence properties of the devices. Relevant results include the need for an unexpected low Si excess for optimizing the device efficiency and, above all, the strong reduction of the influence of Auger de-excitation, which represents the main nonradiative path which limits the performances of such devices and their application in silicon nanophotonics.

  18. Sonocatalytic performance of Er-doped ZnO for degradation of a textile dye.

    Khataee, Alireza; Saadi, Shabnam; Safarpour, Mahdie; Joo, Sang Woo


    Pure and erbium (Er)-doped ZnO samples were synthesized through a sonochemical method and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) analysis. The synthesized samples were used as a catalyst for the sonocatalytic decolorization of Reactive Orange 29 (RO29) as a model organic pollutant. The decolorization efficiency was 63%, 68%, 88%, and 75% for undoped, 2%, 4%, and 6% Er-doped ZnO, respectively. The effect of different experimental parameters including catalyst content, dye concentration and ultrasound power was investigated on the sonocatalytic decolorization of RO29. Among several radical scavengers (i.e. chloride, carbonate and sulfate anions and t-butanol), the chloride anion showed the most inhibitive effect on the sonocatalysis performance. Improvement of the sonocatalytic process by K2S2O8 and H2O2 enhancers was also studied. The reusability of the synthesized sonocatalyst was evaluated in several consecutive runs, and a decline of only 4% was observed in the process performance after five runs. The intermediates produced during the degradation of RO29 were identified by GC-MS analysis.

  19. Upconverted fluorescence in Er-doped ZBLAN glasses for high efficiency solar cells

    Henke, Bastian; Ahrens, Bernd; Johnson, Jacqueline A.; Miclea, Paul T.; Schweizer, Stefan


    Transparent erbium-doped fluorozirconate (FZ) glasses are attractive systems for upconversion-based solar cells. Upconverted fluorescence intensity vs. excitation power dependence was investigated for a series of erbium-doped FZ glasses. It was found that the ratio of the 2-photon upconverted emission in the near infrared at 980 nm to the 3-photon upconverted emissions in the visible at 530, 550, and 660 nm decreases with increasing excitation power. The integrated upconverted fluorescence intensity per excitation power shows "saturation" upon increasing the excitation power, while the point of saturation shifts to lower excitation power with increasing erbium doping level. To demonstrate the potential of these upconverters for photovoltaic applications, the external quantum efficiency (EQE) of a commercial monocrystalline silicon solar cell with an Er-doped FZ glass on top of it was measured. For an excitation power of 1 mW at a wavelength of 1540 nm an EQE of 1.6% was found for a 9.1 mol% Er-doped FZ glass. The samples investigated were not optically coupled to the solar cell and no optical coating was applied to the glass surface.

  20. Texturing in titanium grade 2 surface irradiate with ultrashort pulse laser; Texturizacao em superficies de titanio grau 2 irradiadas com laser com pulsos ultracurtos

    Nogueira, Alessandro Francelino


    The texturing laser micromachining is an important alternative to improve the bonding adhesion between composites and titanium, which are applied to structural components in the aerospace industry. The texturing running on titanium plates is due to the fact that the preferred joining technique for many composite materials is the adhesive bonding. In this work, titanium plates were texturized using laser ultrashort pulses temporal widths of femtoseconds. This process resulted in minimal heat transfer to the material, avoiding deformation of the titanium plate surface as well as the formation of resolidified material in the ablated region. These drawbacks have occurred with the use of nanoseconds pulses. Were performed three types of texturing using laser with femtosecond pulses, with variations in the distances between the machined lines. The analysis of the obtained surfaces found that the wettability increases when there is the increased distance between the texturing lines. Advancing in the analysis by optical profilometry of textured surfaces was observed that there is substantial increase in the volume available for penetration of structural adhesive when the distances between the textured lines are diminished. In tensile tests conducted it was observed that there is an increase in shear strength of the adhesive joint by reducing the distance between the textured lines. (author)

  1. 58 mJ burst comprising ultrashort pulses with homogenous energy level from an Yb-doped fiber amplifier.

    Breitkopf, Sven; Klenke, Arno; Gottschall, Thomas; Otto, Hans-Jürgen; Jauregui, Cesar; Limpert, Jens; Tünnermann, Andreas


    We report on a laser system producing a burst comprising femtosecond pulses with a total energy of 58 mJ. Every single pulse within this burst has an energy between 27 and 31 μJ. The pump is able to rebuild the inversion fast enough between the pulses, resulting in an almost constant gain for every pulse during the burst. This causes a very homogenous energy distribution during the burst. The output burst has a repetition frequency of 20 Hz, is 200 μs long and, therefore, contains 2000 pulses at a pulse repetition rate of 10 MHz.

  2. Fast dynamics of 1.5 μm photoluminescence in Er-doped SiO2 sensitized with Si nanocrystals

    Timmerman, D.; Saeed, S.; Gregorkiewicz, T.


    In order to investigate origin of fast photoluminescence at 1.5 μm reported to appear in Er-doped SiO2 sensitized with silicon nanocrystals, time-resolved photoluminescence measurements were compared between high temperature annealed Er-doped and Er-free samples. We confirm that this fast

  3. Time-lapse ultrashort pulse microscopy of infection in three-dimensional versus two-dimensional culture environments reveals enhanced extra-chromosomal virus replication compartment formation

    Gibbs, Holly C.; Sing, Garwin; Armas, Juan Carlos González; Campbell, Colin J.; Ghazal, Peter; Yeh, Alvin T.


    The mechanisms that enable viruses to harness cellular machinery for their own survival are primarily studied in cell lines cultured in two-dimensional (2-D) environments. However, there are increasing reports of biological differences between cells cultured in 2-D versus three-dimensional (3-D) environments. Here we report differences in host-virus interactions based on differences in culture environment. Using ultrashort pulse microscopy (UPM), a form of two-photon microscopy that utilizes sub-10-fs pulses to efficiently excite fluorophores, we have shown that de novo development of extra-chromosomal virus replication compartments (VRCs) upon murine cytomegalovirus (mCMV) infection is markedly enhanced when host cells are cultured in 3-D collagen gels versus 2-D monolayers. In addition, time-lapse imaging revealed that mCMV-induced VRCs have the capacity to grow by coalescence. This work supports the future potential of 3-D culture as a useful bridge between traditional monolayer cultures and animal models to study host-virus interactions in a more physiologically relevant environment for the development of effective anti-viral therapeutics. These advances will require broader adoption of modalities, such as UPM, to image deep within scattering tissues.

  4. Temporal spreading generated by diffraction in the focusing of ultrashort light pulses with perfectly conducting spherical mirrors.

    Anaya-Vera, S; García-Martínez, L; Rosete-Aguilar, M; Bruce, N C; Garduño-Mejia, J


    We study femtosecond pulses at the focal plane of a perfectly conducting spherical mirror which is a dispersionless system, that is, it introduces no group velocity dispersion and no propagation time difference to the pulses after reflection. By using the scalar diffraction theory we will show that the neglected terms in the diffraction integral, when using the approximation of the bandwidth being smaller than the frequency of the carrier, have a significant influence on imaging if a laser pulse of a few femtoseconds is used in time-resolved imaging. The neglected terms introduce temporal spreading to extremely short pulses of a few optical cycles incident on the mirror, which avoids a fully compensated pulse, i.e., a one optical cycle pulse, at the focus of the mirror. The study in this paper also applies to refracting optical systems such as microscope objectives or lenses.

  5. Photosensitivity of ion-exchanged Er-doped phosphate glass using 248nm excimer laser radiation.

    Pissadakis, Stavros; Ikiades, Aris; Hua, Ping; Sheridan, Anna; Wilkinson, James


    The photosensitivity to 248nm excimer laser radiation of Er-doped Schott IOG-1 phosphate glass is presented. The photosensitive mechanism is investigated by employing a grating recording process. Index changes of up to ~2.0x10(-3) were measured in silver ion-exchanged samples using diffraction efficiency measurements; whereas changes of only ~10(-5) were measured for non-ion-exchanged samples. Absorption measurements allowed the identification of specific color center bands, which were attributed to the glass matrix and to the silver ions. Investigation of the exposed ion-exchanged glass using scanning electron microscopy and energy dispersive x-ray microanalysis revealed that in addition to the color centers formed, silver ion migration and ionization contribute significantly to the UV-induced index changes.

  6. Structural and photoluminescence properties of Ce, Dy, Er-doped ZnO nanoparticles

    Jayachandraiah, C. [Department of Physics, JNTU, Anantapur-515002 (India); Kumar, K. Siva [Department of Advanced Materials Science and Engineering, Dankook University, Cheonan, Chungnam 330-714 (Korea, Republic of); Krishnaiah, G., E-mail: [Govt. Degree College, Puttur, Chittoor-517 583 (India)


    Undoped ZnO and rare earth elements (Ce, Dy and Er with 2 at. %) doped nanoparticles were synthesized by wet chemical co-precipitation method at 90°C with Polyvinylpyrrolidone (PVP) as capping agent. The structural, morphological, compositional and photoluminescence studies were performed with X-ray diffraction (XRD), Transmission electron microscopy (TEM), Energy dispersive spectroscopy (EDS), FTIR spectroscopy and Photoluminescence (PL) respectively. XRD results revealed hexagonal wurtzite structure with average particle size around 18 nm - 14 nm and are compatible with TEM results. EDS confirm the incorporation of Ce, Dy and Er elements into the host ZnO matrix and is validated by FTIR analysis. PL studies showed a broad intensive emission peak at 558 nm in all the samples. The intensity for Er- doped ZnO found maximum with additional Er shoulder peaks at 516nm and 538 nm. No Ce, Dy emission centers were found in spectra.

  7. Effect of Er doping on the superconducting properties of porous MgB2

    O Erdem; E Yanmaz


    MgB2 bulk sample with porous structure was produced by using the in-situ solid-state reaction method under argon (Ar) atmosphere of 10 bar. Elemental Er in powder form was doped into MgB2 with different compositions (Mg1−Er)B2, where = 0.00, 0.03 and 0.05, in order to investigate the effect of rare-earth (RE) element Er on the structural and electromagnetic properties of porous MgB2. The Er-doped samples result in small grain size structure compared to the undoped one. The lattice constants and of the doped samples, determined from X-ray diffraction (XRD) analysis, increase with the increasing Er content, and consequently the superconducting transition temperature ($T^{\\text{onset}}_{c}$) of MgB2, determined from resistivity measurements, is slightly suppressed. Also, the upper critical field ($B_{c2}$), the irreversibility field ($B_{\\text{irr}}$) and the critical current density ($J_{c}$) values are significantly enhanced in the doped samples. For the best sample ( = 0.03), at 15 K under a magnetic field of 4 T, the $J_{c}$ value reaches 2.4×104 A cm-2, which is higher than that of the porous sample by an order of 103, and the $B_{\\text{irr}}$ value at 20 K reaches 9.7 T. These results imply that the RE element Er fills the pores, enhances the density and the grain connectivity. Hence, the superconducting properties of the porous MgB2 sample improve by Er doping.

  8. Microstructure, Magnetism and Magnetic Field Induced-Strain in Er-Doped Co-Ni-Al Polycrystalline Alloy

    Ju, Jia; Lou, Shuting; Yan, Chen; Yang, Liu; Li, Tao; Hao, Shuai; Wang, Xingyi; Liu, Huan


    A large magnetic field-induced strain (MFIS) was discovered in single-crystal alloys, whereas it is proven difficult for such apparent strain values to be obtained in polycrystalline alloys. In order for an apparent strain discovery to occur, the polycrystalline Co-Ni-Al system was doped by 0-1 at.% of Er and the effects of doping on microstructure, magnetism and MFIS were studied via scanning electron microscopy, x-ray diffraction, transmission electron microscopy and vibrating sample magnetometer in the present work. The microstructure of the alloy was a dual-phase microstructure, including the matrix and the γ phase. Following the Er doping, the γ phase was continuously coarsened, forming a network of precipitates surrounding the grains. Also, a Co-Er-rich intermetallic compound was formed in the Co-rich γ phase when the Er content exceeded 0.1 at.%. The martensitic transformation temperature has a decreasing tendency during the Er being doped from 0 at.% to 1 at.% and the martensitic structure of the sample is of the L10 type, forming twin grains in the (111) twinning plane. On the contrary, the magnetic properties were improved by Er doping, especially saturation magnetization and magneto-crystalline anisotropy constantly increased to 60.45 emu/g and 3.13 × 106 erg/cm3 when the Er content reached 1 at.%, respectively. Also, the strain recovery ratio ( R s) of Co-Ni-Al-Er alloys can be enhanced by thermo-mechanical cycles and Er doping. At 5% of the total strain, the R s value exceeded 83% following thermo-mechanical cycles when the Er doping was 1 at.%. The strain in the applied magnetic field was increased by Er doping and an excess of 140 ppm of MFIS was obtained in the polycrystalline Co-Ni-Al-Er alloys.

  9. Coherent π-electron dynamics of (P)-2,2'-biphenol induced by ultrashort linearly polarized UV pulses: angular momentum and ring current.

    Mineo, H; Lin, S H; Fujimura, Y


    The results of a theoretical investigation of coherent π-electron dynamics for nonplanar (P)-2,2'-biphenol induced by ultrashort linearly polarized UV pulses are presented. Expressions for the time-dependent coherent angular momentum and ring current are derived by using the density matrix method. The time dependence of these coherences is determined by the off-diagonal density matrix element, which can be obtained by solving the coupled equations of motion of the electronic-state density matrix. Dephasing effects on coherent angular momentum and ring current are taken into account within the Markov approximation. The magnitudes of the electronic angular momentum and current are expressed as the sum of expectation values of the corresponding operators in the two phenol rings (L and R rings). Here, L (R) denotes the phenol ring in the left (right)-hand side of (P)-2,2'-biphenol. We define the bond current between the nearest neighbor carbon atoms Ci and Cj as an electric current through a half plane perpendicular to the Ci-Cj bond. The bond current can be expressed in terms of the inter-atomic bond current. The inter-atomic bond current (bond current) depends on the position of the half plane on the bond and has the maximum value at the center. The coherent ring current in each ring is defined by averaging over the bond currents. Since (P)-2,2'-biphenol is nonplanar, the resultant angular momentum is not one-dimensional. Simulations of the time-dependent coherent angular momentum and ring current of (P)-2,2'-biphenol excited by ultrashort linearly polarized UV pulses are carried out using the molecular parameters obtained by the time-dependent density functional theory (TD-DFT) method. Oscillatory behaviors in the time-dependent angular momentum (ring current), which can be called angular momentum (ring current) quantum beats, are classified by the symmetry of the coherent state, symmetric or antisymmetric. The bond current of the bridge bond linking the L and R

  10. Study on ablation of Ni film by ultrashort laser pulse-train%超短激光脉冲序列烧蚀镍薄膜的研究

    韩飞; 闫寒; 周海波; 王琼娥


      超短(飞秒)激光脉冲序列技术能有效地提高激光加工金属的加工精度,它在微/纳制造中具有重要的理论意义和生产价值。为了研究脉冲间隔对激光烧蚀金属加工精度的影响,以过渡金属镍为研究对象,采用双温模型和分子动力学模拟相结合的方法,对飞秒激光脉冲序列(脉冲间隔不同)烧蚀金属镍的过程、现象进行了研究,取得了脉冲序列烧蚀镍薄膜的动态表层电子温度和晶格温度随时间演化的数据和烧蚀区域在不同时刻的快照。结果表明,一定范围内,随着脉冲间隔的增加,脉冲序列烧蚀镍薄膜所产生的纳米粒子更加均匀,烧蚀平面更加平整,初始熔化速度、烧蚀率呈降低趋势,有利于提高加工的精度。%Micromaching by ultrashort laser pulse-train can effectively improve femtosecond laser ablation of metal , which are important both theoretically and practically in micro /nano-laser fabrication applications.In order to study the effect of separation of pulse on the accuracy of laser ablation , the phenomena and process of laser ablation with different separation of pulse train were studied in detail by combining the molecular dynamic simulation and two -temperature model, the electron and lattice temperatures of the layers next to dynamic film surfaces and the snapshots of nickel thin films irradiated by the femtosecond laser pulse trains were obtained .The result is that ,within a certain range, as the increase of the separation of pulse, femtosecond pulse train laser ablation of Ni films can apparently cause more flat ablation plane , slower initial melting speed, smaller and more uniform nanoparticles , smaller ablation ratio,which can effectively improve femtosecond laser ablation of metal .

  11. Supercomputations and big-data analysis in strong-field ultrafast optical physics: filamentation of high-peak-power ultrashort laser pulses

    Voronin, A. A.; Panchenko, V. Ya; Zheltikov, A. M.


    High-intensity ultrashort laser pulses propagating in gas media or in condensed matter undergo complex nonlinear spatiotemporal evolution where temporal transformations of optical field waveforms are strongly coupled to an intricate beam dynamics and ultrafast field-induced ionization processes. At the level of laser peak powers orders of magnitude above the critical power of self-focusing, the beam exhibits modulation instabilities, producing random field hot spots and breaking up into multiple noise-seeded filaments. This problem is described by a (3  +  1)-dimensional nonlinear field evolution equation, which needs to be solved jointly with the equation for ultrafast ionization of a medium. Analysis of this problem, which is equivalent to solving a billion-dimensional evolution problem, is only possible by means of supercomputer simulations augmented with coordinated big-data processing of large volumes of information acquired through theory-guiding experiments and supercomputations. Here, we review the main challenges of supercomputations and big-data processing encountered in strong-field ultrafast optical physics and discuss strategies to confront these challenges.

  12. Efficient burst mode amplifier for ultra-short pulses based on cryogenically cooled Yb³⁺:CaF₂.

    Körner, Jörg; Hein, Joachim; Liebetrau, Hartmut; Seifert, Reinhard; Klöpfel, Diethard; Kahle, Martin; Loeser, Markus; Siebold, Mathias; Schramm, Ulrich; Kaluza, Malte C


    We present a novel approach for the amplification of high peak power femtosecond laser pulses at a high repetition rate. This approach is based on an all-diode pumped burst mode laser scheme. In this scheme, pulse bursts with a total duration between 1 and 2 ms are be generated and amplified. They contain 50 to 2000 individual pulses equally spaced in time. The individual pulses have an initial duration of 350 fs and are stretched to 50 ps prior to amplification. The amplifier stage is based on Yb3+:CaF2 cooled to 100 K. In this amplifier, a total output energy in excess of 600 mJ per burst at a repetition rate of 10 Hz is demonstrated. For lower repetition rates the total output energy per burst can be scaled up to 915 mJ using a longer pump duration. This corresponds to an efficiency as high as 25% of extracted energy from absorbed pump energy. This is the highest efficiency, which has so far been demonstrated for a pulsed Yb3+:CaF2 amplifier.

  13. Coherent control of optical four-wave mixing by two-color $\\omega$-$3\\omega$ ultrashort laser pulses

    Serrat, C


    A theoretical investigation on the phase control of optical transient four-wave mixing interactions in two-level systems driven by two intense temporal coherent femtosecond laser pulses of central angular frequencies $\\omega$ and $3\\omega$ is reported. By solving the full Maxwell-Bloch equations beyond the slowly-varying envelope and rotating-wave approximations in the time domain, the parametric nonlinear coupling to the optical field at frequency $5\\omega$ is found to depend critically on the initial relative phase $\\phi$ of the two propagating pulses; the coupling is enhanced when the pulses interfere constructively in the center ($\\phi=0$), while it is nearly suppressed when they are out of phase ($\\phi=\\pi$).

  14. Spectrum Blueshifting of Ultrashort UV Laser Pulse Induced by Ionization of Supersonic He and Ar Gas Jets

    YAN Lixin; ZHANG Yongsheng; LIU Jingru; HUANG Wenhui; TANG Chuanxiang; CHENG Jianping


    The predominant spectral blueshifting of a sub-picosecond UV laser pulse induced by ultrafast ionization of noble gases was investigated. Spectral measurements were made at various gas densities. Typical quasi-periodic structures in the blueshifted spectrum were obtained. The observations were in connection with the so-called self-phase modulation of laser pulses in the ultrafast ionization process which was simply simulated with an ADK (Ammosov-Delone-Krainov) ionization model. Some quantitative information can be deduced from the measurements and calculations.

  15. The Use of Ultrashort Picosecond Laser Pulses to Generate Quantum Optical Properties of Single Molecules in Biophysics

    Ly, Sonny

    Generation of quantum optical states from ultrashort laser-molecule interactions have led to fascinating discoveries in physics and chemistry. In recent years, these interactions have been extended to probe phenomena in single molecule biophysics. Photons emitted from a single fluorescent molecule contains important properties about how the molecule behave and function in that particular environment. Analysis of the second order coherence function through fluorescence correlation spectroscopy plays a pivotal role in quantum optics. At very short nanosecond timescales, the coherence function predicts photon antibunching, a purely quantum optical phenomena which states that a single molecule can only emit one photon at a time. Photon antibunching is the only direct proof of single molecule emission. From the nanosecond to microsecond timescale, the coherence function gives information about rotational diffusion coefficients, and at longer millisecond timescales, gives information regarding the translational diffusion coefficients. In addition, energy transfer between molecules from dipole-dipole interaction results in FRET, a highly sensitive method to probe conformational dynamics at nanometer distances. Here I apply the quantum optical techniques of photon antibunching, fluorescence correlation spectroscopy and FRET to probe how lipid nanodiscs form and function at the single molecule level. Lipid nanodiscs are particles that contain two apolipoprotein (apo) A-I circumventing a lipid bilayer in a belt conformation. From a technological point of view, nanodiscs mimics a patch of cell membrane that have recently been used to reconstitute a variety of membrane proteins including cytochrome P450 and bacteriorhodopsin. They are also potential drug transport vehicles due to its small and stable 10nm diameter size. Biologically, nanodiscs resemble to high degree, high density lipoproteins (HDL) in our body and provides a model platform to study lipid-protein interactions

  16. Accelerating Protons to Therapeutic Energies with Ultra-Intense Ultra-Clean and Ultra-Short Laser Pulses

    Bulanov, Stepan S; Bychenkov, Valery Yu; Chvykov, Vladimir; Kalinchenko, Galina; Matsuoka, Takeshi; Rousseau, Pascal; Reed, Stephen; Yanovsky, Victor; Krushelnick, Karl; Litzenberg, Dale William; Maksimchuk, Anatoly


    Proton acceleration by high-intensity laser pulses from ultra-thin foils for hadron therapy is discussed. With the improvement of the laser intensity contrast ratio to 10-11 achieved on Hercules laser at the University of Michigan, it became possible to attain laser-solid interactions at intensities up to 1022 W/cm2 that allows an efficient regime of laser-driven ion acceleration from submicron foils. Particle-In-Cell (PIC) computer simulations of proton acceleration in the Directed Coulomb explosion regime from ultra-thin double-layer (heavy ions / light ions) foils of different thicknesses were performed under the anticipated experimental conditions for Hercules laser with pulse energies from 3 to 15 J, pulse duration of 30 fs at full width half maximum (FWHM), focused to a spot size of 0.8 microns (FWHM). In this regime heavy ions expand predominantly in the direction of laser pulse propagation enhancing the longitudinal charge separation electric field that accelerates light ions. The dependence of the ma...

  17. Relativistically induced transparency acceleration of light ions by an ultrashort laser pulse interacting with a heavy-ion-plasma density gradient

    Sahai, Aakash A.; Tsung, Frank S.; Tableman, Adam R.; Mori, Warren B.; Katsouleas, Thomas C.


    -540410.1007/3-540-47789-6_36 2331, 342 (2002)] simulations. We model the acceleration of protons to GeV energies with tens-of-femtoseconds laser pulses of a few petawatts. The scaling of proton energy with laser power compares favorably to other mechanisms for ultrashort pulses [Schreiber , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.97.045005 97, 045005 (2006); Esirkepov , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.92.175003 92, 175003 (2004); Silva , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.92.015002 92, 015002 (2004); Fiuza , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.109.215001 109, 215001 (2012)].

  18. Study on the protection of Er-doped phosphate glass waveguide surface in ion-exchange processing


    A novel method, sputtering K9 glass film, is proposed to solve the surface corrosion of Er-doped phosphate glass during ion-exchange processing for optical waveguide fabrication. The corrosion causes are analyzed to be the intrinsically weak stabilization of phosphate glass structure, hydrophile and weakly acidic property of phosphate radical. Experimental results show that the K9 glass film could not only protect the Er-doped phosphate glass surface from being corroded but also give no influence on the waveguide fabrication. The effect of thickness of K9 glass film on the optical property of waveguide is also investigated and the op- timal thickness is found to be 60―80 nm. It provides a good base for further fabri- cation of active phosphate glass optical waveguide devices.

  19. Microstructure and photoluminescence of Er-doped SiOx films synthesized by ion beam assisted deposition

    Duan Shu-Qing; Tan Na; Zhang Qing-Yu


    Er-doped Sio_ films were synthesized at 500℃ by ion beam assisted deposition technique and annealed at 800 and 1100℃ for 2h in the air atomosphere. The analysis by using energy dispersive x-ray spectroscopy showed that the ratio of Si to O decreased from 3 in the as-deposited films to about 1 in the annealed films. The investigation by using transmission electron microscopy and x-ray diffraction inducated that annealing induces a microstructure change from amorphous to crystlline. The grain sizes in the films were about 10 and 40nm when annealed at 800 and 1100℃, respectively. The films annealed at temperatures of 800 and 1100℃ exhibited a sharp photoluminescence (PL) at 1.533μm from the Er centres when pumped by 980nm laser. The influence of microstructure and grain size on the PL from Er-doped Sio_ films has been studies and discussed.

  20. Stabilization of a fiber-optic two-arm interferometer for ultra-short pulse signal processing applications.

    Park, Yongwoo; Ahn, Tae-Jung; Azaña, José


    We experimentally demonstrate a stable ultrafast first-order temporal differentiator using a fiber-optic Michelson interferometer incorporating a simple feedback stabilization control, which is based on dithering a single wavelength cw reference. Feedback control signals are acquired by a phase-lock-loop and used for automatically adjusting and maintaining the resonance wavelength of the differentiator at the pulse center wavelength without dithering or disturbing the interferometer arms. Picosecond odd-symmetry Hermite-Gaussian waveforms using the implemented first-order differentiator have been stably generated. The demonstrated stabilization system should prove useful for a wide range of ultrafast pulse processing and analysis applications based on the use of two-arm interferometers.

  1. Electrical Equivalent Model for an Optical VCO in a PLL Synchronization Scheme for Ultrashort Optical Pulse Sources

    Bogoni, Antonella; Potì, Luca; Ponzini, Filippo; Ghelfi, Paolo


    The electrical modeling of complex electrooptical devices is a useful task for the correct design of its schemes and for the estimation of its performance. In this paper, we consider an electrooptical phase-locked loop (PLL) used to synchronize an RF system clock to the repetition rate of an optical pulsed source, realized by an active fiber mode-locking (ML) technique in the regenerative configuration. The synchronization scheme is suggested by a description of the pulsed source, for the first time, as an optical voltage-control oscillator (VCO). In particular, we present a simple new all-electrical model for the proposed optical VCO, and we verify its accuracy by the implementation of the whole PLL scheme at 2.5 and 10 GHz.

  2. Self-consistent analyses for potential conduction block in nerves by an ultrashort high-intensity electric pulse

    Joshi, R. P.; Mishra, A.; Hu, Q.; Schoenbach, K. H.; Pakhomov, A.


    Simulation studies are presented that probe the possibility of using high-field (>100kV/cm) , short-duration (˜50ns) electrical pulses for nonthermal and reversible cessation of biological electrical signaling pathways. This would have obvious applications in neurophysiology, clinical research, neuromuscular stimulation therapies, and even nonlethal bioweapons development. The concept is based on the creation of a sufficiently high density of pores on the nerve membrane by an electric pulse. This modulates membrane conductance and presents an effective “electrical short” to an incident voltage wave traveling across a nerve. Net blocking of action potential propagation can then result. A continuum approach based on the Smoluchowski equation is used to treat electroporation. This is self-consistently coupled with a distributed circuit representation of the nerve dynamics. Our results indicate that poration at a single neural segment would be sufficient to produce an observable, yet reversible, effect.

  3. Synthesis, Characterization and Microwave Absorption Properties of Polyaniline/Er-Doped Strontium Ferrite Nanocomposite.

    Luo, Juhua; Wang, Eryong; Xu, Yang


    Er-doped strontium ferrite nanopowders (SrEr0.3Fe11.7O19) were prepared by the sol-gel method, and then their composites of PANI/SrEr0.3Fe11.7O19 with 10 wt% and 20 wt% ferrite were prepared by an in-situ polymerization process. The characterization of obtained samples was accomplished by XRD, FT-IR, TEM, VSM, and vector network analyzer techniques. A successful conjugation of ferrite nanoparticles with polyaniline could be indicated by XRD and FT-IR analysis. TEM confirmed the formation of polyaniline packed on strontium ferrite surface. Magnetization measurements showed the substituted Er3+ of Fe3+ on basis site enhanced the magnetic property notably and the content of polyaniline also influenced the magnetic property prominently. PANI/SrEr0.3Fe11.7O19 possessed the best absorption property with the optimum matching thickness of 3 mm in the frequency of 2-18 GHz. The value of the maximum RL was -42.0 dB at 12.0 GHz with the 5.5 GHz bandwidth.

  4. Spectroscopic properties of transparent Er-doped oxyfluoride glass-ceramics with GdF₃.

    Środa, Marcin; Szlósarczyk, Krzysztof; Różański, Marek; Sitarz, Maciej; Jeleń, Piotr


    Optically active glass-ceramics (GC) with the low-phonon phases of fluorides, doped with Er(3+) was studied. Glass based on SiO₂-Al₂O₃-Na₂F₂-Na₂O-GdF₃-BaO system was obtained. Dopant were introduced to the glass in an amount of 0.01 mol Er₂O₃ per 1 mol of glass. DTA/DSC study shows multi-stage crystallization. XRD identification of obtained phases did not confirm the presence of pure GdF₃ phase. Instead of that ceramization process led to formation of NaGdF₄ and BaGdF₅. The structural changes were studied using FT-IR spectroscopic method. The study of luminescence of the samples confirmed that optical properties of the obtained GC depend on crystallizing phases during ceramization. Time resolved spectroscopy of Er-doped glass showed the 3 and 8 times increase of lifetime of emission from (4)S₃/₂ and (4)F₉/₂ states, respectively. It confirms the erbium ions have ability to locate in the low phonon gadolinium-based crystallites. The results give possibility to obtain a new material for optoelectronic application.

  5. Investigation of the photosensitivity, temperature sustainability and fluorescence characteristics of several Er-doped photosensitive fibers

    Shen, Y H; Mandal, J; Sun, T; Grattan, K T V; Wade, S A; Collins, Stephen F; Baxter, Gregory W; Dussardier, Bernard; Monnom, Gérard


    Three different types of Er doped photosensitive fibers, germanium/erbium (Ge/Er) fiber, tin/germanium/erbium fiber (Sn/Er) and antimony/germanium/erbium fiber (Sb/Er) have been manufactured and studied for use in optical sensor systems. Their characteristics of photosensitivity, the temperature sustainability of fiber Bragg gratings (FBGs) written into these fibers and the fluorescence emission from the Er dopant were investigated and compared. It has been shown in this work that these fibers all show a satisfactory degree of photosensitivity to enable the fabrication of FBGs and a significant level of fluorescence emission within the 1550 nm band for sensor use. The high temperature sustainability of the FBGs written into these fibers was investigated and seen to be quite significant at temperatures as high as 850 ^{\\circ}C, in particular for the Sn/Er and Sb/Er fibers. A fiber laser using the Sb/Er fiber as the gain medium was demonstrated, giving evidence of the strong fluorescence emission from the Er do...

  6. Upconversion luminescence, ferroelectrics and piezoelectrics of Er Doped SrBi4Ti4O15

    Dengfeng Peng


    Full Text Available Er3+ doped SrBi4Ti4O15 (SBT bismuth layered-structure ferroelectric ceramics were synthesized by the traditional solid-state method, and their upconversion photoluminescent (UC properties were investigated as a function of Er3+ concentration and incident pump power. Green (555 nm and red (670 nm emission bands were obtained under 980 nm excitation at room temperature, which corresponded to the radiative transitions from 4S3/2, and 4F9/2 to 4I15/2, respectively. The emission color of the samples could be changed with moderating the doping concentrations. The dependence of UC intensity on pumping power indicated a two-photon emission process. Studies on dielectric properties indicated that the introduction of Er increased the ferroelectric-paraelectric phase transition temperature (Tc of SBT, thus making this ceramic suitable for piezoelectric sensor applications at higher temperatures. Piezoelectric measurement showed that the doped SBT had a relative higher piezoelectric constant d33 compared with the non-doped ceramics. The thermal annealing behaviors of the doped sample revealed a stable piezoelectric property. The doped SBT showed bright UC emission while simultaneously having increased Tc and d33. As a multifunctional material, Er doped SBT ferroelectric oxide showed great potential in application of sensor, future optical-electro integration and coupling devices.

  7. Down- and up-conversion emissions in Er-doped transparent fluorotellurite glass-ceramics

    Miguel, A.; Morea, R.; Gonzalo, J.; Fernandez, J.; Balda, R.


    In this work, we report the near infrared and upconversion emissions of Er3+-doped transparent fluorotellurite glassceramics obtained by heat treatment of the precursor Er-doped TeO2-ZnO-ZnF2 glass. Structural analysis shows that ErF3 nanocrystals nucleated in the glass-ceramic sample are homogeneously distributed in the glass matrix with a typical size of 45±10 nm. The comparison of the fluorescence properties of Er3+-doped precursor glass and glass-ceramic confirms the successful incorporation of the rare-earth into the nanocrystals. An enhancement of the red upconversion emission due to 4F9/2→4I15/2 transition together with weak emission bands due to transitions from 2H9/2, 4F3/2,5/2, and 4F7/2 levels to the ground state are observed under excitation at 801 nm in the glass-ceramic sample. The temporal evolution of the red emission together with the excitation upconversion spectrum suggest that energy transfer processes are responsible for the enhancement of the red emission.

  8. Ultrashort pulse laser dicing of thin Si wafers: the influence of laser-induced periodic surface structures on the backside breaking strength

    Domke, Matthias; Egle, Bernadette; Piredda, Giovanni; Stroj, Sandra; Fasching, Gernot; Bodea, Marius; Schwarz, Elisabeth


    High power electronic chips are usually fabricated on about 50 µm thin Si wafers to improve heat dissipation. At these chip thicknesses mechanical dicing becomes challenging. Chippings may occur at the cutting edges, which reduce the mechanical stability of the die. Thermal load changes could then lead to sudden chip failure. Ultrashort pulsed lasers are a promising tool to improve the cutting quality, because thermal side effects can be reduced to a minimum. However, laser-induced periodic surface structures occur at the sidewalls and at the trench bottom during scribing. The goal of this study was to investigate the influence of these periodic structures on the backside breaking strength of the die. An ultrafast laser with a pulse duration of 380 fs and a wavelength of 1040 nm was used to cut a wafer into single chips. The pulse energy and the number of scans was varied. The cuts in the wafer were investigated using transmitted light microscopy, the sidewalls of the cut chips were investigated using scanning electron and confocal microscopy, and the breaking strength was evaluated using the 3-point bending test. The results indicated that periodic holes with a distance of about 20–30 µm were formed at the bottom of the trench, if the number of scans was set too low to completely cut the wafer; the wafer was only perforated. Mechanical breaking of the bridges caused 5 µm deep kerfs in the sidewall. These kerfs reduced the breaking strength at the backside of the chip to about 300 MPa. As the number of scans was increased, the bridges were ablated and the wafer was cut completely. Periodic structures were observed on the sidewall; the roughness was below 1 µm. The surface roughness remained on a constant level even when the number of scans was doubled. However, the periodic structures on the sidewall seemed to vanish and the probability to remove local flaws increases with the number of scans. As a consequence, the breaking strength was increased to about

  9. Structure of isolated biomolecules obtained from ultrashort x-ray pulses: exploiting the symmetry of random orientations.

    Saldin, D K; Shneerson, V L; Fung, R; Ourmazd, A


    Amongst the promised capabilities of fourth-generation x-ray sources currently under construction is the ability to record diffraction patterns from individual biological molecules. One version of such an experiment would involve directing a stream of molecules into the x-ray beam and sequentially recording the scattering from each molecule of a short, but intense, pulse of radiation. The pulses are sufficiently short that the diffraction pattern is that due to scattering from identical molecules 'frozen' in random orientations. Each diffraction pattern may be thought of as a section through the 3D reciprocal space of the molecule, of unknown, random, orientation. At least two algorithms have been proposed for finding the relative orientations from just the measured diffraction data. The 'common-line' method, also employed in 3D electron microscopy, appears not best suited to the very low mean photon count per diffraction pattern pixel expected in such experiments. A manifold embedding technique has been used to reconstruct the 3D diffraction volume and hence the electron density of a small protein at the signal level expected of the scattering of an x-ray free electron laser pulse from a 500 kD biomolecule. In this paper, we propose an alternative algorithm which raises the possibility of reconstructing the 3D diffraction volume of a molecule without determining the relative orientations of the individual diffraction patterns. We discuss why such an algorithm may provide a practical and computationally convenient method of extracting information from very weak diffraction patterns. We suggest also how such a method may be adapted to the problem of finding the variations of a structure with time in a time-resolved pump-probe experiment.

  10. Ultra-fast Movies Resolve Ultra-short Pulse Laser Ablation and Bump Formation on Thin Molybdenum Films

    Domke, Matthias; Rapp, Stephan; Huber, Heinz

    For the monolithic serial interconnection of CIS thin film solar cells, 470 nm molybdenum films on glass substrates must be separated galvanically. The single pulse ablation with a 660 fs laser at a wavelength of 1053 nm is investigated in a fluence regime from 0.5 to 5.0 J/cm2. At fluences above 2.0 J/cm2 bump and jet formation can be observed that could be used for creating microstructures. For the investigation of the underlying mechanisms of the laser ablation process itself as well as of the bump or jet formation, pump probe microscopy is utilized to resolve the transient ablation behavior.

  11. Ultrashort spatiotemporal optical solitons in quadratic nonlinear media: Generation of line and lump solitons from few-cycle input pulses

    Leblond, Hervé; Mihalache, Dumitru; 10.1103/PHYSREVA.80.053812


    By using a powerful reductive perturbation technique, or a multiscale analysis, a generic Kadomtsev-Petviashvili evolution equation governing the propagation of femtosecond spatiotemporal optical solitons in quadratic nonlinear media beyond the slowly varying envelope approximation is put forward. Direct numerical simulations show the formation, from adequately chosen few-cycle input pulses, of both stable line solitons (in the case of a quadratic medium with normal dispersion) and of stable lumps (for a quadratic medium with anomalous dispersion). Besides, a typical example of the decay of the perturbed unstable line soliton into stable lumps for a quadratic nonlinear medium with anomalous dispersion is also given.

  12. Observation of a highly directional γ-ray beam from ultrashort, ultraintense laser pulse interactions with solids

    Norreys, P. A.; Santala, M.; Clark, E.; Zepf, M.; Watts, I.; Beg, F. N.; Krushelnick, K.; Tatarakis, M.; Dangor, A. E.; Fang, X.; Graham, P.; McCanny, T.; Singhal, R. P.; Ledingham, K. W. D.; Creswell, A.; Sanderson, D. C. W.; Magill, J.; Machacek, A.; Wark, J. S.; Allott, R.; Kennedy, B.; Neely, D.


    Novel measurements of electromagnetic radiation above 10 MeV are presented for ultra intense laser pulse interactions with solids. A bright, highly directional source of γ rays was observed directly behind the target. The γ rays were produced by bremsstrahlung radiation from energetic electrons generated during the interaction. They were measured using the photoneutron reaction [63Cu(γ,n)62Cu] in copper. The resulting activity was measured by coincidence counting the positron annihilation γ rays which were produced from the decay of 62Cu. New measurements of the bremsstrahlung radiation at 1019W cm-2 are also presented.

  13. Adaptive-feedback spectral-phase control for interactions with transform-limited ultrashort high-power laser pulses.

    Liu, Cheng; Zhang, Jun; Chen, Shouyuan; Golovin, Gregory; Banerjee, Sudeep; Zhao, Baozhen; Powers, Nathan; Ghebregziabher, Isaac; Umstadter, Donald


    Fourier-transform-limited light pulses were obtained at the laser-plasma interaction point of a 100-TW peak-power laser in vacuum. The spectral-phase distortion induced by the dispersion mismatching between the stretcher, compressor, and dispersive materials was fully compensated for by means of an adaptive closed-loop. The coherent temporal contrast on the sub-picosecond time scale was two orders of magnitude higher than that without adaptive control. This novel phase control capability enabled the experimental study of the dependence of laser wakefield acceleration on the spectral phase of intense laser light.

  14. A High-Energy, Ultrashort-Pulse X-Ray System for the Dynamic Study of Heavy, Dense Materials

    Gibson, David Jeremy [Univ. of California, Davis, CA (United States)


    Thomson-scattering based x-ray radiation sources, in which a laser beam is scattered off a relativistic electron beam resulting in a high-energy x-ray beam, are currently being developed by several groups around the world to enable studies of dynamic material properties which require temporal resolution on the order of tens of femtoseconds to tens of picoseconds. These sources offer pulses that are shorter than available from synchrotrons, more tunable than available from so-called Ka sources, and more penetrating and more directly probing than ultrafast lasers. Furthermore, Thomson-scattering sources can scale directly up to x-ray energies in the few MeV range, providing peak brightnesses far exceeding any other sources in this regime. This dissertation presents the development effort of one such source at Lawrence Livermore National Laboratory, the Picosecond Laser-Electron InterAction for the Dynamic Evaluation of Structures (PLEIADES) project, designed to target energies from 30 keV to 200 keV, with a peak brightness on the order of 1018 photons • s-1 • mm-2 • mrad-2 • 0.01% bandwidth-1. A 10 TW Ti:Sapphire based laser system provides the photons for the interaction, and a 100 MeV accelerator with a 1.6 cell S-Band photoinjector at the front end provides the electron beam. The details of both these systems are presented, as is the initial x-ray production and characterization, validating the theory of Thomson scattering. In addition to the systems used to enable PLEIADES, two alternative systems are discussed. An 8.5 GHz X-Band photoinjector, capable of sustaining higher accelerating gradients and producing lower emittance electron beams in a smaller space than the S-Band gun, is presented, and the initial operation and commissioning of this gun is presented. Also, a hybrid chirped-pulse amplification system is presented as an alternative to the standard regenerative amplifier technology in high

  15. Ultrashort Pulse Inscription of Photonic Structures in ZnSe and GaAs for Mid Infrared Applications


    Fabrication 3.1 Femtosecond Laser Fabrication Initial fabrication processes described below were carried out with a Fianium Yb:fibre laser set up...b) (a) (c) (d) ~80µm 5 Figure 7. Refocusing cycle causing filamentation and multiple foci. [8] 3.3 Picosecond Laser Fabrication Longer...repetition rate of 500kHz and a maximum average power of 360mW. This is equivalent to a maximum pulse energy of 0.72µJ. Figure 4. Fianium Laser

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

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


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

  17. Morphology and topography of perovskite solar cell films ablated and scribed with short and ultrashort laser pulses

    Bayer, Lukas; Ehrhardt, Martin; Lorenz, Pierre; Pisoni, Stefano; Buecheler, Stephan; Tiwari, Ayodhya N.; Zimmer, Klaus


    The unique properties of halide perovskites are suitable for low-cost high-efficiency photovoltaic applications. For commercialization of this technology, it is pivotal to upscale towards solar modules. Monolithic interconnection of solar cells is a necessary step for realization of thin-film solar modules and the laser scribing of the constituent layers with well-defined profiles of high accuracy is a promising approach for high speed processing. Here the laser ablation and scribing of methylammonium lead iodide perovskite (CH3NH3PbI3: MAPbI3) layers are investigated. Nanosecond (ns) and picosecond (ps) laser pulses were used to ablate and scribe MAPbI3 films on FTO/glass by irradiation from the film- and the glass-side. Depending on the irradiation configuration laser ablation or lift-off delamination was determined to be the dominating mechanism of thin-film removal. Various surface modifications such as film smoothening and decomposition of the MAPbI3 have been observed, especially when nanosecond laser pulses are used. The complete removal of the MAPbI3, film without damaging the FTO/substrate, has been achieved for all studied laser sources.

  18. Influence of Raman Effect on the Propagation Properties of Ultrashort Pulse in Metamaterials%拉曼效应对负折射介质中超短脉冲传输的影响

    张景贵; 李勇帆; 赵晋琴


    Influence of Raman effect on self-focusing propagation properties of ultrashort laser pulse in metamaterials is studied through numerical solutions of ( 3 +1) -dimensional nonlinear Schrodinger equation including the contribution of the Raman delayed response, and the especial attention is paid to the anomalous propagation phenomena not found in ordinary materials. It is found that Raman effect will lead to the occurrence of the blueshifted frequencies during the self-focusing process of ultrashort pulse, opposite to the corresponding case in ordinary materials. However, its influence on the self-focus properties of the self-focusing of ultrashort pulse is the same as the case in ordinary materials, namely, it will make the self-focus occurring firstly in the leading part of pulse. Our works are of very important significance in the practical application, such as controlling a train of ultrashort pulse and self focus etal by using metamaterials.%通过数值法对包含拉曼延迟响应的(3+1)维非线性薛定谔方程进行求解,研究了超短脉冲激光在负折射介质中传输时拉曼效应对自聚焦传输特性的影响,着重分析其不同与常规介质的反常传输现象.结果表明:由于负的折射率影响,拉曼效应将导致超短脉冲在自聚焦过程中频谱发生蓝移现象,这与常规介质对应情形相反;而它对负折射介质中超短脉冲的自聚焦特性的影响与常规介质相同,即拉曼效应将诱导自聚焦效应首先发生在脉冲的前沿.本文研究工作对将来利用负折射介质来操控超短光脉冲串产生、自聚焦等许多实际应用领域研究具有重要的指导意义.

  19. Writing of 3D optical integrated circuits with ultrashort laser pulses in the presence of strong spherical aberration

    Bukharin, M. A.; Skryabin, N. N.; Khudyakov, D. V.; Vartapetov, S. K.


    A novel technique was proposed for 3D femtosecond writing of waveguides and optical integrated circuits in the presence of strong spherical aberration, caused by inscription at significantly different depth under the surface of optical glasses and crystals. Strong negative effect of spherical aberration and related asymmetry of created structures was reduced due to transition to the cumulative thermal regime of femtosecond interaction with the material. The differences in the influence of spherical aberration effect in a broad depth range (larger than 200 µm) was compensated by dynamic adjustment of laser pulse energy during the process of waveguides recording. The presented approach has been experimentally implemented in fused silica. Obtained results can be used in production of a broad class of femtosecond written three-dimensional integrated optical systems, inscripted at non-optimal (for focusing lens) optical depth or in significantly extended range of depths.

  20. Hydrogen migration within a water molecule: formation of HD+ upon irradiation of HOD with intense, ultrashort laser pulses

    Mathur, Deepak; Dharmadhikari, Aditya K.; Dharmadhikari, Jayashree A.; Vasa, Parinda


    We have carried out velocity map imaging experiments on HOD molecules irradiated by 10 fs long pulses of intense (˜1 PW cm-2) laser light (800 nm). We have detected HD+ ions as a signature of unimolecular hydrogen migration within the water molecule; ion momentum maps measured at different laser polarizations yield evidence that such hydrogen migration occurs on ultrafast timescales. We have been able to utilize the momentum maps to deduce that (i) the HD+ ion that is formed is vibrationally excited, and (ii) that the electronic state of the precursor HOD2+ dication has an essentially linear geometrical structure with elongated O-H and O-D bonds. Our results are in agreement with expectations from ab initio quantum chemical computations of potential energy surfaces of the lowest-energy states of HOD, HOD+ and HOD2+.

  1. Effect of nuclear motion on high-order harmonic generation of H$_2^+$ in intense ultrashort laser pulses

    Ahmadi, Hamed; Sabzyan, Hassan; Niknam, Ali Reza; Vafaee, Mohsen


    High-order harmonic generation is investigated for H$_2^+$ and D$_2^+$ with and without Born-Oppenheimer approximation by numerical solution of full dimensional electronic time-dependent Schr\\"{o}dinger equation under 4-cycle intense laser pulses of 800 nm wavelength and $I$=4, 5, 7, 10 $\\times 10^{14}$ W$/$cm$^2$ intensities. For most harmonic orders, the intensity obtained for D$_2^+$ is higher than that for H$_2^+$, and the yield difference increases as the harmonic order increases. Only at some low harmonic orders, H$_2^+$ generates more intense harmonics compared to D$_2^+$. The results show that nuclear motion, ionization probability and system dimensionality must be simultaneously taken into account to properly explain the isotopic effects on high-order harmonic generation and to justify experimental observations.

  2. Generation of near transform-limited ultrashort laser pulses in kilohertz chirped-pulse amplification system by compensating high order phase distortions

    Yongliang Jiang; Bing Zhou; Yuxin Leng; Xiaowei Chen; Ruxin Li; Zhizhan Xu


    The effects of gain narrowing and high order dispersions on the pulse duration in our kilohertz chirpedpulse amplification system have been compensated experimentally. Using an acousto-optic programmable dispersive filter (AOPDF), the spectral full-width at half-maximum (FWHM) is expanded from 30 to50 nm. Stable laser pulses with the duration of 30 fs (FWHM), which is 1.07 times Fourier-transformlimitation, have been acquired by pre-compensating the high order phase distortions using the phase measured by spectral phase interferometry for direct electric-field reconstruction (SPIDER).

  3. Part 2: Ultra-short pulse laser patterning of very thin indium tin oxide on glass substrates

    McDonnell, C.; Milne, D.; Chan, H.; Rostohar, D.; O'Connor, G. M.


    We investigate selective patterning of ultra-thin 20 nm Indium Tin Oxide (ITO) thin films on glass substrates, using 343, 515, and 1030 nm femtosecond (fs), and 1030 nm picoseconds (ps) laser pulses. An ablative removal mechanism is observed for all wavelengths at both femtosecond and picoseconds time-scales. The absorbed threshold fluence values were determined to be 12.5 mJ cm-2 at 343 nm, 9.68 mJ cm-2 at 515 nm, and 7.50 mJ cm-2 at 1030 nm for femtosecond and 9.14 mJ cm-2 at 1030 nm for picosecond laser exposure. Surface analysis of ablated craters using atomic force microscopy confirms that the selective removal of the film from the glass substrate is dependent on the applied fluence. Film removal is shown to be primarily through ultrafast lattice deformation generated by an electron blast force. The laser absorption and heating process was simulated using a two temperature model (TTM). The predicted surface temperatures confirm that film removal below 1 J cm-2 to be predominately by a non-thermal mechanism.

  4. Detection of calculus by laser-induced breakdown spectroscopy (LIBS) using an ultra-short pulse laser system (USPL)

    Schelle, F.; Brede, O.; Krueger, S.; Oehme, B.; Dehn, C.; Frentzen, M.; Braun, A.


    The aim of this study was to assess the detection of calculus by Laser Induced Breakdown Spectroscopy (LIBS). The study was performed with an Nd:YVO4 laser, emitting pulses with a duration of 8 ps at a wavelength of 1064 nm. A repetition rate of 500 kHz at an average power of 5 W was used. Employing a focusing lense, intensities of the order of 1011 W/cm2 were reached on the tooth surface. These high intensities led to the generation of a plasma. The light emitted by the plasma was collimated into a fibre and then analyzed by an echelle spectroscope in the wavelength region from 220 nm - 900 nm. A total number of 15 freshly extracted teeth was used for this study. For each tooth the spectra of calculus and cementum were assessed separately. Comprising all single measurements median values were calculated for the whole spectrum, leading to two specific spectra, one for calculus and one for cementum. For further statistical analysis 28 areas of interest were defined as wavelength regions, in which the signal strength differed regarding the material. In 7 areas the intensity of the calculus spectrum differed statistically significant from the intensity of the cementum spectrum (p minimally invasive method allowing a safe application in laser-guided dentistry.

  5. All-optical control in metal nanocomposites due to a reversible transition between the local-field-enhancement and a local-field-depression upon irradiation by ultrashort control-pulses of light

    Im, Song-Jin


    We theoretically study on non-perturbative effective nonlinear responses of metal nanocomposites based on the intrinsic third-order nonlinear response of metal nanoparticles. The large intrinsic third-order nonlinear susceptibility of metal nanoparticles and an irradiation by ultrashort control pulse of light with a sufficiently high peak intensity and moderate fluence can induce a local-field-depression and a saturated plasmon-bleaching in metal nanoparticles. If the control pulse is on, the metal nanocomposites can behave like a dielectric due to the local-field-depression, while if the control pulse is off, the metal nanocomposites can behave like a metal showing a high absorption due to the local-field-enhancement at the plasmon-resonance. This phenomenon can be applied to an ultrafast and remote control of light in metal nanocomposites.

  6. Er-doped sesquioxides for 1.5-micron lasers - spectroscopic comparisons

    Merkle, Larry D.; Ter-Gabrielyan, Nikolay


    Due to the favorable thermal properties of sesquioxides as hosts for rare earth laser ions, we have recently studied the spectroscopy of Er:Lu2O3 in the 1400-1700 nm wavelength range, and here report its comparison with our earlier results on Er:Y2O3 and Er:Sc2O3. These studies include absorption and fluorescence spectra, fluorescence lifetimes, and inference of absorption and stimulated emission cross sections, all as a function of temperature. At room temperature, optical absorption limits practical laser operation to wavelengths longer than about 1620 nm. In that spectral range, the strongest stimulated emission peak is that at 1665 nm in Er:Sc2O3, with an effective cross section considerably larger than those of Er:Y2O3 and Er:Lu2O3. At 77K, the absorption is weak enough for efficient laser operation at considerably shorter wavelengths, where there are peaks with much larger stimulated emission cross sections. The three hosts all have peaks near 1575-1580 nm with comparably strong cross sections. As we have reported earlier, it is possible to lase even shorter wavelengths efficiently at this temperature, in particular the line at 1558 nm in Er:Sc2O3. Our new spectroscopic studies of Er:Lu2O3 indicate that its corresponding peak, like that of Er:Sc2O3, has a less favorable ratio of stimulated emission to absorption cross sections. Reasons for the differences will be discussed. We conclude that for most operating scenarios, Er:Sc2O3 is the most promising of the Er-doped sesquioxides studied for laser operation around 1.5-1.6 microns.

  7. The time resolved measurement of ultrashort terahertz-band electric fields without an ultrashort probe

    Walsh, D. A., E-mail:; Snedden, E. W. [Accelerator Science and Technology Centre, STFC Daresbury National Laboratory, Warrington WA4 4AD (United Kingdom); Jamison, S. P. [Accelerator Science and Technology Centre, STFC Daresbury National Laboratory, Warrington WA4 4AD (United Kingdom); Photon Science Institute, The University of Manchester, Manchester M13 9PL (United Kingdom)


    The time-resolved detection of ultrashort pulsed THz-band electric field temporal profiles without an ultrashort laser probe is demonstrated. A non-linear interaction between a narrow-bandwidth optical probe and the THz pulse transposes the THz spectral intensity and phase information to the optical region, thereby generating an optical pulse whose temporal electric field envelope replicates the temporal profile of the real THz electric field. This optical envelope is characterised via an autocorrelation based FROG (frequency resolved optical gating) measurement, hence revealing the THz temporal profile. The combination of a narrow-bandwidth, long duration, optical probe, and self-referenced FROG makes the technique inherently immune to timing jitter between the optical probe and THz pulse and may find particular application where the THz field is not initially generated via ultrashort laser methods, such as the measurement of longitudinal electron bunch profiles in particle accelerators.

  8. The time resolved measurement of ultrashort THz-band electric fields without an ultrashort probe

    Walsh, David A; Jamison, Steven P


    The time-resolved detection of ultrashort pulsed THz-band electric field temporal profiles without an ultrashort laser probe is demonstrated. A non-linear interaction between a narrow-bandwidth optical probe and the THz pulse transposes the THz spectral intensity and phase information to the optical region, thereby generating an optical pulse whose temporal electric field envelope replicates the temporal profile of the real THz electric field. This optical envelope is characterised via an autocorrelation based FROG measurement, hence revealing the THz temporal profile. The combination of a narrow-bandwidth, long duration, optical probe and self-referenced FROG makes the technique inherently immune to timing jitter between the optical probe and THz pulse, and may find particular application where the THz field is not initially generated via ultrashort laser methods, such as the measurement of longitudinal electron bunch profiles in particle accelerators.

  9. Optical constants and near infrared emission of Er doped ZnO sol–gel thin films

    Vettumperumal, R. [P.G. and Research Department of Physics, Sri Paramakalyani College, Alwarkurichi 627412, Tamil Nadu (India); Kalyanaraman, S., E-mail: [P.G. and Research Department of Physics, Sri Paramakalyani College, Alwarkurichi 627412, Tamil Nadu (India); Thangavel, R., E-mail: [Department of Applied Physics, Indian School of Mines, Dhanbad (India)


    Erbium (Er) doped zinc oxide (ZnO) sol–gel thin films were deposited on glass substrate using the spin coating method. The effect of erbium concentration and annealing temperature on structural and optical properties was studied. The annealed film was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectrum (EDX), micro-Raman, photoluminescence (PL) and UV–vis spectroscopy. All the films showed a wurtzite structure of polycrystalline nature with an average crystal size of 27.44 nm at 500 °C and 29.28 nm at 600 °C. The Raman spectra confirmed the absence of secondary phases in the Er doped ZnO films and the longitudinal optical phonon mode was upto the fifth order. Densely packed surfaces of the films were observed from SEM images. The presence and distribution of Zn, O and Er elements in the deposited films were confirmed by EDX analysis. The calculated value of exciton binding energy of ZnO film was 60 meV with a maximum value of 72 meV being observed for Er doped films. The near infra-red emission peak was observed at 1.63 eV through PL spectra studies. The average transmission was 80% with the calculated value of optical band gap being 3.26–3.32 eV. An increase in the refractive index value predicts the substitutional incorporation of Er ions in ZnO with the maximum optical conductivity being observed in the UV region. - Highlights: • Higher exciton binding energy in the doped ZnO films. • Near infrared emission is observed and better than ZnO. • Refractive index is calculated by theoretical and experimental means. • Maximum optical conductivity in the UV region.

  10. Interaction of ultra-short ultra-intense laser pulses with under-dense plasmas; Interaction d'impulsions laser ultra-courtes et ultra-intenses avec des plasmas sous denses

    Solodov, A


    Different aspects of interaction of ultra-short ultra-intense laser pulses with underdense plasmas are studied analytically and numerically. These studies can be interesting for laser-driven electron acceleration in plasma, X-ray lasers, high-order harmonic generation, initial confinement fusion with fast ignition. For numerical simulations a fully-relativistic particle code WAKE was used, developed earlier at Ecole Polytechnique. It was modified during the work on the thesis in the part of simulation of ion motion, test electron motion, diagnostics for the field and plasma. The studies in the thesis cover the problems of photon acceleration in the plasma wake of a short intense laser pulse, phase velocity of the plasma wave in the Self-Modulated Laser Wake-Field Accelerator (SM LWFA), relativistic channeling of laser pulses with duration of the order of a plasma period, ion dynamics in the wake of a short intense laser pulse, plasma wave breaking. Simulation of three experiments on the laser pulse propagation in plasma and electron acceleration were performed. Among the main results of the thesis, it was found that reduction of the plasma wave phase velocity in the SM LWFA is crucial for electron acceleration, only if a plasma channel is used for the laser pulse guiding. Self-similar structures describing relativistic guiding of short laser pulses in plasmas were found and relativistic channeling of initially Gaussian laser pulses of a few plasma periods in duration was demonstrated. It was shown that ponderomotive force of a plasma wake excited by a short laser pulse forms a channel in plasma and plasma wave breaking in the channel was analyzed in detail. Effectiveness of electron acceleration by the laser field and plasma wave was compared and frequency shift of probe laser pulses by the plasma waves was found in conditions relevant to the current experiments. (author)

  11. Influencia de los parámetros de procesados en micro-perforado con pulsos ultracortos Influence of processing parameters on micro-perforated with ultrashort pulses

    S Ceballos P


    Full Text Available En este trabajo se emplearon pulsos láser ultracortos (110 fs, 1 kHz; hasta1.1 mJ/pulso para el micro-perforado de acero. El procesado con estos pulsos permitió obtener agujeros circulares, con medidas precisas y sin alteración mecánica ni química apreciable de las zonas adyacentes. Los agujeros se realizaron utilizando el sistema de trepanado óptico (Helical Drilling Optics,HDO de la empresa TGSW-Stuttgart, el cual permitió generar estructuras no sólo de gran profundidad sino además de diámetro variable, gracias a que se pudo variar hasta tres parámetros de proceso simultáneamente (velocidad de rotacion del haz, inclinación y descentrado del haz respecto del eje opticomientras se ejecutaba el procesado. En el presente trabajo se estudió principalmente la influencia de la longitud de onda del láser, en la geometría de las micro-perforaciones. Para ello se realizó la micro-perforación con pulsos láser con la longitud de onda fundamental (λ= 790nm y la del segundo armónico(λ= 395nm, se utilizó un conjunto específico de elementos ópticos para la HDO en cada caso y se compararon los resultados obtenidos lo cual arrojó que no hay ventajas notables al usar el segundo armónico. Se mencionan deficiencias en el dispositivo experimental que impidieron evaluar la influencia de la longitud de onda con total precisión.In this work, ultra short laser pulses (110 fs, 1 kHz; up to 1.1 mJ/pulse were used for micromachining steel samples. Processing with ultra-short laserpulses allowed achieving circular micro holes, with precise measurements and no signi cant chemical or mechanical disruption of adjacent areas. The heli-cal drilling optics system by TGSW-Stuttgart is used to generate the holes.This system allowed producing high aspect ratio and complex structures with variable diameter throughout the hole. To did this, up to three processing pa-rameters may be changed at the same time (beam rotation speed, angle and of the beam and

  12. 物理参数变化对短脉冲激光激励温度场的影响%Influence of physical parameters on ultrashort pulse laser excitation temperature field

    石云飞; 卢立中; 徐晨光; 徐桂东; 王纪俊; 许伯强


    Based on the two-temperature theory, a numerical model to solve the heating process in surface vicinity irradiated by ultrashort pulse laser is established to investigate the influence of temperature-dependent properties of material on temperature field in metal (Au) irradiated by ultrashort pulse laser. Taking account of the temperature-dependent properties of material which includes the electron-phonon coupling factor, electron thermal conductivity, electron heat capacity, lattice heat capacity, as well as the spatial and temporal shapes of the laser pulse, the transient temperature field irradiated by ultrashort pulse laser in metal (Au) is numerical simulated by the finite element method (FEM). The electron and lattice transient temperature distributions in the vicinity of laser-irradiated region are obtained. Moreover, the temperature fields obtained from considering and neglecting the temperature-dependent properties of material are compared. The numerical results indicate that the temperature-dependent properties of material make the electron and lattice temperatures rise faster, the temperature maximum and the irradiated become higher. This study establishes a theory basis for stress field and ultrasound field in metal generated by femto-second laser.%为研究多物理参数(耦合系数、电子热导率、电子热容、晶格热容)同时随温度变化对短脉冲激光辐照金属材料产生温度场分布的影响,基于双温耦合理论,建立了短脉冲激光辐照金属材料金的加热过程的有限元求解模型.在同时考虑脉冲激光的空间、时间分布和多参数同时随温度变化的情况下,得到短脉冲激光辐照金属材料金激励产生的温度场二维瞬态分布,并进一步比较了多物理参数同时随温度变化和采用室温物理参数两种情况下温度场分布的区别.数值结果表明:多物理参数同时随温度变化使电子温度和晶格温度的上升变快,最大值变大,而且使

  13. Optical application of Er-doped ZnO nanoparticles for photodegradation of direct red - 31 dye

    Bhatia, Sonik; Verma, Neha; Bedi, R. K.


    Nowadays, growing world increasing demands of synthetic organic dyes which are widely used in food, leather and textile industries. This paper reports the simple rapid synthesis of Er doped ZnO nanoparticles by simple combustion method. Herein, different concentrations of Er (2.0 at. wt%, 2.5 at. wt %, 3.0 at. wt%, 3.5 at. wt%) were used as dopants. The synthesized nanoparticles were characterized in term of structural, morphological, optical and kinetic properties. These detailed characterization study confirmed that the prepared nanoparticles are well crystalline. It was observed that different concentration of Er greatly influences morphology, band gap and photocatalytic activity on ZnO nanoparticles. The prepared Er doped samples were used as photocatalyst for photodegradation of direct red 31 (DR-31) dye. From the photocatalytic experiment it was observed that the degradation percentage increases with increasing Er concentration up to 2.5 at. wt% and thereafter photocatalytic degradation was decreased. Thus the optimum concentrations of prepared nanoparticles (2.5 at. wt%) are exhibiting almost complete degradation only in 60 min under UV irradiation. Kinetic studied revealed that all the samples follows first order rate constant.

  14. Photoluminescence study of Er-doped zinc–sodium–antimonite glasses

    Zavadil, J., E-mail: [Institute of Photonics and Electronics AS CR, Prague (Czech Republic); Ivanova, Z.G. [Institute of Solid State Physics Bulgarian Academy of Sciences, Sofia (Bulgaria); Kostka, P. [Institute of Rock Structure and Mechanics AS CR, Prague (Czech Republic); Hamzaoui, M.; Soltani, M.T. [Laboratoire de Physique Photonique et Nanomatériaux, Universite de Biskra (Algeria)


    Highlights: • Optical gap found at around 3.1 eV and its compositional tendency was deduced. • Emission spectra are overwhelmed by narrow 4f–4f emission bands of Er{sup 3+}. • Fine structure of emission bands at 980 and 1530 nm measured at 300 and 4 K. • Schematic energy diagram of Stark levels for 3 lowest manifolds of Er{sup 3+} is proposed. • A nature of temperature broadening of 4f–4f PL bands was discussed. - Abstract: Bulk samples of Er-doped zinc–sodium–antimonite glasses have been investigated by transmission and photoluminescence (PL) spectroscopy. Two series of compositions, (Sb{sub 2}O{sub 3}){sub 90−x}(Na{sub 2}O){sub 10}(ZnO){sub x} and (Sb{sub 2}O{sub 3}){sub 80−x}(Na{sub 2}O){sub 20}(ZnO){sub x}, doped with 0.25 mol% Er{sub 2}O{sub 3}, have been chosen for this study. Transmission spectra exhibit sharp absorption bands centred at 450, 489, 521, 545, 652, 795, 975 and 1530 nm, which correspond to absorption of Er{sup 3+} ions and they are attributed to the optical transitions from the ground state {sup 4}I{sub 15/2} to the excited states {sup 4}F{sub 5/2}, {sup 4}F{sub 7/2}, {sup 2}H{sub 11/2}, {sup 4}S{sub 3/2}, {sup 4}F{sub 9/2}, {sup 4}I{sub 9/2}, {sup 4}I{sub 11/2} and {sup 4}I{sub 13/2}, respectively. The optical gap has been found to vary from 3.09 to 3.15 eV with a tendency to decrease at higher Na{sub 2}O and/or ZnO contents. Four extrinsic bands due to OH{sup −}, Si–O, CO{sub 2}, and (CO{sub 3}){sup 2−} carbonate group vibrations have been identified in the infrared region. Emission spectra are overwhelmed by narrow 4f–4f emission bands. Fine structure of emission bands at 980 and 1530 nm, corresponding to radiative transitions from two lowest excited states of Er{sup 3+} ions to the ground state manifold have been investigated at room temperature and at 4 K. A schematic energy diagram of Stark levels splitting for the three lowest manifolds {sup 4}I{sub 11/2}, {sup 4}I{sub 13/2} and {sup 4}I{sub 15/2} has been

  15. Ultrashort Laser Retinal Damage Threshold Mechanisms


    Strickland and Mourou [1] introduced a technique called ‘‘chirped pulse amplification’’ to produce ultrashort laser pulses with extraordinary peak powers...photocoagula- tion of the retinal layers as had been seen in longer exposure studies. Thompson et al. [22] examined in detail the thermal response of...Gewebeveränderungen. Schlüsselwörter: Ultrakurz; Retina; Sicherheit; Femtosekunde; Melanin; Laserinduzierter Durchbruch; Ultraschnell References [1] Strickland D

  16. Mechanoluminescence by impulsive deformation of {gamma}-irradiated Er-doped CaF{sub 2} crystals

    Brahme, Nameeta, E-mail: [School of Studies in Physics and Astrophysics, Pt. Ravishankar Shukla University, Raipur 492101 (India); Shukla, Manju, E-mail: [Institute of Technology, Guru Ghasidas Vishwavidyalaya, Bilaspur 495009 (India); Bisen, D.P.; Kurrey, U.; Choubey, Anil [School of Studies in Physics and Astrophysics, Pt. Ravishankar Shukla University, Raipur 492101 (India); Kher, R.S. [Department of Physics, Govt. Science P.G. College, Bilaspur 495006 (India); Singh, Manisha [Department of Physics, Dr. H.S. Gour University, Sagar (India)


    An impulsive technique has been used for mechanoluminescence (ML) measurements in {gamma}-irradiated Er doped CaF{sub 2} crystals. When the ML is excited impulsively by the impact of moving piston on to {gamma}-irradiated CaF{sub 2}:Er crystals, two peaks are observed in ML intensity with time and it is seen that the peak intensities of first and second peaks (I{sub m1} and I{sub m2}) increase with increasing impact velocity. However the time corresponding to first and second peaks (t{sub m1} and t{sub m2}) shifts towards shorter time values with increasing impact velocity. It is also seen that the total ML intensity I{sub Total} initially increases with the impact velocity and then it attains a saturation value for higher values of the impact velocity. We have presented a theoretical explanation for the observed results. - Research highlights: {yields} Impulsive technique has been used for mechanoluminescence (ML) studies in {gamma}-irradiated Er doped CaF{sub 2} crystals. {yields} ML intensity exhibited two peaks with time (I{sub m1} and I{sub m2}), where the intensity of both the peaks increased with increasing impact velocity. {yields} The time of occurrence of the peaks (t{sub m1} and t{sub m2}) reduced with increasing the impact velocity. {yields} Total ML intensity (I{sub Total}) first increases and then attains a saturation value with an increment in the impact velocity. {yields} A theoretical explanation is presented to the observed results.

  17. Dramatic enhancement of 1.54 μm emission in Er doped GaN quantum well structures

    Al tahtamouni, T. M. [Department of Physics, Yarmouk University, Irbid 21163 (Jordan); Stachowicz, M. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Li, J.; Lin, J. Y.; Jiang, H. X. [Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas 79409 (United States)


    Erbium (Er) doped III-nitride materials have attracted much attention due to their capability to provide highly thermal stable optical emission in the technologically important as well as eye-safer 1540 nm wavelength window. There is a continued need to exploring effective mechanisms to further improve the quantum efficiency (QE) of the 1.54 μm emission in Er-doped III-nitrides. GaN/AlN multiple quantum wells (MQWs:Er) have been synthesized by metal organic chemical vapor deposition and explored as an effective means to improve the QE of the 1.54 μm emission via carrier confinement and strain engineering. The 1.54 μm emission properties from MQWs:Er were probed by photoluminescence (PL) emission spectroscopy. It was found that the emission intensity from MQWs:Er is 9 times higher than that of GaN:Er epilayers with a comparable Er active layer thickness. The influences of the well and barrier width on the PL emission at 1.54 μm were studied. The results revealed that MQWs:Er consisting of well width between 1 and 1.5 nm and the largest possible barrier width before reaching the critical thickness provide the largest boost in QE of the 1.54 μm emission. These results demonstrate that MQWs:Er provide a basis for efficient photonic devices active at 1.54 μm.

  18. Local microstructure and photoluminescence of Er-doped 12CaO·7Al2O3 powder

    WANG Dan; LIU Yuxue; XU Changshan; LIU Yichun; WANG Guorui; LI Xinghua


    Er-doped 12CaO·7Al2O3 (C12A7:Er) powders were prepared using the sol-gel method followed by annealing inorganic precursors. X-ray diffraction (XRD), Raman and absorption spectra revealed that Er ions existed and substituted Ca2+ lattice site in C12A7. The photoluminescence of C12A7:Er at room temperature was observed in the visible and infrared region using 488 nm (2.54 eV) Ar+ line as excitation source, respectively. The sharp and intense green emission bands with multi-peaks around 520 nm and 550 nm correspond to the transitions from the excited states 2H11/2 and 4S3/2 to the ground state 4I15/2, respectively. Furthermore, red emission band around 650 nm was also observed. It was attributed to the electronic transition from excited states 4F9/2 to the ground state 4I15/2 inside 4f-shell of Er3+ ions. The intensive infrared emission at 1.54μm was attributed to the transition from the first excited states of 4I13/2 to the ground state (4I15/2). The temperature dependent photoluminescence of infrared emission showed that the integrated intensity reached a maximum value at near room temperature. The forbidden transitions of intra-4f shell electrons in free Er3+ ions were allowed in C12A7 owing to lack of the inversion symmetry in the Er3+ position in C12A7 crystal field. Our results suggested that C12A7:Er was a candidate for applications in Er-doped laser materials, and full color display.

  19. Evolution Rule of Ultra-short Laser Pulse Area in Homogeneously Broadened Medium%均匀展宽介质中激光超短脉冲面积的演化规律

    张华荣; 蒋月; 李成; 余向阳


    用数值计算方法研究了均匀展宽二能级体系在激光超短脉冲作用下介质参量、入射脉冲面积、弛豫时间和频率失谐量对光脉冲面积演化的影响.计算结果表明,脉冲面积会在最接近输入脉冲面积2π偶数倍的值上振荡,并经过一定的传播距离后,台阶式跳跃到下一个偶数倍2π的值上振荡.%The evolution rule of the ultra-short laser pulse area which propagate through a homogeneously broadened two level system was studied.The numerical result shows that the pulse area will oscillate near the even times of 2π,and then change jumpily into the next even times of 2π after a propagation distance.The mechanism of these phenomena was analyzed particularly.In addition,by considering the medium parameter,the input pulse area,relaxation time,detune respectively,we also investigate the evolution rule of ultar-short pulse′s propagation in a homogeneously broadened two-level atomic medium.

  20. Ultrashort mode-locked lasers with additional Raman active elements

    Trunov, V. I.; Kirpichnikov, A. V.; Pestryakov, Efim V.; Petrov, V. V.; Komarov, A. K.; Komarov, Konstantin P.


    Numerical simulation of ultrashort pulse generation in the laser with a composite active medium and additional Raman active element in a cavity has been done. It was created that for some laser parameters the optimization of a Raman gain and a frequency shift values was resulted in additional shortening of pulse duration.

  1. Graphene thickness-dependent Er-doped Q-switched optical fiber laser

    Wang, Xiaolong; Sang, Mei; Zhu, Pan; Liu, Ke; Yang, Tianxin


    A stable Q-switched laser is useful in the area of remote sensing, range finding, optical imaging, material processing, and fiber communications. With its excellent linear and nonlinear optical characteristics, graphene has been proven to be an attractive material to generate nanosecond, picosecond and femtosecond laser pulses. It has a lot of advantages, such as lower saturation intensity, larger saturable-absorption modulation depth, higher damage threshold, sub-picosecond recovery time and an ultrabroad wavelength-independent saturable-absorption range. In this paper, we demonstrate a graphene based Q-switched fiber laser. Graphene was deposited on the fiber interface by the optically driven deposition method. The thickness of the graphene can be controlled by changing depositing time. The compact Q-switched erbium-doped fiber laser based on graphene operated stably, and got Q-switched pulse sequences output with the repetition rate of 19KHz and the average power of 1.4mW when pump power is 40mW. Higher peak power, shorter pulse duration, and higher repetition rate could be achieved by adjusting the thickness of the graphene layer appropriately. Besides, the pulse duration and output power is proved to be a function of the pump power. The repetition rate of this fiber laser had a characteristic of monotonically increasing, near-linear with the changing of pump power. The stable Q-switching pulse output can be observed on the oscilloscope with differently specific repetition rate and pump power. Theory analysis of this fiber laser and further improvement methods is also studied combined with the experimental results.

  2. 2D Layered Materials of Rare-Earth Er-Doped MoS2 with NIR-to-NIR Down- and Up-Conversion Photoluminescence.

    Bai, Gongxun; Yuan, Shuoguo; Zhao, Yuda; Yang, Zhibin; Choi, Sin Yuk; Chai, Yang; Yu, Siu Fung; Lau, Shu Ping; Hao, Jianhua


    A 2D system of Er-doped MoS2 layered nanosheets is developed. Structural studies indicate that the Er atoms can be substitutionally introduced into MoS2 to form stable doping. Density functional theory calculation implies that the system remains stable. Both NIR-to-NIR up-conversion and down-conversion light-emissions are observed in 2D transition metal dichalcogenides, ascribed to the energy transition from Er(3+) dopants.

  3. Enhanced photocatalytic performance of Er-doped Bi{sub 24}O{sub 31}Br{sub 10}: Facile synthesis and photocatalytic mechanism

    Liu, Zhang Sheng, E-mail:; Liu, Zhi Lin; Liu, Jin Long; Zhang, Jing Wen; Zhou, Ting Fei; Ji, Xiang


    Highlights: • Er-doped Bi{sub 24}O{sub 31}Br{sub 10} have been prepared via a one-pot solvothermal method. • Er doping drastically improves the photocatalytic activity of Bi{sub 24}O{sub 31}Br{sub 10}. • The enhanced activity is attributed to effective electron trapping and up-conversion process resulting from Er{sup 3+}. • Holes and super-oxide radicals are main active species. - Abstract: Erbium (Er) doped Bi{sub 24}O{sub 31}Br{sub 10} samples were successfully prepared by using a solvothermal method. The samples were characterized by XRD, XPS, SEM, TEM, BET, DRS, PL and EIS. The photocatalytic activity was evaluated by the degradation of rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. The result shows that Er dopant induces a significant improvement in the photocatalytic activity. 1.0% Er–Bi{sub 24}O{sub 31}Br{sub 10} sample exhibits the best photocatalytic performance. The enhanced photocatalytic activity is attributed to the effective trapping of photogenerated electron by Er{sup 3+} ion and the up-conversion process resulting from Er dopant. In addition, it is found that holes and super-oxide radicals play main role in the photocatalytic degradation of RhB and MO.

  4. Generation of ultra-short relativistic-electron-bunch by a laser wakefield

    Khachatryan, A.G.; Boller, K.-J.; Goor, van F.A.


    The possibility of the generation of an ultra-short (about one micron long) relativistic (up to a few GeVs) electron-bunch in a moderately nonlinear laser wakefield excited in an underdense plasma by an intense laser pulse is investigated. The ultra-short bunch is formed by trapping, effective compr

  5. Measuring the internal temp erature of dielectrics machined by the ultrashort laser pulse through the black-b o dy irradiation metho d%黑体辐射法测量电介质内部被超短激光脉冲加工后的温度∗

    王承伟; 赵全忠; 钱静; 黄媛媛; 王关德; 李阳博; 柏锋; 范文中; 李虹瑾


    Black-body irradiation method can be utilized for measuring the instantaneous temperatures of electrons and lattice in dielectric machined by the ultrashort laser. One ultrashort laser pulse, of which the pulse energy and pulse duration are 240 µJ and 599 fs respectively, is focused into the fused silica by objective lenses with a magnification of 10 times. The focal point is at the position of 874 µm. The microstructure induced by laser near the focal point is 16 µm wide and 104 µm long. The central region of the microstructure is heavily damaged, and the marginal region is slightly modified. The black-body irradiation spectra are recorded by the system that is composed of objective lenses, a fiber with two lenses, a spectrometer and an intensified charge coupled device (ICCD). Furthermore, other imaging elements can also be used as alternative to objective lenses, for measuring black-body spectra. The image point, which is conjunctive with the machined region due to the imaging effect of the objective lenses, is coupled into the fiber by one lens. Another lens collimates the diverging light beam from the fiber. The collimated light is incident into the spectrometer and dispersed on the ICCD. Because the minimum gate width of ICCD is much larger than the coupled time of electron and lattice, the temperature of electron equals that of lattice when they are characterized by the black-body irradiation method. The temperatures of the electrons and the lattice are regarded as the temperature of dielectric. When the system acquires the reflection peak of incident ultrashort laser, the delay is set to be 0 ns, and the central wavelength of the peak is 784 nm. Therefore, to eliminate the reflection peak, the second harmonic and supercontinuum spectra, the delay for black-body irradiation acquirement is set to be above 6 ns and the machined region should be confined inside the dielectric. The system collects the black-body spectra emitted by the heat-affected zone in

  6. Generation regimes of bidirectional hybridly mode-locked ultrashort pulse erbium-doped all-fiber ring laser with a distributed polarizer.

    Krylov, Alexander A; Chernykh, Dmitriy S; Arutyunyan, Natalia R; Grebenyukov, Vyacheslav V; Pozharov, Anatoly S; Obraztsova, Elena D


    We report on the stable picosecond and femtosecond pulse generation from the bidirectional erbium-doped all-fiber ring laser hybridly mode-locked with a coaction of a single-walled carbon nanotube-based saturable absorber and nonlinear polarization evolution that was introduced through the insertion of the short-segment polarizing fiber. Depending on the total intracavity dispersion value, the laser emits conservative solitons, transform-limited Gaussian pulses, or highly chirped stretched pulses with almost 20 nm wide parabolic spectrum in both clockwise (CW) and counterclockwise (CCW) directions of the ring. Owing to the polarizing action in the cavity, we have demonstrated for the first time, to the best of our knowledge, an efficient tuning of soliton pulse characteristics for both CW and CCW channels via an appropriate polarization control. We believe that the bidirectional laser presented may be highly promising for gyroscopic and other dual-channel applications.

  7. 超短脉冲激光诱导单晶铜熔化的物理机制%Physical mechanisms of ultrashort pulse laser induced melting in copper

    孟然; 刘璇; 周华


    采用校正的分子动力学方法研究了超短脉冲熔化单晶铜的动力学微观机制,建模时将熔化潜热的消耗及自由电子的热传导均考虑在内,使熔化过程的模拟更加真实.皮秒激光熔化单晶铜是一种过热熔化.可归因于液相在固相中的均匀形核.熔沿传播的速度高达5.8 nm/ps,高于铜中声速.熔化发生在热约束区域内部,导致温度分布不太复杂,且卸载波对应力波的影响与应力约束区域相比较弱.%The kinetics and microscopic mechanisms of ultrashort laser melting of a copper film is studied by modified molecular dynamics method.A model considering the thermal conductivity of free electrons and the consumption of latent heat of melting is used to make the simulation more realistic.The mechanism responsible for the melting of copper under picosecond laser pulse irradiation can be attributed to the homogeneous nuclea-tion of the liquid phase inside the solid region.The melting is a overheated melting caused by homogeneous nu-cleation.and the velocity of propagation of"melt front"is found up to be 5.8 nm/ps.Picosecond laser pulse in-duced melting occurring under the condition of thermal confinement results in a less complicate temperature dis-tribution and a weaker effect of unloading wave on stress wave compared with those in stress confinement re-gion.

  8. Formation of upconversion nanoparticles of 18%Yb:1%Er:NAYF4 by ultra-short pulse laser ablation in water

    Gemini, Laura; Hernandez, Marie-Caroline; Kling, Rainer


    Pulsed laser ablation in liquid (PLAL) is nowadays gaining popularity as innovative, reliable and efficient technique to produce high-purity nanoparticles (NPs) of many inorganic and organic materials. In this context, attention has been recently focused on luminescent up-conversion NPs (UCNPs) which, being characterized by sharp emission bands in ultraviolet (UV)-to-near-infrared (NIR) range upon NIR irradiation, are in fact of great interest in many biological and biomedical applications. Moreover, with respect to organic dyes NPs and quantum dots, UCNPs show less toxicity, increased chemical stability, long-lifetime decays and lack of photo-bleaching. Our research focuses on generation of UCNPs of rare earth lanthanide-doped crystalline material, namely 18%Yb:1%Er:NAYF4, by PLAL in water. It is well known that optical properties of NPs strongly depend on their features, as for instance size and shape, which in turn may be controlled by laser ablation parameters. Therefore, two different laser sources are used for the ablation processes in order to find the set of laser parameter, i.e. pulse duration, laser fluence and repetition rate, for which the luminescence of UPNPs is optimized: (i) Amplitude Satsuma HP3 system: 330 fs pulse duration, 1030 wavelength and (ii) Eolite Hegoa system: 50 ps pulse duration, 1030 nm wavelength. UCNPs are finally characterized by spectrophotometer analyses to define emission range and intensity under NIR light and by transmission electron microscopy (TEM) to determine their size and shape.

  9. Damage effect of monocrystalline silicon solar cells under ultrashort pulse laser irradiations%超短脉冲激光对单晶硅太阳能电池的损伤效应

    邱冬冬; 王睿; 程湘爱; 张震; 江天


    Solar energy is one of the leading energy in the future, and researches about solar cells are becoming hot spots gradually. Its properties under energetic particles irradiations have been widely characterized, but there is few about its laser-induced damage. So it' s necessary to study the laser-induced damage of solar cells. Behaviors of monocrystalline silicon solar cells under 532 nm 20 ns and 300 ps pulse laser irradiations were studied. Damage mechanism of monocrystalline silicon solar cells under the irradiations of ultrashort pulse laser was analyzed. When the single pulse energy was fixed, the relation among damage effect, pulse width and repetition frequency was described. The differences of damage mechanism between different types of laser were compared. Through the analysis, the principal factor of solar cells' damage was pointed out, and the damage of solar cells induced by laser irradiation mainly relied on the thermal effect.%太阳能是未来的主要能源之一,关于太阳能电池的研究也逐渐成为热点.长期以来,人们对太阳能电池的高能粒子辐射特性进行了广泛的研究,对其激光辐照损伤特性的研究却很少.随着光电对抗技术的发展,对这方面的研究需求也越来越迫切.研究了532 nm、20 ns和300 ps脉冲激光对单晶硅太阳能电池的辐照效应,分析了超短脉冲激光对单晶硅太阳能电池的损伤机理.对比了超短脉冲激光和长脉冲激光、连续激光的损伤机理的异同.阐述了在激光单脉冲能量一定的情况下,损伤效果与脉宽和重频的关系.通过分析,指出了太阳能电池损伤的主因,激光对太阳能电池的破坏主要是依靠热效应.

  10. Influence of Laser Prepulse in Ultra-short Laser-Driven Proton Acceleration


    Influence of laser prepulse in ultra-short laser-driven proton acceleration was investigated by the differences in spatial distribution and energy spectrum between different foil-targets. The laser system produced pulses having energies of up to

  11. Efficient multi-keV x-ray generation from a high-Z target irradiated with a clean ultra-short laser pulse.

    Zhang, Z; Nishikino, M; Nishimura, H; Kawachi, T; Pirozhkov, A S; Sagisaka, A; Orimo, S; Ogura, K; Yogo, A; Okano, Y; Ohshima, S; Fujioka, S; Kiriyama, H; Kondo, K; Shimomura, T; Kanazawa, S


    Kα line emissions from Mo and Ag plates were experimentally studied using clean, ultrahigh-intensity femtosecond laser pulses. The absolute yields of Kα x-rays at 17 keV from Mo and 22 keV from Ag were measured as a function of the laser pulse contrast ratio and irradiation intensity. Significantly enhanced Kα yields were obtained for both Mo and Ag by employing high contrast ratios and irradiances. Conversion efficiencies of 4.28×10⁻⁵/sr for Mo and 4.84×10⁻⁵/sr for Ag, the highest values obtained to date, were demonstrated with contrast ratios in the range 10⁻¹⁰ to 10⁻¹¹.

  12. LASERS: Ultrashort-pulse erbium-doped fibre laser using a saturable absorber based on single-wall carbon nanotubes synthesised by the arc-discharge method

    Tausenev, A. V.; Obraztsova, E. D.; Lobach, A. S.; Konov, V. I.; Konyashchenko, A. V.; Kryukov, P. G.; Dianov, E. M.


    An erbium-doped fibre laser operating in self-mode-locked regime achieved with the help of a saturable absorber based on single-wall carbon nanotubes synthesised by the arc-discharge method is fabricated and studied. Due to the development of an original method for preparing samples, films of the optical quality containing individual single-wall carbon nanotubes were synthesised. The study of the dependence of resonance absorption at a wavelength of 1.5 μm on the laser radiation intensity transmitted through a film showed that these films have nonlinear transmission and can be used in fibre lasers as saturable absorbers to provide self-mode locking. Stable transform-limited pulses having the shape of optical solitons were generated at a wavelength of 1557.5 nm in the laser with a ring resonator. The pulse duration was 1.13 ps at a pulse repetition rate of 20.5 MHz. The continuous output power achieved 1.1 mW upon pumping by a 25-mW laser diode at 980 nm.

  13. Effects of refractive index changes on four-wave mixing bands in Er-doped photonic crystal fibers pumped at 976 nm.

    Velázquez-Ibarra, L; Díez, A; Andrés, M V; Lucio, J L


    An experimental study of the effects of an auxiliary 976 nm pump signal on the four-wave mixing parametric bands generated with a 1064 nm pump in a normal dispersion Er-doped photonic crystal fiber is presented. The four-wave mixing signal and idler bands shift to shorter and longer wavelengths, respectively, with increasing 976 nm pump power. It is shown that the wavelength-dependent resonant refractive index change in the erbium-doped core under 976 nm pumping is at the origin of the effect.

  14. Er-doped and Er, Yb co-doped oxyfluoride glasses and glass-ceramics, structural and optical properties

    Lisiecki, Radosław; Augustyn, Elżbieta; Ryba-Romanowski, Witold; Żelechower, Michał


    -ceramic fibers indicate that these optical systems may be considered as promising materials for Er-doped optical amplifiers operating within third telecommunication window.

  15. Spectral analysis of K-shell X-ray emission of magnesium plasma produced by ultrashort high-intensity laser pulse irradiation

    V Arora; U Chakravarty; Manoranjan P Singh; J A Chakera; P A Naik; P D Gupta


    Spectral analysis of K-shell X-ray emission of magnesium plasma, produced by laser pulses of 45 fs duration, focussed up to an intensity of ∼1018 W cm-2, is carried out. The plasma conditions prevalent during the emission of X-ray spectrum were identified by comparing the experimental spectra with the synthetic spectra generated using the spectroscopic code Prism-SPECT. It is observed that He-like resonance line emission occurs from the plasma region having sub-critical density, whereas K- emission arises from the bulk solid heated to a temperature of 10 eV by the impact of hot electrons. K- line from Be-like ions was used to estimate the hot electron temperature. A power law fit to the electron temperature showed a scaling of 0.47 with laser intensity.

  16. First evidence of end-cap control in the synthesis of long-chain polyynes by intense ultrashort laser pulse irradiation

    Ramadhan, Ali; Wakabayashi, Tomonari; Shiromaru, Haruo; Fujino, Tatsuya; Kodama, Takeshi; Duley, Walter; Sanderson, Joseph


    Hydrogen- and methyl-capped polyynes were synthesized by irradiating pure liquid toluene with 35 femtosecond, 300 {\\mu}J laser pulses having a central wavelength of 800 nm, generated by a regeneratively amplified Ti:sapphire tabletop laser at a repetition rate of 1 kHz. Raman spectroscopy was used to confirm the presence of polyynes in the irradiated samples while high-performance liquid chromatography was used to separate hydrogen-capped polyynes up to C18H2 and methyl-capped polyynes up to HC14CH3. These represent the first such methyl-capped polyynes and the longest hydrogen capped chains synthesized to date by the ultrafast laser based method. Furthermore our results show that choice of the starting solvent molecule directly influences the end caps of the polyynes which can be produced.

  17. Responses of Rat P2X2 Receptors to Ultrashort Pulses of ATP Provide Insights into ATP Binding and Channel Gating

    Moffatt, Luciano; Hume, Richard I.


    To gain insight into the way that P2X2 receptors localized at synapses might function, we explored the properties of outside-out patches containing many of these channels as ATP was very rapidly applied and removed. Using a new method to calibrate the speed of exchange of solution over intact patches, we were able to reliably produce applications of ATP lasting <200 μs. For all concentrations of ATP, there was a delay of at least 80 μs between the time when ATP arrived at the receptor and the first detectable flow of inward current. In response to 200-μs pulses of ATP, the time constant of the rising phase of the current was ∼600 μs. Thus, most channel openings occurred when no free ATP was present. The current deactivated with a time constant of ∼60 ms. The amplitude of the peak response to a brief pulse of a saturating concentration of ATP was ∼70% of that obtained during a long application of the same concentration of ATP. Thus, ATP leaves fully liganded channels without producing an opening at least 30% of the time. Extensive kinetic modeling revealed three different schemes that fit the data well, a sequential model and two allosteric models. To account for the delay in opening at saturating ATP, it was necessary to incorporate an intermediate closed state into all three schemes. These kinetic properties indicate that responses to ATP at synapses that use homomeric P2X2 receptors would be expected to greatly outlast the duration of the synaptic ATP transient produced by a single presynaptic spike. Like NMDA receptors, P2X2 receptors provide the potential for complex patterns of synaptic integration over a time scale of hundreds of milliseconds. PMID:17664346

  18. Yb,Er-doped CeO2 nanotubes as an assistant layer for photoconversion-enhanced dye-sensitized solar cells

    Zhao, Rongfang; Huan, Long; Gu, Peng; Guo, Rong; Chen, Ming; Diao, Guowang


    Yb,Er-doped CeO2 nanotubes were successfully synthesized using Ag nanowires as a hard template via a facile hydrothermal reaction and subsequent calcination and leaching processes. Yb,Er-doped CeO2 nanotubes as a promising assistant layer were investigated to determine theirs photovoltaic properties in an effort to enhance the power conversion efficiency of dye-sensitized solar cells (DSSCs). The influence factors of photoelectric properties of CeO2:Yb,Er NTs, including diameter of nanotubes, hydrothermal time, calcination temperature, and elements doping, have been studied. Compared with pristine P25 photoanode, the DSSCs fabricated by CeO2:Yb,Er nanotubes and P25 exhibited a power conversion efficiency (η) of 8.67%, an increase of 34%, and incident photo-to-electric conversion efficiency (IPCE) of 92.96%, an increase of 48.83%, which evidence that CeO2:Yb,Er NTs are a promising assistant photoanode material for DSSCs. The enhance mechanism of CeO2:Yb,Er nanotubes has been further revealed according to experimental results.

  19. Theoretical research on time-space conversion method for measuring ultra-short electron pulse width%超短电子脉冲的时空转换测量方法理论研究

    吴建军; 袁锡明; 赵宝升; 田进寿; 李军科


    分析了超快电子枪处于扫描状态下电子束的传输特性,对飞秒量级的超短电子束脉冲通过偏转扫描系统时的偏转距离等物理量进行了数值计算.计算结果显示:为确保电子束能够顺利通过偏转扫描系统并最后轰击直径为30 mm的荧光屏,必须加一个700~1400 V的初始电压,以便抵消负斜坡扫描电压的作用;700~1400 V的初始电压和负斜坡扫描电压的共同作用,是扫描实验成功的一个前提.扫描实验成功的另一个前提是激发光电阴极的光路和控制扫描的电路之间的同步.讨论了前提一带给同步实验的巨大困难,并设计了一个可以在扫描实验中以较高效率调节光路延时的实验系统,该系统可解决脉宽测量实验中扫描斜坡电压信号和超快电子脉冲的同步难题.%The transmission characteristics of ultra-short electron beams of the ultra-fast electron guns in scanning state were analysed,and the deflection distance of the ultra-short electron beams passing the deflection-scan system was calculated.The results indicate that the initial voltage must be within the range of 700-1400 V to counterbalance the effect of the negative scan slope voltage,ensuring that the electron beams will pass the deflection-scan system and finally hit the phosphor screen of 30 mm in diameter,and the cooperative function of the initial voltage and the negative scan slope voltage is one of the two premises of the scan experiment.The other premise is the synchronization of the electrical and the optical signals.Following the discussion of the great difficulty caused by the first promise,an experimental system that can adjust the optical delay more effectively in the scan experiment was designed,which can facilitate the synchronization of the negative scan slope voltage and the ultra-fast electron pulse.

  20. Ultra-short strong excitation of two-level systems

    Jha, Pankaj K.; Eleuch, Hichem; Grazioso, Fabio


    We present a model describing the use of ultra-short strong pulses to control the population of the excited level of a two-level quantum system. In particular, we study an off-resonance excitation with a few cycles pulse which presents a smooth phase jump i.e. a change of the pulse's phase which is not step-like, but happens over a finite time interval. A numerical solution is given for the time-dependent probability amplitude of the excited level. The control of the excited level's population is obtained acting on the shape of the phase transient, and other parameters of the excitation pulse.

  1. Evolutions of Continuous-Wave Perturbed by Pulse and Generation of Ultra-Short Pulse Trains%脉冲扰动下连续波的演化及超短脉冲串产生

    钟先琼; 向安平; 程科; 蔡青


    Based on the nonlinear Schr(o)dinger equation and the stepped Fourier method, the shape and spectrum evolutions of continuous-wave perturbed by an optical pulse with Gaussian-typed continuum spectrum in an optical fiber are numerically simulated. The results show that, due to modulation instability in the anomalous dispersion region of the optical fiber, this pulse perturbed continuous-wave can also evolve into high-repetition-rate pulse trains, which is similar to the case of sine perturbed one. Being different from the latter case, however, the generated pulses are not equal to each other in terms of widths, intensities, and intervals. When soliton parameters are too small or the optical wave is in the normal dispersion region, only attenuation oscillation structures instead of pulse trains can be generated. And the characteristics of pulse trains or oscillation structures will vary with the soliton parameters. These evolution characteristics are obviously different from those of conventional sine perturbed continuous-waves and Gaussian optical pulses.%从光纤中非线性薛定谔方程出发,采用分步傅里叶算法数值模拟了具有高斯型连续谱的光脉冲扰动下连续波在光纤中的波形和频谱演化.结果表明,在光纤负色散区,由于调制不稳定性,该脉冲扰动下的连续波也可能像正弦波扰动下的那样演化成高重复率超短脉冲串,但构成脉冲串的各脉冲并不像正弦波扰动时那样等宽、等高、等间距.当孤子参数太小或在正色散区时,则不能形成脉冲串,只能形成衰减的振荡结构.随着孤子参数的不同,超短脉冲串及振荡结构的特点也会不同.这些演化规律与传统正弦光扰动连续波及高斯光脉冲的情形明显不同.

  2. Frequency stabilization of an Er-doped fiber laser with a collinear 2f-to-3f self-referencing interferometer

    Hitachi, K., E-mail:; Ishizawa, A.; Mashiko, H.; Sogawa, T.; Gotoh, H. [NTT Basic Research Laboratories, NTT Corporation, Atsugi-shi, Kanagawa 243-0198 (Japan); Tadanaga, O. [NTT Device Technology Laboratories, NTT Corporation, Atsugi-shi, Kanagawa 243-0198 (Japan); Nishikawa, T. [Tokyo Denki University, 5 Senju-Asahi-cho, Adachi-ku, Tokyo 120-8551 (Japan)


    We report the stabilization of the carrier-envelope offset (CEO) frequency of an Er-doped fiber laser with a collinear 2f-to-3f self-referencing interferometer. The interferometer is implemented by a dual-pitch periodically poled lithium niobate ridge waveguide with two different quasi-phase matching pitch sizes. We obtain a 52-dB signal-to-noise ratio in the 100-kHz resolution bandwidth of a heterodyne beat signal, which is sufficient for frequency stabilization. We also demonstrate that the collinear geometry is robust against environmental perturbation by comparing in-loop and out-of-loop Allan deviations when the in-loop CEO frequency is stabilized with a phase-locked loop circuit.

  3. Ultra-short strong excitation of two-level systems


    We present a model describing the use of ultra-short strong pulses to control the population of the excited level of a two-level quantum system. In particular, we study an off-resonance excitation with a few cycles pulse which presents a smooth phase jump i.e. a change of the pulse's phase which is not step-like, but happens over a finite time interval. A numerical solution is given for the time-dependent probability amplitude of the excited level. The control of the excited level's populatio...

  4. Ultrashort pulse laser slicing of semiconductor crystal

    Kim, Eunho; Shimotsuma, Yasuhiko; Sakakura, Masaaki; Miura, Kiyotaka


    Meanwhile, by the convention wire-saw technique, it is difficult to slice off a thin wafer from bulk SiC crystal without the reserving space for cutting. In this study, we have achieved exfoliation of 4H-SiC single crystal by femtosecond laser induced slicing method. By using this, the exfoliated surface with the root-mean-square roughness of 3 μm and the cutting-loss thickness smaller than 30 μm was successfully demonstrated. We have also observed the nanostructure on the exfoliated surface in SiC crystal.

  5. Linearly polarized, Q-switched Er-doped fiber laser based on reduced graphene oxide saturable absorber

    Sobon, Grzegorz; Jagiello, Joanna; Kozinski, Rafal; Librant, Krzysztof; Zdrojek, Mariusz; Lipinska, Ludwika; Abramski, Krzysztof M


    We demonstrate generation of linearly polarized pulses from a passively Q-switched Erbium-doped fiber laser. The cavity was designed using only polarization maintaining (PM) fibers and components, resulting in linearly polarized output beam with degree of polarization (DOP) at the level of 97.6%. Reduced graphene oxide (rGO) was used as a saturable absorber for Q-switched operation. The laser was capable of delivering 1.85us pulses with 125nJ pulse energy at 115kHz repetition rate.

  6. 超短波、低频脉冲电疗联合电针治疗腓总神经麻痹的疗效%Therapeutic effect of ultrashort wave,low frequency pulse electrotherapy and electroacupuncture therapy on common peroneal nerve palsy

    刘敏; 李嵩; 张玉淼; 刘春辉; 石汉文


    Objective To observe the effectiveness of ultrashort wave, low frequency pulse electrotherapy and electroacupuncture therapy in treatment of patients with common peroneal nerve palsy. Methods Forty patients with common peroneal nerve palsy were randomly divided into two groups: treatment group (20 cases) and control group (20 cases). The patients in treatment group were treated with ultrashort wave, low frequency pulse electrotherapy and electroacupuncture therapy, while those in control group were treated mainly with drug. All patients were scored with MMT and MCRR pre and post treatment. Results It was shown that the lower limb motor function of all patients was significantly improved after treatment and MMT and MCRR scores of patients in treatment group were higher than those in control group (P<0. 05). Furthermore, the excellent and good rate was 85.00% in treatment group, while it was 60.00% in control group ( P < 0. 05 ). Conclusion Ultrashort wave, low frequency pulse electrotherapy and electroacupuncture therapy can effectively improve the lower limb motor function in patients with common peroneal nerve palsy.%目的 观察超短波、低频脉冲电疗联合电针治疗腓总神经麻痹的疗效.方法 随机选择治疗组20例、对照组20例腓总神经麻痹患者,治疗组在常规药物治疗同时配合超短波、低频脉冲电疗和电针治疗,对照组用常规药物治疗并早期康复治疗.治疗前及治疗8周后用徒手肌力法(MMT)和神经功能愈合标准评分法(MCRR标准)对下肢功能进行评定.结果 治疗后,治疗组MMT评分值较对照组明显增高(P<0.05),治疗组优良率为85.00%,对照组为60.00%,两组间差异有显著性意义(P<0.05).结论 超短波、低频脉冲电疗联合电针治疗可以有效改善腓总神经麻痹患者下肢的运动功能.

  7. Phase-sensitive reflectometer using a single-frequency laser diode and an Er-doped fibre amplifier

    Eftimov, T; Stefanov, I; Popov, A; Vodenicharov, S, E-mail: teftimov@uni-plovdiv.b


    We report on the observation of phase-sensitive Rayleigh backscattering from a single-mode fiber excited by light pulses obtained from a highly coherent single-frequency laser diode and an Erbium doped fiber amplifier (EDFA). The laser diode stability was tested using a highly imbalanced fiber optic Mach-Zehnder interferometer. The CW laser light was first modulated using fiber-optic EO modulator which formed 100ns to 500 ns pulses that correspond to 20 to 100 m of pulse length in the fiber. The backscattered light power is estimated to be about -51 dB lower than the launched power at the input and about N=500 averages are needed for a sensing length of L{sub s} 40 km to be in the useful dynamic range.

  8. Pulse

    ... resting for at least 10 minutes. Take the exercise heart rate while you are exercising. ... pulse rate can help determine if the person's heart is pumping. Pulse ... rate gives information about your fitness level and health.

  9. Polarization Maintaining, Very-Large-Mode Area, Er Fiber Amplifier for High Energy Pulses at 1572.3 nm

    Nicholoson, J. W.; DeSantolo, A.; Yan, M. F.; Wisk, P.; Mangan, B.; Puc, G.; Yu, A.; Stephen, M.


    We demonstrate the first polarization maintaining, very-large-mode-area Er-doped fiber amplifier with 1000 square micron effective area. The amplifier is core pumped by a Raman fiber laser and is used to generate single frequency one microsecond pulses with pulse energy of 368 microJoules, M2 of 1.1, and polarization extinction greater than 20 dB. The amplifier operates at 1572.3 nm, a wavelength useful for trace atmospheric CO2 detection.

  10. Effect of the AlPO4 join on the pump-to-signal conversion efficiency in heavily Er-doped fibers.

    Likhachev, Mikhail E; Bubnov, Mikhail M; Zotov, Kirill V; Lipatov, Denis S; Yashkov, Mikhail V; Guryanov, Aleksei N


    Heavily Er-doped fibers (EDFs) based on P(2)O(5)-Al(2)O(3)-SiO(2) (PAS) ternary glass have been studied. A unique feature of this glass is the formation of a AlPO(4) join having a structure similar to that of SiO(2) glass and a refractive index below it. It is found that the Er(3+) absorption and emission spectra in the PAS EDFs are defined by the dopant (Al(2)O(3) or P(2)O(5)) present in excess and are close to those of the corresponding binary glass (Al(2)O(3)-SiO(2) or P(2)O(5)-SiO(2)). The presence of the AlPO(4) join results in the enhancement of the pump-to-signal conversion efficiency in the PAS EDFs as compared with the EDFs based on the P(2)O(5)-SiO(2) and Al(2)O(3)-SiO(2) (with 1.5 mol. %Al(2)O(3) and less) binary glasses. The PAS host glass is advantageous in the case of large-mode-area active fibers.

  11. Black phosphorus mode-locked Er-doped ZBLAN fiber laser at 2.8 um wavelength

    Qin, Zhipeng; Zhao, Chujun; Wen, Shuangchun; Yuan, Peng; Qian, Liejia


    Mid-infrared saturable absorber mirror is successfully fabricated by transferring the mechanically exfoliated black phosphorus onto the gold-coated mirror. With the as-prepared black phosphorus saturable absorber mirror, a continuous-wave passively mode-locked Er:ZBLAN fiber laser is demonstrated at the wavelength of 2.8 um, which delivers a maximum average output power of 613 mW, a repetition rate of 24 MHz and a pulse duration of 42 ps. To the best of our knowledge, it is the first time to demonstrate black phosphorus mode-locked laser at 2.8 um wavelength. Our results demonstrate the feasibility of black phosphorus flake as a new two-dimensional material for application in mid-infrared ultrafast photonics.

  12. Generation of Ultrashort Light Bullets in Dispersive Kerr Media Using the Fourth-Order Dispersion-Dependent Spatiotemporal Instability

    文双春; 钱列加; 范滇元


    A new method for generation of a train of ultrashort pulses or a sequence of ultrashort light bullets is proposed.This method is based on the fourth-order dispersion-dependent spatiotemporal instability in dispersive Kerr media. The repetition-rate of the generated bullets can be made quite large by increasing the corresponding spatial modulation frequency locating in the new instability region resulted from fourth-order dispersion.

  13. Radiation sources and diagnostics with ultrashort electron bunches

    Catravas, P.; Esarey, E.; Leemans, W.P.


    The basic principles and design of radiation sources (transition radiation, Cerenkov radiation, radiation from periodic structures, etc.) and radiation-based diagnostics will be discussed, with emphasis on radiation from ultra-short electron bunches. Ultra-short electron bunches have the potential to produce high peak flux radiation sources that cover wavelength regimes where sources are currently not widely available (coherent THz/IR) as well as ultrashort X-ray pulses (3-100 fs). While radiation from the electron bunch contains the full signature of the electron beam and/or medium it has travelled through, the deconvolution of a single property of interest can be difficult due to a large number of contributing properties. The experimental implementation of novel solutions to this problem will be described for beams from 30 MeV to 30 GeV, including fluctuational interferometry, source imaging, phase matched cone angles and laser-based techniques, which utilize optical transition radiation, wiggler and Cerenkov radiation, and Thomson scattering. These novel diagnostic methods have the potential to resolve fs bunch durations, slice emittance on fs scales, etc. The advantages and novel features of these techniques will be discussed.

  14. Ultrashort Pulse Generation at Quasi-40-GHz by Using a Two-Section Passively Mode-Locked InGaAsP-InP Tensile Strained Quantum-Well Laser

    KONG Duan-Hua; ZHU Hong-Liang; LIANG Song; QIU Ji-Fang; ZHAO Ling-Juan


    A 1.56 μm passively mode-locked laser diode with a two-section tensile strained multi-quantum-well structure is fabricated.Without any external pulse compression,a Lorentz pulse train with a pulse width of 1.03 ps and a repetition rate of 35.6 GHz is obtained,which is one of the best results that have been reported on similar devices.The optical pulse has a 300 kHz line width and a 50dB peak over the noise floor in the photodetected radio-frequency electrical spectrum.%A 1.56μm passively mode-locked laser diode with a two-section tensile strained multi-quantum-well structure is fabricated. Without any external pulse compression, a Lorentz pulse train with a pulse width of 1.03ps and a repetition rate of 35.6 GHz is obtained, which is one of the best results that have been reported on similar devices. The optical pulse has a 300 kHz line width and a 50 dB peak over the noise floor in the photodetected radio-frequency electrical spectrum.

  15. Ultra-short laser pulse compression by using the group-velocity-matched cascaded quadratic nonlinearity∗%利用群速度匹配的级联二阶非线性实现超短激光脉冲压缩*

    叶荣; 张彬; 李恪宇


      提出了一种采用倾斜脉冲的级联二阶非线性来实现超短激光脉冲压缩的方法.对基于单块BBO晶体中基频光与倍频光群速度匹配的级联二阶非线性的脉冲压缩方案进行了理论分析.对比研究了群速度匹配与失配情况下利用级联二阶非线性进行脉冲压缩的效果,并模拟分析了基频光与倍频光的位相失配量、非线性晶体长度、基频光初始峰值光强和初始脉宽等因素对脉冲压缩效果的影响.结果表明,基频光与倍频光的群速度匹配将会大幅度改善压缩脉冲的时间波形和频谱分布.通过对位相失配量、晶体长度、初始光强等参数的优化和选取可获得较理想的压缩效果.采用倾斜脉冲的级联二阶非线性的脉宽压缩方法,针对中心波长800 nm、脉宽100 fs,峰值光强为50 GW/cm2的基频光脉冲,采用25 mm厚BBO晶体,当基频光与倍频光位相失配量∆k=60 mm−1(对应失谐角1.98◦),晶体外部脉冲前沿倾斜角γ0=74◦时,计算获得了质量较好的20 fs剩余基频光,并同时产生了14 fs的倍频光.%A new method for compressing ultra-short laser pulse has been proposed in which cascaded quadratic nonlinearity with tilt pulse is used. The pulse compression scheme with group velocity matching between fundamental harmonic (FH) and second harmonic (SH) pulses in a single BBO crystal has been analyzed theoretically. The compressed results have been investigated and compared between the cases of group velocity matching and mismatching. Furthermore, the influences of the phase mismatching between the FH and SH pulses, the length of the nonlinear crystal, the initial peak intensity and pulse-duration of the FH pulse on the pulse-duration compression have been analyzed and simulated. The results show that the matched group velocity between FH and SH pulses can improve significantly both the temporal profile and the spectrum distribution of the compressed pulse. High

  16. Ultra-short, off-resonant, strong excitation of two-level systems

    Jha, Pankaj K; Grazioso, Fabio


    We present a model describing the use of ultra-short strong pulses to populate the excited level of a two-level quantum system. In particular, we study an off-resonance excitation with a few cycles pulse which presents a smooth phase jump i.e. a change of the pulse's phase which is not step-like, but happens over a finite time interval. A numerical solution is given for the time-dependent probability amplitude of the excited level. The enhancement of the excited level's population is optimized with respect to the shape of the phase transient, and to other parameters of the excitation pulse.

  17. Using electric fields for pulse compression and group velocity control

    Li, Qian; Thuresson, Axel; Rippe, Lars; Kröll, Stefan


    In this article, we experimentally demonstrate a new way of controlling the group velocity of an optical pulse by using a combination of spectral hole burning, slow light effect and linear Stark effect in a rare-earth-ion-doped crystal. The group velocity can be changed continuously by a factor of 20 without significant pulse distortion or absorption of the pulse energy. With a similar technique, an optical pulse can also be compressed in time. Theoretical simulations were developed to simulate the group velocity control and the pulse compression processes. The group velocity as well as the pulse reshaping are solely controlled by external voltages which makes it promising in quantum information and quantum communication processes. It is also proposed that the group velocity can be changed even more in an Er doped crystal while at the same time having a transmission band matching the telecommunication wavelength.

  18. Effect of Er-doping on the structural and optical properties of Cd{sub 2}V{sub 2}O{sub 7}

    Lozada-Morales, R.; Cid-Garcia, A.; Palomino-Merino, R. [Benemerita Universidad Autonoma de Puebla, Postgrado en Fisica Aplicada, Facultad de Ciencias Fisico-Matematicas, Av. 14, San Claudio, Col. San Manuel, Puebla (Mexico); Lopez-Calzada, G.; Jimenez-Sandoval, S. [Centro de Investigacion y de Estudios Avanzados del IPN, Unidad Queretaro, Apartado Postal 1-798, Queretaro, Qro. 76001 (Mexico); Zayas, Ma.E. [Departamento de Investigacion en Fisica de la Universidad de Sonora, Edificio 3I, Blvd. Edificio 5 E, Luis Encinas s/n, Col. Centro, 83000 Hermosillo, Sonora (Mexico); Zelaya-Angel, O. [Departamento de Fisica, Centro de Investigacion y de Estudios Avanzados, P.O. Box 14-740, Mexico D. F. 07360 (Mexico); Carmona-Rodriguez, J. [Instituto Tecnologico Superior de Poza Rica, Calle Luis Donaldo Colosio S/N, Col. Arroyo del Maiz, C.P. 93230, Poza Rica, Veracruz (Mexico); Rubio-Rosas, E. [Centro de Vinculacion Universitaria, Av. 14, San Claudio, Col. San Manuel, Puebla (Mexico); Portillo-Moreno, O. [Facultad de Ciencias Quimicas, Av. 14, San Claudio, Col. San Manuel, Puebla (Mexico)


    The melt-quenching method was used to prepare two groups of samples using CdO and V{sub 2}O{sub 5} as starting materials. Taking into account that a crystalline-amorphous phase transition would be expected for the CdO-V{sub 2}O{sub 5} system, a first batch was prepared varying the proportions of CdO and V{sub 2}O{sub 5} in the intervals 60-95 and 40-5 wt%, respectively. With the aim of investigating the effect of erbium in the phase transition and crystalline quality of the first group of samples, a second batch was fabricated with the same proportions of CdO and V{sub 2}O{sub 5}, with the addition of 5 wt% of Er(NO{sub 3})5H{sub 2}O as source of Er{sup 3+} ions. It was found that crystalline or amorphous samples could be obtained depending on the relative concentrations of CdO and V{sub 2}O{sub 5}, and that the borderline between amorphous and crystalline samples was affected by the incorporation of Er. From X-ray diffraction, it was possible to identify the formation of the ternary compound Cd{sub 2}V{sub 2}O{sub 7} in the crystalline cases. The Raman and infrared bands in these samples were in agreement with the lattice modes of Cd{sub 2}V{sub 2}O{sub 7}. Additionally, an improvement in the crystalline quality of Cd{sub 2}V{sub 2}O{sub 7} was obtained for the Er-doped samples. The effect of the local environment around the Er{sup 3+} ions on the room temperature photoluminescence was also investigated for the amorphous and crystalline samples. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. Ablation of metals using ultrashort laser pulses in a pump-probe experiment dynamics of laser induced particle emission from metal surfaces on the femto and picosecond time scale

    Schmidt, V


    The main part of this work deals with the dynamics of the laser ablation process of metals (Al, Ag, Fe and Ni) initiated by approx. 50 fs laser pulses. The phenomena have been investigated by interferometric time resolved pump and probe measurements. This work reports one of the first yield measurements of emitted singly charged ions and neutrals from a metal surface induced by laser light. The experiments have been performed using a two-pulse autocorrelation setup in which the differential yield of emitted metal ions is measured as a function of the temporal separation between a pair of excitation pulses with a reflectron-type time-of-flight (TOF) spectrometer. The intensity of each pulse is kept below the ablation threshold, thus only the combined interaction of both pulses causes particle emission. It must be pointed out, that the time information obtained in this way concerns only the initial excitation responsible for ablation, but does not yield information about the dynamics of the way this excitation ...

  20. Amplification of Short Pulse High Power UV Laser


    At recent year, with the development of CPA and other amplification technology, laser intensity achieves great increase and laser power can be high to PW(105) now, this ultrashort pulse lasers offer scientists a route to investigate laser-matter interaction in an absolute new regime.So far the researches on ultrashort pulse laser-matter interaction concentrated on infrared regime, yet ultraviolet laser has the advantage in intense field physics and ICF researches for its short wavelength and less nonlinear effects. KrF excimer is the best medium in UV ultrashort pulse amplification for its small saturation energy and high contrast ratio accessible.