Observation of Non-Lorentzian Spectral Line Shapes in Na-Noble-Gas Systems

Abstract

This Letter reports observations showing that the spectral line shape in the core region of collision-broadened lines contains a dispersion component in addition to the usual Lorentzian. The physical origin of this component is the finite duration of the collisions. For the Na $D$ lines and Xe perturbers, the dispersion component produces an 8% asymmetry 0.1 Å from line center. Calculations based on recent line-broadening theories predict a dispersion component with an amplitude comparable to our experimental results.