A 633 nm vibration-insensitive interferometer for the measurement of low plasma electron densities

Abstract

A vibration-insensitive 633 nm He-Ne laser interferometer for the measurement of plasma electron densities is described. This instrument is a Michelson interferometer with the reference arm located parallel to the test arm so that spurious fringes resulting from mechanical vibration of the optical components are minimised, allowing a resolution of 0.1 fringe to be achieved. A rotating glass plate in the reference arm was used where necessary to determine the sign of the electron density change. The performance of this interferometer is compared with that of a CO2 laser interferometer.