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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Laser. History and essence of scientific discovery
Directory / The most important scientific discoveries The word "laser" is formed from the initial letters of a long phrase in English, which literally means "amplification of light by stimulated emission." “Scientists have long paid attention to the phenomenon of spontaneous emission of light by atoms,” M.M. Koltun writes in the book “World of Physics”, “which occurs due to the fact that an electron excited in some way returns from the upper electron shells of the atom to the lower ones. No wonder the phenomenon The chemical, biological and light luminescence caused by such transitions has long attracted researchers with its beauty and unusualness. But the luminescence light is too weak and scattered, it cannot reach the Moon ... Each atom during luminescence emits its light at different times, not coordinated with neighboring atoms. As a result, chaotic flare radiation appears. Atoms have no conductor! In 1917 year Albert Einstein in one of the articles he theoretically showed that external electromagnetic radiation would allow matching the flashes of radiation of individual atoms to each other. It can cause the electrons of different atoms to fly simultaneously to equally high excited levels. It is not difficult for the same radiation to play the role of a trigger for a "light shot": directed at a crystal, it can cause the simultaneous return of several tens of thousands of excited electrons to their original orbits at once, which will be accompanied by a mighty blindingly bright flash of light, light of almost the same wavelength, or , as physicists say, monochromatic light. Einstein's work was almost forgotten by physicists: research on the structure of the atom was then much more occupied by everyone. In 1939, a young Soviet scientist, now a professor and full member of the Academy of Pedagogical Sciences V.A. Fabrikant returned to the concept of stimulated emission introduced by Einstein into physics. Research by Valentin Alexandrovich Fabrikant laid a solid foundation for the creation of a laser. A few more years of intensive research in a calm peaceful environment, and the laser would have been created. "But this happened only in the fifties thanks to the creative work of the Soviet scientists Prokhorov, Basov and the American Charles Hard Townes (1915). Alexander Mikhailovich Prokhorov (1916-2001) was born in Atorton (Australia) in the family of a working revolutionary who fled to Australia in 1911 from Siberian exile. After the Great October Socialist Revolution, the Prokhorov family returned to their homeland in 1923 and after some time settled in Leningrad. In 1934, Alexander graduated from high school here with a gold medal. After school, Prokhorov entered the Physics Department of the Leningrad State University (LGU), graduating in 1939 with honors. Then he entered the graduate school of the Physical Institute named after P.N. Lebedev Academy of Sciences of the USSR. Here, the young scientist began to study the processes of propagation of radio waves along the earth's surface. He proposed an original method for studying the ionosphere using the radio interference method. From the very beginning of World War II, Prokhorov was in the ranks of the army in the field. He fought in the infantry, in intelligence, received military awards, was wounded twice. Demobilized in 1944, after a second severe wound, he returned to his scientific work interrupted by the war at the FIAN. Prokhorov engaged in research relevant at that time on the theory of nonlinear oscillations, methods for stabilizing the frequency of radio generators. These works formed the basis of his PhD thesis. For the creation of the theory of frequency stabilization of a tube generator in 1948, he was awarded the Academician L.I. Mandelstam. In 1948, Alexander Mikhailovich began research into the nature and character of electromagnetic radiation emitted in cyclic charged particle accelerators. In a very short time, he manages to conduct a large series of successful experiments to study the coherent properties of the magneto-bremsstrahlung radiation of relativistic electrons moving in a uniform magnetic field in a synchrotron - synchrotron radiation. As a result of the research, Prokhorov proved that synchrotron radiation can be used as a source of coherent radiation in the centimeter wavelength range, determined the main characteristics and power level of the source, and proposed a method for determining the size of electron bunches. This classic work opened up a whole avenue of research. Its results were formalized in the form of a doctoral dissertation, successfully defended by Alexander Mikhailovich in 1951. In 1950, Prokhorov began work in a completely new direction in physics - radio spectroscopy, gradually moving away from work in the field of accelerator physics. At that time, a new range of wavelengths, centimeter and millimeter, was mastered in spectroscopy. The rotational and some vibrational spectra of molecules fell into this range. This opened up completely new possibilities in the study of fundamental questions of the structure of molecules. Prokhorov's rich experimental and theoretical experience in the field of theories of oscillations, radio engineering and radio physics was the best suited for mastering this new field. With the support of Academician D.V. Skobeltsyn, in the shortest possible time, together with a group of young employees of the laboratory of vibrations, Prokhorov created a domestic school of radio spectroscopy, which quickly gained leading positions in world science. One of these young employees was Nikolai Gennadievich Basov, a graduate of the Moscow Engineering Physics Institute. Basov was born on December 14, 1922, in the city of Usman, Voronezh province (now the Lipetsk region) in the family of Gennady Fedorovich Basov, later a professor at Voronezh University. The end of school Basov coincided with the beginning of the Great Patriotic War. In 1941, Nikolai was drafted into the army. He was sent to the Kuibyshev Military Medical Academy. A year later, he was transferred to the Kiev military medical school. After graduating from college in 1943, Basov was sent to a chemical defense battalion. From the beginning of 1945 until demobilization, at the end of that year, he was in the ranks of the army. In 1946 Basov entered the Moscow Mechanical Institute. After graduating from the institute in 1950, he entered his graduate school at the Department of Theoretical Physics. Since 1949, Nikolai Gennadievich has been working at the Physical Institute of the USSR Academy of Sciences. His first position was an engineer at the Oscillation Laboratory headed by Academician M.A. Leontovich. Then he becomes a junior researcher in the same laboratory. In those years, a group of young physicists led by Prokhorov began research in a new scientific direction - molecular spectroscopy. At the same time, a fruitful collaboration between Basov and Prokhorov began, which led to fundamental work in the field of quantum electronics. In 1952, Prokhorov and Basov presented the first results of a theoretical analysis of the effects of amplification and generation of electromagnetic radiation by quantum systems, and later they investigated the physics of these processes. Having developed a number of radio spectroscopes of a new type, Prokhorov's laboratory began to obtain very rich spectroscopic information on the determination of structures, dipole moments and force constants of molecules, moments of nuclei, etc. Analyzing the limiting accuracy of microwave molecular frequency standards, which is determined primarily by the width of the molecular absorption line, Prokhorov and Basov proposed to use the effect of a sharp narrowing of the line in molecular beams. “However, the transition to molecular beams,” write I.G. Bebikh and V.S. induced transitions between two energy states of molecules with the absorption of a quantum during the transition from the lower level to the upper one (induced, stimulated absorption) and with the emission of a quantum during the transition from the upper level down (induced, stimulated emission).Therefore, it is proportional to the difference between the populations of the lower and upper energy For two levels separated by an energy distance equal to a quantum of microwave radiation, this population difference is only a small part of the total particle density due to the thermal population of the levels in the equilibrium state at ordinary temperatures according to the Boltzmann distribution. It was then that the idea was proposed that by artificially changing the populations of the levels in a molecular beam, i.e., by creating nonequilibrium conditions (or, as it were, one's own "temperature", which determines the population of these levels), one can significantly change the intensity of the absorption line. If the number of molecules at the upper working level is sharply reduced by sorting out such particles from the beam, for example, using an inhomogeneous electric field, then the intensity of the absorption line increases. An ultra-low temperature is created in the beam, as it were. If, however, molecules are removed from the lower working level in this way, then the system will experience amplification due to stimulated emission. If the gain exceeds the losses, then the system is self-excited at a frequency that is still determined by the frequency of the given quantum transition of the molecule. In the molecular beam, on the other hand, population inversion will be carried out, i.e., a kind of negative temperature will be created.” This is how the idea of a molecular generator appeared, which was outlined in the well-known cycle of classical joint works by AM Prokhorov and N.G. Basov 1952–1955. From here began its development of quantum electronics - one of the most fruitful and most rapidly developing areas of modern science and technology. In essence, the main, fundamental step in the creation of quantum generators was to prepare a nonequilibrium radiating quantum system with population inversion (with a negative temperature) and place it in an oscillatory system with positive feedback - a cavity resonator. It could and should have been made by scientists who combined the experience of studying quantum mechanical systems and radio physical culture. Further extension of these principles to the optical and other ranges was inevitable. Prokhorov and Basov proposed a new method for obtaining population inversion in three-level (and more complex) systems by saturating one of the transitions under the action of powerful auxiliary radiation. This is the so-called "three-level method", later also called the optical pumping method. It was he who allowed in 1958 Fabry-Perot to form a real scientific basis for the development of other ranges. This was successfully used in 1960 by T. Meiman when creating the first ruby laser. While still working on molecular generators, Basov came up with the idea of the possibility of extending the principles and methods of quantum radiophysics to the optical frequency range. Since 1957, he has been looking for ways to create optical quantum generators - lasers. In 1959, Basov, together with B.M. Vulom and Yu.M. Popov prepared the work "Quantum-mechanical semiconductor generators and amplifiers of electromagnetic oscillations". It was proposed to use the inverse population in semiconductors, obtained in a pulsed electric field, to create a laser. This proposal, along with the proposals of US scientists on the use of ruby crystals (C. Townes, A. Shavdov) and gas mixtures (A. Javan), marked the beginning of the systematic development of the optical frequency range by quantum electronics. In 1964, Basov, Prokhorov and Towns (USA) became Nobel Prize winners, which they were awarded for fundamental research in the field of quantum electronics, which led to the creation of masers and lasers. Author: Samin D.K.
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