Fig. 1. Schematic diagram of efficient mid-infrared generation based on intracavity DFG.

Fig. 2. (a) Simulated signal wavelength versus grating period at different crystal temperatures. (b) Simulated tuning curves for $55\,^{\circ }\text{C}$ with $1018~\text{nm}/1080~\text{nm}$ pumping.

Fig. 3. Measured idler and signal spectra under different pumping conditions when the PPLN temperature was controlled at $55\,^{\circ }\text{C}$.

Fig. 4. Measured 3.1 and $3.7~\unicode[STIX]{x03BC}\text{m}$ idler power, conversion efficiency of 1018 and 1080 nm pump waves (a) versus the 1018 nm pump power under strong 1080 nm pumping and (b) versus the 1080 nm pump power under strong 1018 nm pumping. Inset in (a): power scaling of 1018 nm pumped OPO. Inset in (b): power scaling of 1080 nm pumped OPO.