Evolution of internal energy distribution and terahertz radiation of a Josephson junctions stack

Being frequency tunable sources, Josephson junctions are attractive for the generation of high frequency electromagnetic radiation. Recently, coherent off-chip THz radiation with an extrapolated output power of some μW was observed. Different mechanisms, like geometry resonance and heating effect, have been raised to explain how the junctions in the stack are synchronized, while there is no consensus which has been reached. To get further understanding on this issue, it is expected to demonstrate the process that the electromagnetic field and thermal distribution evolve as the detected terahertz(THz) emission signal varies in experiment. To realize this goal, we developed a home-made system, by combining a low-temperature scanning laser microscope (LTSLM) and a THz interferometer. With this setup, we are able to simultaneously detect THz emission and observe LTSLM images. In this talk, we will report the unambiguous observation of the correlation between the standing wave patterns, the hotspot formation and the THz radiation characteristics of the Bi2Sr2CaCu2O8 (BSCCO) junctions stack with a mesa structure. We stress that this joint measurement setup will play an important role in studying solid state microwave or terahertz devices.