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Charles Townes
Charles Townes
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Charles Townes Interview

Inventor of the Maser & Laser

February 2, 1991
Berkeley, California

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  Charles Townes

Where were you when you realized you could create something called the maser? What were the circumstances?

Charles Townes: It happened that I was in Washington, D.C., and it's almost a sort of a fairy story tale -- just what a novelist would write about a discovery. I wake up early in the morning, and Arthur Schawlow, who was a colleague of mine, was in the same room. And I thought, well, I wouldn't wake him up, so I'd go outside, and I went out to the park. The azaleas were out, and a nice bright sun in the early morning, and it was just a beautiful time and I sat down on a bench. But what was on my mind was that we had a meeting coming up of a group of scientists and engineers who'd been trying to find ways of producing short waves. And I had been trying to do that myself for about five years. I'd tried a lot of different techniques. Some of them worked, but not terribly well. And so here I was, I was beginning to puzzle over how could we get anywhere on this. What would we do that day at the meeting? How could we get anywhere on this problem? Why was it we hadn't succeeded? So I went over the things that wouldn't work, why they wouldn't work. And I recognized, well, if it's ever going to work, we're going to have to use molecules. Because molecules already made by nature, very small, they resonate at these high frequencies or short wavelengths, we just somehow have to use those. But of course I'd thought about that before too. And concluded from what's known as the second law of thermodynamics, that if you have a batch of molecules and you heat them up, yes, they will radiate, they will produce these waves, but they won't produce very much, because you heat them up enough so they begin to produce a lot, and then the molecules fall apart. So I dismissed that before, and it wouldn't work. But this time, I thought, well, if it's ever going to work, it has to work that way. You've got to get molecules, but yet it has this problem of the second law of thermodynamics. And it suddenly occurred to me, now wait a minute. One doesn't have to obey the second law of thermodynamics. That's when all the molecules are interacting and exchanging energy and so on. We can keep the molecules from interacting, so we can have some molecules with a lot of energy, other molecules with not so much energy, throw away those, and then we've got a collection of molecules with high energy only. And now we use what was Einstein's idea, that always occurs if you have molecules or atoms with excess energy. If a wave comes along that resonates with them, sort of tickles the molecules and resonates with them, they will give up their energy to the wave, and the wave then passes by and picks up some energy. That's called stimulated emission. The emission of radiation by stimulation of the wave that is coming by. So we have this collection of molecules, all of which have energy, then we can get energy from them by this stimulated emission of radiation. And that was the source of the word "microwave amplification by stimulated emission of radiation." The next problem was how to get such a collection of molecules. What immediately occurred to me was using molecular beams. That's a technique that was common at Columbia University. I was quite familiar with it. I hadn't used it myself but I was very familiar with it, and the idea was to send the beam of molecules, in a vacuum like this, and you put on an electric field which can pull some of them out of the way, and the rest of them go on this way. And so I could -- I knew there was a way of pulling away the molecules that had very low energy, keeping the ones with high energy, then letting them come into a resonator. A resonator -- metal resonator -- where the waves could bounce back and forth, and build up strength as they rob the molecules of energy. A resonator I was familiar with from Bell Labs experience, radar. I was familiar with molecular beams from Columbia University. The particular way of getting lots of molecules, I figured out how many we'd have to have, and they were quite a few. How do we get that many? Ah, yes. Just the month before there had been a German scientists who had come to Columbia University, given a talk about a special way of selecting molecules in a molecular beam. It gave lots of intensity. Very much more intensity than other people had. That way would work, would give us enough. And I could quickly calculate, yes, it looks like it's very likely to work. One can't be sure until you make it work. But I thought it was a very good chance. And of course it was an exciting moment for me to realize that was really the right way to do it.

Charles Townes Interview Photo
Charles Townes Interview Photo

What was the background of this revelation you had that led to the maser? What had you been working on?

Charles Townes: I had been working for a long, long time on trying to generate shorter and shorter waves with shorter and shorter wavelengths. So there was a wave which was closer and closer together -- the peaks were. Because I had found microwaves very useful in studying molecules. Now microwaves have a wavelength of about -- oh, anywhere from about that long to that long -- inches to half a centimeter. But I wanted to get still shorter waves in order to study additional molecules and study new aspects of molecules. So I kept trying to find ways of producing shorter waves. I tried a number of things. And they sort of worked, but none of them really were terribly good. It did enable me to do some new things. I kept looking at this, and we even organized a committee sponsored by the Navy, a committee of scientists and engineers around the country to try to stimulate work and thought in this direction, to try to produce shorter waves.

[ Key to Success ] Vision

Charles Townes Interview Photo
I happened to be chairman of the committee, and we had been meeting for a year off and on, looking at various ideas and so on. I went down to Washington to meet with this group. It was in the spring, and I was in the hotel with my friend Arthur Schawlow, who was working with me at Columbia University. I woke up early in the morning, and I didn't want to wake him, so I went outside in the park. It was a beautiful sunny day, and the azaleas were out and I sat down on the bench, and was admiring the flowers, but also thinking about how we're going to get this done at a meeting of this group later in the day. What really has been our trouble? We just haven't been able to find the right answer. And I thought back and forth about our efforts, and the problems, and what was it that might be done. And I decided, well, somehow it has to be done with molecules, because part of the problem if you make something small enough that it produced these very small waves, and do it with human hands and precisely enough, along with all the other requirements, was very difficult. So we should start with things which are already small, and made by nature for us in a very exact way. I thought through that path once before, as a matter of fact, and concluded that, well, there was a law of thermodynamics that says, yes, you can get some waves, but not very intense.

Molecules can never produce very intense waves, because you heat them up to make them more intense and then you heat them up too hot and they'll fly apart, and you no longer have them. Well, that's a fundamental law of thermodynamics. However, I went through that, and thermodynamics says you can't do it -- and suddenly I realized, well, wait a minute, that's thermodynamics and it applies to things which have a temperature, and equilibrium temperature. All the molecules are reacting in such a way that they randomize themselves, like a normal hot thing. But you don't have to have that. You can isolate molecules and have them in special states, not obeying that particular law of thermodynamics, so one can get around it. Isolate molecules, put all molecules in a particular excited state, and they could all radiate, and could radiate intensively, and they would produce the waves by this effect that Einstein had proposed. Namely, if the wave comes along, it stimulates the molecule, like say jiggling its electrons back and forth, until they give up their energy to the wave, and the wave then is bigger as it goes on past.

[ Key to Success ] Vision

That was a well-known effect. Not everybody had worked with it very much. It hadn't been demonstrated in a very substantial way. But it was clear that, yes, that effect existed. I realized that could be done. Now how to do it?

I had been working at Columbia University, I had a number of friends working on molecular beams, and I knew all about molecular beams as well as the properties of molecules. So I pulled out a piece of paper in my pocket, it was an envelope, and started working with the numbers to see how many molecules would one need in order to produce enough energy so it would be useful, and how can you get that many molecules. And I realized one could send a beam of molecules in a vacuum, have an electric field which pulled out the ones you didn't want, left the ones you did want going straight along. And they'd come into a cavity, and as they entered the cavity, the waves could be bouncing back and forth in the cavity, and take the energy out of the molecules. Now the cavity was something I learned about from microwaves. At Bell Laboratories, I had worked with cavities. The beam was something I had learned about at Columbia University. I knew a lot about that because my friends were working on that. Molecules, of course, I had been working with at Columbia University. So all of these things one puts together, and suddenly I realized, now wait a minute, that can do it. And I showed with calculations that, yes, one can get enough energy to make it work. And of course I was exhilarated by the idea that, yes, it looks like it could work. It was marginal. I said, "Well, it's going to be difficult, but I believe it can be done."

[ Key to Success ] Vision

So I went back to the hotel and talked to my friend Arthur Schawlow about it, and he agreed, that looks like a real idea. But it didn't seem easy. So I waited a while, I wanted to get a student to do his Ph.D. thesis. I always work with students, and students who I was working with, students in the laboratory all the time, and they were undertaking interesting problems.

I thought, "Well now, this is a chancy problem, but maybe there will be a student who's good and would feel like doing it. And so, fortunately, one appeared later that summer, Jim Gordon. And Jim Gordon had had a little experience with beams of molecules already. I talked with him about it, explained, "Well now, this is chancy, it might or might not work. I think it will work, but one can't be sure. On the other hand, there's some good things to do along this direction, that even if it doesn't reach our ultimate goal, there are some good things to do, and it will be an adequate, good thesis program." And so he agreed to undertake it. So he worked on it. I got another person, Herb Zeiger, a young post-doc, who had also had some experience with molecular beams, and he worked with us for a year. Now that problem -- actually doing it -- took about two-and-a-half years. It was not easy, we had to build things up from scratch. We had to make a cavity, we had to make a vacuum system, we had to arrange everything and so on. Get some circuitry, build up some circuits -- and on a student basis -- he was taking courses also. So it took a while, two-and-a-half years. But after that two-and-a-half years -- we worked with it for some time -- and I remember very well, I was sitting in a seminar with other students and we were talking about something, and Jim Gordon burst in and said "It's working!" That was a time that was really great.

I'd say there were two particularly great times. One when I was sitting there on that bench and I realized, see, here is a way it really could be done, and secondly when it actually worked, when we were getting real energy out of molecules and I knew the system was really functioning.

A scientist has to decide: Is he right or is he wrong? And other people won't necessarily agree with you. Two very prominent professors in my department came in one day and said, "Look, you know that's not going to work. We know it's not going to work. Why don't you just stop bothering with it, and wasting time, wasting time and money?" I had spent I guess about 30,000 dollars building this up. And they assured me it wasn't going to work. Now, I had of course been working with it long enough, and thought about it enough that, well, I still think it has a good chance. And so I continued, and a couple of months later it was working. Now also, one should realize that many people came to my laboratory and looked at this, they weren't terribly excited about it. They said, "Well, you know, that's a kind of a nice idea." But nobody else tried to do it. It wasn't that interesting to other people at that time. They hadn't yet really grasped what it meant. And everybody was looking at it, "Well yes, okay, that's a kind of nice idea," but some doubted it would work. And nobody else was interested enough to try to do it, even though they knew all about what I was trying to do. I had showed them. So we could take two-and-a-half years -- no competition -- we just went our own course, and did the things we thought had some chance. And it turned out well. Now, it might have not turned out so well. It would have been interesting in any case, but maybe not quite so successful. So it was worth exploring, I was sure of that.

[ Key to Success ] Courage

We've read that there were actually graduate students who turned you down because they didn't believe it was going to work and they didn't think they would get a decent doctoral thesis out of it. Did you ever doubt yourself, when all these other people were doubting you?

Charles Townes: I listened very carefully to the reasoning that other people had of why it wouldn't work. And some of them had theoretical reasons why they believed it wouldn't work. Others practical reasons. I listened very carefully to that. And I looked at those reasons very carefully, and I convinced myself that, no, they had not really understood it fully. That I thought they were wrong. But I examined it very carefully. I kept examining myself and my own ideas, of course. Now some people agreed with me. But not a large number, and as I say, no one thought it was exciting enough to try to do it themselves. I had no competition at all. Interestingly, when the laser came along, and when I started talking about the laser, then everybody jumped in, and everybody wanted to do it. With the maser, it was really too new and different, and people didn't quite see the future of it. And after the maser was working, then it became the property of the field, the maser did. It became quite popular for a while. And then when Schawlow and I -- Arthur Schawlow and I -- wrote a paper about the laser, then that was exceedingly popular and everybody jumped in to try to make a laser. That was a very different kind of environment. But the really first ideas were not seized on by other people at all, and that's where the scientist has to be ready to be alone a bit.

[ Key to Success ] Perseverance

How do you know you're right, especially when you're talking about a theoretical idea? Is it mostly instinct, or is there another way you know you're right?

Charles Townes Interview Photo
Charles Townes: People think about things in different ways. It really depends on their own personality and mentality and background and so on, and ideas. Some people are very theoretical, and will think in their heads in terms of equations and will write down equations. Some people have more visualization. And for me, I do some of both. I have become so familiar with molecules and atoms and electrons, I write down equations about them to be sure just what they do, but then I can just see them. I visualize them. I can see them. They're friends, and I know what they're going to do. So you have instincts about them, and you just immediately recognize what they're going to do. If it's something that's a little different, you're not quite sure, but then you write down the equation, just to be sure. But you know them, as I say, they're good friends and you know their characteristics very well, and so it's an instinctive kind of thing frequently. You have a model, you sort of see them moving around and what they would do. Now, other people don't necessarily think that way. There are many different things of doing science, but that's a typical case for me. I really, I do a lot of visualization. But on the other hand, I also use equations. If there's some doubt about it, I check it very carefully with equations. Now, I frequently have talked with other people about it to get them to see if they see any problems with it. Sometimes they do, sometimes they don't, sometimes they think they see problems, and I check that and find that they're not right after all. So interaction with other people represents a very good check.

But on that day in Washington, D.C., you must have had a gut feeling you were on to something.

Charles Townes: Yes. Yes, and of course, I thought about the field for a long time. I had worked on it roughly five years, thinking about different ways. I wasn't working steadily on it, but I was thinking about it off and on and seriously over a period of five years, trying various things, and I knew what the limits of everything else was. And I said, all right, if it's ever going to be done, this is the way to do it. And I realized it could be done, and that was very exciting. I knew enough about it that I recognized immediately, and I had all the numbers in my head so to speak, so I could figure out exactly what was needed. And so that I did use equations, in a sense -- very simple equations, numbers -- but I had all that inside my head because I'd been mulling it over long enough that it was very familiar territory. I just hadn't put it all together before.

Did you do anything to celebrate that day? Did you feel particularly high?

Charles Townes: I felt exhilarated. I didn't do anything to celebrate, no. I went back and talked with Arthur Schawlow about it. And I went on to the meeting, and we had our meeting discussing techniques. I didn't talk about it at the meeting, because it was quite new, and I wanted to think about it some more, before I started trying to propound it at the public.

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