The Father of Holography
HUNGARIAN inventor Dennis Gabor is known as the Father of Holography.
When the Firt World War ended in late 1918, he began studies in electrical engineering in Budapest which he finished at the Technical Hochschule Berlin-Charlottenburg, where he obtained a Diploma in Electrical Engineering in 1924. He also attained the degree of Doctor of Engineering (Dr-Ing.) in 1927 with a thesis related to the development of one of the first high speed cathode ray oscillographs.
That year he also joined Siemens
& Halske AG, Berlin, where he started working in one of the physical laboratories, in which Gabor began to develop some of his numerous inventions. As proof of his fruitful work as an inventor, Gabor filed 62 patents between 1928 and 1971. In 1933, a few weeks after Hitler came to power, Gabor left Germany because the company did not renew his contract due to his Jewish origin. In 1934, and after a short period in Hungary, he went to England, where he got a job with the British Thomson-Houston Company in Rugby.
Throughout his entire life Gabor always said he was an engineer and inventor rather than a scientist, even though his work was almost always related to applied physics. But Gabor was also a humanist in the sense of the Renaissance: voracious reader, writer, essayist, man concerned about the technological society of the late twentieth century and member of the Club of Rome. Since 1958 he devoted much of his time to study the future of our industrial civilisation on which he published, among others, the book Inventing the Future, published in 1963, and where he stated:
“You cannot predict the future, but you can create it.”
Holography begins to take its first steps in 1947 in a laboratory of an electrical engineering company where Gabor was working on improving the electron microscope. This instrument had increased one hundred times the resolving power of the best optical microscopes and it was very close to solving the atomic structures, but the system was not quite perfect. Its main limitation was related to the spherical aberration of the magnetic lenses of the microscope. To solve this problem Gabor asked himself: “Why not take a bad electron picture, but one which contains the whole information, and correct it by optical means?”
Gabor came up with the answer to this question while he was waiting for a game of tennis on Easter Day 1947 and it was to consider a two-step process. In the first stage, the recording, the interference pattern between a coherent electron beam (object wave) and a “coherent background” (reference wave) is recorded on a photographic plate. Gabor called this interference pattern “hologram”, from the Greek word “holos”, the “whole”, because it contained the whole information (amplitude and phase) of the object wave.
In the second stage, the reconstruction, the hologram is illuminated with visible light and the original wavefront is reconstructed, so that the aberrations of the electron optics can be corrected by optical methods. Therefore, the physical principles of holography are based on the wave nature of light and they are interference (recording step) and diffraction (reconstruction step). He spent the rest of the year working on his ‘new microscopic principle’.
To obtain contrast interference fringes it is necessary to use a light source of high coherence, which did not exist in times of Gabor (the laser was invented in 1960). Due to this, Gabor made his first hologram in 1948 using a light source that consisted of a mercury arc lamp with a narrow-band green filter, one of the best coherent light sources before the laser.
The object was a tiny circular transparency (1.4 mm diameter) of opaque lettering on a clear background containing the names of Huygens, Young and Fresnel, three physicists who were considered important by Gabor because they developed the physical basis of his technique, which he called “wave-front reconstruction”.