COMPLETE MUELLER MATRIX MEASUREMENT WITH A SINGLE HIGH-FREQUENCY MODULATION

A new Mueller matrix ellipsometer (MME) is presented. It provides the simultaneous measurement of the 16 Mueller matrix coefficients in four modulation periods (80 mu s under the present conditions). This syste m is accurate (error less than or equal to 1%), robust since there are no moving parts, enables low-light-level measurements without a chopp er and lock-in amplifier and can be easily used for real time measurem ents. The setup is based on the polarization modulator-sample-polariza tion detector configuration. The polarization modulation is provided b y a coupled-phase-modulator (CPM) which uses two identical phase-locke d electro-optic phase modulators operating at 50 KHz. With the introdu ction of a coupling object between the two phase modulators, the four Stokes parameters of the light beam, including the intensity, are inde pendently modulated on the basis of the first and second complex harmo nics of the modulation signal. The polarization of light, after intera ction with the sample, is measured with a multichannel division of amp litude polarimeter (DOAP). This DOAP is based on a slightly beveled am orphous-silicon (a-Si) coated glass plate. The high index of refractio n contrast between a-Si and SiO2, provides an efficient polarimeter, l ess sensitive to the angle of incidence than usual dielectric-coated o nes. The spectroscopic capability of the MME is illustrated by prelimi nary measurements of depolarization effects at two laser wavelengths: He-Ne at 632.8 nm and Ar at 488 nm. (C) 1998 Elsevier Science S.A.