The Holo-Diagram. II: a Practical Device for Information Retrieval in Hologram Interferometry

The holo-diagram (hologram-diagram) is a device designed to simplify the making and the evaluation of holograms, e.g., double exposed holograms made for interferometric measurements. It has been demonstrated in an earlier paper how this holo-diagram can be used to find the direction of maximum sensitivity in a holographic arrangement and how the amplitude of displacement in this direction can be evaluated. The aim of this paper is to show how the evaluation of real amplitude and direction of displacement in all three dimensions can be made in a rather simple way by the use of the holo-diagram, a slide rule, and a ruler. No trigonometric calculations have to be made because they are already built into the diagram. An example is given where an approximately vertical movement of the eye behind the photographic plate used to reconstruct the hologram gives the vertical component of the displacement, while a horizontal movement discloses the other two components. A method to calculate a displacement even when the fixed point is out of sight in the finished hologram is also described.