High power optical parametric oscillators for optical refrigeration in solids

A high power singly resonant optical parametric oscillator based on periodically polled LiNbO/sub 3/ (PPLN) is developed to produce >6 W cw signal power tunable in the /spl lambda/=1.7-2.1 /spl mu/m range. This OPO was then used to observe net optical refrigeration in a thulium-doped solid for the first time. The OPO was synchronously pumped by a cw-modelocked (70 ps FWHM) Nd:YAG laser with P/sub ave/=18 W. The observed slope efficiency is more than 42%.