曝光系统离焦对平面全息光栅衍射波前的影响

波前像差是衍射光栅的重要技术指标，它直接影响光栅的分辨率。由光致刻蚀剂记录两束相干光干涉条纹是制作全息光栅的关键步骤。为了提高全息光栅曝光系统调整精度、减小离焦、降低光栅的衍射波前像差，从离焦对反射球面准直镜的准直光平行度的影响程度出发，分析了准直光平行度对全息光栅衍射波前像差的影响。理论分析和数值模拟结果表明，准直镜调整误差直接决定全息光栅衍射波前像差大小。以3种不同刻线密度光栅为例，得出了准直镜调整误差的允许变化范围。

Influence of defocus of exposure system on diffraction

As one of the important technical specifications of diffraction grating, diffraction wave front aberration directly affects the grating resolution. Recording the interference fringe produced from two coherent light beams by use of photoresist is a key process in manufacturing a holographic grating. According to the influence of defocus on collimating light parallelism of reflecting spherical collimating mirror, this paper analyzes the influence of collimating light parallelism on the wave front of holographic grating to improve setting accuracy, minimize defocus of exposure system in holographic grating, and to reduce diffraction wave front aberration of grating. The results of theoretic analysis and numerical simulation show that diffraction wave front aberration of grating is directly determined by the adjusting error of collimating mirror. In addition, by taking three kinds of gratings with different ruling densities for examples, the allowable range of adjusting error of collimating mirror is obtained.