Dual rotating-compensator multichannel ellipsometer: instrument design for real-time Mueller matrix spectroscopy of surfaces and films

We describe the design of a high-speed multichannel ellipsometer in the optical configuration PC1r(ω1)SC2r(ω2)A having frequency-coupled rotating compensators (C1r and C2r) and a fixed polarizer and analyzer (P and A) symmetrically placed about the sample (S) on the polarization generation and detection arms of the instrument. For this instrument the frequency-coupled compensators rotate continuously at ω1= 5ω and ω2=3ω, where π/ω is the fundamental optical period. Although the dual rotating-compensator configuration has been proposed and demonstrated earlier, we focus on its extension to real-time Mueller matrix spectroscopy of surface modification and thin-film growth utilizing high-speed multichannel detection with a wide spectral range. The proposed instrument design provides the capability of extracting all 16 elements of the unnormalized Mueller matrix of an evolving sample at 1024 points from 1.5 to 6.5 eV with potential acquisition and repetition times of 0.2 s. Techniques of data acquisition, data reduction, and instrument calibration are described for the general case of arbitrary compensator retardances and polarizer and analyzer angles. We expect that the proposed instrument will have important applications in studies of surfaces and thin films that exhibit anisotropy and inhomogeneity.