Quantum statistical approach is adopted for calculating the spectral line
shapes of neutral helium in dense plasmas. Stark broadening of isolated He
I lines 5048 Å (

Plasma spectroscopy deals with the characteristics of radiation emitted from a plasma. In dense plasmas, damping of the emitted radiation occurs by means of several mechanisms; the most effective one is pressure broadening (Stark broadening). The interaction between a radiating atom and surrounding perturbing particles leads to Stark broadening. High-speed electrons perturb the emitter by collisions, causing the interruption of the spontaneous emission and altering the emitter energy levels [

Line profile calculation is an interesting tool for both laboratory and astrophysical plasma diagnostics, for example, to determine the internal parameters, to understand the microscopic processes within the plasma, and to check the quality of the predicted experimental and theoretical parameters [

The emission spectra of helium and He-like ions with their simple atomic structures are interesting for plasma diagnostics such as in shock wave tube or pulsed arc plasmas [

Various approaches have been investigated to calculate spectral line shapes in plasmas [

Thermodynamic Green's function approach is a powerful tool to describe the Stark broadening [

In this paper thermodynamic Green's function approach is considered to calculate the pressure broadening of some selected neutral helium lines. In Section

Microscopic formation of the spectral line shapes in dense plasmas arises from perturbation of the radiative atom by collective and many-body effects [

Optical properties of many-particle systems are specified by the dielectric function

The perturber-radiator interaction leads to pressure broadening, which contains electronic and ionic contributions. Describing the ionic contribution in the quasistatic approximation by averaging over the ionic microfield at radiating atom [

The electronic self-energy is obtained by performing a Born approximation with respect to the perturber-radiator interaction [

The vertex function for the coupling between the upper and the lower state is given by

The transition matrix-elements

By using the Born approximation, the electronic self-energy is overestimated. To avoid this we apply a cutoff procedure and add the strong collision term in contrast to partial summation of the three-particle T-matrix, which is quite suitable for treating short-range interactions between particles [

To determine the ionic self-energy, we approximate the time-dependent microfield fluctuation by its static value. In general, dynamic ionic microfield is important for overlapping lines and at low electron density in the line center [

The Stark broadening parameters for the transition

The calculated FWHM and shift (without/with screening) for the line

(Å) | (Å) | (Å) | (Å) | (Å) | (Å) | ||

3.2 | 30.0 | 5.22/5.22 | 5.385/5.378 | — | 2.19/2.05 | 2.56/2.397 | — |

2.0 | 18.0 | 3.10/3.10 | 3.183/3.179 | 3.4 | 1.43/1.35 | 1.783/1.677 | 0.9 [ |

1.03 | 20.9 | 1.58/1.58 | 1.623/1.622 | 1.68 | 0.75/0.68 | 0.862/0.82 | 0.89 [ |

The Stark width and shift of the line

Stark FWHM for the He I line

Stark shift for the He I line

The Stark parameters of the line

The measured Stark FWHM and calculated values for He I

The measured Stark shift and calculated values for He I

The quantum statistical approach has been developed to calculate spectral line shapes in dense plasmas. By using thermodynamic Green's function, a systematic perturbative treatment of the polarization function has been performed [

Moreover, our quantum statistical approaches can be applied not only to investigate the line shapes of two-electron atom but also to complex atoms. Furthermore, the deformation of spectral line profiles can be investigated in a strong magnetic field for stellar diagnostic.

This project is supported by Emmy Noether-Program of the Deutsche Forschungsgemeinschaft, RE1141/11-1. The author would like to thank A. Wierling, G. Röpke, and M. A. Gonzalez for helpful discussions.