HMO in geometrical optics

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Kerr效应对非线性J-C模型辐射谱的影响

研究了Kerr介质腔中非线性J-C模型的辐射谱.导出了双模初始光场处于任意量子态时辐射谱的计算公式,给出了光场处于数态、相干态和压缩真空态时的数值结果,讨论了Kerr效应和初始场强对辐射谱的影响.发现在光子数态的情况下,Kerr效应使低频峰增强、高频峰减弱,并使各峰向右移动.在初始腔场为较强的相干态时,原子辐射谱明显地分成两个拱形的梳状峰群,Kerr效应的增强使左侧峰群增高,右侧的边峰受到抑制.在压缩真空态情况下,边带峰只出现在中心频率双峰的左侧,随Kerr效应和初始场的增强,边峰个数也随之增多.无论哪种情况都破坏谱结构的对称性,在强场条件下Kerr效应的影响更加显著.     

高斯光束在克尔型非线性介质中演化的奇异特性

由光束在克尔型吸收介质中传输的非线性薛定谔方程出发,推导了高斯光束注入介质后满足的耦合方程。在不考虑高阶展开项的前提下,将介质分为无吸收、有吸收两种情况,对脉冲的腰斑半径的演化进行了解析分析,得到注入克尔型非线性介质中的高斯光束,形成“孤波”必须满足光束在束腰处注入,介质没有吸收的条件;当考虑高阶展开项时,通过数值分析发现,无论介质是否存在吸收,光束传输不存在“孤波”形式,而是在注入强度的控制之下。当注入强度较小时,自聚焦过程是它的一个主要结果。但当注入脉冲的强度增加后,除了腰斑半径不为零的区间增加,光束仍保持聚焦的正常现象之外,存在一个阈值。当注入强度超过此阈值时,腰斑半径随着距离的增加而快速增加,聚焦趋势根本就不存在。     

Surface solitons at the interface between semi-infinite linear and thermal nonlinear optical media

We investigate numerically surface-wave solitons occurring at the interface between semi-infinite linear and thermal nonlinear optical media, with the refractive index of the linear medium being greater than that of the nonlinear medium (in the absence of light). We find that the threshold energy flows of the existence of the surface solitons depend on the linear refractive index difference of the two media. Their fitting empirical formula has been obtained. Furthermore, we elucidate that the optical beams propagating in thermal nonlinear optical media, either as a single surface soliton or as a dipole surface soliton, can be attracted to the surface, even when launched from far away.     

Surface waves in a crystal with switching Kerr nonlinearity

In this paper, we explore transverse electric surface waves propagating along the crystal with jump change of Kerr nonlinearity in dependence on field amplitude. The dielectric permittivity in the proposed model of nonlinearity is characterized by abruptly changing unperturbed dielectric constant and Kerr nonlinearity coefficient from one value to another when field amplitude exceeds the threshold value of the switching field. This allows to find exact solutions of model equations in different cases of nonlinearity signs, and to obtain the dependence of wave characteristics, including total power flux, on effective refractive index in explicit form. Such solutions describe two new types of nonlinear surface waves with specific structure depending on electric field amplitude. We derive the conditions of surface domain formation. It is found that the largest percentage of radiation is concentrated within the domain.     

Low-threshold bistable reflection assisted by oscillating wave interaction with Kerr nonlinear medium

Owing to the enormously enhanced oscillating wave, a minute variation of the incident light intensity will give rise to a change in the dielectric constant of the Kerr nonlinear medium and lead to a bistable reflection with an ultra-low threshold intensity, which is closely related to the angle of incidence and the thickness of the Kerr nonlinear medium. The criterion for the existence of optical bistability is derived. Our bistability scheme is simple and not limited to the TM-polarization.     

Incoherently coupled soliton pairs in nonlocal nonlinear media

We show that incoherently coupled soliton pairs can exist in nonlocal Kerr-type nonlinear media. Such solitons can propagate in bright--bright, dark--dark, and gray--gray configurations. When the nonlocal nonlinearity is absent, these bright--bright and dark--dark soliton pairs are those observed previously in local Kerr-type nonlinear media. Our analysis indicates that for a self-focusing nonlinearity the intensity full width half maximum (FWHM) of the bright--bright pair components increases with the degree of nonlocality of the nonlinear response, whereas for a self-defocusing nonlinearity the intensity FWHM of the dark--dark and gray--gray pair components decreases with the increase in the degree of nonlocality of the nonlinear response. The stability of these soliton pairs has been investigated numerically and it has been found that they are stable.     

级联介质的空间排布对光场特性的影响

基于菲涅尔衍射原理，应用傅里叶变换方法，从理论上推导了高斯光束经级联非线性介质传输后任意位置处光场分布的解析表达式,研究了光场峰值强度、峰值出现的位置以及光束的束宽和调制因子等参量在级联介质中的变化规律。结果表明：随着非线性效应的增强，光场峰值强度逐渐增大，峰值距离逐渐缩短，光束束宽不断减小而调制因子逐渐增大。在介质排布中要尽量错开光束峰值位置，采用均匀排布方案虽然可以降低元件受损的风险，但还需对介质均匀配置的间距进行有效优化。     

Spatiotemporal instability in dispersive nonlinear Kerr medium with a finite response time

We investigated the spatiotemporal modulation instability (MI) in a medium with a non-instantaneous Kerr response in which the nonlinear contribution to the refractive index is governed by a relaxing Debye type equation. The expression for the MI gain spectrum in non-instantaneous Kerr medium is obtained, which clearly reveals the influence of the finite time of the nonlinear response (relaxation effect) on the spatiotemporal MI. It is shown that, due to the relaxation effect, the spatiotemporal MI can appear for the case of anomalous dispersion and defocusing nonlinearity, while it cannot appear in instantaneous Kerr medium for the same case, and a new MI gain spectrum appears, adding to the conventional MI gain spectrum similar to that in an instantaneous Ker medium. In addition, the bandwidth of MI gain spectrum is extended and the maximum MI gain is reduced with increasing of the relaxation time. Interestingly, spatiotemporal MI can appear for any spatial frequencies in non-instantaneous Kerr medium for any combination of dispersion and nonlinearity. We have performed an experiment of MI in carbon disulfide (CS₂), a typical non-instantaneous Kerr medium, which shows quantitative agreement with the theoretical analyses.     

Induced focusing and conversion of a Gaussian beam into an elliptic Gaussian beam

We have presented an investigation of the induced focusing in Kerr media of two laser beams, the pump beam and the probe beam, which could be either Gaussian or elliptic Gaussian or a combination of the two. We have used variational formalism to derive relevant beam-width equations. Among several important findings, the finding that a very week probe beam can be guided and focused when power of both beams are well below their individual threshold for self-focusing, is a noteworthy one. It has been found that induced focusing is not possible for laser beams of any wavelength and beam radius. In case both beams are elliptic Gaussian, we have shown that when power of both beams is above a certain threshold value then the effective radius of both beams collapses and collapse distance depends on power. Moreover, it has been found that induced focusing can be employed to convert a circular Gaussian beam into an elliptic Gaussian beam.     

环形光斑激光束在非线性克尔介质中的分束现象

对于非线性克尔介质中的环形斑调制光束,通过数值求解非线性Schrdinger方程,发现当入射光强度超过一定值时,光束在传输过程中发生分束现象.对光分束的阈值、光分束与环半径及半宽度的关系、分束光的特点,以及自聚焦焦点上光强度的横向分布与光分束之间的关系进行了详细的讨论 关键词： 环形光斑 克尔介质 非线性传输 光分束     

非线性光学五十年

文章简要回顾了非线性光学的诞生以及早期的发展,包括二次谐波,激光和频和差频现象,受激拉曼散射,以及激光的一些自作用行为等,介绍了非线性光学的一些重要研究成果和应用,包括非线性光谱学,位相共轭和自适应光学,相干非线性光学以及高次谐波等,最后对非线性光学当前和未来研究热点作了总结和展望.     

一维非均匀Kerr介质的传输矩阵算法

研究了一维非均匀Kerr介质的子层逆向递推传输矩阵算法,给出了数值实现方案.此方法可以方便而精确地模拟非均匀Kerr介质的传输行为.应用此算法模拟一维Kerr缺陷光子晶体的光学双稳开关过程时, 得出了和非线性时域有限差分方法相一致的结果.     

手性分子介质非线性光学研究新进展

文章介绍了近年来手性分子介质及材料的非线性光学性质的研究状况，综述了手性分子非线性微观模型的使用情况，给出了一些典型的二阶、三阶非线性光学实验结果，用这些微观模型可以正确地分析这些结果．同时指出了未来研究的趋势，及研究成果可能应用的领域．     

Divergence of geometrical optics series at the boundary of its applicability: An analytical example in elementary functions (2D Gaussian beam in free space)

An analytical example in elementary functions is presented (2D Gaussian beam diffraction in free space), which demonstrates the divergence of the geometrical optics (GO) series when the conditions for its applicability are violated. This example shows that accounting for higher terms in GO power series leads to divergence and therefore becomes completely useless beyond the boundaries of GO applicability.     

在克尔媒质中原子和光场的量子信息保真度

讨论了在克尔媒质中原子与光场相互作用及拉曼相互作用时原子、光场和整个系统的量子信息保真度的时间演化过程。研究光场的光强、失谐量及克尔参量对保真度的影响。研究表明，当拉比振荡频率与光子数成正比时保真度表现出周期性的等幅振荡。光强的增加将使保真度下降，失谐量的增加会提高保真度，克尔媒质也对保真度的演化产生影响。失谐量为0，克尔参量为0．5g时以及在能级简并的拉曼过程中保真度表现出很规则的等幅周期振荡。     

克尔效应对高斯光束质量M2因子的影响及抑制

用分步傅里叶方法计算了高斯光束在克尔介质中的传输过程,采用最小均方根办法对光场进行二项式曲线拟合得到光束质量因子,计算结果表明：当B积分在2rad以内,克尔效应越强则它对因子影响越大;同时,它的这种影响能力也受到光束宽度和光束腰平面到克尔介质的距离的两个因素的影响,即光束越宽,影响越小,距离越大,影响反而较小;最后,基于B积分的可叠加性,提出用具有负非线性折射率系数的非线性介质来补偿正克尔效应、降低光束因子,并指出两端补偿是最优的方式之一.     

被克尔介质包围的A型三能级原子的粒子布居几率

本文研究了被克尔(Kerr)介质包围的\型三能级原子的粒子布居几率随时间的演化,分析了光场频率与原子本征频率间的单光子失谐量和克尔介质对粒子布居几率的影响.     

克尔介质中艾里孤子的形成及控制

利用分步傅里叶法,数值研究了艾里光束在自聚焦克尔非线性介质中的传输。结果表明,当较强的非线性作用于艾里光束时,主瓣能量在传输过程中会发生脱落形成具有周期振荡的空间孤子。随着非线性的增强,该孤子的振荡周期与半高宽都减小。调节艾里光束的入射角度时,脱落孤子的传输轨迹随之发生变化,不同于艾里光束的是,艾里孤子的传输始终保持直线传输。