Reexamining the Stark width and shift of He II Paschen-α: Studies using laser-induced plasma, Thomson scattering, and computer simulations

We report on experimental and theoretical studies on the Stark profile of the He II Paschen-α line over a wide range of plasma parameters. This line was emitted from a laser-induced plasma with electron densities in the range of 8.1×10²²–4.46×10²⁴ m⁻³ and electron temperatures of 1.2–7.6 eV as independently measured using the two-color Thomson scattering method. The line shapes were calculated using a computer simulation method, treating the ions and electrons on an equal footing and taking into account the full Coulomb interaction between the hydrogenlike atomic radiator and plasma perturbers penetrating the wave-function extent of the bound electron. We found a very good agreement between the experimental and theoretical Stark widths and shifts, which on average agree within 5%. In addition, practical analytical approximations for the linewidth and line shift are provided, validated against extensive calculations in the density and temperature ranges of 10²³–10²⁵ m⁻³ and 1–16 eV, respectively.