Terahertz Reflectivity of YBa2Cu3O7-δ at Cryogenic Temperatures

Modern space-based telescopes operating in the terahertz (THz) spectral range require highly reflecting and cryogenically cooled optics ensuring extremely low noise. The idea of using high-temperature superconductor YBa2Cu3O7-delta as a telescope's mirror coating for providing low dissipation and high reflectivity of the surface for the subTHz frequency band has been explored. We are presenting here some results of measurements of the reflection losses in YBa2Cu3O7-delta at cryogenic and room temperatures (4.2-300 K) in the frequency band 0.166-0.23 THz. High-accuracy measurements of the absolute value of reflectivity have been performed with the help of the resonance technique. The measured reflection losses in the given frequency band were below 1%. For the same frequency range, these values are well above the reflection losses in normal metals such as copper or aluminum, which are normally used to covermirrors of telescopes. We, therefore, conclude that the use of high-T-c superconductors YBa2Cu3O7-delta as a highly reflecting coating for the THz telescope's mirror is not advisable.