Oral History Transcript — Dr. Robert Hellwarth
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Robert Hellwarth; May 28, 1985
ABSTRACT: Covers period from 1948 through 1965, when Robert Hellwarth was an undergraduate at Princeton University, to 1952; a doctoral student at University of Oxford, to 1955; a postdoctoral student at California Institute of Technology, 1955-1956; a research scientist at Hughes Aircraft Company, 1956 on; and a visiting professor at the University of Illinois. Emphasis on the cross-fertilization of his electrical engineering and physics education; his collaboration with R. Feynman and F. Vernon on the theory of masers; Q-switching, and stimulated Raman scattering.
Bromberg:So we ought to look up those questions which also ought to be in your folder, and which I had until an hour ago. Actually what I am starting out with is a little bit on the schooling at Princeton and Oxford, just to get an idea of the kinds of backgrounds you had and the people who might have influenced you as a scientist.
Let me just remember. Thinking back to my time at Princeton, I went there from Detroit as a scholarship student, almost by accident, never having known anyone who had actually gone East to school, having been in the westside workers middle class high school, Cooley High School, where I don‘t know of anyone who had left Michigan to go to college, I think in my experience there. Although in my particular class several for the first time did leave Michigan, so I think those are the first years where the eastern schools came recruiting to broaden their geographical base. In fact, I was a beneficiary of that. In fact, I first refused Princeton and only at some time later when some altercations with my family arose and I wanted to get farther away from Michigan for personal reasons, I called them and asked if they would reconsider my refusal and let me come after all, which they kindly did. In fact, I never applied. The man from Princeton had come around to give talks at the high school to recruit, persuaded us to take the College Boards, and in those days you just…my father wanted me to do that as good experience… and in those days taking the Boards, which is the same as SATs today, was tantamount to applying — you had to put down your first three schools of choice. And if you never wrote to the school at all, they received these exams and a lot of information that you had put, and so, without even applying I was accepted. I turned it down and then rethought it.
My father was an electrical engineer. I have three brothers, two of them graduated in electrical engineering, the third in mechanical engineering — we were all engineers. The other three stayed in Michigan. My father, who died several years ago, was Associate Dean of the School of Engineering at the University of Michigan when he retired I believe, around ‘78 or ‘79. I’m not sure about that, I would have to look that up. And so in those days it was very natural for the sons to follow the father in these matters, and I did not think of anything else to major in when I got to Princeton. They had a small electrical engineering department. I don’t think there were more than four in my graduating class. A handful, in any case, five maybe. I took a combined physics and EE degree. Very soon… I had had a very wonderful physics teacher in high school, so that my…of course in high school you don’t have any introduction to engineering, but I had this introduction to physics which I loved a great deal. A great man named Sam Asher, an ex-marine who was just out of the army. And at Princeton the EE department was a wonderful family, presided over by the department secretary, whose name will doubtless come back to me, and the courses I remember being most influential were those of Walter Johnson, who was chairman at that time and who has written a little book on electrical engineering, which I still keep here. It tells about machines, just a general thing. Walter Mather, and especially Bill Surber. I worked for Surber as a senior, did a senior thesis with him on magnetically controlled servo mechanisms.
Bromberg:He is no relation to Robert?
Hellwarth:No. They are spelled slightly differently. It has an “e” where the other has a “u”. I think my professor had a “u. “Surber” yes. And I think the thesis, the senior thesis was incorporated into later publications of his. We did get some very interesting results. But Surber and Johnson and Mather and the woman… but I think I probably took more courses over in physics in the end, and was more inspired, I think. Sort of, EE was very supportive and sustaining, but the inspiration came from, especially, I first heard about electromagnetic waves and Maxwell’s equations and the idea that electricity was connected with light from Don Hamilton, who was a professor of physics, a wonderful man. I think later he was a dean of the Graduate School, and he helped me again later in my career when I was at Oxford. I was measuring something that he had se-t out to measure as well and we had corresponded, and when he found out I was measuring it, he had his student put that off to measure, and leave it for me and measure other things. So, …which was very. I think in the end he did check the result in his way, and it checked alright.
Bromberg:Was Dicke also someone you saw a lot of?
Hellwarth:Now, Dicke was around, and I didn‘t have a course with him, but I did remember hitchhiking with him on several occasions, and enjoying conversations with Dicke. David Bohm fled the country while I was there, in the McCarthy hearings. And later, I am very surprised that the student newspaper took so little note of the plight of these professors in the McCarthy hearings, that we were almost unaware of them. I didn‘t know that Bohm had fled to Brazil or where ever he had gone until after I left school, and yet it had happened while I was there. People were very quiet about it.
Bromberg:Since I left my files, I remember vaguely you got out in ‘52. Is that a correct memory?
Hellwarth:Yes, I left in ‘52. I would have to check when Bohm left, so maybe he didn’t leave until after that arid the paper wasn’t as derelict as I thought. I don’t know.
Bromberg:Well, no that was… I don’t remember when he left either, although those whole years are very vivid for me, but I certainly remember that those years were very bad ones, ‘51-‘52, some of the worst.
Hellwarth:And the Department must have been in some turmoil, which didn‘t filter down to the undergraduates who were interested mainly in drinking.
Bromberg:I see. So you sort of went through those years without any pressure from the McCarthy…without feeling any direct pressure.
Hellwarth:No. We were very shielded from that, for some reason or other. The students tended to be very apolitical. I don‘t remember much in the way of protest… I don‘t remember any protests about it or any carryings on in the student paper particularly. So, …
Bromberg:Is it safe to assume then that by the time you went to Oxford that you knew that physics was what you wanted to do and not engineering?
Hellwarth:Oh, yes. I think by then it was the conceptual — the ideas — that I found most exciting. I had more advanced classical physics from Professor Rohr1ich in the physics department, who later wrote the definitive book with Youk on protons and electrons; he was a very smart and inspiring man and I had, I guess I started out in my freshman year as all engineers do…their main work is in physics and chemistry, and I took freshman physics from Henry Dewolf Smyth, as I guess practically everyone did in those days. He was very…I believe he was, as well as being a lead scientist in the wartime Manhattan Project, one of its chief historians afterwards.
Bromberg:That’s right. The reason I am copying down names is for the person who is going to transcribe.
Hellwarth:Yes. I had some bad physics teachers, I won’t go… I remember Hamilton, Rohrlich, and Smyth especially, and I had some very good mathematics teachers, I took a lot of math and a man named Bochner and Artin stand out especially…died a long time ago. Artin was…I was told at the time, was very distinguished and famous, a very colorful man who smoked incessantly and spoke with a heavy accent, which, being from the Midwest, I couldn’t place. In those days I wasn’t tuned to placing accents, but it was a very… the symbols so lived for him, and the proofs, squeezing epsilon to zero and the inference was such a brother or a living creature — was very amusing I guess I learned complex variables from Bochner, who wrote a book about it. And that is of course a subject which then threads its way all through physics and quantum mechanics, and one never leaves. I can sure remember a couple of other good mathematicians whose names escape me.
Bromberg:Well, what about in a more personal way, what you were most interested in? Do you happen to remember the kinds of subjects that were most intriguing to you?
Hellwarth:Well, everything these men taught was to me really intriguing.
Hellwarth:Ah, yes, I especially remember Hamilton’s revelations that you could get the velocity of light just from knowing the magnetic permeability and electric permeabi1ity of space. I don’t think my father had fully understood…I can remember explaining it to him excitedly following Christmas break. And then figuring out you could get the same place with the impedances and learning about capacitances and inductances from Surber and Johnson and then from the, again from just the…literally from the capacitance, distributed capacitance and inductance of a line get the velocity of light as it flows down a transmission line from a totally different angle. That probably came later, but the vividness of the electrical engineering approach in terms of little things you could hold in your hand. We had labs filled with capacitors, inductances, and resistances, in those days, being before printed circuits — you could just literally hold everything, you could see each individual one. Vacuum tubes in a funny way made everything a lot easier to picture. Today I think students just have to work with diagrams on paper, and take it on faith, that, if they looked under a microscope those little things are what correspond to the diagrams on the paper.
Bromberg:I should think it would have been rather interesting to have a whole family you could talk to about these things.
Hellwarth:Yes, although the other brothers were younger and had had some. I could talk to them a little bit. But especially my father, that was fun. And I think that Surber, with the project, gave me the confidence that I could actually find… There were a lot of things that were not known, and even with my modest knowledge I could figure out some of these things for myself. That new knowledge was accessible even to the homeliest of determined workers. It was nothing mysterious or out of reach. And I edited the Princeton engineering newspaper and took a lot of interest in the general goings on. And was probably headed for president of the local chapter of the IEEE — did all those things.
Bromberg:Did it make any difference — doing both engineering and physics — are there things you learn in engineering that you don’t learn in physics?
Hellwarth:We learned a completely different side of the same thing. I mean, I learned, in those days I 1earned about electrical motors and electrical generators — nobody hardly ever learns about those anymore — and I could actually design how many windings to put into an armature that would go inside of a standard magnet with so many pulls to get so much torque with so many amps, and all this news. And yet, was constantly aware that this was Faraday’s law, and it was just another side of things we were talking about in physics. In fact, I think I brought a lot of insights to my fellow physics classmates — the insights were always going that way. And I would explain to them how these abstract things were very familiar everyday objects, and they were surprised to find this was actually used in motors.
Bromberg:Somehow that surprises me. You’d think you would be bringing a depth of understanding to your engineering.
Hellwarth:Well, the kind of students that tended to go to Princeton for physics those days were very mathematically oriented, and I think as I look back on it. One of the — now if I can remember his name — one of the chaps in my class became a famous general relativist at Brandeis. I can remember his name in a second…John…Another chap in my class got a Presidential Award for a famous mathematical discovery…Milner, John Milner, who was also the best gymnast that Princeton had in many many years, as well as being their best mathematical — physicist or mathematician. Now that’s funny. It’s like I had a real leg up on my physics brothers who weren‘t taking engineering courses, it seemed to me, even in understanding physics. It‘s hard at the first go round at that age, to develop the models and the pictures which stand you well in working things out later. So, I can pass on to Oxford. I had arranged for myself, in my junior summer, to work in a shipyard in Denmark. I don’t know why I did this. It was not easy. I had to write a lot of letters and I had to arrange for a Danish student to have a summer job in the States, which my father helped me with. They had a sort of work-study programs that were normal for their students and I got myself into. And I decided one way or another I wanted to go to graduate school in Europe. Mostly, it just seemed like it would be such fun. I didn’t think I would learn as much, and that was certainly true, but I would certainly have more fun. And so I applied for every fellowship that I could…
Bromberg:Well, of course, the Bohr Institute would have been one thing, one would think. Did that occur to you after a Danish summer?
Hellwarth:I think it did, and I don’t recall the many fellowships I applied for to get money. But I ended up with a Rhodes Scholarship at Oxford, and when I got to Oxford any doubts that I may have had about what study were erased, because they didn‘t have a graduate engineering program at that time. I went to see my tutor, and he said, “Engineering? Engineers are supposed to go out and engineer. You don’t hang around a university.” They had this microwave group under Professor Bleaney, and I had already studied microwaves, and that was a great overlap between engineering and physics. He was the first to do microwave spectroscopy, and those people who during the war developed radar, had these instruments they carried back to their labs, and they had al1 these wonderful experiments to do the instant the war was over, and he was one of the leaders in this. And whereas most, the big science was being done at Cambridge, this particular kind — the microwave physics — happened to be at Oxford because Bleaney was there. And that suited me fine. He had a lot of space and a big group. I have gotten to know him much better since. He was completely non-directional he said, here is some space, here is the kind of equipment we have, do the best you can with it. And I probably didn’t talk to him more than a couple of times a year while I was there, later talked to him much more. So, unhappily, we didn’t publish together because he didn’t follow very closely what I was doing. It is very sad.
Bromberg:Now you worked with beams, didn’t you?
Hellwarth:I set up the atomic beam lab, that has lived at Oxford ever since. And my last visit there, I think it was last spring, I was visiting Brevis, Bleaney, and having a good time as usual, and he said he had found in the storeroom a piece of my old atomic beam apparatus — in fact a piece that I had invented, that made a key part of an experiment that gave it more accuracy — and he had saved it. He gave it to me and I brought it home. I have it on my mantle piece. He had never taken a very direct interest in the beams effort. A post-doctoral person, Gordon Kemble Woodgate, or Kem to his friends, was a post-doctoral research associate then with Bleaney — worked also to set up the beam. So I was working more with Woodgate in starting from the bare floor and setting up the beams lab.
Bromberg:But did you…was beams something you knew about?
Hellwarth:No. I didn’t know anything about it at all. Neither did Woodgate or anybody. Woodgate had visited at Columbia. I think he may even have been a student there, in fact, he was in the U.S. during the war, he was the age…he was one of those who had been evacuated. I think he had relatives in the United States. And at Columbia he learned about beams from Kusch and Rabi, and had taken back all the plans and notes and all that and was in a very good position to… I think we copied, with our own minor modifications, some designs that had already been used at Columbia. They weren’t really minor. We knew…we set out to do the first measurements of hyperfine structure on a radioactive isotope, and that meant that you really would give up accuracy for sensitivity, because the signal would be very small. You would be working with very…smaller number of atoms than anybody had ever worked with before. And so we designed a machine that had, that could see very smal1 signals at a price of accuracy. Now Norman Ramsey was visiting one of those years, and he was probably, certainly one of the leading men in atomic and molecular beams in the world, and has written the standard work on molecular beams. And he gave lectures, and was a great influence. Actually, I proofread his book for him, which acknowledges, and I got a chance to talk to him and actually included some of our results in, the book. And he had invented a thing called a Ramsey hairpin for increasing the sensitivity of the signals and I adapted it to our apparatus and then…excuse me, increasing the accuracy in the… I mean, how many decimal places you could get in locating the center of a resonance spectral line. And I enjoyed Ramsey enormously. I learned quantum mechanics from a man named Blinstoyle, who gave the lectures on that.
Bromberg:I assume you had been learning some quantum mechanics in Princeton. Was that not so?
Hellwarth:No. In those days, yes we knew only the amount which was in a little book by Born, which was a very brief introduction to quantum mechanics And in England, at least at Oxford, everyone learned Dirac’s formulation of quantum mechanics, rather than the Americans who always learned shifts, so I didn‘t even know…when I came back I could hardly even talk with my peers about quantum mechanics, they had never heard of bras and gets, and I had hardly heard of a wave function.
Bromberg:That’s nice. I hated shifts, I must say. I would have loved to have studied with Dirac.
Hellwarth:Yes. I’m glad for that. The notation…Dirac’s method is so powerful. I mean, what it lacks in the vividness you can see in dealing with ordinary English functions. He dealt in the abstract vector spaces straight off and said, let s get beyond this idea of just a wave function. And in fact, ties together Heisenberg and Schrodinger and Dirac himself, and all the other formulations are so much more easily tied with this way of learning it. And that was a good bit of luck.
Bromberg:I’m interested that you did so much with your hands. I always somehow thought you were mainly a theoretician, but…
Hellwarth:No, I was mainly an experimentalist in those days, as I am today. But in the intervening years, many years I had no experimental beams at my disposal, for one reason or another.
Bromberg:In that kind of thing, is there a very strong correlation between the quantum mechanics you are doing and the molecular or atomic beam experiments you really using the quantum mechanical analysis in the experiments, or parallel things, or what?
Hellwarth:Oh, yes, we were very… It comes in the most clear and vivid way in atomic beams. The Stern-Guerlic is the first atomic beam experiment in which spin up when atoms curve to the right and spin down when silver atoms curve to the left and nothing could be more unclassical, nothing could demonstrate more vividly the weirdness of quantum mechanics than that experiment, so that may have been the most dramatic demonstration of the failure of classical mechanics to understand something.
Bromberg:So that you were therefore… It was a real working out of what you were learning in the classroom to work experimentally? That’s what I am trying to get at.
Hellwarth:Oh yes, it was just a delight. Again, everything I was learning could be directly tied in with this atomic structure and the forces of magnetic fields on atoms with spin and the transitions which we were inducing with their radio frequency fields were the time dependent perturbation theory, just right and are so vividly in the hands, I mean it just couldn’t have been more direct. And in interpreting hyperfine structure, which is the interact ion of the nucleus with the electronic parts of the atom, there is a…we always use a form for the energy of interaction, some unknown constant times the angular momentum of the nucleus dot the angular momentum of the electrons, and then you can go to higher terms that involve quadrupole moments and this to me was a great mystery. And this was an introduction to symmetry. I mean, this is true because of symmetry, and symmetry had not been highly worked out then. And it was this particular…the theorems that involved this were being worked out by a guy named Charles Schwarz, who later became very famous at Berkeley I understand, but he was doing wonderful work and publishing wonderful papers. But Bleaney didn’t understand and I got a hold of and I did and so at least when I thought I was doing my thesis I had some deep interpretation built into the symmetry of nature. That the atoms had to have the levels move in these strange ways as you applied magnetic fields because of deep symmetry principles. One gets an awful lot of data in these beam radio frequency resonance experiments. There are many resonances and they move with electric and magnetic fields in many mysterious ways, and to tie all of this together with very small number of parameters, few constants, was a…that was a very exciting thing to me.
Bromberg:Is there anybody else you met there whose name was particularly important in way or another? Of course, the names that I think of being there are just names I happen to know, like Kompfner, or Scoville…but just names I know in terms of laser…
Hellwarth:Yes, I inherited Kompfner’s space: he had been in…and met him as he left, and met him later in life, but this bare floor had been occupied by Kompfner, who I guess was in Bleaney’s group too as was Scoville and many others that have come to the United States, and have later worked on lasers too, and masers.
Bromberg:I mean these probably aren’t the people to mention, they are just people I happened to think of.
Hellwarth:Willis Lamb came by my last year — I didn’t have anything to do with him — but he took the Chair of Theoretical Physics at Oxford, briefly.
Hellwarth:And certainly it must have had some influence, because we had some talk, and he was certainly interested in masers and the first words of masers were filtering over there, you know, a little bit of talk about that.
Bromberg:Well, I must have that wrong, because I think of Lamb as being at Stanford when you are at Cal Tech, but that is not so? He was already…
Hellwarth:I believe Lamb was there the year after I left. That he…which would have been ‘55 or ‘56, while I was at Cal Tech, but I would have to check on that.
Bromberg:In fact, one of the questions I asked you was: As you came to work with Feynman and Vernon on the paper on masers, whether you were having any contact with people at Stanford, like Lamb and Helmer and then I also put Bloch in there, since that was an obvious…
Hellwarth:Yes, I had never met Bloch, and I had met Lamb at Oxford, and not till many years later back in the States again. And Helmer, I’m sure I met at a meeting and certainly corresponded with him, because I remember getting some of his…getting a pre-print of his before it was published. It’s curious. I’ll bet you Lamb was at Oxford.
Bromberg:I’m sure your memory is…
Hellwarth:I don’t know, I’m not sure, I Just have this strong feeling because I had overlapped him, and I just had the impress ion that he stayed when I left. Although, he probably came back and forth.
Bromberg:Well then, what were you hearing about masers in those days? And were you interested? Did you care?
Hellwarth:Yes. It sounded like the natural next fun thing to work on after I finished my thesis. At some point I decided that would he fun to do. And I think…and that’s what I set out to do when I got to Cal Tech, and I gave a lecture on masers — I guess I must have been studying about it. I guess Hughes, being a microwave company, must have had some charm, and it was after this lecture on masers that Feynman took me aside and said, “Come to my office once in a while. Let’s talk about masers. I want to learn to be an engineer.” And Frank Vernon was an engineering graduate student and he took on his first and maybe his last engineering graduate student.
Hellwarth:I don’t believe he has had any others.
Bromberg:So you were…I just assumed Feynman set the topic. But it was you who…
Hellwarth:No. He got interested in this lecture I gave, he said that sounds fun, let’s learn about it, let’s talk about it.
Bromberg:Was that an ammonia beam lecture?
Hellwarth:Oh, the ammonia beam was the most well-known thing at the time; must have been mainly ammonia beam, yes. We might have… It would be hard to remember that one might have lectured about in those days. I do remember being absolutely terrified. I had never given a lecture before such an audience before — shivering and shaking. I wonder that I could have been heard or understood at all. But I got through it, and it was fun.
Bromberg:I do have another question which may or may not be relevant. Just about this time Hughes was setting up a group under Harold Lyons on masers. That was around ‘55-‘56, maybe a little later and I was just wondering whether anything that was going on at Hughes to set up this group had anything to do with, or any interaction with what you were doing? Your interests, or Cal Teach work?
Hellwarth:Now that’s an interesting question. Of course, I joined Lyons group at some point, I don’t remember when. First I went there, I was working with various men, most of whom now are big whigs in the Hughes Aircraft Company, including the President and the manager at Fullerton, and the manager out at Canoga Park. I mean, these guys were all just group leaders, and some others… And I don’t actually remember when I connected up with Lyons. It would be fun to look back and find out. Somebody must know.
Bromberg:But when you were at Cal Tech you don’t remember any heated discussion with people like Lyons, or…
Hellwarth:I don’t have any connection at Cal Tech with Lyons at all. I don‘t ever remember seeing Lyons at the time I was Tech that year. Surely, I must have met Lyons pretty soon after whenever he came to Hughes Aircraft Company. Do know when that was?
Bromberg:Well, you know I think it was ‘56 and I don’t know exactly when in ‘56, so that makes…
Hellwarth:Probably just about the time I was finishing my one fellowship at Cal Tech and then going to work more or full-time at Hughes.
Bromberg:In fact, I have to apologize for that…
Hellwarth:I think that it is very likely he was not around while I was at Cal Tech.
Bromberg:Well, let me phrase that question differently. Were you much in contact with Hughes at that point? Should I, in asking you for your memories of Cal Tech, should I think of visiting Hughes and talking to the people there as part of the environment?
Hellwarth:No. Hughes work was totally disconnected from the Cal Tech work. At Hughes I was really working on missiles -– guidance — I loved servo mechanisms which I had worked on with Surber in my thesis, and I was back working on guidance and control, a real engineering subject which I really liked, and there was no connection with the work at Cal Tech in those days.
Bromberg:That Cal Tech paper, I thought was very interesting. I was wondering both where it fit in your own lives at the time. I noticed… Again, in my folder I have those notes…I noticed that there was this theoretical interest, that it seemed to be a simple case of a more general system…You are going to be able to remember this better than I. The paper is introduced with a discuss ion of why the maser is of interest in terms of field theoretical systems.
Hellwarth:I don‘t remember the introduction at all. Let me look…That’s an interesting… Ah, yes, I’ll bet I wrote the introduction, because Feynman didn‘t have much interest in electromagnetic resonances and matter… “Becoming a fundamental tool for studying the structure of matter” yes. “Moreover, recently it has become of interest to you such resonances for radio and microwave circuit components, such as highly stable oscillators, high-Q filters, isolators and amplifiers… The purpose of the paper in understanding simple resonances…” Yes. These are the things I was telling Feynman about: filters and oscillators and stuff, what little I knew. I wasn’t…by no means was I an expert. I was just reading like everybody else. I bet I had gone and been able to talk to Towns, or heard him. Hughes was very generous in sending us to meetings in those days.
Hellwarth:Yes, I’m certain of that. He was an inspiration very early on.
Bromberg:The only trouble was that Townes would have started on a sabbatical in September of ‘55 that would have taken him to France and Japan. Maybe he came through Hughes. So while you were at Cal Tech he was mostly abroad.
Hellwarth:Wel1, maybe the inspiration came later.
Bromberg:But Gordon was talking. Jim Gordon was talking.
Hellwarth:Yes. Gordon I met early on. Reading a lot… It is very hard to sort out.
Bromberg:That kind of memory is very hard to recover.
Hellwarth:Yes. But…I described to Feynman some problems Shimoto had been having. Maybe on one visit back east I was able to talk to Shimoto who was working with Townes, rather than Townes himself at that point. And he was getting some funny answers about a maser in which the beam was al1owed to go from one cavity to the next — rather than just through a single cavity. He was having terrible trouble with this, and first they got it wrong, and then they wrote a long, long theory about getting it right and it had pages and pages of math. I don’t remember the outcome of this work of Shimoto’s. At some point they were having a lot of difficulty understanding anything more than just a simple interacting path. And there were several other problems. Helmer’s work was known to be… it had a lot of difficult mathematics and it was very good, but very hard to follow, and see in detail what was going on. And Feynman, of course, was one who always wanted to see everything easily in picture, easily, so right away he thought that there ought to be an easy way to picture how all these hard problems were to be treated.
Bromberg:So the basic idea of this analogy was Feynman’s? This “r” cross “omega”?
Hellwarth:Well, I will bet you. After all, I knew the block equations backwards and forwards from having dealt with them in the atomic beams and in nuclear resonance. So I knew these equations, the block equations. And I am sure I had probably explained them to Feynman, because he hadn‘t heard of nuclear resonance or done a lot of this. I don’t think that I put together right away that any two-level system therefore must — that is quantum mechanics — must satisfy the block equations. That would be the kind of thing that wou1d occur to Feynman instantly….that the two levels was the important thing and not the fact that it was a magnetic spin or something else… So, I don’t… So, I’m sure the “smart” part of the idea was Feynman’s, wherever it would have lain there.
Bromberg:What part did Vernon play in this?
Hellwarth:He was sitting in the office throughout, and talking up, and being a typical graduate student I guess. Very hard to pinpoint anything…
Bromberg:But I think that gives a kind of picture. In some of these collaborative papers the various roles of people are very disjointed and can be easily separated. But in a paper like this, as you are describing it, I get the impression of three interacting people throwing ideas around.
Hellwarth:Yes, I think so. Since I was the one who had Helmer’s paper and had read it. So I re-did Helmer’s. analysis on the last part, to get what I guess we would call… Yes, we refer to Helmer’s Signal Corps contract report — he hadn’t actually published it yet, and this was a pre-print that we had gotten hold of, that he had sent me. Within a few lines we had gotten this formula of Helmer’s, which he had taker, many, many pages to arrive at, so that was one of the things. And we also went on to do Dickey (?) radiation in a very simple way, the formula for how a whole bunch of spins tip and radiate. When they radiate…Under the condition where they radiate much more rapidly than a number proportional to their number, this so-called cooperative radiation which can be done in a line this way to get Dickey’s results. So that was…I think I did that tube, and I think Feynman didn‘t think that, result was very interesting, and wondered whether we should include it.
Bromberg:Are there things that you got out of working with Feynman, or that you got out of working at Cal Tech generally that you incorporated in your bag of tricks? What was Cal Tech like for you?
Hellwarth:It was the most exciting place in the world in those days. I would say yes, everything in retrospect, all the physics that I use today, and it seems like 90% of it I must have learned from Feynman and I had never seen anyone work so quickly and so I had never come across a physicist like that. Certainly nobody at Princeton or at Oxford was like this. And he was pretty fast and terrible when he was young. He is not much less fast or terrible now. And, you know when an idea popped into his head it would take literally no more than 5 or 10 minutes to work this kind of thing out, and this was… He had many more important things to think about, I mean this was maybe an odd afternoon or something that he, or an hour a week that he devoted to his engineering student. Those were the days of…Cal Tech was just the most famous center for all of the particle physics going on at the time, and electrodynamics, and weak forces, and he was working on…he had done the beta decay theory and decided it was wrong because all these experiments didn‘t agree with it, and they were all written out on his board, and later turned out all the experiments were wrong, and he later said, “From now on, to hell with the experimenters, I’ll just trust the…” And the seminars were contentious and exciting and the people were afraid from all over the country to come and give seminars in front of this gang. They were absolutely… I think he carried the spirit that I heard him later…like when he later described Los Alamos, it must have been like that at Los Alamos, and he decided that is always how it should be and it was really like that at Cal Tech in those days.
Hellwarth:It was extremely lively. Cal Tech isn’t like that now, when I go over there, at all I have never experienced anything else quite that alive as those years. After that year, I kept a one-day-a-week… I helped organize the senior lab with some people there. I kept an excuse to keep going back to Cal Tech, to keep in touch and to watch the stuff that was going on.
Hellwarth:So I think I was going something like a day a week for the next half dozen years, then there was a brief time when I couldn’t and later on I was again at some other titles at Cal Tech, at Research Associate and Fellow. Toward the end I had a more formal relationship up ‘till the time in 1970 when I … they wanted me to go there permanently and I thought a lot about it and came here instead. Well, I thought this paper was fun. I went on to do some much more sophisticated work with Feynman on the poleron and field theory and path integrals in which it’s interesting. This was just fun. I don’t think anybody read this paper at the time. None of us were certainly ever invited to talk about it. It lay — as far as I can remember — totally un-noticed, as one of the great joys in life. I don’t think it was ever referred to until “photon echoes” when Sven Hartmann and somebody else, a student, somebody who knew the block equation made spin echoes and put two and two together and said, we can do this with photons too, of course — I think it was Hartmann, who I am go big to work with this fall at Columbia, has been a close Friend ever since we met over this paper. As soon as the photon echo business came in and then probably thereafter it was referred to more than any other paper I ever wrote. It must have been.
Bromberg:About ten years?
Hellwarth:Ok this was ‘57, ‘65 — 8 years or something it lay unnoticed and that is just — what a wonderful experience to have something dug up later.
Bromberg:Did you make use of it?
Hellwarth:I never made it. Oh, I could use it privately. I never made use of it in a paper. It was one of those little things like your pencil sharpener, which you use all the time — you might use but you don’t actual1y put down in a results.
Bromberg:I don’t know what that means. What do you mean you use it privately? You use this model?
Hellwarth:Oh, everybody has their own way of doing physics — their own models. And when you go to write the paper you always write out in a standard way that pretends like you did it right from the…like you wrote down the equations and solved them, or some silly thing which of course you never do. It was part of… Everyone has their own style privately, and it is one of my great regrets that these personal ways of solving problems never get into the 1iterature, so I little, or are so deeply disguised in the final article that it is impossible for a student to guess how the hell the guy actually did it. It is almost always impossible.
Bromberg:Yes, I really didn’t know that. That’s brand new knowledge.
Hellwarth:Well, that’s been my observation. Maybe somebody disagrees, but by God I think my students have found this. Anyhow, that’s a good point to break. This was after the post-doctoral year when I worked with Vernon and Feynman. I guess we submitted that paper some time at the end of that year. Feynman is very slow, so we probably wrote it sometime in the middle of the year, and we had a lot of other things to do. Anyhow, I kept contact with Cal Tech after I went to work at the Culver City plant of Hughes — the main plant. I notice on my vitae it says, let’s see: I was a visiting lecturer from ‘56 to ‘63. I think that is about right. And then, still at Cal Tech, that meant probably went one day a week. I know I helped run the…set up and run the senior experimental laboratory which they had never had for seniors before. And then it says: in ‘66 I resumed connection with Cal Tech, until 1970. Again, a day a week kind of connection while I was at Hughes.
Bromberg:Teaching courses and so forth?
Hellwarth:Yes. Teaching and doing collaborative research with people there. In this case, it was mostly with Professor George in the electrical engineering.
Bromberg:That is the same Professor George who went to Rochester?
Hellwarth:Yes. Nicholas George.
Bromberg:So that as we look at your papers, some of them may very well be papers that arise out of the Cal Tech collaboration rather than out of Hughes work. Is that correct?
Hellwarth:Yes, that is true. Especially, he and I were co-advisors — as I had an official faculty position — we were co-advisors of a very brilliant young man Del Owyoung, who wrote a… And we published a George, and Owyoung, and Hellwarth several things. Also with Bill Cook there, and George, and… That stuff came out of Cal Tech — and papers with Owyoung and George. But that was all in the second part of the collaboration. I didn’t know these gentlemen during those first early years when I stuck over in physics. The second years were over in electrical engineering and on the other side of campus. So I switched campus sides when I resumed my collaboration.
Bromberg:Also in early period were you doing some Joint writing with people at Cal Tech, in those first…?
Bromberg:I noticed there were two papers with Feynman that came out fairly late.
Hellwarth:No, that was during that period ‘56-‘63, I wrote on the poleron with Feynman and also with Platzman and Iddings.
Bromberg:I would be interesting to see how different the kinds of papers you wrote out of your Hughes collaboration, out of your…
Hellwarth:Yes, those had absolutely nothing to do with lasers or Hughes or anything, those papers. A lot of fun. And we had a lot of other papers we probably should have published, but they didn’t seem quite up to Feynman’s standards.
Bromberg:Well, let’s see. At Hughes you were working initially on servo mechanisms you said.
Bromberg:When you went to Hughes did you have…were you able to say what group you wanted to join? Or would they just assign you?
Hellwarth:They assigned me. I didn’t know anything about Hughes. I had applied there and other places from England, where I was doing graduate work, in my last year. I was just out of… Mostly, I just used clippings from; I think the Hughes clipping was from MECHANICS ILLUSTRATED, and PHYSICS TODAY. And I just sent these clippings, in fellowships available, or in the ads, to various places, I don’t remember. It was arranged by mail. I really felt, of course, later that I had a lot of catching up to do with my peers and the men of my year. A lot of them like Ron Shen, and Sorokin, and the other people of my time; I didn’t get to know them until very late, because I wasn’t a graduate student in America. I think it was a great disadvantage. And I hadn’t gone to meetings with them or Jim Gordon, or Zeiger, or all the people in Townes’s group, or Bloembergen’s group, or the great Berkeley group with people there, Whinnery, and the Standford group with Pursell and Lamb. I didn’t know any of these people. I had to get to know them all the hard way. But, everybody who tries this kind of aberration knows this is going to happen before hand.
Bromberg:At Hughes then, how did you get from servo mechanisms into masers? Because you showed me a report that is already ‘58, and you were working on masers, presumably in Lyons group.
Hellwarth:Yes. By then, I guess when Lyons came I must have joined him fairly soon after he came, because I heard this group that was working on this stuff that I liked and was interested in. And that was nice. And then very soon after that a corporate research lab took form. It wasn’t in form when I joined Hughes. And when this lab took form which must have been… Smith would know, I suppose… not far from the time when Lyons came, I tried and soon did manage to join the research lab, from whatever division I was working in before…transferred to the research lab.
Bromberg:And you were still at Culver City?
Hellwarth:In Culver City, yes. I guess it must have been an early experiment. A lot of…maybe IBM and Bell had corporate labs, and Kodak and all these places, but at that time Hughes had only scattered research efforts serving each 1ittle division, and the centralization was, I suppose, a big step for their management to decide to create a central research facility.
Bromberg:Surely IBM comes about the same time. I think it is a real period of corporate laboratory either formation or expansion. So that is an interesting thing that you just posed there. Worth looking at a little bit. So, somehow, in some order there is Lyons forming his maser group and you joining it and the …
Hellwarth:Corporate research labs being formed.
Bromberg:all be in there in this kind of…
Hellwarth:And then, once formed, planning this move to Malibu, which really occurred — I think it was almost two years, or a year and a half after they wanted to. And so much research just went on hold because of this move, that really shouldn’t have. Maymen, I don’t think that he managed to keep working very well, but I think that a lot of the rest of us just felt that I’m going to wait until I get there to do that. Just can’t set the thing up and then move it. And the delay of that move was greatly lamented by many people.
Bromberg:Did it affect you?
Hellwarth:For example, I had an office mate who drove me, very troublesome and very talkative and kept the whole day very difficult. And I said, well I’ll wait until I…before complaining to the manager, I could have probably gotten my office transferred. Well, I said, I am going to move to Malibu anyway, so why bother, I’ll just wait until I move and I will have my own office. And then to spend an extra year, losing four hours a day, to this office mate…or five or whatever. It’s funny to think of those little things. People should be warned to not put up for a minute with conditions which are not, which do not get them a good research environment. Never mind these moves.
Bromberg:Well, what kinds of maser problems were you working on then?
Hellwarth:I had one related to the maser, to make a gyroscope using the two-level systems. The famous spin-gyro, I think we wrote a lot of reports on that, which is a kind of a maser…could be uprated with an inverted populations in a masery form or not. And that report I just found was on maser noise, and did a lot of work on that. Because there was some interest….they knew these devices were very low noise. The question was, were they the lowest possible? Was there any way to make them any lower? Was there any other kind of device you can imagine that would get even lower noise than a maser? That kind of questions.
Bromberg:Did that involve questions like these line width questions? I mean, I know that the Gordon-Zeiger-Townes formula had a line width that was, is twice too big, and there was some question about whether they were attacking it with the proper physics. Is that kind of question that was related?
Hellwarth:That was one of the questions.
Bromberg:Was that a very big question?
Hellwarth:No, I don’t think it was a big question. More interesting was, when these things were not operated as sources — when they were operated as amplifiers rather than as light or microwave sources — as amplifiers, then their noise properties were very much more interesting. And Ted may even have stuck his ruby on the front of the Goldstone dish; he wanted to know then how much further can the space probe get away from earth then before and they could still pick the signals out? And it was really a big question. And it was a hell of a lot further.
Bromberg:Well, it sounds very much like it is connected with what Hughes is doing practically.
Hellwarth:Yes, that noise problem is very much connected with Hughes… And the other thing…of course, we were always interested in just going quietly to shorter wavelengths, not making the big jump to the optical, but there was the “OK, now we’ve done the x band, can‘t we go to the…you know we’ve done it at 23 jega[?]Hertz, can’t we go to 30 jegahertz(?), or 60 jegahertz, or into the millimeter region.” So, we had a big project.
Bromberg:With a maser-like…
Hellwarth:With a maser-like thing to make a hydrogen-cyanide, which had good possibilities to laser in the millimeter region. So I worked designing that kind of thing.
Bromberg:What happened with that?
Hellwarth:I think the laser kind of buried these things when it came along. Interest just got dropped in all these little things. Everybody jumped on to the laser.
Bromberg:As you said, that was going on until the laser came.
Hellwarth:Yes. Probably…It was Maiman’s ability not to get caught on these rather minor next-step problems and to make the jump that the rest of us just didn’t have. Because the company wanted us to go on to the millimeter, they said, “well we are a microwave company, but we might get into the millimeters.” God, never the optical, but maybe the millimeter anyway.
Bromberg:The thing is here, Shalo and Townes publishing at the end of ‘58 and saying, “Let’s make the jump into near infrared and optical.” And that didn’t make an…?
Hellwarth:That didn’t impress Hughes because Hughes says, “All of our business, all of our systems, all of our things are built in the microwaves. We are not an optics firm.” That’s all. It wasn‘t that they were afraid of a jump that wasn‘t their bag. They weren‘t…
Bromberg:But… Who is Hughes? When you say, “That didn‘t impress Hughes.” I mean, how was this personified? Was that…I mean, does your immediate boss say look, don’t fool around with…
Hellwarth:Whoever would have to sign the proposals? And that is why I raised this interesting question, is when did Hughes first allow the first proposal having to do with optics to leave their doors? Now, I imagine certainly the department and the lab head would have to sign the proposal. And my hypothesis is that until Maiman made the laser they were unwilling even to sign off a proposal in the subject.
Bromberg:I see. Where would we get a feeling, get a hold of these maser works that were moving toward the far infrared, or the millimeter waves? Is that going to be in the reports?
Hellwarth:That will all be in the Hughes reports because those were all supported by either internal funds or the signal corps, or somebody. We were always having to write reports about all our stuff.
Bromberg:And how did your projects get chosen? You were just looking around choosing what seemed interesting in the context of the Lyons…I guess it was Lyons, Birnbaum, and then you people? Or, Birnbaum was, Maiman…?
Hellwarth:I don’t know how the structure formally changed. I mean, Birnbaum was always a lieutenant of Lyons, and came with him from the Bureau — the Bureau of Standards — where they worked together.
Hellwarth:I think they were together. I’m not sure now how together they were, now. I’d have to… It would be fun to talk to Lyons. I hope you have a…
Bromberg:Well, he was there on Monday, by the way.
Hellwarth:He was? Did you have a chance to talk to him?
Bromberg:He talked a little bit publically, and Paul Forman has talked to him at some length. And he made a tape for me, which Paul did. I never queried him more closely on it. So the answer to your question is, half. I have half talked to him.
Hellwarth:He could at least remember when he came, when the labs were formed, and who was boss. And I don’t even know…I think Maiman was reporting to Birnbaum, who reported to Lyons. That would be my guess.
Bromberg:Well that is true. I just wondered if you were reporting to the same person.
Hellwarth:Yes, and I was very likely doing the same myself.
Bromberg:So, you were pursuing these things and Maiman was pursuing his ruby, well his laser work, his optical maser work.
Hellwarth:I think that was mostly done sub rosa, and his Hughes work was the ruby maser work.
Bromberg:Now how did you become involved in ruby maser work yourself? Is it what you just said, that when the laser succeeded people sort of stopped what they were doing and started to work on it?
Hellwarth:Yes, that was really what… That was the main effect. I had played around with Ted in Culver City. As I said, Leo Levitt was just starting a preliminary check of the ruby efficiency. Which then Ted, when he saw it was more frequent, went on to measure properly and carefully by himself. But I had more or less…I mean I was wrapped up in these other things and I didn’t really… I don’t know why it didn’t occur to me to pursue it on my own. But when the laser came along, everyone dropped what they were doing and jumped onto the laser.
Bromberg:And the first thing that I read of yours on the laser was ruby pulsations theory. Was that the first thing you did?
Hellwarth:I think that was the first paper I did on the laser. Yes and…
Bromberg:I would be interested in what the situation was at that point, in understanding spikes on a ruby.
Hellwarth:Well, I developed the right equations for a lot of stuff, but it wasn’t the… I don’t think it was the…, certainly not the complete explanation for the spikes. And I am not sure that that is even in, to this day that has remained a very mysterious subject. Now spiking in the helium-neon laser is fairly well understood on the computer — complicated computer calculation — resulting from an instability, it sometimes spikes and it sometimes doesn’t. The ruby maser was always so… it was both pulse and it was transient, and everything was going on… I would be curious at this stage if anybody claims to understand the ruby spiking yet. I wonder. I don’t know offhand anybody who would claim to completely understand that. But in any case, we got a good feel for the dynamics of what was going on, which right away suggested: Well, I don’t know if these spikes are doing that, but at least I could on purpose make spikes by this means, even though whether or not these are being made by this particular means or not.
Bromberg:What are the means we are talking about now? What I remember from that paper is a calculation of the population inversion as a function of time and of the numbers of photons in various modes as a population in time. What is the underlying mechanism that you got the feel for, just so that I know?
Hellwarth:I could see, at this calculation…it was clear that, this model said, if they are happening by themselves – what’s happening is there is a spike that erases the population inversion and then it takes a while to build back up again. And once it builds back up, there is enough for another spike. A simple idea. Then I said, well, if building up a population makes a spike, why not let it build up even more and make a bigger spike? And that was the… Staring at these solutions you could see right away, it seemed I could see right away that if you wanted spikes, and you could certainly have bigger ones if this was what was going on. Of course, people didn’t want spikes; that was amusing. They were a complete surprise — they were expecting a smooth output like the maser, and the spiking was just a surprising annoyance.
Bromberg:So, how did you come to give that paper then at Berkeley?
Hellwarth:Well, I got convinced, very excited, that this could happen and of course at Hughes at that time I didn’t have a lab, we had moved recently. And in fact, when I went to Hughes I got into a lot of proposal writing and report writing, and I was so good at writing reports that the division of labor sort of fell more to me to do that, and let other guys work in the lab. Although, up until that point I had always worked in a lab. For one reason or another I started doing a lot more paper work. I have some notes [PAUSE]
Bromberg:So, we were talking about the whole context for the work on ruby pulsations, and the idea of the giant pulse ruby. You were saying, at that point people were not really interested in increasing the spiking, but rather eliminating the spiking.
Hellwarth:Yes, getting rid of it. And my paper which had of good qualitative agreement with what was being seen was probably not entirely correct. I don’t think, till today…I mean I haven’t heard of anyone offhand who claims to understand the spiking in ruby because no pure ruby laser…laser controlled and pure enough to eliminate all possible side effects I think has been developed. I may be wrong because it is not a laser…The development of the ruby laser essentially stopped in the ‘60s, and one would need to get a perfectly controlled single mode laser, presumably, to start to understand the — as it appears now — spike. Nevertheless, the broad outlines…it was obvious that if you did want the spiking, instead of trying to get rid of it, it occurred to me that might be good to have it, and I could see that one could make the process that looked like it was going on even more pronounced if…in an obvious way, because the equations for the Q-switching were all in the original paper and you just put different conditions on the equations.
Bromberg:Somehow with management general1y interested in work on the ruby laser I would think they would just say, fine, this is another aspect of something we are very much interested in. That didn’t happen? You know I would kind of have expected them to want to do all of this…
Hellwarth:No, I’m not clear. It’s curious. Anyhow, in order to publish at Hughes, then as now, you had to have a patent clearance, and I thought it might be fun to patent the idea of the Q-switch, but I would have to do that before I submitted the paper to the Berkeley Conference, so I did. So I tried to get them to apply for a patent, and they said they didn’t think it would work, and it wasn’t worth applying for a patent. Having said that, they had to give me clearance to publish the paper. So I got the patent clearance to send it in, because they weren’t interested in patenting it.
Bromberg:This is just the lawyers who make this estimation?
Hellwarth:No, they had a patent review committee. I don’t know who was on it ever. Every company has a routine patent review committee.
Hellwarth:Which is scientists, presumably the bosses, I don’t know. Whoever. They can ask anybody’s opinion they want. They just have the lawyers … The lawyers certainly don’t make that decision; it is a scientific decision. And I guess, in a funny way, lucky for me, because if they had wanted to play around with the patent I might not have had permission to submit it for publication, and that would have been harder to talk about it publically. And when I presented it at the Conference, I remember there were some other people from Hughes — at least one — and nobody were very impressed… In fact, I drew on the board, and I have a photograph of myself — somebody took it, every speaker got his photograph taken — and I had on the board the pulse going up to 10 megawatts and about 10 nanoseconds long with the figures on it, which is exactly the pulse that came out of the ruby laser Q-switch when we finally got it going, so…the rise time, the fall time, the peak, and all that, which was all explained in this paper. But, anyhow…People were not… There was a lot of wild things being said, and of the people that I talked to, only Basov was interested, and was supportive. And he went straight home — and he was young and poor himself — and he said, I don’t have any Q-switches, but I have a rotary wheel chopper to break up the beam. I have a hole in a wheel that I can spin fast. And he went home and he put up his chopper wheel and he got some enhancement of the spiking. As the wheel went by the spiking would get a little bigger and then die off. And he published it, saying Hellwarth has the idea that I think will work, here is sort of…this is a little bit of how it might work. I don’t have good apparatus. And that was in this…That’s interesting, here, I was sure it was a Russian journal, and this may not be the reference, I have a reference to Basov in APPLIED OPTICS, and American journal, which probably came later, so…
Bromberg:Well, it probably has the original reference in it.
Hellwarth:Probably the original. In my original paper McClung has the original reference in it, but I don’t have a copy of that.
Bromberg:Ok, well then I can see… Did you have any correspondence with him about that?
Hellwarth:No. Not after that meeting. I didn’t correspond. I saw him many times at other meetings, and we talked a lot. I’m sure… He sent me a reprint when it came out; I don’t look through the Russian journals, so I wouldn’t have known about it. So when it came out he sent me a reprint
Bromberg:I had the impression that you cited a lot of Russian literature in your later papers at least, which made me think that you even might read Russian.
Hellwarth:No I don’t, but I try to keep up because so much is being published. And now… I mean… Well, I got into this Brewin [?] scattering business, which was much more worked on in the Soviet Union than here, and that is one reason why… most of the work is being done in the Soviet Union.
Bromberg:But at any rate, at this point you were not reading Russian journals?
Hellwarth:No, I wasn’t.
Bromberg:Do you have any other impressions, by the way, of that conference. I was interested in having you say that there were a lot of wild ideas floating around, which makes me think, you know it had a certain ambience of people being a little bit…you know, floating a lot of blue sky propositions. Was that a feature of that conference?
Hellwarth:Well, everybody was extremely excited, of course. And, clearly, big things were happening, and…blue sky, I don’t know. My impression was, I guess people were not at all envisaging what was going to happen. I think they were very excited, but I don’t recall hearing any prognostications which later came true. I think it was very hard to imagine what was going to come, and I mean, everybody talked about communications and that was the main theme.
Hellwarth:Because it had such an enormous band width they could now have great communication. That was the thing they saw most, I think. For example, it became a great spectroscopic tool later, but it wasn’t until Porto — who used to work here — started pushing the laser as a spectroscopic tool and did so by himself with very little support or help from anywhere else, on a very low budget. It took years for anyone to get interested in that aspect, and so forth. So a lot of these things were surprisingly not envisioned that well. Myself, happily, at some point in the following spring, I wish I remember at what point, when I met Fred McClung who had a laboratory and apparatus, and his department was breaking up in this great re-organizational turmoil, and he was working…and he switched into the department where the lasers were and had time on his hands and the equipment and the interest, to work on this setup, and started… When I first met Fred McClung, and I would think it must have been mid-‘61, so probably it perhaps was not the experimental results…or maybe it was some preliminary experimental results that… I persuaded Hughes to apply for the patent after all just days before the deadline, and in those days because it had already been spoken about publically, you lost your European rights, but according to patent rules of those days, up to a certain point, you had all American patent rights, even though it had been spoken about publically. So they rushed an application in for the American.
Bromberg:I see, so they re-reviewed it and decided…
Hellwarth:I persuaded them to re-review it and apply. At least I’ll say I must have really believed in it because I kept trying to plug it and drum up interest and get somebody to get money and support or patent or something. And I talked about it at a Physical Society meeting again that spring, at some little — in Pasadena, I remember, one of the local Physical Society meetings.
Bromberg:And the context of your believing in it was just that you could use this high power to do things that would be interesting to do?
Hellwarth:Yes, and I could think with that high power…I imagine you could do…yes, I don’t know. I don’t remember precisely, maybe I should look at all the things I imagined you could do but…
Bromberg:That would be lovely to find a little memorandum, or something like that saying…
Bromberg:Of course at that point you were beginning to get optical harmonic generation, which is certainly one thing you can do with high power. I don’t know if that influenced you at all.
Hellwarth:Yes. I think it must have been very much at about this time that there was the first report of optical harmonic generation.
Bromberg:They were doing that experiment during the summer of ‘61, and it took them the whole summer. They had a tough time with that experiment. So it must be coming out late summer or early fall that would be.
Bromberg:So that might be…
Hellwarth:One thing was clear. One thing I know I did calculate was how easy it would be to get an echo from the moon. For example, if you had a pulse at high… just to get echoes.
Bromberg:I see. Were you also thinking about radar? Would that have entered in there?
Hellwarth:Well, yes. Hughes had already, instantly, been interested in radar, even with the spikes. And they had, right away started radar experiments. They were happy to have put out a giant pulse at all. So it was clear. I could say, “Look, if you can do it, look how much easier and better you could do it if you had this.” Probably that helped persuade them, because they were a big radar company. That was very much in their interest, and the…that was probably 90% … I don’t know, a large fraction of their business. So…and I will say, in all of the ensuing patent fights with Gould, which they eventually won, they wisely and purposely slowed the process down, realizing that they would make a lot more money if the clock started later on the patent. You see, it’s only until these interferences are…It is only when these interferences are settled that the 17 year clock starts. And they managed to put back the starting of the clock, God knows, until ‘70 or something in the seventies.
Hellwarth:So, they are now enjoying enormous proceeds from this patent which is 23 years old and will continue to do so.
Bromberg:I see. I didn’t realize that about the interferences. I somehow thought it started from the date of application.
Bromberg:I don’t mean the date of application, the date of granting.
Hellwarth:No. They managed to hold back the clock so it doesn’t start until… And purposefully, I know, talked to the lawyers, so they really happy to drag the proceedings out and drag them and drag them. Because they could see the business growing exponentially while they…
Bromberg:Do you get involved, by the way, when you and McC1ung got this to work? Does that mean you get involved with people in the radar department and so on? And how to put it into radar…
Hellwarth:Yes, a little bit. There was a group formed to make laser radars, and I worked fairly closely with them, and Eric Woodbury was one of this group who saw the strange light that we later found was Roemen(?) scattering.
Bromberg:So, you though physically at Malibu would be working with Woodbury?
Hellwarth:Woodbury was physically at Culver City while we were physically at Malibu, yes.
Hellwarth:Nevertheless, we kept close touch and went back and forth and you know it was nice, having only been recently at Culver City. I think a lot of us felt very much at home there so we were not as separated as we might have been had we historically not just come from there, recent1y, anyway.
Bromberg:So, I’m getting the picture, which may or may not be correct, that you were already collaborating with Woodbury on the application to radar of giant pulses and then as he began to make his observations, you would have been very close to them. Is that a correct way to see it?
Bromberg:And then, I know that at some point after Woodbury started his observations McC1ung and some co11aborators of his started to work on the same kind of material, I mean these…
Hellwarth:Oh, yes. We certainly heard about it. I was in a conference in Colorado, I remember, and McClung called me up and we were in daily telephone contact, sort of starting to…
Bromberg:There is somebody that crept up here, somebody named Morrel Cohen?
Hellwarth:Morrel Cohen. It was in the summer, a summer conference, and Morrel Cohen was visiting that summer. He was one of the distinguished professor visitors and a long-time friend since, and was a wise, experienced man who was just wonderful inspiration and help — I remember — to all of us youngsters. He was kind of a great elder physicist in our midst and he was very…
Bromberg:I see. So he was somebody you were actually talking to about this?
Hellwarth:Yes. I came back from Colorado, and I guess the other guys were talking to him — everybody was talking to him — because you know summer visitors are sort of fair game. You feel quite free to walk into their off ices arid badger them because that’s sort of what they are there for. And indeed, yes, we did talk to him. I just remembered he was great to talk to. I wish I could remember some specifics.
Bromberg:I am actually quite confused about this whole business of elucidating the stimulated Roemen scattering. And this is the reason. I get the feeling that Woodbury and McClung and these people are seeing things they are associating with Roemen scattering at certain frequencies and multiples of those frequencies and yet it is you who have the insight that it is simulated Roemen scattering, and therefore I am a little confused on what the various insights were, that you had to have. I remember, glancing at your paper — I don’t really read these papers, I sort of look at them — that you point out…There are a couple of things that you point out. One is that the wavelengths are the Roemen scattering wavelengths, and the multiples that you would expect. But another is that I don’t remember what — the intensity or something is proportional to the factor n+1, and this is what you get in at simulated scattering. And I was trying to figure out what were the various insights that you needed to get somewhere with that, and what were the particular insights that you were bringing to the considerations that were going on among all the collaborators on this list, I guess there were…
Hellwarth:Well, first of all, Woodbury and Ng didn’t realize they were seeing Roemen scattering at all, and hypothesized in their paper that what they were seeing was another line of ruby that was thought to exist. And I am ashamed to say, that for a long time we didn’t realize we were seeing Roemen scattering because when we went to look up in the tables — I don’t know who — in the Landolt-Bernstein tables, have tables of Roemen shifts. We didn’t go to…We didn’t have a copy of the standard Roemen works. Why would we? We weren’t an optical shop, and nobody there was an optician. We did have the standard reference tables, and the one I know of, which has Roemen lines, is the great German series about 6 feet long, called Landolt-Bernstein, and it is in German. Well, whoever looked up Roemen lines got instead code numbers, thinking they were wave numbers, and in fact, we later…they didn’t match at all what we were seeing.
I don’t know how long it took us…So we were really put off for a while. I mean, that really held us back. That was a…So the first attempt to identify it with Roemen scattering failed because we had the wrong numbers for the Roemen shift because we couldn’t read German, or whatever. And the peculiar organization of these tables is such that there were numbers like…the Roemen shifts are like 1300 wave numbers, inverse centimeters, and the code tables, the table headings were all the same size, like 2015 or 1847. They were numbers the same size, so we thought we had the Roemen shifts, when we had the table numbers. Well, so I guess we… After more of us started looking at these tables, and we started pursuing them more closely, I guess, we must have come upon there with some doubt and we had to…But I was amused, because I do remember we had that confused at first. And then, secondly, as soon as you saw that it did match these level shifts — now Roemen shift gives the splitting between some two ground state levels—start in one and end up in the other, and the difference in the photon frequencies is this difference. In all of the — in nitro-benzene — and all of the first dozen liquids we tried there was always visible a very slight absorption, to some level near the ruby wavelength. And so, if you made an estimate, it was always possible that these were just lasers, just like a di-laser. So, it would appear always that we had a di-type laser, the ruby was just pumping to an excited level and it was lasing to this other level, which is seen in Roemen scattering when you are off resonance. And we really struggled…We had hoped it was Roemen, it would be more exciting than if it was just another laser. And we inordinately struggled to show that wasn’t a laser.
Now, today, anybody who sticks a liquid in and gets one of these lines, they right away assume its Roemen and it’s very funny because I’ll bet you every once in a while that they’re wrong, that they’re actually getting not Roemen, but this true laser action. And I think I was the only one of the group who had good quantum mechanical background, and I had done all this quantum mechanical noise studies with Feynman that were actually not published, and some of this was published in Vernon’ thesis. A lot of fancy quantum mechanical noise studies, and I had all this, so. And I stimulated the emission forwards and backwards, I thought, that was…And stimulated emission has the n+1 and so, using the perturbation theory and just the straight forward way you use it to treat Einstein-stimulated emission, the next term in the perturbation theory which treats this case also has an n+1 with some other factors, so it had a very close analogy to Einstein-stimulated emission, the n, n+1 was in the same ratio, it was just…only with the populations upside down. I mean, you had gain when you didn’t have inversion rather than gain when you did have inversion. But it was a very close analogy otherwise. And I remember when we realized it was Roemen scattering, we didn’t know what to call the effect, and of course, down in Culver City, the chief of Woodbury and Ng…