Abstract
The dependence of spatial self-focusing on resonator detuning is experimentally investigated in the active medium of a photorefractive oscillator which is a parametric oscillator with narrow gain linewidth. Beam diameter of the TEM00-mode and beat frequency of the TEM00-mode and another simultaneously emitted transverse mode depend on detuning like a dispersion-shaped function. The maximum strength of self-focusing and the corresponding frequency shift are in the resonator strongly reduced with respect to single-pass wave mixing.