A laboratory demonstration of the three-dimensional nature of in-line holography

An experiment is described in which two semi-transparent reticles and a pho tographic plate separated by several centimeters are illuminated by a monoc hromatic point source in a typical in-line configuration. The resulting sha dowgram is a hologram that contains information from both reticles. Illumin ating this complex hologram with a similar point source with the reticles r emoved produces reconstructed real images at two separate locations whose c oordinates are predicted from simple theory, and also produces virtual imag es of the reticles at their original coordinates. This experimentally confi rms the three-dimensional capability of an in-line hologram. As imaging dev ices such as charge-coupled device sensors become cheaper and of higher res olution, a simple demonstration of this aspect of holograms, which can be p rojected to an audience, can be observed by sliding the image sensor along the axis. (C) 1999 American Association of Physics Teachers.