Fast bolometric response by high <i>Tc</i> detectors measured with subnanosecond synchrotron radiation

We have measured a fast response by thin-film YBa2Cu3O7−δ detectors to pulsed, broadband, infrared radiation. Synchrotron light from an electron storage ring was used as the infrared source, providing subnanosecond pulses from far infrared through visible. Pulse responsivities as high as 106 V/J and as fast as 4 ns have been observed. For film thicknesses in the range 400–3200 Å, the detector response follows the film absorptivity while the speed varies inversely with thickness, suggesting a bolometric mechanism. Calculations based on such a model are in accord with the data. We find no evidence for any nonbolometric components in the response.