Abstract
We have demonstrated, for the first time to our knowledge, a coupled tandem optical parametric oscillator (OPO) configuration in which a second ZnGeP2 OPO is: placed within the resonator of the first. KTiOPO4, OPO. A significant enhancement in the overall cascaded efficiency of this OPO compared with standard two-stage OPO's was observed. With a multimode? Nd:YAG laser, an overall optical-to-optical efficiency (from 1.06 mu m to the mid LR) of 5.2% was obtained from operating only similar to 1.4 times above oscillation threshold. The measured overall slope efficiency was attractively high at 35%. With a single set of mirrors we obtained a broad wavelength-tuning range from 2.7 to 8 mu m. (C) 1998 Optical Society of America.