摘要：
In high-power laser system such as Petawatt lasers, the laser beam can be intense enough to result in saturation of nonlinear refraction index of medium. Based on the standard linearization method of small-scale self-focusing and the split-step Fourier numerical calculation method, we present analytical and simulative investigations on the hot-image formation in cascaded saturable nonlinear medium slabs, to disclose the effect of nonlinearity saturation on the distribution and intensity of hot images. The analytical and simulative results are found in good agreement. It is shown that, saturable nonlinearity does not change the distribution of hot images, while may greatly affect the intensity of hot images, i.e., for a given saturation light intensity, with the intensity of the incident laser beam, the intensity of hot images firstly increases monotonously and eventually reaches a saturation; for the incident laser beam of a given intensity, with the saturation light intensity lowering, the intensity of hot images decreases rapidly, even resulting in a few hot images too weak to be visible.
摘要：
In high-power laser system such as Petawatt lasers, the laser beam can be intense enough to result in saturation of nonlinear refraction index of medium. We present an analytical and simulative investigation of hot image formation in an intense laser beam through a saturable nonlinear medium slab based on Fresnel-Kirchhoff diffraction integral and the standard split-step Fourier method. The analytical results are found in agreement with the simulative ones. It is shown that, hot images can still form in an intense laser beam through a saturable nonlinear medium slab, additionally, the saturable nonlinearity does not change the location of hot images, while may decrease the intensity of hot images, i.e., the intensity of hot images decreases with the saturation light intensity lowering, and can stop to increase with the intensity of the incident laser beam heightening due to saturation of nonlinearity. Moreover, variations of intensity of hot images with the obscuration type and the slab thickness are discussed.
摘要：
Based on the angular spectrum representation of the Maxwell equations and the method of stationary phase, this paper presents the far-field analytical expression of a pulsed hollow Gaussian beam with constant waist width diffracted by the circular aperture, and the result can be simplified for the case of the paraxial propagation of pulsed Gaussian beam in the free space. Based on the analytical result, the influences of truncation parameter on the transverse intensity distribution of the pulsed beam are analyzed. Comparisons of normalized temporal intensity between the pulsed Gaussian beam and the fourth order pulsed hollow Gaussian beam are presented. We find that the spatial mode can induce the temporal shape changing. (C) 2014 Elsevier B.V. All rights reserved.
摘要：
We investigate here a new class of optical beams: modified hollow Gaussian beams (MHGBs) in strongly nonlocal nonlinear media (SNNM). A set of analytical expressions for the propagation properties is deduced and some numerical simulations are also carried out to illustrate the propagation properties. It is found that the evolution of the MHGBs in SNNM is periodical, which is the result of the competition between nonlinearity and diffraction. The second-order moment beam width of the MHGBs can keep invariant during propagation like a soliton when the input power equals the critical power, otherwise it varies periodically like a breather. However, the patterns of transverse intensity are always changing with the propagation distance increasing, which is different from solitons or breathers. It is also found that the evolution curve of on-axis intensity may manifest itself in a concave, a platform, or a Gaussian-like shape depending on the input power.
通讯机构：
[Lu, Shizhuan] H;Hengyang Normal Univ, Dept Phys & Elect Informat Sci, Hengyang 421002, Hunan Province, Peoples R China.
关键词：
Spectral switch;Pulsed hollow Gaussian beam;Complex analytic signal representation
摘要：
The spectral characteristics of a pulsed hollow Gaussian beam passing through a circular aperture are studied. Based on the vectorial Rayleigh diffraction integrals, the analytical expressions of the spectra for the complex analytic signal representation and for the complex amplitude envelope representation are derived, respectively, and the comparison between them is made. The influences of the truncation parameter and the beam order on the spectral shifts and on the spectral switches are illustrated. It is shown that the spectrum for the complex analytic signal representation and that for the complex amplitude envelope representation are obvious different as the pulse shorter than an optical period.
作者机构：
[李跃] Hunan Institute of Technology, Hengyang, 421002, China;[游开明; 朱亚培; 刘灿] Faculty of Physics and Electronic Information Science, Hengyang Normal University, Hengyang, 421002, China;[蒋刚毅] Faculty of Information Science and Technology, Ningbo University, Ningbo, 315211, China
通讯机构：
[Zhu, Y.-P.] F;Faculty of Physics and Electronic Information Science, Hengyang Normal University, Hengyang, China
作者机构：
[You Kai-Ming; Dai Zhi-Ping] Hengyang Normal Univ, Dept Phys & Elect Informat Sci, Hengyang 421002, Peoples R China.;[Zhang Shu-Min; Pang Zhao-Guang; Yang Zhen-Jun] Hebei Normal Univ, Dept Phys, Shijiazhuang 050024, Peoples R China.;[Zhang Shu-Min; Pang Zhao-Guang; Yang Zhen-Jun] Hebei Normal Univ, Hebei Adv Thin Film Lab, Shijiazhuang 050024, Peoples R China.
通讯机构：
[Yang Zhen-Jun] H;Hebei Normal Univ, Dept Phys, Shijiazhuang 050024, Peoples R China.
作者机构：
[戴志平; 游开明] Department of Physics and Electronic Information Science, Hengyang Normal University, Hengyang;Hunan;421002, China;[杨振军; 张书敏; 庞兆广] Hebei Province Key Laboratory of Advanced Thin Film Material, College of Physics and Information Engineering, Hebei Normal University, Shijiazhuang;Hebei
通讯机构：
[Yang, Z.] H;Hebei Province Key Laboratory of Advanced Thin Film Material, College of Physics and Information Engineering, Hebei Normal University, Shijiazhuang, Hebei, China
摘要：
Nanosecond-level pulses of specific shape is usually generated by stacking chirped pulses for high-power inertial confinement fusion driver, in which nonlinear imaging of scatterers may damage precious optical elements. We present a numerical study of the characteristics of nonlinear imaging of scatterers in broadband laser stacked by chirped pulses to disclose the dependence of location and intensity of images on the parameters of the stacked pulse. It is shown that, for sub-nanosecond long sub-pulses with chirp or transform-limited sub-pulses, the time-mean intensity and location of images through normally dispersive and anomalously dispersive self-focusing medium slab are almost identical; While for picosecond-level short sub-pulses with chirp, the time-mean intensity of images for weak normal dispersion is slightly higher than that for weak anomalous dispersion through a thin nonlinear slab; the result is opposite to that for strong dispersion in a thick nonlinear slab; Furthermore, for given time delay between neighboring sub-pulses, the time-mean intensity of images varies periodically with chirp of the sub-pulse increasing; for a given pulse width of sub-pulse, the time-mean intensity of images decreases with the time delay between neighboring sub-pulses increasing; additionally, there is a little difference in the time-mean intensity of images of the laser stacked by different numbers of sub-pulses. Finally, the obtained results are also given physical explanations.
