Abstract

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, B²Σ⁺_u, and the ground and first excited vibrational state of the ground electronic state, X²Σ⁺_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.

© 2017 IEEE