Fig. 1. Forward spectra recorded at the gas pressures of (a) 22, (b) 100, and (c) 260 mbar in a pump–probe scheme. (d) Energy level diagram of the ionized and neutral nitrogen molecules in which the B2Σu+(v′=5,4,3)→X2Σg+(v=4,3,2) transitions are indicated with the corresponding lasing wavelengths.

Fig. 2. Forward spectra captured at the different wavelengths of the seed pulses. The central wavelengths of the seed pulses are indicated on the side of the corresponding spectra.

Fig. 3. The temporal evolution of the N2+ laser at the wavelengths of (a) 353.3, (b) 353.8, and (c) 354.9 nm with the time delay between the pump and probe pulses at a gas pressure of 22 mbar.

Fig. 4. The temporal evolution of the N2+ laser at the wavelengths of (a) 353.3 and (b) 353.8 nm with the time delay between the pump and probe pulses at gas pressures of 22, 100, and 260 mbar.