KDP/DKDP倍频晶体是惯性约束聚变系统中的关键元件, 其主截面方向与晶体相位匹配角、晶体吸收系数紧密相关。为了实现KDP/DKDP倍频晶体主截面方向的高精度定位, 本文提出一种光强测量间接定位方法。通过激光器结合稳功率仪及半波片输出稳定线偏振光, 同时旋转相互正交的起偏器与检偏器可获得晶体的最佳消光位置即为主截面方向。推导了该测量系统光强的琼斯矩阵模型, 给出了光强与起偏器、检偏器角度间的关系表达式。采用最小二乘方法拟合经过起偏器、倍频晶体及检偏器的光强变化曲线, 从而可精确定位倍频晶体主截面的方向。通过计算机仿真模拟和实验验证了该方法的正确性和可行性。实验表明, 该方法定位的重复测量精度优于0.02°, 满足惯性约束聚变系统中KDP/DKDP倍频晶体主截面的定位控制精度要求。

A frequency-doubling crystal is one of the most important light components in the inertial confinement fusion (ICF) facility. The principal section is closely related to the phase-matching angle and the absorption coefficient of the frequency-doubling crystal. To orient the principal section accurately, an indirect measurement method is presented based on light intensity. A measurement system was established using a laser, power stabilizer, half-plate, crystal, polarizer, and analyzer. The position of extinction, which was the principal section of the crystal, was obtained by rotating the polarizer and analyzer simultaneously. The Jones matrix model for the measurement system was deduced, and an expression formula for the relationship between light intensity, polarizer, and analyzer was derived. Through least squares curve fitting, the orientation of the principal section can be found. The validity of the model was verified using the simulation and experimental results. The test data show that the repeatability of orientation was better than 0.02°. The location accuracy of this method satisfies the requirements of KDP or DKDP frequency-doubling crystals in the ICF.