Zusammenfassung

In this letter we report on the application of high Tc superconductors for fabrication of far‐infrared Fabry–Perot resonators. Thin films of YBa2Cu3O7−δ deposited on MgO substrates by the laser ablation technique were used as reflectors. Two films on two different MgO plates were arranged parallel at a distance determining the lowest order resonance. We demonstrate operation of a resonator in a frequency range (up to about 300 cm−1) in which MgO is transparent at low temperature.