Tunable Phase Transition via Radiative Loss Controlling in a Terahertz Attenuated Total Reflection based Metasurface

Actively controlling the phase of terahertz wave has received much attention. Here, we present a complete theoretical treatment by using coupled-mode theory to actively control the reflective wave phase in a attenuated total reflection-based metasurface. Controlling is achieved by variations in the air gap, enabling the radiative loss (radiative Q factor) to be continuously adjusted over a narrowband frequency range. A singularity can be found in the phase slope spectrum when the radiation loss is equal to the intrinsic loss determined by material properties. The theoretical results have been verified by simulation and the experimental results. The physical mechanism of this phase transition in attenuated total reflection configuration would pave the way for potential applications such as polarization modulation, and guide further research works for terahertz physics.