Application of YBa2Cu3O7−δ Thin Films on Silicon Substrates for Far-Infrared Fabry-Pérot Resonators

We report on the use of YBa2Cu3O7−δ thin films on silicon substrates as reflectors of a Fabry-Perot resonator in the far-infrared. The peak-transmissivity of the resonator increases with decreasing temperature. At T ≪ T c we obtain a peak transmissivity of ~ 60% and a quality factor of ~ 20 for frequencies, which are smaller than the superconducting energy gap. Because of the small absorption of silicon in the far-infrared, Fabry-Perot resonators with superconducting films on silicon can be used up to high frequencies.