A multiphoton ionization excitation of N2 following collisional energy exchange with optically excited H2 O was demonstrated, and its potential for measuring H2 O–N2 mixing at the molecular level was evaluated. In this process, N2 is sensitized by a collisional energy exchange with H2O molecules excited by a tunable KrF laser. The sensitized N2 molecules are further excited and ionized by two additional photons of the same laser pulse. Independent images of sensitized N2+ emission at 391.4 nm and by OH at 308 nm formed by the dissociation of excited H2O were obtained along a laser beam traversing slow dry-air and N2 jets entering room air. Although effects of O2 and N2 collisional quenching were noted, such images can potentially be used to measure H2O–N2 molecular mixing and the concentration of H2O independently. The detection of H2O nucleation by this technique suggests that imaging of H2O droplet evaporation or visualizing and monitoring H2O condensation may also be possible.
© 1997 Optical Society of America
Gabriel Laufer, Anthony S. Lee, and Harsha K. Chelliah, "Multiphoton excitation ionization of N2 following collisional energy transfer with H2O: a potential measure of molecular mixing," Appl. Opt. 36, 3278-3287 (1997)