Fig. 1. Schematic diagram of the single-frequency injection-seeded Ho:YAG laser. The upper left part of the schematic is the transmission path of the oscillating light inside the CCR. Fiber 1–3, 1908 nm fiber lasers; f1–f9, plano-convex lenses (with focal lengths of f1 and f3 being 160 mm, f2, f4 and f5 400 mm, f6 and f7 200 mm, f8 600 mm, f9 240 mm); AOM, acousto-optic modulator; HWP, half-wave plate; CCR1–CCR4, corner cube reflectors; IOS, isolator; F-R, Faraday rotator; S1, S2, splitters; HR is coated with 1.9–2.1 μm high reflection film; thin-film polarizers TFP1–TFP6 are coated with 1.9 μm pump light and 2.1 μm S-polarized high reflection film as well as 2.1 μm P-polarized high transmittance film.

Fig. 2. Wavelength and Fabry–Pérot interferometer spectrum of the Ho:YAG seed laser.

Fig. 3. Output power of the Ho:YAG seed laser.

Fig. 4. The fluctuations of the power and wavelength of the Ho:YAG seed laser.

Fig. 5. Effect of angular deviation of the CCR on the output power of seed laser under SLM and Q-switched operation.

Fig. 6. Wavelength of the Q-switched Ho:YAG laser.

Fig. 7. Effect of angular deviation of the CCR on the output power of the Q-switched slave laser with different cavity lengths.

Fig. 8. Effect of travel distance of CCR3 on the output power.

Fig. 9. Energy and pulse width of the Q-switched Ho:YAG laser.

Fig. 10. The pulse temporal profiles of the Q-switched Ho:YAG laser (a) with injection seeding and (b) without injection seeding.

Fig. 11. The build-up time of the Q-switched Ho:YAG laser with and without injection seeding.

Fig. 12. Output energy of the Ho:YAG amplifier.

Fig. 13. Energy fluctuation of the Ho:YAG amplifier.

Fig. 14. Beam quality of the Ho:YAG amplifier.

Fig. 15. (a) Beating signal. (b) The FFT spectrum.