Quasi-heterodyne holographic interferometry for flow visualization

Abstract

Quasi-heterodyne holographic interferometry is a technique in which the use of two physically separate reference waves enables one to shift the relative phase between two reconstructed object waves by known, discrete amounts. One object wave corresponds to an undisturbed object field and the other to the same field after the occurrence of some physical change of interest. In this work the values of irradiance at each pixel of a CID array camera viewing an interferogram are recorded for three or more such known phase shifts. The variation of optical path length across the object field can then be computed by a microcomputer at each pixel and displayed as contours on a monitor. This technique has been used previously in solid mechanics and metrology. We demonstrate the usefulness of this technique for the visualization and measurement of gas flows with only small changes in density or temperature.