Fig. 1. Experimental setup. Inset，energy-level diagram of neutral and ionic nitrogen molecule

Fig. 2. Spectrum of the forward emission as a function of the pump laser wavelength

Fig. 3. Suppression of the emission obtained at different pump wavelength

Fig. 4. Experimental results of 1 250 nm pump wavelength

Fig. 5. Experimental results of 1 550 nm pump wavelength

Fig. 6. Results of the 1D Maxwell-Bloch modelling