Doppler-free, Stark broadened profiles at low plasma densities in helium

• Published in: Journal of quantitative spectroscopy & radiative transfer Vol. 230; no. N/A
• Main Authors: Zafar, Abdullah, Martin, Elijah, Shannon, Steven C.
• Format: Journal Article
• Language: English
• Published: United States Elsevier 28.03.2019
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Doppler-free; low-density; quasi-static; Stark broadening
• ISSN: 0022-4073; 1879-1352

This paper utilizes Doppler-free saturation spectroscopy to measure Doppler-free, Stark broadened spectral profi les for the π-polarization of the HeI 2¹P → 6¹D transition in a low density (10¹⁰ ₋ 10¹² cm⁻³) helium plasma. The measurements were performed in an electron-cyclotron resonance discharge at 23 mTorr with electron density being diagnosed using a combination of Langmuir probe and microwave interferometry techniques. The Doppler-free pro files were observed to be nearly symmetric at ne < 10¹⁰ cm⁻³ but markedly asymmetric above this transition point. Electron density is extracted from the spectral data via fi tting to a spectral model based on quasi-static Stark broadening and compared to the measured ne. The quasi-static model is shown to be valid in the low-density regime for 2¹P → 6¹D helium transition.