Ozone tagging velocimetry using narrowband excimer lasers

Ozone tagging velocimetry (OTV), a nonintrusive, unseeded, time-of-flight v elocity measurement technique, consists of a write step, where a 193-nm pul sed excimer laser creates an O-3 line via O-2 uv absorption, and a subseque nt read step, where a 248-nm excimer laser photodissociates the O-3 and flu oresces the vibrationally excited O-2 product, revealing the tag line displ acement. For the first time, instantaneous OTV images and velocity measurem ents are reported in airflows at room temperature. The narrowband lasers ar e tuned to the O-2 Schumann-Runge transitions improving the OTV signal stre ngth by a factor of six over that obtained using two broadband lasers. This improvement is less than expected from absorption ratio estimates, due in part to incomplete laser locking efficiency and possibly to laser bleaching . Diffusion of the O-3 tag line is shown to be important only for write-rea d delay times of the order of milliseconds or greater. Modeling of O-3 conc entration vs time shows O-3 is long lived at room temperature and relativel y insensitive to water vapor, but O-3 peak concentration and lifetime great ly decrease at high temperature, though high pressure increases peak O-3 co ncentration.