Detection of Small Fringe Shift of Optical Interferometer

Abstract

An extremely sensitive optical interferometer system is developed.In order to eliminate the effect of mechanical vibrations on the detection of very small phase shifts produced by a light through a plasma which constitutes one arm of a Mach-Zehnder-interferometer, the triggering of an oscilloscope and a gap switch which starts the discharge is controlled by a pulse generator. The output pulse signals are produced at times only when the signal from a photomultiplier meets the most sensitive position of the fringes. Moreover, a manual switch connects the pulse generator to triggering terminals of the oscilloscope and the gap switch.The minimum electron density here detected is 8 x 1013cm-3for the wave length 5463A. This sensitivity which corresponds to 1.5 x 1013cm-3for 3.39 micron of a He-Ne laser system overlaps the.maximum detectable electron density of a 8 mm microwave interferometer.Any type of optical interferometers which are limited their sensitivity by mechanical vibration will be improved to have a higher sensitivity more than an order of magnitude by adding the system here mentioned.