Holographic interferometry of transparent objects with illumination derived from phase gratings.

Laser speckle in holographic interferograms of three-dimensional transparent objects is eliminated at the expense of limiting the available viewing directions to a finite number. This is accomplished by using a phase grating to divide the object wave into a number of discrete plane waves propagating in various directions. Experimental results of the application of this technique to the study of natural convection above a heated wire are presented. Fringe resolution obtained by this technique is compared with that obtained using plane wave or diffuse illumination. A brief analysis of fringe localization in holographic interferometry is presented in the discussion.