Transverse classical and quantum structures in a triply resonant OPO

Summary form only given. We have developed an experiment to investigate classical and quantum transverse structures in a triply resonant type-II OPO with a KTP-crystal as the amplifying medium. The OPO is single-mode cw-pumped at 532 nm and emits signal and idler fields which are almost frequency-degenerate at 1064 nm. We use a quasi semi-concentric cavity where a large number of higher order transverse modes is frequency degenerate in order to enable simultaneous emission on a large number of transverse modes. This coupling of transverse modes due to the nonlinear medium is a necessary condition for the generation of transverse structures. We have observed simultaneous emission of very high-order-transverse modes (up to the 24th order) together with the TEM00 mode in signal and idler. We have investigated the influence of the thermal self-focusing on the coupling of transverse modes in the signal and in the idler. As the far fields of the transmitted pump-, the signal- and the idler-beams are simultaneously recorded, we have observed for the first time completely different transverse structures of pump, signal and idler beams.