共查询到20条相似文献,搜索用时 0 毫秒
1.
Feng S Winful HG 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》2000,61(1):862-873
We present a model of isodiffracting single-cycle and few-cycle ultrashort electromagnetic pulses. The model is based on exact solutions of the time-dependent paraxial wave equation with space-time coupling effects included. The spatiotemporal structure of these pulses is characterized by a scaling parameter which relates off-axis pulse shapes to the axial temporal waveforms. Depending on the spectrum a pulse may transform itself from a single-cycle pulse to a multicycle pulse along the radial coordinate. This model is also used to describe recirculating pulses in a curved mirror cavity resonator. The Gouy phase shift contributes an absolute phase that results in a pulse-to-pulse temporal instability. 相似文献
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Two-photon conductivity in GaAs and CdS0·5Se0·5 were investigated with modelocked Nd:glass laser pulse excitation, with a view to determine their suitability for picosecond pulsewidth measurement. The contrast ratio using GaAs as twophoton conductor was 1.8 and it increased to 2.4 when CdS0·5Se0·5 was used. The improved contrast ratio in the case of CdS0·5Se0·5 was partly due to the improved resolution of the crystal (2 ps) and partly due to the extended square-law region. 相似文献
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The purpose of this paper is to study the temporal broadening and temporal scintillations of ultrashort optical pulses. We present the general formulation of the temporal broadening and scintillation index of ultrashort (femtosecond) space-time Gaussian pulses propagating through weak optical turbulence and derive analytic approximations for the near- and far-field zones. We then apply the results to cross-link, uplink and downlink communication channels in a laser satellite communication system. We show that both the temporal broadening and scintillations depend mainly on the strength of optical turbulence and the outer scale and increase with these parameters. We also show that 10-30 fs pulses broaden significantly more and have greater scintillations than wide pulses. Furthermore, the horizontal and vertical/slant path temporal broadening are identical and the temporal scintillation indices exhibit similar behaviour. 相似文献
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Nicholson JW Yablon AD Yan MF Wisk P Bise R Trevor DJ Alonzo J Stockert T Fleming J Monberg E Dimarcello F Fini J 《Optics letters》2008,33(18):2038-2040
Femtosecond fiber lasers together with nonlinear fibers are compact, reliable, all-fiber supercontinuum sources. Maintaining an all-fiber configuration, however, necessitates pulse compression in an optical fiber, which can lead to nonlinearities for subhundred femtosecond, nanojoule pulses. In this work we show that using large-mode-area fibers for pulse compression mitigates the nonlinearity, resulting in compressed pulses with significantly reduced satellite pulses. Consequently, supercontinua generated with these pulses are shown to have as much as a 10 dB increase in coherence fringe contrast. By using a hybrid highly nonlinear fiber-photonic crystal fiber, the continuum can be extended to visible wavelengths while still maintaining high coherence. 相似文献
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A. M. Zheltikov 《JETP Letters》2009,90(2):90-95
Multibeam ionization of gas and condensed-phase media with interfering ultrashort laser pulses can help to substantially increase the maximum field intensity and the density of free electrons attainable in the focus of the laser field relative to the regime of single-beam ionization. Multibeam ionization schemes offer new solutions for laser micro- and nanomachining, micro- and nanosurgery, spectral and temporal transformation of ultrashort light pulses, as well as remote sensing of the atmosphere. Subfemtosecond changes in the local refractive index induced in the regime of multibeam tunneling ionization enable the high-speed switching of optical signals. 相似文献
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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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We have applied photoexcitation by ultrashort laser pulses to single crystal thin CrO(2) films to trigger coherent transient magnetization rotation on a subnanosecond time scale, in macroscale single domains. Moreover, by applying the photoexcitation by pairs of temporally separated pump pulses, the transient precession of the magnetization can be phase controlled, depending on the time separation between the pulses. The mechanism behind the photoexcitation originates from the modulation of the magnetocrystalline anisotropy by nonthermal hot electron spins. 相似文献
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Pulse trapping by ultrashort soliton pulses in optical fibers across zero-dispersion wavelength 总被引:1,自引:0,他引:1
A new phenomenon of pulse trapping by the ultrashort soliton pulse of an optical fiber has been experimentally observed. The trapped pulse in the normal-dispersion region copropagates with the soliton pulse in the anomalous-dispersion region along the fiber, and the wavelength of the trapped pulse is shifted to satisfy the condition of group-velocity matching. The wavelengths of the soliton pulse and the trapped pulse change almost continuously as the power of the soliton pulse is varied. Almost perfect conversion efficiencies are observed for soliton self-frequency shift and pulse trapping. 相似文献
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A nonlinear optical medium results by the collective orientation of liquid crystal molecules tightly coupled to a transparent photoconductive layer. We show that such a medium can give a large gain; thus, if inserted in a ring cavity, it results in an unidirectional optical oscillator. We report new dynamical regimes characterized by the generation of spatiotemporal pulses, localized in three dimensions and arising from the random superposition of many longitudinal and transverse modes with different frequencies. 相似文献
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The optical rectification of ultrashort laser pulses with a titled amplitude front in LiNbO3 crystal is studied theoretically. It is shown that the results of calculation are in reasonable agreement with experimental data. 相似文献
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相干合成技术是超快光学领域的重要研究方向之一.当单路脉冲激光的连续谱超过一个倍频程时,精确控制其光谱相位(色散管理)是获得亚周期超短脉冲激光的关键.由于常见的脉冲压缩系统存在光谱带宽限制,因此多通道相干合成技术受到了广泛的关注.本文将充气空心光纤展宽后的超倍频程连续光谱分波段独立压缩,并利用平衡光学互相关方法锁定子脉冲之间的相位延迟,获得了4.1 fs的合成脉冲.实验结果表明相干合成技术在高能量亚周期超快光场调控中存在优势. 相似文献
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The spectral polarization of an ultrashort pulse is fully controlled by a novel pulse shaper design, including three liquid-crystal spatial light modulator arrays at three different orientations. The added degree of controllability permits generation of previously unattainable pulse shapes, with possible applications in multidimensional spectroscopy, coherent control, and ultrafast polarization gating. 相似文献
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Siders C.W. Le Blanc S.P. Babine A. Stepanov A. Sergeev A. Tajima T. Downer M.C. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1996,24(2):301-315
All-optical ultrafast time-resolved plasma diagnostics of plasma-based accelerators (PBA's) are described, with emphasis on the laser wakefield accelerator (LWFA). Specifically, the diagnostic techniques involve replacing the trailing particle bunch in the LWFA with a trailing photon bunch: a weak ultrashort laser pulse. Since this photon pulse is derived directly from the intense pump pulse, practical difficulties such as synchronization and dephasing are eliminated. The interaction of the photon bunch with the plasma wake is essentially a simple time-domain shift in optical phase, which can produce both “DC” phase shifts and frequency blue/red-shifting of the probe pulse spectrum. These phase/frequency shifts are recorded in frequency domain interferograms, which are formally equivalent to time-domain holograms. Experimental results of longitudinal plasma density profiling are presented in which plasma density oscillations (Langmuir waves) in the wake of an intense (Ipeak~3×10 17 W/cm2) laser pulse (~100 fs) were measured with ultrafast time resolution. Phase shifts consistent with large amplitude (~80%) density oscillations at the electron plasma frequency were observed in a fully tunnel-ionized He plasma, corresponding to longitudinal electric fields of ~10 GV/m. Strong radial ponderomotive forces enhance the density oscillations. Finally, proposed single-shot schemes for simultaneous transverse and longitudinal profiling are discussed 相似文献
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Using an optical technique we generate and detect picosecond shear and quasishear coherent acoustic phonon pulses in the time domain. Thermoelastic and piezoelectric generation are directly achieved by breaking the sample lateral symmetry using crystalline anisotropy. We demonstrate efficient detection in isotropic and anisotropic media with various optical incidence geometries. 相似文献
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E. Yu. Loktionov A. V. Ovchinnikov Yu. Yu. Protasov D. S. Sitnikov 《Bulletin of the Lebedev Physics Institute》2010,37(3):82-84
Optical gas-dynamic processes occurring in polymeric targets ((CH2O)
n
, (C2F4)
n
) exposed to ultrashort laser pulses (τ
0.5 ∼ 45 − 70 fs; λ
I,II,III
= 266, 400, 800 nm; and E/S ∼ 0.1 − 40 J/cm2 at r
0 ∼ 20 μm) were studied under normal conditions and in vacuum (p ∼ 10−2 Pa). The dynamics of the mass flow from the target surface (m′ ∼ 10−5 − 10−4 g/J) was studied and the spectral-energy thresholds of laser ablation, the electron density distribution (n
e
∼ 1014 − 1018 cm−3), the mass-averaged velocity of the material flow from the target surface (∼ 103 m/s), and the chemical composition and average temperature in the near-surface plasma formation (T ∼ 5000 K) were determined using interference microscopy, emission spectroscopy, and shadowgraphy. 相似文献
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Fourth-order dispersion suppression of ultrashort optical pulses by second-order dispersion and cosine phase modulation 总被引:1,自引:0,他引:1
A technique for significantly suppressing severe fourth-order dispersion of ultrashort optical pulses in long-distance transmission is analyzed by use of the quadratic phase from the excess second-order dispersion of the fiber link in conjunction with synchronously applied cosine phase modulation of temporally stretched pulses. Numerical simulation predicts much improved transmission of 250-fs pulses at 5-10-GHz repetition rates over ~100 km of fiber by pi-3.5pi phase modulation. 相似文献
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We report the complete spatiotemporal characterization of ultrashort light pulses by use of a self-referencing device based on shearing interferometry in the space and frequency domains. The apparatus combines a spatially resolved spectral shearing interferometer with a spectrally resolved spatial shearing interferometer. The electric field as a function of one transverse spatial coordinate and time is obtained from a single experimental trace by means of a direct and fast algebraic phase reconstruction algorithm. The method has been tested in several common laboratory situations. 相似文献