Cross-resonant optical parametric oscillators: study of and application to difference-frequency generation

We revisit both theoretically and experimentally the study of a two-crystal optical parametric oscillator (OPO) for which the signal and the idler beams are totally and exclusively output coupled after the first and the second crystals, respectively. This geometry, referred as cross-resonant OPO, is useful for applications that require the production of two beams that can be independently adjusted. A theoretical analysis is carried out by use of a plane-wave semianalytical rate-equation approach that completely includes pump depletion and reconstruction effects. We also report on an experimental investigation of a 1.064 mu m pump-pulsed KTP cross-resonant OPO whose performance is compared with that of a singly resonant OPO with a similar oscillation threshold. To illustrate the practical advantages of such a configuration, we performed difference-frequency generation in a CdSe crystal by mixing the signal and idler beams of the cross-resonant OPO to produce mid-infrared radiation over the 8-12 mu m range. (C) 2005 Optical Society of America.