Fig. 1. Experimental setup of the narrow-linewidth, linearly polarized seed laser and fiber amplifier. LD: laser diode; PC: polarization controller; ISO: isolator.

Fig. 2. Reflection spectra of the HR-FBG and transmission spectra of OC-FBG on fast and slow axis, respectively.

Fig. 3. Master oscillator: (a) laser output power versus pump power; (b) spectral linewidth at different output power.

Fig. 4. Laser output power versus pump power.

Fig. 5. Optical spectrum at 1018 W maximum laser.

Fig. 6. An enlarged view of the laser spectrum at different output power.

Fig. 7. Spectral linewidth as a function of laser power.

Fig. 8. Beam quality factor ($M^{2}$) of the output laser beam at 1018 W.