TRANSVERSE EFFECTS AND MODE COUPLINGS IN OPOS

We investigate the triply resonant optical parametric oscillator using a spherical mirror cavity with a pump of arbitrary width. We show tha t, depending on the size of the pump and the cavity geometry, a cross- coupling between different pairs of oscillating cavity modes occurs. T hese coupling integrals for the various mode amplitudes are derived fr om the classical nonlinear field equations in the paraxial approximati on and analytically evaluated for a TEM00 pump field. The correspondin g differential equations for the time evolution of the self-consistent mode amplitudes are derived for typical cavity geometries including t he propagation integrals within the crystal. We discuss the new physic al effects introduced by these couplings in some typical cases. This i ncludes a change of the OPO threshold and stable simultaneous oscillat ion of several mode pairs with fixed relative phases as well as oscill ating self-pulsing type solutions.