<title>Applications Of Phase Modulation Interferometry To The Characterization Of Materials And To Dimensional Metrology</title>

Abstract

The characterization of materials requires the knowledge of the refractive index and its variations under the effect of a given parameter. Whether we are dealing with transmission by a transparent sub-stance or reflection on a metal surface, the measurement of the phase difference introduced between the entrance and exit waves permits us to discover this characteristic of the material. In dimensional metrology, a phase difference at transmission is as much a function of the index as of the thickness, and the metrology of length standards requires the knowledge of the loss of phase at reflection. Thus the lengths considered as possible optical paths, or even the rotations, can also be expressed as a phase difference. These phase differences, demonstrated by normal or differential interferometry, can be measured with a gain in time and sensitivity if this interferametry is done by phase modulation. The very small un-certainties permitted by this process make it particularly interesting to apply to measurements of small phase differences expressing small variations in index or thickness. Its possibilities will be illustrated by examples of characterization of photosensitive materials, determination of loss of phase at reflection, longitudinal localization of objects, dilatometry and torsionetry. This process also permits us to obtain simply the rate of the variations of complex amplitude of a phase object as a function of space or time.