Practical method for improving the accuracy of weakly stressed birefringence detection by circularly polarized instantaneous photoelasticity

Abstract

Due to the mismatch between the quarter-wave plate and the wavelength of the light source, the circularly polarized field photoelastic stress analysis method has an impact on the measurement of the phase delay and the stress direction angle. In particular, the measurement of the phase delay is inaccurate for weakly stressed samples with phase delays less than a quarter-wavelength. In this paper, we first give a method for calculating the mismatch value δ , which requires only one air calibration without prior calibration of the parameters of the quarter-wave plate with other equipment. We then introduce δ into the correction process for the phase delay, derive the correction equation, and give a theoretical comparison of the relative error curves. The results show that the correction method can theoretically limit the maximum amount of error. Finally, we have verified the accuracy of the method by measurements of the internal lens stress before and after the correction and by stitching measurements on SiC wafers.