BROADENING OF SPECTRAL LINES

The Doppler broadening, the natural broadening, and the quasi-static broadening are introduced. The last broadening is due to the Stark effect in the Holtsmark micro-field with the Debye shielding. Plasma electrons give rise to the impact broadening, which is discussed in detail. For neutral hydrogen and hydrogen-like ions for which the linear Stark effect is dominant, the quasi-static broadening tends to be important. For other atom (ion) species, which are subjected to the quadratic Stark effect, the impact broadening tends to be dominant. The Inglis-Teller limit, which results from the line broadening becoming comparable with the line separation, is useful for a rough estimate of plasma density. Convolution of a Lorentzian profile and a Gaussian profile yields a Voigt profile.