THERMAL-RESPONSE TIME OF SUPERCONDUCTING TRANSITION-EDGE MICROCALORIMETERS

We investigate limits on the thermal-response time of superconducting transition-edge microcalorimeters. For operation at 0.1 K, we show tha t the lower limit on the response time of a superconducting transition -edge microcalorimeter is of order 1 mu s due to the heat diffusion ti me, electrical instabilities, the amplifier noise, and the critical cu rrent of the superconducting film. The response time is not limited by self-heating effects and is independent of the intended photon energy . However, design constraints associated with the inductance of the bi as circuit make it difficult to achieve the fastest response times for devices with heat capacities high enough for x-ray and gamma-ray dete ction.