Four beam interferometer manual: Operating instructions for the INEL diffraction Moire interferometer

Abstract

Moire interferometry is an interferometric method for measuring changes of in-plane geometry. It is essentially insensitive to out-of-plane topography or changes in that topography. Changes in geometry are referenced to a particular moment in time when the moire` sensor, a diffraction grating, was attached to the specimen. Distortions experienced by the specimen prior to that time are not directly detectable, although they may be inferred from specimen behavior or condition. In its most common form, moire interferometry is not well suited to large (> 50 mm square), curved ( 200 C) regions. However, various efforts have been made to handle each of these conditions. In general, the moire` process is most straightforward for flat, 25 mm diameter regions of coverage and room temperature. Much smaller or larger regions require more specialized optics, which can become very expensive. This report will discuss various aspects of moire interferometry. In particular, a new four beam (bi-axial) interferometer is described in detail. Issues involved in safety, assembly, calibration and use are fully explained.