光学元件波前梯度的数值计算方法

 惯性约束聚变系统中光学元件的波前梯度均方根是一个关键参数，对其数值计算涉及到的空域处理、频域滤波及梯度算法等关键技术进行了理论分析。分别采用最简单差分算法、中心差分算法、最小二乘拟合算法、“五点法”对实测波前数据进行了梯度均方根值计算。结果表明波前数据的空域处理采用Quad-flip技术较为合适；频域滤波器的选用上应着重考虑滤波的有效性。对于原始波前，4种算法计算梯度均方根值的差别小于0.01 λ/cm(λ=632.8 nm)；而对于截止频率为0.0303 线/mm的低通滤波后波前，其差别小于0.001 λ/cm，该差别对计算结果的影响可以忽略。

Numerical computation of wavefront gradient of optics

Wavefront rms gradient is a very improtant optical parameter used in ICF system. Critical technique involved in numerical computation of wavefront gradient are space processing, frequency filtering and computing algorithm of gradient et al. The simplest difference and central algorithm, least-square method and "five-point" algorithm are applied to compute rms gradient of tested wavefront. The analysis result shows that Quad-flip technique is a good choice for space processing and the filtering validty is more important for frequency filter. For original wavefront, the difference of rms gradient value of four methods is less than 0.01 λ/cm; while for 33 mm low-pass filtered wavefront , the difference is less than 0.001 λ/cm which is neglectable.