Hologram Heterodyne Scanners

In principle, it is possible to conceive of a holographic television system, but a practical system hinges on removing a number of formidable roadblocks. Among these is transducing the holographic information into a relatively narrowband electrical signal by means of a camera that has limited spatial resolution. This problem is shared by both a three-dimensional and a two-dimensional holographic system, but with present technology the 3-D system certainly presents many more problems. The two-dimensional system becomes much more tractable if the camera resolution problem is overcome. It is to this problem and our proposed solution that this paper addresses itself. Consideration of this problem is not new, as evidenced by the early outline of the bandwidth requirements of a holographic television system by E. N. Leith and others in 1965.1 There have also been reports of experiments involving the transmission via television of a Fresnel type of hologram in which the original object was a transparency. 2, 3 The difficulties encountered in these transmissions illustrate the crux of the problem. A hologram consists of low spatial frequency information (dictated by the spatial information content of the object) which has been modulated onto a high spatial carrier frequency derived from the 1875