Sequential hologram interferometry with diffusely illuminated objects

Two simple holographic multiplexing techniques for sequential hologram interferometry of a diffusely illuminated object are described. These techniques enable one to use the frozen-fringe hologram interferometry to study a quasi-continuous change in the object and so regain some of the advantages of real-time hologram interferometry. In the first method of multiplexing with a single reference beam, a small angle prism is used for varying the direction of the reference beam between successive exposures and a double-exposure hologram is recorded at each position of the prism. In the second method of multiplexing with multiple reference beams, a separate reference beam is used for recording each state of the object independently and the interference pattern between any two states is obtained by simultaneous reconstruction of two light fields. The advantage of this method over the previous one is that it is also suitable for dynamic studies. Some reconstructed interferograms of a diffusely illuminated transparent object under different stresses are presented as illustrations.