双频抽运提高SBS相位共轭保真度

相位共轭保真度是相位共轭镜技术用于强激光系统中的一个重要指标。采用四波混频加强SBS的方法 ,其相干拍频驱动声子场 ,能提高SBS相位共轭保真度。对于双频单池结构 ,使用列阵相机测量激光束能量远场角分布 ,在SBS转换效率最佳时 ,对相干驱动SBS相位共轭保真度进行了实验研究     

泵浦脉冲宽度对受激布里渊散射保真度的影响

为了研究泵浦脉冲宽度对受激布里渊散射(SBS)相位共轭保真度的影响,分别采用CCl4、N-hexane、CS2三种不同的SBS介质,在泵浦脉宽分别为12 ns、7 ns和2 ns的情况下,采用列阵相机法对保真度进行实验研究.结果表明:泵浦脉宽对SBS相位共轭保真度有很大影响.当泵浦脉宽远大于介质声子寿命时,保真度保持较高数值,且比较稳定;当泵浦脉宽逐渐接近并近似等于声子寿命时,保真度的值开始逐渐降低,降低的幅度也逐渐增大,稳定性也开始变差;当泵浦脉宽减小到小于声子寿命时,保真度大幅度降低,波动性增大,相位共轭情况很差.     

光束相干驱动声子场提高SBS相位共轭保真度稳定性

光束相干引起的电致伸缩能驱动声子波，从而能加强受激布里渊散射（ＳＢＳ），提高相位共轭保真度稳定性。对折反池结构，采用２ｎｓ陡前沿的脉冲光泵浦，将双级钕玻璃放大器和ＳＢＳ池作为整体，测量了其相位共轭保真度。观测到输出激光的能量远场空间分布和相位共轭保真度稳定性在光束夹角θ５ｍｒａｄ时明显优于θ＞３０ｍｒａｄ。     

激光大气传输中的不完全相位共轭数值模拟

采用含时四维程序数值模拟了激光在湍流大气巾传输的不完全相位共轭。比较了不同孔径信标对探测光的反射率,考察了中弱湍流条件下采用不同孔径信标传输不同距离时硬孔的相位共轭保真度和反射率随湍流结构常数的变化规律,及强湍流条件下采用不同孔径信标时软孔的相位共轭保真度和反射率与高斯孔径的关系。结果显示：中、弱湍流条件下,直到3km传输距离,0．5m的接收孔径都足以提供点信标较为理想的相位共轭补偿,3km传输中等程度湍流下Cn^2=10^-15m^-,大信标有较为明显的优势,其保真度高于小信标．所需的系统放大倍率也远低于小信标;3km传输强湍流下Gn^2=10^-13m^-2/3,大信标的保真度反而低,而PCM孔径小时也能获得较高的保真度。     

固体SBS介质与SBS相位共轭镜的全固化

介绍了固体受激布里渊散射（SBS）介质的普遍特性及最新研究进展,对SBS相位共轭镜全固化中存在的主要问题进行了探讨。指出在适当的抽运条件下,同体介质的SBS负载能力可以高于材料自身固有的光学损伤阈值,并具备实现高相位共轭保真度的潜力。     

瞬态SBS光纤相位共轭镜的低重复频率运转特性

由于光纤中的声子寿命极短,已有的工作大都采用连续波或长脉冲激光作为泵浦源,所激发的受激布里渊散射(SBS)工作在稳态区。实验研究了采用光纤中的瞬态受激布里渊散射作为位相共轭镜的MOPA(master-oscillator-power-amplifier)系统在低重复频率和不同泵浦能量下的输出特性,并与纯丙酮相位共轭镜进行了对比。结果显示：光纤相位共轭镜对重复运转频率(≤15Hz)的变化不敏感,保真度较高;同时,光纤巾的瞬态SBS也能实现有效的脉宽压缩。这意味着光纤共轭镜在短脉冲区也有着潜在的应用前景,并有望成为短脉冲区液体、气体共轭镜的更好的替代品。     

用列阵相机测SBS相位共轭保真度

为准确、方便地测量受激布里渊散射相位共轭保真度，根据保赶集工的光场相关函数定义，提出采用列阵相机测量光束远场能量角分布的方法，来测量保真度，获得的测量结果与其它文献报道的结果一致。     

相位共轭镜和相位共轭腔

本文使用矩阵光学方法分析了:1.相位共轭镜的第Ⅰ和第Ⅱ变换矩阵的物理意义及其等效性;2.相位共轭腔与常规稳定腔的比较;3.相位共轭腔的模式特性;4.有频移的相位共轭腔以及相关的一些问题,5.相位共轭腔的稳定性问题。还对近期的一些理论和实验结果作了比较和讨论。     

光学相位共轭的现状及最新发展

综述了光学相位共轭的发展历史,主要理论成果及实验技术,着重讨论了光学相位共轭。     

提高主振-功率放大系统光束质量的实验研究

设计了一套灯抽运的Nd:YAG主振-功率放大(MOPA)系统,在该系统中使用受激布里渊散射(SBS)相位共轭镜来提高光束质量,其中种子激光源为窄线宽的Cr4+:YAG被动调Q的扭转模激光器,使用两个放大级进行双程放大,在两个放大级之间采用像传递和90°旋光器补偿退偏,在相位共轭镜中采用CCl4,氟里昂112和CS2三种液体进行实验,并测量了SBS反射率和SBS保真度.MOPA系统在20 Hz的重复频率下工作,M2因子为1.6,脉宽为7ns,最大输出能量为600 mJ.     

相位共轭腔的新问题

本文指出在相位共轭腔中存在如下两个新问题:(1)在由球面镜与相位共轭镜构成的谐振腔中,球面波和高斯光束均是腔的本征模;(2)在由高斯反射率镜与相位共轭镜构成的谐振腔中,球面波和高斯光束均不自洽.     

Large signal characteristics of stimulated Brillouin scattering andGaussian beam phase conjugation

Stimulated Brillouin scattering has an inherent threshold. The characteristics above this threshold must be analyzed in terms of a large signal backward traveling-wave parametric interaction. The conventional treatment is valid only below the threshold of stimulated scattering and is limited to small signals. Here, the large signal theory is applied to Gaussian beam phase conjugation. The results agree in all aspects with recent experimental measurements. It is found that, for phase conjugation mirror applications, the threshold can be eliminated by incorporating an auxiliary end mirror     

虚共焦非稳腔腔镜倾斜对光束影响的三维重构

为了直观再现腔镜倾斜对光束分布的影响,用FoxLi数值迭代法及图像重构法,绘得方形镜虚共焦腔在不同倾角下近场及远场光强的三维分布图,并对倾斜后光束特点进行了讨论。结果表明,腔镜倾斜使光束近场分布变差,致使远场光束发生畸变,质量下降。     

全息校正望远镜主镜像差的实验研究

在全息技术校正望远镜主镜像差原理的基础上,采用平行光记录和平行光再现的方法,建立了口径200mm．玻璃基底球面反射镩像差校正的实验装置,进行全息校正实验研究。通过测量像差校正前反射镜面形误差、记录接正厉再现参考光束：与厦叁壹粪枣干涉图、比较像差校正前后光学系统焦点尺寸大小以及分辨率板成像结果,实验验证了全息技术校正望远...     

DPL激光器光束质量研究

利用扭转模获取高光束质量种籽源的同时,进行了高功率二极管均匀泵浦聚光腔设 计,研究相位共轭镜用于改善MOPA激光系统光束质量诸特性。最终获得了重复频率40Hz、单脉冲能量大于400mJ、近衍射极限的高光束质量激光输出。     

高功率DPL光束质量研究

为了在高功率DPL中获取高光束质量输出激光，利用扭转模获取高光束质量种籽源的同时，进行了高重复频率下的热致及光致双折射效应的补偿、高功率二极管均匀泵浦聚光腔设计及相位共轭镜用于改善激光系统光束质量等特性研究。最终获得了重复频率40Hz、单脉冲能量大于400mJ、近衍射极限的高光束质量激光输出。这种方法对高功率激光系统的设计十分有用。     

受激布里渊散射补偿激光波前畸变的试验研究

非线性相位共轭技术以其优越的光学特性在激光对抗领域具有深远的应用潜力,井可能以此开拓激光对抗的一片新领域。本文以受激布里渊散射补偿激光波前畸变作为研究对象,分析实验现象得到了一些有用结论,这将对相位共轭技术应用于激光对抗具有重要的参考意义。     

Test of a Ray-Trace Method for Field Calculations in Antenna Systems Design

A numerical method of beam propagation is based on decomposition of the beam into a set of geometric rays in the Gabor Representation, followed by ray-tracing. The method was developed for the optical design field, whereas here its applicability to MM-wave problems is demonstrated, as are its advantages over other methods for describing diffractive propagation in cases where the components used produce significant aberrations and/or beam clipping. Such cases arise particularly in space borne instruments, due to the limited aperture size (relative to wavelength) and other accommodation constraints. In order to validate this ray-trace method a previously published result, from a paper on the beam-mode method, is used as a test case. This involves the transformation of a gaussian beam by oblique reflection at an off-axis parabolic mirror. The results for ray-trace computation of the aberrated output beam pattern are presented and compared with those of the beam-mode method. At short wavelengths (mirror in the far-field) where the main aberration effect is from beam size variation along the mirror surface, the ray-trace method agrees well with the beam-mode method. At longer wavelengths (mirror in intermediate-field) there is an additional effect of the wavefront centre of curvature varying its position along the mirror, and the ray-trace method is shown to accurately incorporate this effect, whereas the beam-mode method does not. This feature of the ray-trace method should overcome previous restrictions whereby the only designs which could be analysed were those with components either in far-field or collimated regions of the beam.     

Dynamic wavefront correction of Nd:YAG lasers by self-pumped phaseconjugation in photorefractive BaTiO3:Rh

We present an overview of the results we obtained with photorefractive BaTiO₃:Rh in which self-pumped phase conjugation is performed to compensate for dynamic aberrations in Q-switched Nd:YAG lasers. Characterization of the material at 1.06 μm with both cw and nanosecond illumination is detailed. Oxidation of the crystals is proposed to decrease the photorefractive rise time at the expense of absorption. Then an optimized compact ring phase conjugate mirror with high reflectivity and fidelity and a short rise time is described. Finally, such a solid-state mirror is introduced into Q-switched Nd:YAG master oscillator-power amplifier laser sources and provides a diffraction limited beam     

Raman beam cleanup of a severely aberrated pump laser

Distortion-free amplification of a diffraction-limited (D.L.) Stokes beam in a hydrogen Raman amplifier pumped by a severely aberrated XeCl laser (120 × D.L.) has been observed with an attendant power conversion efficiency of the order of 30 percent. The corresponding increase in available far field intensity over that from the aberrated pump beam is 5000. An optical integrator was used to focus the poor quality pump beam into the amplifier and to remove all near-axial components in the pump field. Numerical study of this process using a two-dimensional propagation code shows that the presence of near-axial pump components can cause phase matched four-wave mixing interactions with the Stokes, leading to increased angular divergence of the amplified Stokes beam and the development of secondary sidebands in the far field. When a moderately aberrated pump beam (20 × D.L.) was used, spatial sidebands of the Stokes beam were generated due to increased coherence length for the mixing process, significantly reducing the far field Stokes intensity.