Fig. 1. Schematic of the kilowatt-level linearly polarized narrow-linewidth RFL. NL, narrow linewidth; Cir, circulator; OPM, optical power meter; OSA, optical spectrum analyzer.

Fig. 2. Output characteristics of the linearly polarized narrow-linewidth seed. (a) Output power and FWHM linewidth as functions of pump power, (b) output spectrum at the maximum power level, (c) evolution of the PERs of the pump laser and random laser as functions of pump power.

Fig. 3. Characteristics of the main amplifier. (a) Output and backward power as functions of pump power, (b) output spectrum at maximum power, (c) measurement of beam quality at full power.

Fig. 4. Spectral broadening of the amplified random laser.