THz Time-Domain Spectroscopic Ellipsometry With Simultaneous Measurements of Orthogonal Polarizations

New instrumentation and calibration procedures for terahertz time-domain spectroscopic ellipsometry (THz-TDSE) are demonstrated. The THz-TDSE is capable of simultaneous measurement of two orthogonal components of reflected THz electric fields with no need to rotate a polarizer. In the calibration, the TDSE response function was obtained via the simultaneous polarization measurements reflected by a flat metal mirror, adapted in conventional THz time-domain reflection spectroscopy, and used here for THz-TDSE without the problems of position accuracy. The calibration could be used to determine accurate ellipsometric parameters with high tolerance of imperfect polarizer extinction ratios and of nonideality in the THz reflection components. Results are presented for an opaque Si wafer with heavy doping. The simultaneous measurements rejected significant common-mode noise from the laser, and it extended reliable THz spectra into the frequency range with a low dynamic range of a photoconductive-antenna THz source, which is a fundamental breakthrough for reflection-based measurements and overcomes the hurdle of phase uncertainty.