Fig. 1. Schematic of the photonic crystal rod-based femtosecond fiber CPA laser system. WDM, wavelength division multiplexer; PD-ISO, polarization-dependent optical isolator; AOM, acousto-optic modulator; CFBG, chirped fiber Bragg grating; HWP, half-wave plate; HR, highly reflective mirror; L₁, L_2, L₃, lens with 30 mm, 60 mm, and 20 mm focal length, respectively.

Fig. 2. Optical layout of PP-based transmission grating-pair compressor. G₁ and G₂, gratings; PP₁, PP₂, and PP₃, Porro prisms.

Fig. 3. Spectra of the incident seed and stretched pulses with 0.1 nm resolution. The blue curve shows the spectrum of mode-locked seed pulses and the red curve corresponds to the spectrum of stretched pulses.

Fig. 4. Seed spectrum after reducing the repetition rates to 500 kHz (blue line) and output spectrum of the 35 μm/250 μm LMA DC gain fiber amplification stage (red line).

Fig. 5. Variation tendency of the amplified average power with the increase of pump power in the photonic crystal rod-based main amplification stage.

Fig. 6. Measured results at 51 W of compressed average power: (a) optical spectrum; (b) autocorrelation traces; (c) beam profile; (d) M² factors.

Fig. 7. (a) Output power fluctuations and (b) beam pointing stability of the presented laser system in 8 h at 51 W of average power and around 100 μJ single pulse energy.