B.S.T.J. Briefs: Display of Holograms in White Light

This paper describes a new method for displaying holograms in white light. The method gives reasonably good reconstructions although certain image defects are inherent in the method. It differs from previously reported methods of white light reconstruction1,2 in that the whole spectrum is used for reconstruction and therefore black and white reconstructions can be obtained. The method does not depend on the volume properties of the photographic emulsion. The basic arrangement is shown in Fig. 1. The white light illuminates a hologram which had been formed with a plane off-axis reference beam.3 Behind the hologram there is a Venetian blind structure which blocks off the direct light but lets through the diffracted beam. The diffracted beam is diffracted a second time at a plane transmission grating which can be formed photographically with two plane beams. The angle between the two beams which form the plane grating has to be equal to the mean angle between the subject beam and reference beam used to form the hologram. The reconstruction resulting from the configuration of Fig. 1 will now be explained. Intuitively, one can say that there is a large color dispersion at the first hologram because it can be considered a high spatial frequency diffraction grating. Since the light is diffracted in the opposite direction by the second grating this color dispersion is compensated. In order to be more quantitative, assume that during the formation of the hologram the subject beam A, on the photographic plate is given by Aa = a(x,y) exp (ju8x), (1)