The microwave enhanced bolometer. A cryogenic particle detector with large gain

Abstract

A cryogenic detector is proposed which is a combination of the thermal calorimeter and the nonthermal superconducting detector: a bolometer crystal covered with a superconducting film. The detector is exposed to microwaves with an energy less than the Cooper pair breaking energy of the superconducting film. The primary excitations of the detector are the nonthermal phonon excitations produced by the interaction of a particle with the crystal. Those phonons are absorbed in the superconducting film and produce excess quasiparticles, which absorb the microwaves. The quasiparticles then de-excite by emission of low energy phonons which heat up the crystal. The detector signal is the temperature rise of the crystal. Because a quasiparticle can absorb many microwave photons during its long lifetime, more energy can flow into the bolometer than originally deposited by the energetic particle. The detector is basically a bolometer where the deposited energy is actively thermalized and amplified. Ultimately, the energy resolution of this detector is limited by the gain fluctuation, which is determined by the Poisson limited uncertainty in the number of excess quasiparticles. © 1990.