A feedback stabilization technique is described for a fractional fringe interferometer measuring plasma electron densities. Using this technique, a CO2 laser Michelson interferometer with a pyroelectric detector exhibited a sensitivity of 3.4 x 10(-4) fringe on a 1-ms time scale and, due to acoustic pickup, 1.8 x 10(-2) fringe on a 10-ms time scale. The rise time is 45 micros. Stabilization against slow drifts in mirror distances is achieved by an electromechanically translated mirror driven by a servo system having a 0.2-s response time. A mechanical chopper in one of the two beam paths generates the signal which drives the servo system.
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Schneider et al. (1979) studied this question.