Far-infrared transmittance and reflectance of YBa2Cu3O7-delta films on Si substrates

The transmittance and reflectance of superconductive YBa2Cu3O7-delta (YBCO) thin films deposited on Si substrates have been measured in the far-infrar ed frequency region from 10 to 100 cm(-1) (wavelength from 1000 to 100 mu m ) at temperatures between 10 and 300 K. The effects of interference, optica l resonance, and antireflection on the radiative properties of high-tempera ture superconducting (HTSC) films are observed and quantitatively analyzed. Furthermore, we have measured the reflectance of the HTSC film-substrate c omposites for radiation incident on the substrate side (backside reflectanc e) for the first time. The backside reflectance increases significantly fro m the normal state to the superconducting state at certain frequencies; thi s experimentally demonstrates that HTSC films can be used to build far-infr ared intensity modulators. The complex refractive index of the YBCO films i s determined from the measured transmittance using the Drude model in the n ormal state and a two-fluid model in the superconducting state. The complex refractive index obtained from this study is useful for various applicatio ns of YBCO films, including radiation modulators, detectors, and Fabry-Pero t resonators.