Langmuir probe diagnosis of laser ablation plasmas

Abstract

For laser ablation plumes which are significantly ionised, Langmuir probes have proved to be a relatively simple and inexpensive tool for measuring the plume shape, ion energy distribution and electron temperature. In this paper we describe some recent work on the development of Langmuir probes for laser ablation plume diagnosis. Typically in laser ablation plasma the flow velocity is supersonic, which complicates the interpretation of the I-V probe characteristic. We describe some new work on the behaviour of a flat probe lying parallel to the plasma flow. We also compare our measurements with theoretical models of laser ablation plume expansion and draw some conclusions as to which model is more appropriate for the low temperature plasmas which arise in pulsed laser deposition.