Dynamic Stokes polarimetric imaging system with dual-wavelength operation

Abstract

In this paper, a photoelastic-modulated Stokes polarimetric imaging system operating at a dual-wavelength is demonstrated. Two laser diodes with specific wavelengths alternately impinged on the sample, and, during the measuring period for one wavelength, the initiating time of light was controlled by a programmable pulse generator that modulated the light four times in a modulation cycle. Therefore, the photoelastic-modulated signal could be frozen and captured by a charge-coupled device, and the Stokes vector could be deduced from the measured ellipsometric parameters. In this system, an equivalent phase retardation technique was employed to avoid disrupting the resonance modulation of the photoelastic modulator while shifting the wavelength from one to the other. As a result, the image of the Stokes vector for different wavelengths could be obtained every second. The output polarization states from polarization elements and an uneven heated liquid crystal variable retarder were verified in the experiment.