会聚光束中偏振匀滑的远场特性分析  

Far-Field Characteristics of Polarization Smoothing in Convergent Beams

作　　者：耿远超[1,2] 黄晚晴 李平[1,2] 张颖 刘兰琴[1] 粟敬钦 Geng Yuanchao;Huang Wanqing;Li Ping;Zhang Ying;Liu Lanqin;Su Jingqin(Laser Fusion Research Center,China Academy of Engineering Physics,Mianyang 621900,Sichuan,China;Graduate School,China Academy of Engineering Physics,Beijing 100088,China)

机构地区：[1]中国工程物理研究院激光聚变研究中心,四川绵阳621900 [2]中国工程物理研究院研究生院,北京100088

出　　处：《光学学报》2023年第20期167-176,共10页Acta Optica Sinica

摘　　要：靶点激光焦斑的偏振匀滑是激光聚变驱动器的关键技术。建立数学模型,对会聚光束中的偏振匀滑进行理论分析。指出该技术在光束远场纵向的匀滑效果,推导激光远场横向分离量和纵向分离量分别与偏振匀滑晶体厚度和倾斜角度的关系。通过数值模拟,给出了激光远场焦斑形态参数与晶体参数之间的关系曲线。结果表明,当晶体厚度和偏转角度取特定范围时,焦斑可以得到最佳的匀滑效果。Objective In laser-driven inertial confinement fusion(ICF)drivers used in fusion experiments,shaping and smoothing the target focal spot are key technologies.To improve the irradiation uniformity of the target and reduce various instabilities related to laser-plasma interaction,a distributed and uniform target focal spot is necessary.Moreover,the uniformity of the focal spot must be maintained up to a certain focal depth.Hence,diffractive devices such as continuous phase plates(CPPs)are used to shape the focal spot and beam smoothing techniques are utilized to reduce contrast of the focal spot.Furthermore,polarization smoothing utilizes the birefringence of crystals to separate the beam into two orthogonally polarized beams that are incoherently superimposed,thus reducing the contrast of the focal spot.This study focuses on polarization smoothing in converging beams and presents a mathematical model that fully describes the transmission characteristics of the beam during polarization smoothing.Moreover,this study demonstrates the relationship between the focal spot shape parameters and the smoothing crystal and lens parameters.Furthermore,the longitudinal smoothing effect of the beam far field is quantitatively described for the first time in this study.Herein,the relationship curve between the contrast of the focal spot and crystal parameters is determined and the optimum range of crystal thickness and tilt angle is calculated.The research obtained from this study can provide a reference for the selection of polarization smoothing techniques and the design of smoothing crystals used in laser drivers.Methods A theoretical and numerical model for realizing polarization smoothing in convergent beams is presented in this study.A CPP is used for shaping the focal spot of a thin lens.The front and back surfaces of the polarization smoothing crystal are parallel and the crystal axis is perpendicular to these surfaces.This crystal is placed in the path of the convergent beam behind the lens.The incident light field is a

关 键 词：激光聚变装置 惯性约束聚变 偏振匀滑 焦斑整形 会聚光束 

分 类 号：TL632.1[核科学技术—核技术及应用]