Influence of small-scale phase inhomogeneities on the properties of unstable resonators

Numerical calculations are made of oscillation modes in an unstable resonator with no active medium and containing small-scale phase inhomogeneities. It is shown that, for certain combinations of parameters of the resonator and inhomogeneities, the field of the dominant mode becomes concentrated near the resonator axis and this is accompanied by a sharp rise in the Q factor. The characteristic amplitudes of the inhomogeneities at which such effects may occur represent tenths or even hundredths of the wavelength of the radiation.