Compact, efficient Tm:YAP pumped mid-IR OPO

We describe mid-IR sources utilizing a CSP Optical Parametric Oscillator (OPO) directly pumped by a high efficiency 1.94 μm Tm:YAP Q-switched laser. The OPOs, constructed using the latest generation CSP crystals with low 1.94 μm absorption, were operated at near-degeneracy with mid-IR output in the 3.6-4.2 μm range. Compact Q-switched Tm:YAP lasers, implemented using both a Cr:ZnS saturable absorber Q-switch or a mechanical Q-switching (MQS) technique, were constructed with the Q-switching method’s impact on OPO performance evaluated. Resonant effects were observed for MQS that were absent in the passively Qswitched (PQS) experiment. It was determined that optimizing the OPO resonator length, relative to the cavity length of the Tm:YAP laser, maximized the OPO conversion efficiency. An optimized OPO, pumped at an incident 1.94μm MQS laser power of 7.6W, generated an average mid-IR power of 4.6 W, corresponding to an optical conversion efficiency of 60%, and an overall optical efficiency for mid-IR generation of 21% relative to diode power incident on the Tm:YAP.