Research overview
This paper describes a terahertz frequency-domain ellipsometer that measures the full 4 × 4 Mueller matrix, designed for magnetic resonance studies. Two continuously rotating anisotropic meta wave plates act as polarization state generator and detector, while two wire-grid linear polarizers control the polarization state. A tunable, solid-state continuous-wave source covers 82–125 GHz, and 170–250 GHz with a frequency doubler, with sub-MHz bandwidth. A fast quasi-optical Schottky detector allows the source frequency to be swept rapidly while the wave plates rotate, giving Mueller matrix data at hundreds of wavelengths. Combined with a magnetocryostat (−8 to 8 T, 4–400 K), the instrument can record Zeeman diagrams. The authors determined the thickness of an anisotropic sapphire substrate and validated sensitivity to subtle magnetic resonances with electron paramagnetic resonance measurements on nitrogen-doped SiC.
Key findings
- Full 4 × 4 Mueller matrix ellipsometry in the terahertz range using rotating meta wave plates
- Continuous-wave operation at 82–125 GHz and 170–250 GHz with sub-MHz bandwidth
- Fast frequency sweeping gives Mueller matrix data at hundreds of wavelengths
- Magnetic resonance capability (±8 T, 4–400 K) validated by EPR on nitrogen-doped SiC
