相位测量偏折术中基于多频相移法的寄生反射抑制法

相位测量偏折术(phase measuring deflectometry,PMD) 是一种针对镜面和类镜面物体的光学三维面形测量技术。但在测量透明物体时,后表面反射光将与前表面反射光混合,从而造成条纹图案混叠,进而引入测量误差。为解决这一问题,本文提出了一种基于多频相移法的后表面反射抑制方法。通过分析相位误差与条纹频率之间的关系,并借助调制度曲线和构造的辅助函数,找到一个特殊的频率,理论上该频率下展开的连续相位等于前表面的相位。又由于透镜的复杂性,利用时间相位展开算法逐频展开的连续相位存在级次计算错误,为此提出了改进算法实现级次校正,进而得到该频率下的屏幕坐标,最终完成前表面面形的准确重建。透明镜片的实测结果表明,所提方法能从混叠条纹中顺利解调出前表面相位。

Suppressing parasitic reflection method based on multi-frequency phase-shifting in phase measuring deflectometry

Phase measuring deflectometry (PMD) is a technique for measuring optical three-dimensional profiles of specular and mirror-like objects.However,when measuring the transparent object,the reflection light from its bottom surface mixes with that created by top surface.This phenomenon produces the superimposed fringe patterns which leads to decrease the measurement accuracy.An effective method based on the principle of muti-frequency and phase-shifting is proposed to solve this problem.By analyzing the relationship between the phase errors and fringe frequencies,and utilizing the characteristics of the modulation curves and introducing an auxiliary function,we can find a special frequency at which the unwrapped continuous phase is equal to the phase of the top surface in theory.Due to the complicacy of a lens,the continuous phase order calculated by temporal phase-unwrapping algorithm frequency-by-frequency may be error.So the order correction method is proposed to solve this matter.And then the screen coordination of the top surface can be obtained by the correction algorithm.The top surface shape can be reconstructed subsequently.Experimental results of measurement of a spectacle lens demonstrate that the proposed method can successfully untangle the phase of the front surface from superimposed reflections.