Plastic side flow and elastic recovery influences on optical diffraction effect of diamond turning: theoretical simulation and experimental verification.

Spherical/aspherical mirrors are widely used in optical systems and imaging systems, but their reflectivity is affected by the surface roughness. In this study, the effects of plastic side flow and elastic recovery on the diffraction phenomenon and reflectivity are analyzed systematically. The energy ratio of an ultra-precision turning surface is calculated by rigorous coupled-wave method, the influence of aberration on diffraction efficiency is considered in combination with the specific structural parameters of spherical/aspherical surface, and the appropriate measuring beam diameter is selected. Through predicted results and experimental observations, it can be found that with the increase of plastic side flow height, the energy ratio of zero-order diffracted light reduces, the brightness weakens, and the diffraction light spots become more obvious. This is because large plastic side flow height leads to more complex three-dimensional surface topography and great roughness P-V value. The influence of elastic recovery on the reflectivity is different from that of plastic side flow. As the elastic recovery increases, the roughness P-V value lessens. As a result, the energy ratio of zero-order diffracted light enlarges, and the brightness strengthens. This paper provides a theoretical basis for machining of spherical/aspheric mirrors with high reflectivity.