Fig. 1. Experimental setup of the holmium-doped mode-locked seed laser.

Fig. 2. Schematic of the MOPA system.

Fig. 3. (a) The evolution of the optical spectrum with TDFL 1 power. (b) The waveforms under different TDFL 1 power levels. Inset: the pulse width dependence on TDFL 1 power.

Fig. 4. Mode-locked pulse properties. (a) Pulse sequence within approximately 4 μs. (b) Autocorrelation trace with 50 ps scan range. RF spectra measured at approximately (c) 2 MHz and (d) 400 MHz.

Fig. 5. (a) Output power and pulse energy versus TDFL 1 power. (b) Conversion efficiency versus TDFL 1 power.

Fig. 6. (a) Output spectra of mode-locked pulses under different HDF lengths. (b) Center wavelength and output power versus HDF length.

Fig. 7. (a) Variations of output power and pulse energy of a seed laser with UHNAF length. (b) Variation of output power with increasing TDFL 1 power under different output coupling ratios (k).

Fig. 8. (a) Evolutions of output power and pulse energy as a function of TDFL 2 power. (b) Optical spectrum and waveform at the maximum power of TDFL 2.

Fig. 9. (a) Optical spectra versus output power. (b) Pulse envelope at maximum output power. Inset: pulse train at approximately 80 μs. (c) The RF spectrum captured under output power of 54.4 W. Inset: RF spectrum at approximately 400 MHz.

Fig. 10. (a) Output power and pulse energy with increasing 793 nm pump power. (b) Optical spectra in logarithmic and linear coordinates with spectrum resolution of 0.05 nm at output power of 54.4 W.

Fig. 11. Measured power fluctuation over 1 hour under average output power of 45.4 W.