利用场关联效应抑制瑞利型非简并四波混频的热背底

瑞利型非简并四波混频是测量物质超快纵向弛豫时间的有效手段,将场关联原理应用于具有热吸收的样品中瑞利型非简并四波混频的热背底抑制，给出了抑制热背底的条件，并通过数值模拟证明了其可行性. 关键词： 四波混频 场关联 超快测量     

布里渊增强非简并四波混频

在CS₂介质中观测到由声波引起的布里渊增强非简并四波混频(NFWM)和由分子取向栅产生的瑞利型NFWM.研究发现,分子取向栅与声波之间并不是相互独立的,声波的存在会破坏瑞利型NFWM和布里渊增强NFWM极化之间的相位关系. 关键词： 四波混频 布里渊散射 瑞利散射     

四波混频光谱术

本文介绍我们用四波混频研究光与物质相互作用方面取得的新进展．其中包括拉曼增强非简并四波混频，用时间延迟方法区分分子取向栅及热栅，多能级吸收带的非相干光时间延迟四波混频，激光感生螺旋结构及用时间分辨简并四波混频研究原子的碰撞线宽变窄效应．     

瑞利型增强四波混频的外差探测

将光外差探测方法应用于瑞利型增强四波混频的研究,通过理论分析得到了瑞利型增强四波混频三阶极化率的表达式和外差拍信号的解析解,对拍信号的研究表明这种方法可以保留瑞利型增强四波混频极化过程的完整信息，获得瑞利型增强极化的吸收谱与色散谱.同时分析了三种不同的马尔可夫随机场模型下的差拍信号的区别与联系.     

等离子体四波混频透射放大理论

研究了寻常波在磁化等离子体中四波混频透射放大理论，得到了简并和非简并时的精确解析解，其结果适用于非磁化等离子体中的电磁波四波混频． 关键词：     

瑞利增强非简并四波混频的时域不对称性研究

基于场关联原理,采用非相干光时延四波混频法研究了瑞利增强非简并四波混频的时域特性.利用二阶场关联函数理论揭示出混频信号在时域的细微变化,发现信号展示出时域不对称性并且在τ<0时会出现振荡结构,而这种时域不对称性反映了该三阶非线性极化过程的特点.     

用双光源相位共轭型非相干光时间延迟简并四波混频测量超快速过程

本文提出用双光源相位共轭型非相干光时间延迟简并四波混频测量失相时间和布居弛豫时间的理论,并对其应用进行了讨论.     

应用双非简并四波混频理论研究原子的碰撞效应

在己有实验的基础上,提出了由双光子共振非简并四波混频和碰撞再构非简并四波混频组成用于研究原子碰撞效应的双非简并四波混频理论,分析了缓冲气压、温度、共振失谐和碰撞展宽系数对双非简并四波混频谱线的影响.在由基态、中间态和激发态组成的级联三能级系统中,双非简并四波混频可同时研究碰撞引起的激发态谱线展宽和碰撞引起的中间态能级再分布现象.与测量纵向弛豫碰撞展宽的传统实验方法不同,本文方法是一种纯光学的相干测量技术,可以同时测量激发态与基态间的横向弛豫Γ_(20)和中间态与基态间的横向弛豫Γ_(21)的碰撞展宽.     

GaAs体材料及其量子阱的光学极化退相特性

采用飞秒时间分辨瞬态简并四波混频技术，在室温下测量了GaAs体材料及其量子阱材料GaAs/Al_0.3Ga_0.7As的光学极化超快退相时间，当激光中心波长为785nm，受激载流子浓度为10¹¹cm^-2时，它们的退相时间分别为28fs和46fs.量子阱材料的退相时间比体材料的长，这是由于量子阱中的载流子在垂直于GaAs/AlGaAs界面的运动受到限制，运动呈现二维特性，大大减小了载流子的散射概率.实验中观察到瞬态简并四波混 关键词： 时间分辨简并四波混频 飞秒激光脉冲 退相 密度矩阵     

时间分辨简并四波混频中的量子拍频效应

本文严格处理了准简并二能级系统中时间分辨简并四波混频问题。指出在这种简并四波混频中同样可能存在量子拍频效应。分析了这种量子拍频效应的产生条件和特点。讨论了可能的应用。 关键词：     

最优的双轴晶体非简并四波混频变频共轭波的产生

研究了双轴晶体中通过非简并四波混频产生可变频的共轭波.在KTP中共轭波有各种匹配类型.若选择合适的匹配方向及泵浦和探测波矢的合适角度,使由于离散效应引起的所有光线之间偏离得到最好的补偿.从而增加晶体的有效长度,并显著改善能量的转换效率,得到各种匹配类型的最佳工作条件.     

Distributed feedback in a waveguide by four wave mixing

The theory of four wave mixing, two guided and two radiation modes of planar optical waveguides, with periodic structure of interaction regions is presented. In the degenerate case multiple penetration of the pumping waves through the waveguide enables better utilization of their energy, as compared with the single four wave mixing. In the nondegenerate case the periodic structure enables phase matching between initial and backward guided modes.     

Amplification of a phase-conjugate signal in a nonlinear absorptive Kerr medium

We present the results of amplification of the phase-conjugate reflectivity in an absorptive nonlinear Kerr medium by nondegenerate four-wave mixing. The influence of two-beam coupling on the phase-conjugate signal is observed and analyzed. The frequency domain response of nondegenerate four-wave mixing produces a tunable narrow-band optical filter.     

长腔DFB半导体激光器非简并四波混频波长转换效率

本文从理论上计算了长腔DFB-LD中基于非简并四波混频的波长转换效率,由耦合波方程的数值解,得出波长转换效率与腔长、泵浦光功率、增益系数、DFB-LD谐振光与注入光的频率失谐量等的关系.数值计算结果表明,通过提高泵浦光功率、增益和腔长可有效地增大波长转换效率.     

The diffraction phenomenon in consecutive parametric processes

The manifestation of diffraction effects in two coupled three-frequency collinear processes in the presence of a single intense pump wave in a nonlinear optical crystal with a regular domain structure is considered. A set of three coupled parabolic equations is solved by the Fourier transform method. Attention is focused on the analysis of the functions of image conversion from a signal frequency to a new frequency and to the image gain. It was established that the influence of the subsequent process of image conversion by means of frequency mixing weakly affects the initial process of nondegenerate parametric interaction.     

Tunable Filters with Narrow Band in Bulk SLA for DWDM Networks

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Ultrasonic sizing of short surface cracks

This paper presents a method for ultrasonic sizing of surface cracks based on time domain and frequency domain Rayleigh wave near-field analysis. The procedure allows for the entire range of ratio of crack depth to Rayleigh wavelength a/λ to be covered with one single measurement. In the time domain the time-of-flight method was extended to cracks smaller than the wavelength by correlation of the time delay of the transmitted Rayleigh wave with the crack depth. In the frequency domain, the inverse scattering problem was solved by comparison of the measured scattering coefficients and central frequencies of the reflected and transmitted Rayleigh waves with theoretical curves. The sizing procedure was demonstrated experimentally with narrow slots and real fatigue cracks. The out-of-plane displacement component was measured pointwise in the scattered near field by means of laser interferometry. The determination of the scattering parameters in the near field was enabled by a procedure that allows for the Rayleigh wave to be separated from the other modes scattered at the defect. The experimental results showed good accuracy and repeatability down to the smallest available ratio of crack depth to Rayleigh wavelength a/λ = 0.15.     

激光激发黏弹表面波有限元数值模拟

研究黏弹性材料中激光激发的Rayleigh波的传播特征. 考虑到黏弹性材料的黏性特征,在频域内建立黏弹性材料中激光激发Rayleigh波的有限元数值模型. 在验证有限元频域数值模型正确性的基础上,模拟脉冲激光作用在黏弹性材料上激发出Rayleigh波,进而讨论激光激发的黏弹Rayleigh波的传播特征,并比较黏弹性材料与弹性材料中激光激发的Rayleigh波差异,同时分析了材料的黏性劲度参量变化对Rayleigh波特征的影响. 关键词： 表面波 激光超声 有限元方法 黏弹性