光束取样光栅强激光近场调制及诱导损伤研究

光束取样光栅(BSG)是一种重要的用于光束取样诊断的衍射光学元件.在惯性约束聚变(ICF)终端光学系统中所使用的BSG，强激光产生的近场调制可能导致其自身的激光诱导损伤从而造成元件不能继续正常工作，为了对其在强激光条件下的正常运行提供分析的依据，采用傅里叶模式理论对BSG内部的近场调制特性进行了模拟计算.计算结果表明，BSG基片内部调制度较小，但仍然存在光强分布不均的情况，增加了这些位置产生激光诱导损伤的风险.另外，通过对BSG制作误差分析得出了其近场调制随各种制作误差的变化关系，结果表明BSG刻槽深度误关键词：光束取样光栅激光诱导损伤惯性约束聚变傅里叶模式法

Study on the near field modulation and laser induced damage of beam sampling grating

The beam sampling grating (BSG) is one kind of important diffractive optical elements which is used in sampling and diagnosis. In terminal optical system of the inertial confinement fusion (ICF) system, the modulation produced by strong laser in the near field, may cause laser induced damage to the BSG. It makes the element work abnormally. In order to provide the theoretical basis for protecting this kind of optical element from laser induced damage under the strong laser condition, this paper uses the Fourier modal theory to carry on the numerical simulation of the interior modulation for BSG in near field. The results indicate that the interior modulation of BSG is weak, but the optical field distribution is still not even, thus in these areas the damage probability is higher than in other positions. Moreover, through the fabrication error analysis of BSG, the relationship between modulation in near field and fabrication error was obtained. The computed results indicate that the depth error and the duty cycle error of grooves affect the modulation of the light beam in near field, but the influence of groove depth error is larger than the duty cycle error. However, if the groove depth error does not exceed a definite value, its modulation also remains on a lower level. Therefore the BSG can still work in the ICF driver normally.