Abstract

A time-of-flight velocity measurement technique, utilizing ions formed in a flowing gas by the process of laser-induced breakdown, is described. A highly resolved (spatially and temporally) packet of ions is produced by focusing a pulsed, high energy laser beam in the flow field of a free-jet expansion. The free-jet expansion is formed by exhausting gas through a converging nozzle into a vacuum. Such an expansion represents a flow which undergoes transition from being subsonic and continuum in nature upstream of the nozzle throat, to one that is supersonic and rapidly approaching a collision-free state downstream of the nozzle throat. The ions are produced near the nozzle exit, swept downstream along with the rest of the flow, and collected with a suitable probe. Flow velocities are deduced from measurements of the ion flight path distance and flight time. The apparatus employed for these measurements is described and actual jet-flow velocity measurements presented. In addition, velocity measurements made by the laser-induced breakdown ion time-of-flight technique are compared with similar measurements obtained by an electron beam ion time-of-flight method.

© 1986 Optical Society of America