Generation of the electromagnetic radiation by superconducting films

Coherent microwave radiation has been directly detected from superconducting Nb films in the frequency range up to 600 MHz. The mixed state in the films has been influenced by a superposition of two alternating magnetic fields directed perpendicular to film surface. First of them, which slowly varies in time, sets up a vortex structure in the film, while the second high-frequency electromagnetic field provides a synchronization of Abrikosov vortex motion. The simultaneous action of the fields results in either the amplification or generation of electromagnetic radiation. Harmonic mixing of the radiation is also detected