Fig. 1. Schematic of N-type degenerate two-level system

Fig. 2. Signal transmission spectra under different Rabi frequencies of pumping light

Fig. 3. Gain peak amplitude of signal light versus Rabi frequency of pumping light under different Doppler widths

Fig. 4. Gain profiles of signal light under different Rabi frequencies of pumping light when Doppler shift (δD=0) is not considered. (a1) Ωp=0.70 MHz; (a2) Ωp=0.83 MHz; (a3) Ωp=0.94 MHz; (b1) Ωp=20 MHz; (b2) Ωp=7.06 MHz; (b3)Ωp=4.9 MHz

Fig. 5. Gain profile variation of signal light when Doppler shift and broadening effects are included. (a) Ωp=10 MHz; (b) Ωp=150 MHz

Fig. 6. Schematic of experimental setup

Fig. 7. Experimentally measured gain peak amplitudes of signal light under different pumping powers when Ps=50 μW, Δp=0, and T=95 ℃. (a) Pp=10 mW; (b) Pp=70 mW

Fig. 8. Gain peak amplitude of signal light with different parameters. (a) Pumping power; (b) temperature

Fig. 9. Influence of signal light polarization state on gain peak amplitude