Heterodyne CO2-laser interferometer with direct phase read-out

Abstract

A CO2-laser interferometer with heterodyne detection has been built to measure electron line densities of plasmas in the range of 10(18) to 5 x 10(22) m(-2). Heterodyne operation is accomplished by using two counteracting acousto-optic modulators at a difference frequency of 500 kHz. A digital phase comparator is used to obtain direct read-out of the phase shift. The time resolution is 3.5 micros.