Power absorption in laser-sustained argon plasmas

Abstract

In this experimental investigation, stable and axisymmetric laser-sustained plasmas were produced in flowing argon. Energy was provided by the focused beam from a carbon dioxide laser; two different focusing geometries were used. Spatial distributions of absolute radiance from the plasmas, in a narrow-wavelength band, were measured. The assumption of axial symmetry, along with the assumption of local thermodynamic equilibrium, was used to deduce the radial profiles of temperature in the plasmas. From this and a geometric raytrace, the detailed spatial distribution of power absorption was calculated, as well as the radiation lost from the plasmas. In addition to the focusing geometry, the flow velocity, pressure, and incident laser power were systematically varied in the experiments. The quantitative results indicate clearly that a perceptive analysis of such laser-sustained plasmas must take into consideration the two-dimensionality of both the flowfield and the laser energy distribution in the focused beam.