空域移相偏振点衍射波前检测技术

点衍射干涉仪结构简单、共光路、测量精度高, 空域移相干涉仪抗振性能优越, 两者在波前检测领域获得了广泛的应用. 本文采用激光打孔技术, 通过在金属纳米线栅偏振片上制备小孔, 制作了偏振点衍射板; 结合分光结构的空域移相技术, 搭建了空域移相偏振点衍射干涉仪, 并对一焦距为550 mm, F_#10的平行光管准直物镜透射波前进行测量, 与法国Phasics公司生产的商业化波前传感器SID4的测量结果相比较, 两者峰谷值相差0.09λ, 均方根值相差0.012λ ; 利用35项Zernike多项式拟合两者的测量结果, 将拟合得到的系数在同一坐标轴下绘制成两条曲线, 两者基本重合, 从而验证了所搭建的空域移相偏振点衍射波前检测装置的测试精度. 从而在传统点衍射干涉仪的基础上引入了空域移相技术, 实现了波前的高分辨率、高精度、实时检测, 并且提高了对振动、气流等环境因素的抗干扰能力.

Spatial phase-shifting polarization point-piffraction interferometer for wavefront measurement

Wavefront measurement is widely used in the field of optical manufacturing, military, astronomy, medical treatment, etc., and it reflects the performance of the optical system through evaluating aberrations. Relevant studies have been carried out by many researchers. Among them, point-diffraction interferometer and spatial phase-shifting interferometer are two significant instruments for the wavefront measurement. Point-diffraction interferometer is a simple self-referencing configuration with high precision, and spatial phase-shifting interferometer can be used in the vibration environment or for measuring the dynamic object. Owing to these advantages, they have been widely used in the field of wavefront measurement. In this paper, to realize the combination of these two techniques, we propose a new method of fabricating a polarization point-diffraction plate. Through laser drilling technology, we fabricate a pinhole at a micron level on a wire grid polarizer with a period and depth of 140 nm and 100 nm respectively, and fabricate a polarization point-diffraction plate. We analyze the principle of laser drilling, the orthogonally polarized reference beam and test beam generation mechanism of the polarization point-diffraction plate. The principle of spatial phase-shifting interferometer is deduced by adopting Stokes vector and mueller matrix. Combining with the spatial phase-shifting system with beam splitter, a spatial phase-shifting polarization point-diffraction interferometer is built. In the experimental apparatus, the diameter of the pinhole on the polarization point-diffraction plate is 10.2 μm, the beam splitter is a chessboard phase grating whose period, duty cycle, and etched depth are 34 μm, 0.5, and 577 nm respectively, and the phase-shifting component is a 2×2 wave-plate array which is glued together with a 1/4 wave-plate, a 1/2 wave-plate, a 3/4 wave-plate and a full wave-plate; the four fast-axes of the wave-plates are all along the horizontal direction. The spatial phase-shifting polarization point-diffraction interferometer is used to measure the transmitted wavefront through a collimating lens with a focal length of 550 mm and F_#10 which are used on a collimator. The measured peak-to-valley value, root-mean-square value and Zernike fitting coefficients are in good agreement with those obtained by SID4 wavefront sensor made by Phasics corporation in France, which verifies the reliability of the measuring results obtained by spatial phase-shifting polarization point-diffraction interferometer. The spatial phase-shifting polarization point-diffraction interferometer introduces spatial phase-shifting technology into traditional point-diffraction interferometer, thereby achieving real-time wavefront measurement with high resolution and precision, and also improving the immunity to vibration, air turbulence, etc.