Fig. 1. Experimental setup of the counterpumped RFL. Cir, circulator.

Fig. 2. Power and spectrum characteristics of the counterpumped RFL. (a) Corresponding power of first- and second-order Stokes light as functions of pump power. (b) Output spectra at different pump levels.

Fig. 3. Temporal characteristics of output pulse. Signals of output first-order Stokes light at (a) 5.36 and (b) 6.51 W pump powers. (c) Shapes of output first- and second-order Stokes light at 12.75 W pump level. (d) Evolution of period as function of pump power.

Fig. 4. RF spectra of (a) first-order Stokes light and (c) second-order Stokes light around fundamental repetition frequency with a resolution of 20 Hz. Long-time recording of RF spectra of (b) first-order Stokes light and (d) second-order Stokes light in the range of 0–1 MHz with a resolution of 200 Hz and length of 100 s.

Fig. 5. Calculated (a) output pulse and (b) pulsation period.

Fig. 6. Spatiotemporal distributions of pump light and Stokes light at threshold of first-order Stokes light. Insertion graphs of (a) present the temporal evolution of backward pump power at three different locations. (a) Backward pump power. (b) Forward pump power. (c) Backward Stokes power. (d) Forward Stokes power.

Table 1. Parameters for the Numerical Calculations