Enhanced transmission at the zeroth-order mode of a terahertz Fabry-Perot cavity

Abstract: A planar Fabry-Perot cavity with inter-mirror spacing significantly shorter than the probing wavelength is explored for its "zero-order mode" terahertz transmission. The enhanced transmission observed as d approaches 0 indicates that such cavities satisfy the resonance condition across a broad terahertz bandwidth. The experimental signatures from this elusive, "technically challenging" regime are evidenced using time-domain terahertz spectroscopy and are complemented by numerical calculations. The results raise intriguing possibilities for terahertz field modulation and pave new paths for strong coupling of multiple transition frequencies simultaneously.