Fig. 1. Schematic of optical parametric processes

Fig. 2. Photograph and transmission spectrum of BaGa₄Se₇ and BaGa₄S₇ device^{［24，48］}

Fig. 3. Widely tunable mid-infrared laser source based on BaGa₄Se₇ crystal^{［53，55，56］}

Fig. 4. High energy mid-infrared laser based on BaGa₄Se₇ crystal^［57-60］

Fig. 5. High repetition rate mid-infrared laser based on BaGa₄Se₇ crystal^［64］

Fig. 6. Photograph and transmission diagram of LiGaSe₂ and LiGaS₂ device^［71］

Fig. 7. OPOs based on LiGaSe₂ and LiGaS₂crystal^{［73，74］}

Fig. 8. DFGs based on LiGaSe₂ and LiGaS₂crystal^{［71，77，78］}

Fig. 9. Photograph and transmission spectrum of LiInSe₂ and LiInS₂^{［82，87］}

Fig. 10. Mid-infrared DFG laser source based on LiInS₂^［8，91］

Fig. 11. Mid-infrared laser source based on LiInS₂^{［87，94，95］}

Fig. 12. WGR OPO based on CdSiP₂^［107］

Fig. 13. CdSiP₂-OPO pumped by burst-mode laser^［105］

Fig. 14. High repetition rate mid-infrared laser based on CdSiP₂^{［110-112］}

Fig. 15. Tunable CdSiP₂-OPO in 6~7 μm band^{［115，117］}

Fig. 16. Tunable mid-infrared wave laser source based on CdSiP₂ crystal^{［118，119］}

Fig. 17. Large-sized OP-GaP crystal^［29］

Fig. 18. Multi-period OP-GaP crystal and the tunability of OP-GaP-OPO^［124］

Fig. 19. Temperature tuning DFG source based on OP-GaP^［127］

Fig. 20. Widely tunable mid-infrared wave laser source based on OP-GaP crystal^{［125，126］}