Far‐infrared Fabry–Perot resonator with high Tc YBa2Cu3O7−δ films on silicon plates

We report on a far‐infrared Fabry–Perot resonator consisting of two high Tc YBa2Cu3O7−δ films on silicon plates. By pulsed laser deposition we prepared on the (100) silicon plates c‐axis oriented epitaxial films (thickness ∼30 nm) with zero resistance at 88.5 K. We demonstrate operation of the resonator in the terahertz frequency range, up to ∼20 THz. At low temperature a high peak transmissivity (between 0.2 and 0.6) and a finesse of the order of 10 have been reached.