Dispersion-Corrected Three-Wavelength Laser Heterodyne Measurement of Plasma Densities

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Abstract
A three‐wavelength laser heterodyne system for plasma diagnostics has been developed using the 0.6328, 1.15, and 3.39 μ transitions in He–Ne. In order to use the 3.39 μ transition, an experimental technique has been developed to measure the dispersion introduced by the lasering atoms under the same conditions that are used for plasma measurements. The dispersion‐corrected 3.39 μ data, when combined with the data at 1.15 and 0.6328 μ, give excellent agreement in the measurement of temporally and spatially resolved electron densities and changes in neutral densities in the afterglow of a pulsed argon discharge. The electron‐density measurements agree with integrated electron‐density measurements made with a microwave cavity operating in the TM010 mode.