Intelligent Machines

The Whole Picture

Holography’s microscopic origins.

Holography is part of our everyday lives-from a commemorative 3-D Elvis on the cover of TV Guide to the tiny images designed to discourage credit card counterfeiters. Advances such as holographic video (see “Holograms in Motion,” TR November 2002) suggest that it will also be a compelling part of our future. All these technologies have their origin in a serendipitous discovery by Dennis Gabor, a Hungarian scientist who was trying to make an improvement to the electron microscope.

The electron microscope, invented in the 1930s, had a resolution power more than a hundred times greater than that of the best light microscopes of the time. However, because the aperture of electron lenses couldn’t be increased beyond a certain point, the electron microscope stopped just short of resolving individual atoms. In 1947 Gabor was working at the British Thomson-Houston Company in Rugby, England, speculating on ways to get around this limitation. Gabor thought that perhaps he could take a “bad” picture and then correct it using optical means. Because such a picture would be missing important information-the phase of the electron waves, or their position at a particular point in time-this proved impossible. Gabor theorized that if he could combine the light waves coming off the object with a “coherent reference wave” of the same frequency, the resulting interference pattern would have all the information necessary to construct a 3-D image. Gabor named this interference pattern a “hologram,” from the Greek word holos, or “whole,” because it would contain complete information about the object.

Unfortunately, in 1947 no existing source of coherent light was sufficient to create such images. Gabor and his colleagues continued to research the possibilities of holography for several years, but by 1955 holography had fallen into a period of dormancy.

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It was spectacularly resurrected in 1960 with the invention of the laser, which supplied the missing source of coherent light needed to create holograms. In 1962 Emmett N. Leith and Juris Upatnieks of the University of Michigan decided to duplicate Gabor’s method using the laser and a technique from their own work developing a type of radar. The next year, they published the first laser holograms: a toy train and a bird. Since then Gabor’s principles have been incorporated into devices such as supermarket bar-code scanners and airplane cockpit displays. And if the rash of current activity in 3-D imagery is any guide, holography has a bright future.

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