Spectroscopic studies of plasma during cw laser gas heating in flowing argon

Abstract

Cw laser gas heating in flowing argon was studied using emission spectroscopy. The local electron temperature was calculated from the 415.8-nm Ari line spectra ratio to the adjacent continuum emission. The two-dimensional temperature fields were utilized in the calculation of laser power absorption, beam refraction, radiative losses, and net thermal energy retained by the gas. The experiments were performed over a range of laser powers from 2.5 to 6.4 kW and flow velocities between 15 and 120 cm/s. The plasmas were determined to absorb as much as 78% of the incident laser energy at high powers and low flowrates. The calculations indicate that thermal energy retained by the gas is in excess of 35% of the incident energy at intermediate power levels and high flowrates. The results compare favorably with independent calorimetric and thermometric measurements as well as a numerical model. The primary conclusion is that laser propulsion appears feasible in that the earlier dynamic concerns have been shown to be nonexistent or circumventable.