Efficient near-room-temperature PPMgLN optical parametric oscillator pumped by an electro-optically Q-switched Tm:YAP laser

The transient conversion dynamics of a near-degenerate doubly-resonant optical parametric oscillator (DRO) based on periodically poled MgO:LiNbO 3 (PPMgLN) were investigated using a time-domain coupled-wave model. Operating in the mid-infrared (MIR) region, the DRO is primarily limited in conversion efficiency by intracavity MIR absorption loss. Simulations indicated that when both back conversion and intracavity absorption are considered, shorter pump pulses are more favorable for DRO operation. For experiment verification, an electro-optically (EO) Q-switched Tm:YAP laser delivering 21 ns pulses at 1937.60 nm with a repetition rate of 5 kHz was used as the pump source. The PPMgLN (grating period 30.14 μm) DRO generated tunable MIR radiation covering 3.73–4.02 μm by varying the crystal temperature over 30–59 °C. Under a pump power of 1.52 W, the MIR output power reached 446 mW, corresponding to a conversion efficiency of 29.34%. The efficiency remained above 20% across the temperature range of 30–46 °C. Parasitic pump-parametric sum-frequency mixing was employed as near-infrared probe to trace the MIR spectral evolution, revealing stronger mode competition near degeneracy. The highest output power was obtained at a slightly detuned, near-room-temperature operating condition rather than at exact degeneracy. To the best of our knowledge, this work represents the first demonstration of a PPMgLN-based MIR-DRO pumped by an EO Q-switched laser. It also achieves the highest pump-to-MIR conversion efficiency reported to date for PPMgLN-based MIR sources driven by a free-running pump laser. This work offers a low-complexity route to efficient MIR generation from near-room-temperature PPMgLN DROs.