Charles Townes – Session II

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ORAL HISTORIES
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Interviewed by
Joan Bromberg and Robert Seidel
Interview date
Location
Berkeley, California
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In footnotes or endnotes please cite AIP interviews like this:

Interview of Charles Townes by Joan Bromberg and Robert Seidel on 1984 January 31,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
www.aip.org/history-programs/niels-bohr-library/oral-histories/4917-2

For multiple citations, "AIP" is the preferred abbreviation for the location.

 

Research on nonlinear optics at MIT, 1962-1967. Other laser research in MIT period. Responsibilities as Vice-President and Director of Research at Institute for Defense Analysis (IDA), 1959-1961. Interest at IDA and ARPA in lasers and laser weaponry. Contemporary evaluations of Robert Dicke’s superradiance paper. Townes’s change of research field from nonlinear optics to radio astronomy in the late 1960s.

Transcript

Bromberg:

We’re speaking with Professor Townes in the Berkeley Physics Department and with me is Robert Seidel. As I said, there are just a few points I want to clear up for my own questions and then turn it over to Bob. I see that for the discovery of the high frequency, high intensity sound waves, a number of press releases went out — for example, the AIP issued a press release in something called Science Service. I’d like to get a little feeling for the circumstances, for what kind of weight we should attribute to that excitement?

Townes:

Well, let’s see. That’s something I haven’t thought about in a while. I don’t remember any press releases or anything. Let me see.

Bromberg:

They sort of said that Townes who invented the microwave maser and the laser has now come up with high intensity acoustic waves.

Townes:

Well, I think that’s just the publicity department at MIT. Scientifically I consider that something that’s quite interesting. From the point of view of practical applications, I think there’s been very little application, and I didn’t expect any large amount of applications. However, when a new field is unfolded, you can never tell for sure. But I would guess probably the excitement was because of the analogy with the maser and the laser. They did a great deal for electromagnetic waves and now this was a parallel in sound waves, and so from that analogy, you might think it would have a number of applications and be very interesting to people. As I say, I think scientifically it’s quite interesting, but its applications are likely to be quite specialized in my view.

Bromberg:

Do you happen to remember what you thought of it then in terms of possibilities?

Townes:

I think that’s about what I thought of it then. The trouble with those very high frequency waves is that they don’t travel very far. They’re highly attenuated. You can generate them internally. I think what excitement was there was probably heated up by the parallel with the electromagnetic case, the maser and the laser, plus the fact that somebody in the public relations department decided they wanted to write a story. Actually I don’t remember that particular thing. The coupling between optics and acoustics is, I think, an important thing, as for non-linear optics. In general, it really has no very unique origin and this or the Coherent Raman scattering I believe cannot be claimed as an origin. I think one can pick out a series of fairly unique experiments for example that of Franken, Weinreich, et al, and these experiments. But they were only particular steps, if you look at it more broadly. Raman effects are non-linear, in their coupling of optical and acoustic waves, and had been discovered long before. If you go to low frequencies, there are all kinds of non-linear couplings, including frequency multipliers and piezoelectric effects. I believe the first published mention of non-linearities which could occur in laser beams was in a talk I gave at the 1961 Quantum Electronics Conference in Berkeley. That is not very much remembered now. Hence [words cut off of transcript]. The attached first few pages of this paper may be useful. What I have labeled Experiment II is pertinent to non-linearities. The last sentence poses the general question of multiplication. Another experiment suggested (not included in the attached) were on Raman effects. The coupling of laser light directly to a crystal lattice, and production of really very violent vibrations internally, was at that time new and quite interesting. There had been a long-term acoustics group at MIT. It has had more intensive work in acoustics than almost any other institution except possibly Brown, and so some of the people there were also quite interested.

Bromberg:

Oh, you were in touch with them afterwards?

Townes:

Well, afterwards and during and probably before. Let’s see, there was a youngish man with a Swedish name. I’ve forgotten his name, but we were in close touch with I think it is of considerable interest scientifically, but as I say, I don’t believe that it has many technical applications. We didn’t patent it for quite a while, but partly because it was government and institutional policy, I thought we probably ought to patent it, so we did. I think it was only the third thing that I’d patented after I got into academic life.

Bromberg:

Is that contact with the acoustics group something that I’m going to find worth looking at, in terms of the way in which the thought of you, Garmire and Chiao and the rest went?

Townes:

Well, I don’t think especially. They were interested and we discussed these things with them, but I’m a little hazy about that. You know, without going back and looking at my notes, I can forget things. It seems to me — I’ve forgotten this chap’s name at the moment — it seems to me he may have written a paper or two on these effects. Certainly he talked and consulted with us. I don’t think this interaction was something that was terribly critical. Now, Garmire and Chiao may remember more. They were younger. It might be a little fresher in their minds. They may not have been so distracted by so many things, and may remember more. The whole picture of materials being sort of distorted and deformed by the light waves themselves was something that we were developing, you see, with trapped waves and acoustic waves, molecular vibrations, crystal lattice vibrations and so on. It was a substantial field.

Bromberg:

OK, I only have two more little missing links. Again, this is a question about how much weight to give this. The two cavity maser that apparently Javan worked on and Wang, I don’t know quite what to make of that, and I haven’t found any real material on it. They have a paragraph in a bulletin of the American Physical Society for 1957 on the two cavity maser, but it’s too brief for me to figure out what was going on, and I don’t really know the importance or lack of importance of that.

Townes:

Now, I’d have to think about that too. I remember the two cavity maser.

Bromberg:

I’ve copied down here that something that was especially interesting about it was that you had a phase coherent mix of upper and lower states, in a situation in which the majority of the ensemble was in lower states. I don’t know whether that’s of interest.

Townes:

I’m trying to think what we were trying to do there primarily. Let’s see — it’s some general scientific interest although I don’t think it would have proved or disproved anything that people weren’t pretty sure of anyhow. Normally, a maser is considered to oscillate if you have more systems in the upper state than in the lower state. And it does take off and amplify just from scratch with the molecules that are excited. Once the molecules are excited, then they start to make a transition downward and in a cavity where there’s a field built up, they’re forced into a certain phase. Now, they can leave that cavity and go into another cavity and continue to produce a buildup of radiation, even though there’s not a population inversion. That is rather closely related to Bob Dicke’s super-radiation. It’s essentially the same thing, super-radiation, when you don’t have an inversion of population, but put systems in a special state where there’s coherence between the states, and then they radiate like one big molecule rather than lots of little ones that are all in random phase. So that’s certainly one thing that would have been illustrated. I don’t remember what we were trying to do because I think, while that’s an interesting illustration, it’s not something that would surprise anybody. It’s something I believe people in the field could be assured would happen.

Bromberg:

Somebody told me, it might have been Wolf, Emil Wolf, that Dicke’s paper was extremely hard to understand when it first came out, and people didn’t really — I don’t know if he was telling me that he didn’t understand it particularly, or that other people didn’t, but I was wondering a little bit how the content of that paper became clarified, whether it was a question of the content of that paper gradually becoming clarified for the physics community with time. This might have been a step in the clarification, I don’t know.

Townes:

Maybe, although I thought it was pretty clear. It was not a clearly written paper, I think. Bob Dicke likes novel formulation of problems. He likes to put things in a different way from anybody else, and I think that was part of the trouble. He wanted an elevated and abstract kind of formulation, and the result was that the physics was not so clear to people. I remember looking at it, and at first I was puzzled as to just what he was talking about, and then I realized what it was. Actually it was something that was not new. Nuclear spin resonances, for example, do that all the time. You zap nuclear spins and get them in some kind of synchronous relation, and then you can see the radiation. So that’s super radiation. I think Bob treated it as something really different and separate from what people had not known before. Now, I think his formulation of it was very nice and very general. While his treatment was nice, it didn’t seem to me really new, and I think the apparent disconnection from past physics puzzle people. They didn’t realize that there were known phenomena that he was talking about.

Bromberg:

At any rate it’s useful to know that for example it wasn’t puzzling to you or to Columbia people, I suppose.

Townes:

No, I wouldn’t say so. I would say it was a little obscurely put; you had to read it carefully to see what he’s talking about. I think it may not have been widely understood. But I wouldn’t say that it was something that needed to be proved. In this particular case, I would have taken that as something that would be kind of a nice demonstration but not a critical one, from the point of view of physics, to show the effect in two cavities.

Bromberg:

I’ve been puzzled about how that paper became assimilated or didn’t become assimilated, or what happened to that line of thought within the whole —

Townes:

Super-radiance, you mean?

Bromberg:

— thought about stimulated emission?

Townes:

Well, it was just a kind of a parallel thing. You see, super-radiance differs from normal masers. In normal masers, you start with no phase coherence between molecules, and you just have a population inversion, then it takes off and amplifies. Now, during the process of amplification, it produces what Bob would have called super-radiance, but that’s just the process of amplification. As the atoms start making a descent to the lower state, there’s a coherence between them, so super-radiance is involved, in that sense, I believed it was an understood phenomenon, and didn’t need to be coached in Dicke’s terms. It was a new formulation of things that were known, and so it just kind of continued, and people talked about it. I think Bob emphasized some rather special cases of it, to show how in extreme cases it really looked different from what people had realized. I don’t remember just what those cases were.

Bromberg:

I’m afraid I don’t either. I’m one of the people who didn’t understand that paper.

Seidel:

Why would people take this paper seriously?

Townes:

Which paper?

Seidel:

Dicke’s? I mean, if it’s so obscure.

Townes:

— that’s partly Dicke. Dicke is a very smart physicist, and —

Seidel:

And this was well known.

Townes:

Yes, Dicke is a very smart physicist. He’s done a lot of good things. He talks with enthusiasm. He gave a number of interesting talks about it and so on. Super-radiance was a good catchy name, and I think that was part of it too. I don’t know. You have to perhaps realize that there are styles in physics, and things that get talked about and things that don’t. That doesn’t necessarily reflect exactly their ultimate importance. In my view it was an important formulation, but not something that was strictly new, and many of its applications were things that people had been doing all along. Now also, I think, some people began to confuse it with masers. The super-radiance was just anything that gave you very great intensity, but that’s a fairly low level popular confusion only; I don’t think physicists who work in the field were generally confused over that.

Bromberg:

I have only one more, and that is, to try to get just some account of the reasons, either intellectual or institutional or whatever, that brought you to the end of your non-linear program, because when you came to Berkeley, you just went off into radio astronomy, so I would just like to have how you decided that was the end of that program.

Townes:

Well, let me talk about it somewhat broadly. You’ll find that the fields that I start in are generally not terribly popular fields. I don’t especially like to work in a very popular field, just because there are lots of other people doing the same thing, and then I feel there’s not so much point in my doing it too. And so, I’ve changed from one field to another, off and on, maybe every ten years or so, something like that, partly for that reason, partly for some other reasons. After a field becomes very popular, then as I say, I just don’t think it’s as interesting for me. I’d rather try to open up a new field rather than just continue to work. Even though it might be a very fruitful field, I don’t feel it is especially important for me to work in a field that is already discovered and where many good people have become active. Also if people are rushing in to do something first and in a very competitive way I just don’t find it as pleasant or as important for me. I’d rather be out there by myself doing something I think is important that other people aren’t doing. Now, microwave spectroscopy I left in part because it had become popular. But in part I felt that from the point of view as a physicist, it had come to a stopping point and from there on it was going to be largely for chemists. In fact it’s mostly chemists who are now doing it and doing a good job of it. I had always been interested in astronomy, and debated several times whether to go into astronomy.

When I was at Bell Labs it was a choice between astronomy and microwave spectroscopy; when I was on sabbatical it was a choice between astronomy and going on with quantum electronics. In each case I had chosen against astronomy. When I left MIT, I gave up administrative work, and had enough time then to really start something new. I was interested in astronomy, I felt that the field of lasers had lots of people in it now and was not really where one person was particularly critical. I thought I recognized a lot of potentiality in infra-red astronomy, which was not at that time very well developed nor active. Also the possibility of molecular astronomy seemed promising to me. Now, in molecular astronomy, one of my former students, Alan Barrett, had discovered OH while I was at MIT. It was probably in 1963 that he discovered OH. That was the first molecule in the microwave region that had been detected, and I felt that there must be others, and so that’s one of the things I wanted to do. Nobody was doing anything much in that area. Alan didn’t proceed for some reason I’m not clear about right now, except he had a lot of other things to do and OH had seemed so hard that it might be difficult to find others. So I was interested in both microwave astrophysics and infra-red, where I felt there was a lot of new technology needed.

Now, in microwave work we could also benefit from maser amplifiers, and I started building maser amplifiers when I came out here. But I continued non-linear work for a while here, this was partly because Professor Chiao was interested, and he came out with me, and partly because it was obviously an interesting field and I wanted to do some of that while I was building up astrophysics. My primary purpose in coming out here was to do astrophysics. I had full time to spend on physics for a change, and California was good in astronomy, which was part of the reason I came to California rather than some other place. So I had an overt plan to do astrophysics in those areas which I felt had been relatively unappreciated, and where I sensed a number of important things might be done. That was the general reason, and it was broadly parallel to my reasoning in going into microwave spectroscopy and then later quantum electronics.

Bromberg:

I’m not going to ask this, but I’m just going to mention it as an interesting thing. I’d like to get on with your [Seidel’s] questions, it would be interesting to know what it takes to build up something like the new astronomy program, how much time and equipment and getting graduate students.

Seidel:

Let me pursue that just in one way. Was there anyone on the West Coast when you came here who had similar interests to yours?

Townes:

Well, there was a lot of astrophysics here, on the West Coast. Gerry Neugebauer and Bob Layton down at Cal Tech had really started infra-red astronomy in what I would consider a good scientific way. But they were looking at continuum spectra, continuous radiation from dust. They weren’t terribly knowledgeable about spectroscopy per se, and in any case weren’t doing anything in that area, but they had opened up infra-red continuum radiation work. Professor Welch was here, and head of the radio astronomy laboratory. When I first came he was very helpful and we worked together a great deal. He also was not working on just the type of astronomy I wanted to do, but in fact, he participated in the discovery of the ammonia and water. Berkeley has a good astronomy department; down in Santa Cruz there’s another very good astronomy department, with astronomers that came from Lick.

Seidel:

Which we spun off from here.

Townes:

Yes. So this was a very good atmosphere for astrophysics. There was not anybody here who was well known for infra-red astronomy. Infra-red astronomy was very rare at that time. There were some people working at it a little bit in the astronomy department, but it was a sort of a part time thing and they never did a great deal. The other center for infra-red astronomy was in Arizona at that time, and it was the continuum astronomy as at Caltech. That’s about all there was.

Seidel:

Well, as Joan told you, I’ve heard some of what you had to say. I didn’t unfortunately hear the first tape, but I understand you have discussed some of the things, that the Committee on the Generation and Detection of Submillimeter Waves was doing in the 1950’s in connection with your work. Leaving that aside, as you may know, I’m primarily interested in some of the later aspects of the military interest in laser research and development, but I thought we could pick up from what you had to say the other day, with respect to the level of interest in the late fifties and the early 1960’s. For example, Otting says that between 1958 and 1960, the AFOSR, the Air Force Office of Scientific Research, put what he called the highest priority on research in lasers, and I have the impression from what you said the other day, which begins when you went to IDA, that perhaps this wasn’t quite the case. Do you remember if there was this high priority and why the Air Force?

Townes:

Well, I wouldn’t dispute that if he says they put highest priority on it they probably did, but it was not the most active field in the Pentagon. [1] The most active field at that time was space work. It was space work, that I would have said seemed to have the most activity with a sense of urgency. But that may be in part question of scale versus priority. They’re not necessarily in conflict. The Air Force may have regarded the laser as high priority. Otting was certainly also personally very interested. I have mentioned elsewhere that he had earlier wanted me to discuss extensions of the [text unreadable]. I think everybody considered the laser very interesting and hoped that something could be done, but everybody also had some doubts about it, as a weapon. That was the thing that has been talked about so much, and personally I think it’s all been rather misleading. There’s again some sort of natural affinity for laser beams as weapons, I think, in human beings.

Seidel:

This was rather misleading to whom?

Townes:

Oh, I think to the Pentagon and public generally. It’s possible to make laser weapons, and I thought at that time we should work on them hard and was hopeful we could do something. But it was always rather doubtful in my mind, and I think for most physicists. It was one of those things that in principle would work but had great difficulties, and it’s continued to have substantial difficulties. But there are so many other laser applications which, even for the military, have so far been much more important. Part of the difficulty with lasers, though, comes about because other technologies have improved. For example, in the early days, we were hoping to get something that might work against incoming missiles. That was the big dream. Laser beams are fast and they can be pretty concentrated, so it has a number of attractive features.

Bromberg:

There was also some dissatisfaction, wasn’t there, with Nike Zeus and Nike Hercules and the ABM?

Townes:

Well, they could do limited things only, but as we’ve gone on in the field we’ve recognized that’s the nature of the field. Those things can get a few individual missiles coming in. But missile technology has improved, the numbers of missiles have increased a great deal, and now I think nobody believes that lasers on the ground are going to do very much, nor even lasers in the air. The enthusiasts for missile defense, I think have publicly said that one also shouldn’t put lasers in satellites, since they can then be attacked.

Bromberg:

Should then we be inferring back that around ‘59, ‘60, ‘61, you were feeling much more optimism, or the people like Culver, or whoever, would be much more optimistic about ABMs in general? Do you have any recollections of how —?

Townes:

Well, there were big studies on how to handle ballistic missiles. There was a big study in the early sixties that covered almost all techniques and all kinds of things, and a recent study just repeated much of the same ground, surveying everything that might work.

Seidel:

You’re not talking now about the Hughes high energy laser systems study?

Townes:

No, I’m talking about general ballistic missile defense. Let me try to put this in a little different perspective. I think the Air Force may well have considered it high priority, and they certainly had plenty of money for anybody who wanted to work on lasers to be supported. Otting himself was personally very interested. Hence, I think he’s knowledgeable and I would take what he says very seriously. However, the field was largely open, certainly the basic parts of it were open and not classified, and I think there’s been some misconception about that. In the case of masers, at one time I decided I ought to let the military sponsors I work for know that I think masers have some importance. There was somewhere in the contract with Columbia University that we were supposed to let them know about things that might possibly be useful. So I wrote them a letter saying: here’s the maser, this is what it does, and I think it could have substantial potential. I just wanted to let them know and to find out if they thought it needed to be classified. They wrote back saying that since I’d already given a talk or something at the American Physical Society about it and it was in our quarterly progress reports they felt so much was out already that there was no point in classifying it. Now, whether they would have wanted to classify it otherwise, I don’t know. I suspect not. But they said, officially that since it’s already open anyhow it doesn’t need to be classified. Now, the first proposal for military-type work that I know in the laser field is the TRG proposal. There may have been some others, but I suspect probably nothing very big anyhow. As I remember, that proposal was itself secret. That was classified and had very specific military applications. But the work was not secret. Essentially all the basic TRG work and our work at Columbia had nothing secret about it. We talked about it very freely. I think there are some misconceptions from some of the things that Gordon Gould has said. He said that it was secret so that his own personal notebooks were taken away from him and classified and so he couldn’t work on it. Well, just recently, in a patent flare-up, some of the lawyers sent me his notebooks. They’re not classified. There’s no stamp of SECRET upon them at all.

Bromberg:

Goldmuntz and Gould, as I remember it, has said that he was somewhat separated from the work that Daly was put in charge, that kind of thing.

Townes:

Well, he might have been somewhat separated from some of the work, but not from the basic work, not from making the laser work. To all appearances at the time Gould was right in on the discussions all the time, and clearly his notebook was not classified. I was surprised that Gould said that it had all been so classified that he couldn’t see his own notes. So I called Goldmuntz, and Goldmuntz said no, he didn’t remember that the notebook was ever classified. Then I called Gould, and Gould evidently genuinely thought they were. That was his memory, because I pointed out to him there was no stamp of Secret on it as would have been the case were it really classified. He thought it was. Finally he said, “Well, call Larry Goldmuntz,” and I said, “I just called Larry Goldmuntz and he said it wasn’t classified. Presumably, his memory was playing tricks because all the basic research, including laser construction was quite open. It was not a hush-hush thing at all, but a hot physics topic. Now, on the other hand, military applications, direct military applications of course were classified, and when I went down to IDA — and by the way, this letter which you found yesterday I notice was written to some man in IDA. See, IDA was primary the technical advisor to ARPA and the Pentagon. The Defense Department did not have personnel that they considered adequate to judge all these technical proposals, so they asked IDA to organize a group basically as a contractor, to advise the Pentagon. IDA is a non-profit group but structurally, it was a contractor to the Pentagon, and it had its people sitting in the Pentagon, making recommendations on research and development proposals. Now, when I went down to IDA, my work certainly wasn’t particularly on lasers. There was no particular appeal for me to come down and work on lasers or anything like that.

It was general advice to the Pentagon that was needed IDA ran the Weapons Systems Evaluation Group, and the ARPA group, and also gave some advice to the White House, the State Department and some other agencies. Now, lasers were however a part of that, and because I was interested, here and there I worked on laser possibilities in particular. The effort at that time, as I remember, was two-fold: one, to get high efficiency and high power, and two, to try to see whether the beams could be properly guided and transmitted through the atmosphere. Of course, if you put lasers above the atmosphere, then you don’t have that problem, but that seemed very expensive, and particularly in light of the rather low efficiency we had — I remember Bob Collins arguing with me strongly that it was just no good, it would never work. He said, “Do you realize, with the present efficiency, to get one laser shot that would kill a missile, you have to set off energy from TNT as big as that skyscraper across the street.” I said, “Yes, I know, that’s terribly inefficient, but in principle it can be efficient, and I think we’ve got to explore it.” Well, Bob somewhat reluctantly then continued to monitor the laser program. Now, there were enthusiasts, individuals. Culver certainly was an enthusiast. There were others, and then, lots of people who were somewhat skeptical. Their view was more like, “Yes, I know, it’s very fascinating, very interesting, but is it going to work?” Well, you had this mixture. And that’s why it’s a little difficult for me to say, how would you rank its priority compared to other things.

Seidel:

Well, let me pursue it with some things that you were quoted as saying at that time, and see if this would place you among the ranks of the enthusiasts or the skeptics.

Townes:

I know where I was.

Seidel:

AVIATION WEEK AND SPACE TECHNOLOGY quotes you as having said, “Fundamentally there’s no limit to the power which can be obtained from an optical maser,” and you go on to say that the limitations that were being observed could be overcome by engineering and working out better ways of heat dissipation. Now, there are two interesting things about that to me. One is that taken out of context, that seems to suggest a very enthusiastic optimistic point of view. The second is that it would be the kind of remark that would encourage ARPA and the Air Force and the DOD in general to pursue this search for higher power, and obviously was encouraging AVIATION WEEK AND SPACE TECHNOLOGY, which in some sense represents the aerospace industry, to think this would be an important field for application. Now, would you say one, that that statement represents an optimism on your part, and two, that that statement was taken and used in that respect?

Townes:

Well, I’m moderately optimistic, I suppose you’d say. I believed then and I believe now that we should have a strong program looking into these things. But I would never claim that this is an answer to our prayer, that this is really going to do the job of taking down incoming missiles, though I would say that on general principles it’s possible. My position was something like the following. It’s a new field. We don’t know a lot about it. And we ought to work hard on it, to try to see what could be done. That kind of statement I certainly would have made. I’d still make it. The question is, can we achieve that and how well would it work at whatever specific thing you want to do.

Seidel:

I’m curious though about the response that you may remember to statements like that. In other words, when you make a statement like that, you can carefully qualify it — it will be ripped out of context and used —

Townes:

— yes, well, AVIATION WEEK of course is a bit of a yellow journal anyhow. But I wouldn’t eschew that statement, then or now. If somebody interpreted that to say that we must go all out and spend lots and lots of money on lasers at that point, I would have said, “No, I think we ought to have a vigorous hard hitting program. It may turn out to be very important, and anyhow it has lots of other applications. If it can’t shoot down missiles it can do other things and we ought to have a good program,” but that’s about the way I would argue about it. The same thing is true today. I’ve come out with public statements saying about the Sky Wars scenario that I doubt seriously it will work but I think we should have a good program of trying to examine anti-ballistic systems and see what can be done. I think it’s very important for us to know about it. I’m a little less enthusiastic about lasers now, for that purpose, than I was then, because then it was relatively unknown and also the missiles were less potent. Now you have so many missiles, it’s really just almost impossible for any weapon to work. Now, the X-ray lasers are different. Of course, they’re largely classified. That they exist is not classified. But that’s a different category and I would say somewhat different things about that.

Seidel:

Let me try to put it back in the context of the early sixties if I can. A lot of the things which I have read tend to relate these laser weapons to several, what seem to be fairly farfetched possibilities. For example, there was talk of coupling laser energy with the energy in plasma-surrounded re-entry vehicles, and some way being able then to use this as a way of deflecting or destroying re-entry vehicles. Do you remember discussions of that kind of possibility?

Townes:

Coupling?

Seidel:

Yes.

Townes:

Did you say, by putting plasmas around them?

Seidel:

No, there’s the plasma that surrounds a re-entry vehicle that enters the atmosphere. There was talk of coupling laser or microwave energy in some way with that, with the energy of the plasma, and I don’t know how serious that was. It sounds rather farfetched to me. Do you remember any discussions?

Townes:

I don’t remember discussions of coupling with that plasma. There’s another plasma of this type, that when you shine a laser beam on a metal surface, that evaporates and ionizes the material, and there’s a plasma there.

Seidel:

Yes.

Townes:

Now, coupling to that plasma is a very important process. There was a great deal of discussion of that coupling. I don’t remember any discussion of coupling to the plasma externally produced. I don’t remember any. That doesn’t mean there wasn’t some. If you go back in the records, almost anything has been proposed, somewhere by somebody. It’s a question of what really developed and was taken seriously as important. That certainly was not taken terribly seriously, that I can say, but somebody may well have proposed it.

Seidel:

Do you remember the “Bambi” concept?

Townes:

Yes.

Seidel:

Which was sort of a satellite carrying missiles to intercept boosters. Was there any discussion that you recall of modifying that in some way by using lasers, either for guidance or actually as weapons at that time, that you recall?

Townes:

I can’t recall specifically, but I would say I’m sure there must have been. Yes.

Seidel:

So it was a very lively —

Townes:

Oh yes, everything got discussed, and lasers were certainly one of the bright new hopes. But on the other hand, as I say, there were lots of skeptics too. There were skeptics who believed that it was going to not do all that much. One of the reasons I was troubled about it was the problem of penetration of the atmosphere. Now, that is a fairly fundamental problem. See, you can hope to build very big systems and get lots of energy, you can hope to steer the beams, but the atmospheric transmission is a deep problem. First, there’s dust and rain but particularly rain, clouds I should say, and I worked a good deal on penetrating clouds. I was hopeful that maybe one could penetrate clouds with enough energy, and you can. We had big discussions about that. Some said you couldn’t penetrate clouds, but nevertheless the laser would still be useful. If you had enough of them around, you could protect yourself part of the time. If not, you had to be above the clouds. That was a very expensive step, much more expensive and difficult then than it is now, because the lasers weren’t as efficient and space work was much more difficult. Even now, I think, most people who have looked at it carefully don’t think that’s a particularly viable concept. So getting through the clouds — that is a fundamental problem, not a question of development. Then, somewhere along in there, and I guess it was about the time of our trapping work at MIT, I realized there was also a thermal blooming, and it seems to me I wrote a letter to somebody. I don’t remember the person I wrote, but I made a point of getting in touch with somebody.

Seidel:

At ARPA?

Townes:

Probably, yes. Probably. It might have been somebody in JASON. I was a member of the JASON group still but I wasn’t active at that time. I was too busy at MIT. The thermal blooming now was an additional problem in getting through the atmosphere and the JASON people worked on that and I worked on it some. We tried to think about ways of curing that. My own attention was largely directed towards looking at these fundamental things, rather than developing lasers that would be more powerful. Industry was doing that, and while a difficult problem, it was not a fundamental one. The problem of getting through the atmosphere was what worried me, as to whether it was really going to work usefully. Now, Dr. Bromberg mentioned the meeting of a group of physicists. There was an advisory committee that ARPA —

Seidel:

Yes, I have an Ad Hoc Committee on Optical Masers.

Townes:

Yes.

Seidel:

Met in New York City about Christmas, ‘61, included you. Was organized by William Culver for Eugene Fubini who I guess was Harold Brown’s assistant.

Townes:

— yes —

Seidel:

— and Bloembergen, Norman Kroll, Keith Brueckner, Robert Kingston, couple of other people were added later on.

Townes:

Yes, well, Kroll and Brueckner were part of the business — I think that group met several times, more than once.

Seidel:

This is the only meeting I’ve yet found reference to. I hope to find references to more.

Townes:

It met several times, and we of course looked at the situation, to advise the military as to which direction to move.

Seidel:

— who specifically besides Fubini and Brown? Were you talking to specific people in ARPA that you remember that were particularly concerned with this?

Townes:

My memory is that somebody in ARPA was assigned to keep track of it probably somebody who was monitoring the laser program for ARPA. I sort of vaguely remember these people but I don’t remember any names at this point. I think it was almost always some representative of the Pentagon that would sit with us, and of course would take back the advice, and we sometimes wrote down a few things specifically. Mostly we just talked about it and passed on the information to this character. Then somebody would occasionally talk with Gene Fubini. Several of us knew Fubini quite well and various people in ARPA. Now, the one thing that I remember from that, it’s funny, it’s the small things that stick in your memory, and other things that were sort of all the same, even though they may be important are hazy. I’ve forgotten exactly when anything happened. One thing I remember at one meeting, Bloembergen sort of suddenly swung over, saying, “Well, this thing may really work.” Because he had calculated the amount of energy in a crystal where a certain number of atom impurities had been given quanta of energy hν. “Well, look, a lot of energy.” Basically, an excited crystal it sort of has almost as much energy as dynamite. If you want to excite every atom, it is essentially the equivalent of dynamite. But he wasn’t doing that. He was exciting some fraction of them and said, “Well, look, it is a lot of energy. Now if we can just get it out and delivered, why, that really is very powerful.” And just by describing it that way, I think he put some new impetus behind ARPA, saying, “Well, there is a lot of potential.” But there was so much discussion of lasers here and there, and I was in IDA and it’s a little hard otherwise for me to remember exactly what took place. I do remember a good deal of work on the propagation problem. Keith Brueckner worked on that, and Kroll worked on that some.

Seidel:

This is one of the problems you carried back to MIT, of course, the propagation problem. You continued to work on it there.

Townes:

Well, not really for that purpose. I was just doing physics at MIT without worrying about this problem, but when I realized the thermal blooming, that clearly had some bearing on the propagation problem, so I brought that up with ARPA. But I didn’t see very much of those people during those years. I was just busy.

Bromberg:

In IDA did you interact much with people from industry? The missile developers, the weapons developers?

Townes:

Oh, I had some interaction with AVCO.

Seidel:

Ed Gerry or Kantrowitz?

Townes:

Well, the person I knew was [Arthur] Kantrowitz. I’d known Kantrowitz for a long long time from various committees and things, and I remember he invited me to come out at one point, and talk about masers and lasers, and I talked about them. However, I think that was after I had gone to MIT. I remember discussing the fact that they had all these shock waves and they had excited states and there might be some possibility, and he was very interested, and I believe had been thinking about that already, although I’m not sure. And then within a year or two, they were working on dynamically excited lasers. I have a feeling I probably went out there a couple of times. I remember one occasion in particular. I used to see industrial people coming to MIT, but generally made a point not to consult with any industry because I didn’t want to play favorites, as the Provost at MIT. I refused to go on any boards for the same reason. So I didn’t have any close continuing relations with any one industry. But I saw a lot of industrial people who came to MIT. And of course I visited around Lincoln Laboratory and Draper Laboratory — that was part of my responsibility, to look after those. Particularly at Lincoln Laboratory there was work going on. This reminds me of something that maybe Dr. Bromberg will be interested in.

There are lots of miscellaneous things that you absolutely couldn’t know what to ask about, or bring them up, that occur to me. The Lincoln Laboratory was working on the semi-conductor emission from gallium and they had made a real break-through in finding very efficient emitters. I remember talking with them about why not make a laser? Well, they weren’t terribly interested. They thought they’d just run into something that was really very hot — solid state diode emission, very exciting — and they thought it was better than lasers. Anyhow they weren’t interested in it at the time. But within a few months, they decided it would really be a good thing to go after lasers. The first semiconductor laser that I know of was kind of a three-legged race between IBM, Lincoln Lab, and General Electric. One of my students was at IBM. I knew the Lincoln Laboratory people and Ben Lax very well. The General Electric people, I didn’t know so well, but I happened to run into one of them. Each one very confidentially told me that they now had one going, and they were just rushing into publication on it. They knew the other people were working on it. I think the General Electric people were first, as I remember, I obviously couldn’t say anything to anybody about it at that point, but my memory was that the General Electric people were first and then the IBM and Lincoln Laboratory. But they were all very close.

Everybody knew that it was an interesting thing to do and they were just moving as fast as they could to make the semiconductor laser, and all published independently. These things were happening pretty fast, and also, word got around the community awfully fast. Now, there was another interesting case where I can certify the independence of ideas. And that was the use of collisions of the second kind. [Ali] Javan was my student. Of course he talked with me quite frequently, and he had the idea of collisions of the second kind, that would transfer energy, and that was the origin of the HeNe laser he made later. But Gordon Gould, whom I used to see pretty regularly, also told me about this. He had such an idea, and I’m satisfied he had the idea independently from Javan. However, they were really looking at somewhat different systems. In each case, I just said, “Well, you’d better go ahead and publish as soon as you can get a good story together.” In that case, I don’t know whose initial idea came first, but of course Javan published and then he, Herriott, and Bennett made one work. I don’t believe Gould ever published.

Bromberg:

Javan spoke on that in the First Quantum Electronics Conference.

Townes:

Well, if so that was fairly early. In any case, the ideas were bubbling up all over. That particular thing was not an idea that I had had, which is why I remember it. I think that’s a case where I would give some credit to Gould for some originality. Of course, Javan carried it on through and made the helium-neon laser. But there was active discussion within the community, and comparison of notes back and forth, so that at least hints of what was being done went around pretty rapidly.

Seidel:

I’m interested in the efflorescence of ideas. It seems to have been accompanied also by a very great interest on the part of the military, which of course people like IDA were partly responsible for. But you know, this fact that they say even in retrospect it was given highest priority is interesting, because it seems to me that without that kind of interest perhaps the efflorescence of ideas wouldn’t have found the financial backing to be pursued. But I wonder if there was anything beyond that in the way of stimulation? Do you see that the field was shaped in any decisive way in the early period by the military interest or people interested in applications at all?

Townes:

Well, it was shaped but in ways which were not by overt plan. I would give the military a lot of credit, for example, for supporting the Columbia Radiation Laboratory, which was a general laboratory for working on electronics and microwaves and so on, and they were quite open-minded about what we should work on. Now, their drive however was to have us work on magnetrons. Magnetrons were known to be useful for radar. They kept urging us to do more work on magnetrons. We professors would get together and say, “Now, we’ve got to see if we can do our part here, but how best can we do it?” None of us personally wanted to work on magnetrons. Professors Kroll and Lamb were doing some theory on them which they found of interest. We hired some other people to come in and work on magnetrons. I never worked on magnetrons at all, it wasn’t what I was interested in. The great thing was that the joint services were willing to support a wide variety of things in the general field because they wanted a good general laboratory and one in a university context. I think one should look at the military as something like a patron, so far as the more basic work is concerned. The patron’s money, and hence interest, is essential at some points. But the patron does not produce the ideas, and only on occasion may initiate the emphasis. Nevertheless, the patron’s taste, by choosing what and who in general is patronized and supported is important. Only after there are substantial military applications suggested are military plans or interests usually very important in the actual course of development. There would not, for example, be any enormously [text unreadable].

[1]Note added after interview. I think Otting himself was interested and alert about the laser. However, evidence on the attitude of the Air Force generally, can be shown to be different, I believe. See, for example, the material on the Air Force Studies of the Summer of 1957 and 1958. In 1957 I put into their study of plans for the future several mensions of pushing masers into the infrared region. In 1958 I was not on the study committee, and the result was that the 1957 report was revised to include no mention of masers being pushed to shorter wavelengths as part of the Air Force future. That is clearly not high priority in 1958! After my research proposal to Otting, he may well have put it high on his list, but it couldn't have penetrated the Air Force very far.