  The possibility of enhancing the radiation power and monochromaticity by
optically induced photonic crystal in the superconducting cavity is proposed
and investigated. In such a structure, by periodically irradiating the stacked
Josephson junctions and consequently partially suppression of the
superconductivity in the irradiated positions due to depairing, a periodic
optical configuration is formed. This leads to photonic band gap opening in the
range of the terahertz radiation emitted from the layered superconductor. We
show that such a photonic band gap significantly enhances the impedance
matching at the boundary of the cavity and the waveguide. Since the weak
optical coupling of the outer and inner space of layered superconductor samples
is a serious reason of reducing radiated power especially in the experiments,
the proposed configuration is capable of extremely enhancement in the emitted
power along with attenuation of the undesired harmonics.
