Continuous-wave, singly resonant OPO at 3 \mu m
  We report a continuous-wave, singly resonant optical parametric oscillator (SRO) at 3.3 \mu m by using a MgO:PPLN crystal as the gain medium and a Yb-fiber laser at 1.064 \mu m as the pump source. At 25-W pump power, the SRO generated 7.4 and 0.2-W powers at 1.57 and 3.3 \mu m, respectively. The 3.3-\mu m SRO has a single-longitudinal-mode output with a ~5-MHz linewidth. We observed thermally induced optical bistability in the SRO due to the slight absorption of the 3.3-\mu m wave in the MgO:PPLN crystal. Pump depletion was clamped at 60% while spectral hole burning was observed in the depleted pump. 
S. T. Lin, Y. Y. Lin, Y. C. Huang, A. C. Chiang, and J. T. Shy