Influence of Random Bulk Inhomogeneities on Quasi-Optical Cavity   Resonator Spectrum
  We suggest the statistical spectral theory of oscillations in quasi-optical cavity resonator filled with random inhomogeneities. It is shown that inhomogeneities in the resonator result in intermode scattering leading to the shift and broadening of spectral lines. The shift and broadening of each line essentially depends on frequency distance to adjacent spectral lines. With increasing the distance the influence of inhomogeneities sharply reduces. The solitary spectral lines which have the distance to the nearest lines quite large is slightly changed due to small inhomogeneities. Owing to such selective influence of inhomogeneities on the spectral lines the effective spectrum rarefaction appears. Both the shift and broadening of spectral lines as well as spectrum rarefaction in quasi-optical cavity millimeter wave resonator were detected experimentally. We found out that inhomogeneities result in stochastization of the resonator spectrum in that mixed state appears, i.e. the spectrum acquires both regular and random parts. The active self-oscillator system based on the inhomogeneous quasi-optical cavity millimeter wave resonator with Gunn diode was studied as well. The inhomogeneous quasi-optical cavity millimeter wave resonator (passive and active) can serve as a model of semiconductor quantum billiard. Based on our results we suggest using such billiards with spectrum rarefied by random inhomogeneities as an active system of semiconductor laser. 
E.M. Ganapolskii, Z.E. Eremenko, Yu.V. Tarasov