近简并四波混频相位共轭介质中的光强分布

从求解耦合波方程出发，详细研究了非线性光学介质中由近简并四波混频所产生的相位共轭过程。以上述波方程的解为基础，给出作为混频结果的反射传播相位共轭波沿介质轴向的光强分布，得到比以往文献中所报道的更为精确的结果，从而为选择工作物质的最佳尺寸提供了理论依据。     

共振简并四波混频光学相位共轭的研究

本文考虑了非线性极化强度对cos(k·r)的依赖关系,对共振增强简并四波混频的半经典处理提出了修正,得到相位共轭反射率满足的Riccatti方程.使用可调谐连续波CO_2激光器和SF_6气体作非线性介质作了实验研究.获得了(0.2～0.8)×10~(-4)的反射率.     

向列型液晶中简并四波混频相位共轭的理论研究

研究向列型液晶中由光致分子重取向引起的简并四波混频光学相位共轭现象,着重讨论液晶薄膜厚度d、探测光与一泵浦光之间的夹角θ_ω以及光的入射面和液晶指向矢之间的夹角β对相位共轭光产生效率的影响.     

光学相位共轭与四波混频

回顾并论述了光学相位共轭及四波混频技术的发展过程，介绍了四波混频相位共轭的原理、相关的介质材料、应用前景及技术发展趋势。     

Nd:YAG激光在单晶硅中的四波混频相位共轭

以单晶硅作非线性介质,用调Q脉冲Nd:YAG激光作四渡混频,获得了相位共轭反射光波.从光激发电子-空穴对浓度及其所产生的相位光栅出发,理论计算了相位共轭镜的反射率.实验获得的共轭镜反射率为125%,并与实验中显示了其对相位干扰的补偿特性.     

受激布里渊散射相位共轭波的四波混频放大

本文介绍了一种产生相位共轭波的方法.此方法兼有四波混频方法和受激布里渊散射方法的优点,可得到转换效率大于1的高质量的相位共轭波.     

超短脉冲简并四波混频时间分辨研究

研究了简并以混频的时间分辨曲线，数值模拟了由延迟时间引起的两种不同光栅的时间分辨曲线以及曲线的约化半宽度与约化弛豫时间ｔｒ／ｔｐ的变化关系。     

半导体激光器激活层中的四波混频和相位共轭光的发生

本文提出了一种从半导体激光器中发生和检测相位共轭光的新方法,并用1.3μm分布反馈半导体激光器作了实验验证。本方法不仅可以用来发生相位共轭光,还可以用来研究振荡运转中的激光激活介质的非线性光学特性。     

甲基橙掺杂聚乙烯醇薄膜简并四波混频特性的实验教学研究

介绍了在近代物理实验课中开设甲基橙掺杂聚乙烯醇薄膜的简并四波混频特性的实验设计，论述了实验原理和实验中采用的非线性介质的结构与性能．研究了泵浦光与探测光之间的夹角等实验条件对实验结果的影响，得到了相位共轭光强度与探测光和泵浦光的关系．分析了实验中产生的信号光强度和反射系数的变化及产生这种变化的机制．     

Eu∶Fe∶LiNbO_3晶体非简并四波混频的研究

用波长为６２３．８ｎｍ的Ｈｅ－Ｎｅ激光作信号光和一束泵浦光，用波长为４８８．０ｎｍ的Ａｒ＋激光作另一束泵浦光，在Ｅｕ∶Ｆｅ∶ＬｉＮｂＯ＿３晶体中实现了非简并四波混频，获得了波长为４８８．０ｎｍ的变频相位共轭光，同时还产生了波长为６３２．８ｎｍ的同频相位共扼光。本文对上述实验结果进行了定性分析。     

Optical phase conjugation by resonant degenerate four-wave mixing in liquid phase medium

In this paper, frequency-doubled Nd:YAG laser's phase conjugation has been investigated experimentally using resonant degenerate four-wave mixing (DFWM). The iodine solution was used as resonant medium. In this way, the energy of the DFWM phase conjugation beam arrived at 43μJ/pulse while the total pump beam's energy reached 8mJ/pulse. The relation between the pulse energy of the DFWM phase conjugation beam and that of the pump beam was investigated. We also measured the optical field distributions of pump beam and DFWM phase conjugation beam, from which it can be noticed that the DFWM phase conjugation can improve the laser beam quality. At the same time, we observed the influence of the pump beam's disturbance on the DFWM signal.     

Transient degenerate four-wave mixing in molecular systems

The dependence of the degenerate four-wave mixing (DFWM) signal on laser intensity, molecular transition moment and molecular concentration were examined experimentally by taking the iodine molecule (l₂) as a testing example. The experimental results will be interpreted by a non-steady-state DFWM theory, an extension of the non-degenerate two-level system previously proposed. The distinctive physical feature of this mechanism is that the present observation is the result of non-stationary evolution of the excited-state population, in contrast to the conventional theory based on the steady-state treatment. In this study, we have also taken into account the magnetic sub-levels of molecular rovibronic quantum states. The non-steady-state model we developed in this paper is applicable to fast pump and slow relaxation conditions, thus being more suitable for gas-phase systems than the condensed-phase where fast relaxations usually take place.     

Optical chaos in multiple degenerate four-wave mixing

Spatial evolution has been studied of an ensemble of equal-frequency light waves involved in several four-wave mixing processes under linear photoabsorption. It is shown that this system may exhibit spatial chaos caused by competition of optical mixing processes with strong energy exchange between the waves. For pulsed radiation, the temporal envelopes of interacting waves undergo modulations which may also be of chaotic character. Also discussed are possible variants of identifying chaos in systems of interacting light waves experimentally and the role of accompanying photoprocesses (photoabsorption, self-action of radiation).     

Gas-phase velocimetry by nearly degenerate four-wave mixing

We demonstrate a new velocimetry technique for gas flows based on Nearly Degenerate Four-Wave Mixing (NDFWM). Measurements were performed on nitric oxide in a free-jet expansion using helium and argon as carrier gases, at flow velocities on the order of 1000 m/s. We obtained velocities by analyzing experimental spectra from the jet using a perturbative treatment of NDFWM that we extended to include an arbitrary bulk velocity. The results agreed with independent velocity measurements based on Laser-Induced Fluorescence (LIF), as well as with theoretical flow-field velocities, to better than 5% in all cases studied.     

Slow light with degenerate backward-wave four-wave mixing

We report on a slowing down of light pulses using degenerate backward-wave four-wave mixing in a photorefractive crystal. The delay and width of the output pulse for the amplified transmitted beam and for the phase-conjugated beam are studied as a function of the input pulse width. We demonstrate that the four-wave mixing process ensures a larger slowing down of short pulses compared to the photorefractive two-beam coupling scheme and guarantees the elimination of forerunners, which are among the principal drawbacks for slowing down of short pulses with two-beam coupling. The technique may be extended to slowing down of light with degenerate or nearly degenerate backward-wave four-wave mixing based on other types of nonlinearities.     

Theory of degenerate four-wave mixing in three-level atoms

We derive a theoretical model for phase conjugation in three level atoms. The atoms are assumed to be at rest and the intensities I₁ and I₂ of the pump beams can take arbitrary large values. We calculate the lineshape for a thin optical medium in the case of plane waves and of gaussian beams. In the case of a thick optical medium, we show that the gain saturates if I₁ ≠ I₂.     

Doppler-free two-photon spectroscopy using degenerate four-wave mixing

Using recently developed techniques of degenerate, four-wave mixing, Doppler-free two-photon spectra can be obtained. The signal level for such an experiment in xenon is calculated and found to be readily detectable as well as competing favorably with the method of observing fluoresence following two-photon absorption.     

Broadband degenerate four-wave mixing of OH for flame thermometry

Received: 7 July 1997/Revised version: 23 December 1997