Far-infrared Fabry Perot filter of high transmission with high-Tc superconductor reflectors

We report on a far-infrared Fabry Perot filter with high-T _c superconductor reflectors that has a high peak-transmission. The filter consists of two plane parallel MgO plates, with the adjacent surfaces coated with YBa₂Cu₃O₇-gd thin films. The resonance frequencies are mainly determined by the distance between the films. We present data for a filter that has for the first order resonance at a frequency of 80 cm^?1a quality factor of 55 and a peak-transmissivity of 0.16. The shape of the transmission curve is determined by standing waves between the films and within the plates.