Output of a Josephson stimulated terahertz amplified radiation emitter

The angular dependence of the radiation-zone output power and electric polarization of the stimulated terahertz amplified radiation (STAR) emitted from a $dc$ voltage applied across cylindrical and rectangular stacks of intrinsic Josephson junctions is calculated. 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 models 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 for general radiation directions. Existing Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ crystals atop perfect electric conductors could have STAR emitter power in excess of 5 mW, acceptable for many device applications.