White-Light Holograms

The paper explains why coherent light has played a major role in holography referred to as photography by wave-front reconstruction. It is shown that the coherence requirement differs for different kinds of holograms. A succinct description is given of a few advances that contributed to the substantial reduction in the coherence requirement for both making and viewing holograms. Particular attention is given to the off-axis hologram, the Denisyuk hologram, the Lippmann process for color photography, the Benton hologram made in two steps and composite or multiplex hologram. It is concluded that holography is by no means dependent on highly coherent illumination, either in the making process or in the viewing process.