Optical lasing during laser filamentation in the nitrogen molecular ion: Ro-vibrational inversion

• Published in: 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) p. 1
• Main Authors: Richter, Maria, Morales, Felipe, Spanner, Michael, Smirnova, Olga, Ivanov, Misha
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.06.2017
• Subjects: Ions; Laser excitation; Nitrogen; Pump lasers; Sociology; Statistics
• DOI: 10.1109/CLEOE-EQEC.2017.8086819

Summary form only given. Inducing and controlling lasing in the open air is an intriguing challenge. Several recent experiments on laser filamentation in air have demonstrated generation of population inversion and lasing at the 391 nm and 428 nm lines in the nitrogen molecular ion [1-8], corresponding to transitions between the ground vibrational state of the second excited electronic state, B 2 Σ u + , and the ground and first excited vibrational state of the ground electronic state, X 2 Σ g + , see figure. Importantly, lasing at these transitions appears to be a very general effect, arising during filamentation of virtually any incident radiation, from visible to mid-infrared. We propose a mechanism that explains the population inversion between the B 2 Σ + u and X 2 Σ + g states based on the combined effect of several processes: (i) tunnel ionization of the neutral nitrogen molecule to the different relevant ionic states, using numerically calculated, angular-resolved strong-field ionization rates, (ii) laser-induced ultrafast electronic excitations in the ion, (iii) molecular vibrations, (iv) alignment of the molecule induced by the strong laser pulse, and (v) molecular rotation upon ionization.