Some applications of thin-film high-temperature superconductors, such as bolometers, radiation shielding, and space-cooled electronics, require knowledge of the superconducting-state radiative properties. At present, no general predictive model of the radiative properties has been presented. In this work, reflectance predictions based on two of the major theories of the superconducting state, the classical Drude–London theory and the quantum-mechanical Mattis–Bardeen theory, are compared with the available experimental data to determine the best method for predicting the radiative properties of thin-film Y-Ba-Cu-O. It is seen that the Mattis–Bardeen theory is more successful than the Drude–London theory in predicting the reflectance. Consequently, approximate formulae for the Mattis–Bardeen theory are developed, thus enhancing the theory’s usefulness for engineering calculations.

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