Electron Density Measurement in the HCN Laser Using Faraday Mode Splitting Technique

Abstract

The Faraday mode-splitting, or self-heterodyne, technique has been used to measure electron density along the optical axis of the HCN laser (337 μm). The measurement indicates an afterglow electron density of 4.5 × 10¹¹ cm⁻³; this result agrees with microwave measurements made across the laser axis. The sensitivity of the measurement is about 2 orders of magnitude better than an interferometric measurement at the same wavelength. The technique is easy to instrument, but care is required to interpret the results in the present application. The gain of the HCN laser is probably sufficient to permit use of this technique, in some cases, to measure the density of an external plasma.