Fig. 1. Cladding pumped thulium-doped fiber laser. (a) Schematic of laser; (b) external cavity for tunable operation; (c) output power versus launched pump power; (d) output power versus operating wavelength for cladding pumped 2.6 m fiber (inset: output power at 1941 nm versus launched pump power)^[6]

Fig. 2. Thulium-doped fiber laser amplifier with output power of 300 W. (a) Schematic of laser; (b) output power versus pump power^[8]

Fig. 3. 600 W single mode single frequency thulium-doped fiber laser amplifier. (a) Schematic of laser amplifier; (b) output power curve of single frequency amplifier; (c) output spectrum at 608 W (inset: OSA resolution limit of 0.05 nm)^[2]

Fig. 4. 1000 W thulium-doped all-fiber laser. (a) Schematic of laser; (b) output power versus pump power^[3]

Fig. 5. 530 W thulium-doped fiber laser with all-fiber structure. (a) Schematic of laser; (b) spectrum with the output power of 500 W^[12]

Fig. 6. Tunable thulium-doped fiber laser at 2 µm. (a) Schematic of laser (internally marked a is the tuning structure and b is the free-running structure); (b) output power versus pump power; (c) output power of the tunable laser versus operating wavelength (inset: output power at 1930 and 1990 nm versus launched pump power); (d) spectral output of the grating-based laser and the free-running structures^[15]

Fig. 7. Research scheme of high power tunable thulium fiber laser^[11]

Fig. 8. 342 W narrow linewidth continuous-wave thulium-doped fiber laser with all-fiber structure. (a) Schematic setup of the seeder; (b) schematic setup of the two-stage amplifiers; (c) output power versus incident pump power^[26]

Fig. 9. High-power thulium-doped superfluorescent fiber source. (a) Schematic of light source; (b) spectrum for the copropagating ASE; (c) spectrum for the counterpropagating ASE^[30]

Fig. 10. Output signal in quasi-continuous-wave mode and continuous-wave mode

Fig. 11. 1940 nm quasi-continuous-wave thulium-doped fiber laser. (a) Schematic of the laser; (b) output power versus pump power at 793 nm; (c) output spectrum at the average power of 10 W^[38]

Fig. 12. 564 W quasi-continuous-wave thulium-doped fiber laser. (a) Schematic of laser; (b) peak output power at 10 Hz and 5% duty cycle; (c) near-field (top) and far-field (bottom) beam profiles^[39]

Fig. 13. Three quasi-continuous-wave thulium-doped fiber laser products. (a) TLM-50/500-QCW from IPG; (b) IFL QCW 650 from Futonics; (c) MIRON150/750 laser prototype from MIL MED TECH

Fig. 14. Single mode thulium fiber oscillator^[42]

Fig. 15. Water absorption coefficient at different wavelengths^[55]

Fig. 16. SOLTIVE™ Premium medical quasi-continuous-wave thulium-doped fiber laser system from Olympus

Fig. 17. LKSPTm120 laser treatment equipment from LAKH of China

Table 1. Main researches on high power thulium-doped continuous-wave fiber laser in recent 20 years

Table 2. Main researches on tunable thulium-doped continuous-wave fiber laser in recent 20 years.

Table 3. Main researches on narrow-linewidth thulium-doped continuous-wave fiber laser in recent 10 years

Table 4. Main researches on thulium-doped ASE continuous-wave source in recent 15 years

Table 5. Parameters of several typical products for quasi-continuous-wave thulium-doped fiber laser

Table 6. Typical research parameters of nanosecond short-pulsed thulium-doped fiber laser

Table 7. Comparison between thulium-doped fiber laser and Ho∶YAG laser^{[55, 61, 65]}

Table 8. System parameters of several main medical quasi-continuous-wave thulium-doped fiber lasers