【作者】 李恪宇；

【导师】 蔡邦维；

【作者基本信息】 四川大学 ， 光学， 2003， 硕士

【摘要】 在为实现惯性约束聚变（ICF）而进行现代大型激光驱动器的设计时，限制能量特性的一个关键因素，就是光路中大口径谐波转换晶体上所出现的破坏性非线性效应。当泵浦光强度超过产生非线性效应的阈值时，激光通过谐波转换晶体后，不但光束波前质量将有可能变差，而且还会损失一部分能量，更严重的是光学元件的致命破坏。在KDP和KD^*P谐波转换晶体中，沿着垂直泵浦光方向的横向受激拉曼散射（TSRS），是上述所说的非线性效应中，最有可能出现的破坏性非线性效应。因此，本论文以我国ICF驱动装置——神光—Ⅲ原型样机（TIL）的研制为背景，针对装置为用户型装置的要求，考虑驱动器谐波转换晶体运行的安全性，紧密结合中物院多项基金的任务要求，对其中的TSRS进行了探索研究。全文共分八章，取得的主要成果及创新点如下： （1）首次建立了谐波转换晶体的TSRS物理模型 本文根据量子力学原理，在考虑如下物理过程和参量的基础上：光与物质的双光子相互作用；Stokes光的傍轴衍射；Langevin（郎兹万）噪声源；晶体表面反射和端面反射；增益系数、光束口径、脉宽和三倍频光能量密度，推导出高通量激光在KDP和KD^*P谐波转换晶体中的TSRS物理模型和空间上的近轴算符Maxwell-Bloch-Langevin方程组。 （2）编写了TSRS计算程序，并将计算程序进行了校核 本文在谐波转换晶体TSRS物理模型的基础上，编写了TSRS计算程序。为了验证本文所编制程序正确与否，将美国LLNL实验室的相关参数代入本文编写的TSRS计算程。结果表明，在采用相同参数的条件下，二者计算结果一致。同时还将本文计算结果与美国LLNL实验室的计算结果进行了全面、细致的比较，从而证明了本文所编程序及计算方法的正确性和可靠性。 （3）首次开展了ICF驱动器谐波转换晶体中TSRS的研究 ICF驱动器一般采用KDP或KD^*P晶体作为三倍频晶体，而KD^*P晶体的造价要远远高于KDP晶体。同时，两者产生的（F_S）_peak，（Stokes光能量密度最大值）却不同。究竟选择何种晶体作为三倍频晶体，主要取决于它能否承受住TSRS光的光损伤及驱动器的性价比。本文针对神光一IH原型样机（T工L）的技术指标，在长脉冲和短脉冲两种脉宽条件下，对谐波转换晶体的TSRS进行了定量研究。在考虑驱动器运行的可靠性、稳定性及性价比的基础上，为工CF驱动器选择何种晶体（KDP还是KD，P晶体）作为三倍频晶体提供了理论依据。（4）首次进行了高强度情况下谐波转换晶体的TSRS特性研究 为了形成了研究的系统性和普适性，在国内外首次对TSRs、的特性进行了定量研究。在1一4GW/c扩强度条件下，考虑了3。光的强度调制、光束口径、脉宽和强度等因素对谐波转换晶体中TSRS的影响，并计算得出了一些相关阐值，得到了驱动器工作的临界状态，为防止出现TSRS的光损伤提供了理论依据，对高功率激光驱动器的工程设计具有实用价值。 （5）谐波转换晶体TSRS实验平台的设计 通过计算，发现TSRS效应随晶体增益系数g的变化非常敏感，而现有文献对g值的说法不一。为了能提供晶体选择的确切依据，需通过实验测定g值，然后再通过理论计算分析，为最终确定选择何种晶体作为三倍频晶体提供判据。（6）高强度三倍频近场测量实验与模拟计算的误差分析 在ICF的三倍频实验中，以往的研究多注重于高强度和高转换效率，而有关高强度三倍频光束质量的研究在国内还未见实验报道.因此，本文首次通过测量高强度三倍频实验的1。光和3。光的近场光束质量，并将测量和模拟计算所得到3。光近场光束质量作了对比，重点对两者之间所存在的误差进行了探讨，并定性分析了模拟计算程序中还没考虑到的影响3。光光束质量的主要因素，建议在以后的模拟计算程序中再进行优化设计，最后讨论了改善3。光光束质量应采取的必要措施，这对进一步的理论和实验具有参考价值。更多还原

【Abstract】 A serious factor, which influences on limiting energy characteristics of the modem large laser facilities for realizing Inertial Confinement Fusion (ICF), is an appearance of destructive effects in the frequency conversion crystals of large aperture placed in to the beams. At the case of excess of nonlinear effects appearance threshold, not only are quality reduction of the wave front passing optical elements and energy losses possible, but also the fatal destruction of optical elements in themselves are the most grievous. The Transverse Stimulated Raman Scattering (TSRS) is the most probable destructive nonlinear effects in arranges of the above-mentioned classes. Therefore, motivated by the establishment of prototype (TIL) of SG-HI laser facility of China which will act as ICF driver and integrated with the fund requires of CAEP (China Academic of Engineering physics), TSRS in frequency conversion crystals were studied and the security of crystals was considered according to the require that the ICF driver is one for consumer. This thesis was divided into eight chapters, and the main results and innovations obtained here can be summarized as follows:(1) The physics model of TSRS in frequency conversion crystals has been built up firstly.Based on quantum-mechanical viewpoints and the following physical processes and parameters: the two-photo interaction of light with matter, paraxial diffraction of stokes, Langevin noise sources, reflection at the faces and the edges of crystals, gain coefficient, beam aperture, pulse width and fluence of 3, the physics model of TSRS in KDP and KDP crystals acting as high- fluence frequency convector and the paraxial operator Maxwell-Bloch-Langevin equations have been built up.(2) The calculation programming of TSRS has been written and verified.Based on physics model of TSRS in frequency convector crystals, the calculation programming of TSRS has been written. To prove whether the calculation programming of this article is correct or not, the correlative parameters of LLNL in American have been used in this article. The calculation shows the results of LLNL and this article were consistent in the case of the same input parameters. At the same time, the two calculation results have been compared synthetically and particularity, therefore the calculation programming and method of this article have been proved correct and reliable.(3) The TSRS in frequency convector crystals of ICF lasers have been studied for the first time.The KDP or KDP crystals was chose as frequency conversion crystals commonly and the cost of KDP crystals was higher than KDP crystals. At one time, the(peak Stokes fluence) in the two types of crystal was different. It was decided by which crystals can endure the damage of Stokes and the ratio between performance and price to choose which crystals as frequency convectors. According to the technology parameters of the prototype (TIL) of SG-III laser facility, TSRS in frequency convector crystals has been studied quantificationally at two cases of long and short pulse. Based on the reliability, stability and the ratio between performance and price when drivers works, theoretical evidences have been supplied to choose which type of crystals as tripling ones.(4) The characteristics of TSRS in frequency convectors on high-fluence radiation have been studied.The characteristics of TSRS have been studied firstly to form the system and general of study. On the radiation range of l-4GW/cm2, the effects of the modulation in intensity, beam aperture, pulse width and intensity of 3 w on TSRS in frequency convector crystals have been analyzed in detail. The interrelated thresholds have been gained by calculating and theoretical evidences have been offered to prevent TSRS from damaging frequency conversion crystals, which will be applied to the engineering design of the laser drivers on high-fluence .(5) The experiment scheme of TSRS in frequency convector crystals has been designed.It’s found that the effect of TSRS更多还原