Radially and time-resolved measurements of electron density in an operating copper vapour laser

Abstract

A practical technique for the measurement of free electron density, as a function of time and radial position, in the plasma of an operating copper vapour laser (CVL) is described. The method employs a two-colour interferometer to measure the refractive index of the plasma at both and 670 nm. Results of such measurements of electron density in a 40 W commercial CVL are presented. A high residual electron density present prior to the discharge is observed, together with a relatively modest increase during the discharge. These observations are related to the operating characteristics of the laser, in particular the phenomenon known as the `phantom current'. The source and propagation of errors are considered and a maximum error of is calculated.