Spectral narrowing in coherent Rayleigh-Brillouin scattering

Coherent Rayleigh-Brillouin scattering is a four-wave mixing technique that provides information on various physical properties of the scattering medium in the spectral domain. Being based on density gratings generated by dipole forces, the method requires two pump beams of sufficient spectral width to span the full response bandwidth of the scattering medium. We provide experimental data on the scattered spectrum as a function of the coherence between the two pump beams and derive the corresponding pump beam spectrum. We argue that all experiments on coherent Rayleigh-Brillouin scattering to date, have, in fact, been performed in the incoherent regime and show that orders of magnitude in scattering efficiency are to be expected when the experiments are performed with bandwidth-limited picosecond laser pulses.     

在热压缩态中测量相位算符的涨落

利用热场动力学的方法计算了热压缩态中测量相位算符的涨落，引入了两种类型的基础量子涨落，一种是与测量相位的两个正交分量相联系，另一种是与一个测量相位分量和光子数相联系。由此，研究了热压缩压中测量相位涨落的两种压缩及其与温度的关系。     

发散光束抽运的宽带光参量啁啾脉冲放大系统的理论研究

对发散光束抽运的光参量啁啾脉冲放大器的增益带宽进行了系统的理论研究.采用空间傅里叶变换和四阶Runge-Kutta算法，分别模拟了非衍射极限情况下的高斯光束和空间频谱为矩形的发散光束作为抽运光时的增益曲线.结果表明：不管是在可见光或是在近红外光谱区，用发散光束均可以明显地改善光参量啁啾脉冲放大系统的增益带宽.选取合适的发散角和抽运光强，可以获得高增益、宽谱带的信号光输出. 关键词： 光参量啁啾脉冲放大 增益带宽 发散角 高斯光束     

Nonlocal pulse shaping with entangled photon pairs

Nonlocal shaping effects in the time or spectral profiles of an entangled photon pair emerging from a pulsed parametric down-converter are observed by spectrally or temporally filtering one of the twin beams. In particular, we demonstrate the appearance of fourth-order ("ghost") interference fringes in the spectrum of one beam conditioned by photodetection at the output of an unbalanced Michelson interferometer placed in the path of the other beam. The coherence time of the pump is the limiting factor for the sharpness of the details in the shaped biphoton spectrum.     

Relation of pump-beam quality and conversion efficiency in the Raman downward conversion

To investigate the full conversion of pump power to the Stokes waves in stimulated Raman scattering with a single-pass cell, unconverted pump energies have been analyzed in detail in relation to the first Stokes, second Stokes and first anti-Stokes energies. Adoption of a long focusing configuration with a high-pressure cell was found to be effective but insufficient to suppress the four-wave mixing effect, because a small amount of pump energy always remained undepleted. Comparison of the results using pump beams of various spectral and spatial mode characteristics from alexandrite and Nd:YAG lasers revealed that the spatial mode quality was the most critical parameter for full depletion of a pump pulse.     

Excitation of Electron Plasma Waves by Beating Two Self-Trapped Laser Beams

This paper presents the detailed studies of the focusing of pump beams and the excited electron plasma waves(EPW) in a PBWA(Paema-Beat-Wave-Accelerator) by beating two self-trapped laser beams. The equations governing the saturated amplitude of EPW in nonuniform pump beams have been derived analytically. With these the condition for self-trapping of pump beams has been studied self-consistently. The optimum frequency mismatch parameter and the corresponding optimum initial plasma density as well as the maximum amplitude of the EPW have been obtained analytically. The transverse distributions of the EPW for Gaussian pump profile have been calculated numerically and show peculiar characteristics for certain frequency mismatch parameters. In addition, the effect of the radial component of the EPW on the bunch of accelerated particles in PBWA has been briefly discussed.     

Compact fluorescence depletion microscope system using an integrated optical element

The performance of a fluorescence depletion microscope system depends critically on the precise alignment of both the pump and the erase beams with the axis of the focusing objective lens. In this article we propose a technique with which the need for separate alignment of the pump and erase beams is eliminated. Besides being insensitive to alignment errors, our technique is much more compact than present systems, and can serve as a basis for a commercial fluorescence depletion microscope.     

Time-resolved entanglement and photon number correlation of twin beams: Application to quantum key distribution scheme

Quantum entanglement and intensity correlations in continuous variable (CV) regimes have investigated in the time domain in addition to many analogous investigations performed in the frequency domain. The specific signatures of time-resolved CV quadrature entanglement and intensity difference squeezing have been analyzed for periodically-pulsed optical parametric oscillator (OPO). An application to quantum key distribution scheme based on intensity correlation of twin beams has also been considered. The text was submitted by the author in English.     

Parametric amplification of chirped optical pulses under pump depletion

We present simple analytical solutions of coupled wave equations describing chirped pulse parametric amplification under pump depletion. The evolution of the duration and spectrum of amplified pulses in OPA pumped by Gaussian and supergaussian pulses has been investigated both numerically and analytically. Also, the dependence of the energy conversion efficiency from pump to signal was determined for a range of parameter values, and an optimum ratio of signal and pump pulse durations was evaluated.     

Photorefractive mutually pumped phase conjugation with partially coherent beams

We investigate the mutually pumped phase-conjugation process in photorefractive media with partially coherent pump beams. We consider the effects of transmission, reflection, and 2k-reflection gratings as well as the depletion of both pump beams. The theoretical results can be employed to qualitatively explain the experimental observations.     

真空度对强紫外激光在空气中长程传输的影响

 采用瞬态受激旋转拉曼散射(SRRS)模型，并充分考虑非线性介质分子密度、增益系数、泵浦光的衰减、斯托克斯光的非线性放大以及初始的随机斯托克斯散射场等因素，研究了空气真空度对强紫外激光在空气长程传输过程中产生的SRRS效应的影响。结果表明，真空度对SRRS效应的阈值传输距离和Stokes光的转换效率的影响较大，随着真空度的提高，Stokes光的转换效率将降低，产生SRRS效应的阈值传输距离将增大。因此，在实际工作中，可以采用真空度较高的激光传输环境来抑制SRRS效应的产生，以减小入射泵浦光能量的衰减并提高光束质量。     

LDS751染料分子的时间分辨荧光谱

本文介绍用飞秒时间分辨荧光凹陷探测技术,获得激发态分子时间分辨荧光光谱的方法。文中描述了实验方法及其特点,给出了ＬＤＳ７５１染料分子的飞秒时间分辨荧光光谱。     

双束“自陷”激光驱动的电子等离子体波的拍频激发

本文提出并详细研究了应用两束“自陷”激光激发电子等离子体波(EPW)来维持等离子体拍频加速器(PBWA)中光束及其激发的EPW的会聚。文中导出了EPW饱和振幅所满足的方程,自洽地研究了泵浦光束的“自陷”条件,并解析地得到了最佳离谐条件及其对应的最佳初始等离子体密度以及EPW的最大振幅。在高斯型自陷泵浦光束情况下,文中应用数值法计算了EPW的横向分布。对于一定的离谐参量,此分布呈现出独特的性质。此外,本文还得到了由泵浦光束的非均匀性所产生的EPW电场的径向分量,并简要地讨论了它对PBWA中粒子加速的影响。 关键词：     

位相畸变对强紫外激光在空气中长程传输的影响

 采用瞬态受激旋转拉曼散射（SRRS）模型,详细考虑了激光脉冲的位相变化、时间波形、泵浦光的衰减、斯托克斯光的非线性放大以及初始的随机斯托克斯散射场等诸多因素,研究了空间位相畸变对空气中长程传输过程中产生的SRRS效应的影响。研究结果表明：位相畸变对阈值条件和时间特性影响较小,而对光束质量影响较为明显;随着位相畸变的增大,光束的能量分布变得极不均匀,光束的光强对比度也明显变大,从而使激光光束质量变差,而且当传输距离达到阈值条件后,随着传输距离的增加,光束质量将进一步变差。     

利用非平衡光纤Mach-Zehnder干涉仪探测频率非简并纠缠态光场

采用两对光纤构成的非平衡Mach-Zehnder干涉仪,对非简并光学参量振荡腔产生的20mW频率非简并孪生光束间的强度差与位相和的关联噪声进行测量,在分析频率为2MHz处测得关联噪声分别低于散粒噪声基准31和13dB,从实验上证实了在较低分析频率处孪生光束之间有较高量子纠缠. 关键词： 光学参量振荡腔 孪生光束 光纤Mach-Zehnder干涉仪     

Comparison of SRS thresholds under pumping by Gaussian and Bessel beams

In the paraxial approximation, it has been shown that the quasi-stationary SRS amplification coefficient in the near-threshold region is determined by the product of the pump intensity in the beam center and the overlap integral of the transverse structure of the pump and the Stokes component. Expressions for the overlap integral and the scattering powers have been obtained and analyzed for the following cases: the pump and the Stokes field are Gaussian beams; the pump and the Stokes field are Bessel beams; the pump is a Bessel beam and the Stokes field is an axial Gaussian beam. Relations between the SRS excitation thresholds in different cases have been found.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 778–787, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

1.0 MeV电子辐照致VO_2(B)薄膜结构与光谱改变研究

本文以能量为1.0 MeV的电子束辐照VO2(B)薄膜,对电子辐照在薄膜中产生的缺陷进行了理论计算,同时使用X射线衍射仪、原子力显微镜、分光光度计对薄膜进行测试,分析了电子辐照对薄膜结构、形貌与紫外-可见光谱(280~880nm)的影响。结果显示:电子辐照可以在薄膜中引入点缺陷并产生退火效应,电子辐照使薄膜的表面晶粒细化,辐照后薄膜光谱的吸收峰位发生移动,其移动的最大位移达到21nm,辐照后薄膜的光学禁带宽度也有所增加。     

Time-modulated entangled states of light

We investigate time-modulated EPR entangled states and intensity quantum correlation of twin light beams in application to time-resolved quantum communication. As a proper device generating such states, the nondegenerate optical parametric oscillator driven by the time-modulated pump field is considered. The text was submitted by the authors in English.     

强紫外激光在空气中长程传输受激旋转拉曼散射效应

 采用瞬态受激旋转拉曼散射（SRRS）模型，详细考虑了激光脉冲波形、介质的非线性极化、泵浦光的衰减、斯托克斯光的非线性放大以及拉曼线宽等诸多因素，对强紫外激光束在空气中长程传输过程产生的SRRS效应进行了研究。讨论了产生SRRS效应的阈值条件，详细分析了SRRS效应对激光光束质量的影响。     

Experimental characterization of quantum-correlated twin beams and a quantum channel with twin beams

We report the generation and characterization of quantum-correlated twin beams and their application to a quantum channel. Compared with our previous results, the characterization of twin beams and the quantum channel have been studied with 7.0-dB intensity difference squeezing. The measured inference variance of twin beams is decreased to 0.40 ± 0.02. For the quantum channel, the bit error rate will be 0.035 by using 7.0-dB intensity difference squeezing compared with our previous result of 0.067 by using 4.9-dB intensity difference squeezing.