SELECTION-RULES FOR TRANSVERSE-MODE EXCITATION IN NONLINEAR RING AND FABRY-PEROT RESONATORS

We establish that the energy transfer between transverse modes in nonl inear Fabry-Perot resonators with curved mirrors, having degenerate or nearly degenerate modes, is governed by selection rules. Although the se rules are derived in a perturbative limit, assuming a thin medium c entered in the resonator, we have found numerically and experimentally that they still account for the otherwise unexpected enhancement or s uppression of certain modes in more realistic cases. The existence of selection rules constitutes a fundamental difference between standing wave and traveling wave cavities and therefore prevents, in principle, the possibility of describing experiments on transverse effects perfo rmed in Fabry-Perot cavities with (simpler) ring resonator models.