三波混频光参量放大器中带宽的研究

对三波混频光参量放大器中参量过程的带宽进行了研究 ,给出了具有普遍意义的参量带宽和增益带宽的数学显式模型 ,这些模型引入了非线性晶体长度、群速、色散、增益系数等变量对带宽的影响 ,依据这些模型对影响参量放大器中带宽的各种因素进行了模拟计算、分析和比较 ,结果表明 :信号光和闲置光之间的群速度失配是影响参量放大过程带宽的主要因素 ,当信号光和闲置光之间实现群速度匹配时 ,可以获得最宽的带宽 ,因此对于任何三波混频光参量放大器中的参量过程 ,都可以通过选择合适的非共线角、非线性晶体长度、抽运光强度来获得最宽的带宽 ,从而支持超宽带增益     

常温常压下碘蒸气的简并四波混频光谱技术

报道了以碘蒸气为介质进行的前向简并四波混频(DFWM)布局光谱技术的试验研究。在试验中采用了具有自稳分光系统的前向简并四波混频布局。试验发现在常温常压条件下,由于碰撞猝灭会大大降低激光诱导荧光(LIF)光谱的检测灵敏度,几乎观察不到碘蒸气荧光光谱,但却可获得较强的碘蒸气的简并四波混频信号。这是目前已知测定了常温常压下I2在554～556 nm中的前向简并四波混频光谱。常温常压下气相介质的简并四波混频光谱技术,对痕迹量原子、分子和自由基的探测以及对燃烧诊断等方面的研究与应用具有重要意义。     

Group-velocity matched femtosecond parametric oscillation by noncollinear quasi-phase matching

A general model of noncollinear femtosecond parametric oscillation in periodically poled gratings is proposed, in which the group velocities of interacting waves are matched, based on a noncollinear quasi-phase matching (QPM) scheme. We demonstrate that group velocity matching and quasi-phase matching can be simultaneously achieved for ultrashort pulses. The corresponding noncollinear angles and grating periods are calculated for periodically poled lithium niobate (PPLN) and periodically poled KTP (PPKTP). With a suitable choice of parameters, the effective interaction length in the crystal can be remarkably increased, and an enhancement of parametric gain by orders of magnitude obtained, thus reducing the operational threshold significantly.     

大气压附近不同温度对碘气体简并四波混频光谱的影响

非线性激光光谱技术在气相介质的痕迹量检测方面有广泛应用。实验采用了具有自稳分光系统的前向简并四波混频(DFWM)布局,在大气压附近不同压强和不同温度条件下研究了碘气体的DFWM 光谱。在饱和泵浦和探测光强的情况下,发现温度与压强的变化对碘在波长555~556 nm 及558~559 nmDFWM 光谱结构影响较大,其中波长为555.1 nm 的跃迁对温度相当敏感。同时仍有少数碘的DFWM 光谱线较强是因为跃迁(558.81 nm)对温度不敏感,可以利用该谱线来探测不同温度下气相介质的浓度变化。所以不同温度与压强对碘气体DFWM 光谱影响的研究在气相介质痕迹量的检测以及燃烧诊断等方面有重要的应用价值。     

基于不同非共线结构的光参量放大器的带宽特性研究

研究了多种非共线结构下基于周期极化铌酸锂晶体的皮秒脉冲光参量放大器的调谐带宽和参量带宽特性,确定了当能够获得大且稳定的调谐带宽时应使用的最佳非共线结构、抽运光波矢和晶体光栅矢量间的最佳非共线角θ以及最佳极化周期,同时给出了用于计算不同温度下周期极化铌酸锂晶体的最佳极化周期的数学公式。此外,通过对相位失配进行泰勒级数展开,分别得到了保留一阶、二阶和三阶导数项时的参量带宽计算公式,随后将利用这些公式和相位失配表达式计算得到的参量带宽进行了对比,进而分析了高阶导数项对参量带宽的影响。在此基础上提出了一个用于最大化光参量放大过程的调谐带宽和参量带宽、确定非共线角α和工作温度等最佳工作参数的可行方案。     

A simple analytic approach to degenerate four-wave mixing by comparison with real-time holography

A simple analytic theory for degenerate four-wave mixing (DFWM) is presented. From the fundamental relationship between real-time holography and DFWM simple expressions for the DFWM signal are developed. The basic assumption in our approach is that the four waves are coupled only by the grating created by the forward-probe interference and that the intensities of the forward beam and the probe beam are not affected by the four-wave interaction. In general, this is only true when the backward pump beam intensity is much smaller than both the forward beam intensity and the probe beam intensity. However, within this restricted parameter range we obtain simple analytic expressions for the DFWM signal including the effects of linear losses in the nonlinear medium. For thin nonlinear media the signal intensity is determined by a squared Bessel-function of first order, and for thick nonlinear media the signal intensity is determined by a squared sine-function. The theory is restricted to small values of the signal reflectivity. Finally, we have investigated the DFWM signal from a CdS-sample with aQ-switched frequency doubled Nd:YAG laser. At a sample temperature of 375 K we obtain a third-order susceptibility ofchi^{(3)} = 4.4 cdot 10^{-7}ESU. We apply the theory to these experiments.     

Transient coherent degenerate four-wave mixing

A set of coupled equations is derived and used to analyze transient coherent degenerate four-wave mixing (DFWM) in a two-level system. The numerical results show that in the case of near-resonance, intense pumping, and short pulses, the properties of degenerate four-wave mixing have interesting coherent interaction characteristics, such as quasi-periodicity in the pump pulse area, probe pulse areas, and energy reflectivity, oscillatory behavior of the DFWM pulse, and generation of a DFWM signal in the case of delayed incidence, where the three incident pulses do not overlap in the medium     

CdSSe掺杂玻璃中的光致暗变效应研究

本文用DFWM和荧光光谱方法研究了光致暗变效应对CdSSe掺杂玻璃光学性质的影响,解释了经过强光照射的样品,DFWM反射率,荧光强度和透射率降低的原因.     

推拉型有机化合物的非线性特性研究

合成一种新的推拉型偶氮化合物并将掺入ＰＭＭＡ中制成光学薄膜器件，用Ｚ扫描技术测量了该材料的非线性折射率，用ＤＦＷＭ装置研究了该材料在可见光长波区光存储特性，获得了良好的实时和短时存储信息，存储功率密度小于０．１Ｗ／ｃｍ＾２。分析了这种非共振吸收区光存储机理。     

高速调制光束的互泵浦相位共轭器的研究

利用光折变晶体中高速振幅调制光束的简并四波混频（ＤＦＶＶＭ）理论和互泵浦相位共轭器（ＭＰＰＣ）的两作用区模型，对高速振幅调制光束的ＭＰＰＣ进行研究，给出了ＭＰＰＣ的共轭反射率、透过率以及作用区中光扇开系数的表示式及数值结果．实验上所得到的互泵浦相位共轭光的规律与理论相吻合．     

单发次皮秒脉冲宽度的二阶自相关法测试

理论分析非共线二次谐波转换中非共线夹角与相位匹配角、温度及波长的变化关系,综合考虑非共轴二次谐波转换中群速度延迟、色散等因素影响,合理给出入射光斑直径、两束光之间的夹角、位相匹配角、晶体尺寸等设计参数。利用非线性晶体(KDP)非共线匹配倍频效应,研制了针对皮秒脉冲测试的单发次自相关仪,并对单发次皮秒输出脉冲宽度进行测试分析。     

Theory of degenerate four-wave mixing an anisotropic, opticallyactive photorefractive crystals

A theory is presented of degenerate four-wave mixing (DFWM) of arbitrary polarized waves in an anisotropic optically active photorefractive crystal. Using the method of coupled waves, a system of differential equations is deduced describing the coupling process. This system is specified to DFWM in crystals of the Bi₁₂GeO₂₀ -type and numerically solved based on the shooting method. Some peculiarities of phase conjugation in these crystal are discussed     

周期性极化晶体的群速匹配飞秒脉冲光学参量放大

研究了周期性极化晶体非共线参量放大的群速匹配和群速色散.提出了估算光学参量放大(OPA)光谱带宽的一般性方法.光谱带宽由波矢失配中泰勒级数展开式的第一、第二项决定,当展开式中一级项为零时,三个非共线相互作用波是群速是匹配的,这时参量带宽由群速色散决定.选择合适的光栅周期,能获得调谐范围较宽的群速匹配脉冲参量放大,参量带宽与晶体长度、非共线角及群速色散有关.研究了增益带宽与晶体长度及抽运光强度的关系,也研究了离散角和有效非线性系数等.由于群速匹配,参量带宽很大,大大增加了最大有效长度和能量转换效率.     

BBO晶体Ⅰ类相位匹配从可见光到近红外光宽带参量放大的带宽研究

超快激光的应用,需要有高功率、窄脉宽和宽调谐的激光光源。飞秒光参量放大是产生可调谐、短至几个飞秒光脉冲的一种重要方法。为获得极窄的飞秒光脉冲,飞秒光参量放大器就应该有尽可能大的本征带宽。理论研究了BBO晶体在Ⅰ类非共线相位匹配条件下的宽带参量放大特性。将多色相位匹配技术应用于飞秒光参量放大,推导出信号光带角色散时的宽带运转条件。分别介绍了从可见光到近红外光选取合适的参数实现宽带运转的方法。基于400nm蓝光抽运的BBO晶体光参量放大器(OPA),系统地分析了非共线角和信号光角色散值对相位失配和参量带宽的影响。研究结果表明选取适当非共线角和在近红外光中引入适当的角色散可极大提高参量带宽。     

吸收介质中三阶极化率的测量

全光学信息处理、光计算机的发展依赖于具有大的三阶非线性光学材料,因此介质的三阶非线性极化率的测量就显得特别重要。吴存恺等提出了用简并四波混频方法测量透明介质的三阶极化率,G.R.Olbright用于涉法测量了CdS_xSe(1-x)玻璃的非线性折射率。本文将讨论用简并四波混频测量吸收介质的三阶极化率的方法。     

GaAs中EL2能级参与的ps光折变效应中空间电荷场的退化

采用光学简并四波混频方法,测量了共轭信号强度随延迟时间改变的变化曲线,实验发现,其中存在一个快变与一个慢变信号,经分析表明,空间电荷场的退化很慢,它能维持到ns的量级。     

Camera Calibration With Three Noncollinear Points Under Special Motions

Plane-based (2-D) camera calibration is becoming a hot research topic in recent years because of its flexibility. However, at least four image points are needed in every view to denote the coplanar feature in the 2-D camera calibration. Can we do the camera calibration by using the calibration object that only has three points? Some 1-D camera calibration techniques use the setup of three collinear points with known distances, but it is a kind of special conditions of calibration object setup. How about the general setup—three noncollinear points? We propose a new camera calibration algorithm based on the calibration objects with three noncollinear points. Experiments with simulated data and real images are carried out to verify the theoretical correctness and numerical robustness of our results. Because the objects with three noncollinear points have special properties in camera calibration, they are midway between 1-D and 2-D calibration objects. Our method is actually a new kind of camera calibration algorithm.      

Noncollinear interactions in parametric luminescence

A quantum mechanical perturbation treatment of optical parametric luminescence in nonlinear crystals is briefly given. The expression obtained for the emitted signal power applies to noncollinear phase-matching situations. Next, a detailed analysis of these interactions is given, with results in the form of signal wavelength versus observation angle, with fixed pump direction. The nonlinear crystal is LiNbO3and the pump is one of the lines from an argon ion laser. The effect of temperature is studied. Emphasis is on large observation angle effects, and on the singularities arising from the particular dispersion curves of the crystal. Experimental results provide a good check on noncollinear matching predictions. The far-field signal wavelength dependence on angle as measured from pump beam is approximately quadratic for small angles, and linear for the particular temperature that gives the collinear degenerate interaction. For larger angles, the law is not simple, and there is a limiting cone of directions with no matched signal outside. This cone appears brightest in far field. Applications discussed include the accurate measurement of nonlinear susceptibilities of crystals, the design of tunable optical parametric oscillators, and the measurement of refractive indices in strong absorption regions.     

Investigation on phase matching in a THz-wave parametric oscillator

The characteristics of noncollinear phase matching and quasi-phase-matching in the THz-wave parametric oscillator(TPO) are investigated.The expression of the effective parametric gain length under the condition of noncollinear phase matching configuration is deduced.The relationship between the poling period of periodically poled LiNbO3 crystal and the generated THz frequency under the condition of quasi-phase-matching configuration is analyzed.Based on the analyses above we propose a new TPO configuration which ensures the three mixing waves interact collinearly.The effects of operation temperature on phase matching are analyzed.     

Characterization and modeling of a noncollinearly phase-matchedfemtosecond optical parametric oscillator based on KTA and operating tobeyond 4 μm

We describe the design and operation of a critically phase-matched femtosecond optical parametric oscillator based on KTA. By employing a small pump-signal noncollinear angle, tuning of the idler to beyond 4 μm is achieved using a Ti:sapphire pump laser. A Gaussian-beam model is described which can be used to identify the optimal noncollinear phase-matching geometry. Idler and signal pulses are characterized fully both temporally and spectrally and interferometric autocorrelation data at 3.5 μm showing idler pulses of only eight optical cycles duration are presented