Measurements of helium 23S metastable atom density in low-pressure glow discharge plasmas by self-absorption spectroscopy of HeI 23S–23P transition

Abstract

The helium 23S metastable atom densities are experimentally evaluated by self-absorption spectroscopy of the HeI 23S–23P transition spectra in two kinds of cylindrical glow discharge plasmas, which have different radii and are operated under different pressures of 300 and 20 Pa. The spectra are measured by using an interference spectroscopy system with a wavelength resolution of about 60 pm, and the relative intensities of the fine structure transitions are analyzed. It is found that the method is in principle applicable to plasmas with the pressure up to about the atmospheric pressure and electron density on the order of up to 1022 m−3. For a plasma with an absorption length of 10 mm and a spatially uniform temperature of 300 K, the method is sensitive to the metastable atom density roughly from 1016 to 1019 m−3.