Abstract

A multiphoton ionization excitation of N₂ following collisional energy exchange with optically excited H₂O was demonstrated, and its potential for measuring H₂O–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 ${\mathrm{N}}_2^{+}$ 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

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