Some Developments on 3-D Photography

Although the basic principles of holography have been known for over 30 years (holography was invented by Dennis Gabor in 1948), it was not until the invention of lasers in the 1960's that the full capabilities of holography could be demonstrated. A laser is a source of pure, regular or "coherent" light and, in general, this type of light is necessary for recording holograms of 3-D objects. However, the use of lasers has disadvantages when practical applications of holography are considered. They are expensive and in some cases hazardous. Could their use be minimised in any way?

A major advance in this regard was made by the Russian investigator Yu. N. Denisyuk. He had the remarkable idea of combining holography with a form of colour photography invented by the French physicist Gabriel Lippmann in 1891. With Denisyuk's idea, while lasers are still needed to record the hologram, in the reconstruction or playback process (Figure 2) the laser can be replaced by an ordinary light bulb. Further, by using three lasers during recording, corresponding to the three primary colours (red, green and blue), the hologram yields a full-colour image.

There is one rather special way, known as the "multiplex technique," in which the use of lasers can be avoided altogether. The method involves making the hologram from a large number of ordinary photographs. For example, a person is seated on a slowly rotating platform, and an ordinary cinecamera takes hundreds of pictures, recording his appearance from all directions. The pictures are then synthesised into a single hologram from which a 3-D image can be reconstructed. The technique has made it possible to record some degree of motion in the hologram; a person can be seen moving his hand or giving a smile. It's rather like the early days of moving pictures, but this time it's in true 3-D!

Practical Applications

Making and viewing holograms is fascinating, but what practical applications does holography have?

One might immediately think of 3-D movies and television, where holography would provide the ultimate in reality. While it may be possible in principle to produce such a system, for the moment it is a long way off. The problem is due to the vast information content of the hologram plate. A 200-mm (8-inch)-square hologram plate has a potential information content over 300,000 times as great as a single static television picture. Present television systems come nowhere near the ability to handle such a vast amount of information.

At present, holography is finding application as a display and advertising medium. A company responsible for many of the billboards on the London Transport Underground has expressed its interest in using holograms for advertisement purposes. And the sales representative of the future may well carry holograms as samples of bulky or heavy products.

In museums, treasures can be replaced by holographic replicas. This technique has been pioneered in the U.S.S.R., and the Hermitage Museum, Leningrad, is now making a library of holograms for loan to other museums. Production of 3-D portraits will no doubt be an important application in the near future.

Holography has also found some important applications in industry and research. For example, in the production of high-precision motorcar cylinders, a hologram can be made of a perfect specimen. The holographic image is then exactly superimposed over the real production-line cylinders; any flaws and defects immediately show up as a characteristic fringe pattern. Errors in shape of less than a micron can be detected. (A micron is one millionth of a metre [0.00004 of an inch]!)

In research, events that happen too fast for the eye to catch can be holographed by using pulsed lasers. Pulsed lasers, like a super flashgun fitted on the holographic camera, emit pulses of light that last for only an instant. A ruby laser, for example, can produce a flash lasting for only 0.00000003 of a second! The light flash effectively captures an event that happens in less than a millionth of a second, or freezes the motion of an extremely fast-moving object. The event is recreated in the holographic image. Vibrations in objects, such as machinery or musical instruments, can be studied, and the method offers possibilities for analysing rapid chemical reactions.

Holography is still a rather expensive and cumbersome operation when compared with ordinary photography. It is also somewhat limited, at present, as regards the size of hologram that can be made. So rather than replacing photography, holography has emerged as an advanced form of photography for use in certain special areas. It represents another use of natural laws-actually, laws of the Creator-for the benefit and enjoyment of mankind. As further improvements are made in the process and in reducing the cost, there is no doubt that new ideas will be conceived for using holography to touch our lives much more than at present.