Fabry-Perot Dilatometer

Abstract
A dilatometer based upon the principle of the Fabry‐Perot interferometer is described. The device is capable of measuring displacements as small as 10−7 cm or less. The measurements are made directly in terms of the wavelength of a spectral line such as the green line of 198Hg. No calibration of the apparatus is required, and it is not necessary to know the distance between the mirrors or the focal length of the lens which forms the fringes. Neither is it necessary to know the calibration of the micrometer eyepiece so long as it may be assumed that the screw is regular. The instrument should be useful for measuring magnetostriction, piezoelectric, electrostriction, and thermal expansion coefficients, especially when small samples must be used.

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