In this design microwave photons are propagating in a sapphire rod, and are being absorbed by a superconductor deposited on the surface of the rod. The frequency of the radiation is tuned to be less than the energy gap in the superconductor, so that the pair breaking is not taking place. This photon pumping redistributes the electron-hole quasiparticles: their distribution function is non-equilibrium, and the “phonon-deficit effect” takes place. There is a dielectric material deposited on top of superconductor, which serves asthe “cold finger” of the cooler. Its “acoustical density” is supposed to be smaller than that of the superconducting material, so phonons are being “rectified” and propagate from, but not to it: the energy flows from the “cold finger” into the superconductor. The best reported rectification achieved as of today is about factor of five, which is marginal for our design. To further enhance the rectification, one can use the acoustical filtering. It can be arranged between the superconductor and the “cold finger”. Having a remarkably high heat conductivity and high acoustic density, the sapphire rod serves not only as a photonic wave-guide, but also as a thermal heat sink. It is thermally anchored to the bigger external heat-bath. Spectral phonon filters are arranged between sapphire and superconducting film, so that sapphire would only receive and absorb excess phonons without supplying deficient phonons to the superconductor. We performed calculations using parameters of existing materials;majordetails characterizing the designhave been taken into account. Opportunities are “cool” enough to be pursued experimentally.
Melkonyan G., Gulian A. Prospective solid-state photonic cryocooler based on the “phonon-deficit effect”. Phys. Procedia, 2015, vol. 67, pp 1187 – 1192. https://doi.org/10.1016/j.phpro.2015.06.186
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