Optical properties of YBaCuO thin films at Far-Infrared monochromatic light

By using monochromatic sources of radiation we measured the reflectivity and transmission vs temperature behavior of YBaCuO thin film in the Far Infrared region in the range 300-20 K. A smooth change of optical properties is observed from critical temperature down to 40 K with an evident reduction of the losses for all the frequencies we examined. To analyze the use of YBaCuO films as semireflecting elements in submillimeter devices we made a preliminary study of the optical properties of the substrate in the same conditions. The permanence of the sample in a superconducting phase can be deduced from its room-temperature transmittance, as it changes drastically if some degeneracy occurs in the film.