Oral History Transcript — Dr. James Gordon
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James Gordon; November 4, 1983
ABSTRACT: Recollections of Gordonís thesis work under Charles H. Townes on operating the ammonia beam maser and its use as a spectrometer; the construction of a second maser, 1951-1954.
Well, could we begin a little bit biographically? Could you explain how you came to the university, your work there as graduate student bringing you into contact with Townes, and how you became enlisted in his physics project?
I went to MIT for my bachelorís degree; I went to Columbia graduate school might have probably been 1949, 1948. Then after a couple of years, I finished course work and I was thinking about a graduate thesis. I was sort of there at the time, and I think Townes called me and said, ďWe were discussing a project weíd been working on; ďIíd like you to come down and join
the conversation.Ē And I think thatís basically how I got into it.
Forman:Had you been working for him or with him before that?
Well, I was on a research assistantship at that point, and I guess I was working in the Radiation Laboratory, and so I had been assisting I guess for about a year, Joe Hartman (who was doing an experiment measuring the microwave spectrum of oxygen under Townes). So I was there at the time, and I guess Townes had, this project had been started a little bit, and heíd had the idea some while before that, he was thinking about making some experiments and had — in fact, I think in an earlier time, had talked to two other guys, graduate students, and talked about the idea of the maser. It didnít have the name maser at that point. And they decided they would not try it because it was too iffy, as far as getting it going was concerned.
Forman:Do you recall how you heard about these graduate students who were disinclined to take this up?
Gordon:No, I canít remember. I think Townes may have told me. Probably he told me.
Forman:Do you recall if there were others present at this conversation into which you were drawn? And also if the maser, as it later was called —
— yes, at the time, see, when I got into it, I guess you can find, see from the Columbia Radiation Lab. Report, both Herb Zeiger who was a post-doc at that point, was already involved a little bit, and George (?) also who was doing some of the calculations on it, and continued to do some calculations on my work, and so Herb was already involved, when I first got into it. It hadnít been going for very long, when they were thinking about deuterated ammonia, as a possibility.
Forman:Do you recall what kinds of warnings Townes gave you when he presented this project? It was certainly an iffy thing.
Yes. Well, now, Iíd have to do a little thinking about the exact timing on this, because I remember that we had done, a lot of calculations, and had calculated, using a focusing device as really harmonic behavior for an atom; the way we were thinking of it, so you could think of really making a focus from a source which would be a point or slit or something like that, and actually focus that onto an opening in the cavity , which would enhance the selectivity of the, you know, the atomic state selectivity of the system.
And we were doing calculations on that basis, and calculated using an annular ring as a source and an annular ring cavity, tried to calculate, which was George (?)ís calculations, with pen and pencil or pencil and paper, calculate how many molecules might get into the cavity on that basis, and it looked very — sort of on the borderline. I remember that what you needed was just about what you got, and youíd like to have a factor of ten or so as a safety factor, to make it work, make sure it would work.
So on that basis, it was still very iffy, as it had been before, but in thinking about it, we realized that we could do some spectroscopy with it, even if it didnít oscillate, and I think that was the basis on which started going ahead, because it was spectroscopy.
I donít know, my recollection is that I realized at the time that it would have high resolution as a spectrometer, because the molecules were traveling a long distance in the cavity. You could look at them for that whole length of time, and therefore you could expect line lengths which were narrower than the normal broad lines.
So we could see some spectroscopy, and I didnít know much about the spectrum of ammonia at that point. So Townes, I guess, realized that, given the fact that you could have a little bit better resolution, it was more hyperfine structure of ammonia that had not been seen before that could be studied. And so it could be a thesis project even if it didnít turn into a maser.
Forman:OK, this was a criterion I suppose for a dissertation topic, that there had to be some physics in there, and is, the device itself would be —
— well, there would be some physics in there, but something had to work. If it was going to be either an oscillator or nothing, that wouldnít — would not have been a very good dissertation project. I could have worked a couple of years on it and got absolutely nothing, to show. But there was clearly going to be something to show.
OK, and so you saw it as a continuation of your interest in spectroscopy -Ė which had been around as a result of your previous work as an assistant.
Gordon:Well — yes. I thought it was something that could be an advance, and it certainly would be interesting to make it work, as it finally did, as an oscillator. So —
Forman:Do you recall any reactions of fellow graduate students to your setting yourself up for this project, instead of looking for some other kind of dissertation?
Well, nothing terribly — nothing outstanding, I donít think. Now, during the first year, when we designed most of the apparatus and built and did a lot of the conception on it, Herb Zeiger was there as a post-doc, still, — he spent about a year there on the project. No, I think everybody realized there werenít any serious thoughts one way or the other about it. It seemed like an interesting project, and it was not clear to anybody that — I donít know what, I canít read Towneís mind, but it wasnít clear, it didnít seem obvious to anybody that this was going to revolutionize the world at the time it happened. There wasnít any great excitement over it. We went up to — while we were thinking about it, we went up and talked to several people, talked to the president of MIT, named Strandberg, who had done some work in ammonia, and told him what we were doing, and he wished us good luck, but again there wasnít any — he told us what were some of the problems we might run into.
Forman:Did you have any contact with Lyon at the Bureau of Standards?
Gordon:Yes. Now, I guess that I donít know that we had much — did we have any (?) I canít really remember whether we had contact with him before the actual original operation of the thing or later, when it became clear that it was an interesting atomic clock possibility.
I know we.... had contact with him after that.
Forman:He had done some beam work with ammonia, I think.
Gordon:I think he had. Yes, I think he had. But he wasnít particularly — as far as I know, he wasnít particularly excited about what we were doing. He told us, he talked with us and was very friendly and so on. But I donít know — it wasnít, I think it was a good project. Townes was a very busy guy in those days, with a lot of graduate students doing projects. The apparatus was in a big room on the 10th floor, 11th floor I guess, at Columbia, and another apparatus which was a high temperature spectrometer, I remember. It was a big (?) that came out vertically out from floor to ceiling, and had heater coils inside, and we were doing spectroscopy at high temperatures, 800 degrees and so on.
I remember, the story came out several years later that we kept getting these strange spectra that they didnít recognize and couldnít figure out what they were. It turned out that they were ammonia. The ammonia was permeating the room.
But you know, there were a number of things that were a little bit out of the ordinary. I suppose the high temperature spectrometer was one and the maser was one.
Forman:The other experiments were established molecular physics, in a way?
Gordon:Yes. Well, for all we knew at the time, this was too. If it worked as an oscillator, that was fine, but if it didnít., it also was OK too, and then we go back to studying physics. It turned out we did both and thatís nice.
Forman:Do you recall any interactions with Robert Dicke? He might have been interested in the experiment, the-coherence ideas.
Gordon:Again, my conceptions of what happened when are kind of fuzzy. I know thereís a patent, itís the Dicke patent that demonstrates a sort of a pancake like cell. We knew we were aware of the high resolution aspects of that cell, somewhere along the way.
Forman:How had you thought making use of it, do you recall?
Gordon:Well, it was kind of — as I remember, that, again, I — you know, Iíd have to go back and look at these things. I know, we may have been using, the fact that molecules could live a long time if they were going along parallel to the height of this, along the long direction of the cell, produced, was supposed to produce high resolution, and in the same way — it was similar in a sense to our cavity resonator, which was very long in one dimension, and molecules coursed along that long dimension could be observed in high resolution.
In fact, we did notice, I noticed, in the maser cavity itself, just absorption, when it was all warmed up at room temperature, just a little ammonia was in that cell, that you could see it, and you could see its (?) shape was not the standard (?) shape that you see in a wave card. It had a little bit of a sharp peak on it, and you could see a little bit higher resolution because of the fact that some of the molecules went the length of the cavity, and those were seen in high resolution. Still, you didnít know — whether it was sensitive to molecules going every which way.
So it was similar to Dickeís cavity in a sense. But I donít think we had any, very much close correlation with Dicke at this time.
Forman:What about Joe Weber. You pointed out the 1953 publication. He did visit your laboratory occasionally, I think.
Gordon:I donít think I met Joe Weber. I donít know that I was aware of his work, until well into what we were doing... in fact, I think when I originally wrote my thesis papers, Iím not sure Weber was referenced in there. I think that was partly because I was not aware of his work at that point. He was not, and I think that was because I didnít know. At the time he was here I think I learned about that later.
Forman:OK, back to Lincoln or Latham (?) laboratory. You were in this room on the 11th floor, and there was the other experiment. How many of you were working there? You were all part of Townesís equipment?
Gordon:We were all part of Townesís equipment. I would say, letís see — there were probably, I remember at least three or four experiments in that one room going on. But Stitch was there Ralph Stitch, who was at Hughes for years, and Hornig who was at Syracuse. Ali Javan was in that room doing experiments. Others I donít remember. Working on our experiment at that time were Zeiger and myself.
Forman:And where was Townes?
Gordon:Townes was always around, but he wasnít, I mean he didnít do much of the laboratory — he wasnít in the 1aboratory very often. We had frequent conferences with him, and he certainly kept up to date on what was going on and how we did things, but he did not partake of the daily chores in the lab.
Forman:So he was in his office.
Gordon:In his office.
Forman:Youíd go around seeing him there?
Gordon:He had quite a few graduate students, and weíd see him. I think we had some meetings in which we just — you know, that he called — and we could go see him when we wanted to.
He had quite a few graduate students. I think he was writing his microwave spectroscopy book along in that time. So he was quite a busy fellow, which was I think very good. In a way it was very good, because he didnít stick his nose in too much, but yet in broader terms he was very influential and was always helpful. We had no feeling that he wasnít there. But I know some professors have their nose in all the time. Itís hard on the graduate students.
Forman:OK, now, you began working with Zeiger who was post-doc had beam experience. So you had a year essentially together with Zeiger, and how did this collaboration go in this first year? What do you recall that you accomplished there together?
Gordon:Well, essentially we designed and built — or at least in large measure I think, built the first maser beam. When would that have been?
Forman:The summer of Ď52.
Gordon:Summer of Ď52. And December of Ď53 when the thing first finally?
Forman: Yes, December, or January Ď54.
Gordon:We first saw some results in December and reported in January. Shortly before Christmas, I think, we saw a breath in the spectrometer. I guess the January progress report shows that. Anyway, Herb was there for most of the time when the experimental apparatus was being designed. He did a lot of unnecessary calculations on molecular beams, from his molecular beam experience; — he knew that one had to calculate the number of molecules you expect to come down to the end. It turned out most of those calculations were superfluous, but nevertheless there was quite a bit of work done calculating the strength of the beams that we could expect.
But anyway, itís easy to check dates but he was — I think he was there for something like a year, and then he went off to Lincoln Laboratory. And then I guess I was working on it alone, until the time when it started to work, which would I guess have been another year or a little more.
And then Wang came in, after that, did a little work on it.
Forman:Where did Wang come from?
Gordon:Well, he had gotten a, heíd gotten a — heíd also done a — he was working in the lab too, come to think of it. He had done a spectroscopy thesis on some nuclear resonance, and was just finished when we were very busy and had two masers, we were doing a lot of experimental work, and he came over and joined our project. He was still on it after I left.
Forman:So this was after the second maser had been built.
Gordon:It was certainly after the first maser had been built and worked, and then I guess in about six months we built the second one, and some time in there he came in and joined working on the project.
Forman:Your schooling had been as an experimentalist, apparatus, and builder — what were the shop facilities, and what kind of assistance did you have from machinists?
Gordon:Oh, it was a very good shop, actually. Radiation Laboratory had its own shop, with very good mechanics in the shop.
So most of this was built, most of the actual fabrication was done in this mechanical shop. It was a big room with lots of machines in it and very well run, and they did a lot of work on a lot of projects, building microwave tubes I think and things like that. But there was no problem there. I didnít actually do any of that myself.
Well, I didnít know — I guess I was an experimentalist at that point. I didnít know whether I was an experimentalist or — I clearly was not a pure theoretician, but I was not a pure experimentalist either. The papers that came out on this maser contained a fair amount of theory as well as experiments.
Had you anticipated developing that side of your interests when you got into the project? Had you thought about being a sort of theoretical dissertation or how had that developed?
Were you emulating Townes?
Gordon:Not as a conscious decision. No, I was, I think, I was fairly adept academically and I liked doing theory as well as experiments. So I enjoyed both. I probably wasnít, I certainly was not, well, I wasnít really into the theory enough to make it, to do theory as a complete, you know, to concentrate totally on it. I guess partly it was a natural result of my work as a lab assistant. I guess my first job was, I got a teaching assistantship, and then next year was a lab assistant. What was the reason that I changed? The job was there. But I enjoyed doing experiments as well. I enjoyed both of them. OK?
Forman:There werenít lab technicians of any sort who were having special technical expertise, it was simply, the shop would make up apparatus as required, and you had to make it work?
Gordon:Well, in principal, there was a shop. There was a wiring shop where we could get electronica gear made up to design, which my recollection is, was not as good as the mechanical shop. But otherwise, no, there was no laboratory assistant type people involved at all. We had to build everything.
Gordon:It probably explains this very ďklugyĒ vacuum system.
Forman:The original idea was to do this with these rotational transitions of deuterated ammonia, so you would be down at millimeter waves. Then you decided that it would be more prudent —
Gordon: — to build ammonia —
Forman:— with the inversion transition of — do you recall questions about this, making this decision? Do you recall it that or any other turning point in the direction of the experiment?
Gordon:In terms of going to ammonia, I guess in the original I know, it was MD3 in the first progress report, and then , I guess I just had sort of gotten involved at that point, because the changeover to ammonia came very quickly, I think, after I started, the original , before the construction of anything happened, before that time. It was very early on in the game. And Iím not sure I had all that much to do with that. I really donít have any strong recollections of that.
I think one turning point was certainly the time when we thought about it in terms of the thesis, and decided on the fact that the hydroxylation spectroscopy was available. We decided weíd go ahead with it, instead of doing something else; weíd go ahead with it.
Forman:Do you remember when that was? That was right at the beginning, late in Ď51?
Forman:OK, in the later stage when you actually did do some spectroscopy with it, with the first maser, in the spring of Ď54, —
Gordon:— yes —
Forman:— and then somewhere in there, it would have been clear that here was an important dissertation —
Gordon:— Well — yes. I think it was not long after we saw a spectrum of ammonia, that was the beginning of Ď54, I guess, it was in the next six months or so that everything pretty much happened.
We saw the spectrum from the molecular beam. It was indeed sharp and then we moved it — in this picture, thereís some micrometer screws on the source, and weíd expected that the source beam was focused into the silted annular ring in the cavity, and that weíd better optimize that. So we tried to optimize it and we moved the source around and moved the cavity around, and nothing happened. It was the same. There was no real strong focusing action.
I guess it was an obvious point that one ought to get rid of all these annular rings and just open up the whole end of the cavity. And you had no particular selectivity, so by knocking out the end of the — taking the cavity, which had a little annular ring and a block there, just knock that block out, and so now a big hole in the cavity, so we ended up with getting about ten times as much intensity at that point. And it was that factor of ten we needed to make the thing oscillate.
Forman:OK. This was after you had gotten the [???] resonance out of it?
Gordon:Yes. That was after weíd seen, not an oscillation, but a resonance, an emission resonance. And then once you got it, of course, you could fiddle with the controls and make it better.
Forman:OK, but the annular orifice in the cavity was to correspond to an annular —
Gordon:— orifice in the —
Forman:— in the diffuser.
Forman:So you then also, did you —?
Gordon:(crosstalk) — well, we did do a little work on the fuser diffuser but it turned out that, there wasnít much you could do, there wasnít too much you could do with the effuse because itís limited by pressure, and if you make it bigger, then you have to lower the pressure; and you donít really gain that much. So the effuse, it wasnít very sensitive to what you did over there. You got about the same pressure, effective pressure. At the cavity end, it did matter.
Forman:Do you remember playing around with different effuser designs? The question of Zachariasís crinkly foil?
Gordon:I remember, Townes brought that one to us. Weíd been making, I think we were making little things with little holes, punching little holes in it to make the effuser, or making a little annular slit, and he brought this idea of the crinkly foil. I think it, as I remember, came from a fellow named Powell in Germany who had used that in some electrodynamics experiments. I think thatís where it originated.
Forman:Did you meet Powell?
Forman:But Townes had met him and spoke of him?
Gordon:I think so. And so we made some crinkle foil and used that as an effuser, and it worked a little better, but it wasnít — but again, it wasnít very sensitive, whatever you did down at that end.
Forman:Were these still annular?
Gordon:They were still annular, and at the time that still seemed OK. I mean, it gets a large length. You want to get a slit that you keep as far apart from it as you can and still have it as long as possible annular slits, I think, are almost as good as any other.
OK, itís your impression, you held onto the annular effuser to a fairly late stage in this whole thing. Though of course, once you pulled the plug on the cavity, whyÖ
Gordon:Pulling the plug on the cavity was the most important difference that increased the intensity.
Forman:OK, what about the chopper, the 33?
Gordon:The 33 cycle chopper?
Gordon:Well, that — what about it? In some of the spectroscopic work we used that for locked in detection.
Forman:You used it still for spectroscopic work?
Forman:And then just got rid of it afterwards? Because —
Forman:Thereís something to these boxes on the first maser. Do you think these boxes had anything to do with the chopper?
Gordon:May have been. Could be. Thatís possible. Because I donít see them here. Iíll look at that picture again. Well, there might be a chopper, because there was a chopper in there.
I made a very crude locked in detector, which operated off that 33 cycle chopper — so we could get a little more sensitivity in detecting the beam.
Itís not something that made the industry, but it worked. For some of the spectroscopy work that I did with Layne. He was there at the time.
Forman:This technique of chopping and locking onto the low frequency signal, this was something that was pioneered by Dicke in the early microwave experiments.
The lock-in itself was a fairly common critter around the various laboratories in those days. I donít think there were commercial lock-ins yet but many people were using them. It was not something we invented or brought from Dicke or what.
All right, you had your first one operating. You were about to oscillate. You got the resonance which showed these quadripole lines.
Gordon:The quadripole lines and magnetic hyperfine structure on the top due to the flipping of the hydrogen, the quadripole lines connected to the nitrogenís, some of the fine structure of the quadripole lines is flipping of the hydrogen spin.
Forman:OK, and this you then published in the PHYSICAL REVIEW. Do you have any recollection of reaction to that, reactions to the maser at that point, reactions to the maser before you had the second maser and could display some of these extraordinary properties?
Gordon:There was a letter in the PHYSICAL REVIEW Letters in Ď54, and then the first two papers came out in Ď55. I guess by the time of those two papers we had two masers. The first letter, I guess, we did not.
I should be able to tell you something about it Ö I do remember that, you know, before we got the second maser operating, there was a guy, one of our cohorts who was named Michael Danos who was from, where was he from? Anyway, I think he was a nuclear physicist, I guess. We had a bet on whether the output of the maser was going to be coherent or not. And I won a bottle of bourbon on the bet. He bet it was going to look like noise, just amplified noise. And I guess I bet it was going to be coherent, and so, just like any other oscillator — so when the second maser came along — anyway, thatís an illustration I guess that it was not obvious to everyone that it was going to be coherent oscillation, when it emerged.
Forman:OK. The building of the second maser and getting into operation, you had the first maser going in the spring, effectively, and you wrote a paper on this maser. In the late summer, you went off on a long trip to Europe, coming back in the middle of October.
Gordon:It wasnít that long, was it?
Forman It wasnít that long, but considering the relatively crucial phase of the maserís development, —
Gordon:I was supposed to be all finished by that time. It was all planned earlier.
Forman:OK, so where — this vacation trip to Europe, where was your dissertation in relation to that?
Gordon:It was written.
Forman:You speak of it, I know this from a letter that you wrote to Townes from Europe, you speak of it as a paper, not as a dissertation.
Gordon: Well, they were the same.
Forman: Perhaps itís this paper, here.
Gordon:Actually what ended up as my dissertation was in fact just exactly the two papers in í55? Thatís it. There was no other dissertation.
Forman:OK. At this point, do you recall where the second maser was? When you left in late summer?
Gordon:I think essentially all the work had been done by that time. It was just a matter of getting it written. It the second maser must have been operating then.
Forman:On the 29th of November, Townes wrote to [???] saying, ďA short while ago, the second ammonia oscillator was completed and we are able to beat the two oscillators together to check theory against your idea about what stability can be obtained. ď So it certainly suggests that it was only after you came back that you set it in operation, but I wondered about this hiatus.
Gordon:Well, I guess I must have been off about a month, maybe a month or six weeks. But anyway, that had been planned for quite a while with a friend. It seems to me that second maser took something on the order of six months to make. It would have been started shortly after we achieved the oscillation on the first one. Townes right away wanted to build another one. He said, ďThereís no way we can test this without another one.Ē
Forman:I guess you were less than enthusiastic, to it.
Gordon:Well, we thought it was a good idea. Yes. The time schedule is about right. But I was working on; I guess I was working on the spectroscopy paper at that point. Spectroscopy didnít require the other maser.
Right, I guess I donít really very clearly know the answer to your question.
Forman:But now, the enormous interest in this, at the point at which there were two masers going, certainly you yourselves would have been pretty impressed at what was coming out, but at the same time, the difference between the general interest among physicists before this, and even after you had gotten spectroscopic results, and what happened after you got the two beating against one another was considerable.
Forman:And then there was the publicity and considerable hoopla. Photographers coming up to take your pictures —
Gordon:— taking pictures —
Forman:What are your recollections of this, how it developed?
Gordon:Well, thatís an interesting question. I think a lot of that time I was very busy trying to write this all up. I wasnít paying much attention.
Forman:Iím sure. Obviously so much was going on: over your head, in a certain way.
Gordon:A lot of it was going on over my head.
Forman:Townes was doing this and you just experienced the fallout in a way.
Gordon:Thatís right. In terms of dating the times when things happened, thereís a photograph, I donít know whether it has a date on it, but the one thatís in the Smithsonian exhibit, of a beat note which would have been shortly after the first or second one was made. Whether that photograph is dated, Iím not sure. It was a Polaroid photograph of a beat note.
Forman:Yes. I donít quite remember.
Gordon:But if it has a date on it, it would essentially be the date very close to when the second one was done.
Forman:OK. Iím sure if the date was on it, we put the date in the caption.
Gordon:OK. Well, I guess I was aware of a lot of what was going on. People were coming into the lab, and that was nice. Shimoda from Japan came over, and the guy from Jet Propulsion Laboratories, somebody came down for a while. I think at that point, we must have talked with Harold Lyons, for example. I donít remember him being there. I just sort of know that we were in contact with him. It may have been at conferences and things like that. Iíd see more people around working on it after that, after it worked. But still, you know, it was a device that seemed to have potential for spectroscopy. It seemed to have potential as an atomic clock. But nothing really extra — I mean, there were other atomic clocks around which were certainly competitive. There was no assurance that this would be a better atomic clock than the cesium beam clock.
It had certain purely specialized spectroscopy usage. You had to have a molecule with a rate, a spark effect in response to an electric field so the focuser could work on it. Not every molecule will do that.
So while you could get very high resolution in those spectra could see it, it wasnít much less sensitive than a standard spectrometer. As a spectrometer.
It wasnít obvious that it was a very good — you know, it was a — oh, the amplification, again, it had very low noise in its amplification. We saw that after a while. But there again, itís a fairly specialized — all of the uses, though very nice, were very specialized. There was no grand — I donít think I wasnít aware of any grand excitement. There was lot of interest around it was something unusual.
My recollection — I somehow have a recollection, back in the time when the thing first oscillated, first major oscillator, that it must have been a Friday afternoon or something like that, and the microwave spectroscopy seminar was on, and I remember I wasnít at that seminar because I was working on this machine, and I
came into the seminar and announced that it had worked!
There must have been a certain amount of excitement.
But at least, to me it was not obvious that — it was an interesting thing and had some very specialized and nice uses, but it was not the maser — thatís still true, you know — itís a specialized device. And while it was, there was a lot of interest in making a low noise amplifier for a while, particularly a solid state one, interest in that has sort of waned since then.
Forman:OK and you stayed on how long in 1955 before going on to Bell Labs?
Gordon:About June — no, Iím sorry, I guess I stayed there, I think, made the change to Bell Labs at the end ofí55, December.
Forman:Townes had left in the summer for sabbatical in Europe. You were there after he left, was gone.
Gordon:Thatís right. I think I came to Bell Labs, I must have come to Bell Labs in January Ď55, came to Bell Labs before these papers were published.
Forman:So really just after all this press publicity and so on came out.
Gordon:Thatís right. And then Shimoda and Tcym — I donít know exactly what his first name is, but itís Tcym ( whoís now back in Red China, I guess — stayed on and worked on it further, and published a later paper about the thing.
Thatís right, I think thatís when I left, was at the end of Ď54, could that be? These papers came out in Ď55. It was December Ď54, January Ď55, I went to Bell Labs.