The pseudoscopic inversion of holograms

Holograms are apparently the first sources of reverse relief images (pseudoscopic images, as they are more commonly known) in optics. The pseudoscopic inversion amounts to an interchange of distant points on the reconstructed image with nearer points. This inversion readily accounts for the interchange of near and distant objects and the interchange of convex and concave shapes (and vice versa) that are displayed in the pseudoscopic image. This letter wishes to present a very simple physical argument to explain the effect which the author has found very useful in understanding the formation of the real image in general. The argument is based on the concept of zone plates. That is, each point on the object, when illuminated with the laser during the recording process, creates a spherical wave which then interferes with the reference wave to create a zone-plate pattern on the hologram. This pattern shows both positive and negative focal properties and, when illuminated with a reconstruction wavefront identical to the reference wavefront used in the recording process, will produce a real image of the original object point the same distance away from the hologram as the original object point.