Complete high-frequency measurement of Mueller matrices based on a new coupled-phase modulator

Abstract

A new polarization modulator is presented. It uses two phase-locked identical electro-optic phase modulators at 50 kHz. Thanks to a coupling object introduced between the two phase modulators, the four Stokes parameters of the light beam are independently modulated on the basis of the first and second complex harmonics of the modulation signal. A Mueller matrix ellipsometer (MME) using this new modulation and a multichannel polarimeter are also described. The data processing and the feedback control of Pockels cells is based on a numerical Fourier transform system. It allows one to measure simultaneously, in one modulation period (20 μs), the 16 coefficients of any Mueller matrix. This MME takes advantage of an easy-to-operate calibration method. The high-frequency modulation of the four parameters of the polarization enables low-light-level measurements (without any chopper and lock-in) and presents spectroscopic capabilities. It provides a promising tool for the study of many subjects of growing interest like, for example, rough surfaces treatment or particle characterization.