Fractional Fringe HCN Laser-Interferometer

Abstract

An HCN laser-interferometer is reported with better than 1/100 of a fringe phase shift sensitivity at a wave-length of 337 μ. Applied to plasma density measurement this corresponds to electron density line integrals of 3.3×1012 cm−2 or lower. The fractional fringe technique involves sinusoidally driving the reference path mirror in a focused Michelson interferometer; changes in the effective path length alter the relative magnitude of even and odd harmonics in the resultant interferometer signal. Results are shown from application of this diagnostic to the Burnout V plasma.