Ultra-high Q terahertz whispering-gallery modes in a silicon resonator

We report on the first experimental demonstration of terahertz (THz) whispering-gallery modes (WGMs) with an ultra high quality (Q) factor of $1.5 \times {10}^{4}$ at 0.62THz. The WGMs are observed in a high resistivity float zone silicon (HRFZ-Si) spherical resonator coupled to a sub-wavelength silica waveguide. A detailed analysis of the coherent continuous wave (CW) THz spectroscopy measurements combined with a numerical model based on Mie-Debye-Aden-Kerker (MDAK) theory allows to unambiguously identify the observed higher order radial THz WGMs.