Sandwich hologram interferometry. 3:Contouring

This new holographic contouring method produces interference fringes formed by illumination shearing during recording in combination with observation shearing during reconstruction. One holographic plate is exposed after which the point source of light illuminating the object is displaced laterally to produce a shear of the illumination beam. A second exposure is made on another plate, whereupon the two plates are processed and bonded together with their emulsions outward. When this sandwich hologram is reconstructed, contouring fringes are formed that represent the intersection of the object by a set of interference surfaces. A tilt of the sandwich hologram produces a shear of the observation that results in a corresponding rotation of the intersecting surfaces of up to 180 deg in every direction of the three-dimensional reconstructed object space. Thus, sign, direction, and magnitude of object slant can be evaluated by measuring the analogous sandwich tilt. The possibility of studying cross sections in any random orientation from a single sandwich hologram could be very useful for measuring and demonstration purposes.