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Interview of Joseph Anthony Giordmaine by Joan Bromberg on 1984 June 4,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Graduate and postgraduate work at Columbia University under Charles H. Townes, 1955-1961; the maser receiver for the Naval Research Laboratory. The early quantum electronics conferences at Schwanga Lodge (1959), Berkeley (1961) and Puerto Rico (1965). Nonlinear optics researches at Bell Laboratories and Munich's Technische Hochschule, 1961 to about 1968; optical parametric oscillators. Picosecond pulse measurement techniques.
I’d like to add a few remarks on the recollections of the Schwanga Lodge Conference and the kind of impression that that made on me. I guess the presentations there by Art Schawlow and. others which addressed the issue of extending the maser techniques to the optical or long wavelength Infrared and optical regions certainly made a very strong impression. They were among the strongest influences on me and many others at that time and led me to the feeling that the future in this business and the opportunities were in optics and led me to the feeling, led me indirectly to the conclusion when I went to Bell Labs to make the transition to optical research initially my idea was to make the transition to high resolution spectroscopy and spectroscopy as I mentioned before.
Do you remember anybody else talking to you about those papers at that meeting?
It was a topic of very general discussion, and I think that was one of the most exciting areas of discussion at the meeting, these possibilities of extending, I recall, rather than any particular discussions I simply recall the climate of the meeting as being one that was leaning very much toward, groping toward, the possibilities of extension to the optical region. Because one thinks of Seroken and Stevenson and one thinks of Weider, Irwin Weider, and of course Maiman as all people who in some way or other might have been inspired or have their research direction slightly altered or something by the meeting. So if any particular comments come to your mind, I guess... I guess the one thing I can say there was that the overall climate focused on the extension to higher frequencies in a very strong element in the discussions there.
Interesting, because of course you can’t tell that from the proceedings at all. There it’s a very minor part.
Now going down the list of topics here, I came to the discussion of the work that I did on picoseconds optical pulses and techniques for measurement of picoseconds optical pulses. I became involved in these picoseconds pulse considerations first during a sabbatical at the Technical University in Munich with Wolfgang Kaiser. Wolfgang Kaiser had a group including graduate students, particularly Max Maier at the time, who were involved in stimulated Raman studies, stimulated Raman back—scattering studies. Now in stimulated Raman back—scattering, the fact that the Raman pulse, the stimulated Raman pulse, is observed in the direction coming back to the laser allows a radically different technique for, allows a radically different phenomenon to occur in stimulated Raman scattering. Namely, the generation of a pulse which is much shorter than the pulse, than the laser pulse that’s generating the radiation? The idea being that as the relatively long laser pulse of a few nanoseconds or longer is generating the Raman Effect in the liquid. The light that is generated at the far end of the Raman cell from the laser, it occurred to us working together at Munich, propagating back to the laser, if the pulse conditions were correct, that pulse propagating back to the laser could build up to such an intensity that it would start sweeping out the laser light in front of it so that all the laser light would become accumulated in this backward traveling pulse, so that this backward traveling pulse would acquire a very sharp leading edge, and in the attempts to study that phenomenon, the problem immediately came up, well how do you measure pulses that are as short as, short, small fractions of nanoseconds into the tenths of picoseconds kind of regime. Well it occurred to us, the group of us working in Munich at the time, that a way to do that was by a correlation experiment in which you take the pulse that’s coming out, whose length you want to study, and you correlate it with itself because that’s the shortest pulse that you have available in the experiment, and this was done in our initial case by splitting the pulse into two beams then taking the two beams and combining them in a second harmonic crystal and looking at the output of that second harmonic crystal, as you change the relative delays of the two pulses that are coming in.
How did that idea come up? Was it one of several or did somebody particularly have experience with that correlation technique in the group? No, I think it came up, the work was being done in a stimulated Raman kind of framework, but all of us had exposure and familiarity with second harmonic generation techniques, and I had been involved in that for some five years at the time so that it was natural for us to come up with the idea of a second harmonic correlation method. I mean perhaps more natural for our group than for other groups. So that in the course of discussions, among the three of us, particularly Kaiser and Maier and myself, this idea came up and it worked very quickly. The experimental work was done mostly by Maier, with myself and Kaiser doing mostly the consulting and coming in and watching, and this worked very quickly, and we published a paper which, together with the work that was done independently by John Armstrong at IBM Laboratories, which is on a completely independent track, these two papers came out almost at the same time. I think ours came out first but Armstrong’s had a slightly earlier submission date. But these two papers came out at about the same time, and these were the first papers on optical correlation measurements of picoseconds light pulses. After I returned to Bell Labs later, in work with Stanley Shapiro, who came to Bell Labs at that time as a postdoc, we came up with ways of extending that technique involving two photon spectroscopy, two photon pulse generation, I’m sorry, two photon detection of ultra—short pulses in liquids.
Now we could talk about that although I would like to get a little more information on your trip to Munich. I don’t know which to do first. Maybe we should go back a little bit to Munich because I would like to know when you came there what you were planning to do and what, how the work there compared with your U.S. experience. This was the first time you were going to do your physics in another situation, in another country?
That’s right, yes, yes.
I think it’s very interesting from the point of view we’re not yet interviewing European or Japanese workers, so it is interesting to get from Americans any feeling for different approaches or different strengths and weaknesses or influences that will give us some insight into that. I would like to know what you think on that.
I think the experience of Kaiser’s lab at Munich is a good prototype example. Kaiser had had exposure to the laser techniques at Murray Hill at Bell Labs, and in fact, he was one of the first, earliest groups at Bell Labs working on fluoride crystals as possible laser sources before the first laser was demonstrated by Maiman. So he had been thinking about laser opportunities here since before 1961 in collaboration with Geoffrey Garrett to a large extent. Now in ‘62, or around that time, Kaiser had a sabbatical in Europe. When he returned, he and I worked together for a year or two, first on the use of crystal, first on the use of various special crystal geometries as reflectors for lasers. Then we also started to work on the stimulated Raman Effect, working toward the demonstrations of the stimulated Raman Effect in calcite and the demonstration of coherent scattering of light from stimulated excitations of phonons in crystals. In the area of ‘64 or late ‘63, Kaiser left to accept the chair in the Physics Department at the [???] in Munich and started to build up his group there.
So he was really building it up from scratch?
He was building it up absolutely from scratch and there had been relatively little optical experience there. There was some optical spectroscopy experience there but very little laser experience. So that he was starting from scratch, so that by the time I arrived there in March of #66, this work was well along and there were several laboratories set up generating nanosecond laser pulses using queue—switched laser techniques. They had a lot of strength although they were somewhat isolated there compared to laboratories in this country working on these pulse laser techniques. They had the strength of a large and very dedicated body of graduate students who worked very hard and often worked at nights and on weekends and I think their effectiveness, I think owed in large part to a tradition that Kaiser brought from the United States of being familiar with American work habits and the intensity of the work and transmitted that to the graduate students in his organization and I think he transmitted to them a sense of urgency and some of the competitive sense, competitive quality that characterized American work in laser physics in those early years. So he brought that over there with him and so by the 1966 period the group there including Maier and Penskover and a number of other students was indeed a very active group with several lasers in operation so that the time I arrived there they were able to carry out stimulated experiments of some degree of real sophistication so that the, recognizing the possibilities for the backward stimulated Roman processes, the generation of extremely short pulses, they were able to, as soon as the idea of detecting the pulses by these auto correlation techniques, as soon as that idea emerged in our group, they were able to demonstrate it very quickly.
Maier was one of these students?
Maier was a student at that time, yes, yes. He’s now a professor at the University of Beiroit. At that time he was a graduate student and he was able to demonstrate this very quickly. Another key member of the student group there at that time was Alfred Laubereau. These people were very strong experimentalists and they had solved many of the problems of poor reproducibility of the laser pulses which dogged the work in this field at that time.
Was this work of a sophistication comparable to Bell or comparable, not that high or how would you?
Oh I’d say it was in this field. I mean the amount of work going on in this field at Bell wasn’t very large, I mean there might have been three groups at Bell doing work in this area, no more at that time. The experiments were relatively primitive by today’s standards namely one laser pulse perhaps every minute or so and the single pulse methods of analysis and so on. So that I would say that at that time and continuing thereafter, they were at a comparable level to the experiments at Bell Labs.
Had you gone over, by the way, with some very concrete plans that you wanted to work out with Kaiser or you went over and sort of pitched in to their research program?
Yes, I’d say it was more of the latter. I mean, Kaiser and I had started a series, some experiments on stimulated Raman experiments before he left and that we continued to correspond on and his group was very much involved with stimulated Raman so it seemed that I could play a role there and I fully expected to pitch in to their work. I also was involved in another project there, namely a project with a graduate student named Zimbro on Cerenkov radiation, kind of Cerenkov radiation in a second harmonic experiment. That emission occurred from a distribution of second harmonic polarization in ways that satisfied the same kind of relation that Cerenkov radiation bears to the particles that generate Cerenkov radiation in nuclear physics, and the result was that the second harmonic generation came off in a ring like, somewhat like Cerenkov radiation comes off. But the principle activity there was in the stimulated Raman and on the pulse generation. I think that work and John Armstrong’s work in this country really launched the idea of, launched the subsequent work in the detection of picoseconds pulses and I think, I like to think that it was a real incentive and a push to really develop the picoseconds pulse work further.
You were pretty much in touch with Armstrong as you come back?
Oh after we came back, well I guess at the time our papers came out we knew what each other were doing but, at the time, neither of us knew that we were working on that particular subject. No, when I came back, shortly after I came back, the idea of combining the pulses in liquids and using the auto correlation technique in liquid’s so that the pulses instead of crossing in a second harmonic generation crystal and in which the auto correlation had to be done by moving the or introducing a delay into one of the paths of the optical beams and doing a whole string of delay measurements, which was an extremely demanding process, because it required that the laser operate reproducibly over the many pulses that were required to do the auto correlation experiment. That was very demanding on the lasers at that time because they simply weren’t that reproducible, they were multi—mode lasers, their mode structure changed from pulse to pulse, at times, they were not actually single transverse mode lasers at that time, although you want to try to make them as close to single transverse mode as possible. Because of the poor mode characterizations of these lasers, they were not very reproducible, so that a great deal of care had to be taken to get a series of measurements that could be used to make these pulse duration measurements, so that the pulse duration tended to be often the whole experiment rather than just the technique that was, rather than an available technique to study the physics of the process. So at the time I came back to Bell Labs, I guess I was very sensitive to the need for an improved process and, together with Stan Shapiro, came up with the idea of combining the pulses traveling in opposite directions in liquids. Now at the time that we had this idea, the question of the two photon emission in liquids came up. Namely, what liquids could you use that the two photon on linear process would absorb two photons of the laser light and then radiate it, what liquid could you use that have an adequate intensity? So at that point we went to Peter Randsepez because he had done a lot of work on two photon generations in liquids and had a thorough knowledge of the chemistry and the relation of the chemistry to the optical properties and asked his help in selecting a liquid. At that point, when we came to him, he told us that he had come up, he had had similar ideas of his own which we hadn’t realized and, so immediately subsequent to that he suggested some appropriate liquids to us and then Shapiro immediately in working in my laboratory at the time demonstrated the two photon absorption process, the two photon detection of pulse lengths.
Randsepez himself was not involved in this experimental effort?
Yes, he was involved primarily in, yes, his contribution which was a very important one was to suggest and provide some of the liquids involved that had the very strong two photon absorption coefficient.
And were you also kind of in this as a consultant, as you were with Maier, or were you actually in there working with Shapiro?
Well at that point, Shapiro did most of the, almost all of the experimental work, and it was Shapiro who really was in the lab at the time the effect was really seen for the first time, and many others contributed too. Ken Wecht, who is my technician for many years at Bell Labs, he’s a Senior Technical Associate at Bell Labs, he contributed a crucial part of the experiment. Our idea was to combine the pulses moving in opposite directions by a beam splitter, you beam split the pulse and pass the pulse in opposite directions through the liquid and you just take a picture of the liquid with an ordinary open shutter camera. And this was the principle, and this was feasible and this worked. It was Wecht who, I believe, who had the idea that if you just take the pulse and [???] it into the liquid with a mirror in the liquid and then it reflects back off the mirror, that you would get the same effect.
This was a very exciting time because there were a number of elements in the physics that were only very poorly understood at the beginning, namely the relation between the distribution of light in this two photon generation experiment and the duration of the pulse. With certain model, with certain kinds of pulses, namely ones that did not have chirping, ones whose whole frequency spectrum was determined by the width of the pulse itself rather than by some internal frequency variation during the pulse, with pulses of that type, the distribution of light in this two photon fluorescence technique gave immediately the pulse duration. However, it wasn’t understood fully at the beginning that if the pulse had frequency variation during its duration that that frequency duration, that frequency variation, would in fact influence the result and distort the results, so that it became clear largely as the result of collaborations with others, namely, Michele Duguay and John Klauder. John Klauder having had a very extensive background in thinking about optical coherence phenomenon, John Klauder had interacted with physicists at Rochester in earlier years and had made very important [???] optical coherence theory and the issues here now became very closely related to the statistical properties of radiation, and as he became more involved with the problem, it was clear to him that there were very serious issues here that had to be resolved before the results of the two photon fluorescence experiments could unambiguously be used to determine the pulse width.
I’d like to actually go a little more slowly than we are so that we can get a little more into the hurly—burly of, you know, I’m wondering who was reacting to the two photon fluorescence right away, who was interested at this point in this kind of thing’ as this a situation where all the mode locking people DeMaria and Harris and so on, you know, this was the audience for this?
Yes, that was the principle audience at this point.
Did you give any talks where you were interacting with these people and you might recall what the discussions were?
Oh yes, one of the key talks here was a Quantum Electronics Conference at the time which was held in Miami, and I believe this was the ‘68 conference This came in for a very extensive discussion, namely the question of resolving the relation between the displays that one got in techniques of this kind and the duration of the pulses, and I think the discussions that occurred at the Miami Quantum Electronics were, I think left a general understanding of what was going on. Namely, that in order to have an unambiguous demonstration of the pulse widths from the two photon fluorescence experiment; you had to know something about the frequencies spectrum of the pu1se.
Did Klauder already, he was participating or he came in after the Miami meeting.
No, he had been involved before the Miami meeting, I believe it was around the time of the meeting but I believe it is somewhat before.
And he’s at Bell? These are conversations you’re having here?
Yes, these are all, yes; Duguay and Klauder were both at Bell.
That’s interesting because I did ask you before about the impact of coherent studies and this apparently is a place where they do affect the course of one’s understanding.
That’s right, that’s right. This kind of analysis of a phenomenon like this is very natural to someone involved in statistical, who has thought deeply about statistical properties of radiation, so that Klauder was able to make a very important contribution to the understanding of this process and with the way it actually worked in measuring pulse durations because of his background in that area.
Was there a lot of mode locking in going for picoseconds pulses right here at the time?
Yes there was Peter Randsepez had his own laboratory concerned with picoseconds pulses and as did Michele Duguay.
So there must have been a lot of discussion with them?
Yes, oh yes, yes.
But Shank and Ipan were not doing their work yet? You don’t recall them as participants in this?
They were beginning, I believe, around this time. But at that time, most of the interactions that I had were with people at Murray Hill.
Oh, they weren’t at Murray Hill?
No. They were at Holmdel.
Okay, if you have any memories of the way the issues came up or ideas that were reached in discussion or even how some of these crucial ideas first appeared, you know, we can always come back to that or if you have any memories now just to get some of the detail on the, on how events played themselves out. Or another thing, of how you characteristically worked up these things. This is something we haven’t talked about very much, but I’m always interested to see whether a person mostly does, carries out some theoretical calculations first or carries out some cut-and—try experiments and then, you know, the interaction of theoretical with experimental, or even whether the experiment sends you back to redo certain parts of theory. For example, did Klauder’s work send you back to any new, doing library work, this kind of thing, is always...
Well, I tended to work in a mode that combined experimental results and theoretical work at the level of coherent wave interactions and essentially at the level of the Bloombergen type of analysis of nonlinear materials. I tend to combine theoretical work at that kind of level and experiments, and in some cases, some of the results that I obtained, that I felt were the most important in my own results, was cut-and—tried. An example of that was the second harmonic generation work, the initial phase matching result, in which the initial possibility of increasing the emission substantially was obtained by cut—and-try, then I went back to the theory and tried to understand that better, and that led to the full understanding of the possibility of phase matching. On the other hand, the two photon fluorescence spectroscopy, that was a case in which the theoretical understanding preceded the experimental work, because there was a recognition that the technique for measuring the two, the pulse length, really required any kind of nonlinearity, essentially any kind of nonlinearity allowed you to the correlation experiment, and it was clear from the fact that there were two photon absorption processes going on that that two photon absorption process and the peaks in the distribution of the two photon fluorescence could provide a very simple way of making the pulse measurements.
I see, I didn’t, I guess I didn’t see that clearly when you first described that. In fact my first question about the Committee on Basic Research for ARO is really whether this was the first such committee you were on, just to fix...
On the Committee on Basic Research that advised the Army Research Office at Durham was a mechanism that the Army Research Office used to review papers in Quantum Electronics. At least, the responsibility that I had was in, specifically in Quantum Electronics and when an academic or industrial researcher submitted a proposal for research to the Army Research Office, it would go to the Quantum Electronics member of the Committee and I would select reviewers of that proposal, up to three reviewers for the proposal, and these were typically, I would make an effort to find reviewers both in industry and in the academic area and then I would receive their reviews and then send their reviews back to the Army Research Office management along with my summary of the proposal so that, and of course, along with the original reviews themselves, and, so this provided a, I believe, a very effective mechanism for getting a combination of academic reactions to the proposal as well as to, a reaction from industrial people. So I think that that mechanism of this Committee and the way it functioned in basic research was a very effective mechanism of having a variety of inputs, not just academic inputs, into evaluation of basic research proposals that the Army supported. Ultimately, I think the Army supported at that time, research that, with criteria that really stimulated, really fundamental understanding in areas that, at least the reviewers and I at the time considered were open—ended. There was no attempt made to look hopefully in a narrow, short—term kind of view, a long—term view was taken. But it had to be in an area that looked in some way pregnant that looked in some way open — ended and the Army Research Office was very responsive to suggestions and the composite view of the industrial and academic reviewers was almost invariably responded to in a positive way by the Army Research Office.
I didn’t know about the existence of this kind of refereeing, process which is interesting, and also reinforces what you hear universally about these agencies, ONR and so on, in this period. The way in which they supported research, I think is a very interesting...
Many of these agencies showed a tremendous vision, I think, in stimulating work in Quantum Electronics. The Office of Naval Research was another, as well as the Air Force Office of Scientific Research; I think all of these organizations had the freedom and the flexibility and the vision to, that really resulted in this, was a large factor in the rapid motion of this field at that time, rapid growth at the time.
The personnel of the ARO, were they mostly civilian scientists, were they people you knew, you got to know in this way?
Yes, they were the people that I interacted with were civilian scientists These were very knowledgeable people, and I gained a tremendous respect for their judgment and for the charter of their organization really in supporting forward—looking work.
If you have any other comments about this subject, I’d be glad to hear them, in terms of laser technology in physics, generally, and otherwise, should we go back to the very beginning again?
All right, let’s do that.
Now here are some holes which you may or may not recollect what should fill these holes, but I want you to see if we could. I want to go back to 1956 before you heard of Bloombergen’s work and just when you’re beginning to explore with hang and Javan, possible solid state masers that are going to do what Townes wants them to do for radio astronomy. Whether you have any memory of the first tax you took, the first things you’d started to calculate or else whether you know where we could find those things in notebooks and so on, that would just indicate where you were looking prior to hearing of the Bloombergen scheme.
Well at the moment, the only thing that was available in a solid state device, and we are convinced that we had to have a solid state device in order to have the bandwidth and the game bandwidth product that would be needed to have a practical amplifier, it was clear that that had to be a solid, that was the only way that you could get the adequate inversion of population. Townes had demonstrated, during his sabbatical in France along with Combreseau and Honing, that you could demonstrate negative temperatures using a temporarily inverted population by various kinds of adiabatic fast passage so—called techniques, in which one swept the magnetic field, to sweep the magnetic resonance through the frequency of the cavity and lead to an inversion of the population in a transient kind of way. So that the first thinking that we did was simply based on those kinds of considerations, and we acquired the initial work, in fact, can largely consist of setting up the laboratory at that point, with the paramagnetic resonance apparatus, there was no solid state work at Columbia at that time as I mentioned, so this laboratory had to be set up and the initial intention was to reproduce some of the Townes’ experiments involving those two-level systems. But by the time the laboratory got set up, before the laboratory really got set up adequately to do serious work in the field of the Bloombergen work [???], and so that by the time the lab was ready the Bloombergen technique was available and everything meshed together in a very fortunate kind of way.
Good, that fills that very nicely. And so you just picked up on that immediately. I mean, well it was just a matter of reading it and saying, “Yes, Oh yes!” It was clear that, it was immediately clear that that was from Bloombergen’s result and I guess the first results from Thayer, Scoville and Sydell that that was the way to go.
Although that must have been somewhat later Bloombergen’s work, the Sydell, Thayer and so on is just the very end of in July of ‘56, I don’t really know the date it hit the desks of all of you. It must, was it one of these little seminars that Townes liked to hold that somebody reports on the Bloombergen, or you don’t recall that in detail?
No, I don’t recall how we learned about the Bloombergen work, but it was clear from the very beginning that his calculations were sufficiently clear and the physics, once it had been, like all very important theories and contributions, once you had the idea, it is very clear that there was the potential there for the gain in bandwidth that one would need. So it was from the very beginning, I’ve forgotten whether we saw that in a preprint form or just how we first saw it, but it was clear that would do the job, and I believe we immediately, at that point, started, well by the time, we were building the laboratory at that time so all of this is sort of merged together, but, by the time the lab was completed, I believe the Scoville experiment had been reported.
And probably since Townes was consulting there he might have known a little bit earlier than others.
Yes, that’s right. In fact, Townes’ consulting at Bell Labs was a significant input to the graduate students at Columbia. We tended to know what was going on at Bell and had good contact with Bell Labs people so that the experiments, for example, of people like Thayer, Thayer gave at least one seminar at Columbia and preprints from Bell Labs were available at Columbia as soon as they were generated at Bell Labs, so this speeded up our work considerably, so that we would have been available, we would have been aware of the Scoville—Thayer work long before it came to publication.
Now another little gap. You were working with potassium chromo cyanide and that wasn’t satisfactory, clearly and then there was the result of Cacouchie and his group on Ruby, which I assume you got at through the Journals again.
Yes, that was through the Journals, well it may have been through a preprint or through the Journals, I’m not sure which it was. But, at the time, we had fully designed the experiment, fully designed the amplifier to be used at the Naval Research Laboratory using potassium chromo cyanide, with the expectation that there would be maybe a factor of three or so improvement in [???] noise, but it was the best that we had and that was what we were going to do. But when the Ruby came along, of course, again it was very quickly clear that that would make possible a factor of ten improvements and really make a significant improvement.
That’s nice, I mean, well you sketched that picture somewhat yesterday but the fortuitousness of these things comes out even more strongly with these details that you’re giving now.
I really want to emphasize that the decision to commit the effort to this kind of direction, with a hope that it would be productive, really involved an appreciation on the part of Townes of what the pace of work was going to be, and I think that vision was something that he was extremely accurate at and doing that kind of guessing wrong can be very hard on graduate students and can lead them to a thesis that is not a very exciting one and not a very productive one and one and one that takes an awfully long time. J3ut Townes had, I think the record of Townes’ graduate students, their duration of their thesis was a little longer than the average for physics students, generally, but not much longer, but I think he had a record of being very often right in predicting, in starting a project that would require facilities that didn’t exist even conceptually at the time but that became available later.
Was it a stressful time from that point of view, or you just were sure it’s going to work? I mean, here you were, you were the graduate student on whom the...
Well, Townes was the kind of person who conveyed a sense of confidence. You always had the feeling that somehow it would work out. He had a way of conveying his sense of confidence about it and you tended not to worry too much. I had a lot of other, enough other things to worry about, the project was tough in itself. There was always some problem to overcome, but the fact that, but he managed to convey a sense of confidence that the graduate students themselves really couldn’t, because they didn’t have the vision of the field, but they benefited enormously from this sense of confidence that Charlie Townes transmitted and that led to a pretty high moral in his group.
Now I did want to make sure that we had on record some of the chief difficulties that you were facing that you just mentioned, whether in getting these things to work.
Well I think a lot of them were, really just had to do with the logistics of operating a liquid helium [???] at the focus of a radio astronomy antenna. This must have been one of the very first occasions where liquid helium was actually used at the focus of a large radio telescope. So, just working out the details of the helium transfer and the transport of the [???] from the base of the antenna up to the focus, the techniques to get the project moving fast and using commercially available gear where that was possible. For example, the low [???], a rather bulky and large unit that provided the low [???] signal was built into this just simply to save time so that we wouldn’t have to develop it. But just fitting all these things together, making them work and making them compatible with the antenna application I think was the major problem, and there were many unexpected problems. For example, in the early trials of the antenna, it was found that the gain of the antenna varied periodically over, with a period of about somewhat less than an hour, very slow if you just set the antenna to follow a radio source so that it was tracking the radio source, set everything up so that everything should be constant under those conditions, you would see a very, very slow periodic variation of thesignal coming out of the apparatus which quickly identified as being new to something in the amplifier, it wasn’t the radio source, it was in the amplifier I remember Charlie Townes, who was really available on a consultant basis at that point, the graduate students Were down there, together with the Naval Research Laboratory staff, really doing the physical work, the observations and solving the day-to—day problems and so on But we couldn’t solve this one and Townes, at least within a few days, at least at the time when it became a real problem, Townes came on for one of his roughly weekly visits at that point and told us just let it alone, just let it go for some hours, just watch it We tended to watch it for an hour and then make some adjustments and do some other diagnostic experiments and so on. He insisted that we just let it go and at that point, letting it go for hours, we could see this very regular periodic [???] variation in the output of the apparatus Well, it occurred to Townes that what was really happening is that as the liquid helium was going down in the [???], as it was being consumed, the wave guide through which the radiation is coming down into the [???] to the cavity at the bottom of the [???], of course passed through the liquid helium interface, and the liquid helium interface was moving, and it turns out that the variation is due to the reflections from the liquid helium interface and that interface was slowly moving as the level of the liquid went down. Again, a completely obviously trivial kind of phenomenon but one that he was way ahead of anybody else in immediately being able to identify. Of course once one recognized that could be corrected simply by filling the waveguide with some microwaves, with some very open—structure dielectric that didn’t let the liquid helium into the waveguide. But he contributed a lot of insights to these day-to-day hurdles that came up in the course of any experiment that involves a very complex and new kind of apparatus. So there were a number of hurdles also, the electronics, the devising a locking apparatus that locked the frequency of the pumped microwave signal to the three-level maser that locked the frequency to the resonant frequency of the cavity itself. We devised a novel solution to that problem. There are a great many, as in any complex project, a great many hurdles of that kind to overcome, but, as a graduate student, you tended to be completely absorbed in those kinds of everyday problems and really didn’t, you didn’t really ask whether the whole project would be successful, you just knew that you were going to go out and do the very best job possible with whatever we had and it was just fortunate again, that measure of Charlie Townes’ vision, that the right facilities and the right materials became available at the very time we wanted them.
Now one other thing I wanted to fill in is, I guess at Harvard it was Artman and Shapiro who were working on the Harvard telescope and at Michigan I don’t really know yet, I think it was Capucchi, but I don’t know, I just wonder if you ran into these people at meetings or was your telescope don so much in advance of theirs that you never really had much interaction with them?
Well ours was the first maser application to a radio telescope. But, at the timer between the time that that telescope was working and the time that we wound up our observations, it was a relatively short time. I guess we were on the air for less than 18 months altogether in Washington. Then I was the first to leave, I guess that must have been 1959 and then Alsoff continued to work on the antenna for some months after me...
So you worked for about a year then.
That’s right, yes, yes. But, it was a measure of the difficulty. I mean, this was the first apparatus of this, designed in order to be able to be put on the air as soon as possible, it wasn’t really designed as a day in, day out research kind of tool. So, in fact, when Alsoff and I left then the work on masers at the Naval Research Laboratory then was continued by Penzias and others of Townes’ group at another Naval Research Laboratory antenna in Green Bay, Virginia. No, I’m sorry, not in Green Bay, Virginia. It’s another Naval Research Laboratory antenna not located in Washington.
Okay. Now something that we didn’t really take up at all was any reactions you might have had to Maiman’s laser, so I wonder if you were at Columbia? And that was during the summer. Were you at Columbia that summer of ‘60?
Yes, I believe I was, yes. Yes, that was a real surprise because I guess at the time we were aware of Ali Javan’s work on lasers which we had very close contact with at Columbia. He had a lot of contacts with Columbia and we were in very close contact with that. I think the general consensus was that the general belief at that time, knowing the work at Bell Labs that Schawlow was doing and knowing the difficulty with the crystal sources, experimenting with and knowing that the gas laser that Javan was working on was theoretically well understood, I mean it was known that that should work. Javan had published a paper in advance, I guess in ‘59 or ‘58, I’m not sure, on the theory of gain in gases pumped by electron collisions, and it was clear that that should work. So I think everyone believed that that would likely be the first laser that worked. So it was a great surprise to hear of Maiman’s result, and I think it was recognition here that our way of thinking at Columbia at least that we were very oriented around gas lasers. The original Townes’ proposal had been for a gas laser, an alkali vapor laser There was a recognition at that point that the solids were going to have a much bigger role than was anticipated at that time I think the emphasis at Columbia on the gas lasers and the alkali lasers reflected the fact that that was the tradition at Columbia Alkali vapors had been used at Columbia for many years, there was familiarity with alkali vapor beams in molecular beam spectroscopy, atomic spectroscopy, done in the Columbia laboratories of Polycarp Kush So that was a natural direction to take in considering [???] lasers and it was a natural direction for Javan to take, too, to pursue the direction of gases because that was the experience at Columbia, the tradition at Columbia had the Quantum Electronics background due to Townes’ early ideas and it had a tremendous resource of knowledge on high resolution spectra, of atomic systems in gases. So that combining those two would be the trend to think of lasers in those terms was a very natural one and it would have been impossible, I think, for a solid state laser concept to have come out of Columbia
Except that you had this, you had your work in this magnetic resonance sort of laboratory that you set up.
That’s right, but that wasn’t an inherently Columbia kind of idea or Townes’ kind of idea. That was really Bloombergen’s idea, and Bloombergen was working himself in the context of the NMR studies of per cell and pound so that, that was, I think, an idea that of course it was a brilliant idea but it was more natural to come out of the Harvard source, whereas the solid state laser just would not have come out of the Columbia tradition because there was no tradition of solid state physics there Ours was, the solid state maser work done there was really an applied kind of thing, the concept had come from elsewhere.
I see. Yes, that’s very clear. The other thing is that some people have told me that they really didn’t pay much attention to Maiman’s paper because it was rather sketchy and that it was not until a little later in the year, now it doesn’t sound like that happened at Columbia, it sounds as if like July when Hughes, I guess, released their press release around July 7, 1960, and it was also routed about a little bit before that, you know. It sounded as if you people picked it up pretty quickly and got interested.
Oh yes. There was a tremendous effort at Bell Labs at that time even, realizing lasers and alkali in various fluoride crystals, because we had great strength in growing the fluoride crystals in very high quality at that time and there was a good understanding of them and they subsequently did demonstrate laser action. And it was ironic that we had such a background here in ruby crystals as well, with Art Schawlow here. But, I guess, the belief evolved here for some various good reasons that the ruby just wasn’t going to work, but that was not the way it turned, that was not nature’s view. I think when the Maiman work was announced, it was very quickly followed up here by the first demonstrations of really coherent light, Maiman’s work clearly demonstrated a laser, but I guess some work here immediately afterwards, the first that demonstrated the real coherence properties of the beam, the real directive nature of the beam and so that his discovery was followed up, I hear, very quickly indeed.
Now another thing is that you spoke about your coming to Javan’s laboratory very shortly after he got his laser working, which I guess, is either the end of ‘60 or the beginning of ‘61.
I believe I paid two visits here. One was at an earlier stage, I believe during the point, during the time when he was developing the laser, then I believe there was a second visit that I paid during, just after, somewhat after the laser had worked.
Okay. I had those two visits down, but I had them at the wrong time. At any rate, you did say on the tape we did before that you were, at that point, very favorably impressed by the level of the sophistication of the equipment and the level of support. But now I would like to just ask whether there was anything about the work on the laser, per say, or Javan and Bennett and Harriet’s approach to it that you recall that is worth recording here or it may not be that there is anything, but I just wonder from those two visits looking at how they were progressing in the first one and how they had succeeded in the second, whether there was anything that impressed itself upon you as surprising or interesting or having an impact on your own thinking or anything...
No, I guess that by that point I was sufficiently far, I had become sufficiently familiar with solid state ideas through my application of laser techniques to radio astronomy that, even at that point, I think I was already sort of on the way to becoming a solid state engineer, or a solid state physicist and I followed the work very closely, but I really didn’t try to extend the work myself. I didn’t push it. I didn’t push in that direction.
Then it’s clear that that wouldn’t have been anything you would have picked up pointers from? All right. Another thing we didn’t talk about was the conference in Berkeley in ‘61, the second Quantum Electronics Conference. Were you at that one?
Yes, I was, yes
Again, it’s the stuff that’s not likely to get into the proceedings that I’d like to request you to probe your memory for anything you remember of attitudes or excitements or skeptical reactions, you know, that might enrich one’s feeling of how the field looked at that point or general consensuses. That would have been in March. Let me just try to demonstrated, and by that time, the stimulated emission laser action in some of the fluoride crystals had been demonstrated by Bell Labs people and the IBN people and, at this point, the whole theme of the conference was clearly the optical work the number of the papers there that, the coherence idea is in the coherent, the analogs of the coherent spin population and all the resonance, complex resonance phenomena that were familiar in nuclear magnetic resonance in paramagnetic resonance in adiabatic rapid passage kinds of effects and all these complex coherent interaction between intense light and distributions of optical electric [???], would be in many ways analogous with that of microwave physics and nuclear magnetic resonance physics and that there would be a similar richness at that point, so at this point, which was in the last months of my stay at Columbia, when I was doing work related to paramagnetic relaxation which really wasn’t going anywhere at that point.
I really began at that point to, I mean, my feeling was reinforced that the optics was going to be an extremely open—ended kind of field with a lot of physics involved and especially, I guess, the idea of coherent interactions, the idea that the radio frequency physics was going to be able to be taken over into the optical regime became really quite evident at that point. And, I think in my case, and I’m sure the case of many others, it reinforced people’s decision to move into the optical field in a very big way
Did that, this is just a parenthetical question, was the Nash paper on the phonon bottle neck something that resolved that going nowhereness of your work at that point or that was just a little addendum? I noticed you did one when you here at Bell, kind of a follow-up to your work at Columbia on paramagnetic relaxation.
On, yes well, that dotted the “I’s” and crossed the “T’s” to a large extent. But, I think the, filled in some of the mathematical details, but I think physics really had been explored by that tame between our original work and the subsequent work of Bloombergen on spin flint scattering I think by then the physics of that had been largely played out
I’m very glad to have that memory of Berkeley. It makes sense of a lot of things. Then another little point is, we got you to Bell Labs last Thursday and you specified that Collins was especially important, that you were also talking to Schawlow and, who I guess, again was about to leave at that point and Kaiser and Nelson, Kislieuk, and I wondered if you had any memories of the principle interests or controversies or excitements or ideas that they were conveying to you when you were talking, and this was just this very early phase where you were just interested in this general way about lasers and you may or may not …
Yes, well I think one question that came up again and again and that was still relatively poorly understood was the issue of the optical modes and the, which was clarified in most people’s minds I think by the work of Fox and Lee who did the original calculations, computer calculations, and that was followed by Boyd’s work and I guess Boyd, Gordon, on the confocal resonator, the original work I guess was Fox and Lee, primarily on planar resonators then, I’ve forgotten whether it used the confocal resonator as well. But in any case, the Boyd and Gordon work really clarified the role of the confocal resonator and really settled and made clear in a physical way what the, what an optical mode was. But during those early points, early period in the late ‘60s, late ‘61, early ‘62, certainly late ‘60, the mode concept really wasn’t very well understood and everything seemed to be, everything in the optical regime that we take for granted now seemed very new. I mentioned a couple of experiments in particular. There was an experiment of Kaiser and Garrett down at that time on the whispering modes of a dielectric resonator, and they demonstrated that if you had a crystal in the shape of a sphere or cylinder in which light could run around the surface, inside the surface of the cylinder, much like the whispering modes in some European cathedrals, you can talk at one end of a hall which has a dome and you can hear yourself very clearly at the other end of the dome because of the so—called whispering mode propagation of the acoustic waves around that spherical, around the dome surface. The fact that that could occur in optics was something that was, I think people looked at as being very novel at that time. Another novel experiment that was done at that time was done by Ivan Kaminow on modulation. At that time, the subject of modulation of light was really not very well understood. There had been some experiments in the late ‘60s, by I believe Forester, on modulation of noncoherent light that is of white light, barely showing the existence of sidebands on the light. But there was, because of the evolving state of understanding of the statistical properties of incoherent beams of light, behavior of modulated beams of light was still a matter of a lot of conjecture in the properties, for example, of a light beam that’s modulated sidebands and their behavior, expected behavior, when you try to heterodyne them, beat them together at a detector, was the topic and the statistics of that process was the topic of a lot of interest. I think at the time, by late ‘61 or sometime in ‘62, when Ivan Kaminow did an experiment using a laser in which he passed a laser through a crystal which was being modulated by a microwave klystron so that the light beam acquired sidebands separated in frequency from the central frequency by the frequency of the microwave modulating radiation, namely a conventional, what we look at on today as conventional modulated light, of the kind that’s used in optical communications systems. The fact that you could take this light into a spectrometer and actually see those sidebands on the light, I mean that was something that was well worthy of a publication, and that was the first time that one had demonstrated these clearly, these modulated sidebands on light produced by a microwave in a microwave modulation experiment. So that it was a point where…
That was something you were also in contact with.
Yes. I was in close contact with Kaminow at that time and followed that worked very closely. But all of those processes lent further support to the idea that light was something that could be considered, many ways, that intense light, coherent light, could in many ways be considered the same as microwave radiation except that it’s at a higher frequency. It was that kind of feeling that evolved through conferences such as the Berkeley Conference, these experiments on modulation, the understanding of the mode behavior of light that could be explained in a wave kind of way that was analogous to the kinds of descriptions of microwave phenomenon. All of that led you to a way of thinking in a confidence in dealing with questions of light phenomenon that I think we’re very helpful to me in dealing with the questions of, for example, phase matched second harmonic generation, the subsequent work on stimulated Raman backscattering. At that point I had already acquired the facility of thinking of light just as wave motion that was sort of demythologized, I mean, coming to Bell Labs, before the laser, light was a kind of quantum phenomenon [???], no one knew all the electromagnetic theory of light but one didn’t have a facility, one didn’t have the ability to think of it in as comfortable a way, in a comfortable way that you have to think about something in order to really do something innovative, to push the thing a little bit further ahead, you ought to be extremely comfortable in thinking about it and develop the facility. It wasn’t until these kinds of experiments that I’ve mentioned, some of which I mentioned the... to make an original contribution to the field, I think around the time of that Berkeley Conference there was enough new experimental results on coherent light... pushed the field ahead because that kind of confidence that I described really emerged around the time of the Berkeley Conference.
It also explains in a way, new way from my point of view, some of the excitement that was felt about the laser, but there is one thing that I didn’t realize that I’d just like to pick up. In other words, in your phase velocity matching experiments, you were also bringing to bear some of your microwave experience and feeling for things? I thought you said that, I thought I heard that some of this way of thinking in confidence with microwaves was feeding into that.
That’s right. I mean you were thinking of terms, you were thinking of the physical interactions with the media in terms of super position of traveling wave trains in a way that was a very natural way to think having worked in the microwave field, and it’s true that the large fraction of the earliest light wave contributions were all made by people who had had previous, well now, with perhaps very few exceptions, but almost all, made by people who had come from a microwave background, who brought that mode of thinking into optics.
Just as the microwave people who did work on microwave spectroscopy during the war came, as you’ve pointed out in your articles, came from the previous background in microwave technology during the war, there was a whole set of people for whom that microwave physics now, the coherent interactions, that were the physics people studied during the late ‘40s and the ‘50s, using the previous microwave technology, then that physics of the coherent interaction, coherent behavior of matter, that became the technology at microwave frequencies that was then carried into the optical region by the graduate students, if you like, of those people who brought microwaves into the physics lab during the war and then the next generation, after the war, then the next generation, if you like, brought that kind of, those coherent materials of behavior into the optical regime from the radio frequency regime, as a kind of next generation, if you like, transfer of technology into a new area of physics done using light waves.
I think that’s a very illuminating point to just understand the general flow of what was going on Now I have exhausted my questions.