New interferometric method for piezoelectric measurements

Abstract
A new interferometric technique has been developed for measuring the amplitude of very small ac displacements. The technique, utilizing a spherical Fabry–Perot interferometer, is more sensitive and less susceptible to acoustic vibrations than previous methods. We have used this technique to measure displacements as small as 4×10−4 Å, and the theoretical sensitivity in a well‐isolated environment is about 10−5 Å.