共查询到20条相似文献,搜索用时 0 毫秒
1.
Smoothing by spectral dispersion (SSD) is employed to smooth the laser irradiation in inertial confinement fusion and its effectiveness can be affected by nonlinear effects because of some special modulation of itself. In the paper, the spatial evolution dependent on the time period of the sinusoidal phase modulated laser from SSD is investigated theoretically and numerically when the modulated laser is affected by the small-scale self-focusing(SSSF). Although the effects of SSSF for SSD's modulation and noise can be eliminated by temporal average, the time-dependent modulation intensity of laser with SSD or noise will increased quickly. The results show that the low-frequency spatial modulation from SSD sometimes can affect beam quality bigger than the small-scale noise because of its controlled small initial amplitude. The simulation results agree with the theoretical analysis. 相似文献
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Sergey Mironov Vladimir Lozhkarev Grigory Luchinin Andrey Shaykin Efim Khazanov 《Applied physics. B, Lasers and optics》2013,113(1):147-151
An original method for suppressing small-scale self-focusing in laser beams with the intensity of several TW/cm2 has been proposed, justified theoretically and verified in experiment. The idea underlying the method is to filter spatial perturbations during beam propagation in free space. 相似文献
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Yoshio Hayasaki Maki Nishitani Hidetomo Takahashi Hirotsugu Yamamoto Akihiro Takita Daichi Suzuki Satoshi Hasegawa 《Applied Physics A: Materials Science & Processing》2012,107(2):357-362
In holographic femtosecond laser processing, diffractive parallel pulses are distorted by phase discontinuities and mutual interference between the neighborhoods in the reconstructed image of a Fourier computer-generated hologram when the interval is smaller than the beam diameter. We investigated holographic fabrication on a glass surface using parallel pulses with different intervals. We found the closest parallel pulses with sufficient separation to avoid mutual interference in holographic femtosecond laser processing. The minimum interval was 2.8 times larger than the diffracted beam diameter. The experimental results were also supported by a computer simulation. Our findings will be very useful in the design of holographic laser processing systems. 相似文献
4.
Mínguez-Vega G Lancis J Caraquitena J Torres-Company V Andrés P 《Optics letters》2006,31(17):2631-2633
We report spatial and temporal dispersion compensation for fan-out of femtosecond pulses with a low-frequency diffraction grating by means of a hybrid diffractive-refractive lens triplet. In this way, we achieve a multifocal light structure with nearly diffraction-limited light spots even for 20 fs pulse duration. The spatial chromatic compensation, which drastically reduces the lateral walk-off of the various spectral components, also allows us to improve the available bandwidth at the dispersion-compensated diffraction orders. In fact, the temporal width of the output pulse is essentially limited by the group-delay dispersion term, which is shown to be small. The high spatiotemporal resolution provided by our proposal permits parallel multifocal processing of materials with femtosecond pulses. 相似文献
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Using molecular-dynamics, we study the thermodynamic evolution of a simple two-dimensional Lennard–Jones system during laser ablation for pulse durations ranging from 200 fs to 400 ps. We briefly review results previously obtained for fs pulses where the evolution of the material was shown to be solely a function of the locally absorbed energy (provided that only thermal effects are important), i.e., is adiabatic. For longer pulses (100 and 400 ps) the situation becomes more complex, as the relaxation path also depends on the position in the target and on the timescale on which expansion occurs. We show that, in contrast to fs pulses, the material ejected following ps laser irradiation does not enter the liquid–vapor metastable region before ablation occurs, hence showing that phase explosion is not the dominant mechanism in this regime. Following on from previous work, we propose that trivial fragmentation is the main ablation mechanism. PACS 79.20.Ds; 79.20.Ap; 61.80.Az 相似文献
6.
The dynamics of the femtosecond pulse propagation in a plasma channel is investigated by the pumpprobe longitudinal diffractometry and second harmonic generation frequency-resolved optical gating (SHGFROG) technique. The spatial characteristics, corresponding to the electronic density and the size of the channel, can be observed by the recorded ring pattern, and the spectral and temporal characteristics are recorded by the SHG-FROG traces. The spatiotemporal characteristics will help us to better understand the dynamics of the plasma induced by the femtosecond pulse and the femtosecond pulse propagating in the plasma channel. 相似文献
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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 (P 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. 相似文献
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S. A. Aseev B. N. Mironov V. G. Minogin S. V. Chekalin 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(7):931-933
A combination of femtosecond laser techniques and nanomicroscopy creates promising new possibilities for studying both matter and a whole number of ultrafast physical processes. The results obtained at the Institute for Spectroscopy as a result of developing a new area of femtosecond nanomicroscopy are presented. 相似文献
12.
Martínez-Cuenca R Mendoza-Yero O Alonso B Sola ÍJ Mínguez-Vega G Lancis J 《Optics letters》2012,37(5):957-959
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. 相似文献
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L. A. Golovan I. O. Djun A. E. Dokukina S. V. Zabotnov A. A. Ezhov P. K. Kashkarov N. E. Maslova I. O. Ostapenko V. I. Panov V. U. Timoshenko 《Bulletin of the Russian Academy of Sciences: Physics》2009,73(1):39-41
It is shown by atomic force microscopy that nanoparticles formed upon ablation of surface of single-crystal and porous silicon by femtosecond laser pulses have a lateral size from several tens to 200 nm and a height from 2 to 30 nm. Dependences of the nanoparticle sizes and surface concentrations on the residual pressure, which demonstrate the gas atmosphere influence on the nanoparticle formation, are obtained. 相似文献
15.
A. V. Kuznetsov A. S. Kuzakov E. F. Martynovich 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(1):64-67
The formation of fluorescent channels with color centers in LiF crystals under the action of the multiple filamentation of femtosecond laser pulses is studied experimentally and theoretically for pulse powers around four orders of magnitude higher than the critical self-focusing value. 相似文献
16.
A. A. Zemlyanov Y. E. Geints 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):349-357
The generic scenario of intense femtosecond laser pulse propagation in the
air from the viewpoint of evolution of its integral effective parameters
(energy transfer coefficient, effective radius, effective duration, limiting
angular divergence) is considered. The analysis of variation of the
effective parameters along the propagation path in the single and multiply
filamentation scenarios based on numerical calculations is presented. It is
shown that the process of self-action of the ultrashort radiation is
characterized by the formation in a medium of the nonlinearity layer, after
which optical pulse propagates quasi-linearly with the limiting angular
divergence that depends mainly on initial pulse power. The effective pulse
temporal duration and the effective beam radius increase after the passage
through the nonlinearity layer, and their values are mostly determined by
the initial beam power also. The coefficient of energy transmission of
femtosecond laser radiation is lower than in the linear medium and has a
tendency to decrease with the increase of the pulse power. 相似文献
17.
Ultrafast temperature relaxation processes in Au film including two temperature relaxation and thermal diffusion relaxation with femtosecond laser pulse excitation were investigated numerically by Finite Element Method (FEM). With the temperature dependent thermal parameters, the full 2D temperature field evolution in picosecond and nanosecond domains were obtained. It is proposed that the heat transfer depth can be alternatively localized or enhanced by the distinct temperature relaxation mechanisms. Moreover, the effect of laser parameters and Au film thickness and surface reflectivity on the two temperature relaxation time were analysed. 相似文献
18.
Self-compression of high-intensity femtosecond pulses has been observed in a number of atomic and molecular gases and solid bulk material. The evolution of the femtosecond pulse parameters during the self-compression has been studied under a variety of experimental conditions. Generation of spatiotemporal solitons has been achieved by the combined action of self-compression and self-focusing. 相似文献
19.
The chirped optical pulses undergoing self-focusing and splitting into multiple filamentation passing through a Kerr medium—carbon
disulfide (CS2) are studied experimentally and numerically. At the particular spatial position, modulation growth takes place from the experimental
result. The process of modulation growth with different pulsed chirp is analyzed. It is found that with the pulsed chirp increasing
(equal to the pulse width increasing), modulation growth of chirped optical pulses is delayed and the average input power
also increases. The simulation results are in agreement with the experimental results. 相似文献
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