Fizikai Szemle nyitólap |
Tartalomjegyzék |
Zsolt Bor
Dept. of Optics and Quantum Electronics
József Attila University, Szeged
Optics was not classified as an independent discipline until the beginning of this century. Most of the Hungarian scientists [1], working in the field of optics, were also good in other fields of science. Furthermore, valuable results in optics were achieved by a number of great scientists whose interest was not specially optics. One of the earliest example is Ányos Jedlik's (1800-1895) dividing machine which was able to produce 1200 diffraction grating grooves in 1 mm, as early as in 1845. Jedlik's main interest was electrotechnics; he fabricated electromotors preceding his contemporaries by several years [2]. He is best known by discovering the principle of self induction and demonstrating it by means of the dynamo. The monkteacher used all these inventions in order to enhance his lecture-demonstrations, not for making publications.
In the light of the above example, a few snapshots from the history of optics in Hungary will be given. In the first part the most charismatic scientists and their results will be presented which will be followed by a lexical summary of current research topics in optics in Hungary.
The "Petzval-objective"
József Petzval (1807-1891), in spite of his German origin from Szepesség, considered himself Hungarian [3]. He became professor of the Technical University of Vienna, and was the member of several scientific societies and the founder of the Vienna Photographical Society.
Fig. 1. The "Petzval objective": on the object side a glued chrone-flint achromat, and on the side of the photo plate an unglued flint-chrone achromat is standing. The spherical and chromatic aberration of this objective is very low, coma is practically not present.
His research interest involved numerous fields of pure and applied optics. He designed the first high F-number objective in 1841. This "Petzval-objective" (Fig. 1) consists of two achromats: one glued and the other one with an air gap, which forms an asymmetric arrangement with a focal length of 149 mm. In its own time it had outstanding optical properties and, with some minor modifications, it is still used today, as an objective in projectors. Petzval was a skilled lens maker as well; his lenses were built into Voigtländer cameras, some of which is still working. A crater preserves his name on the far side of the Moon. His contribution to the theory of lens systems is also well known. The "Petzval sum", first published in 1843, describes the image field bending in any lens systems:
with f1 f2 , ... the focal length of each lens and n1, n2 ,… their respective refractive indices.
Pál Selényi and the wide angle interference experiment; the electrography
At the end of the last century the Industrial Revolution together with the growing need for scientific knowledge provided a rich soil for the education of science and technology. Pál Selényi (1884-1954) studied physics and mathematics at the Budapest University [4]. After finishing his studies he started to work for the newly established Applied Physics Department of the University (Fig. 2). In his early works he was engaged in studying the nature of light. A well-known result from this period is his wide angle interference experiment whose preliminaries go back to the discovery of the photoeffect by Einstein, and Hertz 's experiments on the reflection of radio waves. Einstein's hypothesis was that elementary light sources emit electromagnetic waves into small solid angles which was supported by the fact that interference is easiest to achieve with lightwaves intersecting one another under small angles. The famous Young experiment can serve as an example: light passing through a pair of holes in close proximity results in the appearance of an interference pattern on the screen behind the holes, but only if the angle included by the incoming beams does not exceed angles of a couple of degrees.
Fig. 2. The schematic of Selényi's optical arrangement for the wide angle interference experiment. Small scattering centers, grown on a 10
m thick mica plate, are covered by a glass prism, and illuminated through the mica plate. The direct beam (1) and the beam totally reflected from the back surface of the mica plate (2) produce the interference pattern.
Wide angle interference experiments, in which the two light rays emitted from the same light source under obtuse angles is made to interfere with one another, attempted to disprove this theory. Although wide angle interference had already been observed by Hertz for radio waves, by Wiener, Drude and Nerst for light-waves Selényi was the first who performed them in a clearly unrefutable way owing to the simplicity of his experimental setup and the novel way of producing minute light sources by means of light scattering on small particles. The use of very small light sources is a prerequisite of wide angle interference, as satisfying the dsin
coherence condition is only possible at angles,
around 90º when the dimensions d of the source is comparable to the half of the illuminating wavelength. Selényi's idea was to grow tiny sulphur particles by immersing a 10
m thick mica plate into the vapour of sulphur, and use them as secondary light sources by scattering light
on them. In the arrangement (Fig. 2) he placed a glass prism over the mica plate, enclosing the scattering centers between the prism and the mica plate. Shining the light of a traditional light source through the mica plate an interference pattern was observed which can only be explained by the interference of the directly scattered (1) and scattered and back reflected (2) beams originating from the scattering sulphur particles. Selényi improved his experiments tilt perfection and successfully described the finest details of the observed complex phenomena.
Selényi was a physicist with great technological interest. He worked for various companies, e.g. for the development laboratory of the Tungsram Ltd. He published more than hundred articles in the field of optics, vacuum technology, photometry and electrography, studied and developed photocells, seleniumdiodes and photoelements. His pioneering work in electrostatic picture recording formed the basis of xerography. In fact Selényi published and patented several fundamental idea of electrography and produced better quality electrografic copies well before C. F. Carlson to whom the invention of electric recording is ascribed to.
Tungsram, the Hungarian home for research on light sources
Within the Egyesült Izzólámpa és Villamossági Rt. (Tungsram Ltd.) a research laboratory was established for improving light sources, mainly electric bulbs, in 1923. The head of this laboratory was Ignácz Pfeiffer (1867-1941), whose research staff consisted of such talents as Zoltan Bay (1900-1992), Imre Bródy (18911944), Tivadar Millner (1899-1988), György Szigeti (1905-1978) and Ernő Winter (1897-1971), to mention but a few. Bródy's most important result was the invention of the krypton filled light bulb. To prevent the evaporation of the tungsten filament these bulbs were filled with high density krypton gas, and to compensate for the increased beat conduction some nitrogen was also added. György Szigeti worked together with Zoltan Bay on metal-vapour lamps and fluorescent light sources. They took out a U.S. patent on "Electroluminescent light sources" made of silicon carbide; these sources were the ancestors of the light emitting diodes (LEDs). In 1933-34 the plasma lamp, invented by Dennis Gabor, was the subject of research in the laboratory.
Zoltan Bay, amongst others he worked for the Tungsram Ltd. to improve the performance of light bulb.
Dennis Gabor, the father of holography
Dennis Gabor(1900-1979), born as Dénes Gábor, was an engineer by his profession. He studied at the Technical University of Budapest and at the Charlottenburg Technical University in Berlin. At the beginning of his career he studied the properties of high voltage electric transmission lines using cathode-beam oscillographs. This aroused his interest in electron optics. Studying the fundamental processes making the oscillograph work, lead him to other electron-beam devices such as electron-microscopes and TV tubes. He even wrote his Ph.D. thesis on cathode ray tube (1927). After finishing his work on plasma lamps he immigrated to Great Britain where he worked for the Thomson Houston Company until 1948. His research was focused on electron optics, which lead him to the invention of holography. The Basic idea was that for perfect optical imaging all the information has to be used; not only the amplitude, as usual optical imaging does, but the phase as well. In this way a complete (holo) spatial picture (graf) can be obtained. Gabor published his theory in a series of papers between 1946 and 1951. At this time coherent light sources were not available, so his theory had to wait for more then a decade until the first practical application was realized. The invention of the laser (1962), the first coherent light source was soon followed by the first hologram (1963). Due to the rapid development of lasers and the wide variety of holographic applications (e.g. information storage, recognition of patterns, art) brought acknowledged success and worldwide attention to Gabor. He received numerous awards including the NOBEL PRIZE in Physics (1971).
Dennis Gabor, the inventor of holography.
Lajos Jánossy, studying the nature of photons
Lajos Jánossy's (1912-1978) investigations concerning Basic quantum mechanical problems drew his attention to the wave-particle duality, especially to experimental test by optical measurements. When light passes through a partially reflecting mirror in a Michelson interferometer, it is splitted into two parts and after reflection from two mirrors these parts are rejoined and an interference pattern is formed. Jánossy suggested two fundamental experiments. In the first one the existence of interference was probed for low and high beam intensities. The intensity of the incident beam impinging on the beam splitter was reduced to ensure that only one photon was present within the interferometer at any time. Recording the interference pattern for longer time periods reproduced the pattern obtained with high intensity illumination, proving the wave characteristics of light. On the other hand, replacing the two mirrors by photon counters, no correlated signals could be observed. This result is in good agreement with the particle nature of photons as a single photon can only be measured by one detector. Jánossy developed a theory for the fluctuations of light emitted by independently radiating atoms, too.
Spectroscopy in Hungary
In the field of spectroscopy pioneering work was done in various Hungarian laboratories. From the 1920s Rezső Schmid (1904-1943) and Lóránt Gerő (1910-1945) carried out research in the field of molecular spectroscopy studying binary and polyatomic molecules. A whole school of spectroscopists originated from this root, researchers like Ágoston Budó (1914-1969), István Kovács (19131996) to mention the two most famous ones. Their work concerned about the spectra of diatomic molecules, multiplett terms, intensity distributions and predissociation phenomena.
Ágoston Budó, the pioneer of luminescent research in Szeged.
Research in the field of optics at the Szeged University
As a native of Szeged, let me talk somewhat more about optics at the József Attila University, Szeged. From 1924 to 1949 Pál Frőhlich headed the Department of Experimental Physics. He was interested in phosphorescence in crystals and that of dyes solved both in solutions and gelatine. Ágoston Budó followed him as the bead of institute between 1950 and 1969. He was the first who worked on molecular luminescence in Szeged [5]. After World War II, in spite of the country's isolation, luminescence parameters were measured at extremely high precision using instruments that were solely built in the departmental workshop. Reabsorption of fluorescence light, radiative and nonradiative energy transfer in dye solutions were in the focus of research [6]. Measurement of the lifetime and polarization of luminescence lead to better understanding of the motion and the structure of molecules in solutions. After his early death István Ketskeméty continued his work on this field. Measurements on the upper limit and on the wavelength dependence of the fluorescence efficiency in the antistokes spectral range was used to improve the thermodynamic theory of luminescence. László Szalai (1920-1997) applied luminescence to biological processes such as photosynthesis. Since the late seventies research on laser physics has started to take over the role of central topic relying upon the experience on fluorescence of dyes. Results achieved by developing numerous nitrogen laser systems and producing ultrashort laser pulses brought an international recognition both to the department and the university.
Optics and laser physics today in Hungary - a brief overview
The subjects of modern optics and laser physics became interrelated and continuously developing. In the field of laser physics and non-linear optics there is strong R&D activity in university departments, at research institutes, as well as in small companies. In the following, a brief and lexical account of the topics of optics research in Hungary will be presented. The relevant URLs of each unit are also given in brackets for further references.
At the CENTRAL PHYSICAL RESEARCH INSTITUTE OF THE HUNGARIAN ACADEMY OF SCIENCES several departments are engaged in optics research.
Closing remarks
In the past years, optics played a constantly growing role in modern technology (e.g. in information and data processing, optical control of industrial production, pattern recognition, sensor technology, photography, materials processing, microelectronic applications). Today, 7% of all physics papers published throughout the world deals with various aspects of optics: Optics is a field of science in which Hungarian scientists traditionally had, currently have and will presumably have considerable contribution.
I would like to thank Zsolt Geretovszky and Zsolt Tóth for their help in preparing the manuscript.
References