Fig. 1. Generation mechanism and basic properties of oxygen atomic lasing^[22]. (a) Schematic of oxygen atomic lasing pumped by a 226 nm ultraviolet picosecond laser; (b) the spectrum of oxygen atomic lasing measured from backward direction along the pump laser propagation path, and the inset shows the far-field profile of backward oxygen atomic lasing; (c) the backward coherent emission versus the side incoherent emission integrated over the solid angle

Fig. 2. N₂ lasing produced by collisional excitation of excited argon atoms^[29]. (a) Energy-level diagram of N₂ lasing produced by the collisional excitation of excited argon atoms (Ar^*); (b) spectrum of fluorescence from the 0.1 MPa nitrogen gas induced by 3.9 μm laser pulses, these radiations correspond to the electronic transition from C state to B state of nitrogen molecules, and the corresponding vibrational levels a

Fig. 3. N₂ lasing produced by electron impact excitation. (a) Electron impact excitation cross sections for B state and C state of N₂ molecules, electrons residing in the shaded region are capable of producing population inversion^[64]; (b) backward emission at 337 nm induced by the 9.3 mJ and 800 nm femtosecond laser pulses as a function of the angle of the quarter wave plate, angles 0°, 90°, 180°, 270° correspond to the linearly po

Fig. 4. N2+ lasing driven by mid-infrared femtosecond laser pulses. (a) Multi-wavelength

Fig. 5. N2+ lasing induced by 800 nm (pump) and 400 nm (probe) femtosecond laser pulses. (a) Schematic for generating

Fig. 6. Dynamic evolution of the populations in three electronic states of N2+ (i.e., X, A and B) driven by the 800 nm laser pulses^[51]. (a) With X-A coup

Fig. 7. Schematic for establishing population inversion in molecular nitrogen ions with 800 nm femtosecond laser pulses^[43]

Fig. 8. Dynamic evolution of electronic state population of N2+ ions calculated with the transient ionization-coupling model^[52]. (a) Schematic for study

Fig. 9. N2+ lasing produced by near-infrared (800 nm) and mid-infrared (1580 nm) pump lasers^[53]. (a)

Fig. 10. Coherent control of N2+ lasing. (a) Schematic of a V-type three-level quantum system created in

Fig. 11. Resonant nonlinear optical effects in nitrogen molecular ions. (a) Ultraviolet spectra in the nitrogen gas excited by the 1580 nm pump laser as a function of gas pressures^[56]; (b) the comparison of ultraviolet spectra from the 2-kPa nitrogen gas and 20-kPa argon gas in the same conditions^[56]; (c) measured probe spectra as a function of the pump-probe delay when injecting an ultraviolet probe las

Fig. 12. High-order Raman scattering based on N2+ lasing^[42]. (a) Schematic of the experimental setup for high-order Raman scattering produced with