Fig. 1. Schematic setup of the high-power bi-mode femtosecond fiber laser. Amp, amplifier; AOM, acousto-optic modulator; RS, Raman scattering; M, mirror; GP, grating pair.

Fig. 2. (a) Optical spectrum of the seed, measured at the output of the seed. (b) The optical spectrum when laser power is 66.6 W, measured after the end cap. The spectral resolution of both (a) and (b) is 0.02 nm. (c) The pulse train of the laser source operating at the burst mode with a duty cycle of 90%. The inset shows the intrapulses in the burst envelope.

Fig. 3. (a) Pulse profile at the 1064-nm band before compression, measured at an output power of 66.6 W. (b) ACF measured at an output power of 40.82 W and a duty cycle of 90%.

Fig. 4. Performance of the fundamental wavelength component (i.e., 1064 nm). (a) Long-term power stability of the main optical fiber amplifier measured at an output power of 66.6 W (before compressing). (b) Slope efficiency. (c) Laser beam quality M² measurement.

Fig. 5. (a) Optical spectra of the fiber laser source operating with a duty cycle of 10%; from top to bottom, the average output powers at ∼1.1 µm are 0.018, 1.926, 11.56, and 17.23 W, respectively. (b) Optical spectra with duty cycles of 90%, 50%, 20%, and 10%, respectively.

Fig. 6. Performances of the 1125-nm wavelength component. (a) Slope efficiency; (b) beam quality M² measured at an output power of 17.23 W and a duty cycle of 10%. The inset shows the laser beam profile.