Fig. 1. Fundamental absorption features (plotted as spectral line intensities) of 11 molecular gases^[4]

Fig. 2. Schematic diagrams of different types of nonlinear frequency down-conversion^[32]

Fig. 3. Schematic diagrams of DRO and SRO^[36]

Fig. 4. Experimental setup of the 161 W ZGP OPO & OPA system pumped by the Ho∶YAG MOPA system^[51]. (a) Two-stage amplifier Ho∶YAG MOPA system dual-end-pumped by Tm∶YLF lasers; (b) ZGP OPO & OPA cascade system

Fig. 5. Experimental setup of the 103.9 W ZGP OPO & OPA system pumped by the Ho∶YAG MOPA system^[54]. (a) Ho∶YAG oscillator; (b) first-stage amplifier; (c) second-stage amplifier; (d) ZGP OPO; (e) ZGP OPA

Fig. 6. Experimental setup of the 71 mJ ZGP OPO & OPA system pumped by Ho∶YAG MOPA system^[55]

Fig. 7. Experimental setup of the 200 mJ ZGP OPO & OPA system pumped by Ho∶YLF laser^[59]

Fig. 8. Experimental setup of the modulated peak output power of 99 W of ZGP OPO at 25% duty cycle^[60]

Fig. 9. Parameter relationship curves of ZGP crystal under different conditions^[61].(a) Calculated effective parametric gain length versus pump beam radius for ZGP crystals of different lengths; (b) calculated coupling coefficient versus propagation distance in ZGP crystal for different pump beams radii

Fig. 10. Experimental setup diagram of ZGP OPO with high conversion efficiency of 75.7%^[61]

Fig. 11. Experimental setup of 6.5 W ZGP OPO pumped by Tm³⁺ doped single oscillator fiber laser^[64]

Fig. 12. Experimental setup of high conversion efficiency ZGP OPO pumped by holmium doped all fiber MOPA^[68]. (a) Fiber MOPA with three amplification stages; (b) V-shaped cavity ZGP OPO

Fig. 13. Experimental setup of ZGP OPO pumped by Tm³⁺∶Ho³⁺ codoped fiber laser^[71]. (a) Tm³⁺∶Ho³⁺ codoped fiber laser system; (b) ZGP OPO

Fig. 14. Experimental setup of ZGP OPO pumped by Tm∶YLF solid laser^[75]

Fig. 15. Experimental setup of high beam quality FIRE cavity ZGP OPO pumped by Ho³⁺∶LLF MOPA^[86]

Fig. 16. Experimental setup of high beam quality RISTRA ZGP OPO pumped by Ho³⁺∶LLF MOPA^[87]