Fig. 1. Experimental setup for 976 nm end-pumped Er∶Yb∶LPS microchip laser^[10]

Fig. 2. Experimental setup for fiber laser resonantly pumped Er∶YAG single-frequency laser with F-Ps^[23]

Fig. 3. Structure of 8-type Er∶YAG single-frequency laser with ring cavity^[24]

Fig. 4. Er∶YAG NPRO single-frequency laser^[36]

Fig. 5. Experimental setup for single-frequency twisted-mode-cavity Er∶YAG laser^[38]

Fig. 6. Single-frequency fiber laser based on distributed Bragg reflector^[44]

Fig. 7. Injection seeded Er∶YAG single-frequency laser at 1645 nm fabricated by CTI Inc.^[45]

Fig. 8. High repetition frequency injection seeded Er∶YAG single-frequency laser at 1617 nm^[40]

Fig. 9. Injection seeded Er∶YAG single-frequency laser with multi-reflection architecture^[59]

Fig. 10. Experimental facility of Er∶YAG single-frequency laser based on Pound-Drever-Hall locking technique^[75]

Fig. 11. Injection seeded Ho∶YLF single-frequency laser^[5]

Fig. 12. Planar waveguide amplifier of Mitsubishi Inc.^[87-88]. (a) Waveguide structure; (b) schematic of planar waveguide amplifier