Energy spectra of phonons emitted from a nonequilibrium superconducting thin film

Results of a theoretical investigation of the energy spectra of phonons generated by a superconducting thin film under IR and optical pumping, phonon injection via heat pumping, and electron injections through SIS tunnel junctions are reported. The coupled quasiparticle and phonon kinetic equations and a modified BCS gap equation are used as the basis of our study. The use of the thin films as phonon generators or phonon convertors to produce narrow band phonons of energy in the meV range and the mechanisms that limit the bandwidth are discussed.