Standoff Detection of Trace Molecules by Remote High Gain Backward Lasing in Air

Abstract : This research explored the potential for backward lasing from natural constituents in air with the objective of developing revolutionary methods for standoff detection of trace gases. Backward lasing enables far-field monitoring through modulation methods. The approach utilizes the very high gain available from multiphoton pumping of atomic species, which can be created by the dissociation of molecules in air. Lasing has been demonstrated from oxygen, nitrogen and water vapor. In each of these cases the lasing is achieved by two photon pumping of the atomic fragments, leading to high gain backward lasing from oxygen, nitrogen, and hydrogen atoms. The research has demonstrated that predissociation significantly enhances the efficiency, and in the cases of nitrogen and water vapor it is essential. Backward lasing from two simultaneously pumped, closely separated regions in the air provides a method for the reduction of pulse to pulse fluctuations. Further reduction in pulse to pulse fluctuations will be possible if the dissociate step is eliminated by using argon, which requires three photon pumping. Backward lasing from argon in air has been achieved, but at argon concentrations of 10 . Future work is expected to reduce this threshold to the 1 natural concentration of argon in air.