Fig. 1. Experimental setup of counter tandem pumping

Fig. 2. Experimental results of counter tandem pumping fiber amplifier. (a) Output power and efficiency versus pump power; (b) output spectra at powers of 70 W (seed laser) and 8380 W; (c) time sequence and corresponding spectrum (inset) of laser at power of 8380 W; (d) output beam quality at power of 8380 W