Model interferometry with air-holograms

Abstract

An “air-hologram” is formed by the superposition of collimated object and reference light beams in a standard transmission holographic bench. Since no model is initially placed in the system, the reconstruction is simply the collimated beam that had passed through the model space. Insertion of transparent model material changes the optical path-length profile causing interference between the existing beam, which traverses the model, and the reconstructed beam which had traversed air only—hence, the designation “air-hologram”.

Using this method, model material can be inspected and selected for optical flatness. Interference in the unloaded models can then be eliminated by simple rotation of the hologram. Real-time holographic interferometry is performed in the same manner as is photoelasticity. Further, it is shown how errors caused by large model displacements can be minimized.