An instantaneous polarization phase-shifting interferometric system with stroboscopic illumination by using a photoelastic modulator

Abstract

We present a phase-shifting interferometric system that uses the photoelastic modulator (PEM) with the stroboscopic illumination technique. The laser diode is controlled by a programmable pulse generator for triggering four short pulses at their specific temporal phase angles of a modulation cycle for phase-shifting operation. Thereby, the intensity variation of the PEM modulated signal can be freezed and the interferograms captured by a charge-coupled device. In this configuration, no mechanical operations are required in phase-shifting by using the stroboscopic illumination technique, and fast interference fringe measurements are possible. We performed experiments to demonstrate the phase map of two static samples and confirmed that the method is applicable to imaging the complex phase distributions of dynamic objects at speed of 2 Hz. The thickness deviation is almost less than 5% for an ultra-thin transparent film.