Nonequilibrium kinetics of electrons and phonons in superconductors in intense UHF fields

The dependence of the superconducting gap of a thin superconducting film under irradiation by a UHF field is investigated for different values of the amplitude and frequency of the electromagnetic field and arbitrary temperatures. It is shown that the maximal stimulation of superconductivity does not exceed several percent. The distribution functions of nonequilibrium quasiparticles are found for different values of the parameters of the problem. A theoretical investigation of phonon emission from the film under UHF pumping is given. It is shown that in a small spectral interval of frequencies near the double gap value the film does not emit, but absorbs phonons from the substrate. This result is closely related to the stimulation of superconductivity by the UHF field and is due to the effective supercooling of the electron subsystem. The role of heating processes due to inelastic electron-electron collisions, which increase the total number of quasiparticles, is considered and their influence on the kinetics of nonequilibrium electrons and phonon emission is investigated.