应力双折射对偏振相移干涉检测的影响

Influence of Birefringence on Polarization Phase Shifting Interferometry

偏振相移干涉中标准镜头及其他元件的应力双折射会产生检测误差.利用琼斯矩阵对偏振相移原理进行误差分析,发现应力双折射会引起CCD上产生8个相干光干涉,检测误差与CCD像面上的测试光和参考光的振幅之比、检测腔的相位、应力双折射的大小和方向等因素有关.检测误差在每1根干涉条纹中会出现2次周期性变化,误差的峰谷值最大可以达到应力双折射的4倍.当应力双折射的方向具有一致性时可以减小检测误差,当方向完全一致时,检测误差完全消除.通过对一个12英寸的材料进行分析发现,边缘处4英寸材料的应力双折射中心处为18nm,产生的检测误差峰谷值为72nm;边缘处材料的应力双折射为22nm,方向具有更好的一致性,产生的检测误差峰谷值为24.9nm.

The birefringence of transmission flat/sphere and other components introduces measurement error in Polarization Phase Shifting Interferometry （PPSI）. Based on the principle of PPSI, the measurement error was analyzed by using the Jonse maxtrix formulations. It was found that the birefringence generated eight beams interference on the CCD, and the measurement error was a function of the ratio of amplitude of test beam and reference beam, the testing cavity phase, the amount and orientation of birefringence. The measurement error varied 2 periods in every fringe. The maximal PV of measurement error would be 4 times of birefringence and the measurement error would be compressed if the orientation of birefringence was consistent. When the birefringence was of the same orientation, the measurement error could be eliminated. A ？12 inches material was analyzed. The results show that the birefringence of the Ф4 inches area in the center was 18 nm, which introduced the measurement error of 72 nm （PV）. The birefringence of the material at the edge was 22 nm and the measurement error was 24.9 nm （PV） because of the consistence of birefringence orientation.