title: Low-threshold bidirectional air lasing.
abstract: Air lasing refers to the remote optical pumping of the constituents of ambient air that results in a directional laserlike emission from the pumped region. Intense current investigations of this concept are motivated by the potential applications in remote atmospheric sensing. Different approaches to air lasing are being investigated, but, so far, only the approach based on dissociation and resonant two-photon pumping of air molecules by deep-UV laser pulses has produced measurable lasing energies in real air and in the backward direction, which is of the most relevance for applications. However, the emission had a high pumping threshold, in hundreds of GW/cm^{2}. We demonstrate that the threshold can be virtually eliminated through predissociation of air molecules with an additional nanosecond laser. We use a single tunable pump laser system to generate backward-propagating lasing in both oxygen and nitrogen in air, with energies of up to 1  μJ per pulse.
authors.affiliation: College of Optical Sciences, University of Arizona, 1630 East University Boulevard, Tucson, Arizona 85721, USA.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Laurain
authors.affiliation: College of Optical Sciences, University of Arizona, 1630 East University Boulevard, Tucson, Arizona 85721, USA.
authors.forename: Maik
authors.initials: M
authors.lastname: Scheller
authors.affiliation: College of Optical Sciences, University of Arizona, 1630 East University Boulevard, Tucson, Arizona 85721, USA.
authors.forename: Pavel
authors.initials: P
authors.lastname: Polynkin