Dual hologram interferometry

Abstract

This report describes dual hologram interferometry, a new electro-optic technique used to calculate two-dimensional density distributions from measurable changes in index of refraction. Using this technique, two scenes recorded at different times are stored in separate holograms. One hologram contains reference data depicting the subject in an undisturbed state and the other hologram describes the same subject in a test or disturbed condition. Desired interference patterns are obtained by super-imposing the two separate scenes which are simultaneously reconstructed from each hologram. Specific interferograms, infinite fringe and various finite fringe patterns, are obtained by carefully regulating the optical attitude between the holograms and the reference beam during reconstruction of the scenes. In this project, dual hologram interferometry is used to describe quantitatively free convection from a uniformly heated right circular cylinder. Temperature distributions through the boundary layer and local heat transfer coefficients are determined at different azimuth positions. The results are compared both to experimental data obtained from another holographic technique and to a theoretical prediction of this specific test. This investigation shows that dual hologram interferometry accurately records changes in index of refraction which means the technique can be used to accurately measure experimental fluid flow data.