by Marina KHAL1ZEVA, journalist

In 2010 the scientific community celebrated the 50th anniversary of the creation of laser. This invention is one of the greatest achievements of the 20th century, leading to mastery of nuclear energy, space exploration, creation of radiolocation devices, and computer production. The Russian Academy of Sciences and its institutes carried out a series of events on the occasion of this anniversary. The final event was a two-day session of the General meeting, held in December at the Big Hall of the Russian Academy of Sciences. There more than 500 leading scientists of our country discussed the use of optical quantum generators in nanotechnologies, thermonuclear synthesis, metrology, fiber optics, and other perspective branches of science, technology, and medicine.

TURNS OF HISTORY

The first working laser* was demonstrated by Theodore Maiman from the Research Laboratory of Hughes Aircraft Company in Malibu, California. The active sub-

* Laser ( Light Amplification by Simulated Emission of Radiation) is an optical quantum generator, transforming pumping energy (light, electrical, thermal, chemical, etc.) into a coherent monochromatic polarized narrow beam.--Ed.

stance in this laser was ruby, a mineral from aluminum oxide with a slight admixture of chromium (Cr), coloring it red. The scientist realized that Cr atoms, separated by large intervals, can "give light" no worse than gas. In order to create optical resonance, he pulverized a thin layer of silver onto polished parallel ends of a small cylinder from synthetic ruby, made according to a special

design by the Union Carbide Company, and placed it into a spiral tube, generating bright light flashes. On May 16, 1960, a bright ray of light was released from this simple, fine and compact device. From this event, recorded in Maiman's working notebook, the mankind started a real breakthrough into the laser era.

"It can be regarded as a revolutionary achievement in the world science of the 20th century, which changed civilization and stimulated technological revolution," said Academician Yuri Osipov, President of the Russian Academy of Sciences, opening the forum. He spoke about the basic works, which led to the creation of new type generators and amplifiers. He noted that the first step in this direction was made by the author of relativity theory Albert Einstein, Nobel Prize winner of 1921 and Honorary Member of the USSR Academy of Sciences from 1926. In 1916, he hypothesized the existence of a quantum system of induced or forced (simulated) radiation (this principle underlies quantum electronics and laser physics). And in 1927, Paul Diraque, an outstanding English scientist, future Nobel Prize winner (1933), Foreign Member of the USSR Academy of Sciences (from 1931) substantiated and summarized these conclusions.

In the 1930s and 1940s, scientists of various countries studied potentialities of "negative absorption" (amplification) in the stimulated atom system. One of them was

Valentin Fabrikant from P. Lebedev Physical Institute (FIAN), who published his Doctor's Thesis related to this subject in 1940. Ten years later together with his colleagues he suggested a new method for intensification of electromagnetic radiation, based on the use of the medium in which the greater part of molecules had excessive energy. But, unfortunately, this work by Russian scientists, which became known to the public only 8 years later, was left unnoticed, and attempts to create a working optical amplifier failed.

The means to create laser, pointed out Osipov, was found by radiophysicists, exploring the spectra of substances in the microwave band, not specialists in optics. In the middle of the 1950s, these experiments were in progress at the institutes of the USSR Academy of Sciences. At FIAN they were headed by Alexander Prokhorov and his disciple Nikolai Basov (Academicians from 1966). In the USA these experiments were headed by Charles Townes, Professor of Columbia University (RAS Foreign Member from 1994).

In 1954, Prokhorov and Basov suggested a molecular gas generator and a centimeter band amplifier. The same year Charles Townes with his disciple James Gordon and Herbert Zeiger, research assistant, experimentally realized this device on a bundle of ammonium molecules. However, this and other devices suggested during that period worked only in the microwave band.

The next step in the "laser saga" started in 1958, when Basov, Prokhorov, and Townes, independently of each other, suggested creation of a generator forming not microwave, but visible radiation--the light we are used to. This in fact was laser (though the authors of the invention called it maser), realized by Maiman two years later. Research results of two Russian and one American predecessors, in fact laying the base for creation of an optical quantum generator, were awarded Nobel Prize in 1964.

Townes, who recently turned 95, was expected in Moscow at the General Meeting of the Russian Academy of Sciences. Unfortunately, the scientist could not come to Russia, but he sent a greeting letter in which he highly appreciated the work of his Soviet colleagues.

Demonstration of ruby laser (said President of the Academy) stimulated greatly the development of this technology. At the end of 1960, Ali Javan, American physicist, constructed a gas generator working on a mixture of helium and neon, the atoms of which released infrared coherent radiation. In the Soviet Union a device of this kind, initiating studies of devices on other gaseous active substances, was launched in 1962 at FIAN.

Creation of the first semiconductor injection laser on gallium arsenide (its author was Robert Hall, USA, 1962) was preceded by theoretical studies of monocrys-tals, carried out in 1958-1961 by a team of scientists headed by Nikolai Basov*. Generators of this type are used in fiber optics**. The years that followed were full of technological improvements and inventions aimed mainly at an increase of capacity, improvement of compactness and prolongation of service time of the devices.

"Today,--Osipov concluded,--lasers are used to solve the problems of energy (regulated thermonuclear synthesis), in high precision physics, metrology, micro- and nanoelectronics, in space navigation, systems of communication and information transmission, in precision engineering, in materials processing technologies, for creation of effective instruments for medicine, and in other spheres of human activities."

The program of the session included 15 reports on the majority of these spheres of laser use. They were presented by leaders of scientific schools developing these

* See: N. Basov et al., "Laser Fusion, a Review of Progress", Science in Russia, No. 1, 2001.--Ed.

** See: A. Prokhorov, Ye. Dianov, "Fiber Optics: Problems and Prospects", Science in Russia, No. 1, 2001.--Ed.

breakthrough trends at the institutes of the Russian Academy of Sciences.

FROM HETEROSTRUCTURES TO QUANTUM POINTS

In 2000, the Nobel Committee awarded Academician Zhores Alferov, Director of A. loffe Physico-Technological Institute, RAS (St. Petersburg), and American scientists Herbert Kremer from California University (Santa Barbara) and Jack Kilby from Texas Instruments Company for studies of semiconductor heterostructures*, started at the end of the 1950s, and creation on the basis of these structures of lasers, photodiods, and superfast transistors, resulting in creation of new electronics, which radically changed our life by the end of the 20th century.

In his report "Semiconductor Lasers and Nanotech-nologies" Academician Alferov spoke in detail about the works carried out at the Institute he headed, which were highly appreciated**.

The interest to heterostructures--a multilayer "sandwich" from joined semiconductors of different chemical composition--was quite justified: they opened new vistas in creation of ultrarapid electronic devices with information capacity, minimized in size to virtually atomic dimensions. However, at first few people believed in per-spectiveness of this trend of research. The available crystals were chemically unstable, while the sizes of the lattices did not coincide, which led to numerous defects

* Heterostructure (Greek heteros--another, different) is a lamellar structure formed during a close contact of two and more heterogeneous semiconductors, differing by width of prohibited zones, permanent crystal lattice, and other parameters.--Ed.

** See: R. Sures, E. Tropp, "On Fame's Eternal Beadroll", Science in Russia. No. 2, 2010.--Ed.

* Epitaxis (Greek ep--ion and taxis--location, order) is regular superimposing of one crystal material onto another, when every next layer has the same orientation as the previous one.--Ed.

during their contact. Alferov recollected that the scientists could not choose appropriate semiconductor pairs for a long time. But at the end of the 1960s, when devices of molecular radiation epitaxis* were created, which allowed modulation of semiconductor parameters, there sprang up a new idea-to form required heterotransition by layer-by-layer superimposition of one monocrystal (to be more exact-its film) onto the surface of another one. Having coped with numerous difficulties, the team of the future Nobel Prizewinner found in 1967 a GaAs-AlGaAs heteropair, which then became classical in the microelectronic world.

Alferov recollected: "When we published this work, we were happy that we were the first to find this unique, virtually ideal reticular-coordinated system for GaAs." However, almost simultaneously (one month later!) this heterostructure was independently obtained in the USA by scientists of the IBM Company. This problem was developed by other US companies as well, for example, Bell-Telephone, IBM, and RCA. There was a sort of a race between them and the Leningrad Physico-Techno-logical Institute: who would be the first to make semiconductor heterolaser working in a continuous mode at ambient temperature? Our compatriots--Alferov with his team including Yefim Portnoi, Dmitry Tretyakov, Dmitry Garbuzov, Vyacheslav Andreyev, Vladimir Korolkov--created it in 1970, one month before Morton Panish's team from Bell-Telephone.

It is noteworthy that the semiconductor pair found by the scientists largely stimulated the development of molecular epitaxial technologies, which led to creation of a new generation of optoelectron devices. Assigned feedback lasers with low threshold generation, highly effective light guides, phototransistors, thyristors, solar elements were created at the beginning of the 1970s at the Center of Nanoheterostructure Physics under A. loffe Physico-Technological Institute, created on the basis of a small laboratory headed by Zhores Alferov. The concept of obtaining heterostructures by using multicomponent (quadruple) compounds (for example, InGaAsP) was formulated during the same period. Based on these heterostructures, injection quantum dimensional infrared and visible band lasers with unprecedented transformation efficiency were created. They were used for fiberoptic extra-distant communication lines. Alferov emphasized considerable contribution of the director of the Center Pyotr Kopyev, Corresponding Member of the Russian Academy of Sciences, to development of these technologies in Russia.

The properties of low dimensional nanostructures (quantum wires and quantum points--10 nm ultrasmall objects) have been studied here from 1993, understanding even at that time their perspectiveness for nanotech-nologies. Two years later the first device on their basis was demonstrated: a quantum point-based injection laser. Later on its spectral band was extended to 1.3 urn, a parameter essential for use in fiber-optic communication lines.

Of the latest realized achievements Alferov named surface radiating devices (the light in them is released vertically upward, perpendicularly to the surface). They work as a cheap light emitting diods, only with an ideal quality of the spectrum, narrow diagram of direction, they are thermostable, well integrated due to their very small size (up to microns). The specialists managed to realize an ultraviolet band vertical laser--the very laser required for optical recording.

LASER THERMONUCLEAR SYNTHESIS

Nikolai Basov and Oleg Krokhin (Academician from 2000, now Head of the Quantum Radiophysics Department of FIAN) were the first who suggested using potent laser radiation for heating compact plasma to thermonuclear temperatures in their report presented at the Presidium of the USSR Academy of Sciences on March, 1962. A year later at the 3rd conference on quantum electronics in Paris the scientists presented their first theoretical estimations. The interest to the problem was so great that there soon emerged an independent scientific trend--laser thermonuclear synthesis. Krokhin and his colleague Sergei Garanin, Corresponding Member of the Russian Academy of Sciences, from the All-Russia Institute of Experimental Physics* (Sarov, Nizhni Novgorod region), where the most powerful lasers in the country and in Europe were created, spoke about some stages of its development in Russia and outlined future plans.

Laser light releases significant energy within a short period. As Krokhin noted, as early as in 1962 our scientists showed that pulsed sources could be created with radiation energy of 100 J during 1 n/sec with a power of 10¹¹ Wt. If a beam of this magnitude is directed to a substance, it would immediately evaporate without melting (physicists call it sublimation of the process). And if laser radiation is focused, then 10 Wt would fall to 1 mm"--this, in fact, is a capacity of all electric power stations of the world! Energy density, its concentration are tremendous: temperatures in the focus point reach a level

* See: A. Vodopshin, "On a Visit to Khariton", Science in Russia, No. 5, 2009.--Ed.

required for initiation of thermonuclear reactions. Hence, lasers can be used for realization of regulated thermonuclear synthesis. The way out was suggested by Basov and Krokhin in 1964: pressing out and heating deuterium-tritium targets by potent laser beams, destined by Nature for rapid introduction of a tremendous portion of energy into a small volume.

Experiments on attaining high densities and temperatures of pressed out fuel started in the mid-1970s at FIAN. The first devices for obtaining neutron impulses from plasma heated by laser have been developed there by a team of scientists headed by Basov and Prokhorov.

At first the experiments were carried out on a Kalmar device. Its 9 beams simultaneously hit the deuterium target (a globule just 0.2 mm in diameter) located in a vacuum chamber. However, its power was far from the required, though in the most successful experiments the emergence of neutrons (precursors of a starting thermonuclear reaction) could be fixed. And though they Were few, their presence indicated that the scientists chose the right way.

Later on lasers were improved, their capacity increased, the target was modified. In order to assess the complexity of the problems, Krokhin offered an example. Estimations made by theoreticians showed that the reaction would be better if gaseous deuterium were at first pumped under 100 atm pressure into a glass globule 100-200 µm in diameter, with wall thickness not exceeding 2-3 µm, quite uniform over its entire surface (permissible deviation not exceeding 1 percent). To make even one such globule was a difficult task. However, it was solved at FIAN, and rather quickly. The other system, Delfin (Dolphin), consisted of 212 beams, each

with a capacity over 100 times higher than a beam released by Kalmar. At the beginning of experiments, the temperature in the center of the target of this device reached 100 mln ºC, and 10,000 times more neutrons were released.

Disintegration of the USSR had a great impact on the Russian projects of laser thermonuclear synthesis. "The financial support in fact stopped by the beginning of the 1990s, we could no longer effectively use even the experimental devices available by that time," Krokhin said. "Today the main research institution in this sphere in Russia is All-Russia Institute of Experimental Physics in Sarov."

Sergei Garanin, a representative of this Institute, in his report pointed out the latest results in physics and technology of thermonuclear synthesis, though the subject of interaction between laser radiation and substances has been studied by his team for over 40 years. The attention of the Institute was focused mainly on the creation of chemical and gaseous lasers, but recently the interest shifted towards potent neodymium systems of a mega-joule level.

In 1999, a new generation device Iskra-6 has been realized there. This laser is characterized by radiation parameters approximating the thermonuclear reaction initiation threshold. In order to verify its scientific and technological parameters, a Luch modulus (2001) has been designed with high efficiency, two power amplifiers, each with 9 plates of neodymium phosphate glass, and a laser beam section of 20x20 cm. Garanin noted that "the cleanliness of the premises in which it is located is 300 dust particles per 1 m , and in the most important parts of the system even cleaner, 3 dust particles per 1 m³".

The device constructed on the basis of Russian elements is a result of efforts of virtually all leading laser centers of Russia. S. Vavilov State Optical Institute, A. loffe Physico-Technological Institute, RAS Institute of Applied Physics (Nizhni Novgorod), Luch Research and Production Amalgamation (Podolsk, the Moscow Region), and other organizations contributed to its creation. "Luch is a device of a national scale," said the reporter, "it is open to everyone who is in search of a reliable and rapid solution of the regulated thermonuclear synthesis problem. Its effective work today gives us grounds to approach the creation of a next generation system with laser energy of 4.6 MJ. Its planned parameters will be superior to the characteristics of NIF device working at Laurence Livermore National Laboratory in the USA and LMJ device created in France."

ON FAST ELECTRONS

Studies of electromagnetic radiation of terahertz (sub-millimeter) band frequencies attracted greater attention during the recent decade. A source of this kind is a free electron laser with the highest power of 0.5 kWt, which was created in 2003 at the Siberian Center of Photochemical Studies, Siberian Branch of the Russian Academy of Sciences by scientists from G. Budker Institute of Nuclear Physics in Novosibirsk. In 2009 simulated radiation generation mode was attained there on the second line of the system. This appreciably extended the spectrum of multidisciplinary studies carried out on the device. Why do chemists, biologists, geologists, solid body physicists--scientists from 12 institutes of the Siberian Branch of the Russian Academy of Sciences and Novosibirsk University--exhibit so great interest in experiments on this device? One of the creators of this equipment Nikolai Vinokurov, Dr. Sc. (Phys. & Math.), answered this question.

Free electron lasers, he said, use the simulated so-called ondulatory radiation phenomenon. This idea, to be more exact, the device proper--the ondulator, where an electron moves along a wave-like trajectory, due to which the particle releases radiation--was suggested in 1947 by the Nobel Prize winner of 2003 Academician (from 1966) Vitaly Ginzburg. The ondulator was initially intended for detection of cosmic rays, but later became an obligatory element in short wave electromagnetic radiation generators. In 1960, Robert Phillips (USA) inserted it in a vacuum electron device. The resultant ubitrone became a prototype of a free electron laser. However, the first source of terahertz radiation was demonstrated by John Maidy from Stanford University (1976).

The pioneers of this trend at G. Budker Institute of Nuclear Physics were doctors of physico-mathematical sciences Vladimir Bayer, Alexander Milstein, Nikolai Vinokurov, and Academician (from 1970) Alexander Skrinsky*. The work by the two latter authors "On the Threshold Power of an Optic Klystron" (1977) in fact opened a new trend of research--creation of a free electron laser on the base of recuperator accelerators.

Vinokurov noted that the main advantage of devices of this kind was their capacity to generate monochromatic radiation at any preset wavelength (from 0.1 nm to 1 mm--7 orders of magnitude) and smoothly rearrange it. Other lasers worked in more narrow bands. The peak radiation power for these devices can reach ˜100 kWt in case of retention of the diffraction quality of the radiation source. In addition, the device can smoothly transform the electron beam energy into electromagnetic radiation, that is, in a way, it can be "equated" with the electron beam tube used in old TV sets or a radiolamp. According to Vinokurov, there were no sources of this kind in the world 5 years ago and today they are available at the American National Center of Accelerators (Jefferson's Laboratory) and the Japanese Institute of Nuclear Research in Takai.

The Siberian laser works on a recuperator accelerator. As Vinokurov said that was an independent technological achievement. What for? The electrons passing through an ondulator release no more than 1 percent of the bundle energy to electromagnetic radiation. What is to be done with the remaining energy? Return it to the

* See: A. Skrinskv, "Cognition of Matter", Science in Russia, No. 6, 2007.--Ed.

accelerator. This method, planned by scientists from G. Budker Institute of Nuclear Physics at the initial stage of designing, is called recuperation. In other words, returning the "worked out" bundle to the system, specialists compensate for the entire input power, moreover, amplify it only at the expense of constant circulation of the electron bundle in the system. Hence, recuperation provides a higher current and nullifies radiation danger of the device. A propos, in 2009 Nikolai Vinokurov was awarded State Prize of the Russian Federation "For Development and Creation of Free Electron Lasers".

The device is already allowed for collective use. Staff members of A. Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences (Novosibirsk), intend to use terahertz radiation to study cleavage of molecules. This basic work may bring about results which can have practical application. If the expected results are attained, creation of new technologies of substance pulverization on the surface will start.

Light-induced chemical reactions have been studied for many years at the Laboratory of Laser Photochemistry of the Institute of Chemical Kinetics and Combustion in Novosibirsk (the system is located in the territory of this Institute). At first CO₂ laser with a wavelength of about 10 µm was used, for which molecules were specially synthesized. Now there is no need in it, for there is a source of greater power, working with molecules not at a selected, but at any wavelength. One more detail. In cooperation with their Novosibirsk colleagues from the Institute of Cytology and Genetics* and G. Budker Institute of Nuclear Physics the chemists are improving the so-called "soft ablation" method (Latin ablatio-taking away) for transition of molecules (for example, DNA, nanoparticles) from solid or liquid phase into aerosol under the effect of terahertz radiation for further analysis. This work can be done only here: low quantum energy (˜0.01 eV) does not destroy covalent bonds of molecules, as they retain their biological activity.

COMPUTER MODEL IN POLYMER

The Institute of Problems of Laser and Information Technologies, the Russian Academy of Sciences (Shatura, Moscow Region) has been effectively developing a new trend in recent years: laser stereolithography (technology for operative making of prototypes, models, and functional objects by their three-dimensional computer models). Academician Vladislav Panchenko devoted the greater part of his report to this subject, the results of which are in great demand primarily in medicine.

The studies were initiated at the beginning of 1994 by the Center of Forensic Medical Expert Evaluations of the RF Ministry of Health. At that time they carried out identification of the remains of the former Russian Emperor Nikolai II, his family members and servants shot in the cellar of Ipatyev's house in Yekaterinburg on the night of July 16, 1918, and found under the Old Koptyakov embankment not far from the city. In 1995, a plastic copy of the skull of a man found there was made at the Institute on the basis of X-ray computer tomography data. The copy was made with precision fit for verification by appropriate organs. This experience has proved to be so excellent, that "lasers in biomedicine" became one of the priority trends.

Up to the recent time, Panchenko pointed out, an X-ray picture was the only objective and rapid method for obtaining information about posttraumatic defects, alien objects, state of implants and endoprostheses, traces of surgical interventions on the bones of a living human being. However, a two-dimensional image of the X-ray

* See: V. Shumny, "Priorities of Biology". Science in Russia, No. 5, 2007.--Ed.

"shadow" of the studied object could not show all specific features of its shape and surface relief; moreover, it distorted true dimensions. Introduction of computer tomography to clinical practice made it possible to obtain highly accurate three-dimensional models of different human organs and structures. Nevertheless, in the first half of the 1990s it took 10 hours to obtain ample data essential for, say, reconstruction of the skull. As for bone tissue, magnetic resonance tomographs of that period in fact did not "see" it. Only emergence of spiral X-ray computer devices at the end of the 1990s radically changed the situation. The tomogram of the head became a routine procedure taking no more than 1 min. This stimulated introduction of stereolithography to practical medicine. In addition to virtual three-dimensional models, the physician could have their material copies.

Panchenko emphasized that the technology (also called rapid prototyping) concentrated the latest achievements in quantum electronics, nonlinear optics, physics and chemistry of high-molecular compounds, precision mechanics. Its essence is as follows. At first a three-dimensional image of, say, the skull is obtained by X-ray and magnetic resonance tomography. The model is then stratified into very thin layers and information about each layer is transferred to the computer, connected to the stereolithographic device. Laser ray directed by the scanner "transfers" it to a special vessel filled with liquid photopolymerized composite. There is no need to solidify the entire object in this process. Quite the contrary--only the elements of the detail should be "glued" on each layer and the surrounding space left liquid. That is why the regulated laser beam is used: it "shows" zones which should be polymerized, and which should not. As a result, unilluminated zones remain liquid, while illuminated ones solidify, forming the body of the prototype detail. Thus, the physician gets a precise polymeric copy of the patient's skull, which enables him to evaluate anatomical nuances for this patient and determine the treatment strategy.

The technologies of preoperative biomodeling are now used at 25 hospitals in various regions of Russia. They are used in oncology, neurosurgery, maxillofacial and reconstructive surgery, and other spheres of public health.

Stereolithographic devices LS-120, LS-250, LS-350/500 rapidly create models, nodes, details, and constructions of any shape and complexity. They can be used not only in medicine, but in aerospace, automobile, power industry. It is noteworthy that they are manufactured only by the 3-D System Company in the USA and by our Institute in the Moscow Region. In 2009, its head Vladislav Panchenko and our medical colleagues Alexander Potapov, Deputy Director of N. Burdenko Institute of Neurosurgery, Dr. Sc. (Med.) and Valery Chissov, Head of P. Hertzen Oncological Institute, were awarded State Prize of the Russian Federation "For a Complex of Research Works Aimed at Development of Laser and Information Technologies for Medicine".