A Tunable 350–780 GHz CW solid state oscillator of intrinsic Josephson junctions in a high-Tc superconductor

We report on THz emission measurements and low temperature scanning laser imaging of Bi
2
Sr
2
CaCu
2
O
8
intrinsic Josephson junction stacks. Coherent emission is observed at large dc input power, where a hot spot and a standing wave, formed in the “cold” part of the stack, coexist. By changing bias current and bath temperature the emission frequency can be varied over a wide range of 350–780 GHz; the variation matches the well-known Josephson-frequency relation. The linewidth of radiation, recently measured with an integrated superconductor-insulator-superconductor (SIS) receiver, is as narrow as 6 MHz, much smaller than expected from a purely cavity-induced synchronization. Thus, an additional mechanism seems to play a role. Some scenarios, related to the presence of the hot spot, are discussed.