Spatially resolved LAAS diagnostics of a free-burning ar arc: Analysis of line broadening

Abstract

Spatially resolved laser atomic absorption spectroscopy (LAAS) diagnostics are applied to a free-burning DC arc in argon at atmospheric pressure. The novel LAAS apparatus is capable of mode-hop free wavelength tuning over the larger range than in conventional systems (up to 300 GHz in the present work). It allows for the measurements of both the absorption coefficient and the spectral line profile continuously from the hot arc center to the non-equilibrium arc wings. The results of such measurements are presented in this work with the emphasize on the combined analysis of laser absorption, which gives densities of excited atoms, and line broadening, which delivers information on either electron density (in case of Stark broadening) or neutral atom density (in case of van der Waals broadening). Contributions by different broadening mechanisms (Stark, Doppler, van der Waals, Resonance) are separated and analyzed. Experimentally retrieved density and temperature profiles of electrons and neutral atoms are compared with the predictions of a self-consisted nonequilibrium arc model. Stark widths of Ar I lines 750.38, 751.46, and 763.51 nm are obtained in the temperature range of 11000–18000 K with the aim to extend the rather scarce data for those lines. The measured widths are compared with existing values from literature and theoretical predictions.