Optical response of epitaxial films of YBa2Cu3O7−δ

We present the results of measurements of optical detection in epitaxial films of YBa2Cu3O7−δ, at wavelengths of 0.63 and 10.6 μm. In contrast to the behavior observed in granular materials, these films appear to show no evidence of nonequilibrium response (breaking of Cooper pairs by photons), but only a bolometric effect (heating of the sample by radiation) in the resistive transition regime. This suggests that epitaxial films do not contain intrinsic links weak enough to be modulated by the incident radiation. For 0.63 μm radiation, mechanically chopped at 725 Hz, measurements of a 10 μm ×90 μm bridge yield a bolometric responsivity of approximately 4×103 V/W, and a detectivity D* of more than 108 cm Hz1/2/W.