Abstract

The high-voltage atmospheric-pressure spark is commonly used for elemental analysis of alloys. Emission from atoms vaporized from the cathode is used for determining composition of the cathode. Particulates represent a sink for free atoms which might otherwise be useful for emission or absorption measurements of the cathode’s composition. Condensation kinetics are not well understood, nor are free atom lifetimes known. Mie scattering can be used to monitor particulates in situ, but polarization of incident laser light must be controlled if size information is to be recovered from the scattered light. Although work to date has used a He–Ne laser, work at 416 nm (He–Cd laser) or bluer wavelengths would substantially improve signal-to-noise ratio and would also reduce the minimum detectable particle size. We report appartus for controlling ellipticity and major axis orientation of incident laser light. The approach used does not require ideal wave plates or ideal mirrors to be used. Observations or particulates produced when sparking to aluminum cathodes will also be reported. Particulate size, spatial distribution, and trajectories are discussed.

© 1985 Optical Society of America