A
lthough holography has long been closely identified with lasers,
Dennis Gabor made the first hologram a dozen years before Theodore
Gabor was trained in electrical engineering but fascinated by physics, and he
spent his career in research and development. Born in Hungary in 1900, he worked
in Germany after earning a Ph.D. from the Technical University of Berlin. He
moved to Britain when Hitler came to power. He invented holography in 1947
while working at the research laboratory of British Thomson-Houston Company
in Rugby. The idea came to him while waiting for a tennis court on Easter. He was
wondering how he could improve the resolution of electron microscopes, which had
been limited to a few nanometers at the time.
With the imperfections in electron optics limiting resolution, Gabor recalled
later, “Why not take a bad electron picture, but one that contains the whole information, and correct it by optical means?” He originally envisioned illuminating
an object with a beam of coherent electrons. The pattern of interference between
electrons scattered from the object and those not deflected would record phase and
intensity of the electron wavefront. Recording the interference pattern and illuminating it with coherent light would reconstruct the wavefront of the scattered
electrons, generating a high-resolution image of the object.
A sister company, Metropolitan Vickers, made electron microscopes, so managers okayed Gabor’s project. Lacking a way to record electron interference patterns,
Gabor started by using light as a model, although he had not worked with optics
before. At the time, the best available source of coherent light was a high-pressure
mercury lamp, but its coherence length was only 0.1 mm. Filtering the output
through a 3-µm pinhole left only enough light to make 1-cm holograms of 1-mm
transparencies, but illuminating them yielded recognizable images.
A
Dennis Gabor’s first hologram from his May 15, 1948, Nature article. (a) Original micrograph, 1. 4 mm diameter. (b) Micrograph,
directly photographed through the same optical system used for the reconstruction. (c) Interference diagram obtained by projecting the micrograph on a photographic plate with a beam diverging from a point focus. (d) Reconstruction of the original by optical
synthesis of the original.
