Dennis Gabor - Winner of the 1971 Physics Nobel Prize

E. Ingelstam, Stockholm The 1971 Nobel Prize in Physics was Gabor originally thought of using awarded to Dennis Gabor for ‘ his the principle to make an electron invention and development of the microscope image in two steps : first holographic method To start with, a to record the field of an object as a short explanation of this principle may hologram using electron rays, and be in order. In imaging processes then to reconstruct this with visible where light falls on a so-called light to produce a high-resolution square-law detector (one responding three-dimensional image. Suitable to the intensity of light or the square electron sources were, however, not of the amplitudes of the light waves) available and, for technical reasons, half the information, namely the the idea could not be tested. But by phase of the optical waves, is lost. successful experiments with light This is true for photographic emul­ Gabor was able to show that the sions, photosensitive layers in photo­ principle was correct. In three papers, tubes, TV camera tubes etc. from 1948 to 1951, he gave an exact ations will be found in the book by In order to obtain the phase, it is analysis of the method, and his equa­ Collier, Burckhardt and Lin : Optical necessary to have a reference phase. tions contain all requisite information Holography (Academic Press, 1971). This is the case in interferometry even for present-day uses. Gabor is really an inventor and, in where two wave fields are super­ The break-through of holography this respect, accords well with the imposed on each other so that one came with the arrival of lasers as original idea of Alfred Nobel that the becomes the reference wave of the light sources capable of generating prizes should honour inventions. He other. The novelty of Gabor’s inven­ coherent wave trains of such length has also treated important problems tion is the use of this principle for two- as to make possible the reconstruction in information theory and now, as step imaging. In the first step a wave of three-dimensional images of con­ Emeritus Professor of Applied Physics reflected on to the object whose siderable depth. Emmett Leith and his at Imperial College, London, and also image is required (or passing through group at Michigan University, USA, at the CBS Laboratories in Stanford, it if it is transparent) falls on a photo­ and many other institutes after them USA he continues to add to the deve­ graphic plate which, at the same brought about very rapid technical lopment of the field by assiduously time, is illuminated by another wave development and numerous scientific contributing ideas for solving practical from the same source but not touch­ achievements. and theoretical problems. ing the object (the reference wave). Holography enables the position of Dennis Gabor’s interest in futurology In general a very complicated inter­ each point of the object to be determ­ and social questions is also well ference pattern is produced on the ined to a fraction of a wavelength known. The last day of his stay in photographic emulsion. The more thanks to the phase in the wave Stockholm after the distribution of the details of the object at various field. Thus the hologram has rather prizes he spent in discussions of the distances and in different directions unexpectedly enriched optical meas­ peculiarities and problems of welfare- from the plate are involved, the more urement techniques and, in particular, state society. He is very outspoken in complex will be this pattern. Gabor made possible interferometric meas­ his personal views on such questions called the plate a ‘ hologram ’ (from urements on many objects. The chang­ as is shown in his book ‘Innovations, holos = whole, entire) because it ing shape of an object at different Scientific, Technological and Social’ contains the whole information of times, e.g. in vibration, can be stored (Oxford University Press, 1970). He the object, not only that relating to in one and the same hologram by calls for better matching between amplitude but also phase. exposing the plate several times. advanced technology and backward Once exposed, the hologram is When the different stored wave fields social institutions and is excited available at any time for the second are reconstructed simultaneously they about ideas of international citizen­ step of the imaging process. If a new interfere with each other and the ship and the education of peace spe­ reference wave falls on it, preferably image of the object is covered with cialists. One has the feeling that at the same angle as before, the holo­ interference lines, which, directly in NASA may not be very fond of him. gram pattern will act as an optical wavelengths, correspond to the Although he appreciates the collective grating or as a myriad of Fresnel changes of shape between exposures. effort put into the Apollo projects he zones diffracting the wave so that the Very rapid sequences of events, even questions their motivation and states former wavefield from the object is in plasma physics, are amenable to that such an effort would deserve reconstructed. In general two images analysis through hologram exposures much higher priority if dedicated to of the object are formed, one real made with short light flashes from large-scale social projects, provided and one virtual, the latter being a true modern pulsed lasers. A good survey the same unity of purpose could be three-dimensional reproduction. of present-day techniques and applic­ achieved.

3