::History of holography

Denis Gabor made the first hologram while working on electron microscopes in England in 1947. He used a mercury arc lamp and produced a hologram of a small transparency containing the names of famous scientists. His main problem was the lack of a coherent light source.

The invention of the laser in the 1960s gave holography the coherent light source needed to give the size, brightness and depth of image which have intrigued and delighted viewers ever since. At first lasers were only available in universities and research laboratories, but now they are much cheaper, making them available to individuals. Further development introduced pulsed lasers which give a very powerful flash of only a few nanoseconds, enabling holograms to be made of living subjects.

In 1962 Emmett Leith and Juris Upatnieks of the University of Michigan recognized from their work in side-reading radar that holography could be used as a 3-D visual medium. In 1962 they read Gabor's paper and "simply out of curiosity" decided to duplicate Gabor's technique using the laser and an "off-axis" technique borrowed from their work in the development of side-reading radar. The result was the first laser transmission hologram of 3-D objects (a toy train and bird). These transmission holograms produced images with clarity and realistic depth but required laser light to view the holographic image. Their pioneering work led to standardization of the equipment used to make holograms. Today, thousands of laboratories and studios possess the necessary equipment: a continuous wave laser, optical devices (lens, mirrors and beam splitters) for directing laser light, a film holder and an isolation table on which exposures are made. Stability is absolutely essential because movement as small as a quarter wave- length of light during exposures of a few minutes or even seconds can completely spoil a hologram. The basic off-axis technique that Leith and Upatnieks developed is still the staple of holographic methodology.

Yuri Denisyuk, a Russian, devised an elegant method of using a single beam to act as both reference and object beam. Placing the film between the laser and the object allows the beam to pass through the film and be reflected off the object, so that the reference beam impinges on the film from one side, and the object beam from the other.

Transmission holograms illuminated by white light give a "rainbow smear" effect. In 1968 Stephen Benton discovered a way of eliminating this effect. He made a transfer hologram masking off the master hologram through a narrow horizontal slit; when the second hologram is flipped, the image of the slit appears in front of the hologram close to the viewpoint, and only light of one colour is seen. This gives rise to the "rainbow" effect; as the viewpoint is moved vertically, the colour of the hologram changes.

The invention of an embossing technique meant that holograms could be mass-produced for use as security devices and to enhance magazine covers.

In 1972 Lloyd Cross developed the integral hologram by combining white-light transmission holography with conventional cinematography to produce moving 3-dimensional images. Sequential frames of 2-D motion-picture footage of a rotating subject are recorded on holographic film. When viewed, the composite images are synthesized by the human brain as a 3-D image.