Observation of stimulated emission of electromagnetic waves by Josephson tunnel junctions

Indirect observations are reported of stimulated emission of electromagnetic radiation by superconducting Josephson tunnel junctions or microbridges in such junctions exhibiting the properties of a strip resonator. Excitation in the resonator of a field of frequency ω by Josephson radiation of frequency ω_J = 2ω gave rise to a current step in the current-voltage characteristics of Nb–oxide–Pb tunnel junctions and this step indicated that lasing occurred at the frequency ω.