Radiation from a Josephson STAR-emitter

Abstract

We calculate the angular dependence of the radiation-zone output power and electric polarization of stimulated terahertz amplified radiation (STAR) emitted from a $dc$ voltage applied across cylindrical and rectangular stacks of intrinsic Josephson junctions. During coherent emission, a spatially uniform $ac$ Josephson current density in the stack acts as a surface electric current density antenna source, leading to an harmonic radiation frequency spectrum, as in experiment, but absent in all cavity modesl of cylindrical mesas. Spatial fluctuations of the $ac$ Josephson current cause its fundamental mode to lock onto the lowest finite energy cylindrical cavity mode, causing it to resonate, leading to a non-uniform magnetic surface current density radiation source, and a non-trivial combined fundamental frequency output power with linear polarization We also present a model of the superconducting substrate, and present results for rectangular mesas.