N. G. Basov

On the 14th of September 1984, a well-known American physicist Prof. A. Guenther, who is the specialist in nonresonant laser interaction with matter and in high-power optics, came on a visit to Lebedev Physical institute. On behalf of a group of American scientists Prof. A. Guenther had an interview With the director of the institute academician N. G. Basov he asked to tell about the history and progress in quantum electronic investigations held at Lebedev Physical Institute. Below is the interview acad. N. G. Basov gave to Prof. A. Guenther.^[1]

Guenther:

We would like to start off the interview by asking about the environment at the Lebedev prior to the time of your work in the early days (what kind of resources, budget, professional staff, technicians, etc., for your research were available). Did most of the communications among researchers take place at formal seminars, over luncheon, or what? Were you on a 7-day-a-week day and evening schedule or a more relaxed. Who were the key members of your group, e.g. the molecular spectroscopy group, and what were their special areas of expertise.

Basov:

In the field of molecular spectroscopy I began to work as a third-year student of Moscow Institute of Physical Engineers (MIFI). It was in autumn 1948. I was invited to join Lebedev Physical Institute (FIAN) by acad. Mikhail Aleksandrovich Leontovich who was the head of theoretical physics department of MIFI and the head of the laboratory of oscillations at FIAN I had to fulfill some theoretical tasks. At that time there were performed at FIAN the investigations of synchrotron radiation on a small synchrotron. Those investigations were headed by Aleksandr Mikhailovich Prokhorov. A. M. Prokhorov suggested that I should put the synchrotron into operation in the regime of multiple resonance, i.e. when the frequency of the exciting field is 4-6 times multiple to the cycle frequency of Particles. In order to record the radiation we had to construct special instruments for the detection of centimeter waves. Apart from that work, acad. S. I. Vavilov, who was at that time the director of FIAN, entrusted A. M. Prokhorov with the radiospectroscopic investigations. We built radiospectroscopes, organized a seminar in A. Prokhorov’s group, studied the theory and experiment of radiospectroscopy. Such was the background, so to say.

Guenther:

We would like to begin by getting the background to your 1954 “maser paper”. What research had you been doing prior to this time that was important for laying a basis in ideas and experimental techniques? What was the genesis of your ideas for a stimulated emission device? How did you bring these to fruition?

Basov:

With the radiospectroscopes working, we had to solve a number of particular problems which had been raised, such as a possibility of measuring nuclear moments on a Stark spectroscope. We were much embarrassed by a low sensitivity of our radiospectroscope. The populations of upper and lower levels in the centimeter waverange were almost the same, the relative difference between them was about 0.001. And we dreamed of such a “real” population of levels, which might give us a one thousand times higher sensitivity. Such was one of the first steps towards the future development of maser laser technology. The second step, of no less importance, was the necessity to increase the resolution of the microwave frequency region, i.e. to narrow the spectral linewidth. In this respect, the usage of molecular beams in the radiospectroscopy looked very promising. We considered the opportunities of using the molecular beams for the needs of spectroscopy. Quite a number of methods were proposed, such as the interaction of beams in an open waveguide, in a cavity, etc. We expected to obtain an opportunity to considerably reduce the linewidth having a time-of-flight characteristic instead of intermolecular collisions. It was also much easier, with the use of molecular beams, to increase the sensitivity on account of the changing population.

It was understood that deviation of the particle beams in nonhomogeneous electric and magnetic fields, due to Stark and Zeeman effects, allowed one to solve, in principle, that problem. So, what we needed was a molecule with a large dipole moment. The first molecule chosen for that purpose was CsF. It has also become clear soon that apart from the absorption which had been traditionally used in spectroscopic investigations, one could successfully use the radiation by means of selecting the molecules in the upper level, but not in the lower one. By transmitting a beam of upper-level molecules through the cavity, in order the radiated field made a back action on the beam, one could reach the oscillation threshold. Such was the basis of our work. We built experimental arrangements and performed experiments. The results of our investigations were reported in May 1952 at the Conference on Radiospectroscopy held at the USSR Academy of Sciences. When we approached the problem of field-molecule interaction, the achievement of self excitation condition had become a highly desirable goal. The theory of oscillators was traditionally well studied at the laboratory of oscillations. And since the theory of oscillations deals mostly with the problem of self excitation, it allowed us to discover condition for the achievement of self excitation in a beam resonator system. So, as early as 1952, that problem had become quite topical.

By using the existing at that time approximation, we tried to perform “Arithmetic’s” of that problem in order to achieve the corresponding solutions. The theory of nonlinear oscillations had been actively studied at the laboratory of oscillations. The fore-runners of that movement were the academician L. I. Mandelshtam, N. D. Papaleksi, the corresponding member S. M. Rytov and many other coworkers of the laboratory. At the Conference on Radiospectroscopy we reported on the opportunity of achieving the self excitation condition with respect to CsF molecule. During our report and in the course of discussions the question was raised: “Why not the ammonia?” (the ammonia being the classical substance in radiospectroscopy). The ammonia could also be used, we replied, but it needed somewhat different conditions than CsF. We had a cylindrical condensers and some other sorting systems had been required. Such was a preceding situation. At the beginning of 1953 we wrote, together with A. M. Prokhorov, a paper to the Journal of Experimental and Theoretical Physics (Sov. Phys. JETP). And just before the paper had to appear in the journal, we had found out that in calculations for the coefficients of selfexcitation condition we had omitted 21 to some power. So, we had to take the paper back for the revision, and as a result it was published only in a year. Thus, the year of its publication is 1954, though the paper had been sent to the journal in the end of 1953.^[2] Before the publication of that paper, in 1953 there had been very interesting discussions of some other problem. Masers had not yet been put it operation, and it was not clear whether the molecular radiation in the cavity, due to the intrinsic field, would be coherent. That problem was raised by us, and it was actively discussed, especially with our theoreticians from the theoretical department of FIAN.

I especially remember our many-hour discussion of this problem with V. Ya. Fainberg, who is the professor today. We also discussed it with acad. L. D. Landau. And really, the problem was by no means trivial. We thought that the radiation had to be absolutely monochromatic, and width of the radiation band would tend to zero under the self excitation condition. That question seemed absolutely clear for us, we had the evidence of physical processes for that. But everyone with whom we debated on that problem gave the negative answer: the radiation bandwidth would be the same as the spectral linewidth. The work on the cavity selfexcitation by a beam of molecules was reported many times at various seminars at Moscow University, FIAN and other places. The work^[3] can be considered as the first publication in the field of quantum electronics. We were now anxious to investigate the processes accompanying the oscillation. Some time passed before the theory of dispersion was put forward for the molecular beams with account of the saturation effect, and the equations for a molecular oscillator were derived. There appeared another paper^[4], which was the second one in the field of quantum electronics, and it had also been made together with A. M. Prokhorov. That work^[5] was reported at the Conference of Faraday Society in England, where Prof. A. M. Prokhorov, as far as I remember, had met Prof. Ch. Townes for the first time. I believe those two papers made a good foundation for a further development of investigations in quantum electronics. But as a whole, the fast progress in quantum electronics owed a lot to a high scientific level of the laboratory of oscillations. In the laboratory and at the Institute one could obtain any consultation and help with experimental devices, and any new proposal could be critically discussed on the spot.

I think there was no other place in the Soviet Union, which had been more suitable for such work than FIAN. In that sense we were really lucky to work there And the whole atmosphere of that very strict approach to all investigation problems did not allow our imagination, on the one band, to go very far away, and on the other, it turned our imagination into equations, which were later solved, and into the experimental arrangements which soon gave evidence to the theoretical predictions. All that, I’d say, determined those exceptionally favorable conditions for the research work which existed at that time at the institute. That atmosphere was created mostly by the Institute’s director acad. S. I. Vavilov. Then those traditions were continued and further developed by acad. D. V. Skobeltsyn, his successor on the post of director. I’d wander from the subject a bit: acad. Skobeltsyn is 92 now, and he continues to work actively at our Institute writing very interesting papers. He was the director of FIAN when masers and lasers had been under way, and he actively stimulated those works.

Guenther:

We have been seeking to learn from our American interviewees whether their war-time work had an influence on their research on stimulated emission devices. We would be very glad to learn about the Soviet experience, as a comparison. Was there any military research during World War II which was decisive for the path of your post-war career? Could you please tell us about it, and how it influenced your physics.

Basov:

I myself was the war participant. Just after the beginning of the Great Patriotic War in 1941 I was recruited, became the student of Military-Medical Academy, and after three years in the Academy graduated as the doctor’s assistant. On the 31st of December 1945 I was demobilized and from February 1946 became the student of MIFI. So, during the war I had not any idea about lasers, masers or even radars. FIAN had made quite a lot for the victory during the war Acad. S. I. Vavilov, our director, showed vividly in his papers the role played by the Institute during the wars. But I joined FIAN in 1948, a few years after the war, and didn’t find the presence of any military investigations at the Institute. All our thoughts were about mastering the physics in full measure in order to develop our national economy. As far as masers and lasers are concerned, then of course, one should mention that the centimeter waves used in radiolocation had been the creation of the war. The radio engineering and radio physics were well represented at our laboratory as radio astronomy and radio spectroscopy. But we were dealing with those problems without any connection with military investigations. In our investigations we aimed at creation of such radiation sources that would continuously cover a wide range of centimeter waves (just with that purpose we studied the synchrotron radiation). That was necessary for the atmospheric investigations, for the analysis of various substances and their properties in the cm wavelength region. One didn’t feel any war spirit in the laboratory. I’m somewhat younger than Aleksandra Mikhailovich. He too was in the army during the war, but he was not involved in the radio engineering at the wartime either. We, therefore, were not the radar investigators. In this respect we and the American scientists have some different approaches to the development of quantum electronics. I’d like to mention that before the war the physical sciences in the Soviet Union were on quite a high level.

The soviet scientists ranked high in the world science. We were quite aware of that, and were infected by the sprit of seeking and striving in the research work from the scientists of the old generation. We were inspired by their ideals and tried to implant them to the young. Such was the atmosphere of the afterward period. The main goal of our Institute today is to stimulate the development of new ideas and trends in physics as we understand it and as it is formulated by our Government and the Academy of Sciences. On these positions we worked in the postwar years. Here again I’d like to say a few words about some other works held at the Institute, namely, the works of acad. D. Skobeltsyn who was dealing with cosmic rays. The flow of energy from the space was called the rays, but those were not really the rays, but a flow of particles. These particles were discovered by acad. D. Skobeltsyn with the help of the Wilson chamber placed in the magnetic field. Acad. G. S. Landsberg had discovered the combination light scattering, and acad. P. A. Cherenkov (whose jubilee we have recently celebrated) had discovered the new type of the radiation which is called today after his name. There had been a lot of asepsis around that radiation. Now we can see how wise the Vavilov’s approach was: be promoted the development of those trends in physics. One can name many other interesting investigations performed at Lebedev Physical Institute. To them one can add all works in the field of quantum electronics, works on the masers which had been under investigation at that time. Masers were considered as oscillating nonlinear systems, and that approach helped a lot in the solution of many key problems.

Guenther:

We are very interested to understand the way in which the work of the scientists is different countries effected each other, and whether the nature of the interaction changed as years went on. We would appreciate it very much if you would tell us when, and how, you first learned of the work of the Townes group, of Bloembergen, and Scovil and his collaborators? What foreign journals did you customarily read in the 1950s? What international conferences were most important? Did this change in the late 1950s? In the 1960s? Could you address the role of the Academy of Sciences of the USSR in laser development as opposed to other entities such as the military or industry which were cost important in the USA?

Basov:

That’s quite a complicated question, and somewhat controversary, I’d say, as is always the case in real life. We knew quite well the names of Ch. Townes, N. Bloembergen, W. Gordy, M. Strenberg and many others from their works. With the help of those works we, young scientists, were introduced into the radiospectroscopy. The first meeting with Ch. Townes was in 1955 at the Conference of the Faraday Society, where acad. A. M. Prokhorov had been present. He told us a lot about that meeting with Ch. Townes. As for the scientific journals, we were, of course, reading all the soviet journals and many of the American scientific journals. Our library received practically all the physical journals. The majority of papers on radiospectroscopy were published in “Physical Review”, “Chemical Physics” and other journals. In view of our intensive works on a molecular oscillator we were investigating, since 1952, the possibility of using both CsF and ammonia. I have seen the paper by Ch. Townes in “Phys. Rev.” (in letters to the Editor) just at that time when we were on the way of completion of our work. And in one and a half month we have already put the molecular oscillator into operation. What were the difficulties and what was the difference between the Townes approach and that of ours to the molecular oscillator? There were, perhaps, two points. First, we wanted to obtain a molecular beam of high intensity. For that we used a multichannel source of a molecular beam, a grating with many holes. We diaphragmed the beam to obtain a more effective sorting of molecules, which Townes did not do. He had one hole in the source. The intensity of our beam was 30 times higher than his. We did everything in our power to obtain the beam of high intensity, but Townes found an easier solution to the problem. The second distinction between our works was that we were ready to examine weak transitions, so in ammonia we investigated almost all the rotational-inversion transitions.

We made a cavity of high quality with large holes for the Input and output of molecular beams. It had cut-off waveguides which allowed us to fill almost all the cavity area with the molecular beam. Such a design had a number of advantages which were later realized in the research of various ammonia transitions etc. After our molecular oscillator had been put into operation we had a lot of visitors from all over the Soviet Union; we received them from morning till evening, showed the beatings between individual oscillators. We were the first to obtain the beatings. We’ve made three oscillators; between two of them the beatings were observable, and we studied the stability of the radiation frequency. Very soon we understood that the stability of the order of 10^-10 could be achieved. When we demonstrated our results quite an obvious question emerged: whether the same effect could be observed in other regions of the radiative frequency, viz., in optics. I should like to note that we did our best to find out an optimal scheme for a molecular selection in different beams. We rejected quadruple selector in favor of a ring one. Together with V. S. Zuev we obtained the radiation at 18 cm wavelength in the deuterized ammonia, where it had been rather difficult to use the quadruple condenser, so the ring selector was used instead. We investigated thoroughly the saturation effect trying to reproduce it on radiofrequency.

We were not very much surprised by the appearance of Bloembergen and Scovil’s works (1956 and 1957) on the amplification in paramagnetic crystals. As is known, our own proposals made together with A. M. Prokhorov on the usage of three-level systems for the production of inversion by the radiation pumping, were dated by 1955.^[6] We studied closely the physics of ocular oscillators. A. N. Oraevsky and myself considered different problems in the theory of molecular oscillators. They were the problems of frequency stability, the radiation coherence, various effects such as the Townes running-wave effect in the cavity, which proved to be very important; it broadened the oscillation line and reduced the stability. We thought of the ways of its compensation. Thus an oscillator appeared with two counter-propagating beams. It enabled us to obtain experimentally the frequency stability of the order of 10^-12. Such a stability was used for the frequency standard. Our oscillators were modernized at the All-Union Institute of Physical-Technical and Radioengineering Measurements which dealt with the service of tie in the Soviet Union, and they worked there for quite a long time. That was one of the applications of the high frequency stability effect from those oscillators. Many papers were devoted to high-resolution spectroscopy provided by molecular oscillators. We measured and detected a super-fine structure in the inverse spectra of the deuterized ammonia (that work was started by V. S. Zuev, he designed a spectroscope, and the work was completed by A. S. Bashkin). But the fact was that the focus of attention had been shifted to the optical region. For me personally, of great importance was the first International Conference on Quantum Electronics and Resonance Phenomena held in New York, in September 14-16, 1959. There I have met Townes, Schawlow, Javan, Scovil, Lamb, Van Fleck, B. Lax and many other outstanding physicists of today. There were about one hundred conference Participants present, they represented various scientific associations, which had made a great contribution into the development of postwar physics.

Guenther:

Please tell us what led you to examine “lasing” action in semiconductors in 1957. How did these researches develop? If you were working with colleagues, we would be glad to know who they were. How did you organize the work among yourselves? What were the accomplishments at each state of the semiconductor work? If there were any “false trails” or anecdotes that were historically interesting, we should like to know about them also.

Basov:

With the development of a molecular oscillator there had been a desire to use the same effect in other wave ranges, in optics for example. We began to discuss that problem with Yu. M. Popov who had worked at that time at the laboratory of luminescence in FIAN. We had known each other very well since our student years at MIFI. The work on optical oscillators had brought us to the understanding of semiconductor laser problems. We proposed to realize a band-band and band-impurity breakdown by short current pulses followed by thermolization of the current carriers, by tilling of the levels and the degeneration of the conduction band. For that proposals we received the author’s certificate of 1958 (N. Basov, B. Vul, Yu. Popov). The conditions of inverse population in semiconductors were the subject of our first paper^[7] which I had reported at the first Conference on Quantum Electronics in Bloomingburg. And there I’ve heard the reports of Ch. Townes and A. Schawlow, in which they suggested the possibility of a ruby laser, and A. Javan’s proposal for a gas-discharged laser. Our own work was not on the conference program, and as far as I remember, my report on semiconductor lasers had been heard over the luncheon. But, nevertheless, it had been welcomed by the conference participants, here I may quote Profs. B. Lax and Ch. Townes, with whom I discussed the idea of semiconductor lasers. We had long discussions of that problem with B. Lax. He thought that the large line width was an obstacle to semiconductor; the quality of the line, so to say, was measured only in unite, and that the generation should be sought not in such broad lines, out in narrower ones. B. Lax considered impurity levels (the Landau levels) more suitable for that, but we wanted to use mostly band-band transitions. Soon our next publication appeared together with O. N. Krokhin and Yu. M. Popov, where we had proposed three more types of the excitation for semiconductor lasers. That was the optical pumping.

At one time much attention was paid to that work in press, the excitation of a semiconductor by a ruby laser. Then, the pumping by fast electrons. The third stage of semiconductor laser investigations was the usage of a degenerate p-n junctions, where the direct pumping by the current allowed realization of the state with inverse population. Particular interest was attracted to the problem of electron-beam-pumped semiconductor lasers, it was especially discussed at the second Conference on Quantum Electronics. Today all these methods have been realized. Historically, we began with the breakdown. It seemed to be the simplest technique, though it had been realized only in 1968, the last in turn, since very good current fronts were required for that. At our laboratory the streamer lasers were devised, which allowed the generation on many substances. They had quite a number of interesting applications, like the obtaining of picoseconds pulses etc. With the experimental realization of p-i junction lasers the American scientists were somewhat ahead of us. To be more exact, the researchers from Ioffe Physical-Technical Institute were the first to obtain narrowing in the luminescent spectrum of GaAs basing on our works. Then the first publication by Hall with collaborators appeared, then the work by Nathan et al. We had the experimental observation just a few weeks later, but it was not so very important since lasers of that type were made practically independently. Further investigations performed at A. F. Ioffe Physical-Technical Institute in the group of Zh. I. Alferov (who is the academician today) resulted in the construction of semiconductor lasers on heterostructures. In the beginning of 1964 we obtained (together with O. V. Bogdankevich) the laser action in the green spectral region in CdS pumped by fast electrons. In 1964 we obtained the laser action in semiconductors at one- and two-photon excitation by the laser radiation. I. Zubarev, who is present here, is one of the participants of that work. Those works made a significant contribution to the nonlinear optics. They demonstrated both the efficacy of the coherent summation of the radiation from individual lasers, and the possibility of the efficient excitation of various media by the laser radiation. At present, many laser systems operate on that principle. Many other types of lasers were made.

We worked by the program of the Academy of Sciences of the USSR. Laser programs were well financed for that time. The budget permitted one to finance five laboratories of FIAN, the optical and semiconductor laboratories among them. In 1959 we organized a regular laser seminar, we have got the report on those works. And the first large review about the opportunities of new types of lasers has been published in 1960 in “Uspekhi Fiz. Nauk” (Sov. Phys. UFN).^[8] Here I read the last paragraph from the text of that review: “There are a lot of various proposals concerning the methods for achieving negative temperature various quantum systems, and some theoretical problems. Most of them have been reported in this review. But not a single paper has been published so far on the possibility of amplification and Oscillation regimes in the infrared and optical waveranges. But as seen from this review, there are no principal restrictions to their realization, and thus one can hope that in near future oscillators and amplifiers operating in IR and optical regions would appear”. The review was sent to the journal just a few months before T. Maiman’s communication in press about the realization of a rub; laser in July, 1960.

Guenther:

Please ten us how you came to invent the idea of three-level masers, using pumping.

Basov:

Well, it was understood that using the saturation effect one can equalize the populations of levels. It was quite evident that for the third level one can obtain the population inversion. So we investigated thoroughly the pumping methods and the usage of various types of energy for the pumping, especially, in semiconductor lasers, where I’ve already mentioned four methods. And here I can tell about some other methods of pumping, which had been used for lasers. Those were the thermal pumping technique, from which gas dynamic lasers emerged, and the combined pumping which included an electron beam previously used in semiconductors, and the electric discharge technique. In 1970 a special type of a nonselfsustained high-current discharge was discovered; it was obtained for the first time by V. A. Danilychev. Thus, so called electroionization lasers appeared. In USA similar lasers were devised at Los Alamos in Prof. K. Boyer’s group and at AVCO by Profs. Kantrowitz, Daugherty and coworkers in 1971. In 1966 we started investigations in the vacuum ultraviolet which resulted in the appearance of the first excimer laser on xenon in 1970 (N. G. Basov, V. A. Danilychev, Yu. M. Popov). We continue now these investigations. Today we have quite a number of new types of lasers, new materials, and new methods of excitation. We are working on new proposals concerning the methods of excitation, new materials and new types of lasers.

Much work has been done on improving the coherence of lasers by means of the stimulated scattering. We succeeded in increasing, by about three to four orders, the radiation coherency for Nd-lasers, ruby lasers, and lasers on molecular dissociation. Drs. A. Z. Grasiuk and I. G. Zubarev were actively engaged in this work. There has been achieved a considerable narrowing of the line, reduction of the beam divergence; the radiation brightness was increased by four to five orders. This work is being continued. We have devised various types of lasers to be used in laser fusion investigations. For the fusion experiments it is necessary to focus the radiation from the distance of hundred meters, into a minimal spot, where a very good radiative coherence is required. Various experimental techniques were tried for that. One can use lasers as pumping sources, and increase considerably the coherence by the stimulated Raman scattering, or the stimulated Mandelshtam-Brillouin scattering (SMBS) technique. We work actively with lasers based on stimulated scattering. There was some other problem on the way. The SMBS photons are propagating in the direction opposite to that in which the photons enter nonlinear medium. With what accuracy does it happen? The investigation of this problem resulted in the discovery of the phase conjugation phenomenon. Together with some other colleagues, Dr. F. S. Faizullov, who is present here, was awarded USSR State Prize for the discovery of this effect, which is also one of the means for increasing the radiation coherence. So, for example, we have lasers with the beam diameter of 4 cm, lenses of low quality and focal length of a few meters, and they focus the radiation onto the era of about 50 μm, i.e. using some intrinsic effects, we obtain the ultimate diffraction divergen e and the ultimate coherence. This works has not yet been completed, it has many other trends. We try to use the phase conjugation in the far IR region for long pulses, for supershort pulses. Later on numerous investigations were carried out at FIAN on the improvement of laser parameters, the search for new laser materials, or different methods of pumping. Here I’d like to mention that about two thirds of the number of all working lasers originated, in one way or another, from Lebedev Physical Institute. They are excimer lasers, electroionization lasers, various types of semiconductor lasers; all of them have been proposed by us for the first time.

Then goes a three-level pumping, the thermal pumping, including gasdynamic lasers, the application of stimulated scattering for increasing the radiation coherence; the discovery of the phase conjugation method and its usage for increasing of the spatial coherence; the photodissociation lasers which were actively developed, viz. by V. S. Zuev (the photodissociation laser was first proposed also in FIAN By S. G. Rautian and I. I. Sobelman), etc. One should also mention the chemical laser, where many various methods for pulsed and CW chemical lasers were proposed. For chemical lasers a group of our colleagues was awarded this year the Lenin prize, which is the supreme award for scientists in this country. A. N. Oraevsky, who is present here, is one of the laureates of this prize. For semiconductor lasers two Lenin prizes were awarded, and at present the USSR State Prize is proposed for the semiconductor lasers on quaternary compounds, in which the priority belongs to the Soviet scientists. I wouldn’t discuss in detail the question of priority here, since many scientists work in our field of research, but the contribution of soviet scientists is quite significant. All this is the result of systematic work of many laboratories of FIAN. Results of the first stage of this work are contained in the Institute’s report of December, 1961. In that report almost all types of lasers were mentioned: Raman lasers, photodissociation lasers, a great number of new crystals, semiconductor lasers. The research program was fulfilled in the course of three-four years, since 1958, when the wide-scale laser investigations had been started in the Soviet Union. The report contains many interesting results.

Guenther:

Can you tell us something about your method, or “style” of working. What types of theory did you prefer to use in your work on lasers and masers? Were theoretical or experimental results more important, in general, in stimulating your research? How much did theoretical analysis contribute to the successful outcome of the work, how much laboratory experience, and how much other factors? Did certain types of problems attract you more than others? For example, when you divided work between yourself and your co-workers, what parts of the problem did you prefer to work on yourself? Did your style of work remain the same from the war through 1960s or did it change as your position and responsibilities changed?

Basov:

We, young people, were raised in the laboratory of oscillations. Later on we organized the independent laboratory named the laboratory of quantum radio physics. What were the first steps? Our main goal was the work connected with the invention of new methods for the electromagnetic wave oscillation, and that work inspired us greatly I shared my ideas with the colleagues and together we sought for the solutions. The laboratory grew rapidly, in 1959 we were only 20, and in 1970 already 500 including a great number of your researchers. Many dissertations were maintained, about 60 doctors of sciences in quantum electronics, and 200-250 candidates of physical-mathematical sciences. The pledge of success, I believe, was in the fruitful cooperation between young scientists and the main staff. The young researchers enjoyed everyone’s confidence; it was equal respect both for very young investigators and our young professors. That, perhaps, was the main approach. It was not that I invented it, that style of work was always characteristic of FIAN, and it owe a lot, I think to our teachers acad. S. I. Vavilov and D. V. Skobeltsyn and so it spread to all laboratories. That allowed us to attract scientific forces to our work. At present, some of those who worked with us left for the industrial investigations, and others for the allied Institute dealing with laser physics. But the core of the Institute’s professional staff remained. That determined our success in physical investigations.

Guenther:

We have been asking our U.S. scientists about how commercial applications of lasers influenced their scientific work, and we would be very pleased to learn about the Soviet experience as a comparison. In the course of your research, did you have contracts with any of the ministries to help them with civilian products? Can you tell us something about the products? Did this work stimulate any new scientific direction? We would be very glad to bear about such episodes of interaction between fundamental and practical scientific work.

Basov:

When we began to work with lasers, there had been many opportunities to work with applications. We felt that lasers had a tremendous field of applications. Gradually, two directions in the applied research appeared at our laboratory. The first one was the laser thermonuclear fusion which had been proposed in the course of laser investigations (N. G. Basov, O. N. Krokhin). Concerning history, I’d like to remind of some interesting achievements in this field. For the first time there were obtained thermonuclear neutrons, the hypothesis of compression for the needs of fusion was put forward, and a spherical target compression up to a few g/cm³ density was achieved. There were proposed shell targets in order to compress substance by long radiation pulses of mean intensity. It was shown for the first time at FIAN, that shell systems of high aspect ratio moved steadily. Those problems were treated by us in a close collaboration with the researchers from Keldysh Institute of Applied Mathematics, USSR Academy of Sciences. The second direction was optoelectronic investigations which are now in full swing. It has been suggested that two new kinds of arithmetics should be used in optics, that is, the arithmetics of residual classes and the arithmetics connected with operators stored in the memory. Large memory of optical computers offers quite a new type of data processing. There have been devised the projection TV and the address tube.

On the basis of electron-beam-pumped semiconductor laser this address tube can be used in optical mass memory systems and for the projection of colored TV image on a large screen with quality close to the cinema screen. Much work has been done on elaborating the methods for data storage, the investigation of media for the memory. We carry out a lot of research work on the optical information processing; optical communication lines ware made for the computer complexes, the communication channels between the processors and output arrangements. Quite successful are the investigations of picosecond pulses and solid-state analogs of photomultipliers. Such is the scope of work performed at the laboratory of optoelectronics. Considerable progress has been achieved in such traditional for FIAN direction as the frequency standards, which had become optical. We had several proposals for the methods of obtaining superstable oscillation frequencies. For today, we have about 10-14 frequency stability in the optical region, and we hope to approach the next sign in the near future. We are also engaged in the spectroscopic investigations, where many new methods have been offered. This is, first of all, an intracavity laser spectroscopy which allows us to analyze the smallest amounts of substances. For these investigations the scientists of FIAN received the prize of the USSR Academy of Sciences. The method offers an opportunity to analyze the substance inside the cavity. A multiple passage of the light through the cavity gives an equivalent distance of the absorption of the order of 10⁵-10⁷m. As a result, one can analyze the spectra of single atoms.

The sensitivity of such a spectroscope for the iodine is about 10 atom/cm³. We have developed the spectroscopy of highly ionized atoms, investigated almost all the elements of the Mendeleev’s periodic table and obtained the spectra of hydrogen-like, helium-like, lithium-like ions of atoms for the elements of different atomic weights. A great number of anomalous features were discovered in the spectra. On this basis we developed the methods for the quantitative and qualitative analysis of various materials, for measuring the temperature, density of plasmas etc. At FIAN the method of isotope separation by means of lasers was developed. This method was proposed by V. S. Letokhov, who had been my postgraduate student at that time. On the basis of this method R. V. Abartzumian obtained very good results on the isotope separation. There were some other interesting proposals concerned with nonequilibrium states, which yielded interesting results on the separation of nitrogen isotopes. To continue our talk, I’d like to mention the investigations in laser ranging of the Moon. The distance to the Moon has been measured with accuracy up to 10 cm.

At our laboratory we are dealing with laser-stimulated chemical reactions. Many interesting problems have been solved, viz., an eleotroionization method has been proposed for the obtaining of various substances, so some new polymers and compounds were obtained. Of course, by carrying out the research work at FIAN we understood the needs of industry in lasers, and so there was organized the branch of our Institute in Kuibyshev city on Volga river, headed by V. A. Katulin, our pupil. It is now a big Institute, which attends to the industrial region of Kuibyshev with its motor-car, ball-bearing and chemical industries. Various methods which were developed at FIAN for practical purposes are successfully applied there. Recently we’ve organized the laboratory of laser applications in medicine headed by R. V. Ambartzumian. Despite the fact that it is only 2.5-3 years old, some excellent results have been already obtained on the treatment of infarctions, arrhythmia, dental diseases. Quite unexpected methods have been elaborated. A few words about dental treatment. How can the medicine be pushed through enamel inside the tooth pulp? The task seemed quite hopeless. Still, with the usage of Q-switched pulsed lasers it became possible. Like in the case of laser fusion, such lasers can produce extremely high pressure, about thousand and ten thousand atm. by means of the substance evaporation. And then the enamel channels become penetrable for the finite dose of medicine. Now this method finds extensive applications. But though we are deeply involved in applications, we are still the laser laboratory, and apart from applications we try to devise new types of lasers. Here I’d like to mention V. A. Danilychev’s work. He has recently constructed a very good technological laser on xenon.

The spectrum of this laser is in the IR region (1.73 um), with the electron-excited atomic levels active. For the technological needs this laser is likely to surpass CO and CO₂ lasers. It can use glass optics and has a higher coherence In conclusion, some words about the importance of investigations on the properties of the coherent radiation. No need to say how important and significant are the numerous laser applications, like for example, laser fusion or optoelectronics. And of course, they have a promising future. So today the laser ignition, we believe, is the most probable means for the realization of the thermonuclear reaction. But the point is that owing to lasers we investigated numerous methods of energy conversion into the inverse population of atomic levels, and achieved a nonenthropic kind of energy in the optical region. Due to this unique quality, the energy can successfully be transformed into other types of energy. In particular, light oscillations can produce the highest temperature achievable at laboratory conditions. In this connection many purely physical questions have been raised, particularly, what temperature can be achieved at all. Practically, the answer to this question is in the laser fusion, and theoretically we understand that the temperature is determined by the Planck’s law (the number of photons per mode). So, the Planck’s law proves to be, so to say, the fourth law of thermodynamics. The fact that the nonenthropic energy can be obtained by means of lasers determines the today’s applications in quantum electronics. And this determines the tasks of research in the field of quantum electronics. They are: the mastering of new spectral regions, the achievement of the highest coherence and the maximum efficiency in these regions. These problems must be solved not only practically, but we must get a clear physical understanding of the possible phenomena. In conclusion, I’d like to thank Prof. A. Guenther who undertook this difficult task, and to wish his commission the success in fulfillment of this task.