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1.
We report measurements of the extinction ratio (ER) of white light generated upon irradiation of BK7 glass by ultrashort (36 fs) laser pulses with incident power approximately 10(3) times larger than the critical power for self-focusing. At low incident powers, the continuum is symmetric about the incident laser wavelength; at high powers it becomes broader and distinctly asymmetric towards the blue side. We observe that ER degrades by 100-fold after the onset of multiphoton-induced free-electron generation (at incident intensity approximately 2 TW cm-2), which also corresponds to the onset of asymmetry in white-light spectra. 相似文献
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Work supported by Russian Fund for Basic Research, Project 93-02-14271. 相似文献
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G. P. Agrawal 《Optics & Laser Technology》1981,13(3):141-144
The atmospheric propagation of a sequence of short, intense laser pulses is considered. The pulses propagate in a self-induced low-density channel, the effectiveness of which depends on a set of three variables. Using a simple model for the laser-atmosphere interaction, the range of successive pulses is determined by numerical solutions to the paraxial wave equation. The dependence of the length, width, and depth of the created channel on the important variables is explored. 相似文献
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The long light filaments generated in air by powerful ultrashort laser pulses, previously attributed to self-channeling, were investigated by use of gigawatt pulses from a Ti:sapphire chirped-pulse-amplification laser system. A filament contained only a small fraction of the pulse energy and always ended at the diffraction length of the beam (~100 m), independently of the pulse energy. These features are explained by the moving-focus model, which is presented as an alternative to the self-channeling model. Computer simulations involving ionization of the air also support the moving-focus model. 相似文献
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Reported are interactions of high-intensity laser pulses ( lambda = 810 nm and I=3x10(18) W/cm(2)) with plasmas in a new parameter regime, in which the pulse duration ( tau = 29 fs) corresponds to 0. 6-2.6 plasma periods. Relativistic filamentation is observed to cause laser-beam breakup and scattering of the beam out of the vacuum propagation angle. A beam of megaelectronvolt electrons with divergence angle as small as 1 degrees is generated in the forward direction, which is correlated to the growth of the relativistic filamentation. Raman scattering, however, is found to be much less than previous long-pulse results. 相似文献
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The results are presented on the observation of X-ray spectra of plasmas formed by 250-psec laser pulses focusing on Ti, Fe and Cr targets. Specific characteristics of the spectra obtained are explained on the basis of a transient heating model. 相似文献
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Coherent dynamics of multiphoton excitation of molecular vibrational modes by subpicosecond IR laser pulses differs greatly from that of picosecond pulse excitation. The resonance response of a molecule is primarily determined by the power broadening rather than the laser carrier frequency. Selective excitation of high vibrational levels is possible with the use of subpicosecond pulses. 相似文献
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We propose a technique for time resolution of the polarization state of ultrashort light pulses that also provides the overall time-varying phase of the pulse. This method is based on a spectral polarimetric analysis of the pulse after propagation through a Kerr medium. The feasibility of this method is demonstrated both numerically and experimentally. 相似文献
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The phase modulation of intense ( I = 10(18) W/cm(2)) ultrashort laser pulses ( tau(p) = 70 fs) after reflection from steep, dense plasmas has been temporally resolved for the first time in particle-in-cell simulations. The position of the turning point from where the pulse reflects has been compared to the phase modulation, over a range of angles of incidence. At normal incidence or s polarization the phase modulation almost exactly represents the movement of the turning point due to the light pressure. As the angle of incidence is increased for p polarization, the simple Fresnel relationship between phase modulation and displacement of the reflection position, Delta phi(t) = -2k(0)Delta x(t)cos theta(0), increasingly breaks down. 相似文献
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Previous conclusions on the propagation of ultrashort light pulses in a resonant medium are found to be in error. There is no physical basis for rejecting the nd u and dn u solutions. 相似文献
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A magnetic-dipole vortex is generated in the behind of an ultraintense and ultrashort laser pulse in a near critical density plasma. The vortex is self-sustained by its magnetic field pressure which expels background electrons, and resulting sheath field accelerates electrons to drive high amplitude electric current inside the vortex. The electron energy spectra shows nonthermal distribution with relatively high energy. The vortex is stable for a long period since it is in the electromagnetic equilibrium, whose structure and characteristics are explained by a simple analytical model. 相似文献
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理论研究和数值模拟发现入射光和反射光在低密度等离子体中形成的干涉场可以产生深度的等离子体密度调制. 对于中等强度的入射光,譬如1015W/cm2 ,产生密度调制的时间尺度在几十个光周期的范围. 这样的等离子体密度调制可以起类似布拉格反射镜的 作用,使得后面的入射光在临界面以下的区域产生相位反射. 因为密度调制的周期是光在等 离子体中波长的一半,其产生的反射率可以接近100%. 相位反射也可以在不均匀的低密度 等离子体中产生,它可以极大地减少等离子体对光的吸收,因此在惯性约束核聚变中需要考 虑到它的影响.
关键词:
相位反射
密度调制
激光等离子体
粒子模拟 相似文献
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We study experimentally the behavior of the spectrum shape and Stokes frequency shift of stimulated Brillouin scattering (SRS)-compressed
radiation within a broad range of incident-laser-pulse intensities from the threshold up to eight times the threshold values.
We show that, at pulse compression of reflected radiation to subnanosecond durations (smaller than inverse spontaneous line
widths), its spectrum monotonously shifts with increase in the exciting light intensity such that its Stokes shift decreases.
At intensities increasing four times the threshold, the spectrum splits and acquires a twohumped shape, which is explained
by the phase modulation near the SBS resonance. We construct an analytical model of self-phase modulation in SBS compression,
describing the spectral splitting and chirping formation. 相似文献
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We analyze the effect of the varying transverse field profile associated to the linear propagation of ultrashort pulses along an optical waveguide. This effect has been systematically ignored in the literature. Based on numerical calculations, we analyze the magnitude of such effect to justify the use of the standard model, at least for pulses larger than about 5–7 optical carrier cycles. Theoretical considerations are presented about the extreme difficulty of even establishing the initial mathematical condition of the propagation problem under such circumstances. 相似文献
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A. Sagisaka H. Honda K. Kondo H. Suzuki K. Nagashima T. Kawachi A. Nagashima Y. Kato H. Takuma 《Applied physics. B, Lasers and optics》2000,71(4):549-554
X-ray spectra from nitrogen clusters irradiated with ultrashort laser pulses are reported. The line spectra of H-like and
He-like nitrogen ions have been observed by irradiation with 100 fs, 800 nm pulses at 7×1017 W/cm2 irradiance. The generation of highly charged ions of N6+ and N7+ is explained by the optical field-induced ionization and the subsequent collisional ionizations in the clusters. The He-δline
has anomalously high brightness compared to other He-like lines. It is ascribed to charge exchange, which preferentially populates
the n=5 level of N5+.
Received: 7 October 1999 / Published online: 23 February 2000 相似文献