A double Michelson interferometer for accurate measurements of electrostrictive constants

Abstract
The limitations of a Michelson He‐Ne laser interferometer used to measure electrostrictive strains is analyzed. It is found that Coulomb forces from the electric leakage field lead to mechanical vibrations of the sample and sample holder to such an extent as to disturb the measurement. A new double He‐Ne laser interferometer to measure the upper and the lower sides of the sample has been developed to eliminate the influence of mechanical vibrations of the sample holder. Experiments show that the error in electrostrictive expansion measurements carried out with a double interferometer can be more than a factor of 10 smaller than those resulting from measurements with a single Michelson interferometer. Noise characteristics of the double interferometer are minimized by the use of optical isolators, which leads to a decrease of the shot‐noise contribution of the photodiode.
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