High-power continuous-wave mid-infrared difference-frequency generation in the presence of thermal effects

We report performance studies of high-power, continuous-wave (cw), mid-infrared (mid-IR) difference-frequency generation (DFG) in MgO:PPLN at 2262 nm based on a narrowband Yb-fiber laser as pump and a Tm-fiber laser as signal source. Using a 50-mm-long crystal, we generate as much as 3.84 W of DFG output power at a single-pass conversion efficiency up to 0.57%/W, with a passive power stability better than 0.53% rms and passive spectral stability better than 0.01% over 1 h. The DFG beam also exhibits excellent spatial beam quality in T E M 00 mode profile with M 2 < 1.2 , and a beam pointing stability better than 16 µrad over > 1 h . Simulations based on focused Gaussian beam theory provide an accurate estimate of the generated DFG output power and confirm thermal effects. Detailed thermal analysis indicates the role of linear absorption at the interacting wavelengths in local heating within the focal volume of the MgO:PPLN crystal. To the best of our knowledge, this is the highest cw DFG output power and conversion efficiency achieved in bulk MgO:PPLN in the mid-IR.