Spatial Emission Properties of a Surface-Wave-Sustained Plasma (Surfatron) in Helium

Abstract

Spatially resolved measurements of plasma-emission sources can greatly aid in their application to atomic-emission spectrometry. In this study, detailed two-dimensional emission profiles of a plasma sustained by electromagnetic surface waves from a surfatron have been measured with an imaging spectrometer. In helium, and under the operating conditions described, the plasma is found to possess a “doughnut” shape much like the inductively coupled plasma (ICP) in argon. Emission from the following types of spectral features was found to be confined to the plasma annulus: (1) He(I) lines; (2) molecular bands; (3) background continuum; (4) difficult-to-excite transitions from nonmetallic analytes. In contrast, two-dimensional profiles for metallic analytes (introduced in the form of an aerosol from a glass-frit nebulizer) show localized maxima along the central axis of the plasma. Spatially resolved measurements have suggested ways in which the surfatron can be employed to advantage for atomic emission spectrometry. Possible excitation mechanisms to account for the spatial properties of the surfatron are also offered.