Fabry-Perot resonators built with YBa2Cu3O7-delta films on Si substrates

Fabry-Perot resonators were built front two superconductive YBa2Cu3O7-delta (YBCO) films separated by a spacer. Each film of 35-nm thickness was depos ited on a Si substrate, about 204 mum thick. A slow-scan Michelson interfer ometer was employed to measure the transmittance of the resonator in the fa r-infrared frequency region from 10 to 90 cm(-1) at temperatures between 10 and 300 K. Measurements showed that in the normal state the peak (or reson ant) transmittance decreases as temperature is lowered, whereas in the supe rconducting state it cart increase with decreasing temperature. The transmi ttance of the resonator was calculated using properties of individual refle ctors obtained previously. resonant transmittance was predicted based on ni t optimization analysis in which the When the effect of partial coherence i s taken into consideration, the calculated transmittance is in good agreeme nt with the experiments. Furthermore, the maximum possible resonant transmi ttance was predicted based on nit optimization analysis in which the cavity length is varied. The effect of the YBCO film thickness on the transmittan ce peaks was also studied, showing that the resonant transmittance decrease s but the finesse increases as the film thickness is increased. This study should help improve the future design of Fabry-Perot resonators based on HT SC thin films.