Terahertz Time-Domain Ellipsometry With Spintronic Emitters: Pauli Coefficients as a Superior Alternative to Jones and Mueller Matrices

In this article, we introduce terahertz complete time-domain spectroscopic ellipsometry (THz-cTDSE), extending traditional ellipsometry by determining full Jones and Mueller matrices for in-depth material characterization. This marks the first application of spintronic terahertz emitters in ellipsometry, achieving pure linear polarization for precise magnetization-based switching. Our complete phase-resolved ellipsometry transforms Jones matrices into an intuitive framework of diattenuations and retardations across all Stokes bases—Pauli exponential coefficients—previously unattainable with incomplete ellipsometry. A novel calibration technique ensures accurate Jones matrix reconstruction without requiring precise alignment of polarizing components, approaching the precision typical of visible-range ellipsometry. We demonstrate THz-cTDSE on quartz and Hg$_{2}$Cl$_{2}$ crystals, advancing the analysis of anisotropic materials.