Spontaneous-Emission Profiles of Argon-Ion Laser Transitions

Abstract

Experimental studies are reported of spontaneous-emission profiles observed in the axial and radial directions from high-current arc discharges of the type used in cw argon-ion lasers. The greatly increased sensitivity from a new computer-oriented method of line-profile analysis has permitted observation of linewidth parameters over a wide range of discharge current and pressure. These studies have shown the existence of several interesting new effects and have required a substantial modification of previously held concepts regarding the nature of line broadening in these discharges. A new theory for line-profile analysis in the radial direction is presented which incorporates the Tonks-Langmuir potentials and provides a correction for an arbitrary number of charge-exchange collisions in the radial acceleration of ions to the wall. A modification of the earlier theory of Kagan and Perel is suggested which brings that method of transverse line-profile analysis into reasonably close agreement with the present (more complex) method of analysis. Values for the mean radial velocity and electron temperature are obtained from profile analysis in the transverse direction. Studies of ion and neutral temperatures based on Voigt profile analysis in the axial direction are presented, along with the determination of the average electron density based on Stark broadening of the neutral and ionic lines. Precise values of the natural widths on the major argon-ion laser transitions are determined through extrapolations of the axially observed Lorentz-width data taken at low pressures to zero discharge current.