WorldWideScience

Sample records for femtosecond pulse pairs

  1. Interaction of femtosecond laser pulses with metal photocathode

    Institute of Scientific and Technical Information of China (English)

    Liu Yun-Quan; Zhang Jie; Liang Wen-Xi

    2005-01-01

    The features of interaction of femtosecond laser pulses with photocathode are studied theoretically in this paper.The surface temperature of the metal cathode film while femtosecond laser pulses irradiation is studied with twotemperature model. With a simple photoelectric model we obtain the optimum metal film thickness for the backilluminated photocathode. The generated ultrashort photocurrent pulses are strongly dependent on the temperature of the electron gas and the lattice during the femtosecond laser pulse irradiation on the photocathode.

  2. Femtosecond Timing Distribution Using Optical Pulses

    CERN Document Server

    Winter, A; Winter, A

    2005-01-01

    Fourth-generation light sources, such as the European X-ray Free Electron Laser (XFEL) require timing signals distributed over distances of several kilometers with a stability in the order of femtoseconds. A promising approach is the use of a mode-locked laser that generates sub-picosecond pulses which are distributed in timing stabilized optical fiber links. A good candidate for a laser master oscillator (LMO) is a mode-locked Erbium-doped fiber laser, featuring extremely low phase noise far from the carrier. Results on the development of the LMO locked to an external reference microwave oscillator to suppress low frequency jitter, the distribution via timing stabilized optical fiber links and the reconversion of the optical pulses to a low phase noise microwave RF signals with overall femtosecond stability are presented.

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

    DEFF Research Database (Denmark)

    Bache, Morten; Zhou, Binbin

    2012-01-01

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

  4. Synthesis of picosecond pulses by spectral compression and shaping of femtosecond pulses in engineered quadratic nonlinear media.

    Science.gov (United States)

    Marangoni, M; Brida, D; Conforti, M; Capobianco, A D; Manzoni, C; Baronio, F; Nalesso, G F; De Angelis, C; Ramponi, R; Cerullo, G

    2009-02-01

    Narrow-bandwidth picosecond pulses of predetermined spectral and temporal shapes are generated with high efficiency by frequency conversion of femtosecond pulses in lithium tantalate crystals with engineered quasi-phase-matching structures. We give examples of the synthesis of Gaussian and super-Gaussian picosecond pulses and also of a pair of synchronized phase-coherent picosecond pulses with a predetermined carrier-frequency difference.

  5. Femtosecond parabolic pulse shaping in normally dispersive optical fibers.

    Science.gov (United States)

    Sukhoivanov, Igor A; Iakushev, Sergii O; Shulika, Oleksiy V; Díez, Antonio; Andrés, Miguel

    2013-07-29

    Formation of parabolic pulses at femtosecond time scale by means of passive nonlinear reshaping in normally dispersive optical fibers is analyzed. Two approaches are examined and compared: the parabolic waveform formation in transient propagation regime and parabolic waveform formation in the steady-state propagation regime. It is found that both approaches could produce parabolic pulses as short as few hundred femtoseconds applying commercially available fibers, specially designed all-normal dispersion photonic crystal fiber and modern femtosecond lasers for pumping. The ranges of parameters providing parabolic pulse formation at the femtosecond time scale are found depending on the initial pulse duration, chirp and energy. Applicability of different fibers for femtosecond pulse shaping is analyzed. Recommendation for shortest parabolic pulse formation is made based on the analysis presented.

  6. Characteristics and Applications of Spatiotemporally Focused Femtosecond Laser Pulses

    Directory of Open Access Journals (Sweden)

    Chenrui Jing

    2016-12-01

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

  7. Novel ultrasensitive plasmonic detector of terahertz pulses enhanced by femtosecond optical pulses

    Science.gov (United States)

    Shur, M.; Rudin, S.; Rupper, G.; Muraviev, A.

    2016-09-01

    Plasmonic Field Effect Transistor detectors (first proposed in 1996) have emerged as superior room temperature terahertz (THz) detectors. Recent theoretical and experimental results showed that such detectors are capable of subpicosecond resolution. Their sensitivity can be greatly enhanced by applying the DC drain-to-source current that increases the responsivity due to the enhanced non-linearity of the device but also adds 1/f noise. We now propose, and demonstrate a dramatic responsivity enhancement of these plasmonic THz pulse detectors by applying a femtosecond optical laser pulse superimposed on the THz pulse. The proposed physical mechanism links the enhanced detection to the superposition of the THz pulse field and the rectified optical field. A femtosecond pulse generates a large concentration of the electron-hole pairs shorting the drain and source contacts and, therefore, determining the moment of time when the THz induced charge starts discharging into the transmission line connecting the FET to an oscilloscope. This allows for scanning the THz pulse with the strongly enhanced sensitivity and/or for scanning the response waveform after the THz pulse is over. The experimental results obtained using AlGaAs/InGaAs deep submicron HEMTs are in good agreement with this mechanism. This new technique could find numerous imaging, sensing, and quality control applications.

  8. Quenching Plasma Waves in Two Dimensional Electron Gas by a Femtosecond Laser Pulse

    Science.gov (United States)

    Shur, Michael; Rudin, Sergey; Greg Rupper Collaboration; Andrey Muraviev Collaboration

    Plasmonic detectors of terahertz (THz) radiation using the plasma wave excitation in 2D electron gas are capable of detecting ultra short THz pulses. To study the plasma wave propagation and decay, we used femtosecond laser pulses to quench the plasma waves excited by a short THz pulse. The femtosecond laser pulse generates a large concentration of the electron-hole pairs effectively shorting the 2D electron gas channel and dramatically increasing the channel conductance. Immediately after the application of the femtosecond laser pulse, the equivalent circuit of the device reduces to the source and drain contact resistances connected by a short. The total response charge is equal to the integral of the current induced by the THz pulse from the moment of the THz pulse application to the moment of the femtosecond laser pulse application. This current is determined by the plasma wave rectification. Registering the charge as a function of the time delay between the THz and laser pulses allowed us to follow the plasmonic wave decay. We observed the decaying oscillations in a sample with a partially gated channel. The decay depends on the gate bias and reflects the interplay between the gated and ungated plasmons in the device channel. Army Research Office.

  9. Drilling of Copper Using a Dual-Pulse Femtosecond Laser

    Directory of Open Access Journals (Sweden)

    Chung-Wei Cheng

    2016-02-01

    Full Text Available The drilling of copper using a dual-pulse femtosecond laser with wavelength of 800 nm, pulse duration of 120 fs and a variable pulse separation time (0.1–150 ps is investigated theoretically. A one-dimensional two-temperature model with temperature-dependent material properties is considered, including dynamic optical properties and the thermal-physical properties. Rapid phase change and phase explosion models are incorporated to simulate the material ablation process. Numerical results show that under the same total laser fluence of 4 J/cm2, a dual-pulse femtosecond laser with a pulse separation time of 30–150 ps can increase the ablation depth, compared to the single pulse. The optimum pulse separation time is 85 ps. It is also demonstrated that a dual pulse with a suitable pulse separation time for different laser fluences can enhance the ablation rate by about 1.6 times.

  10. A Novel Femtosecond Laser System for Attosecond Pulse Generation

    Directory of Open Access Journals (Sweden)

    Jianqiang Zhu

    2012-01-01

    Full Text Available We report a novel ultrabroadband high-energy femtosecond laser to be built in our laboratory. A 7-femtosecond pulse is firstly stretched by an eight-pass offner stretcher with a chirp rate 15 ps/nm, and then energy-amplified by a two-stage optical parametric chirped pulse amplification (OPCPA. The first stage as preamplification with three pieces of BBO crystals provides the majority of the energy gain. At the second stage, a YCOB crystal with the aperture of ~50 mm is used instead of the KDP crystal as the gain medium to ensure the shortest pulse. After the completion, the laser will deliver about 8 J with pulse duration of about 10 femtoseconds, which should be beneficial to the attosecond pulse generation and other ultrafast experiments.

  11. Phosphate Nd:glass materials for femtosecond pulse generation

    Science.gov (United States)

    Agnesi, Antonio; Carrà, Luca; Reali, Giancarlo

    2008-08-01

    Two different phosphate Nd-doped glasses have been investigated in a diode-pumped femtosecond laser. To our knowledge, only Schott's phosphate glasses were previously used in femtosecond oscillators. A slightly different behaviour was observed in our experiments, with respect to earlier reports: clean sech 2-pulses with duration <400 fs were routinely generated with wavelength corresponding to the fluorescence peak ≈1054 nm, whereas shorter pulses occurred at red-shifted wavelengths near 1067 nm. With a single 1-W pump diode (broad area emitter), cw slope efficiency as high as 32% and 139-fs pulse generation were demonstrated.

  12. Tight focusing of femtosecond elliptically polarised vortex light pulses

    Institute of Scientific and Technical Information of China (English)

    Hua Li-Min; Chen Bao-Suan; Chen Zi-Yang; Pu Ji-Xiong

    2011-01-01

    This paper studies the tight focusing properties of femtosecond elliptically polarised vortex light pulses. Based on Richards-Wolf vectorial diffraction integral, the expressions for the electric field, the velocity of the femtosecond light pulse and the total angular momentum of focused pluses are derived. The numerical calculations are also given to illustrate the intensity distribution, phase contour, the group velocity variation and the total angular momentum near the focus. It finds that near the focus the femtosecond elliptically polarised vortex light pulse can travel at various group speeds, that is, slower or faster than light speed in vacuum, depending on the numerical aperture of the focusing objective system. Moreover, it also studies the influence of the numerical aperture of the focusing objective and the time duration of the elliptically polarised vortex light pulse on the total angular momentum distribution in the focused field.

  13. Correlation functions formed by a femtosecond pulse interferometer

    NARCIS (Netherlands)

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

    2008-01-01

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

  14. Resonant dispersive waves generated with multi-input femtosecond pulses

    Science.gov (United States)

    Wang, Kai; Peng, Jiahui; Sokolov, Alex

    2010-10-01

    We investigated the resonant dispersive waves generated by high-order dispersion theoretically. We considered different femtosecond pulses propagating in the kagome-lattice hollow-core photonics crystal fibers. The two third order and fourth order resonant dispersive waves would be produced in the visible range to produce the ultrashort pulse.

  15. Nonlinear femtosecond pulse compression in cholesteric liquid crystals (Conference Presentation)

    Science.gov (United States)

    Liu, Yikun; Zhou, Jianying; Lin, Tsung-Hsien; Khoo, Iam-Choon

    2016-09-01

    Liquid crystals materials have the advantage of having a large nonlinear coefficient, but the response time is slow, normally up to several minisecond. This makes it is hard to apply in ultra fast optical devices. Recently, fentosecond (fs) nonlinear effect in choleteric liquid crystals is reported, nonlinear coefficient in the scale of 10-12 cm2/W is achieved. Base on this effect, in this work, fentosecond pulse compression technique in a miniature choleteric liquid crystal is demonstrated1,2. Cholesteric liquid crystals (CLC) is a kind of 1-dimensional phontonic structure with helical periodic. In a 10 μm thick CLC, femtosecond pulse with 100 fs is compressed to about 50 fs. CLC sample in planar texture with 500μm thick cell gap is further fabricated. In this sample, femtosecond pulse with 847 fs can be compressed to 286 fs. Due to the strong dispersion at the edge of photonic band gap, femtosecond pulse stretching and compensation can be achieve. In this experiment, laser pulse with duration 90 fs is stretched to above 2 picosecond in the first CLC sample and re-compressed to 120 fs in the second sample. Such technique might be applied in chirp pulse amplification. In conclusion, we report ultra fast nonlinear effect in cholesteric liquid crystals. Due to the strong dispersion and nonlinearity of CLC, femtosecond pulse manipulating devices can be achieved in the scale of micrometer.

  16. Materials processing with a tightly focused femtosecond laser vortex pulse.

    Science.gov (United States)

    Hnatovsky, Cyril; Shvedov, Vladlen G; Krolikowski, Wieslaw; Rode, Andrei V

    2010-10-15

    In this Letter we present the first (to our knowledge) demonstration of material modification using tightly focused single femtosecond laser vortex pulses. Double-charge femtosecond vortices were synthesized with a polarization-singularity beam converter based on light propagation in a uniaxial anisotropic medium and then focused using moderate- and high-NA optics (viz., NA=0.45 and 0.9) to ablate fused silica and soda-lime glass. By controlling the pulse energy, we consistently machine micrometer-size ring-shaped structures with <100nm uniform groove thickness.

  17. Generating long sequences of high-intensity femtosecond pulses

    CERN Document Server

    Bitter, Martin

    2015-01-01

    We present an approach to create pulse sequences extending beyond 150~picoseconds in duration, comprised of $100~\\mu$J femtosecond pulses. A quarter of the pulse train is produced by a high-resolution pulse shaper, which allows full controllability over the timing of each pulse. Two nested Michelson interferometers follow to quadruple the pulse number and the sequence duration. To boost the pulse energy, the long train is sent through a multi-pass Ti:Sapphire amplifier, followed by an external compressor. A periodic sequence of 84~pulses of 120~fs width and an average pulse energy of 107~$\\mu$J, separated by 2~ps, is demonstrated as a proof of principle.

  18. Curing of Epoxy Resin Induced by Femtosecond Laser Pulse

    Institute of Scientific and Technical Information of China (English)

    LI Yubin; ZHANG Zuoguang

    2005-01-01

    The possibility of curing of epoxy resin induced by femtosecond laser beam was explored through choosing different initiators . Absorption spectroscopy, infrared spectroscopy (IR), stereomicroscopy and scanning electron microscopy (SEM) were applied to analyze the structure of epoxy resin systems after irradiation with a femtosecond laser beam. The experimental results show that the epoxy resin systems containing diaryliodonium salts can be cured by irradiation of Jemtosecond laser pulse, while the systems containing benzoin can not be cured. It is found that diaryliodonium salts decompose under the irradiation of femtosecond laser pulse through multi ( two ) -photon absorption, initiating the ring-opening polymerization of epoxy resin. And the appearance of cured area has a sheet structure consisting of many tiny lamellar structures.

  19. Energy deposition dynamics of femtosecond pulses in water

    CERN Document Server

    Minardi, Stefano; Gopal, Amrutha; Tamošauskas, Gintaras; Milián, Carles; Couairon, Arnaud; Pertsch, Thomas; Dubietis, Audrius

    2014-01-01

    We exploit inverse Raman scattering and solvated electron absorption to perform a quantitative characterization of the energy loss and ionization dynamics in water with tightly focused near-infrared femtosecond pulses. A comparison between experimental data and numerical simulations suggests that the ionization energy of water is 8 eV, rather than the commonly used value of 6.5 eV.

  20. Heating of a metal nanofilm during femtosecond laser pulse absorption

    Science.gov (United States)

    Bezhanov, S. G.; Kanavin, A. P.; Uryupin, S. A.

    2014-09-01

    We have studied the temperature evolution of electrons and the lattice of a metal nanofilm interacting with a femtosecond s- or p-polarised pulse. It is shown that even if the film thickness is greater than the skin-layer depth, the temperature distribution during the pulse action may be close to the uniform one because of the high electron thermal conductivity, which leads to a rapid redistribution of energy over the film thickness.

  1. Femtosecond laser ablation of Au film around single pulse threshold

    Institute of Scientific and Technical Information of China (English)

    Xiaochang Ni; Ching-Yue Wang; Yinzhong Wu; Li Yang; Wei Jia; Lu Chai

    2006-01-01

    @@ Ablation process of 1-kHz femtosecond lasers (pulse duration of 148 fs, wavelength of 775 nm) of Au film on silica substrates is studied. The thresholds for single and multi pulses can be obtained directly from the relation between the squared diameter D2 of the ablated craters and the laser fluence φo. From the plot of the accumulated laser fluence Nφth(N) and the number of laser pulses N, incubation coefficient of Au film is obtained to be 0.765. Some experimental data obtained around the single pulse threshold are in good agreement with the theoretical calculation.

  2. Subthreshold pair production in short laser pulses

    OpenAIRE

    Nousch, T.; Seipt, D.; Kampfer, B.; Titov, A. I.

    2012-01-01

    The $e^+e^-$ pair production by a probe photon traversing a linearly polarized laser pulse is treated as generalized nonlinear Breit-Wheeler process. For short laser pulses with very few oscillations of the electromagnetic field we find below the perturbative weak-field threshold $\\sqrt{s} = 2m$ a similar enhancement of the pair production rate as for circular polarization. The strong subthreshold enhancement is traced back to the finite bandwidth of the laser pulse. A folding model is develo...

  3. The Role of Plasma Shielding in Double-Pulse Femtosecond Laser-Induced Breakdown Spectroscopy

    CERN Document Server

    Penczak, John S; Bar, Ilana; Gordon, Robert J

    2013-01-01

    It is well known that optical emission produced by femtosecond laser-induced breakdown on a surface may be enhanced by using a pair of laser pulses separated by a suitable delay. Here we elucidate the mechanism for this effect both experimentally and theoretically. Using a bilayer sample consisting of a thin film of Ag deposited on an Al substrate as the ablation target and measuring the breakdown spectrum as a function of fluence and pulse delay, it is shown experimentally that the enhanced signal is not caused by additional ablation initiated by the second pulse. Rather, particle-in-cell calculations show that the plasma produced by the first pulse shields the surface from the second pulse for delays up to 100 ps. These results indicate that the enhancement is the result of excitement of particles entrained in the plasma produced by the first pulse.

  4. Fabrication of magneto-optical microstructure by femtosecond laser pulses

    Institute of Scientific and Technical Information of China (English)

    Yudong Li; Xiangyang Gao; Meiling Jiang; Qian Sun; Jianguo Tian

    2012-01-01

    We investigate femtosecond laser direct writing (FLDW) in the fabrication of magneto-optical (MO) microstructures.The experimental results show that FDLW can introduce positive refractive index change in the MO materials.With the increase of the writing intensity of femtosecond laser pulses,refractive index change increases,whereas Verdet constant of the damaged area decreases nonlinearly.With suitable writing intensity,we obtain a single-mode waveguide in which Verdet constant is 80% of the bulkMO glass.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-12-15

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-03-01

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

  7. Pulsed homodyne measurements of femtosecond squeezed pulses generated by single-pass parametric deamplification.

    Science.gov (United States)

    Wenger, Jérôme; Tualle-Brouri, Rosa; Grangier, Philippe

    2004-06-01

    A new scheme is described for the generation of pulsed squeezed light by use of femtosecond pulses that have been parametrically deamplified through a single pass in a thin (100-microm) potassium niobate crystal with a significant deamplification of approximately -3 dB. The quantum noise of each pulse is registered in the time domain by single-shot homodyne detection operated with femtosecond pulses; the best squeezed quadrature variance was 1.87 dB below the shot-noise level. Such a scheme provides a basic resource for time-resolved quantum communication protocols.

  8. Pulsed homodyne measurements of femtosecond squeezed pulses generated by single-pass parametric deamplification

    CERN Document Server

    Wenger, J; Grangier, P

    2004-01-01

    A new scheme is described for pulsed squeezed light generation using femtosecond pulses parametrically deamplified through a single pass in a thin (0.1mm) potassium niobate KNbO3 crystal, with a significant deamplification of about -3dB. The quantum noise of each individual pulse is registered in the time domain using a single-shot homodyne detection operated with femtosecond pulses and the best squeezed quadrature variance was measured to be 1.87 dB below the shot noise level. Such a scheme provides the basic ressource for time-resolved quantum communication protocols.

  9. High-Precision Spectroscopy with Counter-Propagating Femtosecond Pulses

    CERN Document Server

    Barmes, Itan; Eikema, Kjeld S E

    2013-01-01

    An experimental realization of high-precision direct frequency comb spectroscopy using counter-propagating femtosecond pulses on two-photon atomic transitions is presented. Doppler broadened background signal, hampering precision spectroscopy with ultrashort pulses, is effectively eliminated with a simple pulse shaping method. As a result, all four 5S-7S two-photon transitions in a rubidium vapor are determined with both statistical and systematic uncertainties below 10$^{-11}$, which is an order of magnitude better than previous experiments on these transitions.

  10. Femtosecond laser pulse train interaction with dielectric materials

    CERN Document Server

    Caulier, O Dematteo; Chimier, B; Skupin, S; Bourgeade, A; Léger, C Javaux; Kling, R; Hönninger, C; Lopez, J; Tikhonchuk, V; Duchateau, G

    2015-01-01

    We investigate the interaction of trains of femtosecond microjoule laser pulses with dielectric materials by means of a multi-scale model. Our theoretical predictions are directly confronted with experimental observations in soda-lime glass. We show that due to the low heat conductivity, a significant fraction of the laser energy can be accumulated in the absorption region. Depending on the pulse repetition rate, the material can be heated to high temperatures even though the single pulse energy is too low to induce a significant material modification. Regions heated above the glass transition temperature in our simulations correspond very well to zones of permanent material modifications observed in the experiments.

  11. Vibrationally-induced electronic population inversion with strong femtosecond pulses

    CERN Document Server

    Sampedro, Pablo; Sola, Ignacio R

    2016-01-01

    We discover a new mechanism of electronic population inversion using strong femtosecond pulses, where the transfer is mediated by vibrational motion on a light-induced potential. The process can be achieved with a single pulse tuning its frequency to the red of the Franck-Condon window. We show the determinant role that the sign of the slope of the transition dipole moment can play on the dynamics, and extend the method to multiphoton processes with odd number of pulses. As an example, we show how the scheme can be applied to population inversion in Na2.

  12. Subthreshold pair production in short laser pulses

    CERN Document Server

    Nousch, T; Kampfer, B; Titov, A I

    2012-01-01

    The $e^+e^-$ pair production by a probe photon traversing a linearly polarized laser pulse is treated as generalized nonlinear Breit-Wheeler process. For short laser pulses with very few oscillations of the electromagnetic field we find below the perturbative weak-field threshold $\\sqrt{s} = 2m$ a similar enhancement of the pair production rate as for circular polarization. The strong subthreshold enhancement is traced back to the finite bandwidth of the laser pulse. A folding model is developed which accounts for the interplay of the frequency spectrum and the intensity distribution in the course of the pulse.

  13. Compact transient-grating self-referenced spectral interferometry for sub-nanojoule femtosecond pulses characterization

    CERN Document Server

    Shen, Xiong; Liu, Jun; Li, Ruxin

    2016-01-01

    The self-referenced spectral interferometry (SRSI) technique, which is usually used for microjoule-level femtosecond pulses characterization, is improved to characterize weak femtosecond pulses with nanojoule based on the transient-grating effect. Both femtosecond pulses from an amplifier with 3 nJ per pulse at 1 kHz repetition rates and femtosecond pulses from an oscillator with less than 0.5 nJ per pulse at 84 MHz repetition rates are successfully characterized. Furthermore, through a special design, the optical setup of the device is even smaller than a palm which will makes it simple and convenient during the application. These improvements extend the application of SRSI technique to the characterization of femtosecond pulses in a broad range. Not only pulses from an amplifier but also pulses from an oscillator or weak pulses used in ultrafast spectroscopy can be monitored with this SRSI method right now.

  14. Amplification of femtosecond pulses in Ti:Al2O3 using an injection-seeded laser

    Science.gov (United States)

    Lagasse, M. J.; Schoenlein, R. W.; Fujimoto, J. G.; Schulz, P. A.

    1989-12-01

    A 440-fsec, 0.1-pJ pulse from a dye laser is injected into a high-repetition-rate Ti:Al2O3 laser pumped by a copper-vapor laser to study the amplification and pulse broadening of femtosecond pulses in Ti:Al2O3. Gains of 2 x 10 to the 7th are achieved with output pulse durations of 1.1 psec. After recompression with a grating pair to compensate dispersion broadening, pulses as short as 275 fsec are obtained.

  15. The photoluminescence of ZnSe bulk single crystals excited by femtosecond pulse

    Institute of Scientific and Technical Information of China (English)

    Li Huan-Yong; Jie Wan-Qi; Zhang Shi-An; Sun Zhen-Rong; Xu Ke-Wei

    2006-01-01

    This paper reports on the photoluminescence spectra of ZnSe single crystal with trace chlorine excited by the femtosecond laser pulse. Three emission bands, including second-harmonic-generation, two-photon-excited peak and a broad band at 500-700nm, were detected. The thermal strain induced by femtosecond pulse strongly influences the photoluminescence of ZnSe crystal. The corresponding strain e in ZnSe crystal is estimated to be about 8.8 × 10-3 at room temperature. The zinc-vacancy, as the main point defect induced by femtosecond pulse, is successfully used to interpret the broad emission at 500-700nm. The research shows that self-activated luminescence possesses the recombination mechanism of donor-vacancy pair, and it is also influenced by a few selenium defects and the temperature.The rapid decrease in photoluminescence intensity of two-photon-excited fluorescence and second-harmonic generation emission at lower temperature is attributed to the fact that more point defects result in the thermal activation of the two-photo-absorption energy converting to the stronger recombination emission of chlorine-zinc vacancy in 500-700nm. The experimental results indicate that the femtosecond exciting photoluminescence shows a completely different emission mechanism to that of He-Cd exciting luminescence in ZnSe single crystal. The femtosecond laser exhibits a higher sensitive to the impurity in crystal materials, which can be recommended as an efficient way to estimate the trace impurity in high quality crystals.

  16. Optimally enhanced optical emission in laser-induced air plasma by femtosecond double-pulse

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Anmin [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun 130012 (China); Li, Suyu; Li, Shuchang; Jiang, Yuanfei; Ding, Dajun [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Shao, Junfeng; Wang, Tingfeng [State Key Laboratory of Laser Interaction with Matter, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); Huang, Xuri [Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun 130012 (China); Jin, Mingxing [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); State Key Laboratory of Laser Interaction with Matter, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China)

    2013-10-15

    In laser-induced breakdown spectroscopy, a femtosecond double-pulse laser was used to induce air plasma. The plasma spectroscopy was observed to lead to significant increase of the intensity and reproducibility of the optical emission signal compared to femtosecond single-pulse laser. In particular, the optical emission intensity can be optimized by adjusting the delay time of femtosecond double-pulse. An appropriate pulse-to-pulse delay was selected, that was typically about 50 ps. This effect can be especially advantageous in the context of femtosecond laser-induced breakdown spectroscopy, plasma channel, and so on.

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

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xi-Peng; JIANG Hong-Bing; TANG Shan-Chun; GONG Qi-Huang

    2009-01-01

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

  18. Rippled area formed by surface plasmon polaritons upon femtosecond laser double-pulse irradiation of silicon.

    Science.gov (United States)

    Derrien, Thibault J-Y; Krüger, Jörg; Itina, Tatiana E; Höhm, Sandra; Rosenfeld, Arkadi; Bonse, Jörn

    2013-12-02

    The formation of near-wavelength laser-induced periodic surface structures (LIPSS) on silicon upon irradiation with sequences of Ti:sapphire femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied theoretically. For this purpose, the nonlinear generation of conduction band electrons in silicon and their relaxation is numerically calculated using a two-temperature model approach including intrapulse changes of optical properties, transport, diffusion and recombination effects. Following the idea that surface plasmon polaritons (SPP) can be excited when the material turns from semiconducting to metallic state, the "SPP active area" is calculated as function of fluence and double-pulse delay up to several picoseconds and compared to the experimentally observed rippled surface areas. Evidence is presented that multi-photon absorption explains the large increase of the rippled area for temporally overlapping pulses. For longer double-pulse delays, relevant relaxation processes are identified. The results demonstrate that femtosecond LIPSS on silicon are caused by the excitation of SPP and can be controlled by temporal pulse shaping.

  19. Energy deposition dynamics of femtosecond pulses in water

    Energy Technology Data Exchange (ETDEWEB)

    Minardi, Stefano, E-mail: stefano@stefanominardi.eu; Pertsch, Thomas [Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Milián, Carles; Couairon, Arnaud [Centre de Physique Théorique, CNRS, École Polytechnique, F-91128 Palaiseau (France); Majus, Donatas; Tamošauskas, Gintaras; Dubietis, Audrius [Department of Quantum Electronics, Vilnius University, Sauletekio 9, bldg. 3, LT-10222 Vilnius (Lithuania); Gopal, Amrutha [Institute of Optics and Quantum Electronics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena (Germany)

    2014-12-01

    We exploit inverse Raman scattering and solvated electron absorption to perform a quantitative characterization of the energy loss and ionization dynamics in water with tightly focused near-infrared femtosecond pulses. A comparison between experimental data and numerical simulations suggests that the ionization energy of water is 8 eV, rather than the commonly used value of 6.5 eV. We also introduce an equation for the Raman gain valid for ultra-short pulses that validates our experimental procedure.

  20. Fibonacci-like photonic structure for femtosecond pulse compression.

    Science.gov (United States)

    Makarava, L N; Nazarov, M M; Ozheredov, I A; Shkurinov, A P; Smirnov, A G; Zhukovsky, S V

    2007-03-01

    The compression of femtosecond laser pulses by linear quasiperiodic and periodic photonic multilayer structures is studied both experimentally and theoretically. We compare the compression performance of a Fibonacci and a periodic structure with similar total thickness and the same number of layers, and find the performance to be higher in the Fibonacci case, as predicted by numerical simulation. This compression enhancement takes place due to the larger group velocity dispersion at a defect resonance of the transmission spectrum of the Fibonacci structure. We demonstrate that the Fibonacci structure with the thickness of only 2.8 microm can compress a phase-modulated laser pulse by up to 30%. The possibility for compression of laser pulses with different characteristics in a single multilayer is explored. The operation of the compressor in the reflection regime has been modeled, and we show numerically that the reflected laser pulse is subjected to real compression: not only does its duration decrease but also its amplitude rises.

  1. Polarization dependent nanostructuring of silicon with femtosecond vortex pulse

    Science.gov (United States)

    Rahimian, M. G.; Bouchard, F.; Al-Khazraji, H.; Karimi, E.; Corkum, P. B.; Bhardwaj, V. R.

    2017-08-01

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

  2. Polarization dependent nanostructuring of silicon with femtosecond vortex pulse

    Directory of Open Access Journals (Sweden)

    M. G. Rahimian

    2017-08-01

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

  3. Optimally shaped narrowband picosecond pulses for femtosecond stimulated Raman spectroscopy.

    Science.gov (United States)

    Hoffman, David P; Valley, David; Ellis, Scott R; Creelman, Mark; Mathies, Richard A

    2013-09-09

    A comparison between a Fabry-Pérot etalon filter and a conventional grating filter for producing the picosecond (ps) Raman pump pulses for femtosecond stimulated Raman spectroscopy (FSRS) is presented. It is shown that for pulses of equal energy the etalon filter produces Raman signals twice as large as that of the grating filter while suppressing the electronically resonant background signal. The time asymmetric profile of the etalon-generated pulse is shown to be responsible for both of these observations. A theoretical discussion is presented which quantitatively supports this hypothesis. It is concluded that etalons are the ideal method for the generation of narrowband ps pulses for FSRS because of the optical simplicity, efficiency, improved FSRS intensity and reduced backgrounds.

  4. Pulsed digital holography system recording ultrafast process of the femtosecond order

    Science.gov (United States)

    Wang, Xiaolei; Zhai, Hongchen; Mu, Guoguang

    2006-06-01

    We report, for the first time to our knowledge, a pulsed digital microholographic system with spatial angular multiplexing for recording the ultrafast process of the femtosecond order. The optimized design of the two sets of subpulse-train generators in this system makes it possible to implement a digital holographic recording with spatial angular multiplexing of a frame interval of the femtosecond order, while keeping the incident angle of the object beams unchanged. Three pairs of amplitude and phase images from the same view angle digitally reconstructed by the system demonstrated the ultrafast dynamic process of laser-induced ionization of ambient air at a wavelength of 800 nm, with a time resolution of 50 fs and a frame interval of 300 fs.

  5. Efficient spectral shift and compression of femtosecond pulses by parametric amplification of chirped light.

    Science.gov (United States)

    Nejbauer, Michał; Radzewicz, Czesław

    2012-01-30

    We present a method for an efficient spectral shift and compression of pulses from a femtosecond laser system. The method enables generation of broadly tunable (615-985 nm) narrow bandwidth (≈10 cm(-1)) pulses from the femtosecond pulses at 1030 nm. It employs a direct parametric amplification--without spectral filtering--of highly chirped white light by a narrow bandwidth (pulse. The system, when pumped with just 200 μJ of the fundamental femtosecond pulse energy, generates pulses with energies of 3-9 μJ and an excellent beam quality in the entire tuning range.

  6. Ablation of carbide materials with femtosecond pulses

    Science.gov (United States)

    Dumitru, Gabriel; Romano, Valerio; Weber, Heinz P.; Sentis, Marc; Marine, Wladimir

    2003-01-01

    The response of cemented tungsten carbide and of titanium carbonitride was investigated with respect to damage and ablation properties, under interaction with ultrashort laser pulses. These carbide materials present high microhardness and are of significant interest for tribological applications. The experiments were carried out in air with a commercial Ti:sapphire laser at energy densities on the target up to 6.5 J/cm 2. The irradiated target surfaces were analyzed with optical, SEM and AFM techniques and the damage and ablation threshold values were determined using the measured spot diameters and the calculated incident energy density distributions.

  7. Schwinger Pair Production in Pulsed Electric Fields

    CERN Document Server

    Kim, Sang Pyo; Ruffini, Remo

    2012-01-01

    We numerically investigate the temporal behavior and the structure of longitudinal momentum spectrum and the field polarity effect on pair production in pulsed electric fields in scalar quantum electrodynamics (QED). Using the evolution operator expressed in terms of the particle and antiparticle operators, we find the exact quantum states under the influence of electric pulses and measure the number of pairs of the Minkowski particle and antiparticle. The number of pairs, depending on the configuration of electric pulses, exhibits rich structures in the longitudinal momentum spectrum and undergoes diverse dynamical behaviors at the onset of the interaction but always either converges to a momentum-dependent constant or oscillates around a momentum-dependent time average after the completion of fields.

  8. Microstructuring of silicon with femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Freund, Waldemar; Richters, Jan P.; Voss, Tobias; Gutowski, Juergen [Institute of Solid State Physics, Semiconductor Optics Group, University of Bremen (Germany)

    2011-07-01

    Silicon structured with ultrashort laser pulses which is called ''black silicon'' due to its dark appearance has been a field of intense studies in recent years. It exhibits a nearly uniform absorptivity beyond 90% in the whole visible to near-infrared spectral region. Therefore, it is a promising material for applications in solar cells and photo diodes. In this talk a brief introduction of microstructuring of silicon with ultrashort laser pulses will be given. Structuring is carried out in a sulfurhexafluoride (SF{sub 6}) atmosphere, which simultaneously allows doping of the silicon with sulfur far above the solubility limit. The structuring leads to a specific quasiperiodic surface morphology at which incident light is reflected multiple times. Thus light absorption in the silicon is considerably enhanced. The extremely high doping with sulfur results in the formation of a distinct defect band which is the origin of high absorptance in the near infrared. Furthermore, sulfur acts as a donor in silicon. Hence, microstructuring of p-doped silicon in SF{sub 6} atmosphere leads to the formation of a p-n{sup +} junction. This is an important step towards the fabrication of efficient solar cells and photo diodes with increased infrared sensitivity on base of easy-to-produce black silicon.

  9. Heavy ion acceleration using femtosecond laser pulses

    CERN Document Server

    Petrov, G M; Thomas, A G R; Krushelnick, K; Beg, F N

    2015-01-01

    Theoretical study of heavy ion acceleration from ultrathin (<200 nm) gold foils irradiated by a short pulse laser is presented. Using two dimensional particle-in-cell simulations the time history of the laser bullet is examined in order to get insight into the laser energy deposition and ion acceleration process. For laser pulses with intensity , duration 32 fs, focal spot size 5 mkm and energy 27 Joules the calculated reflection, transmission and coupling coefficients from a 20 nm foil are 80 %, 5 % and 15 %, respectively. The conversion efficiency into gold ions is 8 %. Two highly collimated counter-propagating ion beams have been identified. The forward accelerated gold ions have average and maximum charge-to-mass ratio of 0.25 and 0.3, respectively, maximum normalized energy 25 MeV/nucleon and flux . Analytical model was used to determine a range of foil thicknesses suitable for acceleration of gold ions in the Radiation Pressure Acceleration regime and the onset of the Target Normal Sheath Acceleratio...

  10. Intermodal four-wave mixing from femtosecond pulse-pumped photonic crystal fiber.

    Science.gov (United States)

    Tu, H; Jiang, Z; Marks, D L; Boppart, S A

    2009-03-09

    Large Stokes-shift ( approximately 4700 cm(-1)) four-wave mixing is generated in a deeply normal dispersion regime from a 20 cm commercial large-mode-area photonic crystal fiber pumped by amplified approximately 800 nm femtosecond pulses. The phase-matching condition is realized through an intermodal scheme involving two pump photons in the fundamental fiber mode and a pair of Stokesanti-Stokes photons in a higher-order fiber mode. Over 7% conversion efficiency from the pump input to 586 nm anti-Stokes signal has been attained.

  11. Modeling crater formation in femtosecond-pulse laser damage from basic principles

    OpenAIRE

    Mitchell, Robert A.; Schumacher, Douglass W.; Chowdhury, Enam A.

    2015-01-01

    We present the first fundamental simulation method for the determination of crater morphology due to femtosecond-pulse laser damage. To this end we have adapted the particle-in-cell (PIC) method commonly used in plasma physics for use in the study of laser damage, and developed the first implementation of a pair-potential for PIC codes. We find that the PIC method is a complementary approach to modeling laser damage, bridging the gap between fully ab-initio molecular dynamics approaches and e...

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

    Directory of Open Access Journals (Sweden)

    Nakamura Kazutaka G.

    2013-03-01

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

  13. Vacuum heating of solid target irradiated by femtosecond laser pulses

    Institute of Scientific and Technical Information of China (English)

    DONG; Quanli(董全力); ZHANG; Jie(张杰)

    2003-01-01

    The interaction of femtosecond laser pulses with solid targets was studied through experiments and particle-in-cell (PIC) simulations. It is proved that the vacuum heating and the inverse bremsstralung process are the main mechanisms of the laser pulse absorption under such conditions. The distribution of hot electrons and that of X-ray are found to have double-temperature structure, which is confirmed by PIC simulations. While the lower temperature is attributed to the resonant absorption, the higher one, however, is caused by the laser-induced electric field in the target normal direction. The time-integrated spectra ofthe reflected laser pulse shows that the mechanism of electron acceleration is determined by the plasma density profile.

  14. Filament propagation length of femtosecond pulses with different transverse modes

    CERN Document Server

    Kaya, N; Kaya, G; Strohaber, J; Kolomenskii, A A; Schuessler, H A

    2014-01-01

    We experimentally studied intense femtosecond pulse filamentation and propagation in water for Gaussian, Laguerre-Gaussian, and Bessel-Gaussian incident beams. These different transverse modes for incident laser pulses were created from an initial Gaussian beam by using a computer generated hologram technique. We found that the length of the filament induced by the Bessel-Gaussian incident beam was longer than that for the other transverse modes under the conditions of the same peak intensity, pulse duration, and the size of the central part of the beam. To better understand the Bessel-Gaussian beam propagation, we performed a more detailed study of the filament length as a function of the number of radial modal lobes. The length increased with the number of lobes, implying that the radial modal lobes serve as an energy reservoir for the filament formed by the central intensity peak.

  15. Features of femtosecond laser pulses interaction with laser nanoceramics

    Science.gov (United States)

    Pestryakov, E. V.; Petrov, V. V.; Trunov, V. I.; Kirpichnikov, A. V.; Merzliakov, M. A.; Laptev, A. V.

    2007-06-01

    In this work we have performed the experimental researches of features for the generation of supercontinuum in laser materials with identical chemical composition: Yb:YAG crystal and Yb:YAG laser nanoceramics. Dependence of width of supercontinuum spectrum in 515-1100 nm spectral range on femtosecond radiation intensity was investigated. At laser intensity ~1.2•10 14 W/cm2 the short-wave wing of a spectrum for nanoceramics has greater intensity and more flat shape in comparison with crystal. Experiments were made at lens focusing of the Ti:Sapphire femtosecond laser system radiation with energy up to 0.5 mJ in explored sample that was inside of integrating optical sphere. Also we investigated the interaction of femtosecond laser pulses and the generation of supercontinuum in Nd:Y IIO 3 nanoceramics. The maximum value of laser intensity in experiments was restricted by optical breakdown on target output surface, i.e. was below threshold of ablation of sample substance.

  16. Nitridation of Nb surface by nanosecond and femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Farha, Ashraf Hassan [Department of Electrical and Computer Engineering and the Applied Research Center, Old Dominion University, Norfolk, VA 23529 (United States); Department of Physics, Faculty of Science, Ain Shams University, Cairo 11566 (Egypt); Ozkendir, Osman Murat [Tarsus Technology Faculty, Mersin University, Tarsus 33480 (Turkey); Koroglu, Ulas; Ufuktepe, Yüksel [Department of Physics, Cukurova University, Adana 01330 (Turkey); Elsayed-Ali, Hani E., E-mail: helsayed@odu.edu [Department of Electrical and Computer Engineering and the Applied Research Center, Old Dominion University, Norfolk, VA 23529 (United States)

    2015-01-05

    Highlights: • Laser nitridation of niobium is performed with nanosecond and femtosecond pulses. • Formation of NbN{sub x} with mixed α, β and δ phases was observed. • For femtosecond laser processed samples, laser induced ripple patterns oriented parallel to the beam polarization were formed. • X-ray absorption near edge structure show formation of Nb{sub 2}O{sub 5} on the surface of the samples. - Abstract: Niobium nitride samples were prepared by laser nitridation in a reactive nitrogen gas environment at room temperature using a Q-switched Nd:YAG nanosecond laser and a Ti:sapphire femtosecond laser. The effects of laser fluence on the formed phase, surface morphology, and electronic properties of the NbN{sub x} were investigated. The samples were prepared at different nanosecond laser fluences up to 5.0 ± 0.8 J/cm{sup 2} at fixed nitrogen pressure of ∼2.7 × 10{sup 4} Pa formed NbN{sub x} with mainly the cubic δ-NbN phase. Femtosecond laser nitrided samples were prepared using laser fluences up to 1.3 ± 0.3 mJ/cm{sup 2} at ∼4.0 × 10{sup 4} Pa nitrogen pressure. Laser induced ripple patterns oriented parallel to the beam polarization were formed with spacing that increases with the laser fluence. To achieve a laser-nitrided surface with desired crystal orientation the laser fulence is an important parameter that needs to be properly adjusted.

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

    DEFF Research Database (Denmark)

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

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

  18. Moving picture recording and observation of femtosecond light pulse propagation using a rewritable holographic material

    Energy Technology Data Exchange (ETDEWEB)

    Yamamoto, Seiji; Takimoto, Tetsuya; Tosa, Kazuya; Kakue, Takashi [Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo, Kyoto 606-8585 (Japan); Awatsuji, Yasuhiro, E-mail: awatsuji@kit.ac.jp [Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo, Kyoto 606-8585 (Japan); Nishio, Kenzo [Advanced Technology Center, Kyoto Institute of Technology, Matsugasaki, Sakyo, Kyoto 606-8585 (Japan); Ura, Shogo [Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo, Kyoto 606-8585 (Japan); Kubota, Toshihiro [Kubota Holography Laboratory, Corporation, Nishihata 34-1-609, Ogura, Uji 611-0042 (Japan)

    2011-08-01

    We succeeded in recording and observing femtosecond light pulse propagation as a form of moving picture by means of light-in-flight recording by holography using a rewritable holographic material, for the first time. We used a femtosecond pulsed laser whose center wavelength and duration were 800 nm and {approx}120 fs, respectively. A photo-conductor plastic hologram was used as a rewritable holographic material. The femtosecond light pulse was collimated and obliquely incident to the diffuser plate. The behavior of the cross-section between the collimated femtosecond light pulse and the diffuser plate was recorded on the photo-conductor plastic hologram. We experimentally obtained a spatially and temporally continuous moving picture of the femtosecond light pulse propagation for 58.3 ps. Meanwhile, we also investigated the rewritable performance of the photo-conductor plastic hologram. As a result, we confirmed that ten-time rewriting was possible for a photo-conductor plastic hologram.

  19. Bistable mode of THG for femtosecond laser pulse

    Science.gov (United States)

    Trofimov, Vyacheslav A.; Sidorov, Pavel S.; Kuchik, Igor E.

    2016-09-01

    We develop an analytical solution for the THG problem with taking into account self- and cross- modulation of interacting waves. Consideration is made in the framework of long pulse duration approximation and plane wave approximation. Using the original approach, we obtain the explicit solution of Schrödinger equations describing the THG in the framework under consideration both for zero-value amplitude of a wave with triple frequency and for its non-zero value. It should be stressed that the main feature of our approach consists in conservation laws using, which correspond to wave interaction process. We found various regimes of frequency trebling and showed that the THG process possesses a bistable feature under certain condition. We found out also the THG mode, at which the intensities of interacting waves do not change along their propagation coordinate. This leads to existence of soliton solution for THG of femtosecond laser pulses.

  20. Heat effects of metals ablated with femtosecond laser pulses

    Science.gov (United States)

    Hirayama, Yoichi; Obara, Minoru

    2002-09-01

    Heat effects of metallic bulk crystals of Au, Ag, Cu, and Fe ablated with femtosecond Ti:sapphire laser pulses is experimentally studied. As a result of X-ray diffraction (XRD) measurements, the XRD peak signal of the area ablated with Ti:sapphire laser is much smaller than that of the crystalline metal sample. While the crystal form of the metal sample is crystalline before laser ablation, the crystal form in the ablated area is partially changed into the amorphous form. The residual pulse energy that did not contribute to the ablation process remains, which leads to the formation of thin layer of melted phase. The melted layer is abruptly cooled down not to be re-crystallized, but to transform into amorphous form. It is evident that the area ablated with femtosecond laser is changed into amorphous metals. This mechanism would be the same as the melt-quenching generally used as the fabrication method of amorphous metals. This experimental result is consistent with the theoretical result.

  1. Compression of Electron Pulses for Femtosecond Electron Diffraction

    Science.gov (United States)

    Zandi, Omid; Yang, Jie; Centurion, Martin

    2014-05-01

    Our goal is to improve the temporal resolution in electron diffraction experiments to 100 fs by compressing the electron pulses using a time-varying electric field. The compressed pulse can be used for a better understanding of the dynamics of molecules under study. A bunch of 3 million electrons is generated at a photocathode by femtosecond UV laser pulses and accelerated to 100 keV in a static electric field. Then, the longitudinal component of the electric field of a microwave cavity is employed to compress the bunch. The cavity's frequency and phase are accurately tuned in such a way that the electric field is parallel to the bunch motion at its arrival and antiparallel to it at its exit. Compression in the transverse directions is done by magnetic lenses. Simulations have been done to predict the bunch profile at different positions and times by General Particle Tracer code. A streak camera has been built to measure the duration of the pulses. It uses the electric field of a discharging parallel plate capacitor to rotate the bunch so that angular spreading of the bunch is proportional to its duration. The capacitor is discharged by a laser pulse incident on a photo switch.

  2. Self-Referenced Spectral Interferometry for Femtosecond Pulse Characterization

    Directory of Open Access Journals (Sweden)

    Xiong Shen

    2017-04-01

    Full Text Available Since its introduction in 2010, self-referenced spectral interferometry (SRSI has turned out to be an analytical, sensitive, accurate, and fast method for characterizing the temporal profile of femtosecond pulses. We review the underlying principle and the recent progress in the field of SRSI. We present our experimental work on this method, including the development of self-diffraction (SD effect-based SRSI (SD-SRSI and transient-grating (TG effect-based SRSI (TG-SRSI. Three experiments based on TG-SRSI were performed: (1 We built a simple TG-SRSI device and used it to characterize a sub-10 fs pulse with a center wavelength of 1.8 μm. (2 On the basis of the TG effect, we successfully combined SRSI and frequency-resolved optical gating (FROG into a single device. The device has a broad range of application, because it has the advantages of both SRSI and FROG methods. (3 Weak sub-nanojoule pulses from an oscillator were successfully characterized using the TG-SRSI device, the optical setup of which is smaller than the palm of a hand, making it convenient for use in many applications, including sensor monitoring the pulse profile of laser systems. In addition, the SRSI method was extended for single-shot characterization of the temporal contrast of ultraintense and ultrashort laser pulses.

  3. Spatiotemporal vector pulse shaping of femtosecond laser pulses with a multi-pass two-dimensional spatial light modulator.

    Science.gov (United States)

    Esumi, Y; Kabir, M D; Kannari, F

    2009-10-12

    A novel non-interferometric vector pulse-shaping scheme is developed for femtosecond laser pulses using a two-dimensional spatial light modulator (2D-SLM). By utilizing spatiotemporal pulse shaping obtainable by the 2D-SLM, we demonstrate spatiotemporal vector pulse shaping for the first time.

  4. Filamentation of arbitrary polarized femtosecond laser pulses in case of high-order Kerr effect.

    Science.gov (United States)

    Panov, Nikolay A; Makarov, Vladimir A; Fedorov, Vladimir Y; Kosareva, Olga G

    2013-02-15

    We developed a model of femtosecond filamentation which includes high-order Kerr effect and an arbitrary polarization of a laser pulse. We show that a circularly polarized pulse has maximum filament intensity. Also, we show that, independently of the initial pulse polarization, the value of a maximum filament intensity tends to the maximum intensity of either linearly or circularly polarized pulse.

  5. Elongation of plasma channel generated by temporally shaped femtosecond laser pulse

    Science.gov (United States)

    Chen, Anmin; Li, Suyu; Qi, Hongxia; Jiang, Yuanfei; Hu, Zhan; Huang, Xuri; Jin, Mingxing

    2017-01-01

    Temporally shaped femtosecond laser pulse is used to generate the air plasma channel. The length of plasma channel is optimized by a genetic algorithm. Compared with the transform-limited pulse, the temporally shaped femtosecond laser produced by the spatial light modulator with the genetic algorithm can lead to a significant increase in length and brightness of plasma channel in atmosphere. In particular, the length of the plasma channel produced by the optimized shaped pulse can be extended by 50%. This method can be especially advantageous in the context of femtosecond laser-induced plasma channel.

  6. Spatiotemporal reshaping and compression of high intensity femtosecond pulses

    Science.gov (United States)

    Trunov, V. I.; Pestryakov, E. V.; Petrov, V. V.; Kirpichnikov, A. V.; Frolov, S. A.; Harenko, D. S.; Bagayev, S. N.

    2007-06-01

    Experimental results of self-compression of femtosecond pulses under filamentation in argon and xenon are presented. The mode of a self-compression in xenon is realized for the first time. The dependence of the spectrum broadening from pressure of these gases, input energy and focusing parameters are studied in detail. The spectral and temporary profiles of the first and the second filaments at multiple filamentation are analyzed. Features of multiple filamentation are revealed in xenon. For the first time experimentally the effect of restriction a number of filaments and effective swapping of energy from one filament to another (more than 70 % of energy in two-filament mode without increasing of their amount is founded). The possible mechanism of the phenomenon related with the saturation of the third order nonlinearity in xenon and influence of the higher fifth-order susceptibility χ (5) are discussed.

  7. Femtosecond laser pulse induced desorption: A molecular dynamics simulation

    Energy Technology Data Exchange (ETDEWEB)

    Lončarić, Ivor, E-mail: ivor.loncaric@gmail.com [Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), P. Manuel de Lardizabal 5, 20018 San Sebastián (Spain); Alducin, Maite [Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), P. Manuel de Lardizabal 5, 20018 San Sebastián (Spain); Donostia International Physics Center DIPC, P. Manuel de Lardizabal 4, 20018 San Sebastián (Spain); Saalfrank, Peter [Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam (Germany); Donostia International Physics Center DIPC, P. Manuel de Lardizabal 4, 20018 San Sebastián (Spain); Juaristi, J. Iñaki [Departamento de Física de Materiales, Facultad de Químicas, Universidad del País Vasco (UPV/EHU), Apartado 1072, 20080 San Sebastián (Spain); Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), P. Manuel de Lardizabal 5, 20018 San Sebastián (Spain); Donostia International Physics Center DIPC, P. Manuel de Lardizabal 4, 20018 San Sebastián (Spain)

    2016-09-01

    In recent simulations of femtosecond laser induced desorption of molecular oxygen from the Ag(110) surface, it has been shown that depending on the properties (depth and electronic environment) of the well in which O{sub 2} is adsorbed, the desorption can be either induced dominantly by hot electrons or via excitations of phonons. In this work we explore whether the ratios between the desorption yields from different adsorption wells can be tuned by changing initial surface temperature and laser pulse properties. We show that the initial surface temperature is an important parameter, and that by using low initial surface temperatures the electronically mediated process can be favored. In contrast, laser properties seem to have only a modest influence on the results.

  8. Microstructuring of Steel and Hard Metal using Femtosecond Laser Pulses

    Science.gov (United States)

    Pfeiffer, Manuel; Engel, Andy; Weißmantel, Steffen; Scholze, Stefan; Reisse, Guenter

    New results on three-dimensional micro-structuring of tungsten carbide hard metal and steel using femtosecond laser pulses will be presented. For the investigations, a largely automated high-precision fs-laser micromachining station was used. The fs-laser beam is focused onto the sample surface using different objectives. The investigations of the ablation behaviour of the various materials in dependence of the laser processing parameters will be presented. In the second part, complex 3D microstructures with a variety of geometries and resolutions down to a few micrometers will be presented. On of the Goal of these investigations was to create defined microstructures in tooling equipments such as cutting inserts.

  9. Pulse reshaping in nearly resonant interaction of femtosecond pulses with dense rubidium vapor

    Science.gov (United States)

    Vdović, Silvije; Skenderović, Hrvoje; Pichler, Goran

    2016-07-01

    Propagation of intense femtosecond pulses resonant with the atomic rubidium vapor results in phenomenon known as conical emission. The origin of this phenomenon is connected with self-phase modulation in time domain accompanied with spatial self-focusing for blue-detuned pulses. When the laser central wavelength is red-detuned the self-defocusing occurs. Using frequency-resolved optical gating measurements and simple modeling of pulse propagation within the linear dispersion theory it is shown that the retrieved phase of the propagated pulse, and the associated instantaneous frequency, shows evidence of both linear dispersion and self-phase modulation. These results are consistent with the theory of the intensity dependent nonlinear refraction index in medium where linear dispersion contributes significantly to pulse reshaping.

  10. Femtosecond photoelectron and photoion spectrometer with vacuum ultraviolet probe pulses

    CERN Document Server

    Koch, Markus; Grilj, Jakob; Sistrunk, Emily; Gühr, Markus

    2014-01-01

    We describe a setup to study ultrafast dynamics in gas-phase molecules using time-resolved photoelectron and photoion spectroscopy. The vacuum ultraviolet (VUV) probe pulses are generated via strong field high-order harmonic generation from infrared femtosecond laser pulses. The band pass characteristic in transmission of thin indium (In) metal foil is exploited to isolate the $9^{\\text{th}}$ harmonic of the 800 nm fundamental (H9, 14 eV, 89 nm) from all other high harmonics. The $9^{\\text{th}}$ harmonic is obtained with high conversion efficiencies and has sufficient photon energy to access the complete set of valence electron levels in most molecules. The setup also allows for direct comparison of VUV single-photon probe with 800 nm multi-photon probe without influencing the delay of excitation and probe pulse or the beam geometry. We use a magnetic bottle spectrometer with high collection efficiency for electrons, serving at the same time as a time of flight spectrometer for ions. Characterization measurem...

  11. Nanodissection of human chromosomes with near-infrared femtosecond laser pulses.

    Science.gov (United States)

    König, K; Riemann, I; Fritzsche, W

    2001-06-01

    Near-infrared laser pulses of a compact 80-MHz femtosecond laser source at 800 nm, a mean power of 15-100 mW, 170-fs pulse width, and millisecond beam dwell times at the target have been used for multiphoton-mediated nanoprocessing of human chromosomes. By focusing of the laser beam with high-numerical-aperture objectives of a scanning microscope to diffraction-limited spots and with light intensities of terawatts per cubic centimeter, precise submicrometer holes and cuts in human chromosomes have been processed by single-point exposure and line scans. A minimum FWHM cut size of ~100 nm during a partial dissection of chromosome 1, which is below the diffraction-limited spot size, and a minimum material removal of ~0.003mum (3) were determined by a scanning-force microscope. The plasma-induced ablated material corresponds to ~1/400 of the chromosome 1 volume and to ~65x10(3) base pairs of chromosomal DNA. A complete dissection could be performed with FWHM cut sizes below 200 nm. High-repetition-frequency femtosecond lasers at low mean power in combination with high-numerical-aperture focusing optics appear therefore as appropriate noncontact tools for nanoprocessing of bulk and (or) surfaces of transparent materials such as chromosomes. In particular, the noninvasive inactivation of certain genomic regions on single chromosomes within living cells becomes possible.

  12. Vibration measurement based on the optical cross-correlation technique with femtosecond pulsed laser

    Science.gov (United States)

    Han, Jibo; Wu, Tengfei; Zhao, Chunbo; Li, Shuyi

    2016-10-01

    Two vibration measurement methods with femtosecond pulsed laser based on the optical cross-correlation technique are presented independently in this paper. The balanced optical cross-correlation technique can reflect the time jitter between the reference pluses and measurement pluses by detecting second harmonic signals using type II phase-matched nonlinear crystal and balanced amplified photo-detectors. In the first method, with the purpose of attaining the vibration displacement, the time difference of the reference pulses relative to the measurement pluses can be measured using single femtosecond pulsed laser. In the second method, there are a couple of femtosecond pulsed lasers with high pulse repetition frequency. Vibration displacement associated with cavity length can be calculated by means of precisely measuring the pulse repetition frequency. The results show that the range of measurement attains ±150μm for a 500fs pulse. These methods will be suited for vibration displacement measurement, including laboratory use, field testing and industrial application.

  13. Phototransfection of mammalian cells using femtosecond laser pulses: optimization and applicability to stem cell differentiation

    CSIR Research Space (South Africa)

    Mthunzi, P

    2010-07-01

    Full Text Available Recently, femtosecond laser pulses have been utilized for the targeted introduction of genetic matter into mammalian cells. This rapidly expanding and developing novel optical technique using a tightly focused laser light beam is called...

  14. Acoustic Diagnostics of Plasma Channels Induced by Intense Femtosecond Laser Pulses in Air

    Institute of Scientific and Technical Information of China (English)

    HAO Zuo-Qiang; WEI Zhi-Yi; YU Jin; ZHANG Jie; LI Yu-Tong; YUAN Xiao-Hui; ZHENG Zhi-Yuan; WANG Peng; WANG Zhao-Hua; LING Wei-Jun

    2005-01-01

    @@ Long plasma channels induced by femtosecond laser pulses in air are diagnosed using the sonographic method. By detecting the sound signals along the channels, the length and the electron density of the channels are measured.

  15. The theory study of Metal absorptivity in femtosecond pulsed laser ablation

    Institute of Scientific and Technical Information of China (English)

    LI Li; ZHANG Duan-ming; LI Zhi-hua; TAN Xin-yu; FANG Ran-ran

    2007-01-01

    In this paper,the effect of the absorptivity of metal on femtosecond pulsed laser ablation is investigated.The formulas for the absorptivity depending on target temperature are derived from Maxwell Equations and the Lambert-Beer's law.Based on this,a new two-temperature model is proposed to describe the femtosecond pulsed laser ablation with metal.Then,using Au as an example,a finite difference method is employed to simulate the space-dependent and time-dependent absorptivity and the target temperature.The temperature evolution of our model is compared with the result obtained form the heat conduction model taking the absorptivity as constant.It is shown that the absorptivity plays an important role in the femtosecond pulsed laser ablation.The results of this paper are helpful in choosing the best technical parameters in femtosecond pulsed laser ablation.

  16. Analysis of THG modes for femtosecond laser pulse

    Science.gov (United States)

    Trofimov, Vyacheslav A.; Sidorov, Pavel S.

    2017-05-01

    THG is used nowadays in many practical applications such as a substance diagnostics, and biological objects imaging, and etc. With developing of new materials and technology (for example, photonic crystal) an attention to THG process analysis grow. Therefore, THG features understanding are a modern problem. Early we have developed new analytical approach based on using the problem invariant for analytical solution construction of the THG process. It should be stressed that we did not use a basic wave non-depletion approximation. Nevertheless, a long pulse duration approximation and plane wave approximation has applied. The analytical solution demonstrates, in particular, an optical bistability property (and may other regimes of frequency tripling) for the third harmonic generation process. But, obviously, this approach does not reflect an influence of a medium dispersion on the frequency tripling. Therefore, in this paper we analyze THG efficiency of a femtosecond laser pulse taking into account a second order dispersion affect as well as self- and crossmodulation of the interacting waves affect on the frequency conversion process. Analysis is made using a computer simulation on the base of Schrödinger equations describing the process under consideration.

  17. Simulation of Femtosecond Pulse Propagation through Hollow Fibre Filled with Noble Gases of Gradient Temperature

    Institute of Scientific and Technical Information of China (English)

    SONG Zhen-Ming; ZHANG Guang-Xiao; CAO Shi-Ying; PANG Dong-Qing; CHAI Lu; WANG Qing-Yue; ZHANG Zhi-Gang

    2008-01-01

    We propose a novel technique for generating intense few to mono-cycle femtosecond pulses.The simulation demonstrate that for the temperature difference of 300K,the spectrum of the output pulses is increased by 67%and the transform limited pulse width is reduced almost by half,compared with those obtained with hollow fibres in uniform temperature.

  18. Numerical simulation for characterizing femtosecond optical pulses with the SPIDER algorithm

    Institute of Scientific and Technical Information of China (English)

    Chai Lu; He Tie-Ying; Gao Feng; Wang Qing-Yue; Xing Qi-Rong; Zhang Zhi-Gang

    2004-01-01

    In this article based on the spectral phase interferometry for direct electric-field reconstruction (SPIDER), the femtosecond pulses with various phase characters are numerically simulated. The spectral phases and amplitudes of the transform-limited pulse, the linear chirped pulse, the cubic dispersion pulse, the quartic dispersion pulse, the self-phase modulation pulse and the pulses with the combination of different chirped characters are retrieved. These characterized pulses are applicable to the real-time measurement as samples for diagnosing the chirped characters of pulses quickly.

  19. Micrograting Polymerization Fabrication with a Single Femtosecond Laser Pulse at 400 nm Wavelength

    Institute of Scientific and Technical Information of China (English)

    郭红沧; 郭亨长; 蒋红兵; 杨宏; 龚旗煌; 王涛; 施盟泉; 吴飞鹏

    2003-01-01

    High diffraction efficiency refractive index-modulated holographic micrograting on a polymer thin film was obtained with a single femtosecond laser pulse interference and photo-polymerization. The diffractive efficiency of the micrograting with an He-Ne laser is up to 78% when the thickness of the film is 90 μm, which corresponds to the refractive index-modulation as large as 2.4 × 10-3. The compared experiment with a femtosecond oscillator laser indicated that a single femtosecond Iaser pulse has the advantages in laser machining over the cw holography method such as high fabrication speed, good surface structure and high diffractive efficiency.

  20. Pulse propagation near zero group-velocity dispersion in a femtosecond dye laser.

    Science.gov (United States)

    Salin, F; Grangier, P; Georges, P; Brun, A

    1990-12-01

    The propagation of femtosecond pulses in a colliding-pulse mode-locked dye laser near zero group-velocity dispersion is studied. The pulse spectrum is shown to exhibit a double-peak structure. This structure and its dependence on the intracavity dispersion can be explained by nonlinear pulse propagation near zero dispersion. A value for the third-order dispersion of the laser cavity is deduced and is found to be predominant for pulses shorter than 50 fsec.

  1. Compression of 1030-nm femtosecond pulses after nonlinear spectral broadening in Corning® HI 1060 fiber: Theory and experiment

    Directory of Open Access Journals (Sweden)

    Michael E. Reilly

    2015-12-01

    Full Text Available We present the design and implementation of femtosecond pulse compression at 1030 nm based on spectral broadening in single-mode fiber, followed by dispersion compensation using an optimized double-pass SF11 prism pair. The source laser produced 1030-nm 144-fs pulses which were coupled into Corning® HI 1060 fiber, whose length was chosen to be 40 cm by using a pulse propagation model based on solving the generalized nonlinear Schrödinger equation. A maximum broadening to 60-nm bandwidth was obtained, following which compression to 60 ± 3 fs duration was achieved by using a prism-pair separation of 1025 ± 5 mm.

  2. Effects of cavity-dispersion noncoaxiality on the generation of ultrabroadband femtosecond pulses

    Institute of Scientific and Technical Information of China (English)

    JIAO ZhongXing; LEI Liang; HUANG ZhiLing; WEN JinHui; LAI Tianshu; LIN WeiZhu

    2008-01-01

    The effects of cavity-dispersion noncoaxiality (CDN) on the generation of ultrabroadband femtosecond pulses in KLM Ti:sapphire laser were investigated theoretically and experimentally. It was predicted that when the laser sub-cavity works near the coaxial operation point, the limitation of CDN on the bandwidth broadening is minimum, which is favorable for ultrabroadband pulse generation. On the basis of this prediction, femtosecond pulses with bandwidth of 650 to 1000 nm were directly generated from a home built KLM Ti:sapphire laser. To our knowledge, they are the broadest bandwidth pulses produced from KLM Ti:sapphire laser with similar oscillator configuration and gain crystal length of 3 mm.

  3. Efficient femtosecond mid-infrared pulse generation by dispersivewave radiation in bulk lithium niobate crystal

    DEFF Research Database (Denmark)

    Zhou, Binbin; Guo, Hairun; Bache, Morten

    2014-01-01

    We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave radiation in bulk lithium niobate crystal. Femtosecond mid-IR pulses centering from 2.8–2.92 µm are generated using the single pump wavelengths from 1.25–1.45 µm.......We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave radiation in bulk lithium niobate crystal. Femtosecond mid-IR pulses centering from 2.8–2.92 µm are generated using the single pump wavelengths from 1.25–1.45 µm....

  4. Investigation of interaction femtosecond laser pulses with skin and eyes mathematical model

    Science.gov (United States)

    Rogov, P. U.; Smirnov, S. V.; Semenova, V. A.; Melnik, M. V.; Bespalov, V. G.

    2016-08-01

    We present a mathematical model of linear and nonlinear processes that takes place under the action of femtosecond laser radiation on the cutaneous covering. The study is carried out and the analytical solution of the set of equations describing the dynamics of the electron and atomic subsystems and investigated the processes of linear and nonlinear interaction of femtosecond laser pulses in the vitreous of the human eye, revealed the dependence of the pulse duration on the retina of the duration of the input pulse and found the value of the radiation power density, in which there is a self-focusing is obtained. The results of the work can be used to determine the maximum acceptable energy, generated by femtosecond laser systems, and to develop Russian laser safety standards for femtosecond laser systems.

  5. Nonadiabatic Induced Dipole Moment by High Intensity Femtosecond Optical Pulses

    OpenAIRE

    Koprinkov, I. G.

    2006-01-01

    Nonadiabtic dressed states and nonadiabatic induced dipole moment in the leading order of nonadiabaticity is proposed. The nonadiabatic induced dipole moment is studied in the femtosecond time domain.

  6. Study on impurity desorption induced by femtosecond pulse laser based on a stochastic process model

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    With the advantages on non-equilibrium heating and desorption induced by electronic transition, the femtosecond pulse laser introduces a new way for solving the problem of impurity pollution adsorbed on a solid thin film in micro-electro-mechanical systems (MEMS). A model based on stochastic processes was established for stimulated desorption induced by the femtosecond pulse laser to interpret the interaction of the optically excited hot electrons with the adsorbed molecules in a metal substrate. Numerical simulation results reveal a time-dependent desorption probability of adsorbed molecules and indicate that how key parameters of femtosecond pulse laser, such as incident laser energy flux, pulse duration, and wavelength of pulse, have a great effect on the desorption probability.

  7. Laser ranging by time-of-flight measurement of femtosecond light pulses

    Science.gov (United States)

    Kim, Young-Jin

    2014-04-01

    Time-of-flight (TOF) measurement of femtosecond light pulses was investigated for laser ranging of long distances with sub-micrometer precision in the air. The bandwidth limitation of the photo-detection electronics used in timing femtosecond pulses was overcome by adopting a type-II nonlinear second-harmonic crystal that permits producing the balanced optical cross-correlation signal between two overlapped light pulses. This method offered a sub-femtosecond timing resolution in determining the temporal offset between two pulses through lock-in control of the pulse repetition rate with reference to the atomic clock. The exceptional ranging capability was verified by measuring various distances from 1.5 m to 700 m. This method is found suited for terrestrial land surveying and space missions of formation-flying satellites.

  8. High precision laser ranging by time-of-flight measurement of femtosecond pulses

    Science.gov (United States)

    Lee, Joohyung; Lee, Keunwoo; Lee, Sanghyun; Kim, Seung-Woo; Kim, Young-Jin

    2012-06-01

    Time-of-flight (TOF) measurement of femtosecond light pulses was investigated for laser ranging of long distances with sub-micrometer precision in the air. The bandwidth limitation of the photo-detection electronics used in timing femtosecond pulses was overcome by adopting a type-II nonlinear second-harmonic crystal that permits the production of a balanced optical cross-correlation signal between two overlapping light pulses. This method offered a sub-femtosecond timing resolution in determining the temporal offset between two pulses through lock-in control of the pulse repetition rate with reference to the atomic clock. The exceptional ranging capability was verified by measuring various distances of 1.5, 60 and 700 m. This method is found well suited for future space missions based on formation-flying satellites as well as large-scale industrial applications for land surveying, aircraft manufacturing and shipbuilding.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-08-15

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

  10. The Effect of Chirped Intense Femtosecond Laser Pulses on the Argon Cluster

    Directory of Open Access Journals (Sweden)

    H. Ghaforyan

    2016-01-01

    Full Text Available The interaction of intense femtosecond laser pulses with atomic Argon clusters has been investigated by using nanoplasma model. Based on the dynamic simulations, ionization process, heating, and expansion of a cluster after irradiation by femtosecond laser pulses at intensities up to 2 × 1017 Wcm−2 are studied. The analytical calculation provides ionization rate for different mechanisms and time evolution of the density of electrons for different pulse shapes. In this approach, the strong dependence of laser intensity, pulse duration, and laser shape on the electron energy, the electron density, and the cluster size is presented using the intense chirped laser pulses. Based on the presented theoretical modifications, the effect of chirped laser pulse on the complex dynamical process of the interaction is studied. It is found that the energy of electrons and the radius of cluster for the negatively chirped pulses are improved up to 20% in comparison to the unchirped and positively chirped pulses.

  11. Generation of 25-TW Femtosecond Laser Pulses at 515 nm with Extremely High Temporal Contrast

    Directory of Open Access Journals (Sweden)

    Marco Hornung

    2015-12-01

    Full Text Available We report on the frequency doubling of femtosecond laser pulses at 1030 nm center wavelength generated from the fully diode-pumped laser system POLARIS. The newly generated pulses at a center wavelength of 515 nm have a pulse energy of 3 J with a pulse duration of 120 fs. On the basis of initially ultra-high contrast seed pulses we expect a temporal intensity contrast better 10 17 200 ps before the peak of the main pulse. We analyzed the temporal intensity contrast from milliseconds to femtoseconds with a dynamic range covering more than 20 orders of magnitude. The pulses were focussed with a f/2-focussing parabola resulting in a peak intensity exceeding 10 20 W / cm 2 . The peak power and intensity are to the best of our knowledge the highest values for 515 nm-laser-pulses achieved so far.

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

    Institute of Scientific and Technical Information of China (English)

    WANG He-Lin; YANG Ai-Jun; LENG Yu-Xin

    2011-01-01

    A high-average-power diode-pumped narrowband regenerative chirped pulse amplifier is developed using the thin-rod Nd:YAG laser architecture for optical parametric chirped-pulse amplification (OPCPA).The effect of the etalons on the amplified pulse in the regenerative cavity is studied experimentally and theoretically.By inserting glass etalons of thickness 1 mm and 5 mm into the regenerative cavity,the pre-stretching pulse from an (O)ffner stretcher is further broadened to above 200ps,which matches the amplification windows of the signal pulses in OPCPA and is suitable for use as a pump source in the OPCPA system.The bandwidth of the amplified pulse is 1.5 nm,and an output energy of 2mJ is achieved at a repetition rate of 10 Hz.Optical parametric chirped pulse amplification (OPCPA)[1-4] has attracted a great deal of attention as the most promising technique for generating ultrashort ultrahigh-peak-power laser pulses because of its very broad gain bandwidth,negligible thermal load on the nonlinear crystal,and extremely high singlepass gain as compared to amplifiers based on laser gain media.For efficient amplification and high fidelity of dispersion compensation in OPCPA,a femtosecond seed pulse is first stretched to several tens of picoseconds with a bulk grating stretcher or a fiber stretcher.%A high-average-power diode-pumped narrowband regenerative chirped pulse amplifier is developed using the thin-rod Nd:YAG laser architecture for optical parametric chirped-pulse amplification (OPCPA). The effect of the etalons on the amplified pulse in the regenerative cavity is studied experimentally and theoretically. By inserting glass etalons of thickness 1 mm and 5 mm into the regenerative cavity, the pre-stretching pulse from an (O)finer stretcher is further broadened to above 200 ps, which matches the amplification windows of the signal pulses in OPCPA and is suitable for use as a pump source in the OPCPA system. The bandwidth of the amplified pulse is 1.5 nm, and an

  13. Electronically driven adsorbate excitation mechanism in femtosecond-pulse laser desorption

    DEFF Research Database (Denmark)

    Brandbyge, Mads; Hedegård, Per; Heinz, T. F.

    1995-01-01

    Femtosecond-pulse laser desorption is a process in which desorption is driven by a subpicosecond temperature pulse of order 5000 K in the substrate-adsorbate electron system, whose energy is transferred into the adsorbate center-of-mass degrees of freedom by a direct coupling mechanism. We presen...

  14. The effect of chirped intense femtosecond laser pulses on the Argon cluster

    CERN Document Server

    Ghaforyan, H; Irani, E

    2016-01-01

    The interaction of intense femtosecond laser pulses with atomic Argon clusters has been investigated by using nano-plasma model. Based on the dynamic simulations, ionization process, heating and expansion of a cluster after irradiation by femtosecond laser pulses at intensities up to 2*1017 Wcm-2 are studied. The analytical calculation provides ionization ratefor different mechanisms and time evolution of the density of electrons for different pulse shapes. In this approach the strong dependence of laser intensity, pulse duration and laser shape on the electron energy, the electron density and the cluster size are presented using the intense chirped laser pulses. Based on the presented theoretical modifications, the effect of chirped laser pulse on the complex dynamical process of the interaction is studied. It is found that the energy of electrons and the radius of cluster for the negatively chirped pulsesare improved up to 20% in comparison to the unchirped and positively chirped pulses.

  15. Double pulse laser-induced breakdown spectroscopy with femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Pinon, V. [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (IESL-FORTH), P.O. Box 1385, GR 71110 Heraklion, Crete (Greece); Universidad de A Coruna, Departamento de Ingenieria Industrial II, E-15403 Ferrol, A Coruna (Spain); Fotakis, C. [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (IESL-FORTH), P.O. Box 1385, GR 71110 Heraklion, Crete (Greece); Nicolas, G. [Universidad de A Coruna, Departamento de Ingenieria Industrial II, E-15403 Ferrol, A Coruna (Spain); Anglos, D. [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (IESL-FORTH), P.O. Box 1385, GR 71110 Heraklion, Crete (Greece)], E-mail: anglos@iesl.forth.gr

    2008-10-15

    This paper presents results obtained in a study of collinear geometry double pulse femtosecond LIBS analysis of solids in ambient environment. LIBS signal enhancement of 3-10 fold, accompanied by significant improvement of signal reproducibility, in comparison with the single pulse case, has been found in different samples such as brass, iron, silicon, barium sulfate and aluminum when an optimum temporal separation between the two ablating pulses is used. The influence of the delay between pulses in the LIBS signal intensity was investigated and two intervals of interaction were established. A first transient regime from 0 to 50 ps, in which the LIBS signal increases until reaching a maximum, and a second regime that ranges from 50 to 1000 ps (maximum inter-pulse delay investigated) in which the signal enhancement remains constant. Emissions from both ionized and neutral atoms show the same pattern of enhancement with a clear tendency of lines arising from higher energy emissive states to exhibit higher enhancement factors.

  16. Optical data storage in nonphotosensitive media by femtosecond laser pulses

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Ultrashort lasers have become powerful tools by inducing extremely nonlinear effects in a wide variety of materials.Femtosecond laser data storage in non-photosensitive media is promising for its high density and fast retrieval. We reviewed the progress of three types of femtosecond laser storage in transparent materials: three-dimensional bit-oriented storage by micro-voids, holographic data storage by two beam interference and storage by computer-generated holograms.

  17. Effect of high-power nanosecond and femtosecond laser pulses on silicon nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Kachurin, G. A., E-mail: kachurin@isp.nsc.ru; Cherkova, S. G.; Volodin, V. A.; Marin, D. V. [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Deutschmann, M. [Laser Zentrum Hannover (Germany)

    2008-02-15

    The effect of high-power nanosecond (20 ns) and femtosecond (120 fs) laser pulses on silicon nanostructures produced by ion-beam-assisted synthesis in SiO{sub 2} layers or by deposition onto glassy substrates is studied. Nanosecond annealing brings about a photoluminescence band at about 500 mn, with the intensity increasing with the energy and number of laser pulses. The source of the emission is thought to be the clusters of Si atoms segregated from the oxide. In addition, the nanosecond pulses allow crystallization of amorphous silicon nanoprecipitates in SiO{sub 2}. Heavy doping promotes crystallization. The duration of femtosecond pulses is too short for excess Si to be segregated from SiO{sub 2}. At the same time, such short pulses induce crystallization of Thin a-Si films on glassy substrates. The energy region in which crystallization is observed for both types of pulses allows short-term melting of the surface layer.

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

    Science.gov (United States)

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

    2006-05-29

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

  19. On e(+)e(-) pair production by colliding electromagnetic pulses

    NARCIS (Netherlands)

    Narozhny, NB; Bulanov, SS; Mur, VD; Popov, VS

    2004-01-01

    Electron-positron pair production from vacuum in an electromagnetic field created by two counterpropagating focused laser pulses interacting with each other is analyzed. The dependence of the number of produced pairs on the intensity of a laser pulse and the focusing parameter is studied with a real

  20. Generation, temporal characterization and applications of femtosecond-/ attosecond extreme ultraviolet pulses

    Science.gov (United States)

    Thomann, Isabell

    The work of this thesis is arranged into three parts: (A) Generation and temporal characterization of extreme ultraviolet (EUV) attosecond pulses. In this work I present the generation and first temporal characterization of sub-optical cycle EUV radiation generated in a noble-gas filled hollow-core waveguide. Two regimes of EUV radiation were characterized, ranging from 200 attoseconds to ˜ 1 femtosecond in duration. The first regime that was characterized distinguishes itself from EUV radiation generated by other methods by its narrow (˜ 1 eV) spectral width, its simple energy tunability and its temporal confinement to ˜ 1 femtosecond. In the second regime, single isolated pulses of 200 attoseconds duration (and accordingly larger bandwidth) were generated. In both regimes dynamic phase-matching effects create an extremely short time window within which efficient nonlinear conversion is possible, while it is suppressed outside this window. Temporal characterization of the generated EUV pulses was approached by two-color pump-probe photoelectron spectroscopy. Therefore an efficient photoelectron spectrometer was set up, detecting electrons in a 2pi collection angle. For the interpretation of the experimental data, an analytical model as well as an iterative algorithm were developed, to allow extraction of complex EUV waveforms. The demonstrated radiation will allow for time-resolved studies of the fastest processes in molecules and condensed matter, while at the same time ensuring adequate energy resolution for addressing individual electronic states. (B) Application of a COLTRIMS reaction microscope in combination with femtosecond EUV pulses to questions in molecular physics. The combination of the sensitive detection capabilities of a COLTRIMS reaction microscope with the high time resolution of pump-probe experiments using femtosecond extreme-ultraviolet pulses makes it possible to answer very fundamental open questions in molecular physics such as the

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

    Energy Technology Data Exchange (ETDEWEB)

    Danilov, P A; Zayarnyi, D A; Ionin, A A; Kudryashov, S I; Makarov, S V; Rudenko, A A; Saraeva, I N; Yurovskikh, V I [P N Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Lednev, V N; Pershin, S M [A M Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

    2015-05-31

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

  2. Wavelength-dependent femtosecond pulse amplification in wideband tapered-waveguide quantum well semiconductor optical amplifiers.

    Science.gov (United States)

    Xia, Mingjun; Ghafouri-Shiraz, H

    2015-12-10

    In this paper, we study the wavelength-dependent amplification in three different wideband quantum well semiconductor optical amplifiers (QWAs) having conventional, exponentially tapered, and linearly tapered active region waveguide structures. A new theoretical model for tapered-waveguide QWAs considering the effect of lateral carrier density distribution and the strain effect in the quantum well is established based on a quantum well transmission line modeling method. The temporal and spectral characteristics of amplified femtosecond pulse are analyzed for each structure. It was found that, for the amplification of a single femtosecond pulse, the tapered-waveguide QWA provides higher saturation gain, and the output spectra of the amplified pulse in all three structures exhibit an apparent redshift and bandwidth narrowing due to the reduction of carrier density; however, the output spectrum in the tapered-waveguide amplifier is less distorted and exhibits smaller bandwidth narrowing. For the simultaneous amplification of two femtosecond pulses with different central frequencies, in all the three structures, two peaks appear in the output spectra while the peak at the frequency closer to the peak frequency of the QWA gain spectrum receives higher amplification due to the frequency (wavelength) dependence of the QWA gain. At a low peak power level of the input pulse, the bandwidth of each window in the tapered structure is larger than that of the conventional waveguide structure, which aggravates the spectrum alias in the amplification of femtosecond pulses with different central frequencies. As the peak powers of the two pulses increase, the spectrum alias in the conventional waveguide becomes more serious while there are small changes in the tapered structures. Also, we have found that in the amplification of a femtosecond pulse train, the linear-tapered QWAs exhibit the fastest gain recovery as compared with the conventional and exponentially tapered QWAs.

  3. Three-dimensional optical storage in fused silica using modulated femtosecond pulses

    Institute of Scientific and Technical Information of China (English)

    Qing Liu(刘青); Guanghua Cheng(程光华); Yishan Wang(王屹山); Zhao Cheng(程昭); Wei Zhao(赵卫); Guofu Chen(陈国夫)

    2004-01-01

    Three-dimensional bitwise optical recording with a density of 500 Gb/cm3 in fused silica using a Ti:sapphire femtosecond laser modulated by binary digits is demonstrated. Laser pulses modulation is realized by modulating two circuits of trigger pulses signal which are used to control laser pulses trapping and switching out from cavity, respectively. Bits are optically readout in both a parallel reading (phase-contrast) and a serial reading (confocal-type) methods. The method for modulating laser pulses can also be used in all of pulsed laser systems which operate in cavity-dumping configuration.

  4. The role of light-induced nanostructures in femtosecond laser micromachining with vector and scalar pulses.

    Science.gov (United States)

    Hnatovsky, Cyril; Shvedov, Vladlen G; Krolikowski, Wieslaw

    2013-05-20

    In this article we compare the results of micromachining of fused silica and silicon with tightly focused scalar (viz., circularly and linearly polarized) and vector (viz., azimuthally and radially polarized) femtosecond laser pulses. We show that drilling with radially polarized pulses produces holes with smoother and better-delineated walls compared with the other polarizations used, whereas linearly polarized pulses can machine 20-nm wide single grooves in fused silica when the electric field of the pulse is aligned perpendicular to the cutting direction. The observed polarization-controlled micromachining is due to the formation of sub-diffraction-limited nanostructures that are optically produced in the multi-pulse irradiation regime.

  5. Construction and characterization of ultraviolet acousto-optic based femtosecond pulse shapers

    Energy Technology Data Exchange (ETDEWEB)

    Mcgrane, Shawn D [Los Alamos National Laboratory; Moore, David S [Los Alamos National Laboratory; Greenfield, Margo T [Los Alamos National Laboratory

    2008-01-01

    We present all the information necessary for construction and characterization of acousto optic pulse shapers, with a focus on ultraviolet wavelengths, Various radio-frequency drive configurations are presented to allow optimization via knowledgeable trade-off of design features. Detailed performance characteristics of a 267 nm acousto-optic modulator (AOM) based pulse shaper are presented, Practical considerations for AOM based pulse shaping of ultra-broad bandwidth (sub-10 fs) amplified femtosecond pulse shaping are described, with particular attention paid to the effects of the RF frequency bandwidth and optical frequency bandwidth on the spatial dispersion of the output laser pulses.

  6. Understanding Femtosecond-Pulse Laser Damage through Fundamental Physics Simulations

    Science.gov (United States)

    Mitchell, Robert A., III

    It did not take long after the invention of the laser for the field of laser damage to appear. For several decades researchers have been studying how lasers damage materials, both for the basic scientific understanding of highly nonequilibrium processes as well as for industrial applications. Femtosecond pulse lasers create little collateral damage and a readily reproducible damage pattern. They are easily tailored to desired specifications and are particularly powerful and versatile tools, contributing even more industrial interest in the field. As with most long-standing fields of research, many theoretical tools have been developed to model the laser damage process, covering a wide range of complexities and regimes of applicability. However, most of the modeling methods developed are either too limited in spatial extent to model the full morphology of the damage crater, or incorporate only a small subset of the important physics and require numerous fitting parameters and assumptions in order to match values interpolated from experimental data. Demonstrated in this work is the first simulation method capable of fundamentally modeling the full laser damage process, from the laser interaction all the way through to the resolidification of the target, on a large enough scale that can capture the full morphology of the laser damage crater so as to be compared directly to experimental measurements instead of extrapolated values, and all without any fitting parameters. The design, implementation, and testing of this simulation technique, based on a modified version of the particle-in-cell (PIC) method, is presented. For a 60 fs, 1 mum wavelength laser pulse with fluences of 0.5 J/cm 2, 1.0 J/cm2, and 2.0 J/cm2 the resulting laser damage craters in copper are shown and, using the same technique applied to experimental crater morphologies, a laser damage fluence threshold is calculated of 0.15 J/cm2, consistent with current experiments performed under conditions similar

  7. Pulsed digital micro-holography of femto-second order by double-wavelength recording

    Institute of Scientific and Technical Information of China (English)

    WANG Ming-wei; WANG Xiao-lei; ZHAI Hong-chen

    2007-01-01

    Double-wavelength recording used in a pulsed digital micro-holographic system to record ultra-fast processing of the order of femto-second is reported for the first time, where a BBO crystal is used to generate harmonic wave of the incident laser wave, and both of the basic and the frequency doubled waves are time-delayed and introduced to a Michelson's interferom eter to record two sub-holograms with different spatial frequencies on a single frame of a CCD. In the experiment, an ultra fast dynamic process of air ionization induced by a single femto-second laser pulse is recorded with holography by this system, and both of intensity and phase difference images digitally reconstructed are obtained through Fourier transformation and digital filtering, which show clearly the dynamic process of formation and propagation of the plasma, with a time resolution of the order of femto-second.

  8. Surface texturing of sialon ceramic by femtosecond pulsed laser

    CSIR Research Space (South Africa)

    Tshabalala, Lerato C

    2017-01-01

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

  9. Application of femtosecond laser pulses for microfabrication of transparent media

    Science.gov (United States)

    Juodkazis, S.; Matsuo, S.; Misawa, H.; Mizeikis, V.; Marcinkevicius, A.; Sun, H.-B.; Tokuda, Y.; Takahashi, M.; Yoko, T.; Nishii, J.

    2002-09-01

    Femtosecond laser microfabrication of 3D optical memories and photonic crystal (PhC) structures in solid glasses and liquid resins are demonstrated. The optical memories can be read out from both transmission and emission images. The PhC structures reveal clear signatures of photonic bandgap (PBG) and microcavity formation.

  10. Wavelength-tunable multicolored femtosecond laser pulse generation in a fused silica glass plate

    Science.gov (United States)

    Kobayashi, Takayoshi; Liu, Jun

    2010-05-01

    We obtained an array of multicolored femtosecond laser pulses with as many as 17 different colors that are spatially isolated. The mechanism of generation was proved to be cascaded four-wave mixing and with the following procedure. The output beam from a femtosecond laser was split into two. One of the two beams was pulse-compressed with a hollow core fiber and the intensity of the other was reduced. The two beams were synchronized and combined with a small crossing angle in a plate of fused silica glass plate. The wavelengths of the sidebands are continuously tunable from near-ultraviolet to near-infrared. The pulse duration, spatial mode, spectrum, and energy stability of the sidebands were studied. As many as fifteen spectral up-shifted pulses and two spectral downshifted pulses were obtained with spectral bandwidths broader than 1.8 octaves. Properties such as pulse energy as high as 1 μmJ, 45 fs pulse duration, smaller than 1.1 times of the diffraction limit Gaussian spatial profile, and better than 2% RMS power stability of the generated sidebands make it can be used in various experiments. The characterization showed that the sidebands have sufficiently good qualities to enable application to for various multicolor femtosecond laser experiments, for example, a multicolor pump-probe experiment.

  11. Femtosecond electron pulse generation and measurement for diffractive imaging of isolated molecules

    Science.gov (United States)

    Zandi, Omid; Wilkin, Kyle J.; DeSimone, Alice J.; Yang, Jie; Centurion, Martin

    2016-09-01

    We have constructed an electron gun that delivers highly charged femtosecond electron pulses to a target with kHz repetition rate. Electron pulses are generated by femtosecond laser pulses in a photoemission process and are accelerated up to 100 kV and compressed to sub-picosecond duration. Compression is essential to compensate for the space charge effect that increases the size of electron pulses in all directions significantly. The pulses are compressed transversely by magnetic lenses and longitudinally by the longitudinal electric field of a radio-frequency cavity. The longitudinal compression is achieved by decelerating the electrons in the leading edge of the pulse, and accelerating the electrons in the trailing edge of the pulse. This results in the pulse compressing and reaching the minimum pulse duration at a known distance from the compression cavity. The short pulse duration and high repetition rate will be essential to observe subpicosecond dynamic processes in molecules in gas phase with a good signal to noise ratio. A streak camera, consisting of a millimeter-sized parallel plate capacitor, was used to measure the pulse duration in situ.

  12. Pair production in short laser pulses near threshold

    Energy Technology Data Exchange (ETDEWEB)

    Nousch, T. [Helmholtz-Zentrum Dresden-Rossendorf, POB 510119, 01314 Dresden (Germany); TU Dresden, Institut fuer Theoretische Physik, 01062 Dresden (Germany); Seipt, D., E-mail: d.seipt@hzdr.de [Helmholtz-Zentrum Dresden-Rossendorf, POB 510119, 01314 Dresden (Germany); TU Dresden, Institut fuer Theoretische Physik, 01062 Dresden (Germany); Kaempfer, B. [Helmholtz-Zentrum Dresden-Rossendorf, POB 510119, 01314 Dresden (Germany); TU Dresden, Institut fuer Theoretische Physik, 01062 Dresden (Germany); Titov, A.I. [Bogoliubov Laboratory of Theoretical Physics, JINR, Dubna 141980 (Russian Federation)

    2012-08-29

    The e{sup +}e{sup -} pair production by a probe photon traversing a linearly polarized laser pulse is treated as generalized nonlinear Breit-Wheeler process. For short laser pulses with very few oscillations of the electromagnetic field we find below the perturbative weak-field threshold {radical}(s)=2m a similar enhancement of the pair production rate as for circular polarization. The strong enhancement below the weak-field threshold is traced back to the finite bandwidth of the laser pulse. A folding model is developed which accounts for the interplay of the frequency spectrum and the intensity distribution in the course of the pulse.

  13. Pair production in short laser pulses near threshold

    Science.gov (United States)

    Nousch, T.; Seipt, D.; Kämpfer, B.; Titov, A. I.

    2012-08-01

    The e+e- pair production by a probe photon traversing a linearly polarized laser pulse is treated as generalized nonlinear Breit-Wheeler process. For short laser pulses with very few oscillations of the electromagnetic field we find below the perturbative weak-field threshold √{ s} = 2 m a similar enhancement of the pair production rate as for circular polarization. The strong enhancement below the weak-field threshold is traced back to the finite bandwidth of the laser pulse. A folding model is developed which accounts for the interplay of the frequency spectrum and the intensity distribution in the course of the pulse.

  14. Propagation of femtosecond pulses in a hollow-core revolver fibre

    Science.gov (United States)

    Yatsenko, Yu P.; Krylov, A. A.; Pryamikov, A. D.; Kosolapov, A. F.; Kolyadin, A. N.; Gladyshev, A. V.; Bufetov, I. A.

    2016-07-01

    We have studied for the first time the propagation of femtosecond pulses through an optical fibre with an air-filled hollow core and a cladding in the form of one ring of noncontacting cylindrical capillaries for high-power radiation transmission in the 1.55-μm telecom range. Numerical analysis results demonstrate that the parameters of the fibre enable radiation transmission in the form of megawatt-power Raman solitons through up to a 25-m length of the fibre and tuning of the emission wavelength over 130 nm. We have experimentally demonstrated femtosecond pulse transmission through fibres up to 5 m in length in the linear propagation regime, without distortions of the pulse spectrum, with a dispersion-induced temporal pulse broadening within 20%.

  15. Effect of electron emission on solids heating by femtosecond laser pulse

    Science.gov (United States)

    Svirina, V. V.; Sergaeva, O. N.; Yakovlev, E. B.

    2011-02-01

    Ultrashort laser pulse interaction with material involves a number of specialities as compared to longer irradiations. We study laser heating of metal by femtosecond pulse with taking into account electron photo- and thermionic emission leading to accumulation of a high positive charge on the target surface and, thus, to the generation of the electric field which causes Coulomb explosion (an electronic mechanism of ablation). Also emission slightly influences the thermal and optical properties of solids.

  16. Irreversible modification of magnetic properties of Pt/Co/Pt ultrathin films by femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Kisielewski, J., E-mail: jankis@uwb.edu.pl [Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525AJ Nijmegen (Netherlands); Laboratory of Magnetism, University of Białystok, Lipowa 41, 15-424 Białystok (Poland); Dobrogowski, W.; Kurant, Z.; Stupakiewicz, A.; Tekielak, M.; Maziewski, A. [Laboratory of Magnetism, University of Białystok, Lipowa 41, 15-424 Białystok (Poland); Kirilyuk, A.; Kimel, A.; Rasing, Th. [Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525AJ Nijmegen (Netherlands); Baczewski, L. T.; Wawro, A. [Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw (Poland); Balin, K.; Szade, J. [A. Chełkowski Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice (Poland)

    2014-02-07

    Annealing ultrathin Pt/Co/Pt films with single femtosecond laser pulses leads to irreversible spin-reorientation transitions and an amplification of the magneto-optical Kerr rotation. The effect was studied as a function of the Co thickness and the pulse fluence, revealing two-dimensional diagrams of magnetic properties. While increasing the fluence, the creation of two branches of the out-of-plane magnetization state was found.

  17. Time-resolved measurement of single pulse femtosecond laser-induced periodic surface structure formation

    OpenAIRE

    Kafka, K. R. P.; D. R. Austin; Li, H.; Yi, A; Cheng, J.; Chowdhury, E. A.

    2015-01-01

    Time-resolved diffraction microscopy technique has been used to observe the formation of laser-induced periodic surface structures (LIPSS) from the interaction of a single femtosecond laser pulse (pump) with a nano-scale groove mechanically formed on a single-crystal Cu substrate. The interaction dynamics (0-1200 ps) was captured by diffracting a time-delayed, frequency-doubled pulse from nascent LIPSS formation induced by the pump with an infinity-conjugate microscopy setup. The LIPSS ripple...

  18. Coherent control with shaped femtosecond laser pulses applied to ultracold molecules

    CERN Document Server

    Salzmann, W; Wester, R; Weidemüller, M; Merli, A; Weber, S M; Sauer, F; Plewicki, M; Weise, F; Esparza, A M; Wöste, L; Lindinger, A; Salzmann, Wenzel; Poschinger, Ulrich; Wester, Roland; Weidemueller, Matthias; Merli, Andrea; Weber, Stefan M.; Sauer, Franziska; Plewicki, Mateusz; Weise, Fabian; Esparza, Aldo Mirabal; Woeste, Ludger; Lindinger, Albrecht

    2005-01-01

    We report on coherent control of excitation processes of translationally ultracold rubidium dimers in a magneto-optical trap by using shaped femtosecond laser pulses. Evolution strategies are applied in a feedback loop in order to optimize the photoexcitation of the Rb2 molecules, which subsequently undergo ionization or fragmentation. A superior performance of the resulting pulses compared to unshaped pulses of the same pulse energy is obtained by distributing the energy among specific spectral components. The demonstration of coherent control to ultracold ensembles opens a path to actively influence fundamental photo-induced processes in molecular quantum gases.

  19. Tunable Multicolored Femtosecond Pulse Generation Using Cascaded Four-Wave Mixing in Bulk Materials

    Directory of Open Access Journals (Sweden)

    Jinping He

    2014-09-01

    Full Text Available This paper introduces and discusses the main aspects of multicolored femtosecond pulse generation using cascaded four-wave mixing (CFWM in transparent bulk materials. Theoretical analysis and semi-quantitative calculations, based on the phase-matching condition of the four-wave mixing process, explain the phenomena well. Experimental studies, based on our experiments, have shown the main characteristics of the multicolored pulses, namely, broadband spectra with wide tunability, high stability, short pulse duration and relatively high pulse energy. Two-dimensional multicolored array generation in various materials are also introduced and discussed.

  20. Generation of elliptically polarized nitrogen-ion laser fields using two-color femtosecond laser pulses

    CERN Document Server

    Li, Ziting; Chu, Wei; Xie, Hongqiang; Yao, Jinping; Li, Guihua; Qiao, Lingling; Wang, Zhanshan; Cheng, Ya

    2015-01-01

    We experimentally investigate generation of molecular nitrogen-ion lasers with two femtosecond laser pulses at different wavelengths. The first pulse serves as the pump which ionizes the nitrogen molecules and excites the molecular ions to excited electronic states. The second pulse serves as the probe which leads to stimulated emission from the excited molecular ions. We observe that changing the angle between the polarization directions of the two pulses gives rise to elliptically polarized molecular nitrogen-ion laser fields, which is interpreted as a result of strong birefringence of the gain medium near the wavelengths of the molecular nitrogen-ion laser.

  1. High-Order Harmonic Generation by Two Non-Collinear Femtosecond Laser Pulses in CO

    Institute of Scientific and Technical Information of China (English)

    WANG Run-Hai; JIANG Hong-Bing; YANG Hong; WU Cheng-Yin; GONG Qi-Huang

    2005-01-01

    @@ We have experimentally studied the high order harmonic generation (HHG) in CO molecules by two femtosecond laser pulses using a pump-probe technique. The delay time between two pulses is longer than the pulse duration, and the pump intensity is about 6.2 × 1014 W/cm2. It is found that the HHG signal is independent of the time delay in the picosecond region, but it is dependent on the distance between the centres of focuses of the two beams. The phase modulation induced by the pump pulse is regarded to be responsible for this.

  2. XUV-laser induced ablation of PMMA with nano-, pico-, and femtosecond pulses

    Energy Technology Data Exchange (ETDEWEB)

    Juha, L. [Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8 (Czech Republic)]. E-mail: juha@fzu.cz; Bittner, M. [Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8 (Czech Republic); Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Chvostova, D. [Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8 (Czech Republic)] (and others)

    2005-06-15

    For conventional wavelength (UV-vis-IR) lasers delivering radiation energy to the surface of materials, ablation thresholds, etch (ablation) rates, and the quality of ablated structures often differ dramatically between short (typically nanosecond) and ultrashort (typically femtosecond) pulses. Various very short-wavelength ({lambda} < 100 nm) lasers, emitting pulses with durations ranging from {approx}10 fs to {approx}1 ns, have recently been placed into routine operation. This has facilitated the investigation of how ablation characteristics depend on the pulse duration in the XUV spectral region. Ablation of poly(methyl methacrylate) (PMMA) induced by three particular short-wavelength lasers emitting pulses of various durations, is reported in this contribution.

  3. Dynamical studies on the generation of periodic surface structures by femtosecond laser pulses

    Directory of Open Access Journals (Sweden)

    Rosenfeld A.

    2013-11-01

    Full Text Available The dynamics of the formation of laser-induced periodic surface structures (LIPSS on fused silica upon irradiation with linearly polarized fs-laser pulses (50 fs pulse duration, 800 nm center wavelength is studied experimentally using a double pulse experiment with cross polarized pulse sequences and a trans illumination femtosecond time-resolved (0.1 ps – 1 ns pump-probe diffraction approach. The results in both experiments confirm the importance of the ultrafast energy deposition and the laser-induced free-electron plasma in the conduction band of the solids for the formation of LIPSS.

  4. Pair production in short intense laser pulses near threshold

    Energy Technology Data Exchange (ETDEWEB)

    Nousch, Tobias; Seipt, Daniel; Kaempfer, Burkhart [Helmholtz-Zentrum Dresden-Rossendorf, POB 510119, 01314 Dresden (Germany); TU Dresden, Institut fuer Theoretische Physik, 01062 Dresden (Germany); Titov, Alexander I. [Bogoliubov Laboratory of Theoretical Physics, JINR, Dubna 141980 (Russian Federation)

    2013-07-01

    We study finite-size effects in the process of e{sup +}e{sup -} pair production via the non-linear Breit-Wheeler process in ultra short laser pulses. Based on the Nikishov-Ritus method we use laser dressed electron and positron wave functions to derive the differential and total pair production cross section, focusing on the effects of a finite pulse duration. For short laser pulses with very few oscillations of the electromagnetic field we find an increase of the pair production rate below the perturbative weak-field threshold. The strong enhancement below the weak-field threshold is traced back to the finite bandwidth of the laser pulse. A folding model accounts for the interplay of the frequency spectrum and the intensity distribution in the course of the pulse.

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

    Science.gov (United States)

    Efimov, Anatoly

    Coherent control of chemical reactions, atomic and molecular systems, lattice dynamics, and electronic motion rely on femtosecond laser sources capable of producing programmable arbitrarily shaped waveforms. To enter the time scale of natural dynamic processes in many systems, femtosecond pulse shaping techniques must be extended to the ultrashort pulse domain (teach our laser to control its own phase by using spectral blueshifting in a rapidly created plasma as a feedback to the algorithm. Control of lattice vibrations has long been sought as a means of studying phonon-related processes in solids. In addition, generation and control of large-amplitude optical phonon modes may open a path to femtosecond time- resolved studies of structural phase transitions and production of ultrashort shaped X-ray pulses. We perform pump-probe phase-resolved measurements and control of optical A1g mode in sapphire through shaped-pulse impulsive stimulated Raman scattering (ISRS). We chose this material as a candidate for possible nonlinear oscillations regime for its wide band gap and superior optical properties allowing for high-energy excitation. To enter a nonlinear regime, however, complex asymmetric multiple-pulse excitation is required. Therefore, we make a detailed proposal of the experimental adaptive feedback implementation for optimization of phonon amplitude based on the coherent probe scattering and a novel phase mask calculation algorithm for the real-time asymmetric pulse train generation.

  6. Optical emission studies of plasma induced by single and double femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Pinon, V. [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (IESL-FORTH), P.O. Box 1385, 71110 Heraklion, Crete (Greece); Universidad de A Coruna, Departamento de Ingenieria Industrial II, E-15403 Ferrol, A Coruna (Spain); Anglos, D., E-mail: anglos@iesl.forth.g [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (IESL-FORTH), P.O. Box 1385, 71110 Heraklion, Crete (Greece); Department of Chemistry, University of Crete, 71003 Heraklion, Crete (Greece)

    2009-10-15

    Double-pulse femtosecond laser ablation has been shown to lead to significant increase of the intensity and reproducibility of the optical emission signal compared to single-pulse ablation particularly when an appropriate interpulse delay is selected, that is typically in the range of 50-1000 ps. This effect can be especially advantageous in the context of femtosecond laser-induced breakdown spectroscopy analysis of materials. A detailed comparative study of collinear double- over single-pulse femtosecond laser-induced breakdown spectroscopy has been carried out, based on measurements of emission lifetime, temperature and electronic density of plasmas, produced during laser ablation of brass with 450 fs laser pulses at 248 nm. The results obtained show a distinct increase of plasma temperature and electronic density as well as a longer decay time in the double-pulse case. The plasma temperature increase is in agreement with the observed dependence of the emission intensity enhancement on the upper energy level of the corresponding spectral line. Namely, intensity enhancement of emission lines originating from higher lying levels is more profound compared to that of lines arising from lower energy levels. Finally, a substantial decrease of the plasma threshold fluence was observed in the double-pulse arrangement; this enables sensitive analysis with minimal damage on the sample surface.

  7. Simulation of femtosecond pulsed laser ablation of metals

    Science.gov (United States)

    Davydov, R. V.; Antonov, V. I.

    2016-11-01

    In this paper a mathematical model for femtosecond laser ablation of metals is proposed, based on standard two-temperature model connected with 1D hydrodynamic equations. Wide-range equation of state has been developed. The simulation results are compared with experimental data for aluminium and copper. A good agreement for both metals with numerical results and experiment shows that this model can be employed for choosing laser parameters to better accuracy in nanoparticles production by ablation of metals.

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

    CSIR Research Space (South Africa)

    Molukanele, P

    2010-09-01

    Full Text Available Deactivation of M13 Bacteriophage in E. Coli using Femtosecond Laser Pulses P. Molukanele 1, 3, A. Du Plessis 1, T. Roberts 1, L. Botha 1, M. Khati 2,3, W. Campos 2, 3 1CSIR National Laser Centre, Femtosecond Science group, Pretoria, South Africa 2CSIR... (host cells) using the cellular synthetic machinery, and cause the synthesis of specialized elements called virions, that can transfer the genome to other cells. M13 bacteriophage (virus which infects only bacteria) is a filamentous virus...

  9. Regular subwavelength surface structures induced by femtosecond laser pulses on stainless steel.

    Science.gov (United States)

    Qi, Litao; Nishii, Kazuhiro; Namba, Yoshiharu

    2009-06-15

    In this research, we studied the formation of laser-induced periodic surface structures on the stainless steel surface using femtosecond laser pulses. A 780 nm wavelength femtosecond laser, through a 0.2 mm pinhole aperture for truncating fluence distribution, was focused onto the stainless steel surface. Under different experimental condition, low-spatial-frequency laser-induced periodic surface structures with a period of 526 nm and high-spatial-frequency laser-induced periodic surface structures with a period of 310 nm were obtained. The mechanism of the formation of laser-induced periodic surface structures on the stainless steel surface is discussed.

  10. Peculiarities of the inverse Faraday effect induced in iron garnet films by femtosecond laser pulses

    Science.gov (United States)

    Kozhaev, M. A.; Chernov, A. I.; Savochkin, I. V.; Kuz'michev, A. N.; Zvezdin, A. K.; Belotelov, V. I.

    2016-12-01

    The inverse Faraday effect in iron garnet films subjected to femtosecond laser pulses is experimentally investigated. It is found that the magnitude of the observed effect depends nonlinearly on the energy of the optical pump pulses, which is in contradiction with the notion that the inverse Faraday effect is linear with respect to the pump energy. Thus, for pump pulses with a central wavelength of 650 nm and an energy density of 1 mJ/cm2, the deviation from a linear dependence is as large as 50%. Analysis of the experimental data demonstrates that the observed behavior is explained by the fact that the optically induced normal component of the magnetization is determined, apart from the field resulting from the inverse Faraday effect, by a decrease in the magnitude of the precessing magnetization under the influence of the femtosecond electromagnetic field.

  11. Ways to produce and measure atto- and femtosecond soft X-ray pulses

    Institute of Scientific and Technical Information of China (English)

    GE YuCheng

    2007-01-01

    The ways to produce and measure atto- and femtosecond soft X-ray pulses are reported. The laser phase relation of high-order harmonic generation (HHG) shows two different radiation energy distributions in time (or laser phase) domain. These energy-phase relations are helpful for realizing the dynamic processes of HHG. Two presented parameterized formulas can be used to calculate the durations of the energy distributions with a bandwidth of the pulse. These formulas are useful in calculating and simulating pulses transports and interactions with mediums. The time structures of atto- and femtosecond soft X-ray pulses can be directly measured with photoelectron spectrum transfer equations and the related laser phase determination methods without any previous pulse shape and the instantaneous frequency assumptions. These equations and methods can be used to evaluate and improve the technical parameters of the ultra-short X-ray sources. They have wide measurement ranges and high time resolutions, which may enable ultra-fast measurements to reach metrological precisions, and lead to a new tide of scientific researches in physics, chemistry, biochemistry, etc. The application of attoand femtosecond X-rays as well as the theoretical and technical problems in measurements are briefly discussed.

  12. Limiting the intensity of femtosecond pulses with anti-stokes excitation of organic dye solutions

    Science.gov (United States)

    Svetlichnyi, V. A.; Meshalkin, Yu. P.; Kirpichnikov, A. V.; Pestryakov, E. V.

    2010-08-01

    Results of experimental investigations into the nonlinear absorption of the symmetric polymethine 1-butyl -3,3-dimethyl-2-[5-(1-butyl-3,3-dimethyl-3H-benz[e]indoline-2-uledene)-1,3-pentadienyl]-3H-benz[e]indolium perchlorate dye solution excited by radiation of a femtosecond titanium-sapphire laser (20 fs, 800 nm, 75 MHz, and 300 mW) by the open aperture z-scan method are presented. Record limitation of the femtosecond laser radiation intensity (by 300 times at a 93% linear transmission of the medium) was achieved. The nonlinear absorption mechanisms in organic dyes with anti-Stokes excitation by wideband high-power pulsed radiation to the absorption band edge and the prospects for organic dye application for limitation of the femtosecond laser radiation intensity are discussed.

  13. Measurement of ablation threshold of oxide-film-coated aluminium nanoparticles irradiated by femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Chefonov, O V; Ovchinnikov, A V; Il' ina, I V; Agranat, M B [Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow (Russian Federation)

    2016-03-31

    We report the results of experiments on estimation of femtosecond laser threshold intensity at which nanoparticles are removed from the substrate surface. The studies are performed with nanoparticles obtained by femtosecond laser ablation of pure aluminium in distilled water. The attenuation (or extinction, i.e. absorption and scattering) spectra of nanoparticles are measured at room temperature in the UV and optical wavelength ranges. The size of nanoparticles is determined using atomic force microscopy. A new method of scanning photoluminescence is proposed to evaluate the threshold of nanoparticle removal from the surface of a glass substrate exposed to IR femtosecond laser pulses with intensities 10{sup 11} – 10{sup 13} W cm{sup -2}. (interaction of laser radiation with matter)

  14. Ablation of silicon with bursts of femtosecond laser pulses

    Science.gov (United States)

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

    2016-03-01

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

  15. Femtosecond pulses cleaning by transient-grating process in Kerr-optical media

    Institute of Scientific and Technical Information of China (English)

    Jun Liu; Kotaro Okamura; Yuichiro Kida; Takayoshi Kobayashi

    2011-01-01

    We use a transient-grating (TG) process in a Kerr bulk medium to clean a femtosecond laser pulse. Using the technique, the temporal contrast of the generated TG signal is improved by more than two orders of magnitude in comparison with the incident pulse in a 0.5-mm-thick fused silica plate. The laser spectrum is smoothed and broadened, and the pulse duration is shortened simultaneously. We expect to extend this technique to a clean pulse with broadband spectral bandwidth at a wide spectral range because it is a phase-matched process.%@@ We use a transient-grating (TG) process in a Kerr bulk medium to clean a femtosecond laser pulse.Using the technique, the temporal contrast of the generated TG signal is improved by more than two orders of magnitude in comparison with the incident pulse in a 0.5-mm-thick fused silica plate.The laser spectrum is smoothed and broadened, and the pulse duration is shortened simultaneously.We expect to extend this technique to a clean pulse with broadband spectral bandwidth at a wide spectral range because it is a phase-matched process.

  16. A second-order autocorrelator for single-shot measurement of femtosecond laser pulse durations

    Indian Academy of Sciences (India)

    M Raghuramaiah; A K Sharma; P A Naik; P D Gupta; R A Ganeev

    2001-12-01

    A second-order autocorrelator for single-shot measurement of ultrashort laser pulse durations has been set up. It is based on recording the spatial profile of non-collinear phase-matched second harmonic generation in a KDP crystal using a CCD camera-framegrabber combination. Performance of the system is described from measurement of 250 femtosecond transform-limited laser pulses from a passively mode-locked, diode pumped Nd:glass laser. It can also be used for measurement of picosecond laser pulses in the multi-shot scanning mode.

  17. Femtosecond x-ray free electron laser pulse duration measurement from spectral correlation function

    Directory of Open Access Journals (Sweden)

    A. A. Lutman

    2012-03-01

    Full Text Available We present a novel method for measuring the duration of femtosecond x-ray pulses from self-amplified spontaneous emission free electron lasers by performing statistical analysis in the spectral domain. Analytical expressions of the spectral correlation function were derived in the linear regime to extract both the pulse duration and the spectrometer resolution. Numerical simulations confirmed that the method can be also used in the nonlinear regime. The method was demonstrated experimentally at the Linac Coherent Light Source by measuring pulse durations down to 13 fs FWHM.

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

    Directory of Open Access Journals (Sweden)

    Vincenzo Piazza

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

  19. Formation of laser-induced periodic surface structures on fused silica upon multiple cross-polarized double-femtosecond-laser-pulse irradiation sequences

    Energy Technology Data Exchange (ETDEWEB)

    Rohloff, M.; Das, S. K.; Hoehm, S.; Grunwald, R.; Rosenfeld, A. [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie (MBI), Max-Born-Strasse 2A, D-12489 Berlin (Germany); Krueger, J.; Bonse, J. [BAM Bundesanstalt fuer Materialforschung und -pruefung, Unter den Eichen 87, D-12205 Berlin (Germany)

    2011-07-01

    The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences consisting of five Ti:sapphire femtosecond (fs) laser pulse pairs (150 fs, 800 nm) is studied experimentally. A Michelson interferometer is used to generate near-equal-energy double-pulse sequences with a temporal pulse delay from -20 to +20 ps between the cross-polarized individual fs-laser pulses ({approx}0.2 ps resolution). The results of multiple double-pulse irradiation sequences are characterized by means of Scanning Electron and Scanning Force Microscopy. Specifically in the sub-ps delay domain striking differences in the surface morphologies can be observed, indicating the importance of the laser-induced free-electron plasma in the conduction band of the solids for the formation of LIPSS.

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

    Directory of Open Access Journals (Sweden)

    J. Szlachetko

    2014-03-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2004-01-01

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

  2. Propagation delay of femtosecond pulses in an optical amplifier

    DEFF Research Database (Denmark)

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

    The recent realization of tunable propagation delay of optical pulses in solid-state and semiconductor optical media1,2 has attracted great attention as such a functionality enables a whole new class of optical components in optical communications systems and signal processing3. The reported...... results show a large reduction in group velocity but this was achieved at the cost of a small bandwidth (e.g. 37 Hz in the case of Bigelow et al.1) of the probe signal. In this paper, we report measurements of slowing down and speeding up of the propagation of 150 fs pulses, having a very large bandwidth....... In the first experiment, we prepare a narrow peak or dip in the SOA gain spectrum by injection of a strong pump pulse4. The resulting dispersion feature is then probed by a weak pulse. In the second experiment, we measure self-slowdown or advancement as pulse energy isincreased5. In both cases, we perform...

  3. Femtosecond-laser-pulse characterization and optimization for CARS microscopy

    CERN Document Server

    Piazza, Vincenzo; Farrokhtakin, Elmira; Ciofani, Gianni; Mattoli, Virgilio

    2016-01-01

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

  4. Filming Femtosecond Molecular Movies with X-ray Pulses

    DEFF Research Database (Denmark)

    Kjær, Kasper Skov

    This thesis describes the investigation of time-resolved phenomena using X-ray techniques, and in particular the new possibilities and challenges arising from the application of these techniques on the femtosecond time-scale. The thesis will review the processes following laser excitation...... of molecular species in solution, describing the interplay between electronic and structural dynamics, as well as the role of the solvent. This will be followed by an introduction of the three X-ray techniques used in this work, and it will be shown how the application of these techniques in a laser pump / X...... yielded by (and the practical challenges connected to) their simultaneous implementation in a single experiment. Finally, the experimental results of a signicant set of laser pump / X-ray probe experiments will be presented and discussed in order to gauge the applicability of these techniques as tools...

  5. Ablation and nanostructuring of metals by femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Ashitkov, S I; Komarov, P S; Ovchinnikov, A V; Struleva, E V; Agranat, M B [Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow (Russian Federation); Zhakhovskii, V V [All-Russian Institute of Automatics, Moscow (Russian Federation); Inogamov, N A [Landau Institute for Theoretical Physics, Russian Academy of Sciences, Chernogolovka, Moscow region (Russian Federation)

    2014-06-30

    Using an interferometric continuous monitoring technique, we have investigated the motion of the surface of an aluminium target in the case of femtosecond laser ablation at picosecond time delays relative to the instant of laser exposure. Measurements of the temporal target dispersion dynamics, molecular dynamics simulation results and the morphology of the ablation crater have demonstrated a thermomechanical (spall) nature of the disruption of the condensed phase due to the cavitation-driven formation and growth of vapour phase nuclei upon melt expansion, followed by the formation of surface nanostructures upon melt solidification. The tensile strength of heated aluminium in a condensed state has been determined experimentally at an expansion rate of ∼10{sup 9} s{sup -1}. (extreme light fields and their applications)

  6. Formation of color centers and light scattering structures by femtosecond laser pulses in sodium fluoride

    Science.gov (United States)

    Bryukvina, L. I.; Pestryakov, E. V.; Kirpichnikov, A. V.; Martynovich, E. F.

    2014-11-01

    Modification of sodium fluoride crystal lattice by means of femtosecond laser pulses with λmax=800 nm, energy 0.5 mJ, duration 30 fs and repetition rate 1 kHz has been considered in the paper. Effective formation of simple and complex aggregate color centers and light scattering nanodefects in the channel of a laser beam in NaF crystal have been shown for the first time. Dependences of color centers concentration on the distance between the channel center and its periphery and along the channel have been presented. Influence of external focusing on color centers creation has been revealed. Explanations of the observed phenomena have been presented on the basis of nonlinear processes taking place under the effect of high-intensity femtosecond pulses.

  7. Nanocomposite tantalum-carbon-based films deposited by femtosecond pulsed laser ablation

    Energy Technology Data Exchange (ETDEWEB)

    Benchikh, N. [Laboratoire Traitement du Signal et Instrumentation, UMR 5516, Universite J. Monnet, 10 rue Barrouin, 42000 Saint-Etienne (France); Garrelie, F. [Laboratoire Traitement du Signal et Instrumentation, UMR 5516, Universite J. Monnet, 10 rue Barrouin, 42000 Saint-Etienne (France); Wolski, K. [Ecole Nationale Superieure des Mines de Saint-Etienne, Centre SMS - URA CNRS 5146, 158 cours Fauriel, 42023 Saint-Etienne, Cedex 02 (France); Donnet, C. [Laboratoire Traitement du Signal et Instrumentation, UMR 5516, Universite J. Monnet, 10 rue Barrouin, 42000 Saint-Etienne (France)]. E-mail: Christophe.Donnet@univ-st-etienne.fr; Fillit, R.Y. [Ecole Nationale Superieure des Mines de Saint-Etienne, Centre SMS - URA CNRS 5146, 158 cours Fauriel, 42023 Saint-Etienne, Cedex 02 (France); Rogemond, F. [Laboratoire Traitement du Signal et Instrumentation, UMR 5516, Universite J. Monnet, 10 rue Barrouin, 42000 Saint-Etienne (France); Subtil, J.L. [Laboratoire Traitement du Signal et Instrumentation, UMR 5516, Universite J. Monnet, 10 rue Barrouin, 42000 Saint-Etienne (France); Rouzaud, J.N. [Laboratoire de Geologie de l' Ecole Normale Superieure de Paris 24, rue Lhomond 75231-Paris Cedex 5 (France); Laval, J.Y. [Laboratoire de Physique du Solide, UPR5 CNRS-ESPCI, 10 rue Vauquelin 75231-Paris Cedex 05 (France)

    2006-01-03

    Nanostructured coatings of metal (tantalum) containing diamond-like carbon (a-C:Ta) have been prepared by femtosecond pulsed laser deposition (PLD). The films, containing 15 at.% tantalum, have been deposited by ablating sequentially graphite and metallic tantalum in vacuum conditions with an amplified Ti:sapphire laser. The coatings have been investigated by X-ray photoelectron spectroscopy, grazing angle X-ray diffraction, energy filtered transmission electron microscopy, scanning and high resolution transmission electron microscopies. Evidence of metallic {alpha}-Ta and {beta}-Ta particles (diameter in the 100 nm range) and smaller quasi-amorphous tantalum clusters embedded in the carbonaceous matrix have been shown. A thin tantalum carbide interface between the carbon matrix and the top surface of the tantalum nodules has also been identified. The ability of femtosecond pulsed laser deposition to synthetize nanocomposite carbon-based films and to control their nanostructure is discussed.

  8. Enhancement of ultrafast electron photoemission from metallic nano antennas excited by a femtosecond laser pulse

    CERN Document Server

    Gubko, M A; Ionin, A A; Kudryashov, S I; Makarov, S V; Nathala, C S R; Rudenko, A A; Seleznev, L V; Sinitsyn, D V; Treshin, I V

    2013-01-01

    We have demonstrated for the first time that an array of nanoantennas (central nanotips inside sub-micron pits) on an aluminum surface, fabricated using a specific double-pulse femtosecond laser irradiation scheme, results in a 28-fold enhancement of the non-linear (three-photon) electron photoemission yield, driven by a third intense IR femtosecond laser pulse. The supporting numerical electrodynamic modeling indicates that the electron emission is increased not owing to a larger effective aluminum surface, but due to instant local electromagnetic field enhancement near the nanoantenna, contributed by both the tip's lightning rod effect and the focusing effect of the pit as a microreflector and annular edge as a plasmonic lens.

  9. Narrow titanium oxide nanowires induced by femtosecond laser pulses on a titanium surface

    Science.gov (United States)

    Li, Hui; Li, Xian-Feng; Zhang, Cheng-Yun; Tie, Shao-Long; Lan, Sheng

    2017-02-01

    The evolution of the nanostructure induced on a titanium (Ti) surface with increasing irradiation pulse number by using a 400-nm femtosecond laser was examined by using scanning electron microscopy. High spatial frequency periodic structures of TiO2 parallel to the laser polarization were initially observed because of the laser-induced oxidation of the Ti surface and the larger efficacy factor of TiO2 in this direction. Periodically aligned TiO2 nanowires with featured width as small as 20 nm were obtained. With increasing pulse number, however, low spatial frequency periodic structures of Ti perpendicular to the laser polarization became dominant because Ti possesses a larger efficacy factor in this direction. The competition between the high- and low-spatial frequency periodic structures is in good agreement with the prediction of the efficacy factor theory and it should also be observed in the femtosecond laser ablation of other metals which are easily oxidized in air.

  10. Role of ambient gas in heating of metal samples by femtosecond pulses of laser radiation

    Science.gov (United States)

    Zhukov, V. P.; Bulgakova, N. M.

    2009-06-01

    In this work we consider an experimentally observed effect of significant increasing of the residual heat in metal targets at their irradiation with femtosecond laser pulses in an ambient gas in respect to the vacuum conditions. Numerical modelling of heating of a platinum target by femtosecond laser pulses in argon under normal conditions has been performed taking into account gas breakdown in the focussing region of the laser beam in front of the target. The applied model is based on a combination of a thermal model describing heating and phase transitions in irradiated samples and a hydrodynamic model to describe motion of the ambient gas perturbed by laser irradiation as a result of multiphoton ionization. The hot ambient gas is shown to heat efficiently the irradiated sample. The hydrodynamic processes in the ambient gas play an important role in heating.

  11. Webcam autofocus mechanism used as a delay line for the characterization of femtosecond pulses

    Energy Technology Data Exchange (ETDEWEB)

    Castro-Marín, Pablo; Kapellmann-Zafra, Gabriel; Garduño-Mejía, Jesús, E-mail: jesus.garduno@ccadet.unam.mx; Rosete-Aguilar, Martha; Román-Moreno, Carlos J. [Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, A. P. 70-186, CP 04510 México D.F. (Mexico)

    2015-08-15

    In this work, we present an electromagnetic focusing mechanism (EFM), from a commercial webcam, implemented as a delay line of a femtosecond laser pulse characterization system. The characterization system consists on a second order autocorrelator based on a two-photon-absorption detection. The results presented here were performed for two different home-made femtosecond oscillators: Ti:sapph @ 820 nm and highly chirped pulses generated with an Erbium Doped Fiber @ 1550 nm. The EFM applied as a delay line represents an excellent alternative due its performance in terms of stability, resolution, and long scan range up to 3 ps. Due its low power consumption, the device can be connected through the Universal Serial Bus (USB) port. Details of components, schematics of electronic controls, and detection systems are presented.

  12. The Electron Trajectory in a Relativistic Femtosecond Laser Pulse

    Institute of Scientific and Technical Information of China (English)

    He Feng; Yu Wei; Lu Peixiang; Xu Han; Shen Baifei; Li Ruxin; Xu Zhizhan

    2005-01-01

    In this report, we start from Lagrange equation and analyze theoretically the electron dynamics in electromagnetic field. By solving the relativistic government equations of electron,the trajectories of an electron in plane laser pulse, focused laser pulse have been given for different initial conditions. The electron trajectory is determined by its initial momentum, the amplitude,spot size and polarization of the laser pulse. The optimum initial momentum of the electron for LSS (laser synchrotron source) is obtained. Linear polarized laser is more advantaged than circular polarized laser for generating harmonic radiation.

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

    Institute of Scientific and Technical Information of China (English)

    LIU Da-Yong; LI Yan; DOU Yan-Ping; GUO Heng-Chang; YANG Hong; GONG Qi-Huang

    2008-01-01

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

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

    Science.gov (United States)

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

    2017-01-01

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

  15. Plasma channels during filamentation of a femtosecond laser pulse with wavefront astigmatism in air

    Energy Technology Data Exchange (ETDEWEB)

    Dergachev, A A; Kandidov, V P; Shlenov, S A [Lomonosov Moscow State University, Faculty of Physics, Moscow (Russian Federation); Ionin, A A; Mokrousova, D V; Seleznev, L V; Sinitsyn, D V; Sunchugasheva, E S; Shustikova, A P [P N Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

    2014-12-31

    We have demonstrated experimentally and numerically the possibility of controlling parameters of plasma channels formed during filamentation of a femtosecond laser pulse by introducing astigmatism in the laser beam wavefront. It is found that weak astigmatism increases the length of the plasma channel in comparison with the case of aberration-free focusing and that strong astigmatism can cause splitting of the plasma channel into two channels located one after another on the filament axis. (interaction of laser radiation with matter. laser plasma)

  16. Laser Micro-Hole Drilling of Soda-Lime Glass with Femtosecond Pulses

    Institute of Scientific and Technical Information of China (English)

    AN Ran; LI Yan; DOU Yan-Ping; FANG Ying; YANG Hong; GONG Qi-Huang

    2004-01-01

    @@ Using tightly focused femtosecond laser pulses, we have drilled micro-holes from the front and rear surface of soda-lime glass in ambient air. The machined holes have small aspect ratio or irregular inner walls. When the drilling is conducted from the rear surface in contact with distilled water, a good quality micro-hole with a high aspect ratio can be obtained. The corresponding formation mechanisms are investigated.

  17. Third-Order Harmonic Generation in Atmospheric Air with Focused Intense Femtosecond Laser Pulses

    Institute of Scientific and Technical Information of China (English)

    朱长军; 秦元东; 杨宏; 王树峰; 龚旗煌

    2001-01-01

    Generation of third-order harmonics at 800 nm of femtosecond laser pulses is studied in neutral atmospheric air and in plasma of optical breakdown in air. Its efficiency is measured at different fundamental laser intensities. A maximum efficiency is observed at the intensity when optical breakdown in atmospheric air starts. The factors that exhibit the main effects on the harmonic generation, including self-focusing in a neutral air and self-focusing in plasma, are discussed.

  18. Second harmonic generation in a centrosymmetric gas medium with spatiotemporally focused intense femtosecond laser pulses

    CERN Document Server

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

    2013-01-01

    We demonstrate unexpectedly strong second harmonic generation (SHG) in Argon gas by use of spatiotemporally focused (SF) femtosecond laser pulses. The resulting SHG by the SF scheme at a 75 cm distance shows a significantly enhanced efficiency than that achieved with conventional focusing scheme, which offers a new promising possibility for standoff applications. Our theoretical calculations reasonably reproduce the experimental observations, which indicate that the observed SHG mainly originates from the gradient of nonuniform plasma dynamically controlled by the SF laser field.

  19. Laser-Induced Continuum Structure of NO Molecules in Two-Colour Femtosecond Pulsed Laser Fields

    Institute of Scientific and Technical Information of China (English)

    WANG Sen-Ming; YUAN Kai-Jun; CONG Shu-Lin

    2006-01-01

    The method of quantum wave packet dynamics is used to study the multiphoton ionization of NO molecules via a two-photon Raman coupling and a laser-induced continuum structure (LICS) state in two-colour strong femtosecond pulsed laser fields.Time-and energy-resolved photoelectron energy spectra are calculated for describing three photoionization channels.The population transfers through the LICS and the Raman coupling passages and discussed.

  20. Density-Functional-Theory Studies of C20 in Femtosecond Laser Pulses

    Institute of Scientific and Technical Information of China (English)

    WANG Zhi-Ping; BIAN Bao-An; WANG Li-Guang

    2010-01-01

    @@ We study the electron response of C20 excited by strong femtosecond laser pulses by applying the time-dependent local-density approximation,an approach which has proven to provide a robust tool for investigations of fullerene.The optical response as well as the full electronic dipolar response and ionization processes of C20 subject to the laser field are explored.A strong correlation between induced electronic dipole oscillations and electron emission is observed.

  1. Non-thermal ablation of expanded polytetrafluoroethylene with an intense femtosecond-pulse laser

    OpenAIRE

    Hashida, M.; Mishima, H.; Tokita, S.; Sakabe, S.

    2009-01-01

    Ablation of expanded polytetrafluoroethylene without disruption of the fine porous structure is demonstrated using an intense femtosecond-pulse laser. As a result of laser-matter interactions near ablation threshold fluence, high-energy ions are emitted, which cannot be produced by thermal dissociation of the molecules. The ion energy is produced by Coulomb explosion of the elements of (-CF_{2}-CF_{2-})n and the energy spectra of the ions show contributions from the Coulomb explosions of the ...

  2. Conical Emission Patterns by Femtosecond Pulses with Different Spectral Bandwidths

    Institute of Scientific and Technical Information of China (English)

    LI Yue-Xun; ZENG Zhi-Nan; GE Xiao-Chun; CHEN Xiao-Wei; LI Ru-Xin; XU Zhi-Zhan

    2008-01-01

    @@ Different conical emission (CE) patterns are obtained experimentally at various incident powers and beam sizes of pump laser pulses with pulse durations of 7fs, 44fs and lOOfs.The results show that it is the incident power but not the incident power density that determines a certain CE pattern.In addition, the critical powers for similar CE patterns are nearly the same for the laser pulses with the same spectral bandwidth.Furthermore, as far as a certain CE pattern is concerned, the wider the spectral bandwidth of pump laser pulse is, the higher the critical power is.This will hopefully provide new insights for the generation of CE pattern in optical medium.

  3. Rotational excitation of molecules with long sequences of intense femtosecond pulses

    CERN Document Server

    Bitter, M

    2016-01-01

    We investigate the prospects of creating broad rotational wave packets by means of molecular interaction with long sequences of intense femtosecond pulses. Using state-resolved rotational Raman spectroscopy of oxygen, subject to a sequence of more than 20 laser pulses with peak intensities exceeding $10^{13}$ W/cm$^{2}$ per pulse, we show that the centrifugal distortion is the main obstacle on the way to reaching high rotational states. We demonstrate that the timing of the pulses can be optimized to partially mitigate the centrifugal limit. The cumulative effect of a long pulse sequence results in high degree of rotational coherence, which is shown to cause an efficient spectral broadening of probe light via cascaded Raman transitions.

  4. Resonant propagation of femtosecond laser pulse in DBASVP molecule:one-dimensional asymmetric organic molecule

    Institute of Scientific and Technical Information of China (English)

    Zhao Ke; Liu Ji-Cai; Wang Chuan-Kui; Luo Yi

    2005-01-01

    We have investigated the resonant propagation of femtosecond laser pulse in 4-trans-[p-(N, N-Di-n-butylamino)-p-stilbenyl vinyl] pyridine medium with permanent dipole moments. The electronic structures and parameters for the compound have been calculated by using density functional theory. In the optical regime, there is one charge-transfer state, and the molecule can thus be simplified as a two-level system. Both the one- and two-photon transitions occur between the ground and charge-transfer states. The numerical results show that the permanent dipole moments have an obvious effect on the propagation of the ultrashort pulse laser. The ideal self-induced transparency disappears for 2π pulse, and second harmonic spectral components occur significantly due to the two-photon absorption process. For the 6π pulse, continuum frequency generation is produced and a shorter duration pulse in time domain with 465 as is obtained.

  5. High Resolution Mode-Selective Excitation by Adaptive Femtosecond Pulse Shaping

    Institute of Scientific and Technical Information of China (English)

    LI Xia; ZHANG Hui; ZHANG Xiang-Yun; ZHANG Shi-An; CHEN Guo-Liang; WANG Zu-Geng; SUN Zhen-Rong

    2008-01-01

    High resolution mode-selective excitation in the mixture of C6H6(992cm-1)and C6D6(945cm-1)is experimentally achieved by adaptive femtosecond pulse shaping based on the genetic algorithm(GA),and second harmonic generation frequency-resolved optical gating(SHG-FROG)is adopted to characterize the original and optimal laser pulses,and its mechanism is experimentally validated by tailoring the frequency components of the pump pulses at the Fourier plane.It is indicated that two-pulse coherent mode-selective excitation of the Raman scattering mainly depends on the effective frequency components of the pump pulse related to specific molecular vibrational mode.The experimental results have attractive potential appfications in the complicated molecular system.

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

    DEFF Research Database (Denmark)

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

    2010-01-01

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

  7. Heat-affected zone of metals ablated with femtosecond laser pulses

    Science.gov (United States)

    Hirayama, Yoichi; Obara, Minoru

    2003-07-01

    The melted area is found on the surface ablated by nanosecond and picosecond laser pulses. However, the heat effect is little on the ablated surface in the case of femtosecond laser due to non-thermal ablation process. Heat-affected zone of metallic bulk crystal ablated with femtosecond Ti:sapphire laser pulses is experimentally studied. As a result of XRD (X-ray diffraction) measurements, the XRD peak signal of the area ablated with Ti:sapphire laser becomes smaller than that of the crystalline metal sample. While the crystallinity of the metal sample is crystalline before the laser ablation, the crystallinity in the ablated area is partially changed into the amorphous form. Because the residual pulse energy that is not used for the ablation process remains, leading to the formation of thin layer of melt phase. The melt layer is abruptly cooled down not to be re-crystallized, but to transform into the amorphous form. It is evident that the area ablated with femtosecond laser is changed into the amorphous metal. Additionally XRD measurements and AR+ etching are performed alternately to measure the thickness of the amorphous layer. In the case of iron, the thickness is measured to be 1 μm approximately, therefore heat-affected zone is quite small.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-01-01

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

  9. Ionization Induced Scattering of Femtosecond Intense Laser Pulses in Cluster Plasmas

    Institute of Scientific and Technical Information of China (English)

    Wang Xiangxin; Wang Cheng; Liu Jiansheng; Li Shaohui; Ni Guoquan

    2005-01-01

    The 45° scattering of a femtosecond (60 fs) intense laser pulse with a 20 nm FWHM (the full width at half maximum) spectrum centered at 790 nm has been studied experimentally while focused in argon clusters at intensity ~ 1016 W/cra2. Scattering spectra under different backing pressures and laser-plasma interaction lengths were obtained, which showed spectral blueshifting, beam refraction and complex modulation. These ionization-induced effects reveal the modulation of laser pulses propagating in plasmas and the existing obstacle in laser cluster interaction at high laser intensity and high electron density.

  10. Nonlinear optical studies in semiconductor-doped glasses under femtosecond pulse excitation

    Indian Academy of Sciences (India)

    C P Singh; K S Bindra; S M Oak

    2010-12-01

    Nonlinear optical studies in semiconductor-doped glasses (SDGs) are performed under femtosecond laser pulse excitation. Z-scan experiments with 800 nm wave- length pulses are used to excite SDG samples in the resonance and non-resonance regimes. Schott colour glass filter OG 515 shows stronger two-photon absorption than GG 420 and both the samples exhibit positive nonlinearity. However, in resonantly excited RG 850 the intensity-dependent Z-scan shows transition from saturable to reverse saturable absorption behaviour with the increase in intensity.

  11. Sub-100nm material processing with sub-15 femtosecond picojoule near infrared laser pulses

    Science.gov (United States)

    König, Karsten; Uchugonova, Aisada; Straub, Martin; Zhang, Huijing; Afshar, Maziar; Feili, Dara; Seidel, Helmut

    2011-03-01

    Ultrabroad band 12 femtosecond near infrared laser pulses at transient TW/cm2 intensities and low picojoule pulse energies (mean powers Cut sizes of sub-wavelength, sub-100 nm which is far beyond the Abbe diffraction limit have been realized without any collateral damage effect in silicon wafers, photoresists, glass, polymers, metals, and biological targets. Multiphoton sub-15fs microscopes may become novel non-invasive 3D tools for highly precise nanoprocessing of inorganic and organic targets as well as two-photon 3D imaging.

  12. Propagation of Ultra-fast Femtosecond Pulses in Silicon-on-insulator Optical Waveguides

    Institute of Scientific and Technical Information of China (English)

    WU Jian-wei; LUO Feng-guang; Cristiano de Mello Gallep

    2007-01-01

    A complete theoretical modeling, avoiding any priori-assumption, is deduced and demonstrated for ultra-fast femtosecond optical pulses in silicon-on-insulator optical waveguides which includes the group velocity dispersion, third-order dispersion, self-phase and cross-phase modulations, self-steepening and shock formation, Raman depletion, propagation loss, two-photon absorption, free-carrier absorption, and free-carrier dispersion. Finally, the temporal and spectral characteristics of 100 fs optical pulses at 1.55 μm are numerically observed in 5-mm-long waveguides while considering different initial chirps and incident peak intensity levels.

  13. High-Energy Ions Emitted from Ar Clusters Irradiated by Intense Femtosecond Laser Pulses

    Institute of Scientific and Technical Information of China (English)

    LI Zhong; LEI An-Le; NI Guo-Quan; XU Zhi-Zhan

    2000-01-01

    We have experimentally studied the energy spectra of Ar ions emitted from Ar clusters irradiated by intense femtosecond laser pulses. The Ar clusters were produced in the adiabatic expansion of Ar gas into vacuum at high backing pressures. The laser peak intensity was about 2×106 W/cm2 with a pulse duration of 45 fs. The maximum and the average energies of Ar ions are 0.2 MeV and 15kev at a backing pressure of 2. S MPa, respectively. They are almost independent of the backing pressures in the range of 0.6 to 4.5 MPa.

  14. Population transfer by femtosecond laser pulses in a ladder-type atomic system

    Institute of Scientific and Technical Information of China (English)

    Fan Xi-Jun; Li Ai-Yun; Tong Dian-Min; Liu Cheng-Pu

    2008-01-01

    The population transfer in a ladder-type atomic system driven by linearly polarized sech-shape femtosecond laser pulses is investigated by numerically solving Schrodinger equation without including the rotating wave approximation (RWA). It is shown that population transfer is mainly determined by the Rabi frequency (strength) of the driving laser field and the chirp rate, and that the ratio of the dipole moments and the pulse width also have a prominent effect on the population transfer. By choosing appropriate values of the above parameters, complete population transfer can be realized.

  15. Resonant femtosecond stimulated Raman spectroscopy with an intense actinic pump pulse: Application to conical intersections

    Science.gov (United States)

    Rao, B. Jayachander; Gelin, Maxim F.; Domcke, Wolfgang

    2017-02-01

    We theoretically investigate the feasibility of characterizing conical intersections with time-resolved resonant femtosecond stimulated Raman spectroscopy (FSRS) using an intense actinic pump pulse. We perform nonperturbative numerical simulations of FSRS signals for a three-electronic-state two-vibrational-mode model, which is inspired by the S 2 ( π π * )- S 1 ( n π * ) conical intersection in pyrazine. Our results show that moderately strong actinic pulses increase the intensity of vibrational fingerprint lines in FSRS transients. They facilitate the extraction of useful spectroscopic information by enhancing peaks revealing the coupling and tuning modes of the conical intersection.

  16. Generating femtosecond X-ray pulses using an emittance-spoiling foil in free-electron lasers

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Y., E-mail: ding@slac.stanford.edu; Coffee, R.; Decker, F.-J.; Emma, P.; Field, C.; Huang, Z.; Krejcik, P.; Krzywinski, J.; Loos, H.; Lutman, A.; Marinelli, A.; Maxwell, T. J.; Turner, J. [SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Behrens, C. [Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg (Germany); Helml, W. [Technische Universität München, James-Franck-Straße 1, 85748 Garching (Germany)

    2015-11-09

    Generation of femtosecond to sub-femtosecond pulses is attracting much attention in X-ray free-electron laser user community. One method is to use a slotted, emittance-spoiling foil which was proposed before (P. Emma et al., Phys. Rev. Lett. 92, 074801 (2004)) and has been widely used at the Linac Coherent Light Source. Direct experimental characterization of the slotted-foil performance was previously unfeasible due to a lack of appropriate diagnostics. With a recently installed X-band radio-frequency transverse deflector, we are able to characterize the electron bunch spoiling effect and X-ray pulse when using the slotted foil. We show that few-femtosecond X-ray pulses are generated with flexible control of the single-pulse duration or double-pulse separation with comparison to the theoretical model.

  17. Transforming graphite to nanoscale diamonds by a femtosecond laser pulse

    Energy Technology Data Exchange (ETDEWEB)

    Nueske, R.; Jurgilaitis, A.; Enquist, H.; Harb, M.; Larsson, J. [Atomic Physics Division, Department of Physics, Lund University, P.O. Box 118, SE-221 00 Lund (Sweden); Fang, Y.; Haakanson, U. [Division of Solid State Physics/Nanometer Structure Consortium at Lund University, P.O. Box 118, S-221 00 Lund (Sweden); Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603-146, 100190 Beijing (China)

    2012-01-23

    Formation of cubic diamond from graphite following irradiation by a single, intense, ultra-short laser pulse has been observed. Highly oriented pyrolytic graphite (HOPG) samples were irradiated by a 100 fs pulse with a center wavelength of 800 nm. Following laser exposure, the HOPG samples were studied using Raman spectroscopy of the sample surface. In the laser-irradiated areas, nanoscale cubic diamond crystals have been formed. The exposed areas were also studied using grazing incidence x-ray powder diffraction showing a restacking of planes from hexagonal graphite to rhombohedral graphite.

  18. Breathing solitary-pulse pairs in a linearly coupled system

    CERN Document Server

    Dana, Brenda; Bahabad, Alon

    2014-01-01

    It is shown that pairs of solitary pulses (SPs) in a linearly-coupled system with opposite group-velocity dispersions form robust breathing bound states. The system can be realized by temporal-modulation coupling of SPs with different carrier frequencies propagating in the same medium, or by coupling of SPs in a dual-core waveguide. Broad SP pairs are produced in a virtually exact form by means of the variational approximation. Strong nonlinearity tends to destroy the periodic evolution of the SP pairs.

  19. Heat-affected zone in microdrilling of metals by femtosecond laser pulses

    Science.gov (United States)

    Audouard, E.; LeHarzic, R.; Huot, Nicolas; Laporte, Pierre; Valette, S.; Fourtunier, R.

    2002-09-01

    Several works on laser-matter interaction has shown the differences in sizes for the Heat Affected Zone (HAZ) obtained with nanosecond and femtosecond regimes in laser cutting or drilling. To understand more clearly the basic phenomena that occur in femtosecond regime during the absorption of light by matter, and specially in the case of metals, we have developed both an experimental and a theoretical approach. We use a new method aimed at quantifying the dimensions of the HAZ, using thin-down samples which are micro-drilled and then observed by a transmission electronic microscopy (TEM) technique. The grain size in the samples is analysed near the micro-holes. According to theoretical studies, the thermal diffusion is due to the smaller value of the electron specific heat compared to the lattice one. The thermal diffusion length is found to be a few hundred of nanometers in the case of metals. We use a thermal model to describe the heat diffusion in the sample in order to obtain a theoretical estimation of the HAZ. Holes are drilled in Aluminum using nanosecond and femtosecond laser pulses and characterized by Transmission Electronic Microscopy (TEM). The method for quantifying the dimensions of the heat affected zone (HAZ) surrounding micro-holes is based on the analyze of the grain size evolution. The experiments are using the same Ti-Sapphire laser source (1 kHz, 800 nm). The regeneratively amplified ultra-short pulses (150 fs) are utilized at a low fluence regime (typically 0.01-0.5 mJ/pulse), while the longer pulses (ns) are obtained from the regenerative amplifier without oscillator seeding (0.5 mJ,τ approximately 7-8 ns). The main conclusion is that a 40 micrometers wide HAZ is induced by nanosecond pulses, whereas the femtosecond regime does not produce any TEM observable HAZ. It has to be noticed that the width of the femtosecond HAZ is roughly less than 2 micrometers , which is our observation limit. These results are in agreement with theoretical

  20. Femtosecond pulse shaping by modulating the refractive index modulation of volume holographic grating.

    Science.gov (United States)

    Yan, Xiaona; Dai, Ye; Gao, Zixuan; Chen, Yuanyuan; Yang, Xihua; Ma, Guohong

    2013-03-25

    Based on the modified Kogelnik's coupled-wave theory, time- and frequency-domain diffractions of a femtosecond pulse from transmitted volume holographic gratings (VHGs) are theoretically studied. Results show that when the refractive index modulation of the VHG changes in a certain range, the number of temporal diffracted pulse will evolve from one to two, then to three, and this pulse number evolution is periodic. This particular phenomenon can be explained by diffraction intensity spectrum and the overmodulation effect of refractive index modulation of transmitted VHG. Moreover, we find centers of all temporal diffracted pulses translate along the negative time axis, and the translation is irrelevant to the refractive index modulations. We will use time delay of volume grating to give a reasonable explanation.

  1. Drilling of aluminum and copper films with femtosecond double-pulse laser

    Science.gov (United States)

    Wang, Qinxin; Luo, Sizuo; Chen, Zhou; Qi, Hongxia; Deng, Jiannan; Hu, Zhan

    2016-06-01

    Aluminum and copper films are drilled with femtosecond double-pulse laser. The double-pulse delay is scanned from -75 ps to 90 ps. The drilling process is monitored by recording the light transmitted through the sample, and the morphology of the drilled holes is analyzed by optical microscopy. It is found that, the breakthrough time, the hole evolution during drilling, the redeposited material, the diameters of the redeposited area and the hole, change as functions of double-pulse delay, and are different for the two metals. Along the double-pulse delay axis, three different time constants are observed, a slow one of a few tens of picoseconds, a fast one of a few picoseconds, and an oscillation pattern. Results are discussed based on the mechanisms of plasma shielding, electron-phonon coupling, strong coupling of laser with liquid phase, oxidation of aluminum, laser induced temperature and pressure oscillations, and the atomization of plume particles.

  2. Microstructuring of soft organic matter by temporally shaped femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Rebollar, Esther, E-mail: e.rebollar@iqfr.csic.es [Instituto de Química Física Rocasolano, IQFR-CSIC, Serrano 119, 28006 Madrid (Spain); Mildner, Jutta; Götte, Nadine; Otto, Dirk; Sarpe, Cristian; Köhler, Jens; Wollenhaupt, Matthias; Baumert, Thomas [Institut für Physik, Universität Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel (Germany); Castillejo, Marta [Instituto de Química Física Rocasolano, IQFR-CSIC, Serrano 119, 28006 Madrid (Spain)

    2014-05-01

    Thin films of the biopolymers gelatine and chitosan were treated using femtosecond pulse shaping techniques combined with a microscope-based setup for material processing. The polymer films were irradiated with laser pulses of 35 fs and a central wavelength of 790 nm provided by an amplified Ti:Sapphire system. The effect of temporal pulse shaping, with quadratic and cubic spectral phases, on the induced morphology was analyzed by characterization of the created surface structures via scanning electron microscopy. We observed different material modification thresholds and different structure sizes for temporally asymmetric pulse shapes. The results indicate the possibility of control of the generated microstructures and are discussed in relation to the formation of free electrons and the different contributions of multi-photon and avalanche ionization processes.

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

    Science.gov (United States)

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

    2015-11-01

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

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

    Science.gov (United States)

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

    2007-07-01

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

  5. Switching of 800 nm femtosecond laser pulses using a compact PMN-PT modulator.

    Science.gov (United States)

    Adany, Peter; Price, E Shane; Johnson, Carey K; Zhang, Run; Hui, Rongqing

    2009-03-01

    A voltage-controlled birefringent cell based on ceramic PMN-PT material is used to enable fast intensity modulation of femtosecond laser pulses in the 800 nm wavelength window. The birefringent cell based on a PMN-PT compound has comparatively high electro-optic response, allowing for a short interaction length of 3 mm and thus very small size, low attenuation of 0.16 dB, and negligible broadening for 100 fs optical pulses. As an application example, agile wavelength tuning of optical pulses is demonstrated using the soliton self-frequency shift in a photonic crystal fiber. By dynamically controlling the optical power into the fiber, this system switches the wavelength of 100 fs pulses from 900 nm to beyond 1120 nm with less than 5 micros time. In addition, a feedback system stabilizes the wavelength drift against external conditions resulting in high wavelength stability.

  6. Pulse width effect on the dissociation probability of CH4+ in the intense femtosecond laser field

    Institute of Scientific and Technical Information of China (English)

    WANG Gao; SONG Di; LIU Yuyan; KONG Fan'ao

    2006-01-01

    The laser pulse width effect on the dissociation probability of CH4+ irradiated by an ultrafast laser has been investigated experimentally and theoretically. The femtosecond laser at 800 nm with an intensity of 8.0 × 1013 W/cm2 was used. The observed relative yield of the primary fragment ion CH3+ increases with increasing pulse width and tends to saturate when the pulse width is longer than 120 fs. The field-assisted dissociation (FAD) model and quasi-classical trajectory (QCT) calculation were applied to predicting the dissociation probability of CH4+.The calculated probability is corrected with the molecular orientation effect and the spatial distribution of laser intensity. The modified results show that the dissociation requires at least 23 fs and saturates with long pulse widths (≥100 rs). The result is approximately consistent with the experimental observation.

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

    Science.gov (United States)

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

    2014-05-05

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

  8. Tight focusing of femtosecond radially polarized light pulses through a dielectric interface.

    Science.gov (United States)

    Pu, Haosen; Shu, Jianhua; Chen, Ziyang; Lin, Zhili; Pu, Jixiong

    2015-09-01

    Based on the Richards-Wolf vector diffraction theory, we have derived the expressions for the electric field and the propagation velocity of femtosecond radially polarized light pulses focused by a high numerical aperture (NA) objective. The intensity distribution in the focus, wavefront spacings, and propagation velocity variation near the focus are investigated in detail by using numerical calculations. It is found that the propagation velocity of focused ultrashort light pulses changes dramatically near the focus, and the propagation velocity of the focused laser pulse is strongly dependent on the NA of an objective and the refractive index of media. Moreover, the usual propagation velocity of light pulses, as expected, decreases as the refractive index of media increases.

  9. Time-of-flight measurement with femtosecond pulses for high precision ranging lidar

    Science.gov (United States)

    Lee, J.; Kim, Y.-J.; Lee, K.; Lee, S.; Kim, S.-W.

    2010-10-01

    The time-of-flight of light pulses has long been used as a direct measure of distance, but the state-of-the-art measurement precision using conventional light pulses or microwaves reaches only several hundreds of micromeres. This is due to the bandwidth limit of the photodetectors available today, which is in the picosecond range at best. Here, we improve the time-of-flight precision to the nanometer regime by timing femtosecond pulses through phase-locking control of the pulse repetition rate using the optical cross-correlation technique that exploits a second-harmonic birefringence crystal and a balance photodetector. The enhanced capability is maintained at long range without periodic ambiguity, being well suited to terrestrial lidar applications such as geodetic surveying, range finders and absolute altimeters. This method could also be applied to future space missions of formation-flying satellites for synthetic aperture imaging and remote experiments related to the general relativity theory.

  10. Multipulse mode of heating nanoparticles by nanosecond, picosecond and femtosecond pulses

    Science.gov (United States)

    Letfullin, Renat R.; Iversen, Christian B.; George, Thomas F.

    2010-02-01

    Nanoparticles are being researched as a noninvasive method for selectively killing cancer cells. With particular antibody coatings on nanoparticles, they attach to the abnormal cells of interest (cancer or otherwise). Once attached, nanoparticles can be heated with UV/visible/IR or RF pulses, heating the surrounding area of the cell to the point of death. Researchers often use single-pulse or multipulse lasers when conducting nanoparticle ablation research. In the present paper, we are conducting an analysis to determine if the multipulse mode has any advantage in heating of spherical metal nanoparticles (such as accumulative heating effect). The laser heating of nanoparticles is very sensitive to the time structure of the incident pulsed laser radiation, the time interval between the pulses, and the number of pulses used in the experiments. We perform time-dependent simulations and detailed analyses of the different nonstationary pulsed laser-nanoparticle interaction modes, and show the advantages and disadvantages of multipulse (set of short pulses) and single-pulse laser heating of nanoparticles. A comparative analysis for both radiation modes (single-pulse and multipulse) are discussed for laser heating of metal nanotargets on nanosecond, picosecond and femtosecond time scales to make recommendations for efficient laser heating of nanomaterials in the experiments.

  11. Laser induced periodic surface structuring on Si by temporal shaped femtosecond pulses.

    Science.gov (United States)

    Almeida, G F B; Martins, R J; Otuka, A J G; Siqueira, J P; Mendonca, C R

    2015-10-19

    We investigated the effect of temporal shaped femtosecond pulses on silicon laser micromachining. By using sinusoidal spectral phases, pulse trains composed of sub-pulses with distinct temporal separations were generated and applied to the silicon surface to produce Laser Induced Periodic Surface Structures (LIPSS). The LIPSS obtained with different sub-pulse separation were analyzed by comparing the intensity of the two-dimensional fast Fourier Transform (2D-FFT) of the AFM images of the ripples (LIPSS). It was observed that LIPSS amplitude is more emphasized for the pulse train with sub-pulses separation of 128 fs, even when compared with the Fourier transform limited pulse. By estimating the carrier density achieved at the end of each pulse train, we have been able to interpret our results with the Sipe-Drude model, that predicts that LIPSS efficacy is higher for a specific induced carrier density. Hence, our results indicate that temporal shaping of the excitation pulse, performed by spectral phase modulation, can be explored in fs-laser microstructuring.

  12. Obtaining Cross-Sections of Paint Layers in Cultural Artifacts Using Femtosecond Pulsed Lasers.

    Science.gov (United States)

    Harada, Takaaki; Spence, Stephanie; Margiolakis, Athanasios; Deckoff-Jones, Skylar; Ploeger, Rebecca; Shugar, Aaron N; Hamm, James F; Dani, Keshav M; Dani, Anya R

    2017-01-26

    Recently, ultrafast lasers exhibiting high peak powers and extremely short pulse durations have created a new paradigm in materials processing. The precision and minimal thermal damage provided by ultrafast lasers in the machining of metals and dielectrics also suggests a novel application in obtaining precise cross-sections of fragile, combustible paint layers in artwork and cultural heritage property. Cross-sections of paint and other decorative layers on artwork provide critical information into its history and authenticity. However, the current methodology which uses a scalpel to obtain a cross-section can cause further damage, including crumbling, delamination, and paint compression. Here, we demonstrate the ability to make controlled cross-sections of paint layers with a femtosecond pulsed laser, with minimal damage to the surrounding artwork. The femtosecond laser cutting overcomes challenges such as fragile paint disintegrating under scalpel pressure, or oxidation by the continuous-wave (CW) laser. Variations in laser power and translational speed of the laser while cutting exhibit different benefits for cross-section sampling. The use of femtosecond lasers in studying artwork also presents new possibilities in analyzing, sampling, and cleaning of artwork with minimal destructive effects.

  13. Photodissociation of Cycloketones by Ultraintense Femtosecond Laser Pulses

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Photodissociation of cyclopentanone (C5H8O) and cyclohexanone (C6H10O) was studied with 800nm, 50fs laser pulse at intensities of 5.0-13.0×1013 W/cm2. A time of flight mass spectrometer was employed to detect the ion signals. Parent ions dominated at lower laser intensities. Fragmentation of the parent ions increases with increasing laser intensity and molecular size. The fragmentation mechanism was discussed.

  14. Propagation of ultrastrong femtosecond laser pulses in PLASMON-X

    CERN Document Server

    Jovanovic, Dusan; Tanjia, Fatema; De Nicola, Sergio

    2011-01-01

    The derivation is presented of the nonlinear equations that describe the propagation of ultrashort laser pulses in a plasma, in the Plasmon-X device. It is shown that the Plasmon-X scheme used for the electron acceleration uses a sufficiently broad beam ($L_\\bot\\sim 130\\,\\,\\mu{\\rm m}$) that justifies the use of the standard stationary 1-D approximation in the electron hydrodynamic equations, since the pulse width is sufficiently bigger than the pulse length ($\\sim 7.5\\,\\,\\mu{\\rm m}$). Furthermore, with the laser power of $W\\leq 250$ TW and the $130\\,\\,\\mu{\\rm m}$ spot size, the dimensionless laser vector potential is sufficiently small $|A_{\\bot_0}|^2/{2} = ({W}/{c^2\\epsilon_0})({\\lambda^2}/{8 \\pi^2 c})({4}/{\\pi L_\\bot^2})({e}/{m_0 c})^2 \\sim 0.26$, the nonlinearity is sufficiently weak to allow the power expansion in the nonlinear Poissons's equation. Such approximation yields a nonlinear Schr\\" odinger equation with a reactive nonlocal nonlinear term. The nonlocality contains a cosine function under the int...

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

    Science.gov (United States)

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

    2017-04-01

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

  16. Plasmon-enhanced terahertz emission in self-assembled quantum dots by femtosecond pulses

    Energy Technology Data Exchange (ETDEWEB)

    Carreño, F., E-mail: ferpo@fis.ucm.es; Antón, M. A., E-mail: antonm@fis.ucm.es; Melle, Sonia, E-mail: smelle@fis.ucm.es; Calderón, Oscar G., E-mail: oscargc@fis.ucm.es; Cabrera-Granado, E., E-mail: ecabrera@fis.ucm.es [Facultad de Óptica y Optometría, Universidad Complutense de Madrid, C/ Arcos de Jalón 118, 28037 Madrid (Spain); Cox, Joel, E-mail: jcox27@uwo.ca; Singh, Mahi R., E-mail: msingh@uwo.ca [Department of Physics and Astronomy, The University of Western Ontario, London N6A 3K7 (Canada); Egatz-Gómez, A., E-mail: Ana.Egatz-Gomez.1@nd.edu [Department of Chemical and Biomolecular Engineering, University of Notre Dame, South Bend, Indiana 46556 (United States)

    2014-02-14

    A scheme for terahertz (THz) generation from intraband transition in a self-assembled quantum dot (QD) molecule coupled to a metallic nanoparticle (MNP) is analyzed. The QD structure is described as a three-level atom-like system using the density matrix formalism. The MNP with spherical geometry is considered in the quasistatic approximation. A femtosecond laser pulse creates a coherent superposition of two subbands in the quantum dots and produces localized surface plasmons in the nanoparticle which act back upon the QD molecule via dipole-dipole interaction. As a result, coherent THz radiation with a frequency corresponding to the interlevel spacing can be obtained, which is strongly modified by the presence of the MNP. The peak value of the terahertz signal is analyzed as a function of nanoparticle's size, the MNP to QD distance, and the area of the applied laser field. In addition, we theoretically demonstrate that the terahertz pulse generation can be effectively controlled by making use of a train of femtosecond laser pulses. We show that by a proper choice of the parameters characterizing the pulse train a huge enhancement of the terahertz signal is obtained.

  17. Sub-wavelength surface structuring on stainless steel by femtosecond laser pulses

    Science.gov (United States)

    Qi, Litao; Hu, Jinping; Lin, Haipeng; Xing, Hualu

    2014-12-01

    In this research, the formation of laser-induced periodic surface structures (LIPSS) on the stainless steel surface by femtosecond laser pulses was investigated under static irradiation and line-scanning experiment. In the experiment, we used a commercial amplified Ti:sapphire laser system that generated 164 fs laser pulses with a maximum pulse energy (Ep) of 1 mJ at a 1 kHz repetition rate and with a central wavelength λ = 780 nm. To obtain a fine periodic ordering of surface nanostructures, the laser beam, through a 0.2 mm pinhole aperture positioned near the 5× objective lens, was focused onto the sample. The samples were mounted on an XYZ-translation stage and irradiated in static and line-scanning experiment. The morphology of the induced periodic structure was examined by scanning electron microscopy. The surface profile was measured by atomic force microscopy. High-spatial-frequency LIPSS (HSFL) with a period of 255 +/- 21 nm were obtained over the entire ablated area. HSFL were found to form on low-spatial-frequency LIPSS (LSFL). From our results we elucidated the relationship between the formation of LSFL and HSFL to obtain an enhanced understanding of the mechanism of HSFL formation by femtosecond laser pulses. A large number of applications have been proposed, such as improvement of the optical properties of the surface, new cutting tool development and hard diamond. More applications could be found as the spatial period of HSFL on different materials comes into sub-100 nm.

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

    Science.gov (United States)

    Ling, Yan; Lu, Fang

    2006-12-20

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

  19. Coherent control of ultracold molecule dynamics in a magneto-optical trap using chirped femtosecond laser pulses

    CERN Document Server

    Brown, B L; Walmsley, I A; Brown, Benjamin L.; Dicks, Alexander J.; Walmsley, Ian A.

    2005-01-01

    We have studied the effects of chirped femtosecond laser pulses on the formation of ultracold molecules in a Rb magneto-optical trap. We have found that application of chirped femtosecond pulses suppressed the formation of 85Rb-2 and 87Rb-2 lowest triplet state molecules in contrast to comparable non-chirped pulses, cw illumination, and background formation rates. Variation of the amount of chirp indicated that this suppression is coherent in nature, suggesting that coherent control is likely to be useful for manipulating the dynamics of ultracold quantum molecular gases.

  20. Coherent control of ultracold molecule dynamics in a magneto-optical trap by use of chirped femtosecond laser pulses.

    Science.gov (United States)

    Brown, Benjamin L; Dicks, Alexander J; Walmsley, Ian A

    2006-05-05

    We have studied the effects of chirped femtosecond laser pulses on the formation of ultracold molecules in a Rb magneto-optical trap. We have found that application of chirped femtosecond pulses suppressed the formation of (85)Rb and (87)Rb(2) a(3)sigma(+)(u) molecules in contrast to comparable nonchirped pulses, cw illumination, and background formation rates. Variation of the amount of chirp indicated that this suppression is coherent in nature, suggesting that coherent control is likely to be useful for manipulating the dynamics of ultracold quantum molecular gases.

  1. Formation of quasi-periodic nano- and microstructures on silicon surface under IR and UV femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Ionin, Andrei A; Golosov, E V; Kolobov, Yu R; Kudryashov, Sergei I; Ligachev, A E; Makarov, Sergei V; Novoselov, Yurii N; Seleznev, L V; Sinitsyn, D V

    2011-09-30

    Quasi-periodic nano- and microstructures have been formed on silicon surface using IR ( {lambda} Almost-Equal-To 744 nm) and UV ( {lambda} Almost-Equal-To 248 nm) femtosecond laser pulses. The influence of the incident energy density and the number of pulses on the structured surface topology has been investigated. The silicon nanostructurisation thresholds have been determined for the above-mentioned wavelengths. Modulation of the surface relief at the doubled spatial frequency is revealed and explained qualitatively. The periods of the nanostructures formed on the silicon surface under IR and UV femtosecond laser pulses are comparatively analysed and discussed.

  2. Laser-driven plasma wakefield electron acceleration and coherent femtosecond pulse generation in X-ray and gamma ranges

    Science.gov (United States)

    Trunov, V. I.; Lotov, K. V.; Gubin, K. V.; Pestryakov, E. V.; Bagayev, S. N.; Logachev, P. V.

    2017-01-01

    The laser wakefield acceleration (LWFA) of electrons in capillaries and gas jets followed by inverse Compton scattering of high intensity femtosecond laser pulses is discussed. The drive and scattered pulses will be produced by the two-channel multi-terawatt laser system developed in ILP SB RAS.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-11-01

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

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

    Science.gov (United States)

    Block, Erica K.

    Femtosecond lasers are now prolific in many disciplines. While the mechanisms of femtosecond-material interactions are widely understood, femtosecond lasers as industrial and medical tools still have shortcomings. Currently conventional state of the art platforms are unable to support low numerical aperture (NA) beams (that provide large focal volumes and long working distances) without sacrificing axial precision. Furthermore inline (refractive) delivery systems that are necessary for industrial and clinical medical applications are currently hindered by nonlinear effects when delivering femtosecond pulses with tens of microJoule pulse energies and greater. In this thesis Simultaneous Space Time Focusing (SSTF) is presented as a new paradigm to move the field of femtosecond micromachining significantly forward. With this system we have delivered microjoule femtosecond pulses with low numerical aperture geometries (thesis we have focused on significantly streamlining the SSTF design into a flexible, single grating, integrated SSTF/chirped-pulse amplification system with an inline (refractive) delivery system to move towards industrial and clinical medical applications. For the first time this design also allows for variation of the beam aspect ratio of an SSTF beam, and thus the degree of pulse-front tilt at focus, while maintaining a net zero-dispersion system. Accessible variation of pulse front tilt gives full spatiotemporal control over the intensity distribution at the focus and another degree of freedom in ablation processes. Finally, real-time visualization of the femtosecond machining process is vital for industrial/medical applications, especially in medical where imaging is through scattering materials. At present a secondary imaging laser system is needed in conjunction with the surgical laser. Using complex, off the shelf, refractive optics we have created a real-time, inline (refractive), delivery system that is robust to scattering and integrated

  5. Propagation delay of femtosecond pulses in an optical amplifier

    DEFF Research Database (Denmark)

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

    The recent realization of tunable propagation delay of optical pulses in solid-state and semiconductor optical media1,2 has attracted great attention as such a functionality enables a whole new class of optical components in optical communications systems and signal processing3. The reported...... measurements as function of injected bias current. Good agreement is found with simple models of the real and imaginary parts of the active material's susceptibility. 1 M.S. Bigelow, N.N. Lepeshkin, and R. Boyd, Phys. Rev. Lett. 90, 113903-1—4 (2003) 2 P.-C. Ku et al., Opt. Lett. 19, 2291—2293 (2004) 3 C...

  6. The role of plasma shielding in collinear double-pulse femtosecond laser-induced breakdown spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Penczak, John [Department of Chemistry (m/c 111), University of Illinois at Chicago, Chicago, IL 60680-7061 (United States); Kupfer, Rotem; Bar, Ilana [Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel); Gordon, Robert J. [Department of Chemistry (m/c 111), University of Illinois at Chicago, Chicago, IL 60680-7061 (United States)

    2014-07-01

    We report an experimental and theoretical study of the mechanism for the enhancement of the laser-induced breakdown signal produced by two collinear femtosecond pulses separated by a suitable delay. A bilayer sample consisting of a 500 nm thick film of Ag deposited on Al was used in the experiments, and a particle-in-cell (PIC) simulation was implemented in the theoretical part of the study. Experiments on the effect of laser polarization, performed at a 30° angle of incidence over a wide range of fluences, together with the PIC results, showed that the plasma produced by the first pulse was further excited by the second pulse. Experiments at normal incidence and a fluence of 200 J/cm{sup 2} showed that the second pulse did not penetrate the Ag layer. In addition, measurements of the effect of pulse delay on the signal supported the conclusion that double pulse enhancement is produced by plasma heating rather than by increased surface ablation. - Highlights: • We study the mechanism for collinear double-pulse enhancement of LIBS produced by a fs laser. • We use a bilayer of Ag on Al to determine which region is reached by the 2nd pulse. • Signal enhancement is produced by plasma heating rather than by increased surface ablation. • Particle-in-cell calculations show that plasma shielding plays a key role.

  7. Evolution of energy deposition during glass cutting with pulsed femtosecond laser radiation

    Science.gov (United States)

    Kalupka, C.; Großmann, D.; Reininghaus, M.

    2017-05-01

    We report on investigations of the energy deposition in the volume of thin glass during an ablation cutting process with pulsed femtosecond laser radiation by time-resolved pump-probe shadowgraphy. For a single laser pulse, the temporal evolution of the transient electronic excitation of the glass volume is imaged up to 10 ps after initial excitation. For an increasing number of laser pulses, the spatial excitation of the glass volume significantly changes compared to single pulse irradiation. Sharp spikes are observed, which reduce the transmission of the illuminating probe pulse. This indicates local maxima of the absorption and, therefore, energy deposition of the pump pulse energy in the glass volume. Furthermore, for an increasing number of pulses, different shapes of the surface ablation crater are observed. To study the correlation between the shape of the surface ablation crater and the energy deposition in the glass volume, simulations of the spatial intensity distribution of the pump pulse are executed by means of linear beam propagation method. We show that the transient excitation spikes observed by pump-probe shadowgraphy can be explained by refraction and diffraction of the laser radiation at the surface ablation crater. Our results provide an experimental validation for the physical reason of an ablation stop for an ablation cutting process. Moreover, the simulations allow for the prediction of damage inside the glass volume.

  8. Polarization operator approach to pair creation in short laser pulses

    CERN Document Server

    Meuren, Sebastian; Keitel, Christoph H; Di Piazza, Antonino

    2014-01-01

    We investigate the nonlinear Breit-Wheeler process inside short laser pulses, i.e. the creation of an electron-positron pair induced by a gamma photon inside a plane-wave background field. To obtain the total pair-creation probability we verify (to leading-order) the cutting rule for the polarization operator in the realm of strong-field QED by an explicit calculation. Furthermore, a double-integral representation for the leading-order contribution to the field-dependent part of the polarization operator is derived. The combination of both results yields a compact expression for the total pair-creation probability inside an arbitrary plane-wave background field. It is shown numerically that with presently available technology pair-creation probabilities of the order of ten percent could be reached for a single gamma photon.

  9. Paired pulse TMS stimulation and human tongue corticomotor pathways

    DEFF Research Database (Denmark)

    Kothari, Mohit; Svensson, Peter; Nielsen, Jørgen Feldbæk

    Objectives: Paired pulse transcranial magnetic stimulation (ppTMS) can be used to assess short-term interval intra-cortical inhibitory (SICI) and facilitatory (ICF) networks. The degree of SICI and ICF varies with interstimulus intervals (ISI) and stimulus intensities of the conditioning stimulus...... intensities (P = 0.984). Post-hoc tests revealed that there was significant SICI with ppTMS ISI of 2, 2.5, 3, and 3.5 ms compared with single pulse stimulation (Pstimulation (P=0.988). There was no interaction between...

  10. Lasing of ambient air with microjoule pulse energy pumped by a multi terawatt IR femtosecond laser

    CERN Document Server

    Point, Guillaume; Brelet, Yohann; Mitryukovskiy, Sergey; Ding, Pengji; Houard, Aurélien; Mysyrowicz, André

    2014-01-01

    We report on the lasing action of atmospheric air pumped by an 800 nm femtosecond laser pulse with peak power up to 4 TW. Lasing emission at 428 nm increases rapidly over a small range of pump laser power, followed by saturation above ~ 1.5 TW. The maximum lasing pulse energy is measured to be 2.6 uJ corresponding to an emission power in the MW range, while a maximum conversion efficiency of is measured at moderate pump pulse energy. The optical gain inside the filament plasma is estimated to be excess of 0.7/cm. The lasing emission shows a doughnut profile, reflecting the spatial distribution of the pump-generated white-light continuum that acts as a seed for the lasing. We attribute the pronounced saturation to the defocusing of the seed in the plasma amplifying region and to the saturation of the seed intensity.

  11. Photoelectron angular distribution in two-pathway ionization of neon with femtosecond XUV pulses

    CERN Document Server

    Douguet, Nicolas; Staroselskaya, Ekaterina I; Bartschat, Klaus; Grum-Grzhimailo, Alexei N

    2016-01-01

    We analyze the photoelectron angular distribution in two-pathway interference between non\\-resonant one-photon and resonant two-photon ionization of neon. We consider a bichromatic femtosecond XUV pulse whose fundamental frequency is tuned near the $2p^5 3s$ atomic states of neon. The time-dependent Schr\\"odinger equation is solved and the results are employed to compute the angular distribution and the associated anisotropy parameters at the main photoelectron line. We also employ a time-dependent perturbative approach, which allows obtaining information on the process for a large range of pulse parameters, including the steady-state case of continuous radiation, i.e., an infinitely long pulse. The results from the two methods are in relatively good agreement over the domain of applicability of perturbation theory.

  12. Broadband supercontinuum generation with femtosecond pulse width in erbium-doped fiber laser (EDFL)

    Science.gov (United States)

    Rifin, S. N. M.; Zulkifli, M. Z.; Hassan, S. N. M.; Munajat, Y.; Ahmad, H.

    2016-11-01

    We demonstrate two flat plateaus and the low-noise spectrum of supercontinuum generation (SCG) in a highly nonlinear fiber (HNLF), injected by an amplified picosecond pulse seed of a carbon nanotube-based passively mode locked erbium-doped fiber laser. A broad spectrum of width approximately 1090 nm spanning the range 1130-2220 nm is obtained and the pulse width is compressed to the shorter duration of 70 fs. Variations of the injected peak power up to 33.78 kW into the HNLF are compared and the broad spectrum SCG profiles slightly expand for each of the injected peak powers. This straightforward configuration of SCG offers low output power and ultra-narrow femtosecond pulse width. The results facilitate the development of all fiber time-domain spectroscopy systems based on the photoconductive antenna technique.

  13. Enhancing strong-field induced molecular vibration with femtosecond pulse shaping

    CERN Document Server

    Bitter, Martin; Milner, Valery

    2012-01-01

    This work investigates the utility of femtosecond pulse shaping in increasing the efficiency of Raman excitation of molecules in the strong-field interaction regime. We study experimentally and theoretically the effect of pulse shaping on the strength of non-resonant coherent anti-Stokes Raman scattering in iodine vapor at laser intensities exceeding $10^{13}$ W/cm$^2$. We show that unlike the perturbative case, shaping strong non-resonant laser pulses can increase the signal strength beyond that observed with the transform-limited excitation. Both adiabatic and non-adiabatic schemes of excitation are explored, and the differences of their potential in increasing the excitation efficiency are discussed.

  14. Selective triggering of phase change in dielectrics by femtosecond pulse trains based on electron dynamics control

    Institute of Scientific and Technical Information of China (English)

    Xu Chuan-Cai; Jiang Lan; Leng Ni; Liu Peng-Jun

    2013-01-01

    In this study we experimentally reveal that the phase change mechanism can be selectively triggered by shaping femtosecond pulse trains based on electron dynamics control (EDC),including manipulation of excitations,ionizations,densities,and temperatures of electrons.By designing the pulse energy distribution to adjust the absorptions,excitations,ionizations,and recombinations of electrons,the dominant phase change mechanism experiences transition from nonthermal to thermal process.This phenomenon is observed in quadruple,triple,and double pulses per train ablation of fused silica separately.This opens up possibilities for controlling phase change mechanisms by EDC,which is of great significance in laser processing of dielectrics and fabrication of integrated nano-and micro-optical devices.

  15. Time-resolved measurement of single pulse femtosecond laser-induced periodic surface structure formation

    CERN Document Server

    Kafka, K R P; Li, H; Yi, A; Cheng, J; Chowdhury, E A

    2015-01-01

    Time-resolved diffraction microscopy technique has been used to observe the formation of laser-induced periodic surface structures (LIPSS) from the interaction of a single femtosecond laser pulse (pump) with a nano-scale groove mechanically formed on a single-crystal Cu substrate. The interaction dynamics (0-1200 ps) was captured by diffracting a time-delayed, frequency-doubled pulse from nascent LIPSS formation induced by the pump with an infinity-conjugate microscopy setup. The LIPSS ripples are observed to form sequentially outward from the groove edge, with the first one forming after 50 ps. A 1-D analytical model of electron heating and surface plasmon polariton (SPP) excitation induced by the interaction of incoming laser pulse with the groove edge qualitatively explains the time-evloution of LIPSS formation.

  16. Characteristics of filamentation in ZK7 glass by negatively chirped femtosecond laser pulses

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The filamentation characteristics of femtosecond laser pulses in ZK7 glass are in- vestigated experimentally as a function of initial negative chirps. It is found that the filament threshold power grows rapidly and the filament length extends over a long distance with increasing initial temporal chirps. The measurement of supercon- tinuum reveals that the plasma generation process within filamentation becomes weaker as the initial negative chirp increases, leading to a self-guiding long light channel dominated by Kerr nonlinearity. The interference of transverse rings in multifilamentation of the chirped laser pulses is observed as well. Analyses and discussions give an interpretation of this chirp-induced ionization-free filamenta- tion. These results indicate that initial chirps will play a crucial role in the filament formation of ultrashort laser pulses in transparent media.

  17. Femtosecond pulse shaping as analytic tool in mass spectrometry of complex polyatomic systems

    Science.gov (United States)

    Laarmann, Tim; Shchatsinin, Ihar; Singh, Pushkar; Zhavoronkov, Nickolai; Schulz, Claus Peter; Hertel, Ingolf Volker

    2008-04-01

    An additional dimension to mass spectrometric studies on building blocks of proteins is discussed in this paper. The present approach is based on tailored femtosecond laser pulses, using the concept of strong-field pulse shaping in an adaptive feedback loop. We show that control strategies making use of coherent properties of the electromagnetic wave allow one to break pre-selected backbone bonds in amino acid complexes that may be regarded as peptide model systems. Studies on different chromophores, such as phenylalanine and alanine, while keeping the backbone structure unchanged elucidates the effect of the excitation dynamics on the relaxation pathways. The observation of protonated species in the corresponding mass spectra indicates that optimal control of ultrafast laser pulses may even be useful to study intramolecular reactions such as hydrogen- or proton-transfer in particular cases. This opens new perspectives for biophysical and biochemical research, since these photochemical reactions are suggested to explain, e.g. photostability of DNA.

  18. Femtosecond X-ray Pulses From a frequency chirped SASE FEL

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Z

    2003-01-14

    We discuss the temporal and spectral properties of self-amplified spontaneous emission (SASE) utilizing an energy-chirped electron beam. A short temporal pulse is generated by using a monochromator to select a narrow radiation bandwidth from the frequency chirped SASE. For the filtered radiation, the minimum pulse length is limited by the intrinsic SASE bandwidth, while the number of modes and the energy fluctuation can be controlled through the monochromator bandwidth. Two cases are considered: (1) placing the monochromator at the end of a single long undulator; (2) placing the monochromator after an initial undulator and amplifying the short-duration output in a second undulator. We analyze these cases and show that tens of femtosecond x-ray pulses may be generated for the linac coherent light source.

  19. Processing Structures on Human Fingernail Surfaces Using a Focused Near-Infrared Femtosecond Laser Pulse

    Science.gov (United States)

    Hayasaki, Yoshio; Takagi, Hayato; Takita, Akihiro; Yamamoto, Hirotsugu; Nishida, Nobuo; Misawa, Hiroaki

    2004-12-01

    We investigated the processing of a human fingernail surface using a tightly focused femtosecond laser pulse. The processed structure in the fingernail surface is strongly dependent on the focus position and irradiation energy of the single laser pulse. We observed a ring, a simple pit, a small pit with a surrounding uplift, an irregular jagged surface, and a swell containing a void, depending on the focus position. We also observed a sudden change in the size of the processed structure according to the irradiation pulse energy. From a linear theoretical estimation based on the diffraction of the laser beam, we found that the sudden change is primarily due to the diffraction pattern generated by the circular aperture of the objective lens. We also describe the processing features by comparing the structures processed in a fingernail with those processed in glass.

  20. Modification of narrow ablating capillaries under the influence of multiple femtosecond laser pulses

    CERN Document Server

    Gubin, K V; Trunov, V I; Pestryakov, E V

    2016-01-01

    Powerful femtosecond laser pulses that propagate through narrow ablating capillaries cause modification of capillary walls, which is studied experimentally and theoretically. At low intensities, laser-induced periodic surface structures (LIPSS) and porous coating composed of sub-micron particles appear on the walls. At higher intensities, the surface is covered by deposited droplets of the size up to 10 $\\mu$m. In both cases, the ablated material forms a solid plug that completely blocks the capillary after several hundreds or thousands of pulses. The suggested theoretical model indicates that plug formation is a universal effect. It must take place in any narrow tube subject to ablation under the action of short laser pulses.

  1. Anisotropy modulations of femtosecond laser pulse induced periodic surface structures on silicon by adjusting double pulse delay.

    Science.gov (United States)

    Han, Weina; Jiang, Lan; Li, Xiaowei; Wang, Qingsong; Li, Hao; Lu, YongFeng

    2014-06-30

    We demonstrate that the polarization-dependent anisotropy of the laser-induced periodic surface structure (LIPSS) on silicon can be adjusted by designing a femtosecond laser pulse train (800 nm, 50 fs, 1 kHz). By varying the pulse delay from 100 to 1600 fs within a double pulse train to reduce the deposited pulse energy, which weakens the directional surface plasmon polarition (SPP)-laser energy coupling based on the initial formed ripple structure, the polarization-dependent geometrical morphology of the LIPSS evolves from a nearly isotropic circular shape to a somewhat elongated elliptical shape. Meanwhile, the controllable anisotropy of the two-dimensional scanned-line widths with different directions is achieved based on a certain pulse delay combined with the scanning speed. This can effectively realize better control over large-area uniform LIPSS formation. As an example, we further show that the large-area LIPSS can be formed with different scanning times under different pulse delays.

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

    Science.gov (United States)

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

    2015-05-01

    Laser induced periodic surface structures (LIPSS) self-organized on Ti surface after irradiations by femtosecond laser beam composed by double pulses with a fixed time delay of 160 fs. The fluence of the first pulse (FPP), responsible for surface plasma formation, was varied in the range 10-50 mJ cm-2 and always kept below the LIPSS formation threshold fluence (FLIPSS) on Ti for 50-single-shots exposure. The fluence of the delayed pulse (FLP), responsible for LIPSS self-organization, was varied in the range 60-150 mJ cm-2 and always kept above FLIPSS. Regardless the specific fluence FLP of the delayed pulse, the interspace of the grating structures increases with the increase of FPP, that is an increase of the surface plasma density. This tendency suggests that a variation of the surface plasma density, due to a variation of FPP, actually leads to a modification of the grating features. Moreover, we observed that the LIPSS periodicities after double pulse exposures are in quite good agreement with data on LIPSS periodicities after single 160 fs pulse irradiations on Ti surface and with the curve predicted by the parametric decay model. This experimental result suggests that the preformed plasma might be produced in the rising edge of the temporal profile of the laser pulse.

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

    Science.gov (United States)

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

    2010-03-29

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

  4. An explanation of trans-ionospheric pulse pairs

    CERN Document Server

    Wu, H -C

    2016-01-01

    Trans-ionospheric pulse pairs are the most powerful natural radio signals on the Earth and associated with lightning. They have been discovered for two decades by satellites, but their origin still remains elusive. Here we attribute these radio signals to relativistic electrons produced by cloud-to-ground lightning. When these electrons strike the ground, radio bursts are emitted towards space in a narrow cone. This model naturally explains the interval, duration, polarization, coherence and bimodal feature of the pulse pairs. Based on electron parameters inferred from x-ray observation of lightning, the calculated signal intensity agrees with the measurement of satellites. Our results are useful to develop global warning system of storms and hurricane based on GPS satellites.

  5. Rippled area formed by surface plasmon polaritons upon femtosecond laser double-pulse irradiation of silicon: the role of carrier generation and relaxation processes

    Science.gov (United States)

    Derrien, Thibault J.-Y.; Krüger, Jörg; Itina, Tatiana E.; Höhm, Sandra; Rosenfeld, Arkadi; Bonse, Jörn

    2014-10-01

    The formation of laser-induced periodic surface structures (LIPSS, ripples) upon irradiation of silicon with multiple irradiation sequences consisting of femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied numerically using a rate equation system along with a two-temperature model accounting for one- and two-photon absorption and subsequent carrier diffusion and Auger recombination processes. The temporal delay between the individual equal-energy fs-laser pulses was varied between 0 and ˜4 ps for quantification of the transient carrier densities in the conduction band of the laser-excited silicon. The results of the numerical analysis reveal the importance of carrier generation and relaxation processes in fs-LIPSS formation on silicon and quantitatively explain the two time constants of the delay-dependent decrease of the low spatial frequency LIPSS (LSFL) area observed experimentally. The role of carrier generation, diffusion and recombination is quantified individually.

  6. Femtosecond pulse generation and amplification in Yb-doped fibre oscillator–amplifier system

    Indian Academy of Sciences (India)

    P K Mukhopadhyay

    2010-11-01

    In recent times ytterbium (Yb) doped fibre-based mode-locked master oscillator and power amplifier have attracted a great deal of interest because of their inherent advantages like flexibility, reliability, compactness, high power handling capability and diffraction limited output beam quality as compared to the solid-state counterpart. But, to successfully develope of high-power femtosecond oscillator–amplifier system based on Yb- doped fibre, an appropriate choice of the mode-locking regime and the amplifier geometry are required. Development of an all-fibre integrated high-power Yb-doped fibre oscillator–amplifier system in which the advantages of a fibre-based system can be fully exploited remained a challenge as it requires the careful optimization of dispersion, nonlinearity, gain and ASE contribution. In this article, femto-second pulse generation in Yb-doped fibre oscillator in different mode-locking regimes are reviewed and the details of development and characterization of an all-fibre, high-power, low-noise amplifier system seeded by an all-normal-dispersion mode-locked Yb-doped fibre laser oscillator is described. More than 10 W of average power is obtained from the fibre oscillator–amplifier system at a repetition rate of 43 MHz with diffraction-limited beam quality. Amplified pulses are de-chirped to sub-160 fs duration in a grating compressor. This is the first 10 W-level source of femtosecond pulses with completely fibre-integrated amplification comprised of commercially available components.

  7. Prepulse controlled electron acceleration from solids by a femtosecond laser pulse in the slightly relativistic regime

    Science.gov (United States)

    Ivanov, K. A.; Tsymbalov, I. N.; Shulyapov, S. A.; Krestovskikh, D. A.; Brantov, A. V.; Bychenkov, V. Yu.; Volkov, R. V.; Savel'ev, A. B.

    2017-06-01

    We present results from the experimental and numerical study of electron heating and acceleration under the action of a 50 fs high contrast laser pulse [intensities ˜(1-4) × 1018 W/cm2] with a controlled preplasma that was created by a 6 ns laser "prepulse" with intensity ˜1012 W/cm2. A substantial increase both in the gamma yield and "temperature" was obtained by the proper adjustment of the time delay between the two pulses (0-5 ns), while the gamma yield dropped to almost zero values if the nanosecond pulse came 10-20 ns in advance of the femtosecond one. Comprehensive optical diagnostics (shadowgraphy, interferometry, and angular resolved self-emission measurements) data allowed us to estimate the electron density profile. The latter profile was used for making numerical Particle-in-cell simulations which describe the gamma yield enhancement well. We also illustrate how the observed drop in the gamma yield within a certain range of delays was due to ionization defocusing of the femtosecond beam in an expanding long-scale (L/λ > 1) preplasma.

  8. White-light generation control with crossing beams of femtosecond laser pulses.

    Science.gov (United States)

    Kolomenskii, A A; Strohaber, J; Kaya, N; Kaya, G; Sokolov, A V; Schuessler, H A

    2016-01-11

    We investigated the variations in generated white-light when crossing two femtosecond laser beams in a Kerr medium. By changing the relative delay of two interacting intense femtosecond laser pulses, we show that white-light generation can be enhanced or suppressed. With a decrease of the relative delay an enhancement of the white-light output was observed, which at even smaller delays was reverted to a suppression of white-light generation. Under choosen conditions, the level of suppression resulted in a white-light output lower than the initial level corresponding to large delays, when the pulses do not overlap in time. The enhancement of the white-light generation takes place in the pulse that is lagging. We found that the effect of the interaction of the beams depends on their relative orientation of polarization and increases when the polarizations are changed from perpendicular to parallel. The observed effects are explained by noting that at intermediate delays, the perturbations introduced in the path of the lagging beam lead to a shortening of the length of filament formation and enhancement of the white-light generation, whereas at small delays the stronger interaction and mutual rescattering reduces the intensity in the central part of the beams, suppressing filamentation and white-light generation.

  9. Coloured Conical Emission in BBO Crystal Pumped by Second Harmonic Femtosecond Pulses

    Institute of Scientific and Technical Information of China (English)

    BI Jie; LI Yu-Hua; YIN Juan-Juan; LU Pei-Xiang

    2009-01-01

    Coloured conical emission (CCE) is investigated experimentally in a β-barium borate crystal excited by intense second harmonic femtosecond pulses. Contrary sequences of green and red conical emission with variable di-ameters are observed at different incidence angles, which is consistent with the calculation results based on the phase matching condition. As its broad range spectrum, CCE offers an alternative means to produce an ultrafast broadband light source. It is found that the spectrum of green CE shifts toward longer wavelengths as the length of BBO crystal increased.

  10. Competition between multiphoton/tunnel ionization and filamentation induced by powerful femtosecond laser pulses in air

    Institute of Scientific and Technical Information of China (English)

    W. Liu; Q. Luo; S. L. Chin

    2003-01-01

    In this work we present experiments by focusing 42 femtosecond laser pulses in air using three different focal length lenses: f=100, 30 and 5 cm. For the longest focal length, only the filament, which is a weak plasma column, is observed. When the shorter focal length lens is used, a high density plasma is generated near the geometrical focus and coexists with a weak plasma channel of the filament. Under the tightest focusing condition, filamentation is prevented and only a strong plasma volume appears at the geometrical focus.

  11. PbTe thin films grown by femtosecond pulsed laser deposition

    Science.gov (United States)

    Rodriguez, E.; Silva, D.; Moya, L.; Cesar, C. L.; Barbosa, L. C.; Schrank, A.; Souza Filho, C. R.; de Oliveira, E. P.

    2007-09-01

    PbTe thin films were grown on BK7 glass and Si(100) substrates using femtosecond pulsed laser deposition at room temperature. The influence of the background pressure and the laser fluence on the structural and optical characteristics of the PbTe films was studied. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the surface and structural properties of the deposited PbTe thin films, respectively. Transmission spectroscopy measurements in the visible and infrared region (VIS-IR) were used to investigate the optical properties of the PbTe thin films.

  12. Polarization-Dependence of Coulomb Explosion of CO Irradiated with an Intense Femtosecond Laser Pulse

    Institute of Scientific and Technical Information of China (English)

    陈建新; 马日; 任海振; 李霞; 杨宏; 龚旗煌

    2003-01-01

    Laser-induced Coulomb explosion of CO is studied experimentally using differently polarized femtosecond laser pulses of 2 × 1015 W/cm2 intensity at λ = 800 nm. The channels of molecular Coulomb explosion are observed to be independent of the laser polarizations. The critical distance R is deduced to be larger for the circularly polarized light in comparison with the linearly polarized light. The initial emissions of C+, C2+, O+, and O2+ions are anisotropic for linear polarization and isotropic for circular polarization. The suppression of ionization occurs for the elliptically and circularly polarized lasers.

  13. Microstructuring of polymer films by femtosecond pulses through optically trapped polystyrene microspheres

    Energy Technology Data Exchange (ETDEWEB)

    Astaf' ev, A A; Shakhov, A M; Sarkisov, Oleg M; Nadtochenko, V A

    2013-04-30

    We report the laser ablation of polymers by femtosecond (18 and 54 fs) pulses focused by 1 and 3.8 {mu}m diameter spherical microlenses, which are held by optical traps. It is shown that this technique allows one to produce surface structures with lateral dimensions up to {lambda}/6 (125 nm). It is found that the size of the structures depends on the diameter of the microlens; the highest spatial resolution is achieved by using 1 {mu}m diameter microlenses. (extreme light fields and their applications)

  14. Optical Kerr effect of tRNA solution induced by femtosecond laser pulses

    Science.gov (United States)

    Kucia, Weronika E.; Sharma, Gargi; Joseph, Cecil S.; Sarbak, Szymon; Oliver, Cameron; Dobek, Andrzej; Giles, Robert H.

    2016-10-01

    The optical Kerr effect (OKE) in a transfer ribonucleic acid (tRNA) solution induced by femtosecond pulses of linearly polarized pump light (λi = 800 nm) and sounded by probe light (λp = 800 nm) was studied. The measurements were performed to find nonlinear optical parameters describing a single molecule (molecular Kerr constant K, mean nonlinear third order optical polarizability cpi) and to compare them with our previous OKE results obtained in ns and ps time range. The OKE experiment has proven to be an efficient method to obtain the nonlinear parameters of single molecules in solution, which reflects dynamic structure changes.

  15. Characterization of Structures Induced in LiTaO{sub 3} by Femtosecond Laser Pulses

    Energy Technology Data Exchange (ETDEWEB)

    Kumatoriya, M; Ando, A [Technology and Business Department Unit, Murata Manufacturing Co. Ltd., Nagaokakyo, Kyoto 615-8555 (Japan); Nakabayashi, M; Miura, K; Hirao, K, E-mail: kumatry@murata.co.jp [Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8520 (Japan)

    2011-05-15

    Optical waveguides were successfully fabricated by femtosecond laser direct writing inside a LiTaO{sub 3} crystal, and the optical properties of these waveguides were investigated. Optimum writing conditions such as pulse energy and duration were determined on the basis of the refractive index changes calculated using the near-field pattern of the light guided through the waveguides. {mu}-Raman spectroscopy results and birefringence observations around the formed waveguides suggested that the local increase in refractive index was caused by anisotropic compressive stress in the laser-irradiated region. The light guided through the formed waveguide showed strong polarization dependence.

  16. Negative Curvature Hollow-core Fibers: Dispersion Properties and Femtosecond Pulse Delivery

    Science.gov (United States)

    Kolyadin, A. N.; Alagashev, G. K.; Pryamikov, A. D.; Mouradian, L.; Zeytunyan, A.; Toneyan, H.; Kosolapov, A. F.; Bufetov, I. A.

    In this work a comparative analysis of dispersion properties of hollow core photonic crystal fibers (HC PCFs) and negative curvature hollow core fibers (NCHCFs) was carried out. It was shown that the main reason for the low dispersion slope of NCHCFs is a strong light localization in the air core in comparison with HC PCFs. The strong light localization in NCHCFs allows not to use the complicated photonic crystal cladding and to reduce the air mode interaction with silica glass elements of the cladding. This conclusion was confirmed by experimental measurement of the group velocity dispersion and femtosecond pulse transmission for the NCHCF.

  17. Thermal Stress-Induced Birefringence in Borate Glass Irradiated by Femtosecond Laser Pulses

    Institute of Scientific and Technical Information of China (English)

    DAI Ye; YU Bing-Kun; LU Bo; QIU Jian-Rong; YAN Xiao-Na; JIANG Xiong-Wei; ZHU Cong-Shan

    2005-01-01

    @@ Thermal stress-induced birefringence in borate glass which has been irradiated by 800-nm femtosecond laser pulses is observed under cross-polarized light. Due to the high temperature and pressure formed in the focal volume, the material at the edge of the micro-modified region is compressed between the expanding region and the unheated one, then stress emerges. Raman spectroscopy is used to investigate the stress distribution in the micro-modified region and indicates the redistributions of density and refractive index by Raman peak shift. We suggest that this technique can develop waveguide polarizers and Fresnel zone plates in integrated optics.

  18. Modeling of optical, transport, and thermodynamic properties of Al metal irradiated by intense femtosecond laser pulses

    CERN Document Server

    Khishchenko, Konstantin V; Andreev, Nikolay E; Fortov, Vladimir E; Levashov, Pavel R; Povarnitsyn, Mikhail E

    2008-01-01

    A theoretical model is developed for the interaction of intense femtosecond laser pulses with solid targets on the basis of the two-temperature equation of state for an irradiated substance. It allows the description of the dynamics of the plasma formation and expansion. Comparison of available experimental data on the amplitude and phase of the complex reflection coefficient of aluminum with the simulation results provides new information on the transport coefficients and absorption capacity of the strongly coupled Al plasma over a wide range of temperatures and pressures.

  19. Red-Shift Conical Emission by Femtosecond Pulses at Low Input Power

    Institute of Scientific and Technical Information of China (English)

    LI Yue-Xun; JI Zhong-Gang; ZENG Zhi-Nan; LIU Jian-Sheng; GE Xiao-Chun; LI Ru-Xin; XU Zhi-Zhan

    2008-01-01

    Red-shift conical emission (CE) is observed by femtosecond laser pulse propagating in BK7 at a low input power (compared to those input powers for generation of blue-shift CE). With the increasing input power the blue-shift CE begins to appear whereas the red-shift CE ring (902 nm in our experiment) disappears accompanied by the augment of the central white spot size synchronously. The disappearing of red-shift CE in our experiment is explained such that the increase of axial intensity is much higher than that of ring emission and the augment of the centrai white spot size with the increasing input laser power.

  20. Heating and ionization of metal clusters in the field of an intense femtosecond laser pulse

    Science.gov (United States)

    Kostenko, O. F.; Andreev, N. E.

    2007-06-01

    Inverse bremsstrahlung heating and thermal electron-impact ionization of a metal cluster are analyzed with account for the spatial structure of the electromagnetic field. It is shown that, for a femtosecond IR radiation pulse with an intensity of ˜1018 W/cm2 and for an iron cluster with an optimum radius of ˜25 nm, the electron temperature is higher than 1 keV. In this case, the L shell of the ions is highly stripped. The X-ray bremsstrahlung yield from clusters with a radius greater than the skin depth is estimated.

  1. Femtosecond correlated photon echo in CdS crystal under two-photon excitation by two pairs of crossed laser beams

    Science.gov (United States)

    Samartsev, V. V.; Leontiev, A. V.; Mitrofanova, T. G.

    2015-07-01

    We consider the possibility of observing a femtosecond correlated photon echo (FCPE) under two-photon excitation of CdS crystal by two pairs of crossed laser beams. The peculiarities of FCPE signals and their possible applications are discussed.

  2. A high-resolution time-of-flight energy analyzer for femtosecond electron pulses at 30 keV

    Science.gov (United States)

    Gliserin, Alexander; Walbran, Matthew; Baum, Peter

    2016-03-01

    We report a time-of-flight spectrometer for electron pulses at up to 30 keV, which is a suitable energy for atomic-resolution femtosecond investigations via time-resolved electron diffraction, microscopy, and energy loss spectroscopy. For realistic femtosecond beams without apertures, the instrument's energy resolution is ˜0.5 eV (full width at half maximum) or 2 × 10-5 at a throughput of 50%-90%. We demonstrate the analyzer's versatility by three first applications, namely, femtosecond electron pulse metrology via optical streaking, in situ drift correction in laser-microwave synchronization for electron pulse compression, and time-resolved electron energy loss spectroscopy of aluminum, showing the instrument's capability of tracking plasmonic loss peak positions with few-meV accuracy.

  3. Efficient noncollinear parametric amplification of weak femtosecond pulses in the visible and near-infrared spectral range.

    Science.gov (United States)

    Krylov, V; Ollikainen, O; Gallus, J; Wild, U; Rebane, A; Kalintsev, A

    1998-01-15

    We report measurement of efficient amplification of weak femtosecond supercontinuum seed pulses by use of a noncollinear optical parametric process in BBO crystal pumped with 150-fs pulses from a frequency-doubled regenerative-amplified Ti:sapphire laser at 390nm . The highest amplification factor, 10(8) , was achieved for 3x10(-16)J energy seed pulses at wavelength of 560nm.

  4. Optimization of Schwinger pair production in colliding laser pulses

    Directory of Open Access Journals (Sweden)

    F. Hebenstreit

    2014-12-01

    Full Text Available Recent studies of Schwinger pair production have demonstrated that the asymptotic particle spectrum is extremely sensitive to the applied field profile. We extend the idea of the dynamically assisted Schwinger effect from single pulse profiles to more realistic field configurations to be generated in an all-optical experiment searching for pair creation. We use the quantum kinetic approach to study the particle production and employ a multi-start method, combined with optimal control theory, to determine a set of parameters for which the particle yield in the forward direction in momentum space is maximized. We argue that this strategy can be used to enhance the signal of pair production on a given detector in an experimental setup.

  5. Optimization of Schwinger pair production in colliding laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Hebenstreit, F., E-mail: hebenstreit@itp.unibe.ch [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Bern University, 3012 Bern (Switzerland); Institut für Theoretische Physik, Universität Heidelberg, 69120 Heidelberg (Germany); Fillion-Gourdeau, F., E-mail: francois.fillion@emt.inrs.ca [Université du Québec, INRS–Énergie, Matériaux et Télécommunications, Varennes, Québec, J3X 1S2 (Canada)

    2014-12-12

    Recent studies of Schwinger pair production have demonstrated that the asymptotic particle spectrum is extremely sensitive to the applied field profile. We extend the idea of the dynamically assisted Schwinger effect from single pulse profiles to more realistic field configurations to be generated in an all-optical experiment searching for pair creation. We use the quantum kinetic approach to study the particle production and employ a multi-start method, combined with optimal control theory, to determine a set of parameters for which the particle yield in the forward direction in momentum space is maximized. We argue that this strategy can be used to enhance the signal of pair production on a given detector in an experimental setup.

  6. Analysis on the damage threshold of MgO:LiNbO3 crystals under multiple femtosecond laser pulses

    Science.gov (United States)

    Su, Zhuolin; Meng, Qinglong; Zhang, Bin

    2016-10-01

    An improved theoretical model of the interaction between multiple femtosecond laser pulses and MgO:LiNbO3 crystals with different doping concentrations has been established based on the classical two-temperature model. The evolutions of electron and lattice temperature with the duration, the repetition frequency and the numbers of multiple femtosecond laser pulses in MgO:LiNbO3 crystals have been simulated numerically by the Crank-Nicholson implicit finite-difference method. Furthermore, the variations of the damage threshold of MgO:LiNbO3 crystals with the parameters of multiple femtosecond laser pulses at different doping concentrations, as well as the influence of doping concentration on damage threshold have also been analyzed. The results show that, the damage threshold of MgO:LiNbO3 crystals increases with the increasing of the duration of the femtosecond laser pulse. The damage threshold of MgO:LiNbO3 crystals first decreases with the increasing of the numbers and the pulse repetition frequency of the laser pulses and then tends to be a constant. The damage threshold of a small amount of MgO-doped LiNbO3 crystals is higher than that of undoped LiNbO3 crystals. Consequently, the resist damage capability of LiNbO3 crystals can be enhanced by doping appropriate MgO in many practical applications.

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

    Energy Technology Data Exchange (ETDEWEB)

    Ksenzov, Dmitry

    2010-07-01

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

  8. Laser Activated Streak Camera for Measurement of Electron Pulses with Femtosecond Resolution

    Science.gov (United States)

    Zandi, Omid; Desimone, Alice; Wilkin, Kyle; Yang, Jie; Centurion, Martin

    2015-05-01

    The duration of femtosecond electron pulses used in time-resolved diffraction and microscopy experiments is challenging to measure in-situ. To overcome this problem, we have fabricated a streak camera that uses the time-varying electric field of a discharging parallel plate capacitor. The capacitor is discharged using a laser-activated GaAs photoswitch, resulting in a damped oscillation of the electric field. The delay time between the laser pulse and electron pulse is set so that the front and back halves of the bunch encounter opposite electric fields of the capacitor and are deflected in opposite directions. Thus, the electron bunch appears streaked on the detector with a length proportional to its duration. The temporal resolution of the streak camera is proportional to the maximum value of the electric field and the frequency of the discharge oscillation. The capacitor is charged by high voltage short pulses to achieve a high electric field and prevent breakdown. We have achieved an oscillation frequency in the GHz range by reducing the circuit size and hence its inductance. The camera was used to measure 100 keV electron pulses with up to a million electrons that are compressed transversely by magnetic lenses and longitudinally by an RF cavity. This work was supported mainly by the Air Force Office of Scientific Research, Ultrashort Pulse Laser Matter Interaction program, under grant # FA9550-12-1-0149.

  9. Tip-based source of femtosecond electron pulses at 30 keV

    Energy Technology Data Exchange (ETDEWEB)

    Hoffrogge, Johannes; Paul Stein, Jan [Max Planck Institute of Quantum Optics, Hans-Kopfermann-Str. 1, 85748 Garching (Germany); Krüger, Michael; Förster, Michael; Hammer, Jakob; Ehberger, Dominik; Hommelhoff, Peter, E-mail: peter.hommelhoff@fau.de [Max Planck Institute of Quantum Optics, Hans-Kopfermann-Str. 1, 85748 Garching (Germany); Department für Physik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 1, 91058 Erlangen (Germany); Baum, Peter [Max Planck Institute of Quantum Optics, Hans-Kopfermann-Str. 1, 85748 Garching (Germany); Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching (Germany)

    2014-03-07

    We present a nano-scale photoelectron source, optimized for ultrashort pulse durations and well-suited for time-resolved diffraction and advanced laser acceleration experiments. A tungsten tip of several-ten-nanometers diameter mounted in a suppressor-extractor electrode configuration allows the generation of 30 keV electron pulses with an estimated pulse duration of 9 fs (standard deviation; 21 fs full width at half maximum) at the gun exit. We infer the pulse duration from particle tracking simulations, which are in excellent agreement with experimental measurements of the electron-optical properties of the source in the spatial domain. We also demonstrate femtosecond-laser triggered operation of the apparatus. The temporal broadening of the pulse upon propagation to a diffraction sample can be greatly reduced by collimating the beam. Besides the short electron pulse duration, a tip-based source is expected to feature a large transverse coherence and a nanometric emittance.

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

    Science.gov (United States)

    2014-01-30

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

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

    Directory of Open Access Journals (Sweden)

    Takehiro Tachizaki

    2013-03-01

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

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

    Science.gov (United States)

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

    2013-03-11

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

  13. Propagation of bright femtosecond pulses in a nonlinear optical fibre with the third-and fourth-order dispersions

    Institute of Scientific and Technical Information of China (English)

    Ao Sheng-Mei; Yan Jia-Ren; Yu Hui-You

    2007-01-01

    We solve the generalized nonlinear Schrodinger equation describing the propagation of femtosecond pulses in a nonlinear optical fibre with higher-order dispersions by using the direct approach to perturbation for bright solitons, and discuss the combined effects of the third- and fourth-order dispersions on velocity, temporal intensity distribution and peak intensity of femtosecond pulses. It is noticeable that the combined effects of the third- and fourth-order dispersions on an initial propagated soliton can partially compensate each other, which seems to be significant for the stability controlling of soliton propagation features.

  14. Observation of propagating femtosecond light pulse train generated by an integrated array illuminator as a spatially and temporally continuous motion picture.

    Science.gov (United States)

    Yamagiwa, Masatomo; Komatsu, Aya; Awatsuji, Yasuhiro; Kubota, Toshihiro

    2005-05-02

    We observed a propagating femtosecond light pulse train generated by an integrated array illuminator as a spatially and temporally continuous motion picture. To observe the light pulse train propagating in air, light-in-flight holography is applied. The integrated array illuminator is an optical device for generating an ultrashort light pulse train from a single ultrashort pulse. The experimentally obtained pulse width and pulse interval were 130 fs and 19.7 ps, respectively. A back-propagating femtosecond light pulse train, which is the -2 order diffracted light pulse from the array illuminator and which is difficult to observe using conventional methods, was observed.

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

    Energy Technology Data Exchange (ETDEWEB)

    Gemini, Laura, E-mail: gemini@fzu.cz [Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University Uji, Kyoto 611-0011 (Japan); Department of Physics, Graduate School of Science, Kyoto University, 606-8502 Kyoto (Japan); FNSPE, Czech Technical University in Prague, Brehova 7, 11519 Prague (Czech Republic); HiLASE Centre, Institute of Physics, ASCR, Za Radnicí 828, 25241 Dolní Břežany (Czech Republic); Hashida, Masaki; Miyasaka, Yasuhiro; Inoue, Shunsuke [Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University Uji, Kyoto 611-0011 (Japan); Department of Physics, Graduate School of Science, Kyoto University, 606-8502 Kyoto (Japan); Limpouch, Jiri [FNSPE, Czech Technical University in Prague, Brehova 7, 11519 Prague (Czech Republic); Mocek, Tomas [HiLASE Centre, Institute of Physics, ASCR, Za Radnicí 828, 25241 Dolní Břežany (Czech Republic); Sakabe, Shuji [Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University Uji, Kyoto 611-0011 (Japan); Department of Physics, Graduate School of Science, Kyoto University, 606-8502 Kyoto (Japan)

    2015-05-01

    Highlights: • LIPSS self-formed on Ti surface upon irradiations by 25 double pulses. • A surface plasma density variation leads to a variation of LIPSS features. • Data from double pulse irradiations well agree with the parametric decay model. • Results confirm the formation of surface plasma during the ultra-short interaction. • Results support once again the validity of the parametric decay model. - Abstract: Laser induced periodic surface structures (LIPSS) self-organized on Ti surface after irradiations by femtosecond laser beam composed by double pulses with a fixed time delay of 160 fs. The fluence of the first pulse (F{sub PP}), responsible for surface plasma formation, was varied in the range 10–50 mJ cm{sup −2} and always kept below the LIPSS formation threshold fluence (F{sub LIPSS}) on Ti for 50-single-shots exposure. The fluence of the delayed pulse (F{sub LP}), responsible for LIPSS self-organization, was varied in the range 60–150 mJ cm{sup −2} and always kept above F{sub LIPSS}. Regardless the specific fluence F{sub LP} of the delayed pulse, the interspace of the grating structures increases with the increase of F{sub PP}, that is an increase of the surface plasma density. This tendency suggests that a variation of the surface plasma density, due to a variation of F{sub PP}, actually leads to a modification of the grating features. Moreover, we observed that the LIPSS periodicities after double pulse exposures are in quite good agreement with data on LIPSS periodicities after single 160 fs pulse irradiations on Ti surface and with the curve predicted by the parametric decay model. This experimental result suggests that the preformed plasma might be produced in the rising edge of the temporal profile of the laser pulse.

  16. The effect of laser contrast on generation of highly charged Fe ions by ultra-intense femtosecond laser pulses

    Science.gov (United States)

    Faenov, Anatoly Ya.; Alkhimova, Maria A.; Pikuz, Tatiana A.; Skobelev, Igor Yu.; Nishiuchi, Mamiko; Sakaki, Hironao; Pirozhkov, Alexander S.; Sagisaka, Akito; Dover, Nicholas P.; Kondo, Kotaro; Ogura, Koichi; Fukuda, Yuji; Kiriyama, Hiromitsu; Andreev, Alexander; Nishitani, Keita; Miyahara, Takumi; Watanabe, Yukinobu; Pikuz, Sergey A.; Kando, Masaki; Kodama, Ruosuke; Kondo, Kiminori

    2017-07-01

    Experimental studies on the formation of highly charged ions of medium-Z elements using femtosecond laser pulses with different contrast levels were carried out. Multiply charged Fe ions were generated by laser pulses with 35 fs duration and an intensity exceeding 1021 W/cm2. Using high-resolution X-ray spectroscopic methods, bulk electron temperature of the generated plasma has been identified. It is shown that the presence of a laser pre-pulse at a contrast level of 105-106 with respect to the main pulse drastically decreases the degree of Fe ionization. We conclude that an effective source of energetic, multiply charged moderate and high- Z ions based on femtosecond laser-plasma interactions can be created only using laser pulses of ultra-high contrast.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-02-14

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

  18. Reflection of femtosecond pulses from soft X-ray free-electron laser by periodical multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Ksenzov, D.; Grigorian, S.; Pietsch, U. [Faculty of Physics, University of Siegen (Germany); Hendel, S.; Bienert, F.; Sacher, M.D.; Heinzmann, U. [Faculty of Physics, University of Bielefeld (Germany)

    2009-08-15

    Recent experiments on a soft X-ray free-electron laser (FEL) source (FLASH in Hamburg) have shown that multilayers (MLs) can be used as optical elements for highly intense X-ray irradiation. An effort to find most appropriate MLs has to consider the femtosecond time structure and the particular photon energy of the FEL. In this paper we have analysed the time response of 'low absorbing' MLs (e.g. such as La/B{sub 4}C) as a function of the number of periods. Interaction of a pulse train of Gaussian shaped sub-pulses using a realistic ML grown by electron-beam evaporation technique has been analysed in the soft-X-ray range. The structural parameters of the MLs were obtained by reflectivity measurements at BESSY II and subsequent profile fittings. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

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

    Science.gov (United States)

    Zhang, Guodong; Cheng, Guanghua

    2015-10-20

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

  20. 3D features of modified photostructurable glass-ceramic with infrared femtosecond laser pulses

    Science.gov (United States)

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

    2011-04-01

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

  1. Two-pathway interferences in photoelectron angular distributions induced by circularly polarized femtosecond pulses.

    Science.gov (United States)

    Douguet, Nicolas; Venzke, Joel; Bartschat, Klaus; Grum-Grzhimailo, Alexei N.; Gryzlova, Elena; Staroselskaya, Ekaterina

    2016-05-01

    Following up on earlier work using linearly polarized radiation, we analyze the characteristics of atomic ionization produced by circularly polarized two-color femtosecond pulses. Two-pathway interferences between nonresonant one-photon and resonant two-photon ionization in the vicinity of an intermediate resonance are considered in detail for atomic hydrogen. Using circularly polarized radiation significantly increases the complexity of the problem, while opening up a rich field of possible further investigations. The principal properties of the photoelectron angular distribution (PAD) are obtained by solving the time-dependent Schrödinger equation and employing a second-order nonstationary perturbative approach. The dependence of the PAD on the intensities, helicities of the harmonics, pulse lengths, and carrier envelope phases is considered in detail. Supported by the NSF under PHY-1430245 and XSEDE PHY-090031.

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

    KAUST Repository

    Chiang, Weiyi

    2014-12-11

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

  3. Femtosecond pulse generation from a Topological Insulator mode-locked fiber laser

    CERN Document Server

    Liu, Hao; Liu, Meng; Zhao, Nian; Luo, Ai-Ping; Luo, Zhi-Chao; Xu, Wen-Cheng; Zhang, Han; Zhao, Chu-Jun; Wen, Shuang-Chun

    2014-01-01

    We reported on the generation of femtosecond pulse in an anomalous-dispersion fiber ring laser by using a polyvinyl alcohol (PVA)-based Topological Insulator (TI), Bi2Se3 saturable absorber (SA). The PVA-TI composite has a low saturable optical intensity of 12 MW/cm2 and a modulation depth of ~3.9%. By incorporating the fabricated PVA-TISA into a fiber laser, mode-locking operation could be achieved at a low pump threshold of 25 mW. After an optimization of the cavity parameters, optical pulse with ~660 fs centered at 1557.5 nm wavelength had been generated. The experimental results demonstrate that the PVA could be an excellent host material for fabricating high-performance TISA, and also indicate that the filmy PVA-TISA is indeed a good candidate for ultrafast saturable absorption device.

  4. MeV femtosecond electron pulses from direct-field acceleration in low density atomic gases

    CERN Document Server

    Varin, Charles; Hogan-Lamarre, Pascal; Fennel, Thomas; Piché, Michel; Brabec, Thomas

    2015-01-01

    Using three-dimensional particle-in-cell simulations, we show that few-MeV electrons can be produced by focusing tightly few-cycle radially-polarized laser pulses in a low-density atomic gas. In particular, it is observed that for the few-TW laser power needed to reach relativistic electron energies, longitudinal attosecond microbunching occurs naturally, resulting in femtosecond structures with high-contrast attosecond density modulations. The three-dimensional particle-in-cell simulations show that in the relativistic regime the leading pulse of these attosecond substructures survives to propagation over extended distances, suggesting that it could be delivered to a distant target, with the help of a properly designed transport beamline.

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

    CERN Document Server

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

    2015-01-01

    We experimentally demonstrate ultrafast dynamic of generation of a strong 337-nm nitrogen laser by injecting an external seed pulse into a femtosecond laser filament pumped by a circularly polarized laser pulse. In the pump-probe scheme, it is revealed that the population inversion between the excited and ground states of N2 for the free-space 337-nm laser is firstly built up on the timescale of several picoseconds, followed by a relatively slow decay on the timescale of tens of picoseconds, depending on the nitrogen gas pressure. By measuring the intensities of 337-nm signal from nitrogen gas mixed with different concentrations of oxygen gas, it is also found that oxygen molecules have a significant quenching effect on the nitrogen laser signal. Our experimental observations agree with the picture of electron-impact excitation.

  6. Nanograting formation on metals in air with interfering femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Miyazaki, Kenzo, E-mail: k-miyazaki@iae.kyoto-u.ac.jp, E-mail: kmiyazaki@wind.ocn.ne.jp [Laser Science Research Section, Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011 (Japan); Center for Collaborative Research and Community Cooperation, University of Miyazaki, Miyazaki 889-2192 (Japan); Miyaji, Godai, E-mail: gmiyaji@cc.tuat.ac.jp [Laser Science Research Section, Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011 (Japan); Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan); Inoue, Toshishige [Laser Science Research Section, Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011 (Japan)

    2015-08-17

    It is demonstrated that a homogeneous nanograting having the groove period much smaller than the laser wavelength (∼800 nm) can be fabricated on metals in air through ablation induced by interfering femtosecond laser pulses (100 fs at a repetition rate of 10 Hz). Morphological changes on stainless steel and Ti surfaces, observed with an increase in superimposed shots of the laser pulses at a low fluence, have shown that the nanograting is developed through bonding structure change at the interference fringes, plasmonic near-field ablation to create parallel grooves on the fringe, and subsequent excitation of surface plasmon polaritons to regulate the groove intervals at 1/3 or 1/4 of the fringe period over the whole irradiated area. Calculation for a model target having a thin oxide layer on the metal substrate reproduces well the observed groove periods and explains the mechanism for the nanograting formation.

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

    DEFF Research Database (Denmark)

    Abu-Samha, Mahmoud; Madsen, Lars Bojer

    2011-01-01

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

  8. Microfiber-based gold nanorods as saturable absorber for femtosecond pulse generation in a fiber laser

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xu-De [Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou, Guangdong 510006 (China); School of Physics and Electronic Information, Huaibei Normal University, Huaibei, Anhui 235000 (China); Luo, Zhi-Chao; Liu, Hao; Liu, Meng; Luo, Ai-Ping, E-mail: luoaiping@scnu.edu.cn; Xu, Wen-Cheng, E-mail: xuwch@scnu.edu.cn [Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou, Guangdong 510006 (China)

    2014-10-20

    We reported on the femtosecond pulse generation from an erbium-doped fiber (EDF) laser by using microfiber-based gold nanorods (GNRs) as saturable absorber (SA). By virtue of the geometric characteristic of microfiber-based GNRs, the optical damage threshold of GNRs-SA could be greatly enhanced. The microfiber-based GNRs-SA shows a modulation depth of 4.9% and a nonsaturable loss of 21.1%. With the proposed GNRs-SA, the fiber laser emitted a mode-locked pulse train with duration of ∼887 fs. The obtained results demonstrated that the GNRs deposited microfiber could indeed serve as a high-performance SA towards the practical applications in the field of ultrafast photonics.

  9. Nanograting formation in air through plasmonic near-field ablation induced by femtosecond laser pulses

    Science.gov (United States)

    Miyaji, Godai; Miyazaki, Kenzo

    2017-02-01

    Superimposed multiple shots of low-fluence femtosecond (fs) laser pulses form a periodic nanostructure on solid surfaces through ablation. We have demonstrated that the self-organization process of nanostructuring can be regulated to fabricate a homogeneous nanograting on the target surface in air. A simple two-step ablation process and an ablation technique using interfering fs laser beams were developed to control plasmonic near-fields generated by fs laser pulses. The results have shown the nature of a single spatial standing wave mode of surface plasmon polaritons of which periodically enhanced near-fields ablate the target surface, to fabricate the nanograting on gallium nitride (GaN) and metals such as stainless steel (SUS) and titanium (Ti).

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

    Science.gov (United States)

    Kuramochi, Hikaru; Takeuchi, Satoshi; Tahara, Tahei

    2016-04-01

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

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

    Science.gov (United States)

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

    2012-10-01

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

  12. Quantification of absorption contributions in microstructured silicon fabricated by femtosecond laser pulses

    Science.gov (United States)

    Peng, Yan; Chen, XiangQian; Zhou, YunYan; Luo, Kun; Xu, Jian; Henderson, Ron; Dai, JianMing; Zhu, YiMing

    2015-06-01

    Microstructured silicon material, fabricated by femtosecond laser pulses, has a lot of crucial applications in silicon-based photovoltaics, photo-detectors, and super-hydrophobic devices etc., due mainly to the high absorption in both visible and infrared regions. However, the mechanisms attributed to its high-absorption characteristics have never been accurately quantified, which limits further the exploitation of this kind of material. Here, we experimentally quantify different absorption contributions in microstructured silicon fabricated by femtosecond laser pulses, which can be attributed to dopant impurities in the silicon substrate, doping impurities induced during the laser fabrication process, absorption enhancement from the light-trapping structure, and surface disordered material formed also during the laser fabrication process. From these analyses, we determine that with the assist of a light-trapping structure, dopant impurities in the silicon substrate contribute much more to the infrared absorption than those of the doping sulfur impurities induced during the fabrication process. Furthermore, the infrared absorption of material can be annealing-insensitive. These results have important implications for the design and fabrication of high-efficiency optoelectronic devices.

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

    Science.gov (United States)

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

    2017-02-01

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

  14. Influence of effective number of pulses on the morphological structure of teeth and bovine femur after femtosecond laser ablation.

    Science.gov (United States)

    Nicolodelli, Gustavo; Lizarelli, Rosane de Fátima Zanirato; Bagnato, Vanderlei Salvador

    2012-04-01

    Femtosecond lasers have been widely used in laser surgery as an instrument for contact-free tissue removal of hard dental, restorative materials, and osseous tissues, complementing conventional drilling or cutting tools. In order to obtain a laser system that provides an ablation efficiency comparable to mechanical instruments, the laser pulse rate must be maximal without causing thermal damage. The aim of this study was to compare the different morphological characteristics of the hard tissue after exposure to lasers operating in the femtosecond pulse regime. Two different kinds of samples were irradiated: dentin from human extracted teeth and bovine femur samples. Different procedures were applied, while paying special care to preserving the structures. The incubation factor S was calculated to be 0.788±0.004 for the bovine femur bone. These results indicate that the incubation effect is still substantial during the femtosecond laser ablation of hard tissues. The plasma-induced ablation has reduced side effects, i.e., we observe less thermal and mechanical damage when using a superficial femtosecond laser irradiation close to the threshold conditions. In the femtosecond regime, the morphology characteristics of the cavity were strongly influenced by the change of the effective number of pulses.

  15. Interaction of atomic hydrogen with pico- and femtosecond laser pulses. Technical report

    Energy Technology Data Exchange (ETDEWEB)

    Parker, J.S.

    1989-12-01

    This thesis presents a theoretical study of the interaction of atomic hydrogen with coherent laser pulses in the 5 femtosecond to 10 picosecond range, in the weak-field limit, and in intense fields. We approach the problem in the weak-field limit by studying the relationship between the Fourier relation of the laser pulse (Delta omega Delta t) and the (Delta E Delta t) relation of the atomic Rydberg wave packet generated by the laser pulse. A derivation of the wave packet based on the WKB approximation is given, permitting the quantity Delta t to be derived for the quantum state, with the conclusion that under certain circumstances a transform-limited laser pulse (satisfying Delta omega Delta t = 1/2) can generate a transform-limited electron (satisfying Delta E Delta t/h = 1/2). A population-trapping effect is found numerically and modeled theoretically. Despite the high field intensities, population representing the excited electron is recaptured from the ionization continuum by bound states during the excitation. Population returns to the atom with just the right phase to strongly inhibit ionization. A theory is presented that models this effect for a variety of laser pulse shapes, with and without the rotating-wave approximation. The numerical integration reveals that a certain amount of above-threshold ionization (ATI) occurs.

  16. Interaction of intense femtosecond laser pulses with high-Z solids

    Energy Technology Data Exchange (ETDEWEB)

    Zhidkov, A.; Sasaki, Akira; Utsumi, Takayuki; Fukumoto, Ichirou; Tajima, Toshiki [Advanced Photon Research Center, Kansai Research Establishment, Japan Atomic Energy Research Institute, Neyagawa, Osaka (Japan); Yoshida, Masatake [National Institute of Material and Chemical Research, Tsukuba, Ibaraki (Japan); Kondo, Kenichi [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa (Japan)

    2000-03-01

    A plasma irradiated by an intense very short pulse laser can be an ultimate high brightness source of incoherent inner-shell X-ray emission of 1-30 keV. The recently developed 100 TW, 20 fs laser facility in JAERI can make considerable enhancement here. To show this a hybrid model combining hydrodynamics and collisional particle-in-cell simulations is applied. Effect of laser prepulse on the interaction of an intense s-polarized femtosecond, {approx}20/40 fs, laser pulse with high-Z solid targets is studied. A new absorption mechanism originating from the interaction of the laser pulse with plasma waves excited by the relativistic component of the Lorentz force is found to increase the absorption rate over 30% even for a very short laser pulse. The obtained hot electron temperature exceeds 0.5-1 MeV at optimal conditions for absorption. Results of the simulation for lower laser pulse intensities are in good agreement with the experimental measurements of the hot electron energy distribution. (author)

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

    Science.gov (United States)

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

    2016-03-01

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

  18. Formation of laser-induced periodic surface structures on fused silica upon multiple parallel polarized double-femtosecond-laser-pulse irradiation sequences

    Energy Technology Data Exchange (ETDEWEB)

    Rosenfeld, Arkadi, E-mail: rosenfeld@mbi-berlin.de [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie (MBI), Max-Born-Strasse 2A, D-12489 Berlin (Germany); Rohloff, Marcus; Hoehm, Sandra [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie (MBI), Max-Born-Strasse 2A, D-12489 Berlin (Germany); Krueger, Joerg [BAM Bundesanstalt fuer Materialforschung und -pruefung, Unter den Eichen 87, D-12205 Berlin (Germany); Bonse, Joern, E-mail: joern.bonse@bam.de [BAM Bundesanstalt fuer Materialforschung und -pruefung, Unter den Eichen 87, D-12205 Berlin (Germany)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer LIPSS formation studied for double-fs-pulses (160 fs, 800 nm) of different fluences. Black-Right-Pointing-Pointer Close to the damage threshold predominantly HSFL are observed. Black-Right-Pointing-Pointer The HSFL period remains almost constant {approx}375 nm (delay independent). Black-Right-Pointing-Pointer At high fluences and for short delays a transient metallic state is created (LSFL regime). Black-Right-Pointing-Pointer A transition of the LSFL period from 750 to 530 nm is observed in the sub-ps delay range. - Abstract: The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences of parallel polarized Ti:sapphire femtosecond laser pulse pairs (160 fs pulse duration, 800 nm central wavelength) was studied experimentally. For that purpose, a Michelson interferometer was used to generate near-equal-energy double-pulse sequences allowing the temporal pulse delay between the parallel-polarized individual fs-laser pulses to be varied between 0 and 40 ps with {approx}0.2 ps temporal resolution. The surface morphologies of the irradiated surface areas were characterized by means of scanning electron and scanning force microscopy. In the sub-ps delay range a strong decrease of the LIPSS periods and the ablation crater depths with the double-pulse delay was observed indicating the importance of the laser-induced free-electron plasma in the conduction band of the solids for the formation of LIPSS.

  19. Pulsed photo-excitation timed with pulsed rf can reveal the radical-pair magnetoreceptor

    CERN Document Server

    Kominis, I K

    2014-01-01

    The radical-pair mechanism is understood to underlie the magnetic navigation capability of birds and possibly other species. Experiments with birds have provided indirect and in cases conflicting evidence on the actual existence of this mechanism. We here propose a new experiment that can unambiguously identify the presence of the radical-pair magnetoreceptor in birds and unravel some of its basic properties. The proposed experiment is based on modulated light excitation with a pulsed laser, combined with delayed radio-frequency magnetic field pulses. We predict a resonance effect in the birds' magnetic orientation versus the rf-pulse delay time. The resonance's position reflects the singlet-triplet mixing time of the magnetoreceptor.

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

    CSIR Research Space (South Africa)

    Botha, N

    2010-08-31

    Full Text Available , Ch, Sharpe-Tudoran, C, Winter, M. & Baumert, T. 2003. Compact, robust, and flexible setup for femtosecond pulse shaping. Review of scientific instruments, 75:4950-4953. 3. Cavallari, M, Gale, G.M, Hache, F, Pavlov, L.I & Rousseau, E 1995. Mid infra...

  1. Optimized Optical Rectification and Electro-optic Sampling in ZnTe Crystals with Chirped Femtosecond Laser Pulses

    DEFF Research Database (Denmark)

    Erschens, Dines Nøddegaard; Turchinovich, Dmitry; Jepsen, Peter Uhd

    2011-01-01

    We report on optimization of the intensity of THz signals generated and detected by optical rectification and electro-optic sampling in dispersive, nonlinear media. Addition of a negative prechirp to the femtosecond laser pulses used in the THz generation and detection processes in 1-mm thick ZnT...

  2. Dynamical theory of spectroscopy with femtosecond pulse excitation(Ⅲ)——Transient rate equation in Liouville space

    Institute of Scientific and Technical Information of China (English)

    陆靖; 范康年

    1999-01-01

    A dynamical theory of spectroscopy with femtosecond pulse excitation is developed in Liouville space. By using density matrix formalism, the transient rate equation that can be reduced to the classical KHD expression in CW case is obtained. This theory is applied to the Raman excitation profile of IBr and the results are in agreement with the experiments.

  3. Formation of ordered nano- and mesostructures in silicon irradiated with a single femtosecond laser pulse in different environments

    Science.gov (United States)

    Romashevskiy, A.; Ashitkov, S. I.; Dmitriev, A. S.

    2016-08-01

    We report on a new class of ordered nano- and mesostructures, including distinct structured areas with subnanoscale roughness, produced by interaction of single tightly focused femtosecond laser pulses with a monocrystalline silicon surface under different environments. The environment was found to have a significant effect on the final morphology of near-surface layers of silicon.

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

    DEFF Research Database (Denmark)

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

    2016-01-01

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

  5. Passively mode-locked soliton femtosecond pulses employing graphene saturable absorber

    Science.gov (United States)

    Lau, K. Y.; Muhammad, F. D.; Latif, A. A.; Abu Bakar, M. H.; Yusoff, Z.; Mahdi, M. A.

    2017-09-01

    We demonstrate a passively mode-locked fiber laser incorporating graphene thin film (GTF) as saturable absorber (SA). The SA is fabricated by sandwiching the GTF between two single mode fiber ferrules through a fiber adaptor. The transmission loss at 1560 nm and non-linear saturation absorption modulation depth for GTF-SA are 0.8 dB and 2.90%, respectively. An erbium-doped fiber laser cavity is constructed to verify the functionality of GTF-SA and is designed to have net anomalous dispersion. It generates large spectral width of 4.99 nm with pulse repetition rate of 9.655 MHz and pulse width of 670 fs. Net anomalous dispersion and time bandwidth product higher than the sech2 transform-limited pulse validate the experimental result. In short, we demonstrate high performance GTF-SA that is able to generate ultrafast pulse duration in femtosecond range effortlessly with simple and green SA fabrication procedures.

  6. Laser induced forward transfer of metals by temporally shaped femtosecond laser pulses.

    Science.gov (United States)

    Klini, A; Loukakos, P A; Gray, D; Manousaki, A; Fotakis, C

    2008-07-21

    Temporally shaped, femtosecond laser pulses have been used for controlling the size and the morphology of micron-sized metallic structures obtained by using the Laser Induced Forward Transfer (LIFT) technique. We report the effect of pulse shaping on the size and morphology of the deposited structures of Au, Zn, Cr on a function of the pulse separation time ??t (from 0 to 10 ps) of double pulses of variable intensities generated by using a liquid crystal spatial light modulator (SLM). The observed differences in size and morphology are correlated with the outcome of pump-probe experiments for the study of electron-phonon scattering dynamics and subsequent energy transfer processes to the bulk in the different metals employed. We propose that in metals with weak electron-lattice coupling, the electron ballistic motion and the resulting fast electron scattering at the film surface, as well as the internal electron thermalization process are crucial to the morphology and size of the transferred material. Therefore, temporal shaping within the corresponding time scales of these processes may be used for tailoring the features of the metallic structures obtained by LIFT.

  7. Thermal characteristics of double-layer thin film target ablated by femtosecond laser pulses

    Institute of Scientific and Technical Information of China (English)

    Gao Xun; Song Xiao-Wei; Lin Jing-Quan

    2011-01-01

    Thermal characteristics of tightly-contacted copper-gold double-layer thin film target under ablation of femtosecond laser pulses are investigated by using a two-temperature theoretical model. Numerical simulation shows that electron heat flux varies significantly on the boundary of copper-gold film with different maximal electron temperature of 1.15 × 103 K at 5 ps after ablating laser pulse in gold and copper films, which can reach a balance around 12.6 ps and 8.2 ps for a single and double pulse ablation, respectively, and in the meantime, the lattice temperature difference crossing the gold-copper interface is only about 0.04 × 103 K at the same time scale. It is also found that electron-lattice heat relaxation time increases linearly with laser fluence in both single and double pulse ablation, and a sudden change of the relaxation time appears after the laser energy density exceeds the ablation threshold.

  8. The influence of femtosecond laser pulse wavelength on embryonic stem cell differentiation

    Science.gov (United States)

    Mthunzi, Patience

    2012-10-01

    Stem cells are rich in proteins, carbohydrates, deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and various other cellular components which are responsible for a diversity of functions. Mostly the building blocks of these intracellular entities play an active role in absorbing ultra-violet (UV) and visible light sources. Light-matter interactions in biomaterials are a complex situation and subsequent damage may not always amount only from wavelength dependent effects but may also be driven by a wealth of other optical parameters which may lead to a variety photochemical reactions. Previously, literature has reported efficient photo-transfection and differentiation of pluripotent stem cells via near infrared (NIR) femtosecond (fs) laser pulses with minimum compromise to their viability. Therefore, in this study the influence of using different fs laser wavelengths on optical stem cell transfection and differentiation is investigated. A potassium titanyl phosphate (KTP) crystal was employed in frequency doubling a 1064 nm fs laser beam. The newly generated 532 nm fs pulsed beam was then utilized for the first time in transient photo-transfection of ES-E14TG2a mouse embryonic stem (mES) cells. Compared to using 1064 nm fs pulses which non-invasively introduce plasmid DNA and other macromolecules into mES cells, our results showed a significant decline in the photo-transfection efficiency following transfecting with a pulsed fs visible green beam.

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

    Energy Technology Data Exchange (ETDEWEB)

    Samek, Ota [ISAS-Institute for Analytical Sciences, Bunsen-Kirchhoff Str.11, 44139 Dortmund (Germany)]. E-mail: samek@ansci.de; 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)

    2005-08-31

    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.

  10. New opportunities for secure communication networks using shaped femtosecond laser pulses inducing filamentation processes in the atmosphere

    Science.gov (United States)

    Alyami, H. M.; Becerra, V. M.; Hadjiloucas, S.

    2013-11-01

    The current study discusses new opportunities for secure ground to satellite communications using shaped femtosecond pulses that induce spatial hole burning in the atmosphere for efficient communications with data encoded within super-continua generated by femtosecond pulses. Refractive index variation across the different layers in the atmosphere may be modelled using assumptions that the upper strata of the atmosphere and troposphere behaving as layered composite amorphous dielectric networks composed of resistors and capacitors with different time constants across each layer. Input-output expressions of the dynamics of the networks in the frequency domain provide the transmission characteristics of the propagation medium. Femtosecond pulse shaping may be used to optimize the pulse phase-front and spectral composition across the different layers in the atmosphere. A generic procedure based on evolutionary algorithms to perform the pulse shaping is proposed. In contrast to alternative procedures that would require ab initio modelling and calculations of the propagation constant for the pulse through the atmosphere, the proposed approach is adaptive, compensating for refractive index variations along the column of air between the transmitter and receiver.

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

    Science.gov (United States)

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

    2017-07-04

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

  12. Quantum interference in laser-assisted photo-ionization excited by a femtosecond x-ray pulse

    Institute of Scientific and Technical Information of China (English)

    Ge Yu-Cheng

    2008-01-01

    The photoelectron energy spectra (PESs) excited by monochromatic femtosecond x-ray pulses in the presence of a femtosecond laser are investigated. APES is composed of a set of separate peaks, showing interesting comb-like structures. These structures result from the quantum interferences between photoelectron wave packets generated at different times. The width and the localization of each peak as well as the number of peaks are determined by all the laser and x-ray parameters. Most of peak heights of the PES are higher than the classical predictions.

  13. Characterization of nonlinear properties of black phosphorus nanoplatelets with femtosecond pulsed Z-scan measurements.

    Science.gov (United States)

    Zheng, Xin; Chen, Runze; Shi, Gang; Zhang, Jianwei; Xu, Zhongjie; Cheng, Xiang'ai; Jiang, Tian

    2015-08-01

    The nonlinear properties of black phosphorus (BP) nanoplatelets (NPs) have been characterized with Z-scan measurements under 800-nm femtosecond pulsed laser excitation. A transition from saturable absorption (SA) to reverse saturable absorption (RSA) with the increase of laser intensity was observed in the open-aperture (OA) measurements. Simultaneously, closed-aperture (CA) measurements were carried out to investigate the nonlinear refractive index of BP NPs together, and a value of n(2) ≃(6.8±0.2)×10(-13) m2/W was obtained. The nonlinear absorption properties were analyzed according to the band structure of BP. A theoretical analysis based on SA and two-photon absorption (TPA) was used to determine the nonlinear absorption coefficients from the experimental results, and the TPA coefficient at 800 nm was estimated about (4.5±0.2)×10(-10) m/W.

  14. Graphene Oxides as Tunable Broadband Nonlinear Optical Materials for Femtosecond Laser Pulses.

    Science.gov (United States)

    Jiang, Xiao-Fang; Polavarapu, Lakshminarayana; Neo, Shu Ting; Venkatesan, T; Xu, Qing-Hua

    2012-03-15

    Graphene oxide (GO) thin films on glass and plastic substrates were found to display interesting broadband nonlinear optical properties. We have investigated their optical limiting activity for femtosecond laser pulses at 800 and 400 nm, which could be tuned by controlling the extent of reduction. The as-prepared GO films were found to exhibit excellent broadband optical limiting behaviors, which were significantly enhanced upon partial reduction by using laser irradiation or chemical reduction methods. The laser-induced reduction of GO resulted in enhancement of effective two-photon absorption coefficient at 400 nm by up to ∼19 times and enhancement of effective two- and three-photon absorption coefficients at 800 nm by ∼12 and ∼14.5 times, respectively. The optical limiting thresholds of partially reduced GO films are much lower than those of various previously reported materials. Highly reduced GO films prepared by using the chemical method displayed strong saturable absorption behavior.

  15. Nanofoaming in the surface of biopolymers by femtosecond pulsed laser irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Gaspard, S.; Oujja, M.; Nalda, R. de [Rocasolano Institute of Physical Chemistry, CSIC, Serrano 119, 28006 Madrid (Spain); Abrusci, C.; Catalina, F. [Institute of Polymer Science and Technology, CSIC, Juan de la Cierva 3, 28006 Madrid (Spain); Banares, L. [Department of Physical Chemistry, Faculty of Chemistry, Universidad Complutense de Madrid, 28040 Madrid (Spain); Lazare, S. [Institut des Sciences Moleculaires UMR 5255, Universite de Bordeaux 1, Talence (France); Castillejo, M. [Rocasolano Institute of Physical Chemistry, CSIC, Serrano 119, 28006 Madrid (Spain)], E-mail: marta.castillejo@iqfr.csic.es

    2007-12-15

    In this work, the nanostructuring induced in femtosecond (fs) laser irradiation of biopolymers is examined in self-standing films of collagen and gelatine. Irradiation by single 90 fs pulses at 800, 400 and 266 nm is shown to result in the formation of a modified layer with submicrometric size structures. The size and uniformity of the observed features are strongly dependent on irradiation wavelength and on the characteristics of the biopolymer (water content and mechanical strength). Examination of the films by laser induced fluorescence serves to assess the chemical modifications induced by laser irradiation, revealing changes in the emission bands assigned to the aromatic amino acid tyrosine and its degradation products. The results are discussed in the framework of a mechanism involving the generation of large free-electron densities, through multiphoton and avalanche ionization, which determine the temperature and stress distribution in the irradiated volume.

  16. Carrier emission of n-type gallium nitride illuminated by femtosecond laser pulses

    Science.gov (United States)

    Li, Runze; Zhu, Pengfei; Chen, Jie; Cao, Jianming; Rentzepis, Peter M.; Zhang, Jie

    2016-12-01

    The carrier emission efficiency of light emitting diodes is of fundamental importance for many technological applications, including the performance of GaN and other semiconductor photocathodes. We have measured the evolution of the emitted carriers and the associated transient electric field after femtosecond laser excitation of n-type GaN single crystals. These processes were studied using sub-picosecond, ultrashort, electron pulses and explained by means of a "three-layer" analytical model. We find that for pump laser intensities on the order of 1011 W/cm2, the electrons that escaped from the crystal surface have a charge of ˜2.7 pC and a velocity of ˜1.8 μm/ps. The associated transient electrical field evolves at intervals ranging from picoseconds to nanoseconds. These results provide a dynamic perspective on the photoemission properties of semiconductor photocathodes.

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

    Science.gov (United States)

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

    2012-02-13

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

  18. Terahertz emission from InSb illuminated by femtosecond laser pulses

    Science.gov (United States)

    Arlauskas, A.; Subačius, L.; Krotkus, A.; Malevich, V. L.

    2017-02-01

    Athough terahertz (THz) radiation from semiconductor surfaces illuminated by femtosecond laser pulses was observed a long time ago, the mechanisms responsible for this radiation still remains questionable, especially in narrow band gap semiconductors. Four different crystallographic orientation {(1 0 0), (1 1 0), (1 1 1) and (1 1 2)} InSb samples were analyzed in this investigation. THz amplitude dependences on the excitation wavelength and azimuthal angle are presented in this paper. We have shown that the second order nonlinear effect—optical rectification—is responsible for THz radiation in InSb. The microscopic origin of this effect is related to the orientation of electrons momenta by the optical radiation and anisotropy of the conduction band at high energies. Monte Carlo simulations have shown that electric field screening by intrinsic carriers diminishes the contribution of the third order nonlinear effect in this material.

  19. Filamentation of femtosecond laser pulse influenced by the air turbulence at various propagation distances

    Science.gov (United States)

    Hu, Yuze; Nie, Jinsong; Sun, Ke; Wang, Lei

    2017-01-01

    The spatial and temporal features of femtosecond laser filamentation, which are induced by a laser with power several times higher than the critical power, influenced by strong air turbulence at various propagation distances have been studied numerically. First, a strong turbulence occurring right before focal lens induces a few counter-balanced energy spikes which prevent the filament generation. Second, with the turbulence right before the filamentation, side filaments formed in the periphery towards the outside area leads the filament to be slightly short. Third, with the turbulence right after the lens, numerous energy spikes of the wave profile arise, but they will merge into one filament gradually, leading to a delayed filamentation onset and a shorter filamentation length. The deformation of temporal pulse shape become more sensitive and the supercontinuum (SC) can be weakened more significantly when strong turbulence takes place in air more previously.

  20. Supercontinuum Generation in Holey Microstructure Fibres with Random Cladding Distribution by Femtosecond Laser Pulses

    Institute of Scientific and Technical Information of China (English)

    李曙光; 侯蓝田; 冀玉领; 周桂耀

    2003-01-01

    It is reported that supercontinuum spectrum from 440 to 1050 nm can be generated in holey microstructure fibres (HMFs) with random cladding distribution by Ti:sapphire femtosecond laser pulses with central wavelength of 800 nm. Based on the method of the effective refractive index and the analogy of step-index fibre, we have calculated the effective mode area and the group velocity dispersion (GVD). It is found that the HMFs have specifically ability of localizing light and controlling GVD. The mechanism of supercontinuum generation in the HMFs with random cladding distribution is that the balance between the GVD and the self-phase modulation in the anomalous dispersion region leads to formation of solitons and fission of high order solitons.

  1. Above-threshold ionization in neon produced by combining optical and bichromatic XUV femtosecond pulses

    CERN Document Server

    Douguet, Nicolas; Bartschat, Klaus

    2016-01-01

    We consider the ionization of neon induced by a femtosecond laser pulse composed of overlapping, linearly polarized bichromatic extreme ultraviolet and infrared fields. In particular, we study the effects of the infrared light on a two-pathway ionization scheme for which Ne 2s22p53s1P is used as intermediate state. Using time-dependent calculations, supported by a theoretical approach based on the strong-field approximation, we analyze the ionization probability and the photoelectron angular distributions associated with the different sidebands of the ionization spectrum. Complex oscillations of the angular distribution anisotropy parameters as a function of the infrared light intensity are revealed. Finally, we demonstrate that coherent control of the asymmetry is achievable by tuning the infrared frequency to a nearby electronic transition.

  2. Amplification of 126 nm femtosecond seed pulses in optical-field-induced Ar plasma filamentation

    Science.gov (United States)

    Kubodera, Shoichi; Deshimaru, Naoyuki; Kaku, Masanori; Katto, Masahito

    2014-10-01

    We have observed amplification of femtosecond (fs) VUV coherent seed beam at 126 nm by utilizing an optical-field-induced ionization (OFI) high-pressure Ar plasma filamentation. We have produced a low-temperature and high-density Ar plasma filamentation inside a high-pressure Ar cell by irradiating a high-intensity laser with an intensity of approximately 1014 W cm-2. Argon excimer molecules (Ar2*) as an amplifier medium were produced inside the high-pressure cell and were used to amplify a weak VUV ultrashort seed pulse at 126 nm, which was generated by harmonic generation of another short pulse infrared laser at 882 nm. We have measured the amplification characteristics and the OFI plasma diagnosis by utilizing the fs VUV pulses at 126 and 882 nm, respectively. The maximum optical gain value of 1.1 cm-1 was observed. Temporal behaviors of the plasma temperature and density in the nano-second time scale indicated a high-density and low-temperature plasma produced by using the OFI. These plasma behaviors were utilized to reproduce the optical amplification characteristics with our OFI excimer simulation code.

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

    Science.gov (United States)

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

    2014-01-01

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

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

    Science.gov (United States)

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

    2010-03-01

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

  5. Self-trapping of intensities changing under SHG and SWG for high intensive femtosecond laser pulse

    Science.gov (United States)

    Trofimov, Vyacheslav A.; Kharitonov, Dmitry M.; Fedotov, Mikhail V.

    2017-05-01

    SHG and SFG (SWG) and THG are used widely in many practical applications such as a substance diagnostics, and imaging of various physical, chemical and biological processes as well as for laser radiation frequency conversion. One of very interesting phenomena under the frequency conversion takes place if a basic wave incident intensity is enough high: a synchronic mode of the laser pulse intensities changing along a propagation coordinate appears under certain conditions. First of all, we investigate this phenomenon using the frame-work of long pulse duration approximation and plane wave approximation without applying the basic wave energy non-depletion approximation. Applying an original approach we derive the solution of Schr¨odinger equations describing the THG via a SHG process and summary frequency wave generation (SFG) process for femtosecond pulses. Among many modes of the frequency conversion process under consideration we found out analytically the mode corresponding to synchronous intensities changing for the interacting waves. We derive conditions of such mode realization in dependence of the problem parameters. After that we verify our analytical consideration using a computer simulation of the problem on the base of the corresponding Schr¨odinger equations. Computer simulation shown also a new phenomenon at three-wave interaction: interacting wave intensities changing with two (or more) oscillation periods.

  6. Regular sub-wavelength surface structures induced by femtosecond laser pulses on nickel

    Science.gov (United States)

    Qi, Litao

    2015-02-01

    In this research, the formation of laser-induced periodic surface structures (LIPSS) on the nickel surface by femtosecond laser pulses was investigated. In the experiment, we used a commercially available amplified Ti:sapphire laser system that generated 164 fs laser pulses with a maximum pulse energy (Ep) of 1 mJ at a 1 kHz repetition rate and with a central wavelength λ= 780 nm. To obtain a fine periodic ordering of surface nanostructures, the laser beam, through a 0.2 mm pinhole aperture positioned near the 10× objective lens, was focused onto the sample. The samples were mounted on an XYZ-translation stage and irradiated in static and line-scanning experiment. The morphology of the induced periodic structure was examined by scanning electron microscopy. The surface profile was measured by atomic force microscopy. LIPSS with a period of around 700 nm entirely covered the irradiated area. Large area of LIPSS in the nickel surface was produced in line-scanning experiment. The mechanism of the formation of LIPSS in the entire irradiated area in static irradiation was discussed. The function of a 0.2 mm pinhole aperture was studied. The regular LIPSS on the nickel surface changed the optical property of the surface. The regular LIPSS on nickel surface could be also applied on the micro-mould fabrication.

  7. Intricate Plasma-Scattered Images and Spectra of Focused Femtosecond Laser Pulses

    Science.gov (United States)

    Ooi, C. H. Raymond; Talib, Md. Ridzuan

    2016-08-01

    We report on some interesting phenomena in the focusing and scattering of femtosecond laser pulses in free space that provide insights on intense laser plasma interactions. The scattered image in the far field is analyzed and the connection with the observed structure of the plasma at the focus is discussed. We explain the physical mechanisms behind the changes in the colorful and intricate image formed by scattering from the plasma for different compressions, as well as orientations of plano-convex lens. The laser power does not show significant effect on the images. The pulse repetition rate above 500 Hz can affect the image through slow dynamics The spectrum of each color in the image shows oscillatory peaks due to interference of delayed pulse that correlate with the plasma length. Spectral lines of atomic species are identified and new peaks are observed through the white light emitted by the plasma spot. We find that an Ar gas jet can brighten the white light of the plasma spot and produce high resolution spectral peaks. The intricate image is found to be extremely sensitive and this is useful for applications in sensing microscale objects.

  8. Controlled assembly of high-order nanoarray metal structures on bulk copper surface by femtosecond laser pulses

    Science.gov (United States)

    Qin, Wanwan; Yang, Jianjun

    2017-07-01

    We report a new one-step maskless method to fabricate high-order nanoarray metal structures comprising periodic grooves and particle chains on a single-crystal Cu surface using femtosecond laser pulses at the central wavelength of 400 nm. Remarkably, when a circularly polarized infrared femtosecond laser pulse (spectrally centered at 800 nm) pre-irradiates the sample surface, the geometric dimensions of the composite structure can be well controlled. With increasing the energy fluence of the infrared laser pulse, both the groove width and particle diameter are observed to reduce, while the measured spacing-to-diameter ratio of the nanoparticles tends to present an increasing tendency. A physical scenario is proposed to elucidate the underlying mechanisms: as the infrared femtosecond laser pulse pre-irradiates the target, the copper surface is triggered to display anomalous transient physical properties, on which the subsequently incident Gaussian blue laser pulse is spatially modulated into fringe-like energy depositions via the excitation of ultrafast surface plasmon. During the following relaxation processes, the periodically heated thin-layer regions can be transferred into the metastable liquid rivulets and then they break up into nanodroplet arrays owing to the modified Rayleigh-like instability. This investigation indicates a simple integrated approach for active designing and large-scale assembly of complexed functional nanostructures on bulk materials.

  9. Performance comparison of pulse-pair and wavelets methods for the pulse Doppler weather radar spectrum

    CERN Document Server

    Lagha, Mohand; Bergheul, Said; Rezoug, Tahar; Bettayeb, Maamar

    2012-01-01

    In the civilian aviation field, the radar detection of hazardous weather phenomena (winds) is very important. This detection will allow the avoidance of these phenomena and consequently will enhance the safety of flights. In this work, we have used the wavelets method to estimate the mean velocity of winds. The results showed that the application of this method is promising compared with the classical estimators (pulse-pair, Fourier).

  10. Dynamics of the formation of laser-induced periodic surface structures on dielectrics and semiconductors upon femtosecond laser pulse irradiation sequences

    Science.gov (United States)

    Höhm, S.; Rohloff, M.; Rosenfeld, A.; Krüger, J.; Bonse, J.

    2013-03-01

    The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica and silicon with multiple ( N DPS) irradiation sequences consisting of linearly polarized femtosecond laser pulse pairs (pulse duration ˜150 fs, central wavelength ˜800 nm) is studied experimentally. Nearly equal-energy double-pulse sequences are generated allowing the temporal pulse delay Δ t between the cross-polarized individual fs-laser pulses to be varied from -40 ps to +40 ps with a resolution of ˜0.2 ps. The surface morphologies of the irradiated surface areas are characterized by means of scanning electron and scanning force microscopy. Particularly for dielectrics in the sub-ps delay range striking differences in the orientation and spatial characteristics of the LIPSS can be observed. For fused silica, a significant decrease of the LIPSS spatial periods from ˜790 nm towards ˜550 nm is demonstrated for delay changes of less than ˜2 ps. In contrast, for silicon under similar irradiation conditions, the LIPSS periods remain constant (˜760 nm) for delays up to 40 ps. The results prove the impact of laser-induced electrons in the conduction band of the solid and associated transient changes of the optical properties on fs-LIPSS formation.

  11. Picosecond to femtosecond pulses from high power self mode-locked ytterbium rod-type fiber laser

    OpenAIRE

    Deslandes, Pierre; Perrin, Mathias; Saby, Julien; Sangla, Damien; Salin, François; Freysz, Eric

    2013-01-01

    International audience; We have designed an ytterbium rod-type fiber laser oscillator with tunable pulse duration. This system that delivers more than 10 W of average power is self mode-locked. It yields femtosecond to picosecond laser pulses at a repetition rate of 74 MHz. The pulse duration is adjusted by changing the spectral width of a band pass filter that is inserted in the laser cavity. Using volume Bragg gratings of 0.9 nm and 0.07 nm spectrum bandwidth, this oscillator delivers nearl...

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

    Science.gov (United States)

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

    2014-01-01

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

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

    Science.gov (United States)

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

    2014-09-01

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

  14. Self-compression of femtosecond pulses in argon with a power close to the self-focusing threshold

    Institute of Scientific and Technical Information of China (English)

    Chen Xiao-Wei; Zeng Zhi-Nan; Dai Jun; Li Xiao-Fang; Li Ru-Xin; Xu Zhi-Zhan

    2008-01-01

    Self-compression of femtosecond pulses in noble gases with an input power close to the self-focusing threshold has been investigated experimentally and theoretically.It is demonstrated that either multiphoton ionization (MPI) or space-time focusing and self-steepening effects can induce pulse shortening,but they predominate at different beam intensities during the propagation.The latter effects play a key role in the final pulse self-compression.By choosing an appropriate focusing parameter,action distance of the space-time focusing and self-steepening effects can be lengthened,which can promote a shock pulse structure with a duration as short as two optical cycles.It is also found that,for our calculation eases in which an input pulse power is close to the self-focusing threshold,either group velocity dispersion(GVD) or multiphoton absorption (MPA) has a negligible influence on pulse characteristics in the propagation process.

  15. Coherent femtosecond low-energy single-electron pulses for time-resolved diffraction and imaging: A numerical study

    Energy Technology Data Exchange (ETDEWEB)

    Paarmann, A.; Mueller, M.; Ernstorfer, R. [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin (Germany); Gulde, M.; Schaefer, S.; Schweda, S.; Maiti, M.; Ropers, C. [Courant Research Center Physics and Material Physics Institute, University of Goettingen, Friedrich-Hund-Platz 1, 37077 Goettingen (Germany); Xu, C. [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin (Germany); Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, 390, Qinghe Road, Jiading, Shanghai 201800 (China); Hohage, T. [Institute of Numerical and Applied Mathematics, University of Goettingen, Lotzestr. 16-18, 37083 Goettingen (Germany); Schenk, F. [Courant Research Center Physics and Material Physics Institute, University of Goettingen, Friedrich-Hund-Platz 1, 37077 Goettingen (Germany); Institute of Numerical and Applied Mathematics, University of Goettingen, Lotzestr. 16-18, 37083 Goettingen (Germany)

    2012-12-01

    We numerically investigate the properties of coherent femtosecond single electron wave packets photoemitted from nanotips in view of their application in ultrafast electron diffraction and non-destructive imaging with low-energy electrons. For two different geometries, we analyze the temporal and spatial broadening during propagation from the needle emitter to an anode, identifying the experimental parameters and challenges for realizing femtosecond time resolution. The simple tip-anode geometry is most versatile and allows for electron pulses of several ten of femtosecond duration using a very compact experimental design, however, providing very limited control over the electron beam collimation. A more sophisticated geometry comprising a suppressor-extractor electrostatic unit and a lens, similar to typical field emission electron microscope optics, is also investigated, allowing full control over the beam parameters. Using such a design, we find {approx}230 fs pulses feasible in a focused electron beam. The main limitation to achieve sub-hundred femtosecond time resolution is the typical size of such a device, and we suggest the implementation of more compact electron optics for optimal performance.

  16. Photodissociation/photoionization processes of chlorobromomethane induced by femtosecond laser pulses with pump-probe scheme

    Institute of Scientific and Technical Information of China (English)

    ZHANG Feng; WEI ZhengRong; CAO ZhenZhou; ZHANG ChangHua; ZHANG Bing

    2008-01-01

    The photodissociation/photoionization processes of chlorobromomethane (CH2BrCl) induced by femtosecond laser pulses have been investigated using pump-probe scheme combined with the time-of-flight mass spectra. The dominate photoproducts are observed at different delay time of the pump (400 nm) and probe (800 nm) pulses and the corresponding time-dependence of them is obtained. The results show that the decaying time of the molecule CH2BrCl in the A-band is in the 100 fs. The decaying tendencies of the fragment ions (CH2Cl+ and CH2Br+) and the parent ion (CH2BrCl+) are almost the same and the relative ratios of the yields of them keep constant during the delay time of 0 to 150 fs. These facts suggest that the fragment ions come from the fragmentation of the parent ions in excited electronic states. The probabilities to form CH2Cl+ and CH2Br+ are obtained from the relative ratio of the ion intensity and are about 71.6% and 14.2%, respectively.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-06-06

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

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

    Science.gov (United States)

    Yatsuhashi, Tomoyuki; Nakashima, Nobuaki

    2010-07-22

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

  19. Femtosecond pulses and dynamics of molecular photoexcitation: RbCs example

    CERN Document Server

    Londono, B E; Mahecha, J E; Crubellier, A; Luc-Koenig, E

    2012-01-01

    We investigate the dynamics of molecular photoexcitation by unchirped femtosecond laser pulses using RbCs as a model system. This study is motivated by a goal of optimizing a two-color scheme of transferring vibrationally-excited ultracold molecules to their absolute ground state. In this scheme the molecules are initially produced by photoassociation or magnetoassociation in bound vibrational levels close to the first dissociation threshold. We analyze here the first step of the two-color path as a function of pulse intensity from the low-field to the high-field regime. We use two different approaches, a global one, the 'Wavepacket' method, and a restricted one, the 'Level by Level' method where the number of vibrational levels is limited to a small subset. The comparison between the results of the two approaches allows one to gain qualitative insights into the complex dynamics of the high-field regime. In particular, we emphasize the non-trivial and important role of far-from-resonance levels which are adia...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-06-06

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

  1. Tailoring the surface plasmon resonance of embedded silver nanoparticles by combining nano- and femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Doster, J.; Baraldi, G.; Gonzalo, J.; Solis, J.; Hernandez-Rueda, J.; Siegel, J., E-mail: j.siegel@io.cfmac.csic.es [Laser Processing Group, Instituto de Optica, Serrano 121, 28006 Madrid (Spain)

    2014-04-14

    We demonstrate that the broad surface plasmon resonance (SPR) of a single layer of near-coalescence silver nanoparticles (NPs), embedded in a dielectric matrix can be tailored by irradiation with a single nanosecond laser pulse into a distribution featuring a sharp resonance at 435 nm. Scanning electron microscopy studies reveal the underlying mechanism to be a transformation into a distribution of well-separated spherical particles. Additional exposure to multiple femtosecond laser pulses at 400 nm or 800 nm wavelength induces polarization anisotropy of the SPR, with a peak shift that increases with laser wavelength. The spectral changes are measured in-situ, employing reflection and transmission micro-spectroscopy with a lateral resolution of 4 μm. Spectral maps as a continuous function of local fluence can be readily produced from a single spot. The results open exciting perspectives for dynamically tuning and switching the optical response of NP systems, paving the way for next-generation applications.

  2. Ordered YBCO sub-micron array structures induced by pulsed femtosecond laser irradiation.

    Science.gov (United States)

    Luo, C W; Lee, C C; Li, C H; Shih, H C; Chen, Y-J; Hsieh, C C; Su, C H; Tzeng, W Y; Wu, K H; Juang, J Y; Uen, T M; Chen, S P; Lin, J-Y; Kobayashi, T

    2008-12-08

    We report on the formation of organized sub-micron YBa(2)Cu(3)O(7) (YBCO) dots induced by irradiating femtosecond laser pulses on YBCO films prepared by pulse laser deposition with fluence in the range of 0.21 approximately 0.53 J/cm(2). The morphology of the YBCO film surface depends strongly on the laser fluences irradiated. At lower laser fluence (approximately 0.21 J/cm(2)) the morphology was pattern of periodic ripples with sub-micrometer spacing. Slightly increasing the laser fluence to 0.26 J/cm(2) changes the pattern into organized sub-micron dots with diameters ranging from 100 nm to 800 nm and height of 150 nm. Further increase of the laser fluence to over 0.32 J/cm(2), however, appeared to result in massive melting and led to irregular morphology. The mechanism and the implications of the current findings will be discussed. Arrays of YBCO sub-micron dots with T(c) = 89.7 K were obtained.

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

    Directory of Open Access Journals (Sweden)

    Venkatakrishnan Krishnan

    2011-01-01

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

  4. A Simple Picosecond Pulse Generator Based on a Pair of Step Recovery Diodes

    CERN Document Server

    Zou, Lianfeng; Caloz, Christophe

    2016-01-01

    A picosecond pulse generator based on a pair of step recovery diodes (SRD), leveraging the transient response of the SRD PN junction and controlling the pulse width by a resistor, is proposed. We first explain the operation principle of the device, decomposing the pulse generation into different phases, and then demonstrate an experimental prototype with two different resistance, and hence pulse width, values.

  5. Efficient localized heating of silver nanoparticles by low-fluence femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Huang, H.; Sivayoganathan, M. [Centre for Advanced Materials Joining, University of Waterloo, Ontario, N2L 3G1 (Canada); Department of Mechanical & Mechatronics Engineering, University of Waterloo, Ontario, N2L 3G1 (Canada); Duley, W.W. [Centre for Advanced Materials Joining, University of Waterloo, Ontario, N2L 3G1 (Canada); Department of Physics & Astronomy, University of Waterloo, Ontario, N2L 3G1 (Canada); Zhou, Y., E-mail: nzhou@uwaterloo.ca [Centre for Advanced Materials Joining, University of Waterloo, Ontario, N2L 3G1 (Canada); Department of Mechanical & Mechatronics Engineering, University of Waterloo, Ontario, N2L 3G1 (Canada)

    2015-03-15

    Highlights: • Obtained efficient localized heating (melting) of silver nanoparticles plasmonic structure, which is induced by the excitation of surface plasmon under femtosecond laser irradiation. • Resonance condition is not required here for surface plasmon induced efficient heating; this is different from previous studies where surface plasmon resonance is usually used to obtain enough heating generation. Compared to the previous studies of off-resonance laser heating, the laser fluence used in this study to obtain melting of silver nanoparticles is much lower, only 7.2 mJ/cm{sup 2}. • Beside surface plasmon itself induced heating, surface plasmon induced polymer shell deformation which resulted in electron and ion emission was identified to have certain contribution to the heating of silver nanoparticles plasmonic structure. - Abstract: Highly localized heating can be obtained in plasmonic nanomaterials using laser excitation but the high fluences required often produce unacceptable damage in and near irradiated components and structures. In this work we show that plasmonic nanostructures involving aggregated Ag nanoparticles (Ag NPs) can be heated effectively without attendant damage to the surrounding material when these structures are irradiated with many overlapping femtosecond (fs) laser pulses at very low fluence. Under these conditions, the effectiveness of heating is such that the temperature of 50 nm Ag NPs can be raised to their melting point from room temperature. Aggregates of these NPs are then observed to grow into larger spherical particles as laser heating continues. Imaging of these materials shows that the initiation of melting in individual Ag NPs depends on the local geometry surrounding each NP and on the polarization of the incident laser radiation. Finite difference time domain (FDTD) simulations indicate that melting is triggered by localized surface plasmon (LSP)-induced electric field enhancement at “hotspots”.

  6. Momentum signatures for Schwinger pair production in short laser pulses with a subcycle structure.

    Science.gov (United States)

    Hebenstreit, F; Alkofer, R; Dunne, G V; Gies, H

    2009-04-17

    We investigate electron-positron pair production from vacuum for short laser pulses with a subcycle structure, in the nonperturbative regime (Schwinger pair production). We use the nonequilibrium quantum kinetic approach and show that the momentum spectrum of the created electron-positron pairs is extremely sensitive to the subcycle dynamics-depending on the laser frequency omega, the pulse length tau, and the carrier phase varphi-and shows several distinctive new signatures. This observation could not only help in the design of laser pulses to optimize the experimental signature of Schwinger pair production but also ultimately lead to new probes of light pulses at extremely short time scales.

  7. 88 W 0.5 mJ femtosecond laser pulses from two coherently combined fiber amplifiers.

    Science.gov (United States)

    Seise, Enrico; Klenke, Arno; Breitkopf, Sven; Limpert, Jens; Tünnermann, Andreas

    2011-10-01

    The generation of 0.5 mJ femtosecond laser pulses by coherent combining of two high power high energy fiber chirped-pulse amplifiers is reported. The system is running at a repetition frequency of 175 kHz producing 88 W of average power after the compressor unit. Polarizing beam splitters have been used to realize an amplifying Mach-Zehnder interferometer, which has been stabilized with a Hänsch-Couillaud measurement system. The stabilized system possesses a measured residual rms phase difference fluctuation between the two branches as low as λ/70 rad at the maximum power level. The experiment proves that coherent addition of femtosecond fiber lasers can be efficiently and reliably performed at high B-integral and considerable thermal load in the individual amplifiers.

  8. Role of the temperature dynamics in formation of nanopatterns upon single femtosecond laser pulses on gold

    Science.gov (United States)

    Gurevich, Evgeny L.; Levy, Yoann; Gurevich, Svetlana V.; Bulgakova, Nadezhda M.

    2017-02-01

    In this paper we investigate the role of two-temperature heating dynamics for formation of periodic structures on metal surfaces exposed to single ultrashort laser pulses.The results of two-temperature model (TTM) two-dimensional simulations are presented on the irradiation of gold by a single 800-nm femtosecond laser pulse the intensity of which is modulated in order to reproduce an initial electron temperature perturbation, which can arise from incoming and scattered surface wave interference. The growing (unstable) modes of the lattice temperature distribution along the surface may be significant in the laser induced periodic surface structures formation. After the end of the laser pulse and before the complete coupling between lattice and electrons occurs, the evolution of the amplitude of the subsequent modulation in the lattice temperature reveals different tendencies depending on the spatial period of the initial modulation. This instabilitylike behavior is shown to arise due to the perturbation of the electronic temperature which relaxes slower for bigger spatial periods and thus imparts more significant modulations to the lattice temperature. Small spatial periods of the order of 100 nm and smaller experience stabilization and fast decay from the more efficient lateral heat diffusion which facilitates the relaxation of the electronic temperature amplitude due to in-depth diffusion. An analytical instability analysis of a simplified version of the TTM set of equations supports the lattice temperature modulation behavior obtained in the simulations and reveals that in-depth diffusion length is a determining parameter in the dispersion relation of unstable modes. Finally, it is discussed how the change in optical properties can intensify the modulation-related effects.

  9. Decelerating chirped soliton formation at femtosecond laser pulse propagation in a medium with one-photon absorption and gold nanorods

    Science.gov (United States)

    Trofimov, V. A.; Lysak, T. M.

    2017-01-01

    We demonstrate the possibility of decelerating chirped soliton formation at femtosecond pulse propagation in a medium with gold nanoparticles. We take into account the dependence of one-photon absorption on the nanorod aspect ratio and time-dependent nanorod aspect ratio changing due to nanorod reshaping because of laser energy absorption. The soliton formation occurs due to laser radiation trapping by the nanorod reshaping front. We show analytically that a chirp induced by the negative phase grating is crucial for this trapping.

  10. Mask-Free Patterning of High-Conductivity Metal Nanowires in Open Air by Spatially Modulated Femtosecond Laser Pulses.

    Science.gov (United States)

    Wang, Andong; Jiang, Lan; Li, Xiaowei; Liu, Yang; Dong, Xianzi; Qu, Liangti; Duan, Xuanming; Lu, Yongfeng

    2015-10-28

    A novel high-resolution nanowire fabrication method is developed by thin-film patterning using a spatially modulated femtosecond laser pulse. Deep subwavelength (≈1/13 of the laser wavelength) and high conductivity (≈1/4 of the bulk gold) nanowires are fabricated in the open air without using masks, which offers a single-step arbitrary direct patterning approach for electronics, plasmonics, and optoelectronics nanodevices.

  11. Fabrication of polarization-independent single-mode waveguides in lithium niobate crystal with femtosecond laser pulses

    CERN Document Server

    Qi, Jia; Liao, Yang; Chu, Wei; Liu, Zhengming; Wang, Zhaohui; Qiao, Lingling; Cheng, Ya

    2016-01-01

    We report on fabrication of depressed cladding optical waveguides buried in lithium niobate crystal with shaped femtosecond laser pulses. Depressed cladding waveguides of variable mode-field sizes are fabricated by forming the four sides of the cladding using a slit-beam shaping technique. We show that the waveguides fabricated by our technique allows single-mode propagation of the light polarized in both vertical and horizontal directions.

  12. Three-dimensional simulation on explosions of hydrogen atomic clusters irradiated by an intense femtosecond laser pulse

    Institute of Scientific and Technical Information of China (English)

    Xia Yong; Liu Jian-Sheng; Ni Guo-Quan; Xu Zhi-Zhan

    2004-01-01

    Using classic particle dynamics simulations, the interaction process between an intense femtosecond laser pulse and icosahedral hydrogen atomic clusters H13, H55 and H147 has been studied. It is revealed that with increasing number of atoms in the cluster, the kinetic energy of ions generated in the Coulomb explosion of the ionized hydrogen clusters increases. The expansion process of the clusters after laser irradiation has also been examined, showing that the expansion scale decreases with increasing cluster size.

  13. Formation of femtosecond laser induced surface structures on silicon : insights from numerical modeling and single pulse experiments

    CERN Document Server

    Derrien, Thibault J Y; Sarnet, Thierry; Sentis, Marc; Itina, Tatiana E

    2011-01-01

    Laser induced periodic surface structures (LIPSS) are formed by multiple irradiation of femtosecond laser on a silicon target. In this paper, we focus and discuss the surface plasmon polariton mechanism by an analysis of transient phase-matching conditions in Si on the basis of a single pulse experiment and numerical simulations. Two regimes of ripple formation mechanisms at low number of shots are identified and detailed. Correlation of numerical and experimental results is good.

  14. Polarization-independent etching of fused silica based on electrons dynamics control by shaped femtosecond pulse trains for microchannel fabrication.

    Science.gov (United States)

    Yan, X; Jiang, L; Li, X; Zhang, K; Xia, B; Liu, P; Qu, L; Lu, Y

    2014-09-01

    We propose an approach to realize polarization-independent etching of fused silica by using temporally shaped femtosecond pulse trains to control the localized transient electrons dynamics. Instead of nanograting formation using traditional unshaped pulses, for the pulse delay of pulse trains larger than 1 ps, coherent field-vector-related coupling is not possible and field orientation is lost. The exponential growth of the periodic structures is interrupted. In this case, disordered and interconnected nanostructures are formed, which is probably the main reason of etching independence on the laser polarization. As an application example, square-wave-shaped and arc-shaped microchannels are fabricated by using pulse trains to demonstrate the advantage of the proposed method in fabricating high-aspect-ratio and three-dimensional microchannels.

  15. Generation of a few femtoseconds pulses in seeded FELs using a seed laser with small transverse size

    Science.gov (United States)

    Li, Heting; Jia, Qika

    2016-09-01

    We propose a simple method to generate a few femtosecond pulses in seeded FELs. We use a longitudinal energy-chirped electron beam passing through a dogleg where transverse dispersion will generate a horizontal energy chirp, then in the modulator, a seed laser with narrow beam radius will only modulate the center portion of the electron beam and then short pulses at high harmonics will be generated in the radiator. Using a representative realistic set of parameters, we show that 30 nm XUV pulse based on the HGHG scheme and 9 nm soft x-ray pulse based on the EEHG scheme with duration of about 8 fs (FWHM) and peak power of GW level can be generated from a 180 nm UV seed laser with beam waist of 75 μm. This new scheme can provide an optional operation mode for the existing seeded FEL facilities to meet the requirement of short-pulse FEL.

  16. Direct generation of intense extreme ultraviolet supercontinuum with chirped 11-mJ pulses from a femtosecond laser amplifier

    CERN Document Server

    Zeng, Bin; Li, Guihua; Yao, Jinping; Ni, Jielei; Zhang, Haisu; Cheng, Ya; Xu, Zhizhan

    2011-01-01

    We report on the generation of intense extreme ultraviolet (EUV) supercontinuum with photon energies spanning from 35 eV to 50 eV (i. e., supporting an isolated attosecond pulse with a duration of ~271 as) by loosely focusing 11-mJ chirped pulses from a femtosecond laser amplifier into a 10-mm long gas cell filled with krypton gas. We observe that when high-order harmonics are generated with transformed-limited ~35 fs pulses, only discrete harmonics can be produced; whereas for negatively chirped 188 fs pulses, EUV supercontinuum can be observed in single-shot harmonic spectrum. The dramatic change of spectral and temporal properties of the driver pulses after passing through the gas cell indicates that propagation effects play a significant role in promoting the generation of the EUV supercontinuum.

  17. Picosecond to femtosecond pulses from high power self mode-locked ytterbium rod-type fiber laser.

    Science.gov (United States)

    Deslandes, Pierre; Perrin, Mathias; Saby, Julien; Sangla, Damien; Salin, François; Freysz, Eric

    2013-05-06

    We have designed an ytterbium rod-type fiber laser oscillator with tunable pulse duration. This system that delivers more than 10 W of average power is self mode-locked. It yields femtosecond to picosecond laser pulses at a repetition rate of 74 MHz. The pulse duration is adjusted by changing the spectral width of a band pass filter that is inserted in the laser cavity. Using volume Bragg gratings of 0.9 nm and 0.07 nm spectrum bandwidth, this oscillator delivers nearly Fourier limited 2.8 ps and 18.5 ps pulses, respectively. With a 4 nm interference filter, one obtains picosecond pulses that have been externally dechirped down to 130 fs.

  18. Probing spatial properties of electronic excitation in water after interaction with temporally shaped femtosecond laser pulses: Experiments and simulations

    Science.gov (United States)

    Winkler, Thomas; Sarpe, Cristian; Jelzow, Nikolai; Lasse H., Lillevang; Götte, Nadine; Zielinski, Bastian; Balling, Peter; Senftleben, Arne; Baumert, Thomas

    2016-06-01

    In this work, laser excitation of water under ambient conditions is investigated by radially resolved common-path spectral interferometry. Water, as a sample system for dielectric materials, is excited by ultrashort bandwidth-limited and temporally asymmetric shaped femtosecond laser pulses, where the latter start with an intense main pulse followed by a decaying pulse sequence, i.e. a temporal Airy pulse. Spectral interference in an imaging geometry allows measurements of the transient optical properties integrated along the propagation through the sample but radially resolved with respect to the transverse beam profile. Since the optical properties reflect the dynamics of the free-electron plasma, such measurements reveal the spatial characteristics of the laser excitation. We conclude that temporally asymmetric shaped laser pulses are a promising tool for high-precision laser material processing, as they reduce the transverse area of excitation, but increase the excitation inside the material along the beam propagation.

  19. Production rate enhancement of size-tunable silicon nanoparticles by temporally shaping femtosecond laser pulses in ethanol.

    Science.gov (United States)

    Li, Xin; Zhang, Guangming; Jiang, Lan; Shi, Xuesong; Zhang, Kaihu; Rong, Wenlong; Duan, Ji'an; Lu, Yongfeng

    2015-02-23

    This paper proposes an efficient approach for production-rate enhancement and size reduction of silicon nanoparticles produced by femtosecond (fs) double-pulse ablation of silicon in ethanol. Compared with a single pulse, the production rate is ~2.6 times higher and the mean size of the NPs is reduced by ~1/5 with a delay of 2 ps. The abnormal enhancement in the production rate is obtained at pulse delays Δt > 200 fs. The production-rate enhancement is mainly attributed to high photon absorption efficiency. It is caused by an increase in localized transient electron density, which results from the first sub-pulse ionization of ethanol molecules before the second sub-pulse arrives. The phase-change mechanism at a critical point might reduce nanoparticle size.

  20. Femtosecond laser pulse optimization for multiphoton cytometry and control of fluorescence

    Science.gov (United States)

    Tkaczyk, Eric Robert

    This body of work encompasses optimization of near infrared femtosecond laser pulses both for enhancement of flow cytometry as well as adaptive pulse shaping to control fluorescence. A two-photon system for in vivo flow cytometry is demonstrated, which allows noninvasive quantification of circulating cell populations in a single live mouse. We monitor fluorescently-labeled red blood cells for more than two weeks, and are also able to noninvasively measure circulation times of two distinct populations of breast cancer cells simultaneously in a single mouse. We build a custom laser excitation source in the form of an extended cavity mode-locked oscillator, which enables superior detection in whole blood or saline of cell lines expressing fluorescent proteins including the green fluorescent protein (GFP), tdTomato and mPlum. A mathematical model explains unique features of the signals. The ability to distinguish different fluorescent species is central to simultaneous measurement of multiple molecular targets in high throughput applications including the multiphoton flow cytometer. We demonstrate that two dyes which are not distinguishable to one-photon measurements can be differentiated and in fact quantified in mixture via phase-shaped two-photon excitation pulses found by a genetic algorithm. We also selectively enhance or suppress two-photon fluorescence of numerous common dyes with tailored pulse shapes. Using a multiplicative (rather than ratiometric) fitness parameter, we are able to control the fluorescence while maintaining a strong signal. With this method, we control the two-photon fluorescence of the blue fluorescent protein (BFP), which is of particular interest in investigations of protein-protein interactions, and has frustrated previous attempts of control. Implementing an acousto-optic interferometer, we use the same experimental setup to measure two-photon excitation cross-sections of dyes and prove that photon-photon interferences are the

  1. 530 W, 1.3 mJ, four-channel coherently combined femtosecond fiber chirped-pulse amplification system.

    Science.gov (United States)

    Klenke, Arno; Breitkopf, Sven; Kienel, Marco; Gottschall, Thomas; Eidam, Tino; Hädrich, Steffen; Rothhardt, Jan; Limpert, Jens; Tünnermann, Andreas

    2013-07-01

    We report on a femtosecond fiber laser system comprising four coherently combined large-pitch fibers as the main amplifier. With this system, a pulse energy of 1.3 mJ and a peak power of 1.8 GW are achieved at 400 kHz repetition rate. The corresponding average output power is as high as 530 W. Additionally, an excellent beam quality and efficiency of the combination have been obtained. To the best of our knowledge, such a parameter combination, i.e., gigawatt pulses with half a kilowatt average power, has not been demonstrated so far with any other laser architecture.

  2. Laser-phase determination methods and transfer equations for direct temporal structure measurements of atto- and femtosecond XUV pulses

    Institute of Scientific and Technical Information of China (English)

    Ge Yu-Cheng

    2006-01-01

    In this paper the laser-phase determination methods and transfer equations are presented to directly reconstruct the detailed temporal structures of ultra-short extreme ultraviolet (xuv) pulses from the measured photoelectron energy spectra (PES). Each transfer equation includes one of PID (proportional-integral-differential) terms of PES. The intensity and instantaneous frequency of attosecond xuv can be retrieved from the integral term of PES. The intensity profiles of narrow bandwidth atto- and femtosecond xuvs can be rebuilt from the proportional and differential terms of PES respectively. The methods and equations 05 bc used to improve time resolutions in measuring ultrashort pulses.

  3. A Simple Method for the Evaluation of the Pulse Width of an Ultraviolet Femtosecond Laser Used in Two-Photon Ionization Mass Spectrometry

    Directory of Open Access Journals (Sweden)

    Tomoko Imasaka

    2016-05-01

    Full Text Available A simple method was proposed for on-site evaluation of the pulse width of an ultraviolet femtosecond laser coupled with a mass spectrometer. This technique was based on measurement of a two-photon ionization signal in mass spectrometry by translation of the prism in the pulse compressor of the femtosecond laser. The method was applied to optical pulses that were emitted at wavelengths of 267, 241, and 219 nm; the latter two pulses were generated by four-wave Raman mixing using the third harmonic emission of a Ti:sapphire laser (267 nm in hydrogen gas. The measurement results show that this approach is useful for evaluation of the pulse width of the ultraviolet femtosecond laser used in mass spectrometry for trace analysis of organic compounds.

  4. Experimental investigation and 3D-simulation of the ablated morphology of titanium surface using femtosecond laser pulses

    Science.gov (United States)

    Liu, Dong; Chen, Chuansong; Man, Baoyuan; Meng, Xue; Sun, Yanna; Li, Feifei

    2015-12-01

    The femtosecond laser ablated morphology on titanium surface is investigated theoretically and experimentally. A three dimensional two temperature model (3D-TTM) is used to simulate the surface morphology of titanium sample which is irradiated by femtosecond laser pulses. The electron heat capacity and electron-phonon coupling coefficient of titanium (transition metal) are complex temperature dependent, so the two parameters are corrected based on the theory of electron density of states (DOS). The model is solved by the finite difference time domain (FDTD) method. The 3D temperature field near the target surface is achieved. The radius and depth of the ablated crater are obtained based on the temperature field. The evolutions of the crate's radius and depth with laser fluence are discussed and compared with the experimental results. It is found that the back-flow of the molten material and the deposition of the material vapor should be responsible for the little discrepancy between the simulated and experimental results. The present work makes a better understanding of the thermodynamic process of femtosecond laser ablating metal and meanwhile provides an effective method tool to predict the micro manufacturing process on metals with femtosecond laser.

  5. Two-temperature relaxation and melting after absorption of femtosecond laser pulse

    CERN Document Server

    Inogamov, N A; Ashitkov, S I; Khokhlov, V A; Petrov, Yu V; Komarov, P S; Agranat, M B; Anisimov, S I; Nishihara, K

    2008-01-01

    The theory and experiments concerned with the electron-ion thermal relaxation and melting of overheated crystal lattice constitute the subject of this paper. The physical model includes two-temperature equation of state, many-body interatomic potential, the electron-ion energy exchange, electron thermal conductivity, and optical properties of solid, liquid, and two phase solid-liquid mixture. Two-temperature hydrodynamics and molecular dynamics codes are used. An experimental setup with pump-probe technique is used to follow evolution of an irradiated target with a short time step 100 fs between the probe femtosecond laser pulses. Accuracy of measurements of reflection coefficient and phase of reflected probe light are ~1% and $\\sim 1\\un{nm}$, respectively. It is found that, {\\it firstly}, the electron-electron collisions make a minor contribution to a light absorbtion in solid Al at moderate intensities; {\\it secondly}, the phase shift of a reflected probe results from heating of ion subsystem and kinetics o...

  6. High-power femtosecond-terahertz pulse induces a wound response in mouse skin

    Science.gov (United States)

    Kim, Kyu-Tae; Park, Jaehun; Jo, Sung Jin; Jung, Seonghoon; Kwon, Oh Sang; Gallerano, Gian Piero; Park, Woong-Yang; Park, Gun-Sik

    2013-08-01

    Terahertz (THz) technology has emerged for biomedical applications such as scanning, molecular spectroscopy, and medical imaging. Although a thorough assessment to predict potential concerns has to precede before practical utilization of THz source, the biological effect of THz radiation is not yet fully understood with scant related investigations. Here, we applied a femtosecond-terahertz (fs-THz) pulse to mouse skin to evaluate non-thermal effects of THz radiation. Analysis of the genome-wide expression profile in fs-THz-irradiated skin indicated that wound responses were predominantly mediated by transforming growth factor-beta (TGF-β) signaling pathways. We validated NFκB1- and Smad3/4-mediated transcriptional activation in fs-THz-irradiated skin by chromatin immunoprecipitation assay. Repeated fs-THz radiation delayed the closure of mouse skin punch wounds due to up-regulation of TGF-β. These findings suggest that fs-THz radiation initiate a wound-like signal in skin with increased expression of TGF-β and activation of its downstream target genes, which perturbs the wound healing process in vivo.

  7. Micro/nanostructured surface modification using femtosecond laser pulses on minimally invasive electrosurgical devices.

    Science.gov (United States)

    Lin, Chia-Cheng; Lin, Hao-Jan; Lin, Yun-Ho; Sugiatno, Erwan; Ruslin, Muhammad; Su, Chen-Yao; Ou, Keng-Liang; Cheng, Han-Yi

    2016-01-29

    The purpose of the present study was to examine thermal damage and a sticking problem in the tissue after the use of a minimally invasive electrosurgical device with a nanostructured surface treatment that uses a femtosecond laser pulse (FLP) technique. To safely use an electrosurgical device in clinical surgery, it is important to decrease thermal damage to surrounding tissues. The surface characteristics and morphology of the FLP layer were evaluated using optical microscopy, scanning electron microscopy, and transmission electron microscopy; element analysis was performed using energy-dispersive X-ray spectroscopy, grazing incidence X-ray diffraction, and X-ray photoelectron spectroscopy. In the animal model, monopolar electrosurgical devices were used to create lesions in the legs of 30 adult rats. Animals were sacrificed for investigations at 0, 3, 7, 14, and 28 days postoperatively. Results indicated that the thermal damage and sticking situations were reduced significantly when a minimally invasive electrosurgical instrument with an FLP layer was used. Temperatures decreased while film thickness increased. Thermographic data revealed that surgical temperatures in an animal model were significantly lower in the FLP electrosurgical device compared with that in the untreated one. Furthermore, the FLP device created a relatively small area of thermal damage. As already mentioned, the biomedical nanostructured layer reduced thermal damage and promoted the antisticking property with the use of a minimally invasive electrosurgical device. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2016.

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

    Directory of Open Access Journals (Sweden)

    Belén Sotillo

    2017-02-01

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

  9. Systematic study of spatiotemporal dynamics of intense femtosecond laser pulses in BK-7 glass

    Indian Academy of Sciences (India)

    Ram Gopal; V Deepak; S Sivaramakrishnan

    2007-04-01

    In this paper we present a systematic study of the spatial and temporal effects of intense femtosecond laser pulses in BK-7 over a broad range of input powers, 1–1000 times the critical power for self-focusing (cr) by numerically solving the nonlinear Schrödinger equation (NLS). Most numerical studies have not been extended to such high powers. A clear-cut classification of spatio-temporal dynamics up to very high powers into three regimes – the group-velocity dispersion (GVD) regime, the ionization regime and the dominant plasma regime – as done here, is a significant step towards a better understanding. Further, we examine in detail the role of GVD in channel formation by comparing BK-7 to an `artificial' medium. Our investigations bring forth the important observation that diffraction plays a minimal role in the formation of multiple cones and that plasma plays a diffraction-like role at very high powers. A detailed study of the spatio-temporal dynamics in any condensed medium over this range of powers has not been reported hitherto, to the best of our knowledge. We also suggest appropriate operational powers for various applications employing BK-7 on the basis of our results.

  10. Dissociative ionization of H2+ using intense femtosecond XUV laser pulses

    CERN Document Server

    Yue, Lun

    2014-01-01

    The dissociative ionization of H2+ interacting with intense, femtosecond extreme-ultraviolet laser pulses is investigated theoretically. This is done by numerical propagation of the time-dependent Schr\\"{o}dinger equation for a colinear one-dimensional model of H2+, with electronic and nuclear motion treated exactly within the limitations of the model. The joint-energy spectra (JES) are extracted for the fragmented electron and nuclei by means of the t-SURFF method. The dynamic interference effect, which was first observed in one-electron atomic systems, is in the present work observed for H2+, emerging as interference patterns in the JES. The photoelectron spectrum and the nuclear energy spectrum is obtained by integration of the JES. Without the JES, the photoelectron spectrum itself is shown to be inadequate for the observation of the dynamic interference effect. The resulting JES are analyzed in terms of two models. In one model the wave function is expanded in terms of the "essential" states of the syste...

  11. Ultrafast spin-transfer torque driven by femtosecond pulsed-laser excitation

    Science.gov (United States)

    Koopmans, Bert

    A hot topic in the field of ultrafast laser-induced manipulation of the magnetic state is that of the role and exploitation of laser-induced spin currents. Intense debate has been triggered by claims that such a spin-transfer, e.g. in the form of super-diffusive spin currents over tens of nanometers, might be a main contributor to the demagnetization process in ferromagnetic thin films after femtosecond laser excitation. In this presentation the underlying concepts will be introduced and recent developments reviewed. Particularly we demonstrate the possibility to apply a laser-induced spin transfer torque on a free magnetic layer, using a non-collinear multilayer configuration consisting of a free in-plane layer on top of a perpendicularly magnetized injection layer, as separated by a nonmagnetic spacer. Interestingly, this approach allows for a quantitative measurement of the amount of spin transfer. Moreover, it might provide access to novel device architectures in which the magnetic state is controlled by fs laser pulses. Careful analysis of the resulting precession of the free layer allows us to quantify the applied torque, and distinguish between driving mechanisms based on laser-induced transfer of hot electrons versus a spin Seebeck effect due to the large thermal gradients. Further engineering of the layered structures in order to gain fundamental understanding and optimize efficiencies will be reported. A simple model that treats local non-equilibrium magnetization dynamics to spin transport effects via a spin-dependent chemical potential will be introduced.

  12. Femtosecond pulsed laser textured titanium surfaces with stable superhydrophilicity and superhydrophobicity

    Science.gov (United States)

    Li, Bao-jia; Li, Huang; Huang, Li-jing; Ren, Nai-fei; Kong, Xia

    2016-12-01

    A facile and highly-efficient laser scanning process coupled with a simple silanization modification was used to prepare textured titanium (Ti) surfaces with stable superhydrophilicity and superhydrophobicity. Femtosecond pulsed laser scanning along two mutually perpendicular directions led to the formation of binary structures featuring micrometer-scale spikes covered with nanometer-scale ripples. The period of the spikes significantly increased and the period of the ripples irregularly changed in the narrow range of 550-600 nm with the increase of laser fluence. The obtained laser-textured Ti surfaces were hydrophilic or even superhydrophilic, and the superhydrophilic laser-textured Ti surface using a laser fluence of 1.5 J/cm2 was observed to retain its wetting property after 30 days of storage in ambient atmosphere. After silanization, all the laser-textured Ti surfaces exhibited high hydrophobicity or superhydrophobicity, and the superhydrophobic laser-textured Ti surfaces using laser fluences of 1.5 and 1.8 J/cm2 remained stable when stored in air for over 30 days. The results imply the potential applications of these surfaces in a variety of fields.

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

    Science.gov (United States)

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

    2017-03-01

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

  14. Femtosecond laser pulses for chemical-free embryonic and mesenchymal stem cell differentiation

    Science.gov (United States)

    Mthunzi, Patience; Dholakia, Kishan; Gunn-Moore, Frank

    2011-10-01

    Owing to their self renewal and pluripotency properties, stem cells can efficiently advance current therapies in tissue regeneration and/or engineering. Under appropriate culture conditions in vitro, pluripotent stem cells can be primed to differentiate into any cell type some examples including neural, cardiac and blood cells. However, there still remains a pressing necessity to answer the biological questions concerning how stem cell renewal and how differentiation programs are operated and regulated at the genetic level. In stem cell research, an urgent requirement on experimental procedures allowing non-invasive, marker-free observation of growth, proliferation and stability of living stem cells under physiological conditions exists. Femtosecond (fs) laser pulses have been reported to non-invasively deliver exogenous materials, including foreign genetic species into both multipotent and pluripotent stem cells successfully. Through this multi-photon facilitated technique, directly administering fs laser pulses onto the cell plasma membrane induces transient submicrometer holes, thereby promoting cytosolic uptake of the surrounding extracellular matter. To display a chemical-free cell transfection procedure that utilises micro-litre scale volumes of reagents, we report for the first time on 70 % transfection efficiency in ES-E14TG2a cells using the enhanced green fluorescing protein (EGFP) DNA plasmid. We also show how varying the average power output during optical transfection influences cell viability, proliferation and cytotoxicity in embryonic stem cells. The impact of utilizing objective lenses of different numerical aperture (NA) on the optical transfection efficiency in ES-E14TG2a cells is presented. Finally, we report on embryonic and mesenchymal stem cell differentiation. The produced specialized cell types could thereafter be characterized and used for cell based therapies.

  15. Ionization effects in the generation of wake-fields by ultra-high contrast femtosecond laser pulses in argon gas

    Energy Technology Data Exchange (ETDEWEB)

    Makito, K.; Shin, J.-H. [Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka (Japan); Zhidkov, A.; Hosokai, T.; Masuda, S. [Photon Pioneers Center, Osaka University, 2-8, Yamadaoka, Suita, Osaka (Japan); Japan Science and Technology Agency (JST), CREST, 2-8 Yamadaoka, Suita, Osaka (Japan); Kodama, R. [Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka (Japan); Photon Pioneers Center, Osaka University, 2-8, Yamadaoka, Suita, Osaka (Japan); Japan Science and Technology Agency (JST), CREST, 2-8 Yamadaoka, Suita, Osaka (Japan)

    2012-10-15

    Difference in mechanisms of wake-field generation and electron self-injection by high contrast femtosecond laser pulses in an initially neutral Argon gas and in pre-ionized plasma without ionization is studied via 2D particle-in-cell simulations including optical ionization of the media. For shorter laser pulses, 40 fs, ionization results only in an increase of the charge of accelerated electrons by factor of {approx}3 with qualitatively the same energy distribution. For longer pulses, 80 fs, a more stable wake field structure is observed in the neutral gas with the maximal energy of the accelerated electrons exceeding that in the fixed density plasma. In higher density Argon, an ionizing laser pulse converts itself to a complex system of solitons at a self-induced, critical density ramp.

  16. Ionization effects in the generation of wake-fields by ultra-high contrast femtosecond laser pulses in argon gas

    Science.gov (United States)

    Makito, K.; Zhidkov, A.; Hosokai, T.; Shin, J.-H.; Masuda, S.; Kodama, R.

    2012-10-01

    Difference in mechanisms of wake-field generation and electron self-injection by high contrast femtosecond laser pulses in an initially neutral Argon gas and in pre-ionized plasma without ionization is studied via 2D particle-in-cell simulations including optical ionization of the media. For shorter laser pulses, 40 fs, ionization results only in an increase of the charge of accelerated electrons by factor of ˜3 with qualitatively the same energy distribution. For longer pulses, 80 fs, a more stable wake field structure is observed in the neutral gas with the maximal energy of the accelerated electrons exceeding that in the fixed density plasma. In higher density Argon, an ionizing laser pulse converts itself to a complex system of solitons at a self-induced, critical density ramp.

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

    Science.gov (United States)

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

    2017-07-01

    Novel dual-scale structures were obtained by femtosecond double pulse train (subpulse delay Δt > 0 ps) one-step irradiating silicon in water. The dual-scale structures consist of microspikes of ∼2 μm width and ∼0.5 μm height, and nanoripples with a mean period of 146 nm or nanoparticles with a mean diameter of 90 nm which entirely cover on the microspikes, for linearly polarized or circularly polarized femtosecond laser respectively. The formation of dual-scale structures involves the following processes: (1) Continuously laser energy deposited at femtosecond to picosecond timescales within silicon surfaces and central regions, will result in enhanced capillary waves and thinner melted silicon layers. Hence, the microspikes can be induced at laser fluences below ablation threshold; (2) Later (>500-800 pulses), a mass of debris and bubbles produced will lead to the remarkably and uniformly scattering or shielding of subsequent incident laser energy. Hence, the nanostructures can be induced. The novel structures exhibit high-sensitive surface enhanced Raman scattering with an enhancement factor of 108 for Rhodamine 6G detecting. Besides, the novel structures have application potentials in improving the silicon hydrophobicity, antireflection, etc.

  18. Soda-lime glass microlens arrays fabricated by laser: Comparison between a nanosecond and a femtosecond IR pulsed laser

    Science.gov (United States)

    Delgado, Tamara; Nieto, Daniel; Flores-Arias, María Teresa

    2016-11-01

    We present the manufacturing of microlens arrays on soda-lime glass substrates by using two different IR pulsed lasers: a nanosecond Nd:YVO4 laser (1064 nm) and a femtosecond laser based on Ytterbium crystal technology (1030 nm). In both cases, the fabrication technique consists of the combination of a direct-write laser process, followed by a post-thermal treatment assisted by a CO2 laser. Through the analysis of the morphological characteristics of the generated microlenses, the different physical mechanisms involved in the glass ablation process with a nanosecond and a femtosecond laser are studied. In addition, by analyzing the optical features of the microlenses, a better result in terms of the homogeneity and quality of the spot focuses are observed for those microlenses fabricated with the Nd:YVO4 nanosecond laser. Microlens arrays with a diameter of 80 and 90 μm were fabricated.

  19. Femtosecond pulse erbium-doped fiber laser by a few-layer MoS(2) saturable absorber.

    Science.gov (United States)

    Liu, Hao; Luo, Ai-Ping; Wang, Fu-Zao; Tang, Rui; Liu, Meng; Luo, Zhi-Chao; Xu, Wen-Cheng; Zhao, Chu-Jun; Zhang, Han

    2014-08-01

    We report on the generation of a femtosecond pulse in a fiber ring laser by using a polyvinyl alcohol (PVA)-based molybdenum disulfide (MoS(2)) saturable absorber (SA). With a saturable optical intensity of 34  MW/cm(2) and a modulation depth of ∼4.3%, the PVA-based MoS(2) SA had been employed with an erbium-doped fiber ring laser as a mode locker. The mode-locking operation could be achieved at a low pump threshold of 22 mW. A ∼710  fs pulse centered at 1569.5 nm wavelength with a repetition rate of 12.09 MHz had been achieved with proper cavity dispersion. With the variation of net cavity dispersion, output pulses with durations from 0.71 to 1.46 ps were obtained. The achievement of a femtosecond pulse at 1.55 μm waveband demonstrates the broadband saturable absorption of MoS(2), and also indicates that the filmy PVA-based MoS(2) SA is indeed a good candidate for an ultrafast saturable absorption device.

  20. Ultra-fast pulse radiolysis system combined with a laser photocathode RF gun and a femtosecond laser

    CERN Document Server

    Muroya, Y; Watanabe, T; Wu, G; Kobayashi, T; Yoshii, K; Ueda, T; Uesaka, M; Katsumura, Y

    2002-01-01

    In order to study the early events in radiation physics and chemistry, two kinds of new pulse radiolysis systems with higher time resolution based on pump-and-probe method have been developed at the Nuclear Engineering Research Laboratory, the University of Tokyo. The first one, a few picosecond (2 ps at FWHM) electron beam (pump) from an 18 MeV S-band Linac using a laser photocathode RF gun (BNL/KEK/SHI type: GUN IV) was operated with a femtosecond laser pulse (100 fs at FWHM), which also acted as the analyzing light (probe). The synchronization precision between the pump and the probe was 1.7 ps (rms). In a 1.0 cm sample cell, a time resolution of 12 ps was achieved. The second one, a picosecond (4 ps at FWHM) electron pulse from a 35 MeV S-band Linac employing a conventional thermionic gun with a sub-harmonic buncher, was synchronized with the femtosecond laser pulse, with a synchronization jitter of 2.8 ps (rms). A time resolution of 22 ps was obtained with 2 cm cell. This makes it possible to do the puls...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-10-12

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

  2. Generating Efficient Femtosecond Mid-infrared Pulse by Single Near-infrared Pump Wavelength in Bulk Nonlinear Crystal Without Phase-matching

    DEFF Research Database (Denmark)

    Zhou, Binbin; Guo, Hairun; Bache, Morten

    2014-01-01

    We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave radiation in bulk lithium niobate crystal. Femtosecond mid-IR pulses centering from 2.8-2.92 μm are generated using the single pump wavelengths from 1.25-1.45 μm. © 2014 Optical Society of America...

  3. Role of the temperature instabilities for formation of nano-patterns upon single femtosecond laser pulses on gold

    CERN Document Server

    Gurevich, Evgeny L; Gurevich, Svetlana V; Bulgakova, Nadezhda M

    2016-01-01

    In this paper we investigate whether the periodic structures on metal surfaces exposed to single ultrashort laser pulses can appear due to an instability induced by two-temperature heating dynamics. The results of two-temperature model (TTM) 2D simulations are presented on the irradiation of gold by a single 800 nm femtosecond laser pulse whose intensity is modulated in order to reproduce a small initial temperature perturbation, which can arise from incoming and scattered surface wave interference. The growing (unstable) modes of the temperature distribution along the surface may be responsible for the LIPSS (Laser Induced Periodic Surface Structures) formation. After the end of the laser pulse and before the complete coupling between lattice and electrons occurs, the evolution of the amplitude of the subsequent modulation in the lattice temperature reveals different tendencies depending on the spatial period of the initial modulation. This instability-like behaviour is shown to arise due to the perturbation...

  4. Femtosecond double-pulse fabrication of hierarchical nanostructures based on electron dynamics control for high surface-enhanced Raman scattering.

    Science.gov (United States)

    Zhang, Ning; Li, Xin; Jiang, Lan; Shi, Xuesong; Li, Cong; Lu, Yongfeng

    2013-09-15

    This Letter presents a simple, efficient approach for high surface-enhanced Raman scattering by one-step controllable fabrication of hierarchical structures (nanoparticles+subwavelength ripples) on silicon substrates in silver nitrate solutions using femtosecond double pulses based on nanoscale electron dynamics control. As the delays of the double pulses increase from 0 fs to 1 ps, the hierarchical structures can be controlled with (1) nanoparticles--the number of nanoparticles in the range of 40-100 nm reaches the maximum at 800 fs and (2) ripples--the subwavelength ripples become intermittent with decreased ablation depths. The redistributed nanoparticles and the modified ripple structures contribute to the maximum enhancement factor of 2.2×10(8) (measured by 10(-6)  M rhodamine 6G solution) at the pulse delay of 800 fs.

  5. Fully coherent spectral broadening of femtosecond pulses from an Er:fiber system

    Directory of Open Access Journals (Sweden)

    Brida D.

    2013-03-01

    Full Text Available Coherence properties of the ultrabroadband output from a highly nonlinear germanosilicate fiber pumped by a femtosecond Er:fiber source are investigated. Conditions necessary to achieve full spectral coherence are demonstrated experimentally and analyzed theoretically.

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

    CSIR Research Space (South Africa)

    Molukanele, P

    2011-09-01

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

  7. Single-shot 3D structure determination of nanocrystals with femtosecond X-ray free electron laser pulses

    CERN Document Server

    Xu, Rui; Song, Changyong; Rodriguez, Jose A; Huang, Zhifeng; Chen, Chien-Chun; Nam, Daewoong; Park, Jaehyun; Gallagher-Jones, Marcus; Kim, Sangsoo; Kim, Sunam; Suzuki, Akihiro; Takayama, Yuki; Oroguchi, Tomotaka; Takahashi, Yukio; Fan, Jiadong; Zou, Yunfei; Hatsui, Takaki; Inubushi, Yuichi; Kameshima, Takashi; Yonekura, Koji; Tono, Kensuke; Togashi, Tadashi; Sato, Takahiro; Yamamoto, Masaki; Nakasako, Masayoshi; Yabashi, Makina; Ishikawa, Tetsuya; Miao, Jianwei

    2013-01-01

    Coherent diffraction imaging (CDI) using synchrotron radiation, X-ray free electron lasers (X-FELs), high harmonic generation, soft X-ray lasers, and optical lasers has found broad applications across several disciplines. An active research direction in CDI is to determine the structure of single particles with intense, femtosecond X-FEL pulses based on diffraction-before-destruction scheme. However, single-shot 3D structure determination has not been experimentally realized yet. Here we report the first experimental demonstration of single-shot 3D structure determination of individual nanocrystals using ~10 femtosecond X-FEL pulses. Coherent diffraction patterns are collected from high-index-faceted nanocrystals, each struck by a single X-FEL pulse. Taking advantage of the symmetry of the nanocrystal, we reconstruct the 3D structure of each nanocrystal from a single-shot diffraction pattern at ~5.5 nm resolution. As symmetry exists in many nanocrystals and virus particles, this method can be applied to 3D st...

  8. Spin-resolved photoelectron spectroscopy using femtosecond extreme ultraviolet light pulses from high-order harmonic generation

    Science.gov (United States)

    Plötzing, M.; Adam, R.; Weier, C.; Plucinski, L.; Eich, S.; Emmerich, S.; Rollinger, M.; Aeschlimann, M.; Mathias, S.; Schneider, C. M.

    2016-04-01

    The fundamental mechanism responsible for optically induced magnetization dynamics in ferromagnetic thin films has been under intense debate since almost two decades. Currently, numerous competing theoretical models are in strong need for a decisive experimental confirmation such as monitoring the triggered changes in the spin-dependent band structure on ultrashort time scales. Our approach explores the possibility of observing femtosecond band structure dynamics by giving access to extended parts of the Brillouin zone in a simultaneously time-, energy- and spin-resolved photoemission experiment. For this purpose, our setup uses a state-of-the-art, highly efficient spin detector and ultrashort, extreme ultraviolet light pulses created by laser-based high-order harmonic generation. In this paper, we present the setup and first spin-resolved spectra obtained with our experiment within an acquisition time short enough to allow pump-probe studies. Further, we characterize the influence of the excitation with femtosecond extreme ultraviolet pulses by comparing the results with data acquired using a continuous wave light source with similar photon energy. In addition, changes in the spectra induced by vacuum space-charge effects due to both the extreme ultraviolet probe- and near-infrared pump-pulses are studied by analyzing the resulting spectral distortions. The combination of energy resolution and electron count rate achieved in our setup confirms its suitability for spin-resolved studies of the band structure on ultrashort time scales.

  9. Narrow linewidth Yb-doped double-cladding fiber laser utilizing fiber Bragg gratings inscribed by femtosecond pulses

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Zhinan; Shi Jiawei; Zhang Jihuang; Wang Haiyan; Li Yuhua; Lu Peixiang, E-mail: oeyhli@gmail.com, E-mail: lupeixiang@mail.hust.edu.cn [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2011-02-01

    A narrow-linewidth high power laser in all fiber format at 1064 nm is demonstrated. The resonant cavity is composed of two distributed Bragg reflector (DBR) fiber gratings, which were inscribed into the core of the double-cladding fiber by use of 800 nm femtosecond laser pulses and a phase mask. The spectrum of the laser exhibited a narrow linewidth of 21 pm at the output power of 0.8 W. The wavelength and power of the laser featured long term stability.

  10. Broadband coherent anti-Stokes Raman scattering light generation in BBO crystal by using two crossing femtosecond laser pulses.

    Science.gov (United States)

    Liu, Jun; Zhang, Jun; Kobayashi, Takayoshi

    2008-07-01

    As broad as 12000 cm(-1) coherent anti-Stokes Raman scattering (CARS) light from ultraviolet to infrared was generated in a BBO crystal by using two crossing femtosecond laser pulses with 30% conversion efficiency. More than fifteenth-order anti-Stokes and second-order Stokes Raman sidebands were observed with nice Gaussian spatial mode. The effect of the crossing angle between two input beams on the spectrum and emitting angle of the Raman sidebands was studied in detail. Calculation shows that the phase-matching condition determines the frequencies and angles of the sidebands.

  11. Tunable, continuous-wave Ti:sapphire channel waveguide lasers written by femtosecond and picosecond laser pulses.

    Science.gov (United States)

    Grivas, Christos; Corbari, Costantino; Brambilla, Gilberto; Lagoudakis, Pavlos G

    2012-11-15

    Fabrication and cw lasing at 798.25 nm is reported for femtosecond (fs) and picosecond (ps) laser-inscribed channel waveguides in Ti:sapphire crystals. Lasing in channels written by fs (ps) pulses was obtained above a threshold of 84 mW (189 mW) with a maximum output power and a slope efficiency of 143 mW (45 mW) and 23.5% (7.1%), respectively. The emission wavelength was tuned over a 170 nm range by using a birefringent filter in an external cavity.

  12. High spatial frequency periodic structures induced on ferric ion-doped Polyvinyl Pyrrolidone film by femtosecond laser pulses

    CERN Document Server

    Lai, Chen; Wang, Yunxia; Li, Qiang; Wu, Lijun

    2016-01-01

    Utilizing continues-wave or pulsed laser to induce nano-structures on various material surfaces is one significant method in nano-fabrication technology. In this report, we investigate the formation of high spatial frequency periodic structures on Polyvinyl Pyrrolidone (PVP) film by a linearly polarized femtosecond laser. Ferric (Fe) ions are introduced into the film to improve the photosensitivity. Regular nano-gratings with spatial periods at the range of 60-100nm, which are about one tenth of the irradiating wavelength, can be induced. The period direction of the nano-gratings is perpendicular to the polarization of the femtosecond laser. By tuning the laser energy and scanning speed, we find that the nano-gratings can be formed in a wide range of experimental parameters. As high laser energy can excite not only metals, but also semiconductors and polymers, we believe the formation of the nano-gratings is due to the interaction between the incident femtosecond laser and surface plasmons. The laser processa...

  13. Amplification of femtosecond vacuum ultraviolet laser pulses at 126 nm in an optical-field-induced ionized argon plasma

    Science.gov (United States)

    Kubodera, Shoichi; Kaku, Masanori; Katto, Masahito; Miyazaki, Kenzo

    2012-10-01

    Short-wavelength lasers in the vacuum ultraviolet (VUV) spectral region between 100 and 200 nm have not yet been developed to the same degree as visible and infrared lasers. We have been developing the argon excimer laser at 126 nm by using an optical-field-induced ionized (OFI) argon plasma. We have observed the gain of 0.86 /cm at 126 nm in the OFI Ar plasma, which was produced inside a hollow fiber with a diameter of 250 microns and a length of 5 cm. In this paper, we have used the OFI plasma gain medium as an amplifier of the 126 nm radiation. A femtosecond 126 nm pulse was produced by the seventh-order nonlinear wavelength conversion of a femtosecond Ti:sapphire laser at 882 nm. The femtosecond wavelength-converted coherent VUV beam was then injected inside the OFI plasma that was produced by the same Ti:sapphire laser, resulting in a 2.4-fold increase of the VUV intensity with one-pass amplification. The gain-length product of 0.87 with the one-pass amplification was evaluated, which was consistent with the value we have observed in the previous measurements. The further extension of the OFI plasma by using a hollow fiber would be plausible to increase the gain-length product and the VUV amplified intensity.

  14. Generation of intense femtosecond optical vortex pulses with blazed-phase grating in chirped-pulse amplification system of Ti:sapphire laser

    Science.gov (United States)

    Lin, Yu-Chieh; Nabekawa, Yasuo; Midorikawa, Katsumi

    2016-11-01

    We demonstrate the generation of an intense femtosecond optical vortex (OV) pulse by employing an OV converter set between two laser amplifiers in a chirped-pulse amplification (CPA) system of a Ti:sapphire laser. The OV converter is composed of a liquid-crystal spatial light modulator (LC-SLM) exhibiting a blazed-phase computer-generated hologram, a concave mirror, and a flat mirror in the 4f setup. Owing to the intrinsic nature of the 4f setup, the OV converter is free from chromatic and topological-charge dispersions, which are always induced in a spiral phase plate conventionally used to convert an intense Gaussian laser pulse to an OV pulse, while we can avoid damage to the LC-SLM by the irradiation of a low-energy pulse before the second amplifier. We have increased the throughput of the OV converter to 42% by systematically investigating the diffraction efficiency of the blazed-phase hologram on the LC-SLM, which relaxes the gain condition required for the second amplifier. The combination of the high-throughput OV converter and the two-stage amplification enables us to generate OV pulses with an energy of 1.63 mJ and a pulse duration of 60 fs at a wavelength of 720 nm, at which the gain of the Ti:sapphire laser is only 60% of the peak gain around 800 nm.

  15. Flexible control of femtosecond pulse duration and separation using an emittance-spoiling foil in x-ray free-electron lasers

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Y. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Behrens, C. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Coffee, R. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Decker, F. -J. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Emma, P. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Field, C. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Helml, W. [Technische Univ. Munchen, Garching (Germany); Huang, Z. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Krejcik, P. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Krzywinski, J. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Loos, H. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Lutman, A. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Marinelli, A. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Maxwell, T. J. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Turner, J. [SLAC National Accelerator Lab., Menlo Park, CA (United States)

    2015-06-22

    We report experimental studies of generating and controlling femtosecond x-ray pulses in free-electron lasers (FELs) using an emittance spoiling foil. By selectivity spoiling the transverse emittance of the electron beam, the output pulse duration or double-pulse separation is adjusted with a variable size single or double slotted foil. Measurements were performed with an X-band transverse deflector located downstream of the FEL undulator, from which both the FEL lasing and emittance spoiling effects are observed directly.

  16. 1.56 µm sub-microjoule femtosecond pulse delivery through low-loss microstructured revolver hollow-core fiber

    Science.gov (United States)

    Krylov, Alexander A.; Senatorov, Andrey K.; Pryamikov, Andrey D.; Kosolapov, Alexey F.; Kolyadin, Anton N.; Alagashev, Grigory K.; Gladyshev, Alexey V.; Bufetov, Igor A.

    2017-03-01

    We report for the first time, to the best of our knowledge, on ~1 MW peak power femtosecond pulse delivery through  ≈10 m-long air-filled microstructured revolver hollow-core fiber (RHCF) in the telecom spectral band near 1.56 µm wavelength. We have developed a high-power all-fiber master oscillator power amplifier source based on the novel large-mode area erbium-doped double-clad fiber with 980 nm multi-mode diode pumping that emits up to 530 nJ pulses shorter than 400 fs with 1.42 W maximum average power. These pulses have been further launched into low-loss (<30 dB km‑1) RHCF with eight non-touched cylindrical capillaries-based cladding and 61 µm core size with more than 80% efficiency. Owing to low dispersion and nonlinearity of the RHCF developed, the output pulse characteristics (spectral and temporal) are close to the input ones for low and moderate pulse energies. However, we have observed significant nonlinear spectral filtering together with pulse shortening (down to 353 fs) at the maximum output average power of 0.94 W. We believe that the system developed may be highly promising for high-precision material processing and other high-energy and high-power laser applications.

  17. High harmonic generation from bulk diamond driven by intense femtosecond laser pulse

    CERN Document Server

    Apostolova, Tzveta

    2016-01-01

    We investigate the high-harmonic generation (HHG) from bulk diamond induced by intense 15 fs laser pulse and photon energy 1.55 eV. For laser intensity in the range $I \\in [1,50]$ TW/cm$^2$, we find that HHG spectra from diamond exhibits two plateaus with high harmonics extending beyond the 50th order. Consistently with experimental observations, we find that the cutoff energy of the two plateaus scales linearly with the field strength. The first plateau is due to recombination of electron-hole pairs near the Brillouin zone center. The appearance of weak second plateau region for high field strength with $F \\sim$ 1 V/$\\AA$ results in emission of highly energetic XUV photons.

  18. Ag nanoparticles formed by femtosecond pulse laser ablation in water: self-assembled fractal structures

    Energy Technology Data Exchange (ETDEWEB)

    Santillán, Jesica M. J. [CONICET La Plata-CIC, Centro de Investigaciones Ópticas (CIOp) (Argentina); Fernández van Raap, Marcela B., E-mail: raap@fisica.unlp.edu.ar; Mendoza Zélis, Pedro; Coral, Diego [CONICET, Instituto de Física La Plata (IFLP) (Argentina); Muraca, Diego [Universidade Estadual de Campinas, Instituto de Física “Gleb Wataghin” (IFGW) (Brazil); Schinca, Daniel C.; Scaffardi, Lucía B., E-mail: lucias@ciop.unlp.edu.ar [CONICET La Plata-CIC, Centro de Investigaciones Ópticas (CIOp) (Argentina)

    2015-02-15

    We report for the first time on the formation of self-assembled fractals of spherical Ag nanoparticles (Nps) fabricated by femtosecond pulse laser ablation of a solid silver target in water. Fractal structures grew both in two and three Euclidean dimensions (d). Ramified-fractal assemblies of 2 nm height and 5–14 μm large, decorated with Ag Nps of 3 nm size, were obtained in a 2d geometry when highly diluted drops of colloidal suspension were dried at a fast heating rate over a mica substrate. When less-diluted drops were dried at slow heating rate, isolated single Nps or rosette-like structures were formed. Fractal aggregates about 31 nm size in 3d geometry were observed in the as-prepared colloidal suspension. Electron diffraction and optical extinction spectroscopy (OES) analyses performed on the samples confirmed the presence of Ag and Ag{sub 2}O. The analysis of the optical extinction spectrum, using the electrostatic approximation of Mie theory for small spheres, showed the existence of Ag bare core, Ag–Ag{sub 2}O and air–Ag core–shell Nps, Ag–Ag{sub 2}O being the most frequent type [69 % relative abundance (r.a.)]. Core-size and shell-thickness distribution was derived from OES. In situ scattering measurements of the Ag colloidal suspension, carried out by small-angle X-ray scattering, indicate a mass fractal composed of packaged 〈D{sub SAXS}〉 = (5 ± 1) nm particles and fractal dimension d{sub f} = 2.5. Ex situ atomic force microscopy imaging displayed well-ramified structures, which, analyzed with box-counting method, yield a fractal dimension d{sub f} = 1.67. The growing behavior of these 2d and 3d self-assembled fractals is consistent with the diffusion-limited aggregation model.

  19. Investigation of all-in-fiber Yb doped femtosecond fiber oscillator for generation of parabolic pulses in normal dispersion fiber amplifier

    Science.gov (United States)

    Frankinas, S.; Bartulevicius, T.; Michailovas, A.; Rusteika, N.

    2017-07-01

    In this work femtosecond passively mode-locked environmentally stable Ytterbium fiber oscillator generating pulses with duration of 380 fs is presented. Short pulse duration and smooth spectrum were obtained from the oscillator using chirped fiber Bragg grating with very low anomalous chromatic dispersion (0.15 ps2) and semiconductor saturable absorber mirror. Linearly chirped parabolic pulses were produced after amplification of the oscillator pulses in low concentration ytterbium doped fiber amplifier. Transform limited duration of the generated parabolic pulses was 110 fs.

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

    DEFF Research Database (Denmark)

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

    2011-01-01

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

  1. Generation of spherical and cylindrical shock acoustic waves from optical breakdown in water, stimulated with femtosecond pulse

    CERN Document Server

    Potemkin, F V; Podshivalov, A A; Gordienko, V M

    2014-01-01

    Using shadow photography technique we have observed shock acoustic wave from optical breakdown, excited in water by tightly focused Cr:Forsterite femtosecond laser beam, and have found two different regimes of shock wave generation by varying only the energy of laser pulse. At low energies a single spherical shock wave is generated from laser beam waist, and its radius tends to saturation with energy increasing. At higher energies long laser filament in water is fired, that leads to the cylindrical shock wave generation, which longitude increases logarithmically with laser pulse energy. From shadow pictures we estimated maximal velocity in front or shock wave of 2300+/-150m/s and pressure of 1.0+/-0.1 GPa

  2. Ti : sapphire laser synchronised with femtosecond Yb pump laser via nonlinear pulse coupling in Ti : sapphire active medium

    Science.gov (United States)

    Didenko, N. V.; Konyashchenko, A. V.; Konyashchenko, D. A.; Kostryukov, P. V.; Kuritsyn, I. I.; Lutsenko, A. P.; Mavritskiy, A. O.

    2017-02-01

    A laser system utilising the method of synchronous pumping of a Ti : sapphire laser by a high-power femtosecond Yb3+-doped laser is described. The pulse repetition rate of the Ti : sapphire laser is successfully locked to the repetition rate of the Yb laser for more than 6 hours without the use of any additional electronics. The measured timing jitter is shown to be less than 1 fs. A simple qualitative model addressing the synchronisation mechanism utilising the cross-phase modulation of oscillation and pump pulses within a Ti : sapphire active medium is proposed. Output parameters of the Ti : sapphire laser as functions of its cavity length are discussed in terms of this model.

  3. Widely Tunable Femtosecond Soliton Pulse Generation by Using Soliton-Frequency Shift in a Photonic Crystal Fibre

    Institute of Scientific and Technical Information of China (English)

    CHENG Chun-Fu; WANG Xiao-Fang; SHEN Bai-Fei

    2004-01-01

    Femtosecond Raman solitoh generation, tunable from 800 to 1044nm, has been theoretically investigated for a photonic crystal fibre pumped by a 200-rs pulse. A highly nonlinear photonic crystal fibre with a length of only 57.7cm and a nonlinear coefficient of 0.075 (Wm)-1 is used to achieved such a broadband. It is found that the spectral bandwidth increases with the input peak power. In particular, it is also found that the output wavelengths of the resulting sub-40 fs Raman solitons can also be tuned effectively by varying the initial pulse chirp. There exists an optimal positive chirp which maximizes the bandwidth, corresponding to the formation of only one long-wavelength Raman soliton.

  4. Imaging the ultrafast Kerr effect, free carrier generation, relaxation and ablation dynamics of Lithium Niobate irradiated with femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Lechuga, Mario, E-mail: mario@io.cfmac.csic.es; Siegel, Jan, E-mail: j.siegel@io.cfmac.csic.es; Hernandez-Rueda, Javier; Solis, Javier [Laser Processing Group, Instituto de Optica, CSIC, Serrano 121, 28006 Madrid (Spain)

    2014-09-21

    The interaction of high-power single 130 femtosecond (fs) laser pulses with the surface of Lithium Niobate is experimentally investigated in this work. The use of fs-resolution time-resolved microscopy allows us to separately observe the instantaneous optical Kerr effect induced by the pulse and the generation of a free electron plasma. The maximum electron density is reached 550 fs after the peak of the Kerr effect, confirming the presence of a delayed carrier generation mechanism. We have also observed the appearance of transient Newton rings during the ablation process, related to optical interference of the probe beam reflected at the front and back surface of the ablating layer. Finally, we have analyzed the dynamics of the photorefractive effect on a much longer time scale by measuring the evolution of the transmittance of the irradiated area for different fluences below the ablation threshold.

  5. Numerical Simulation and Analysis on 3D Temperature Field of the Metal Ablated with Femtosecond Pulse Laser

    Energy Technology Data Exchange (ETDEWEB)

    Yang Li; Yang Wei [Science College, Civil Aviation University of China, Tianjin 300300 (China); Wang Chingyue, E-mail: y_lyang@yahoo.com.cn [Key Laboratory of Opto-electronic Information Science and Technology, Ministry of Education, Tianjin University, Tianjin 300072 (China)

    2011-02-01

    To describe femtosecond laser ablation on the metal, numerical simulation on the basis of the double-temperature equation for three-dimension temperature field of the copper ablated with femtosecond pulse laser was performed by finite-difference method. Based on imbalance of the electronic and lattice's temperatures, the calefactive process of the electron and the lattice was obtained, respectively. The dependence of the electron-lattice coupling time on irradiated laser fluence was studied. The ablation depth and the ablation radius of the copper for single pulse fluence were calculated. The dependence of the start ablation (phase explosion arises) time of the copper on irradiated laser fluence was studied. The results indicate that the material jet due to phase explosion is earlier and the duration of ablation is longer with the increase of the laser fluence. When the laser fluence is higher than 1.5 J/cm{sup 2} the ablation start time is about 2-3 ps.

  6. Real-space observation of molecular motion induced by femtosecond laser pulses.

    Science.gov (United States)

    Bartels, Ludwig; Wang, Feng; Möller, Dietmar; Knoesel, Ernst; Heinz, Tony F

    2004-07-30

    Femtosecond laser irradiation is used to excite adsorbed CO molecules on a Cu110 surface; the ensuing motion of individual molecules across the surface is characterized on a site-to-site basis by in situ scanning tunneling microscopy. Adsorbate motion both along and perpendicular to the rows of the Cu110 surface occurs readily, in marked contrast to the behavior seen for equilibrium diffusion processes. The experimental findings for the probability and direction of the molecular motion can be understood as a manifestation of strong coupling between the adsorbates' lateral degrees of freedom and the substrate electronic excitation produced by the femtosecond laser radiation.

  7. Crystallization of Ge2Sb2Te5 thin films by nano- and femtosecond single laser pulse irradiation

    Science.gov (United States)

    Sun, Xinxing; Ehrhardt, Martin; Lotnyk, Andriy; Lorenz, Pierre; Thelander, Erik; Gerlach, Jürgen W.; Smausz, Tomi; Decker, Ulrich; Rauschenbach, Bernd

    2016-01-01

    The amorphous to crystalline phase transformation of Ge2Sb2Te5 (GST) films by UV nanosecond (ns) and femtosecond (fs) single laser pulse irradiation at the same wavelength is compared. Detailed structural information about the phase transformation is collected by x-ray diffraction and high resolution transmission electron microscopy (TEM). The threshold fluences to induce crystallization are determined for both pulse lengths. A large difference between ns and fs pulse irradiation was found regarding the grain size distribution and morphology of the crystallized films. For fs single pulse irradiated GST thin films, columnar grains with a diameter of 20 to 60 nm were obtained as evidenced by cross-sectional TEM analysis. The local atomic arrangement was investigated by high-resolution Cs-corrected scanning TEM. Neither tetrahedral nor off-octahedral positions of Ge-atoms could be observed in the largely defect-free grains. A high optical reflectivity contrast (~25%) between amorphous and completely crystallized GST films was achieved by fs laser irradiation induced at fluences between 13 and 16 mJ/cm2 and by ns laser irradiation induced at fluences between 67 and 130 mJ/cm2. Finally, the fluence dependent increase of the reflectivity is discussed in terms of each photon involved into the crystallization process for ns and fs pulses, respectively. PMID:27292819

  8. Extended-area nanostructuring of TiO2 with femtosecond laser pulses at 400 nm using a line focus.

    Science.gov (United States)

    Das, Susanta Kumar; Dasari, Kiran; Rosenfeld, Arkadi; Grunwald, Ruediger

    2010-04-16

    An efficient way to generate nanoscale laser-induced periodic surface structures (LIPSS) in rutile-type TiO(2) with frequency-converted femtosecond laser pulses at wavelengths around 400 nm is reported. Extended-area structuring on fixed and moving substrates was obtained by exploiting the line focus of a cylindrical lens. Under defined conditions with respect to pulse number, pulse energy and scanning velocity, two types of ripple-like LIPSS with high and low spatial frequencies (HSFL, LSFL) with periods in the range of 90 nm and 340 nm, respectively, were formed. In particular, lower numbers of high energetic pulses favour the generation of LSFL whereas higher numbers of lower energetic pulses enable the preferential creation of HSFL. Theoretical calculations on the basis of the Drude model support the assumption that refractive index changes by photo-excited carriers are a major mechanism responsible for LSFL. Furthermore, the appearance of random substructures as small as 30 nm superimposing low spatial frequency ripples is demonstrated and their possible origin is discussed.

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

    Science.gov (United States)

    Chen, Junbao; Xia, Wei; Wang, Ming

    2017-06-01

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

  10. Generation and Amplification of Tunable Multicolored Femtosecond Laser Pulses by Using Cascaded Four-Wave Mixing in Transparent Bulk Media

    Science.gov (United States)

    Liu, Jun; Kobayashi, Takayoshi

    2010-01-01

    We have reviewed the generation and amplification of wavelength-tunable multicolored femtosecond laser pulses using cascaded four-wave mixing (CFWM) in transparent bulk media, mainly concentrating on our recent work. Theoretical analysis and calculations based on the phase-matching condition could explain well the process semi-quantitatively. The experimental studies showed: (1) as many as fifteen spectral up-shifted and two spectral down-shifted sidebands were obtained simultaneously with spectral bandwidth broader than 1.8 octaves from near ultraviolet (360 nm) to near infrared (1.2 μm); (2) the obtained sidebands were spatially separated well and had extremely high beam quality with M2 factor better than 1.1; (3) the wavelengths of the generated multicolor sidebands could be conveniently tuned by changing the crossing angle or simply replacing with different media; (4) as short as 15-fs negatively chirped or nearly transform limited 20-fs multicolored femtosecond pulses were obtained when one of the two input beams was negatively chirped and the other was positively chirped; (5) the pulse energy of the sideband can reach a μJ level with power stability better than 1% RMS; (6) broadband two-dimensional (2-D) multicolored arrays with more than ten periodic columns and more than ten rows were generated in a sapphire plate; (7) the obtained sidebands could be simultaneously spectra broadened and power amplified in another bulk medium by using cross-phase modulation (XPM) in conjunction with four-wave optical parametric amplification (FOPA). The characterization showed that this is interesting and the CFWM sidebands generated by this novel method have good enough qualities in terms of power stability, beam quality, and temporal features suited to various experiments such as ultrafast multicolor time-resolved spectroscopy and multicolor-excitation nonlinear microscopy. PMID:22399882

  11. Generation and Amplification of Tunable Multicolored Femtosecond Laser Pulses by Using Cascaded Four-Wave Mixing in Transparent Bulk Media

    Directory of Open Access Journals (Sweden)

    Jun Liu

    2010-04-01

    Full Text Available We have reviewed the generation and amplification of wavelength-tunable multicolored femtosecond laser pulses using cascaded four-wave mixing (CFWM in transparent bulk media, mainly concentrating on our recent work. Theoretical analysis and calculations based on the phase-matching condition could explain well the process semi-quantitatively. The experimental studies showed: (1 as many as fifteen spectral up-shifted and two spectral down-shifted sidebands were obtained simultaneously with spectral bandwidth broader than 1.8 octaves from near ultraviolet (360 nm to near infrared (1.2 μm; (2 the obtained sidebands were spatially separated well and had extremely high beam quality with M2 factor better than 1.1; (3 the wavelengths of the generated multicolor sidebands could be conveniently tuned by changing the crossing angle or simply replacing with different media; (4 as short as 15-fs negatively chirped or nearly transform limited 20-fs multicolored femtosecond pulses were obtained when one of the two input beams was negatively chirped and the other was positively chirped; (5 the pulse energy of the sideband can reach a μJ level with power stability better than 1% RMS; (6 broadband two-dimensional (2-D multicolored arrays with more than ten periodic columns and more than ten rows were generated in a sapphire plate; (7 the obtained sidebands could be simultaneously spectra broadened and power amplified in another bulk medium by using cross-phase modulation (XPM in conjunction with four-wave optical parametric amplification (FOPA. The characterization showed that this is interesting and the CFWM sidebands generated by this novel method have good enough qualities in terms of power stability, beam quality, and temporal features suited to various experiments such as ultrafast multicolor time-resolved spectroscopy and multicolor-excitation nonlinear microscopy.

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

    CERN Document Server

    Kuchmizhak, A A; Vitrik, O B; Kulchin, Yu N

    2015-01-01

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

  13. Autocorrelation measurement of femtosecond laser pulses based on two-photon absorption in GaP photodiode

    Energy Technology Data Exchange (ETDEWEB)

    Chong, E. Z.; Watson, T. F.; Festy, F., E-mail: frederic.festy@kcl.ac.uk [Biomaterials, Biomimetics and Biophotonics Division, King' s College London—Dental Institute, SE1 9RT London (United Kingdom)

    2014-08-11

    Semiconductor materials which exhibit two-photon absorption characteristic within a spectral region of interest can be useful in building an ultra-compact interferometric autocorrelator. In this paper, we report on the evidence of a nonlinear absorption process in GaP photodiodes which was exploited to measure the temporal profile of femtosecond Ti:sapphire laser pulses with a tunable peak wavelength above 680 nm. The two-photon mediated conductivity measurements were performed at an average laser power of less than a few tenths of milliwatts. Its suitability as a single detector in a broadband autocorrelator setup was assessed by investigating the nonlinear spectral sensitivity bandwidth of a GaP photodiode. The highly favourable nonlinear response was found to cover the entire tuning range of our Ti:sapphire laser and can potentially be extended to wavelengths below 680 nm. We also demonstrated the flexibility of GaP in determining the optimum compensation value of the group delay dispersion required to restore the positively chirped pulses inherent in our experimental optical system to the shortest pulse width possible. With the rise in the popularity of nonlinear microscopy, the broad two-photon response of GaP and the simplicity of this technique can provide an alternative way of measuring the excitation laser pulse duration at the focal point of any microscopy systems.

  14. Calcium-mediated paired pulse depression in juvenile rat dorsal striatum

    Institute of Scientific and Technical Information of China (English)

    Yufeng Xie; Michael F. Jackson; John F. MacDonald

    2012-01-01

    As the major division of the basal ganglia, neostriatum forms mutual connections with multiple brain areas and is critically involved in motor control and learning/memory. Long-term synaptic plasticity has been widely studied in different species recently. However, there are rare reports about the short-term synaptic plasticity in neostratium. In the present study, using field excitatory postsynaptic potentials recording, we reported one form of short-term synaptic plasticity that is paired pulse de-pression in juvenile rat dorsal striatum slices induced by stimuli of the white matter. The field exci-tatory postsynaptic potentials could be abolished by α-amino-3-hydroxy-5-methylizoxazole-4- propionic acid receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, but not by gamma-aminobutyric acid type A receptor antagonist bicuculline or dopamine D1 receptor antago-nist SKF-81297. The paired pulse depression in the corticostratial pathway was different from paired pulse facilitation in the hippocampal CA1 synapse. In addition, the paired pulse depression was not affected by bath application of gamma-aminobutyric acid type A receptor antagonist or dopamine D1 receptor antagonist. However, low calcium and high magnesium could attenuate the paired pulse depression. These findings suggest a more complicated plasticity form in the dorsal striatum of juvenile rats that is different from that in the hippocampus, which is related with extracellular calcium.

  15. Theoretical Description of the Third Order Parametric Wave Mixing in a Gas-Filled Capillary of Femto-Second Laser Pulse

    Institute of Scientific and Technical Information of China (English)

    CHEN Bao-Zhen; HUANG Zu-Qia

    2004-01-01

    The theoretical signal-pressure curves are calculated from approximate analytical solutions of the coupledequations describing the third order parametric wave mixing in a gas-filled capillary of femto-second laser pulses. Thecomparison with the corresponding experimental curves suggests that the following three factors exert important influ-ences on the degree of fitting between the theoretical and experimental results: the walk-off, the phase modulation, andthe third order harmonic of idler pulse.

  16. Liquid assisted ablation of zirconium for the growth of LIPSS at varying pulse durations and pulse energies by femtosecond laser irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Bashir, Shazia [Institute of Applied Physics, Vienna University of Technology, Vienna (Austria); Centre for Advanced Studies in Physics, GC University Lahore (Pakistan); Rafique, M. Shahid [Institute of Applied Physics, Vienna University of Technology, Vienna (Austria); Department of Physics, University of Engineering and Technology Lahore (Pakistan); Husinsky, Wolfgang [Institute of Applied Physics, Vienna University of Technology, Vienna (Austria)

    2015-04-15

    Highlights: •Femtosecond laser ablation of Zr has been investigated. •The ablation was performed in ethanol environment. •The surface morphology of irradiated targets was explored by SEM analysis. •The compositional modification was performed by Raman spectroscopy. •The effect of pulse duration as well as pulse energy was revealed. -- Abstract: Investigations have been performed to explore the optimized conditions for the growth of Laser Induced Periodic Surface Structures (LIPSS) by varying pulse durations and pulse energies during ultrashort pulsed laser ablation of zirconium (Zr). The Ti: Sapphire laser with central wavelength of 800 nm, maximum pulse energy of 1 mJ is used to ablate Zr targets in the wet environment of ethanol. Scanning Electron Microscope (SEM) analysis was performed for central as well as the peripheral ablated area to characterize nano and microstructures formed on the Zr surface. Raman spectroscopy was carried out to explore the chemical and compositional changes produced in laser ablated Zr. In order to explore the effect of varying pulse durations ranging from 25 to 100 fs, targets were exposed to 1000 succeeding pulses keeping the pulse energy constant at 600 μJ. The micrographs of peripheral ablated areas reveal the formation of nano scale ripples or Laser Induced Periodic Surface Structures (LIPSS) for all pulse durations. LIPSS are more distinct and well organized for the shortest pulse duration of 25 fs. Whereas, LIPSS become diffused and indistinct with the increase in the pulse duration. This is the clear indication that shortest pulse duration (in our case 25 fs) is most suitable for the growth of nanoscale ripples. In order to explore the effect of varying pulse energies on the growth of LIPSS, targets were exposed to 1000 succeeding pulses with energies ranging from 200 μJ to 600 μJ for a pulse duration of 25 fs. In the peripheral ablated areas LIPSS are grown for all pulse energies. For the lowest pulse energy of

  17. Three-wave mixing mediated femtosecond pulse compression in β-barium borate.

    Science.gov (United States)

    Grün, A; Austin, Dane R; Cousin, Seth L; Biegert, J

    2015-10-15

    Nonlinear pulse compression mediated by three-wave mixing is demonstrated for ultrashort Ti:sapphire pulses in a type II phase-matched β-barium borate (BBO) crystal using noncollinear geometry. 170 μJ pulses at 800 nm with a pulse duration of 74 fs are compressed at their sum frequency to 32 fs with 55 μJ of pulse energy. Experiments and computer simulations demonstrate the potential of sum-frequency pulse compression to match the group velocities of the interacting waves to crystals that were initially not considered in the context of nonlinear pulse compression.

  18. Efficient broadband 400  nm noncollinear second-harmonic generation of chirped femtosecond laser pulses in BBO and LBO.

    Science.gov (United States)

    Gobert, O; Mennerat, G; Maksimenka, R; Fedorov, N; Perdrix, M; Guillaumet, D; Ramond, C; Habib, J; Prigent, C; Vernhet, D; Oksenhendler, T; Comte, M

    2014-04-20

    We report on 400 nm broadband type I frequency doubling in a noncollinear geometry with pulse-front-tilted and chirped femtosecond pulses (λ =800  nm; Fourier transform limited pulse duration, 45 fs). With moderate power densities (2 to 10  GW/cm2) thus avoiding higher-order nonlinear phenomena, the energy conversion efficiency was up to 65%. Second-harmonic pulses of Fourier transform limited pulse duration shorter than the fundamental wave were generated, exhibiting good beam quality and no pulse-front tilt. High energy (20 mJ/pulse) was produced in a 40 mm diameter and 6 mm thick LBO crystal. To the best of our knowledge, this is the first demonstration of this optical configuration with sub-100-fs pulses. Good agreement between experimental results and simulations is obtained.

  19. Direct-writing of PbS nanoparticles inside transparent porous silica monoliths using pulsed femtosecond laser irradiation

    Science.gov (United States)

    Chahadih, Abdallah; El Hamzaoui, Hicham; Bernard, Rémy; Boussekey, Luc; Bois, Laurence; Cristini, Odile; Le Parquier, Marc; Capoen, Bruno; Bouazaoui, Mohamed

    2011-10-01

    Pulsed femtosecond laser irradiation at low repetition rate, without any annealing, has been used to localize the growth of PbS nanoparticles, for the first time, inside a transparent porous silica matrix prepared by a sol-gel route. Before the irradiation, the porous silica host has been soaked within a solution containing PbS precursors. The effect of the incident laser power on the particle size was studied. X-ray diffraction was used to identify the PbS crystallites inside the irradiated areas and to estimate the average particle size. The localized laser irradiation led to PbS crystallite size ranging between 4 and 8 nm, depending on the incident femtosecond laser power. The optical properties of the obtained PbS-silica nanocomposites have been investigated using absorption and photoluminescence spectroscopies. Finally, the stability of PbS nanoparticles embedded inside the host matrices has been followed as a function of time, and it has been shown that this stability depends on the nanoparticle mean size.

  20. Multiphoton absorption is probably not the primary threshold damage mechanism for femtosecond laser pulse exposures in the retinal pigment epithelium

    Science.gov (United States)

    Glickman, Randolph D.; Johnson, Thomas E.

    2004-07-01

    Laser induced breakdown has the lowest energy threshold in the femtosecond domain, and is responsible for production of threshold ocular lesions. It has been proposed that multiphoton absorption may also contribute to ultrashort-pulse tissue damage, based on the observation that 33 fs, 810 nm pulse laser exposures caused more DNA breakage in cultured, primary RPE cells, compared to CW laser exposures delivering the same average power. Subsequent studies, demonstrating two-photon excitation of fluorescence in isolated RPE melanosomes, appeared to support the role of multiphoton absorption, but mainly at suprathreshold irradiance. Additional experiments have not found a consistent difference in the DNA strand breakage produced by ultrashort and CW threshold exposures. DNA damage appears to be dependent on the amount of melanin pigmentation in the cells, rather than the pulsewidth of the laser; current studies have found that, at threshold, CW and ultrashort pulse laser exposures produce almost identical amounts of DNA breakage. A theoretical analysis suggest that the number of photons delivered to the RPE melanosome during a single 33-fsec pulse at the ED50 irradiance is insufficient to produce multiphoton excitation. This result appears to exclude the melanosome as a locus for two- or three-photon excitation; however, a structure with a larger effective absorption cross-section than the melanosome may interact with the laser pulses. One possibility is that the nuclear chromatin acts as a unit absorber of photons resulting in DNA damage, but this does not explain the near equivalence of ultrashort and CW exposures in the comet assay model. This equivalence indicated that multiphoton absorption is not a major contributor to the ultrashort pulse laser damage threshold in the near infrared.

  1. Broadband directional couplers fabricated in bulk glass with high repetition rate femtosecond laser pulses.

    Science.gov (United States)

    Chen, Wei-Jen; Eaton, Shane M; Zhang, Haibin; Herman, Peter R

    2008-07-21

    A femtosecond fiber laser was applied to fabricate broadband directional couplers inside bulk glass for general power splitting application in the 1250 to 1650-nm wavelength telecom spectrum. The broadband response was optimized over the 400-nm bandwidth by tailoring the coupling strength and the waveguide interaction length to balance the differing wavelength dependence of the straight interaction and bent transition regions. High spatial finesse of the femtosecond-laser writing technique enabled close placement (approxiamtely 6 microm) of adjacent waveguides that underpinned the wavelength-flattened broadband response at any coupling ratio in the 0% to 100% range. The spectral responses were well-represented by coupled mode theory, permitting simple design and implementation of broadband couplers for bulk 3D optical circuit integration.

  2. Preparation of porous microstructures on NiTi alloy surface with femtosecond laser pulses

    Institute of Scientific and Technical Information of China (English)

    LIANG ChunYong; YANG Yang; WANG HongShui; YANG JianJun; YANG XianJin

    2008-01-01

    Porous microstructures on Nickel-Titanium (NiTi) alloy surfaces were prepared by linearly polarized femtosecond lasers with moving focal point at a certain speed. It was found that various novel micro-structures from feather-like ripples to cluster-like porous textures could be formed with increasing laser energy. Particularly, when the laser energy was 400 μJ, a periodic porous metal surface was gen-erated. Measurement of X-ray diffraction showed that the grains on the sample surface were refined through femtosecond laser ablation processes, but the crystal structures still kept their original states. Analysis by X-ray photoelectron spectroscopy revealed that Ni/Ti on the sample surface was changed with an evident oxidization of titanium element under different laser energies. This investigation pro-vides a new approach to improve the biocompatibility of NiTi-based implant devices.

  3. Paired pulse TMS stimulation and human tongue corticomotor pathways

    DEFF Research Database (Denmark)

    Kothari, Mohit; Svensson, Peter; Nielsen, Jørgen Feldbæk;

    (CS) and the test stimulus (TS). The aim of the present methodological study was to optimize stimulus parameters for ppTMS studies of tongue motor control by examining the influence of different ISI and intensities of the CS on SICI and ICF. Methods: 17 healthy volunteers participated (mean age: 22.......6±0.8 years). ppTMS was applied to the “hot-spot” of the tongue motor cortex and motor evoked potential (MEPs) were recorded from the tongue muscles with surface EMG electrodes. TS intensity was set at 120% of resting motor threshold (rMT). Single pulse and six different ISIs for ppTMS: 2, 2.5, 3, 3.5, 10, 15...... different intensities of CS and ISIs. Conclusion: Significant SICI but no ICF was evoked with the present stimulus paradigms. The two stimulus intensities of the CS evoked similar responses. These results may be applied in future studies on the effect of tongue training on SICI and ICF in the tongue motor...

  4. Surface and structural modifications of titanium induced by various pulse energies of a femtosecond laser in liquid and dry environment

    Science.gov (United States)

    Bashir, Shazia; Rafique, M. Shahid; Nathala, Chandra Sekher; Husinsky, Wolfgang

    2014-01-01

    The surface and structural modification of titanium (Ti) has been explored after the interaction of ultrashort laser pulses with the surface target. The targets were exposed by femtosecond Ti: Sapphire laser pulses in liquid (ethanol) and dry (air) environment. In order to explore the effect of pulse energy, the targets were exposed to 1,000 succeeding pulses for various pulse energies ranging from 200 to 500 μJ for pulse duration of 25 fs. SEM analyses were performed for central as well as the peripheral ablated areas of the target. It was found that in the case of ethanol (both for central and peripheral ablated areas) there is a grain growth along with nanoscale pores and dots when the target was irradiated for 200 μJ. For intermediate energies (300-400 μJ), grains of 1-2 μm with distinct boundaries are formed in the central ablated area. Whereas in the peripheral ablated area, laser-induced periodic surface structures (LIPSS) and globules are grown. For the highest pulse energy (500 μJ), distinct grains are observed for both regions. However, in the peripheral area the grains are of bigger size with cracks along the boundaries. In case of ablation in air, in the center of ablated areas, island-like structures with multiple ablative layer or LIPSS and nanoscale spheres are observed both for lower and intermediate pulse energies. For the highest pulse energy only nanoscale LIPSS could be observed. For ablation in air at the peripheral areas, well-defined, laser-induced periodic surface structures are observed for all pulse energies. Raman spectroscopy reveals that the liquid (ethanol) environment forms the carbonyl compounds with the metal and induces C-C stretching vibration, whereas in case of air, hydroxo complexes are formed. It has been found that surface treatment of Ti with ultrashort (25 fs) laser radiation in ethanol environment allows the growth of particular surface structures in the form of grains and simultaneously induces changes in its

  5. High spatial frequency laser induced periodic surface structure formation in germanium by mid-IR femtosecond pulses

    CERN Document Server

    Austin, Drake R; Lai, Yu Hang; Wang, Zhou; Zhang, Kaikai; Li, Hui; Blaga, Cosmin I; Yi, Allen Y; DiMauro, Louis F; Chowdhury, Enam A

    2016-01-01

    Formation of high spatial frequency laser induced periodic surface structures (HSFL) in germanium by femtosecond mid-IR pulses with wavelengths between $\\lambda=2.0$ and $3.6 \\; \\mathrm{\\mu m}$ was studied with varying angle of incidence and polarization. The period of these structures varied from $\\lambda/3$ to $\\lambda/8$. A modified surface-scattering model including Drude excitation and the optical Kerr effect explains spatial period scaling of HSFL across the mid-IR wavelengths. Transmission electron microscopy (TEM) shows the presence of a $30 \\; \\mathrm{n m}$ amorphous layer above the structure of crystalline germanium. Various mechanisms including two photon absorption and defect-induced amorphization are discussed as probable causes for the formation of this layer.

  6. Specific features of direct formation of graphite-like microstructures in polycarbonate samples by single femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Ganin, D V; Lapshin, K E; Obidin, A Z; Vartapetov, S K [Physics Instrumentation Center, A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Troitsk, Moscow Region (Russian Federation)

    2015-11-30

    We present the result of the experiments on producing graphite-like cylindrical microstructures by focusing single femtosecond laser pulses into the bulk of a transparent polymer (polycarbonate). The microstructures are embedded in a cladding with a modified refractive index, possessing waveguide properties. In the experiments with nontransparent screens and diaphragms, placed in the laser beam in front of the entrance pupil of the objective with a large numerical aperture, we have found that the paraxial rays are blocked by the peripheral ones, which reduces the length of the destruction region in the pre-focal zone. In the experiments with transparent screens and diaphragms, introducing optical delays τ{sub d} between the paraxial and peripheral rays, the quantitative dependence of the destruction region length in the pre-focal zone on the value of τ{sub d} is determined. (interaction of laser radiation with matter. laser plasma)

  7. Direct detection of delayed high energy electrons from the 181Ta target irradiated by a moderate intensity femtosecond laser pulse

    Science.gov (United States)

    Savel’ev, A.; Chefonov, O.; Ovchinnikov, A.; Agranat, M.; Spohr, K. M.

    2017-03-01

    We depict an experimental study of delayed fast, negatively charged particles from femtosecond laser-plasma interaction at an intensity of I ∼ 1017 W cm‑2. Plates of 2 mm thickness made of 181Ta (∼100% abundance) and natural W were used as targets. We distinguished certain delayed events due to detection of negative H‑, C‑ and O‑ ions. However, most events which were delayed by 0.5–5 μs with respect to the instantaneous plasma formation caused by the laser pulses, were identified as electrons with energies of 3–7 keV. A comparative analysis between the tantalum and tungsten spectra was undertaken. This revealed a close similarity between the measured spectrum for tantalum and the predicted spectrum for electrons arising from to the internal conversion decay of the 6.237 keV nuclear isomeric state in 181Ta.

  8. High aspect ratio microstructuring of transparent dielectrics using femtosecond laser pulses: method for optimization of the machining throughput

    Science.gov (United States)

    Hendricks, F.; der Au, J. Aus; Matylitsky, V. V.

    2014-10-01

    High average power, high repetition rate femtosecond lasers with μJ pulse energies are increasingly used for material processing applications. The unique advantage of material processing with sub-picosecond lasers is efficient, fast and localized energy deposition, which leads to high ablation efficiency and accuracy in nearly all kinds of solid materials. This work focuses on the machining of high aspect ratio structures in transparent dielectrics, in particular chemically strengthened Xensation™ glass from Schott using multi-pass ablative material removal. For machining of high aspect ratio structures, among others needed for cutting applications, a novel method to determine the best relation between kerf width and number of overscans is presented. The importance of this relation for optimization of the machining throughput will be demonstrated.

  9. Highly efficient, widely tunable, 10-Hz parametric amplifier pumped by frequency-doubled femtosecond Ti:sapphire laser pulses.

    Science.gov (United States)

    Zhang, J Y; Xu, Z; Kong, Y; Yu, C; Wu, Y

    1998-05-20

    We report a 10-Hz, highly efficient, widely tunable (from the visible to the IR), broadband femtosecond optical parametric generator and optical parametric amplifier (OPA) in BBO, LBO, and CBO crystals pumped by the frequency-doubled output of a regeneratively amplified Ti:sapphire laser at 400 nm. The output of the system is continuously tunable from 440 nm to 2.5 microm with a maximum overall efficiency of approximately 25% at 670 nm and an optical conversion efficiency of more than 36% in the OPA stage. The effects of the seed beam energy, the type of the crystal and the crystal length, and the pumping energy of the output of the OPA, such as the optical efficiency, the bandwidth, the pulse duration, and the group velocity mismatch between the signal and the idler and between the seeder and the pump, are investigated. The results provide useful information for optimization of the design of the system.

  10. Broadband colored-crescent generation in a single {beta}-barium-borate crystal by intense femtosecond pulses

    Energy Technology Data Exchange (ETDEWEB)

    Wang, L.; Fan, Y. X.; Zhu, H.; Yan, Z. D.; Zhu, S. N.; Wang, Z. L. [Department of Physics and National Laboratory of Solid State Microstructures, Nanjing University, 210093 Nanjing (China); Zeng, H. [State Key Laboratory of Precision Spectroscopy, East China Normal University, 200062 Shanghai (China); Wang, H.-T. [Department of Physics and National Laboratory of Solid State Microstructures, Nanjing University, 210093 Nanjing (China); School of Physics, Nankai University, 300071 Tianjin (China)

    2011-12-15

    A visible colored crescent with a bandwidth broader than 220 nm is observed experimentally by loosely focused femtosecond pulses in a bulk quadratic nonlinear crystal ({beta}-BBO crystal) at certain incident angles. Through the analysis based on a simple collinear phase-matching model, we suggest that the colored crescent might be the coexistence of spontaneous parametric down-conversions (SPDCs) in the infrared range and the corresponding efficient second-order harmonic generations (SHGs) that occur in a wide spectrum. We further provide a possible mechanism for the SHG process in which the phase-mismatching angles of the frequency doubling of SPDCs in {beta}-BBO crystal are assumed to be compensated by the strong diffraction effect during the self-focusing process of the generated intense SPDC signals.

  11. Formation of femtosecond laser induced surface structures on silicon: Insights from numerical modeling and single pulse experiments

    Energy Technology Data Exchange (ETDEWEB)

    Derrien, T.J.-Y., E-mail: thibault.derrien@lp3.univ-mrs.fr [Lasers, Plasmas and Photonic Processes Laboratory (LP3), UMR 6182 CNRS - Universite de la Mediterranee, Parc Scientifique et Technologique de Luminy, 163 Avenue de luminy - C. 917, 13288 Marseille cedex 9 (France); Torres, R.; Sarnet, T.; Sentis, M. [Lasers, Plasmas and Photonic Processes Laboratory (LP3), UMR 6182 CNRS - Universite de la Mediterranee, Parc Scientifique et Technologique de Luminy, 163 Avenue de luminy - C. 917, 13288 Marseille cedex 9 (France); Itina, T.E. [Hubert Curien laboratory (LaHC), UMR 5516 CNRS - Universite Jean Monnet, Bat. F, 18 rue du Professeur Benoit Lauras, 42000, Saint Etienne (France)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer Theoretical conditions for exciting SPP in Si are verified. Black-Right-Pointing-Pointer SPP model explains why a seed is needed to produce single shot ripples. Black-Right-Pointing-Pointer Two regimes of ripples are identified and explained by numerical simulations. Black-Right-Pointing-Pointer The presented results have a strong correlation with experiments. - Abstract: Laser induced periodic surface structures (LIPSS) are formed by multiple irradiation of femtosecond laser on a silicon target. In this paper, we focus and discuss the surface plasmon polariton mechanism by an analysis of transient phase-matching conditions in Si on the basis of a single pulse experiment and numerical simulations. Two regimes of ripple formation mechanisms at low number of shots are identified and detailed. Correlation of numerical and experimental results is good.

  12. Multidiagnostic analysis of ultrafast laser ablation of metals with pulse pair

    OpenAIRE

    LUNNEY, JAMES

    2010-01-01

    PUBLISHED Copper targets are irradiated in the ablation regime by pairs of equal, time-delayed collinear laser pulses separated on a timescale going from 2 ps to 2 ns. The ablation plume is characterized by ion probe diagnostic, fast imaging, and temporally and spatially resolved optical emission spectroscopy. The variation in the ablation efficiency with the delay between the pulses is analyzed by measuring the ablation crater profile with a contact profilometer. The second ...

  13. Paired-pulse facilitation achieved in protonic/electronic hybrid indium gallium zinc oxide synaptic transistors

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Li Qiang, E-mail: guoliqiang@ujs.edu.cn; Ding, Jian Ning; Huang, Yu Kai [Micro/Nano Science & Technology Center, Jiangsu University, Zhenjiang, 212013 (China); Zhu, Li Qiang, E-mail: lqzhu@nimte.ac.cn [Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)

    2015-08-15

    Neuromorphic devices with paired pulse facilitation emulating that of biological synapses are the key to develop artificial neural networks. Here, phosphorus-doped nanogranular SiO{sub 2} electrolyte is used as gate dielectric for protonic/electronic hybrid indium gallium zinc oxide (IGZO) synaptic transistor. In such synaptic transistors, protons within the SiO{sub 2} electrolyte are deemed as neurotransmitters of biological synapses. Paired-pulse facilitation (PPF) behaviors for the analogous information were mimicked. The temperature dependent PPF behaviors were also investigated systematically. The results indicate that the protonic/electronic hybrid IGZO synaptic transistors would be promising candidates for inorganic synapses in artificial neural network applications.

  14. Development of high resolution Michelson interferometer for stable phase-locked ultrashort pulse pair generation.

    Science.gov (United States)

    Okada, Takumi; Komori, Kazuhiro; Goshima, Keishiro; Yamauchi, Shohgo; Morohashi, Isao; Sugaya, Takeyoshi; Ogura, Mutsuo; Tsurumachi, Noriaki

    2008-10-01

    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.

  15. First-principles simulations for excitation of currents in linear carbon chains under femtosecond laser pulse irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Su, Gaoshi [School of Mechatronical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Jiang, Lan, E-mail: jianglan@bit.edu.cn [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Wang, Feng [School of Physics, Beijing Institute of Technology, Beijing 100081 (China); Qu, Liangti [Key Laboratory of Cluster Science, Ministry of Education, School of Chemistry, Beijing Institute of Technology, Beijing 100081 (China); Lu, Yongfeng [Department of Electrical Engineering, University of Nebraska–Lincoln, Lincoln, NE 68588-0511 (United States)

    2016-07-15

    We discuss the response of linear carbon chains to a femtosecond laser pulse. The influence of the chain structure on the excited currents was taken into account. The simulation results showed that excited currents were reversible when laser intensity was relatively weak. An unexpected decrease of current amplitude was found for a laser pulse with a wavelength of 200 nm, which may indicate the transient break of pi bonds in linear carbon chains. For chains with more than 10 atoms, the excited current oscillated with increasing amplitude during simulation time, which was due to the formation of plasma-like resonance. - Highlights: • Excited currents is reversible when laser intensity was relatively weak. • A laser pulse with a wavelength of 200 nm can induce the transient break of pi bonds in linear carbon chains. • The excited current oscillate to form plasma-like resonance under laser field driving. • In the carbon chains with odd numbers, the uniform distribution of pi bonds created a “path” for electrons.

  16. Pair annihilation in laser pulses: Optical versus x-ray free-electron laser regimes

    OpenAIRE

    Ilderton, Anton; Johansson, Petter; Marklund, Mattias

    2011-01-01

    We discuss the theory and phenomenology of pair annihilation, within an ultra-short laser pulse, to a single photon. The signature of this process is the uni-directional emission of single photons with a fixed energy. We show that the cross section is significantly larger than for two-photon pair annihilation in vacuum, with XFEL parameters admitting a much clearer signal than optical beams.

  17. Spectral Compression of Intense Femtosecond Pulses by Self Phase Modulation in Silica Glass

    DEFF Research Database (Denmark)

    Iwaszczuk, Krzysztof; Zhou, Binbin; Bache, Morten

    2012-01-01

    We experimentally demonstrate spectral compression of mJ fs pulses by self phase modulation in silica glass. Spectral narrowing by factor 2.4 of near-transform-limited pulses is shown, with good agreement between experiment and numerical simulation.......We experimentally demonstrate spectral compression of mJ fs pulses by self phase modulation in silica glass. Spectral narrowing by factor 2.4 of near-transform-limited pulses is shown, with good agreement between experiment and numerical simulation....

  18. Time dependence of X-ray polarizability of a crystal induced by an intense femtosecond X-ray pulse

    Directory of Open Access Journals (Sweden)

    A. Leonov

    2014-11-01

    Full Text Available The time evolution of the electron density and the resulting time dependence of Fourier components of the X-ray polarizability of a crystal irradiated by highly intense femtosecond pulses of an X-ray free-electron laser (XFEL is investigated theoretically on the basis of rate equations for bound electrons and the Boltzmann equation for the kinetics of the unbound electron gas. The photoionization, Auger process, electron-impact ionization, electron–electron scattering and three-body recombination have been implemented in the system of rate equations. An algorithm for the numerical solution of the rate equations was simplified by incorporating analytical expressions for the cross sections of all the electron configurations in ions within the framework of the effective charge model. Using this approach, the time dependence of the inner shell populations during the time of XFEL pulse propagation through the crystal was evaluated for photon energies between 4 and 12 keV and a pulse width of 40 fs considering a flux of 1012 photons pulse−1 (focusing on a spot size of ∼1 µm. This flux corresponds to a fluence ranging between 0.8 and 2.4 mJ µm−2. The time evolution of the X-ray polarizability caused by the change of the atomic scattering factor during the pulse propagation is numerically analyzed for the case of a silicon crystal. The time-integrated polarizability drops dramatically if the fluence of the X-ray pulse exceeds 1.6 mJ µm−2.

  19. Electron-Positron Pair Production in Structured Pulses of Electric Fields

    CERN Document Server

    Kohlfürst, Christian

    2012-01-01

    The non-perturbative electron-positron pair production in time-dependent electric fields is investigated. The quantum kinetic formalism is employed in order to calculate the electron density for various field configurations. The corresponding set of first order, ordinary differential equations is analyzed and numerically solved. The focus of this study lies on the dynamically assisted Schwinger effect in pulsed electric fields with at least two different time scales. Furthermore, interference effects arising in setups with multiple pulses are examined and first results for an optimization of the particle number yield by pulse-shaping are given.

  20. Difference frequency generation of femtosecond mid infrared pulses employing intense Stokes pulses excitation in a photonic crystal fiber.

    Science.gov (United States)

    Yao, Yuhong; Knox, Wayne H

    2012-11-05

    We demonstrate a novel method of generating milli-watt level mid-IR (MIR) pulses based on difference frequency mixing of the output from a 40 MHz Yb fiber Chirped Pulse Amplifier (CPA) and the intense Stokes pulses generated in a photonic crystal fiber (PCF) with two closely spaced zero dispersion wavelengths (ZDW). By taking advantage of the unique dispersion profile of the fiber, high power narrowband Stokes pulses are selectively generated in the normal dispersion region of the PCF with up to 1.45 nJ of pulse energy. Mixing with 12 nJ of pump pulses at 1035 nm in a type-II AgGaS(2) crystal yields MIR pulses around 5.5 µm wavelength with up to 3 mW of average power and 75 pJ of pulse energy. The reported method can be extended to generation of other MIR wavelengths by selecting PCFs with different second ZDWs or engineering the fiber dispersion profile via longitudinal tapering.

  1. Group-delay Dispersion in Double-prism Pair and Limitation in Broadband Laser Pulses

    Institute of Scientific and Technical Information of China (English)

    程昭; 赵卫

    2002-01-01

    A general expression of group-delay dispersion is obtained without any approximation for a pair of double prisms with an arbitrary apex angle. This expression also includes the change of dispersion resulting from change in insertion of the prism material into the beam by translating prism-pairs. The high-order dispersion can be calculated by means of this expression. The limitation for generation of negative group-delay dispersion by use of prism-pairs is presented for ultrashort laser pulses with broadband spectrum.

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

    Science.gov (United States)

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

    2017-08-01

    A simple but new toxic chemical free method, Femtosecond Laser Ablation in Microfluidics (FLAM) was proposed for the first time. ZnSe quantum dots of 4-6 nm were synthesized and with the use of hyperbranched Polyethyleneimine (PEI) as both structural and functional coated layer. These aqueous nanosized micelles consisting of quantum dots exhibit deep defect states emission of bright green light centered at 500 nm. A possible mechanism for the enhanced board band emission was discussed. The properties of toxic matters free and enhanced photoluminescence without doped transition metal ions demonstrate an application potential for biomedical imaging.

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

    Science.gov (United States)

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

    2012-09-01

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

  4. Multi-meter fiber-delivery and pulse self-compression of milli-Joule femtosecond laser and fiber-aided laser-micromachining.

    Science.gov (United States)

    Debord, B; Alharbi, M; Vincetti, L; Husakou, A; Fourcade-Dutin, C; Hoenninger, C; Mottay, E; Gérôme, F; Benabid, F

    2014-05-01

    We report on damage-free fiber-guidance of milli-Joule energy-level and 600-femtosecond laser pulses into hypocycloid core-contour Kagome hollow-core photonic crystal fibers. Up to 10 meter-long fibers were used to successfully deliver Yb-laser pulses in robustly single-mode fashion. Different pulse propagation regimes were demonstrated by simply changing the fiber dispersion and gas. Self-compression to ~50 fs, and intensity-level nearing petawatt/cm(2) were achieved. Finally, free focusing-optics laser-micromachining was also demonstrated on different materials.

  5. Finite pulse effects on $e^{+}e^{-}$ pair creation from strong electric fields

    CERN Document Server

    Taya, Hidetoshi; Itakura, Kazunori

    2014-01-01

    We investigate electron-positron pair creation from the vacuum in a pulsed electric background field. Employing the Sauter-type pulsed field $E(t) = E_0 {\\rm sech}^2(t/\\tau)$ with height $E_0$ and width $\\tau$, we demonstrate explicitly the interplay between the non-perturbative and perturbative aspects of the pair creation in the background field. In the constant field limit (the long pulse limit), Schwinger's non-perturbative formula is reproduced, while in the short pulse limit the leading-order perturbative treatment is justified. We show that two dimensionless parameters $eE_0 \\tau^2$ and $eE_0 \\tau /m_e$ characterize the importance of multiple interactions with the fields and the transition from the perturbative to the non-perturbative regime. We also reveal that pair creation is enhanced compared to Schwinger's formula when the field strength is relativity weak $|eE_0|/m_e^2 \\lesssim 1$ and the pulse duration is relatively short $m\\tau \\lesssim 1$ and that the enhancement is predominantly described by ...

  6. Optimized Second Harmonic Generation of Femtosecond Pulse by Phase-Blanking Effect in Aperiodically Optical Superlattice

    Institute of Scientific and Technical Information of China (English)

    KONG Yan; CHEN Xian-Feng; XIA Yu-Xing

    2008-01-01

    @@ In order to minimize the effect of the unconsidered frequency components on the generated compression pulse,the phasing-blanking effect is taken into account of designing the one-dimensional aperiodic domain reversal structure. Hierarchic genetic algorithm for the design of a domain reversal grating to modulate the spectrum and phase of the generated SH pulse simultaneously are presented. Our simulation shows that the quality of an output pulse is fairly improved.

  7. Fluorescence Enhancement Ratio Dropdown at Low Fluences during Femtosecond Double Pulse Laser Ablation

    Institute of Scientific and Technical Information of China (English)

    Sima SINGHA; Robert J. GORDON; HU Zhan

    2008-01-01

    In the study of double pulse ablation of materials (silicon and copper), a dropdown of double pulse to single pulse fluorescence signal enhancement at low fluences is observed. The dropdown is analysed with a simple theoretical one-dimensional heat diffusion model and verified by fluorescence time constants change as a function of fluence. The dropdown is explained as a result of liquid-solid mixture layer at the liquid and solid boundary. The effect of the layer becomes important at low fluences.

  8. Extracting third order optical nonlinearities of Mn(III)-Phthalocyanine chloride using high repetition rate femtosecond pulses

    Science.gov (United States)

    Makhal, Krishnandu; Mathur, Paresh; Maurya, Sidharth; Goswami, Debabrata

    2017-02-01

    Third order nonlinearities of Mn(III)-Phthalocyanine chloride in dimethyl-sulphoxide under 50 fs pulses, operating at 94 MHz, by eliminating cumulative thermal effects have been investigated and reported by us. Modifications were done in data acquisition during Z-scan experiment, which included recording of time evolution waveform traces in an oscilloscope and not collection of Z versus transmission and utilization of a chopper of a suitable duty cycle. Time evolution traces were further processed analytically through MatLab® programming, which yielded Z-scan traces similar to what was obtained with single shot 50 fs pulse. We observed reverse saturable absorption at 800 nm owing to excited state absorption. We show that the nonlinear refractive index (γ) and nonlinear absorption coefficient (β) are over estimated almost 100 times, when MHz pulses are used compared to a situation, where thermo-optical nonlinearities are accounted. Illumination and dark periods are carefully set in a way, so that the sample is able to completely recover its initial temperature before arrival of the next pulse. Magnitudes of γ and β were found to be -(6.5-4.9) × 10-16 m2/W and (5.4-6.2) × 10-10 m/W under the MHz condition, whereas they were -(0.18-2.2) × 10-18 m2/W and (9.5-15) × 10-12 m/W under the thermally managed condition, respectively. To reveal the associated fast nonlinearity, femtosecond transient absorption experiment was performed, which inferred excited state absorption and ground state bleaching across the 450-780 nm region. Dynamics associated with these processes are reported along with fluorescence lifetime obtained through the TCSPC technique. Structure optimization using TDDFT calculations and HOMO-LUMO gaps with orbital pictures are also shown.

  9. Electron dynamics and optical properties modulation of monolayer MoS2 by femtosecond laser pulse: a simulation using time-dependent density functional theory

    Science.gov (United States)

    Su, Xiaoxing; Jiang, Lan; Wang, Feng; Su, Gaoshi; Qu, Liangti; Lu, Yongfeng

    2017-07-01

    In this study, we adopted time-dependent density functional theory to investigate the optical properties of monolayer MoS2 and the effect of intense few-cycle femtosecond laser pulses on these properties. The electron dynamics of monolayer MoS2 under few-cycle and multi-cycle laser irradiation were described. The polarization direction of the laser had a marked effect on the energy absorption and electronic excitation of monolayer MoS2 because of anisotropy. Change in the polarization direction of few-cycle pulse changed the absorbed energy by a factor over 4000. Few-cycle pulse showed a higher sensitivity to the electronic property of material than multi-cycle pulse. The modulation of the dielectric properties of the material was observed on the femtosecond time scale. The negative divergence appeared in the real part of the function at low frequencies and photoinduced blue shift occurred due to Burstein-Moss effect. The irradiation of femtosecond laser caused the dielectric response within the infrared region and introduced anisotropy to the in-plane optical properties. Laser-based engineering of optical properties through controlling transient electron dynamics expands the functionality of MoS2 and has potential applications in direction-dependent optoelectronic devices.

  10. Convection roll-driven generation of supra-wavelength periodic surface structures on dielectrics upon irradiation with femtosecond pulsed lasers

    Science.gov (United States)

    Tsibidis, George D.; Skoulas, Evangelos; Papadopoulos, Antonis; Stratakis, Emmanuel

    2016-08-01

    The significance of the magnitude of the Prandtl number of a fluid in the propagation direction of induced convection rolls is elucidated. Specifically, we report on the physical mechanism to account for the formation and orientation of previously unexplored supra-wavelength periodic surface structures in dielectrics, following melting and subsequent capillary effects induced upon irradiation with ultrashort laser pulses. Counterintuitively, it is found that such structures exhibit periodicities, which are markedly, even multiple times, higher than the laser excitation wavelength. It turns out that the extent to which the hydrothermal waves relax depends upon the laser beam energy, produced electron densities upon excitation with femtosecond pulsed lasers, the magnitude of the induced initial local roll disturbances, and the magnitude of the Prandtl number with direct consequences on the orientation and size of the induced structures. It is envisaged that this elucidation may be useful for the interpretation of similar, albeit large-scale periodic or quasiperiodic structures formed in other natural systems due to thermal gradients, while it can also be of great importance for potential applications in biomimetics.

  11. Single-pulse femtosecond laser Bessel beams drilling of high-aspect-ratio microholes based on electron dynamics control

    Science.gov (United States)

    Zhao, Weiwei; Li, Xiaowei; Xia, Bo; Yan, Xueliang; Han, Weina; Lu, Yongfeng; Jiang, Lan

    2014-11-01

    Microholes drilling has attracted extensive research efforts for its broad applications in photonics, microfluidics, optical fibers and many other fields. A femtosecond (fs) laser is a promising tool for high-precision materials processing with reduced recast/microcracks and minimized heat affected zones. But there remain many challenges in hole drilling using conventional fs laser with Gaussian beams, such as low aspect ratio and taper effects. We report small-diameter and high-aspect-ratio microholes with taper free drilling in PMMA (polymethyl methacrylate) using single-pulse fs laser Bessel beams. Axicon is used to transform Gaussian beams into Bessel beams, which then irradiate in the sample by a telescope consisting of plano-convex lens and microscope objective. Using this technique, we enhance the aspect ratio of microholes by 55 times as compared with Gaussian beams. We attribute this high aspect ratio and high quality microholes formation to the unique spatial intensity distribution and propagation stability of Bessel beams, which can effectively adjust the transient localized electron density distribution leading to a long and uniform localized-interacted zone. By using the optimized pulse energy and focal depth position, the microholes diameter ranges between 1.4-2.1 μm and the aspect ratio can exceed 460. This efficient technique is of great potentials for fabrication of microphotonics devices and microfluidics.

  12. Optical tomography of human skin with subcellular spatial and picosecond time resolution using intense near infrared femtosecond laser pulses

    Science.gov (United States)

    Koenig, Karsten; Wollina, Uwe; Riemann, Iris; Peukert, Christiane; Halbhuber, Karl-Juergen; Konrad, Helga; Fischer, Peter; Fuenfstueck, Veronika; Fischer, Tobias W.; Elsner, Peter

    2002-06-01

    We describe the novel high resolution imaging tool DermaInspect 100 for non-invasive diagnosis of dermatological disorders based on multiphoton autofluorescence imaging (MAI)and second harmonic generation. Femtosecond laser pulses in the spectral range of 750 nm to 850 nm have been used to image in vitro and in vivo human skin with subcellular spatial and picosecond temporal resolution. The non-linear induced autofluorescence originates mainly from naturally endogenous fluorophores/protein structures like NAD(P)H, flavins, keratin, collagen, elastin, porphyrins and melanin. Second harmonic generation was observed in the stratum corneum and in the dermis. The system with a wavelength-tunable compact 80 MHz Ti:sapphire laser, a scan module with galvo scan mirrors, piezoelectric objective positioner, fast photon detector and time-resolved single photon counting unit was used to perform optical sectioning and 3D autofluorescence lifetime imaging (t-mapping). In addition, a modified femtosecond laser scanning microscope was involved in autofluorescence measurements. Tissues of patients with psoriasis, nevi, dermatitis, basalioma and melanoma have been investigated. Individual cells and skin structures could be clearly visualized. Intracellular components and connective tissue structures could be further characterized by tuning the excitation wavelength in the range of 750 nm to 850 nm and by calculation of mean fluorescence lifetimes per pixel and of particular regions of interest. The novel non-invasive imaging system provides 4D (x,y,z,t) optical biopsies with subcellular resolution and offers the possibility to introduce a further optical diagnostic method in dermatology.

  13. Visible and ultraviolet photoelectron spectroscopy of fullerenes using femtosecond laser pulses

    OpenAIRE

    Campbell E. E. B.; Henderson G. G.; Johansson J. O.

    2013-01-01

    Photoelectron spectra are presented for C60 excited with fs pulses of wavelengths 532 and 267 nm. The spectra indicate a quick redistribution of the excitation energy. Excitation of SAMO states is observed with 532 nm excitation, but due to the relatively large photon energy of the 267 nm pulses, these orbitals are not populated for this wavelength.

  14. Coherently-combined two channel femtosecond fiber CPA system producing 3 mJ pulse energy.

    Science.gov (United States)

    Klenke, Arno; Seise, Enrico; Demmler, Stefan; Rothhardt, Jan; Breitkopf, Sven; Limpert, Jens; Tünnermann, Andreas

    2011-11-21

    We present a fiber CPA system consisting of two coherently combined fiber amplifiers, which have been arranged in an actively stabilized Mach-Zehnder interferometer. Pulse durations as short as 470 fs and pulse energies of 3 mJ, corresponding to 5.4 GW of peak power, have been achieved at an average power of 30 W.

  15. Mode-selective terahertz emission from rippled air irradiated by femtosecond laser pulses

    Science.gov (United States)

    Shin, Junghun; Zhidkov, Alexei; Jin, Zhan; Hosokai, Tomonao; Kodama, Ryosuke

    2014-04-01

    Terahertz (THz) emission from rippled air is studied in multidimensional particle-in-cell simulations that include optical field ionization. The ionization modulation in a plasma channel produced by a laser pulse propagating along a ripple and the pulse self-focusing result in THz mode selection with the generation of intense signals having quasi-monochromatic spectral distributions.

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

    Science.gov (United States)

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

    2017-10-01

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

  17. Modeling of fast phase transitions dynamics in metal target irradiated by pico- and femtosecond pulsed laser

    Energy Technology Data Exchange (ETDEWEB)

    Mazhukin, V.I. [Institute of Mathematical Modeling, Russian Academy of Sciences, Miusskaya sq. 4A, 125047 Moscow (Russian Federation); Lobok, M.G. [Institute of Mathematical Modeling, Russian Academy of Sciences, Miusskaya sq. 4A, 125047 Moscow (Russian Federation)], E-mail: immras@orc.ru; Chichkov, B. [Laser Zentrum Hannover e.V. Holleritallee 8, 30419 Hannover (Germany)], E-mail: b.chichkov@lhz.de

    2009-03-01

    We investigate laser pulse influence on aluminum target in irradiance range 10{sup 9} to 10{sup 16} W/cm{sup 2}, pulse duration between 10{sup -8} and 10{sup -15} s, Gaussian time profile with wavelength of 0.8 {mu}m. For all computations energy density was 10 J/cm{sup 2}. Plasma in the evaporated material is generated at the energy density above 10 J/cm{sup 2}as the modeling showed. Long and short laser pulses distinguish by the mechanisms of energy transformation. For short laser pulses there is volumetric energy absorption, together with rapid phase transitions it lead to overheating in solid and liquid states, overheated solid temperature rises up to (6-8)T{sub m}. Under influence of the energy saved in overheated solid, duration of the phase transitions becomes nanosecond, which is several orders of magnitude longer than laser pulse.

  18. Forward acceleration and generation of femtosecond, megaelectronvolt electron beams by an ultrafast intense laser pulse

    Institute of Scientific and Technical Information of China (English)

    Xiaofang wang(王晓方); Quandong Wang(汪权东); Baifei Shen(沈百飞)

    2003-01-01

    We present a new mechanism of energy gain of electrons accelerated by a laser pulse. It is shown that when the intensity of an ultrafast intense laser pulse decreases rapidly along the direction of propagation, electrons leaving the pulse experience an action of ponderomotive deceleration at the descending part of a lower-intensity laser field than acceleration at the ascending part of a high-intensity field, thus gain net energy from the pulse and move directly forward. By means of such a mechanism, a megaelectronvolt electron beam with a bunch length shorter than 100 fs could be realized with an ultrafast (≤30 fs),intense (>1019 W/cm2) laser pulse.

  19. Quadratic System Identification: a statistical framework for the paired-pulse paradigm.

    Science.gov (United States)

    Arunajadai, Srikesh G

    2010-03-01

    System Identification refers to the problem of identifying a model or description of a system based on a stretch of input and the corresponding output from the system. The paired-pulse paradigm or the conditioning test pulse paradigm is often used in neurophysiology experiments. In this work we provide a statistical framework for the conditioning test pulse paradigm which also serves as a system identification tool for quadratic or second order Volterra systems. A nonparametric spectral domain based methodology is proposed for the quadratic system identification. It is shown that by carrying out the analysis in the spectral domain one needs to perform only a single set of double pulse experiments as opposed to multiple sets of experiments in the time domain. Simulation studies are performed to assess the performance of the methodology and to study the conditions under which the methods are expected to perform well.

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

    Science.gov (United States)

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

    2017-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-08-01

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

  2. Nitrogen fluorescence induced by the femtosecond intense laser pulses in air

    Institute of Scientific and Technical Information of China (English)

    He Li; Suyu Li; Shuchang Li; Dunli Liu; Dan Tian; Anmin Chen; Ying Wang; Xiaowei Wang; Yunfeng Zhang; Mingxing Jin

    2016-01-01

    Our experiments show that external focusing and initial laser energy strongly influences filament generated by the femtosecond Ti–sapphire laser in air. The experimental measurements show the filament length can be extended both by increasing the laser energy and focal length of focusing lens. On the other hand, the plasma fluorescence emission can be enhanced by increasing the laser energy with fixed focal length or decreasing the focal length. In addition, the collapse distance measured experimentally are larger than the calculated ones owing to the group-velocity-dispersion effect. In addition, we find that the line widths of the spectral lines from N2 is independent of filament positions, laser energies and external focusing.

  3. Diffractive imaging of a molecular rotational wavepacket with femtosecond Megaelectronvolt electron pulses

    CERN Document Server

    Yang, Jie; Vecchione, Theodore; Robinson, Matthew S; Li, Renkai; Hartmann, Nick; Shen, Xiaozhe; Coffee, Ryan; Corbett, Jeff; Fry, Alan; Gaffney, Kelly; Gorkhover, Tais; Hast, Carsten; Jobe, Keith; Makasyuk, Igor; Reid, Alexander; Robinson, Joseph; Vetter, Sharon; Wang, Fenglin; Weathersby, Stephen; Yoneda, Charles; Centurion, Martin; Wang, Xijie

    2015-01-01

    Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angstrom spatial precision is one of the critical challenges in the chemical sciences, since the nuclear geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. We performed a gas-phase electron diffraction experiment using Megaelectronvolt (MeV) electrons, where we captured the rotational wavepacket dynamics of nonadiabatically laser-aligned nitrogen molecules. We achieved an unprecedented combination of 100 fs root-mean-squared (RMS) temporal resolution and sub-Angstrom (0.76 {\\AA}) spatial resolution that makes it possible to resolve the position of the nuclei within the molecule. In addition, the diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in 300 fs. Our results demonstrate a significant and promising step towards making atomical...

  4. Selective Excitation of Terahertz Magnetic and Electric Dipoles in Er3 + Ions by Femtosecond Laser Pulses in ErFeO3

    Science.gov (United States)

    Mikhaylovskiy, R. V.; Huisman, T. J.; Pisarev, R. V.; Rasing, Th.; Kimel, A. V.

    2017-01-01

    We show that femtosecond laser pulse excitation of the orthoferrite ErFeO3 triggers pico- and subpicosecond dynamics of magnetic and electric dipoles associated with the low energy electronic states of the Er3 + ions. These dynamics are readily revealed by using polarization sensitive terahertz emission spectroscopy. It is shown that by changing the polarization of the femtosecond laser pulse one can excite either electric dipole-active or magnetic dipole-active transitions between the Kramers doublets of the 15/2I4 ground state of the Er3 + (4 f11 ) ions. These observations serve as a proof of principle of polarization-selective control of both electric and magnetic degrees of freedom at terahertz frequencies, opening up new vistas for optical manipulation of magnetoelectric materials.

  5. Superposition of orbital angular momentum of photons by a combined computer-generated hologram fabricated in silica glass with femtosecond laser pulses

    Institute of Scientific and Technical Information of China (English)

    Guo Zhong-Yi; Qu Shi-Liang; Sun Zheng-He; Liu Shu-Tian

    2008-01-01

    This paper introduces a novel method to realize the superposition of orbital angular momentum of photons by combined computer-generated hologram (CCGH) fabricated in silica glass with femtosecond laser pulses.Firstly,the two computer-generated holograms (CGH) of optical vortex were obtained and combined as a CCGH according to the design.Then the CCGH was directly written inside glass by femtosecond laser pulses induced microexplosion without any pre-or post-treatment of the material.The vortex beams with different vortex topological charges (including new topological charges) have been restructured using a collimated He-Ne laser beam incidence to the CCGH normally.A theoretical and experimental explanation has been presented for the generations of the new topological charges.

  6. Noncollinear parametric generation in LiIO(3) and beta-barium borate by frequency-doubled femtosecond Ti:sapphire laser pulses.

    Science.gov (United States)

    Krylov, V; Kalintsev, A; Rebane, A; Erni, D; Wild, U P

    1995-01-15

    In LiIO(3) and BBO crystals the wave-matching conditions for femtosecond noncollinear parametric light generation at lambda = 390 nm pumping wavelength are investigated. In the LiIO(3) crystal simultaneous phase- and group-velocity-matching angles are determined. Parametric generation occurred at 0.45-2.9-mu;m wavelengths by pumping with the second harmonic of 150-fs Ti:sapphire laser pulses and is in qualitative agreement with calculated directions in both crystals.

  7. Broadband Asymmetric Conical Emission via Cascaded Second-Order Nonlinear Polarization during the Propagation of Femtosecond Laser Pulses in a BBO Crystal

    Institute of Scientific and Technical Information of China (English)

    WEN Jing; JIANG Hong-Bing; YU Jing; YANG Hong; GONG Qi-Huang

    2011-01-01

    @@ We investigate the propagation of femtosecond laser pulses in a 5-mm-thick BBO crystal along the direction of type-Ⅰ phase-matched second-harmonic generation.An intensity-asymmetric broadband conical emission (500- 2000 nm) is demonstrated when a suitable chirp is introduced.It is generated by optical parametric amplification pumped by the second-harmonic light and seeded by the fundamental light which is broadened by cascaded nonlinear processes during second-harmonic generation.

  8. Prepulse effects on the interaction of intense femtosecond laser pulses with high-Z solids

    Energy Technology Data Exchange (ETDEWEB)

    Zhidkov, Alexei; Sasaki, Akira; Utsumi, Takayuki; Fukumoto, Ichirou; Tajima, Toshiki; Saito, Fumikazu; Hironaka, Yoichiro; Nakamura, Kazutaka G.; Kondo, Ken-ichi; Yoshida, Masatake

    2000-11-01

    K{alpha} emission of high-Z solid targets irradiated by an intense, short (<100 fs) laser pulse in the 10 keV region is shown to be sensitive to the electron energy cutoff, which is strongly dependent on the density gradient of the plasma corona formed by a long prepulse. The absorption rate of short laser pulses, the hot electron distribution, and x-ray emission from a Cu slab target are studied via a hybrid model, which combines the hydrodynamics, collisional particle-in-cell, and Monte Carlo simulation techniques, and via a direct spectroscopic measurement. An absorption mechanism originating from the interaction of the laser pulse with plasma waves is found to increase the absorption rate by over 30% even for a very short, s-polarized laser pulse. Calculated and measured x-ray spectra are in good agreement, confirming the electron energy cutoff.

  9. [Femtosecond laser-assisted lens surgery depending on interface design and laser pulse energy: results of the first 200 cases].

    Science.gov (United States)

    Mayer, W J; Klaproth, O K; Ostovic, M; Hengerer, F H; Kohnen, T

    2014-12-01

    This study was designed to evaluate the effectiveness and safety of femtosecond laser-assisted lens surgery depending on interface design and laser pulse energy settings. In this non-randomized, consecutive case series200 eyes underwent femtosecond laser-assisted (LenSx, Alcon) lens surgery between November 2012 and June 2013. Group 1 consisted of 85 eyes with 60 cataracts and 25 refractive lens exchanges (RLE) which were treated with a curved direct contact interface, and group 2 consisting of 115 eyes with 72 cataracts and 43 RLEs treated with a modified interface using an additional soft contact lens (SoftFit™, Alcon) between the corneal surface and the interface. The degree of opacity of the lens in cataract eyes was measured with a Scheimpflug camera. Afterwards, phacoemulsification was performed with intraocular lens (IOL) implantation in all eyes. Primary endpoints were the effective phacoemulsification time (EPT), the average laser treatment time and the occurrence of intraoperative complications. The mean EPT in group 1 was 1.62 ± 1.12 s (cataract 1.94 ± 1.31 s, RLE 1.29 ± 1.01 s) and in group 2 the mean EPT was 1.66 ± 0.92 s (cataract 1.98 ± 1.28 s, RLE 1.33 ± 1.22 s, p = 0.32 between groups). The laser treatment lasted on average 48.90 ± 2.45 s (group 1) and 49.70 ± 2.87 s (group 2) with an average lens fragmentation thickness of 3401.48 ± 401.12 µm (all groups). In four cases of group 1, a second applanation of the interface was necessary. Furthermore, one anterior capsule tear, 39 cases of intraoperative wrinkling of the corneal surface and 21 cases in which the corneal incision had to be opened manually were documented in group 1. In group 2 no second applanation of the interface, no anterior capsule tears and no corneal wrinkling but 9 cases with a manual opening of corneal incisions were documented (p interface and reduced laser pulse energy.

  10. Pulsed excitation of Rydberg-atom-pair states in an ultracold Cs gas

    CERN Document Server

    Saßmannshausen, Heiner; Deiglmayr, Johannes

    2015-01-01

    Pulsed laser excitation of a dense ultracold Cs vapor has been used to study the pairwise interactions between Cs atoms excited to $n$p$_{3/2}$ Rydberg states of principal quantum numbers in the range $n=22-36$. Molecular resonances were observed that correspond to excitation of Rydberg-atom-pair states correlated not only to the $n$p$_{3/2}+n$p$_{3/2}$ dissociation asymptotes, but also to $n$s$_{1/2}+(n+1)$s$_{1/2}$, $n$s$_{1/2}+n'$f$_{j}$, and $(n-4)$f$_{j}+(n-3)$f$_{j}$ $(j=5/2,7/2)$ dissociation asymptotes. These pair resonances are interpreted as arising from dipole-dipole, and higher long-range-interaction terms between the Rydberg atoms on the basis of i) their spectral positions, ii) their response to static and pulsed electric fields, and iii) millimeter-wave spectra between pair states correlated to different pair-dissociation asymptotes. The Rydberg-atom--pair states were found to spontaneously decay by Penning ionization and the dynamics of the ionization process were investigated during the first...

  11. Femtosecond pulse laser ablation of chromium: experimental results and two-temperature model simulations

    Science.gov (United States)

    Saghebfar, M.; Tehrani, M. K.; Darbani, S. M. R.; Majd, A. E.

    2017-01-01

    In this work, the results of experimental and computational single- and multi-shot ablation threshold and the incubation effect of chromium metal sample, irradiated by ultrashort laser pulses, are presented. The experimental value of the ablation threshold is determined based on D2 method by measuring the outer ablation crater diameters as a function of incident laser pulse energy using 800 nm, 30 fs, laser pulses. The value of 0.19 ± 0.04 (J/cm2 ), is obtained for the single-shot ablation threshold fluence. The experimental results are compared with time-dependent heat flow calculations based on the two-temperature model and the effect of number and separation time of two consecutive laser pulses with the same total fluence is studied for the Cr target. Moreover, the role of pulse width and absorbed fluence in thermal equilibrium time between electrons and lattice is investigated in two-temperature model. The thermal equilibrium between electron and lattice is established after a few picoseconds for low fluences and after a few tens of picoseconds at higher fluences.

  12. Strong-field Breit-Wheeler pair production in short laser pulses: Relevance of spin effects

    Science.gov (United States)

    Jansen, M. J. A.; Kamiński, J. Z.; Krajewska, K.; Müller, C.

    2016-07-01

    Production of electron-positron pairs in the collision of a high-energy photon with a high-intensity few-cycle laser pulse is studied. By utilizing the frameworks of laser-dressed spinor and scalar quantum electrodynamics, a comparison between the production of pairs of Dirac and Klein-Gordon particles is drawn. Positron energy spectra and angular distributions are presented for various laser parameters. We identify conditions under which predictions from Klein-Gordon theory either closely resemble or largely differ from those of the proper Dirac theory. In particular, we address the question to which extent the relevance of spin effects is influenced by the short duration of the laser pulse.

  13. Strong-field Breit-Wheeler pair production in short laser pulses: Relevance of spin effects

    CERN Document Server

    Jansen, M J A; Krajewska, K; Müller, C

    2016-01-01

    Production of electron-positron pairs in the collision of a high-energy photon with a high-intensity few-cycle laser pulse is studied. By utilizing the frameworks of laser-dressed spinor and scalar quantum electrodynamics, a comparison between the production of pairs of Dirac and Klein-Gordon particles is drawn. Positron energy spectra and angular distributions are presented for various laser parameters. We identify conditions under which predictions from Klein-Gordon theory either closely resemble or largely differ from those of the proper Dirac theory. In particular, we address the question to which extent the relevance of spin effects is influenced by the short duration of the laser pulse.

  14. Dynamics of vortex-antivortex pairs and rarefaction pulses in liquid light.

    Science.gov (United States)

    Feijoo, David; Paredes, Angel; Michinel, Humberto

    2017-03-01

    We present a numerical study of the cubic-quintic nonlinear Schrödinger equation in two transverse dimensions, relevant for the propagation of light in certain exotic media. A well-known feature of the model is the existence of flat-top bright solitons of fixed intensity, whose dynamics resembles the physics of a liquid. They support traveling wave solutions, consisting of rarefaction pulses and vortex-antivortex pairs. In this work, we demonstrate how the vortex-antivortex pairs can be generated in bright soliton collisions displaying destructive interference followed by a snake instability. We then discuss the collisional dynamics of the dark excitations for different initial conditions. We describe a number of distinct phenomena including vortex exchange modes, quasielastic flyby scattering, solitonlike crossing, fully inelastic collisions, and rarefaction pulse merging.

  15. Femtosecond pulses at 50-W average power from an Yb:YAG planar waveguide amplifier seeded by an Yb:KYW oscillator.

    Science.gov (United States)

    Leburn, Christopher G; Ramírez-Corral, Cristtel Y; Thomson, Ian J; Hall, Denis R; Baker, Howard J; Reid, Derryck T

    2012-07-30

    We report the demonstration of a high-power single-side-pumped Yb:YAG planar waveguide amplifier seeded by an Yb:KYW femtosecond laser. Five passes through the amplifier yielded 700-fs pulses with average powers of 50 W at 1030 nm. A numerical simulation of the amplifier implied values for the laser transition saturation intensity, the small-signal intensity gain coefficient and the gain bandwidth of 10.0 kW cm(-2), 1.6 cm(-1), and 3.7 nm respectively, and identified gain-narrowing as the dominant pulse-shaping mechanism.

  16. Efficient terahertz wave generation from GaP crystals pumped by chirp-controlled pulses from femtosecond photonic crystal fiber amplifier

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jiang; Shi, Junkai; Xu, Baozhong; Xing, Qirong; Wang, Chingyue [Ultrafast Laser Laboratory, College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronic Information Technology (Ministry of Education), Tianjin University, Tianjin 300072 (China); Chai, Lu, E-mail: lu-chai@tju.edu.cn, E-mail: yanfengli@tju.edu.cn; Liu, Bowen; Hu, Minglie; Li, Yanfeng, E-mail: lu-chai@tju.edu.cn, E-mail: yanfengli@tju.edu.cn [Ultrafast Laser Laboratory, College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronic Information Technology (Ministry of Education), Tianjin University, Tianjin 300072 (China); MOEMS Key Laboratory (Ministry of Education), Tianjin University, Tianjin 300072 (China); Fedotov, Andrey B. [Physics Department, Russian Quantum Center, International Laser Center, M.V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Zheltikov, Aleksei M. [Physics Department, Russian Quantum Center, International Laser Center, M.V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Department of Physics and Astronomy, Texas A and M University, College Station, Texas 77843 (United States)

    2014-01-20

    A chirp-tunable femtosecond 10 W, 42 MHz photonic-crystal-fiber oscillator-amplifier system that is capable of delivering sub-60 fs light pulses at 1040 nm is used to demonstrate high-efficiency terahertz radiation generation via optical rectification in GaP crystals only a few millimeters in length. The optimization of the chirp of the fiber-laser pulses is shown to radically enhance the terahertz output, indicating one possible way to more efficiently use these extended nonlinear crystals in compact fiber-pumped terahertz radiation sources.

  17. Visible supercontinuum radiation of light bullets in the femtosecond filamentation of IR pulses in fused silica

    Science.gov (United States)

    Chekalin, S. V.; Kompanets, V. O.; Dokukina, A. E.; Dormidonov, A. E.; Smetanina, E. O.; Kandidov, V. P.

    2015-05-01

    We report experimental and theoretical investigations of visible supercontinuum generation in the formation of light bullets in a filament produced by IR pulses. In the filamentation of a 1700 - 2200 nm pulse in fused silica, bright tracks are recorded resulting from the recombination glow of carriers in the laser plasma produced by a sequence of light bullets and from the scattering in silica of the visible supercontinuum generated by the light bullets. It is found that the formation of a light bullet is attended with an outburst of a certain portion of supercontinuum energy in the visible range. The energy outburst is the same for all bullets in the sequence and becomes smaller with increasing pulse wavelength.

  18. Design of large-mode-area three layered fiber structure for femtosecond laser pulse delivery

    Science.gov (United States)

    Babita; Rastogi, Vipul; Kumar, Ajeet

    2013-04-01

    This paper presents three layered fiber that has been designed for delivering pulses of 100-fs through the fundamental mode. Design of the fiber ensures no intermodal coupling, low bending loss, and high fabrication tolerances while maintaining large-mode-area. We numerically demonstrate propagation of 55.5-kW peak power, 1550-nm wavelength, 100-fs duration laser pulse through fundamental mode of 4-m long fiber having mode area of 1900 μm2. Mode stability while propagation through the fiber has been ascertained by keeping enough spacing between the effective indices of LP01 and LP11 modes. Distortion-free propagation of the pulse has been achieved by keeping ratio of dispersion to nonlinear length close to 1.

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

    KAUST Repository

    Chiang, Weiyi

    2013-09-19

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

  20. Multibeam second-harmonic generation by spatiotemporal shaping of femtosecond pulses.

    Science.gov (United States)

    Martínez-Cuenca, Raúl; Mendoza-Yero, Omel; Alonso, Benjamín; Sola, Íñigo Juan; Mínguez-Vega, Gladys; Lancis, Jesús

    2012-03-01

    We present a technique for efficient generation of the second-harmonic signal at several points of a nonlinear crystal simultaneously. Multispot operation is performed by using a diffractive optical element that splits the near-infrared light of a mode-locked Ti:sapphire laser into an arbitrary array of beams that are transformed into an array of foci at the nonlinear crystal. We show that, for pulse temporal durations under 100 fs, spatiotemporal shaping of the pulse is mandatory to overcome chromatic dispersion effects that spread both in space and time the foci showing a reduced peak intensity that prevents nonlinear phenomena. We experimentally demonstrate arbitrary irradiance patterns for the second-harmonic signal consisting of more than 100 spots with a multipass amplifier delivering 28 fs, 0.8 mJ pulses at 1 kHz repetition rate.

  1. Femtosecond pulsed laser ablation of molybdenum carbide: Nanoparticles and thin film characteristics

    Science.gov (United States)

    De Bonis, A.; Santagata, A.; Sansone, M.; Rau, J. V.; Mori, T.; Teghil, R.

    2013-08-01

    In this paper we have used pulsed laser deposition (PLD) technique to ablate a Mo2C target in vacuum by using an ultra-short pulse laser, with a 250 fs pulse duration, carrying out the study of both plasma and film characteristics. The aim of the work is to connect the film structure and morphology to the characteristics of the nanoparticles found in the plasma produced by the target ablation. To analyze the plasma we have used ICCD fast imaging and optical emission spectroscopy while the films have been characterized by X-ray diffraction, scanning electron microscopy and atomic force spectroscopy. The obtained results have been interpreted considering an ablation model which justifies the emission of molten nanoparticles directly from the target.

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

    Science.gov (United States)

    Muradyan, Gevorg; Muradyan, Atom Zh.

    2009-09-01

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

  3. High-Energy, Multicolor Femtosecond Pulses from the Deep Ultraviolet to the Near Infrared Generated in a Hydrogen-Filled Gas Cell and Hollow Fiber

    Directory of Open Access Journals (Sweden)

    Kazuya Motoyoshi

    2014-07-01

    Full Text Available We investigate four-wave mixing in hydrogen gas using a gas cell and a hollow fiber for the generation of high-energy, multicolor femtosecond (fs optical pulses. Both a hydrogen-filled gas cell and hollow fiber lead to the generation of multicolor fs pulses in a broad spectral range from the deep ultraviolet to the near infrared. However, there is a difference in the energy distribution of the multicolor emission between the gas cell and the hollow fiber. The hydrogen-filled gas cell generates visible pulses with higher energies than the pulses created by the hollow fiber. We have generated visible pulses with energies of several tens of microjoules. The hydrogen-filled hollow fiber, on the other hand, generates ultraviolet pulses with energies of a few microjoules, which are higher than the energies of the ultraviolet pulses generated in the gas cell. In both schemes, the spectral width of each emission line supports a transform-limited pulse duration shorter than 15 fs. Four-wave mixing in hydrogen gas therefore can be used for the development of a light source that emits sub-20 fs multicolor pulses in a wavelength region from the deep ultraviolet to the near infrared with microjoule pulse energies.

  4. Tunable propagation delay of femtosecond pulse in quantum-dot optical amplifier at room temperature

    DEFF Research Database (Denmark)

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

    2005-01-01

    Optically induced dispersion over a large bandwidth of 2.6 THz is used to slow or speed up a 150 fs pulse in a quantum-dot optical amplifier. A group refractive index change of 4*10-3 is observed.......Optically induced dispersion over a large bandwidth of 2.6 THz is used to slow or speed up a 150 fs pulse in a quantum-dot optical amplifier. A group refractive index change of 4*10-3 is observed....

  5. Tunable propagation delay of femtosecond pulses in a quantum-dot optical amplifier at room temperature

    DEFF Research Database (Denmark)

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

    2005-01-01

    Optically induced dispersion over a large bandwidth of 2.6 THz is used to slow or speed up a 150 fs pulse in a quantum-dot optical amplifier. A group refractive index change of 4*10-3 is observed......Optically induced dispersion over a large bandwidth of 2.6 THz is used to slow or speed up a 150 fs pulse in a quantum-dot optical amplifier. A group refractive index change of 4*10-3 is observed...

  6. Ablation morphology of germanium with multi-pulse femtosecond laser%多脉冲飞秒激光对锗材料的烧蚀效应

    Institute of Scientific and Technical Information of China (English)

    辛建婷; 谭放; 罗国强; 马小军; 赵宗清; 韩丹

    2011-01-01

    开展了脉宽为40 fs的不同数量激光脉冲对锗材料的烧蚀效应实验,采用扫描电镜、激光共聚焦显微镜等方法对不同数量的飞秒激光脉冲作用下锗材料表面烧蚀区进行了检测,并对作用后材料烧蚀形貌演化规律进行了分析,初步分析了锗材料烧蚀区周围形成的不同环区的形貌特征及成因,对各环区烧蚀形貌特征随激光作用脉冲数的增加而产生的形貌演化过程进行了观测.并给出单脉冲飞秒激光对锗材料的烧蚀阈值为1.2 J·cm-2,采用激光共聚焦显微镜测得该阈值条件下单个飞秒激光脉冲对锗材料的烧蚀深度约为150 nm.%Ablation morphology on germanium surface using multi-pulse femtosecond laser is reported. The SEM and laser focus give magnified views of the ablated portion. The ablation morphology shows a periodic surface structure with various laser pulses. And the formation of amorphous rings and ripples in the damage spot is discussed. The ablation threshold is 1. 2 J ? cm-2 and the ablation depth with single femtosecond laser pulse is about 150 nm. It is meanful for research the interaction of femtosec-ond laser and material, and the application of femtosecond laser in micromachining.

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

    Directory of Open Access Journals (Sweden)

    S. Kedenburg

    2016-11-01

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

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

    Science.gov (United States)

    Kedenburg, S.; Steinle, T.; Mörz, F.; Steinmann, A.; Nguyen, D.; Rhonehouse, D.; Zong, J.; Chavez-Pirson, A.; Giessen, H.

    2016-11-01

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

  9. Field emission study from an array of hierarchical micro protrusions on stainless steel surface generated by femtosecond pulsed laser irradiation

    Science.gov (United States)

    Singh, A. K.; Suryawanshi, Sachin R.; More, M. A.; Basu, S.; Sinha, Sucharita

    2017-02-01

    This paper reports our results on femtosecond (fs) pulsed laser induced surface micro/nano structuring of stainless steel 304 (SS 304) samples and their characterization in terms of surface morphology, formed material phases on laser irradiation and field emission studies. Our investigations reveal that nearly uniform and dense array of hierarchical micro-protrusions (density: ∼5.6 × 105 protrusions/cm2) is formed upon laser treatment. Typical tip diameters of the generated protrusions are in the range of 2-5 μm and these protrusions are covered with submicron sized features. Grazing incidence X-ray diffraction (GIXRD) analysis of the laser irradiated sample surface has shown formation mainly of iron oxides and cementite (Fe3C) phases in the treated region. These laser micro-structured samples have shown good field emission properties such as low turn on field (∼4.1 V/μm), high macroscopic field enhancement factor (1830) and stable field emission current under ultra high vacuum conditions.

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

    DEFF Research Database (Denmark)

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

    2008-01-01

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

  11. Self-Channeling of Femtosecond Laser Pulses for Rapid and Efficient Standoff Detection of Energetic Materials

    Science.gov (United States)

    2009-01-01

    Laser Pulses for Rapid and Efficient Standoff Detection of Energetic Materials Matthieu Baudelet, Martin Richardson, Townes laser Institute, CREOL...2007 [3] D.A. Cremers and L.J. Radziemski, Handbook of laser-induced breakdown spectroscopy, Wiley, 2006 [4] A.W. Miziolek, V. Palleschi and I

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

    DEFF Research Database (Denmark)

    Henriksen, Niels Engholm; Møller, Klaus Braagaard

    2003-01-01

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

  13. Nonlinear absorption and optical limiting in Duran glass induced by 800 nm femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Jamshidi-Ghaleh, Kazem [Department of Physics, Azerbaijan University of Tarbiat Moallem, Tabriz (Iran, Islamic Republic of); Mansour, Nastaran [Department of Physics, Shahi Beheshti University, Tehran (Iran, Islamic Republic of)

    2007-01-21

    Nonlinear absorption of Duran glass by irradiation of a focused 200 fs pulsed laser were investigated using the z-scan technique at 800 nm. Optical limiting behaviour in this glass has also been measured. The limiting threshold was measured to 33 {mu}J pulse energy (peak intensity of 2.4 x 10{sup 12} W cm{sup -2}) in this sample. The decrease in transmitted intensity is around 75% compared with the theoretical linear transmission for incident pulses pulse energies 320 {mu}J (peak intensity of 5 x 10{sup 12} W cm{sup -2}). A comparison of the theoretical analyses with the experimental results shows that three-photon absorption and three-photon generated free-carrier absorption within the glasses are the main mechanisms for the observed nonlinear response. The values of the three-photon absorption coefficient and the photo-generated free-carrier cross section are measured as {gamma} = 2 x 10{sup -24}cm{sup 3} W{sup -2} and {sigma} = 1.2 x 10{sup -18} cm{sup 2}, respectively.

  14. Effcient and pure femtosecond-pulse-length source of polarization-entangled photons

    CERN Document Server

    Weston, Morgan M; Wollmann, Sabine; Boston, Allen; Ho, Joseph; Shalm, Lynden K; Verma, Varun B; Allman, Michael S; Nam, Sae Woo; Patel, Raj B; Slussarenko, Sergei; Pryde, Geoff J

    2016-01-01

    We present a source of polarization entangled photon pairs based on spontaneous parametric downconversion engineered for frequency uncorrelated telecom photon generation. Our source provides photon pairs that display, simultaneously, the key properties for high-performance quantum information and fundamental quantum science tasks. Specifically, the source provides for high heralding efficiency, high quantum state purity and high entangled state fidelity at the same time. Among different tests we apply to our source we observe almost perfect non-classical interference between photons from independent sources with a visibility of $(100\\pm5)\\%$.

  15. Finite pulse effects on fermion pair creation from strong electric fields

    Science.gov (United States)

    Taya, Hidetoshi; Fujii, Hirotsugu; Itakura, Kazunori

    2014-09-01

    In the early stage of heavy ion collisions, there appear extraordinarily strong (color) EM fields. In the presence of such strong fields, we encounter essentially new phenomena that are not observed in the vacuum: Among those is fermion pair creation from the vacuum. In this talk, we consider fermion pair creation from the vacuum in a strong electric field with finite duration. Employing the Sauter-type pulsed electric field with height E0 and width τ, we demonstrate explicitly the interplay between the non-perturbative and perturbative aspects of the pair creation in a strong field with finite duration. We identify that two dimensionless parameters ν = | g E0 | τ2 and γ = | g E0 | τ / m characterize the importance of multiple interactions with the field and the transition from the perturbative to the non-perturbative regime. We also show that the pair creation is enhanced compared to Schwinger's formula when the field strength is relativity weak | g E0 | / m2 < 1 and the pulse duration is relatively short mτ < 1 , and reveal that the enhancement is predominantly described by the lowest order perturbation with a single photon. We also discuss some recent developments and applications.

  16. Femtosecond laser induced microripple on PDMS surface

    Institute of Scientific and Technical Information of China (English)

    Jin Xie; Changhe Zhou; Wei Wang; Tengfei Wu

    2009-01-01

    laser pulses and the subsequent cool-down solidification of the melting PDMS along with the movement of the femtosecond laser spot. This result will be helpful to understand the interaction between the femtosecond laser and the polymer.

  17. Femtosecond Laser Filamentation

    CERN Document Server

    Chin, See Leang

    2010-01-01

    Femtosecond Laser Filamentation gives a comprehensive review of the physics of propagation of intense femtosecond laser pulses in optical media (principally air) and the applications and challenges of this new technique. This book presents the modern understanding of the physics of femtosecond laser pulse propagation, including unusual new effects such as the self-transformation of the pulse into a white light laser pulse, intensity clamping, the physics of multiple filamentation and competition, and how filaments’ ability to melt glass leads to wave guide writing. The potential applications of laser filamentation in atmospheric sensing and the generation of other electromagnetic pulses from the UV to the radio frequency are treated, together with possible future challenges in the excitation of super-excited states of molecules. Exciting new phenomena such as filament induced ultrafast birefringence and the excitation of molecular rotational wave packets and their multiple revivals in air (gases) will also ...

  18. Structural Changes Induced in Grapevine (Vitis vinifera L. DNA by Femtosecond IR Laser Pulses: A Surface-Enhanced Raman Spectroscopic Study

    Directory of Open Access Journals (Sweden)

    Nicoleta E. Dina

    2016-05-01

    Full Text Available In this work, surface-enhanced Raman spectra of ten genomic DNAs extracted from leaf tissues of different grapevine (Vitis vinifera L. varieties, respectively, are analyzed in the wavenumber range 300–1800 cm−1. Furthermore, structural changes induced in grapevine genomic nucleic acids upon femtosecond (170 fs infrared (IR laser pulse irradiation (λ = 1100 nm are discussed in detail for seven genomic DNAs, respectively. Surface-enhanced Raman spectroscopy (SERS signatures, vibrational band assignments and structural characterization of genomic DNAs are reported for each case. As a general observation, the wavenumber range between 1500 and 1660 cm−1 of the spectra seems to be modified upon laser treatment. This finding could reflect changes in the base-stacking interactions in DNA. Spectral shifts are mainly attributed to purines (dA, dG and deoxyribose. Pyrimidine residues seem to be less affected by IR femtosecond laser pulse irradiation. Furthermore, changes in the conformational properties of nucleic acid segments are observed after laser treatment. We have found that DNA isolated from Feteasca Neagra grapevine leaf tissues is the most structurally-responsive system to the femtosecond IR laser irradiation process. In addition, using unbiased computational resources by means of principal component analysis (PCA, eight different grapevine varieties were discriminated.

  19. Ultrarelativistic regime in the propagation of an ultrastrong, femtosecond laser pulse in plasmas

    CERN Document Server

    Jovanović, Dušan; Belić, Milivoj; De Nicola, Sergio

    2014-01-01

    The interaction of a multi-Petawatt, pancake-shaped laser pulse with an unmagnetized plasma is studied analytically and numerically in the regime of fully relativistic electron jitter velocities and in the context of the laser wakefield acceleration scheme. The study is applied to the specifications available at present time, or planned for the near future, of the Ti:Sa Frascati Laser for Acceleration and Multidisciplinary Experiments (FLAME) in Frascati. Novel nonlinear equation is derived by a three-timescale description, with an intermediate timescale associated with the nonlinear phase of the laser wave. They describe on an equal footing both the strong and moderate laser intensity regimes, pertinent to the core and the edges of the pulse. These have fundamentally different dispersive properties since, in the core, the electrons are almost completely expelled by a very strong ponderomotive force and the electromagnetic wave packet is imbedded in a vacuum channel and has (almost) linear properties, while a...

  20. Generation of efficient THz radiation by optical rectification in DAST crystal using tunable femtosecond laser pulses

    Science.gov (United States)

    Venkatesh, Mottamchetty; Thirupugalmani, K.; Rao, K. S.; Brahadeeswaran, S.; Chaudhary, A. K.

    2017-03-01

    We report the efficient THz generation by optical rectification from an indigenously grown organic DAST crystal using the 140 fs oscillator laser pulses tunable in between 780 and 850 nm. The generated THz pulse profile and powers have been measured using the photoconductive (PC) antennas and pyroelectric detector, respectively. The highest THz peak amplitude and power is obtained at 825 nm central wavelength. We have theoretically explained the enhancement of THz radiation based on the matching of average optical group refractive index and average THz refractive index of the DAST crystal at 825 nm. In addition, the dependence of THz peak amplitude and THz power on laser power have been carried out. The measured quantum conversion efficiency (QCE) of 0.5 and 1.5 THz bands are of the order 3.7 × 10-3, 1.4 × 10-3, respectively. Finally, an attempt has been made to study the effect of polarizations on generated THz signal.

  1. Carrier field shock formation of long wavelength femtosecond pulses in dispersive media

    CERN Document Server

    Panagiotopoulos, Paris; Kolesik, Miroslav; Moloney, Jerome V

    2015-01-01

    We numerically demonstrate the formation of carrier field shocks in various dispersive media for a wide variety of input conditions using two different electric field propagation models. In addition, an investigation of the impact of numerous physical effects on carrier wave shock is performed. It is shown that in many cases a field shock is essentially unavoidable and therefore extremely important in the propagation of intense long wavelength pulses in weakly dispersive nonlinear media such as noble gases, air, and single-crystal diamond. The results presented here are expected to have a significant impact in the field of ultrashort nonlinear optics, attosecond pulse generation, and wavepacket synthesis where the use of mid-IR wavelengths is becoming increasingly more important.

  2. Comment on "Direct photodetachment of F$^-$ by mid-infrared few-cycle femtosecond laser pulses"

    CERN Document Server

    Gribakin, G F

    2016-01-01

    Multiphoton detachment of F$^-$ by strong few-cycle laser pulses was studied by Shearer and Monteith using a Keldysh-type approach [Phys. Rev. A 88, 033415 (2013)]. We believe that this work contained errors in the calculation of the detachment amplitude and photoelectron spectra. We describe the necessary corrections to the theory and show that the results, in particular, the interference features of the photoelectron spectra, appear noticeably different.

  3. Importance of a finite speed of heat propagation in metals irradiated by femtosecond laser pulses

    Science.gov (United States)

    Klossika, J. J.; Gratzke, U.; Vicanek, M.; Simon, G.

    1996-10-01

    We study theoretically the propagation of heat in a metal, due to irradiation with an ultrashort laser pulse. The target is treated in an extended two-fluid model for electrons and phonons, which accounts for a finite speed of heat propagation in the electron gas. As a result, the absorbed laser energy is more localized in the electronic system yielding an enhanced peak electron temperature.

  4. Wide-bandgap nonlinear crystal LiGaSsub>2sub> for femtosecond mid-infrared spectroscopy with chirped-pulse upconversion.

    Science.gov (United States)

    Nakamura, Ryosuke; Inagaki, Yoshizumi; Hata, Hidefumi; Hamada, Norio; Umemura, Nobuhiro; Kamimura, Tomosumi

    2016-11-20

    Femtosecond time-resolved mid-infrared (MIR) spectroscopy based on chirped-pulse upconversion is a promising method for observing molecular vibrational dynamics. A quantitative study on nonlinear media for upconversion is still essential for wide applications, particularly at the frequencies below 2000  cm-1. We evaluate wide-bandgap nonlinear crystals of Li-containing ternary chalcogenides based on their performance as the upconversion medium for femtosecond MIR spectroscopy. The upconversion efficiency is measured as a function of the MIR pulse frequency and the chirped pulse energy. LiGaSsub>2sub> is found to be an efficient crystal for the upconversion of MIR pulses in a wide frequency range of 1100-2700  cm-1, especially below 2000  cm-1. By using LiGaSsub>2sub> as an efficient upconversion crystal, we develop a MIR pump-probe spectroscopy system with a spectral resolution of 2.5  cm-1, a time resolution of 0.2 ps, and a probe window of 120  cm-1. Vibrational relaxation dynamics of CO stretching modes of Mnsub>2sub>(CO)sub>10sub> in cyclohexane and bovine serum albumin in Dsub>2sub>O are demonstrated with a high signal-to-noise ratio.

  5. High-energy femtosecond Yb-doped all-fiber monolithic chirped-pulse amplifier at repetition rate of 1 MHz

    Science.gov (United States)

    Lv, Zhi-Guo; Teng, Hao; Wang, Li-Na; Wang, Jun-Li; Wei, Zhi-Yi

    2016-09-01

    A high-energy femtosecond all ytterbium fiber amplifier based on a chirped-pulse amplification (CPA) technique at a repetition rate of 1 MHz seeded by a dispersion-management mode-locked picosecond broadband oscillator is studied. We find that the compressed pulse duration is dependent on the amplified energy, the pulse duration of 804 fs corresponds to the maximum amplified energy of 10.5 μJ, while the shortest pulse duration of 424 fs corresponds to the amplified energy of 6.75 μJ. The measured energy fluctuation is approximately 0.46% root mean square (RMS) over 2 h. The low-cost femtosecond fiber laser source with super-stability will be widely used in industrial micromachines, medical therapy, and scientific studies. Project supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Grant No. 2012BAC23B03), the National Key Basic Research Program of China (Grant No. 2013CB922401), and the National Natural Science Foundation of China (Grant No. 11474002).

  6. High harmonic generation in H$_2^+$ and HD$^+$ by two-colour femtosecond laser pulses

    Indian Academy of Sciences (India)

    Farzana Sharmin; Samir Saha; S S Bhattacharyya

    2013-12-01

    We have theoretically investigated the high harmonic generation (HHG) spectra of H$_2^+$ and HD$^+$ using a time-dependent wave packet approach for the nuclear motion with combined twocolour (1$_L$–3$_L$) pulsed lasers for ωL corresponding to wavelengths 1064 nm and 800 nm. The 1$_L$ and 3$_L$ lasers have peak intensities of $I_1^0 = 5.0 × 10^{13}$ W/cm$^2$ and $I_2^0 = 2.0 × 10^{14}$ W/cm$^2$, respectively. We have taken the pulse duration of $T = 50$ fs for both the fields, and the molecular initial vibrational level 0 = 0. We have argued that for these combinations, the harmonic generation due to transitions in the electronic continuum by tunnelling or multiphoton ionization may be neglected and only the electronic transitions within the two lowest electronic states would be important. Thus, the characteristic features of HHG spectra in the two-colour field are determined, in our model, by the nuclear motions on the two lowest field-coupled electronic states between which interelectronic and intraelectronic (due to the intrinsic dipole moments in case of HD+) radiative transitions can take place. We have studied the role of relative phase ($\\varphi$) of the two fields on the HHG spectra of the molecular ions. In case of HD+, the effect of nonadiabatic (NA) nonradiative interaction between the two lowest Born–Oppenheimer (BO) electronic states (1$s_g$, 2$p_u$) has been taken into account. Our calculations give realistic HHG spectra which are reasonably efficient and extended for both H$_2^+$ and HD$^+$ in the mixed two-colour field without involving the electronic continuum. The use of two-colour (1$_L$–3$_L$) field enables us to generate high harmonics beyond that achievable with a single 1$_L$ or 3$_L$ field of the corresponding intensity, frequency and pulse time.

  7. High-Order Harmonic Generation by Two Non-collinear Coherent Femtosecond Laser Pulses

    Institute of Scientific and Technical Information of China (English)

    陆伟新; 刘婷婷; 杨宏; 孙騊亨; 龚旗煌

    2003-01-01

    We have studied the high-order harmonic generated by two coherent pulses in argon gas produced by a gas jet. A loop in the relationship of the harmonic intensity versus the absolute values of relative phase difference was observed for non-collinear arrangement. Compared with the collinear arrangement, increase of 10 times of the conversion efficiency for 17th-order harmonic generation at an appropriate relative phase difference was obtained. The calculation of the intensity and phase for the laser field near the focus gives a simple reason for these phenomena.

  8. Nanostructured molybdenum carbide thin films obtained by femtosecond pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Teghil, Roberto; De Bonis, Angela [Dipartimento di Chimica ' ' A.M. Tamburro' ' , Universita della Basilicata, Potenza (Italy); IMIP-U.O.S. di Potenza, Consiglio Nazionale delle Ricerche, Tito (Italy); Galasso, Agostino; Sansone, Maria [Dipartimento di Chimica ' ' A.M. Tamburro' ' , Universita della Basilicata, Potenza (Italy); Rau, Julietta V. [ISM, Consiglio Nazionale delle Ricerche, Rome (Italy); Santagata, Antonio [IMIP-U.O.S. di Potenza, Consiglio Nazionale delle Ricerche, Tito (Italy)

    2012-12-15

    The films obtained by ultra-short pulsed laser deposition of a target of molybdenum carbide, at different substrate temperatures, have been characterized by different techniques, including scanning electron microscopy, micro-Raman spectroscopy and X-ray photoelectron spectroscopy. The results indicate that the films are formed by a large number of particles with nanometric dimensions and are composed mainly of Mo{sub 2}C. The presence of an excess of carbon, found in the films, is probably due the presence of a certain amount of graphite in the target (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Thin films deposited by femtosecond pulsed laser ablation of tungsten carbide

    Science.gov (United States)

    De Bonis, A.; Teghil, R.; Santagata, A.; Galasso, A.; Rau, J. V.

    2012-09-01

    Ultra-short Pulsed Laser Deposition has been applied to the production of thin films from a tungsten carbide target. The gaseous phase obtained by the laser ablation shows a very weak primary plume, in contrast with a very strong secondary one. The deposited films, investigated by Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray Photoelectron Spectroscopy and X-Ray Diffraction, present a mixture of WC and other phases with lower carbon content. All films are amorphous, independently from the substrate temperature. The characteristics of the deposits have been explained in terms of thermal evaporation and cooling rate of molten particles ejected from the target.

  10. Laser Mode-Dependent Size of Plasma Zones Induced by Femtosecond Laser Pulses in Fused Silica

    Institute of Scientific and Technical Information of China (English)

    TANG Shan-Chun; JIANG Hong-Bing; LIU Yi; GONG Qi-Huang

    2008-01-01

    We carry out the numerical simulations of #emtosecond laser propagation with TEM00 mode, TEM10 mode and a beam combining both the modes in fused silica. It is found that the transverse size of plasma zones induced by laser pulses with the TEM10 mode is smaller than that induced by the TEMoo mode, while the longitudinal size is almost the same, and the saturated plasma density is higher. The transverse size, the longitudinal size and the ratio of the longitudinal to transverse size, for the beam combining both the modes, all could be reduced at the same time in comparison with the TEMoo mode under the same focusing conditions.

  11. Multiple nanoscale parallel grooves formed on Si{sub 3}N{sub 4}/TiC ceramic by femtosecond pulsed laser

    Energy Technology Data Exchange (ETDEWEB)

    Xing, Youqiang; Deng, Jianxin, E-mail: jxdeng@sdu.edu.cn; Lian, Yunsong; Zhang, Kedong; Zhang, Guodong; Zhao, Jun

    2014-01-15

    Multiple nanoscale parallel grooves were induced on Si{sub 3}N{sub 4}/TiC ceramic by a femtosecond pulsed laser with a pulse width of 120 fs, wavelength of 800 nm and repetition rate of 1000 Hz. Pulse energy, scanning speed and the number of overscans were studied for the formation of regular parallel grooves. The evolution of surface morphology, ablation dimension and surface roughness with different processing parameters was measured by scanning electron microscope (SEM), atomic force microscope (AFM) and white light interferometer. The results show that the uniform multiple nanoscale parallel grooves are obtained by optimizing the pulse energy, scanning speed and number of overscans. The optimum parameters are 2.5 μJ pulse energy and 130 μm/s scanning speed with 1 overscan. At a constant scanning speed of 130 μm/s, the period of the parallel grooves stays relatively constant with increasing pulse energy, fluctuating around 600 nm, which is smaller than the laser wavelength. Additionally, the period was found to increase in a roughly linear fashion with increasing scanning speed. The depth of grooves increases with the increasing pulse energy and decreasing scanning speed; the surface roughness increases with the increasing pulse energy, decreasing scanning speed and increasing number of overscans. Meanwhile, the formation mechanism of laser-induced multiple nanoscale parallel grooves on the Si{sub 3}N{sub 4}/TiC ceramic surface was discussed.

  12. Study of light-induced processes in lithium niobate crystals with femtosecond light pulses; Untersuchung lichtinduzierter Prozesse in Lithiumniobat-Kristallen mit Femtosekunden-Lichtpulsen

    Energy Technology Data Exchange (ETDEWEB)

    Beyer, O.

    2005-12-15

    For the realization of many applications with LiNbO{sub 3} a deeper understanding of nonlinear processes for high light intensities and the charge-carrier dynamics on short time scales is necessary. For the study in this thesis femtosecond pulses with a lifetime of {tau}{approx}200 fs are applied. By pump pulses ({lambda}{sub p}=388 nm) absorption changes are caused, which are detected time-resolvedly by probe pulses ({lambda}{sub r}=776 nm) respectively continuous light ({lambda}{sub r}=785 nm). For the absorption centers absorption cross sections of {sigma}{sub YY}{approx}9.2 x 10{sup -22} m{sup 2} for ordinarily {sigma}{sub Z}Z{approx}6.0 x 10{sup -22} m{sup 2} for extraordinarily polarized light of the wavelength {lambda}{sub r}=776 nm result.Polarization and wavelength dependence as well as the comparison with nanosecond pulses suggest that the absorption centers are small polarons, which exist already 400 fs after the excitation of the charge carriers. At holographic pump probe studies, which are sensitive both for absorption and for refractive-index changes, gratings with two pump pulses are generated and read out by one pump pulse. The time dependence of the diffraction efficiency of the transient grating in LiNbO{sub 3} exhibits first a symmetric maximum, the time width of which is compatible with the expectations from model calculations. Thereafter the diffraction efficiency decreases to a constant value in the picosecond range and decreases further on the nanosecond time scale. By illumination of iron-doped lithium niobate crystals with 1.5 {mu}m femtosecond pulses permanent refractive-index changes in the range {delta}n{approx}10{sup -3} ({lambda}=633 nm) are generated.

  13. Plasmonic laser nanoablation of silicon by the scattering of femtosecond pulses near gold nanospheres

    Energy Technology Data Exchange (ETDEWEB)

    Eversole, D. [University of Texas at Austin, Department of Biomedical Engineering, Austin, TX (United States); University of Texas at Austin, Center for Nanomaterials, Austin, TX (United States); Luk' yanchuk, B. [Data Storage Institute, Agency for Science, Technology and Research, Singapore (Singapore); Ben-Yakar, A. [University of Texas at Austin, Department of Biomedical Engineering, Austin, TX (United States); University of Texas at Austin, Center for Nanomaterials, Austin, TX (United States); University of Texas at Austin, Department of Mechanical Engineering, Austin, TX (United States)

    2007-11-15

    We present the fabrication of nanostructures ablated on silicon(100) by the plasmonic scattering of 780 nm, 220 fs laser pulses in the near-field of gold nanospheres. We take advantage of the enhanced plasmonic scattering of ultrashort laser light in the particle near-field to ablate well-defined nanocraters. Gold nanospheres of 150 nm diameter are deposited onto a silicon surface and irradiated with a single laser pulse. We studied the effect of laser polarization on the morphology of ablated nanostructures and estimated the minimum fluence for plasmonic nanoablation. When the polarization of the incident radiation is directed at a 45 angle into the substrate surface, a near-field enhancement of 23.1{+-}7.6 is measured, reducing the required silicon ablation fluence from 191{+-}14 mJ/cm{sup 2} to 8.2{+-}2.9 mJ/cm{sup 2}. Enhancements are also measured for laser polarizations parallel to the substrate surface when the substrate is angled 0 and 45 to the incident irradiation, giving enhancements of 6.9{+-}0.6 and 4.1{+-}1.3, respectively. Generated nanocrater morphologies show a direct imprint of the particle dipolar scattering region, as predicted in our theoretical calculations. The measured near-field enhancement values agree well with the maximum field enhancements obtained in our calculations. The agreement between theory and measurements supports that the nanocraters are indeed formed by the enhanced plasmonic scattering in the near-field of the nanoparticles. (orig.)

  14. Concentration measurements in molecular gas mixtures with a two-pump pulse femtosecond polarization spectroscopy technique

    Science.gov (United States)

    Hertz, E.; Chaux, R.; Faucher, O.; Lavorel, B.

    2001-08-01

    Recently, we have demonstrated the ability of the Raman-induced polarization spectroscopy (RIPS) technique to accurately determine concentration or polarizability anisotropy ratio in low-pressure binary molecular mixtures [E. Hertz, B. Lavorel, O. Faucher, and R. Chaux, J. Chem. Phys. 113, 6629 (2000)]. It has been also pointed out that macroscopic interference, occurring when two revivals associated to different molecules time overlap, can be used to achieve measurements with picosecond time resolution. The applicability of the technique is intrinsically limited to a concentration range where the signals of both molecules are of the same magnitude. In this paper, a two-pump pulse sequence with different intensities is used to overcome this limitation. The relative molecular responses are weighted by the relative laser pump intensities to give comparable signals. Furthermore, by tuning the time delay between the two-pump pulses, macroscopic interference can be produced regardless of the accidental coincidences between the two molecular temporal responses. The study is performed in a CO2-N2O gas mixture and the concentration is measured with and without macroscopic interference. Applications of the method in the field of noninvasive diagnostics of combustion media are envisaged.

  15. Towards circularly polarized (sub-) femtosecond XUV pulses for ultrafast pump-probe experiments

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Juergen; Chew, Soo Hoon; Kranjec, Mihael; Kleineberg, Ulf [LMU Muenchen, Physik-Department, Garching (Germany); Guggenmos, Alexander; Hofstetter, Michael [MPQ fuer Quantenoptik, Garching (Germany)

    2012-07-01

    Circularly polarized (CP) XUV radiation has been demonstrated to be a useful probe for the experimental investigation of electronic effects in magnetic materials such as magnetic circular dichroism, spin-polarized photoemission, magneto-optical Kerr-effect and others. On the laboratory scale, High Harmonic (HH) gas jet sources which inherently provide coherent and ultrashort linearly polarized XUV pulses in the sub-fs domain, suitable to study ultrafast dynamics, have emerged. In our setup we aim at incorporating in-house fabricated broadband transmission multilayer phase shifters into a laser driven 10kHz repetition rate HH Source in the 50-70eV photon energy range. To our knowledge only little investigation on such polarizers intended for use in HH radiation has been made so far. We examine our phase shifters regarding tunability of energy range, phase retardation, transmission efficiency and spectral bandwidth. For this purpose we use a home-made XUV flat-field spectrometer and a multilayer mirror based polarization analyzer. Combining the expected CP pulses with our TOF-PEEM and ARPES spectrometer will pave the way towards time resolved measurements of exchange-coupled electron dynamics.

  16. Revealing silent vibration modes of nanomaterials by detecting anti-Stokes hyper-Raman scattering with femtosecond laser pulses

    Science.gov (United States)

    Zeng, Jianhua; Chen, Lei; Dai, Qiaofeng; Lan, Sheng; Tie, Shaolong

    2016-01-01

    We proposed a scheme in which normal Raman scattering is coupled with hyper-Raman scattering for generating a strong anti-Stokes hyper-Raman scattering in nanomaterials by using femtosecond laser pulses. The proposal was experimentally demonstrated by using a single-layer MoS2 on a SiO2/Si substrate, a 17 nm-thick MoS2 on an Au/SiO2 substrate and a 9 nm-thick MoS2 on a SiO2-SnO2/Ag/SiO2 substrate which were confirmed to be highly efficient for second harmonic generation. A strong anti-Stokes hyper-Raman scattering was also observed in other nanomaterials possessing large second-order susceptibilities, such as silicon quantum dots self-assembled into ``coffee'' rings and tubular Cu-doped ZnO nanorods. In all the cases, many Raman inactive vibration modes were clearly revealed in the anti-Stokes hyper-Raman scattering. Apart from the strong anti-Stokes hyper-Raman scattering, Stokes hyper-Raman scattering with small Raman shifts was detected during the ablation process of thick MoS2 layers. It was also observed by slightly defocusing the excitation light. The detection of anti-Stokes hyper-Raman scattering may serve as a new technique for studying the Raman inactive vibration modes in nanomaterials.We proposed a scheme in which normal Raman scattering is coupled with hyper-Raman scattering for generating a strong anti-Stokes hyper-Raman scattering in nanomaterials by using femtosecond laser pulses. The proposal was experimentally demonstrated by using a single-layer MoS2 on a SiO2/Si substrate, a 17 nm-thick MoS2 on an Au/SiO2 substrate and a 9 nm-thick MoS2 on a SiO2-SnO2/Ag/SiO2 substrate which were confirmed to be highly efficient for second harmonic generation. A strong anti-Stokes hyper-Raman scattering was also observed in other nanomaterials possessing large second-order susceptibilities, such as silicon quantum dots self-assembled into ``coffee'' rings and tubular Cu-doped ZnO nanorods. In all the cases, many Raman inactive vibration modes were clearly

  17. Interaction of intense femtosecond laser pulses with KDP and DKDP crystals in the short wavelength regime

    Science.gov (United States)

    Duchateau, Guillaume; Geoffroy, Ghita; Belsky, Andrei; Fedorov, Nikita; Martin, Patrick; Guizard, Stéphane

    2013-10-01

    We investigate the electronic photo-excitation and relaxation mechanisms involved in the optical breakdown of potassium dihydrogen phosphate crystal (KH2PO4) and its deuterated form. The dynamics and spectroscopic properties of electron-hole pair formation are investigated using time-resolved measurement of the dielectric function, and luminescence spectroscopy. The non-common mechanical and electronic characteristics of these dielectric materials are revealed by the particular structure of ablation craters and also by the complex dynamics observed in the relaxation of excited carriers. This relaxation occurs in two steps, and varies with the initial carrier density and thus with the laser intensity. We show that the defect states play a key role in the excitation pathways, and also determine the relaxation stage. The latter also depends upon the initial amount of energy of the electron-hole pair after photo-excitation. A model based on kinetic equations describing the evolution of the different level populations allows us to successfully interpret and reproduce the experimental data.

  18. Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses

    Directory of Open Access Journals (Sweden)

    Rebecca Boll

    2016-07-01

    Full Text Available Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I21+. The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse.

  19. Characterization of the thermal refraction in ionic liquids induced by a train of femtosecond laser pulses

    Science.gov (United States)

    López Lago, E.; Nóvoa, J. A.; Nóvoa, D.; Michinel, H.; Cabeza, O.; Rodríguez, J. R.; Varela, L. M.

    2013-11-01

    We investigate the nonlinear refraction induced by a train of ultrashort laser pulses (repetition rate 80.75MHz) in a set of ionic liquids: [EMIM][BF4], [BMIM] [BF4], [HMIM] [BF4], [OMIM] [BF4] and [DMIM] [BF4]. Due to the high repetition rate, linear absorption processes are developed which cause a non local increase of temperature that generates an inhomogeneous and non local spatial variation of the refractive index. This effect is known as thermal refraction. The goal of this work is to characterize by z-scan the induced changes in the refractive index at λ=810nm and to determine the thermooptic coefficient of this liquids at this wavelength

  20. Stealth dicing of sapphire wafers with near infra-red femtosecond pulses

    Science.gov (United States)

    Yadav, Amit; Kbashi, Hani; Kolpakov, Stanislav; Gordon, Neil; Zhou, Kaiming; Rafailov, Edik U.

    2017-05-01

    The quality of the reflecting faces after dicing is critical for the fabrication of efficient and stable laser diodes emitting in the green-violet region. However, high-quality faces can be difficult to achieve for devices grown on a sapphire substrate as this material is difficult to cleave cleanly. We have therefore investigated a technology known as "stealth dicing". The technology uses a pulsed laser to damage a plane of material inside of the wafer due to multi-photon absorption instead of cutting through the wafer surface. If the damage is induced in a line of stress points, the sample can then be cleaved easily along the damaged plane to leave a high-quality surface. The use of this technique also reduces thermal damage and debris.