Ozone tagging velocimetry using narrowband excimer lasers

Ozone tagging velocimetry (OTV), a nonintrusive, unseeded, time-of-flight velocity measurement technique, consists of a write step, where a 193-nm pulsed excimer laser creates an O-3 line via O-2 uv absorption, and a subsequent read step, where a 248-nm excimer laser photodissociates the O-3 and fluoresces the vibrationally excited O-2 product, revealing the tag line displacement. For the first time, instantaneous OTV images and velocity measurements are reported in airflows at room temperature. The narrowband lasers are tuned to the O-2 Schumann-Runge transitions improving the OTV signal strength 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-read delay times of the order of milliseconds or greater. Modeling of O-3 concentration vs time shows O-3 is long lived at room temperature and relatively insensitive to water vapor, but O-3 peak concentration and lifetime greatly decrease at high temperature, though high pressure increases peak O-3 concentration.