Electric field measurement in gas discharges using stark shifts of He I lines and their forbidden counterparts

A spectroscopic method for the measurement of macroscopic electric field strength in discharges, based on Stark shifts of several helium emission lines with their forbidden counterparts, is presented. The shifts of forbidden and allowed pi components are calculated for eight line groups of helium. For practical use, polynomial functions are provided for the shifts of line groups applicable in the visible range. The method is an extension and improvement of a previously established method for two line groups. Line fitting procedures are presented that take into account components of a given helium line group, provide higher accuracy compared to simple evaluation, and enable measurements of lower field values. The method and fitting procedure were experimentally tested and verified by measuring the field distribution in the cathode fall of a low pressure glow discharge. Due to its ab initio basis the presented method can be used for measuring electric field distributions in various types of discharges, independently of other plasma parameters and fulfillment of special conditions.