Diagnostics of laser-ablated carbon plumes by photoionization using a tunable laser

Abstract.

Tunable laser pulses at wavelengths from 250 to 880 nm were fired at plumes produced by laser ablation of a carbon target in He atmosphere. We observed an electrical current due to photoionization, which roughly reflected the behavior of carbon clusters in the plume. The photoionization current had dynamic temporal variations, comprising a rapid increase at the beginning (T_D<0.2 ms, where T_D is the time after a YAG laser pulse for laser ablation irradiates the target), a gradual increase for 0.2<T_D<3 ms, and a slow decrease for T_D>7 ms. The increasing phase of the photoionization current was synchronized with the decreasing phase of C₂ radical density. For He gas pressures lower than 0.8 Torr no photoionization current was detected. The growth rate of the photoionization current was higher for a higher He gas pressure.