197 1 the nobel prize in physics was awarded to dennis gabor, a Hungarian physicist in Imperial College London, London, England (1900- 1979), in recognition of his invention and development of holography.
Gabor invented holography in the 1940s before the advent of laser. At that time, he worked in the research room of a company, and it was necessary to improve the resolution when manufacturing an electron microscope.
At that time, the resolution of electron microscope was 100 times higher than that of the best optical microscope, but it was still not enough to distinguish the crystal lattice. Among them, spherical aberration and diffraction aberration are the main factors limiting the resolution. In order to reduce the diffraction difference, it is necessary to increase the aperture angle. Doubling the aperture angle will reduce the diffraction difference by half, but at this time the spherical aberration will increase by 8 times. In order to give consideration to both, the aperture angle of the electronic lens has to be limited to 0.005 radian, so the theoretical limit of resolution is about 0.4nm, and the resolution lattice must reach at least 0.2nm. Faced with such a difficult problem, Gabor thinks hard. /kloc-one Easter in 0/947, the sky was clear, and Gabor was waiting for a ball game at the tennis court. Suddenly, an idea flashed through his mind and he thought, "Why not take an unclear electronic photo, let it contain all the information, and then correct it optically?" Considering that the electron objective lens will never be perfect, if it is omitted, the phase and intensity information is recorded by coherent electron waves, and then the aberration-free image is reproduced by coherent light, the resolution of the electron microscope can be improved to 0. 1nm, which meets the requirements of observing the crystal lattice.
It was from this idea that Gabor invented holography.
It should be said that the basic concept of holography is the product of wave optics. At the end of 17, Huygens put forward his "secondary wave" principle when he established the wave theory of light, which is a powerful weapon to understand wavefront and diffraction. /kloc-At the beginning of the 9th century, Thomas Young explained his double-slit interference experiment with wave motion theory, and Fresnel supplemented Huygens' principle with the interference idea of light, perfecting the diffraction theory of light. It should be said that on this basis, someone should have invented holography long ago. However, why didn't an expert on electron microscopy accidentally invent holography until the middle of the 20th century? The key point is that Gabor has grasped the core idea of holography: wavefront reconstruction.
Gabor seized the key, as he once said, "In this study, I stood on the shoulders of two great physicists, lawrence bragg and Zelnik". In other words, Gabor's idea to invent holography was inspired by them.
A few years before the invention of holography, dennis gabor read lawrence bragg's book "X-ray Microscope", and Prague reproduced the lattice image by twice diffraction. Although X-rays cannot be imaged through a lens, the spacing between atoms is the same order of magnitude as the wavelength of X-rays, and the interference of periodically arranged atoms on the scattering of incident X-rays will produce a diffraction lattice. The second diffraction of this diffraction pattern by coherent light can restore the lattice image, which is the origin of Gabor two-step imaging method. However, he noticed that Prague's method was not enough to record all the information of Fourier transform. Although the amplitude can be obtained from the square root of the intensity, the phase has been lost, so it is only suitable for those special objects whose absolute phase from the lattice to the diffraction field can be judged in advance, thus knowing the phase change between the incident light and the diffraction line. In order to solve the problem of phase recording, Gabor thought of the "coherent background" used by Zelnik when studying lens aberration. He believes that if there is nothing to compare, it is inevitable to lose phase; However, if a standard is added, that is, the "coherent background" is used as the reference wave, then the reference wave and diffraction wave interfere with each other, and the interference pattern is recorded with a photographic negative, so that an interference image containing phase information can be obtained. Diffraction wave is also called object wave, and Gabor interferogram containing phase information is called "hologram". On the hologram, the phases of the two waves are the same, and the maximum occurs in opposite positions. If you make a positive film, it only transmits light to the maximum extent. Because the reference light at the transparent slit is in phase with the object wave, the wavefront of the object wave can be reconstructed by illuminating the hologram with the reference light. Because no one mastered the concept of wavefront reconstruction in the past, it was not until 1947 that Gabor had "wavefront reconstruction" in his mind that holography was invented.
Gabor considered his electron microscope scheme by reconstructing the wavefront and proposed a two-step process. The first step is electronic analysis, that is, the object is irradiated with an electron beam, and the diffracted electron beam of the object interferes with the coherent background (that is, the undiffracted part of the incident electron beam), and then it is recorded on the negative; The second step is optical synthesis, that is, using the optical system to reproduce and correct the aberration of electron optics, and then shooting the reproduced image on the photographic negative. Gabor and his assistant J.Williams first carried out holographic experiments in the field of optics.
They use a mercury lamp as a light source, monochromatic the incident light through a filter, and achieve the required spatial coherence with the help of a pinhole filter. Their experiment is not easy to do, because the monochromatic light provided by high-pressure mercury lamp is only 0. 1mm, that is, there are only 200 stripes. However, in order to obtain spatial coherence, they must illuminate a pinhole with a diameter of 3μm with a mercury line, which is enough to make a hologram of an object with a diameter of 1cm. They used a micrograph with a diameter of 1mm as the experimental object. Because the light source is very weak, it takes several minutes to expose with the most sensitive photographic latex at that time. The smaller coherence length forces them to arrange everything on the same axis. According to this characteristic, this experiment was called coaxial holographic experiment, which was the only feasible scheme at that time. They tried to find the best compromise between the two contradictory factors, coherence length and intensity. The reconstructed image is not ideal, and there are still system defects in the photo. In addition, coaxial holography will be interfered by inevitable twin images. Gabor tried to separate coaxial twins by focusing, but it was impossible to completely eliminate them. Nevertheless, Gabor realized holographic recording and wavefront reconstruction for the first time in this experiment, and got the first holographic photograph.
Since then, there has been the first upsurge of studying holography. Rogers made the first phase hologram, and comprehensively discussed the holographic theory. He also proposed that holography is also suitable for radio waves and can be used to detect the ionosphere;
A. Bates carried out X-ray holography experiment; The doctoral thesis written by graduate student Hussein El-Sum under the guidance of P.Kirpatrick became an important document for studying Gabor holography at that time.
However, in the early work of holography, people are most concerned about the application in electron microscope. Since 1950, M.E.Haine, J.Dyson and T.Muivey have been engaged in this research, with Gabor as consultant. However, the results have been minimal.
As for the study of pure optical holography, there was little effective work because there was no ideal coherent light source at that time and it was interfered by Gabor coaxial holographic twins. Therefore, in the mid-1950s, the research of holography was at a standstill, and there was almost no new progress. Only E.N.Leith of the University of Michigan is still applying the wavefront reconstruction theory to radar work. There are also some scientists in the Soviet Union who continue to make new explorations.
The appearance of 1960 laser has brought new life to holography. 1963, Liz and J.Upatnicks published the first laser hologram, which immediately caused a sensation, and holography was revived at once!
Because the coherence length of laser is several thousand times longer than that of mercury lamp, off-axis holography is created by the method of "oblique reference wave" in the experiment, which is not limited by coaxial holography. The experimenter easily ruled out the interference of twins. In addition, because the intensity of laser is several million times higher than that of mercury lamp, in a proper exposure time, very fine particles and low-speed photographic emulsion can be used to make large holograms, and a very good reproduction effect can be achieved. The holographic photos, scenery photos and portrait photos of transparent people on dark background published by Lisi et al. for the first time have clear images. 1964, they made holograms with diffuse illumination, and successfully obtained the three-dimensional reconstructed images of three-dimensional objects.
Liz's success is not only because of the laser, but also because of his theoretical preparation from 1955. He combined the communication theory with the concept of holography and applied it to the research of side-looking radar, which is actually two-dimensional holography of electromagnetic waves. Therefore, after the appearance of laser, he applied his oblique reference wave method to laser holography and made a major breakthrough in holography.
Gabor1900 was born in Budapest, Hungary on June 5th. When 15 years old, he suddenly developed a special interest in physics. I taught myself calculus in two years before I went to college. He studied Abbe's microscopic theory and Lippmann's color photography, which played an important role in his research in the following decades. He and his brother set up a small laboratory at home to do some X-ray and radioactive experiments. However, Gabor chose engineering instead of physics in college. Because physics was not a major in Hungary at that time. 1924 graduated from Berlin technical university, and 1927 received his doctorate. During that time, he often went to Berlin University as an auditor, where famous teachers such as Einstein, Planck, Nernst and Laue offered various physics courses. He is engaged in electrical engineering, but his body and mind are almost completely immersed in applied physics. His doctoral thesis is to develop a new cathode ray oscilloscope. He also made magnetoelectric lenses. After receiving his doctor's degree, Gabor came to Siemens, where he invented the high-pressure timely mercury lamp. What prompted him to consider holography was that after working in the laboratory of a British company from 65438 to 0934, the company needed to improve the resolution of the electron microscope. Gabor is very interested in this research topic, and he got many opportunities to carry out optical experiments during the research. The basic idea of holography was formed here.
Gabor died on February 9, 1979 on/kloc-0.