Influence of the lifetime of the laser-excited level and the laser pulse duration on the saturated LIF signal during the prebreakdown phases of a pseudospark discharge

Abstract

Ground state copper vapor number density, sputtered from the cathode of an experimental pseudospark switch is measured using laser-induced fluorescence (LIF) from the copper transition 4/sup 2/P/sub 3/2/-4/sup 2/D/sub 5/2/ at 510.55 nm. Measurements are made in the hollow cathode at several axial positions in the time interval between the trigger pulse and the voltage breakdown. At voltage 1 kV, this interval, referred to as a prebreakdown phase, has a random and variable shot to shot duration, but discharges for which this duration is the same reveal similar properties and can be arranged in groups. The presented results are for prebreakdown duration of 1 /spl mu/s. The metal vapor density is determined from the LIF signal by using both its maximum and integral. This approach follows from a widely used LIF model, which is examined in detail to reveal a less familiar feature, namely the possibility to obtain an estimate of the lifetime of the laser-excited level, which has been considered perturbed by collisions during the discharge. A comparison between this estimate and the lifetime, obtained by the exponential decay of the LIF signal, reveals good agreement.