Oral History Transcript — Dr. Henry Scovil
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Interview with Dr. Henry Scovil
Dr. Henry Scovil; July 5, 1983
ABSTRACT: Bell Laboratories research during 1956 leading to the operation of the first 3-level solid-state maser in Dec. 1956. Some steps toward the development of effective maser amplifiers. Some applications undertaken.
Bromberg:What Iím curious about is, you got to Bell around Ď55, is that right? Dr.
Bromberg:I guess I get the impression that you were working on three level masers even before you heard of Bloembergen's Suggestion. Is that a correct impression?
Scovil:Yes, it is. It was not my main project, but Rudi Kompfner, who was here at the time and was interested in masers, had suggested that perhaps I might do a little thinking about it, because I had had a fair amount of experience in paramagnetism over at Oxford.
Bromberg:Were you working in his group? What was your relation to him?
Scovil:No, I wasn't. I was in quite a different group.
Bromberg:At Murray Hill?
Scovil:I was at Murray Hill, that's right.
Bromberg:So how come Kompfner came to you, when you were in a different group?
Scovil:Well, I think the reason is that, first of all, I was with Rudi Kompfner at Oxford, got my doctorate in the same lab. At that time Oxford was probably the leading lab in the world in paramagnetic resonance, so I was, if you like, an expert in that field. I probably knew more about this particular type of paramagnetic resonance which one would want for masers than anyone else at Bell. I think Rudi knew that.
Bromberg:So there was really a couple of people simultaneously going from paramagnetic resonance to masers? Your group, then the Combrisson, Honig, Townes combination in Paris?
Scovil:That's right, and there were also other groups inside Bell Labs.
Bromberg:OK, tell me a little bit about them.
Scovil:For instance, George Feher was working on spin flip silicon laser, independently of me.
Bromberg:The idea was to work on a two level or a three level at that point.
Scovil:Feher was working on the two level. Kompfner suggested to me that it should be -- those are inherently pulsed-type devices, not continuous, and Kompfner suggested to me that perhaps one could find a way of building a maser to operate on a continuous basis, and I came up with the idea for the three level maser.
Bromberg:So now, with whom were you working at this point?
Scovil:I was working alone at the time. But after I proposed the idea at Bell, some very considerable resources were placed at my disposal. In particular George Feher and his equipment, and Harold Seidel, an electrical engineer, collaborated with me, and we designed and built, you know, a maser as quickly as we could.
Bromberg:By the way, you had already worked with gadolinium ethyl sulfate at Oxford?
Scovil:That's correct. It was part of my thesis.
Bromberg:So did you start out with that material?
Scovil:Yes, I did, because I had very detailed information on it, and I didn't have to do any measurements. I could calculate things almost precisely immediately.
Bromberg:So, then it was really a coincidence that Bloembergen came to suggest the same material?
Bromberg:Yes, that's one of the two things he mentions in his paper.
Scovil:I forgot. You know, if you looked at what materials might work, there were some which were fairly obvious, and that was one of them. See, I had the advantage that I had already grown the material in the past at Oxford. I had the raw stuff to do it here, and I had very detailed information from my thesis.
Bromberg:Now, what were the main lines then that you followed, and what were the main novel things, things you were discovering as you worked along? And then the other question I'd like to ask is, what was the interaction with Nicolaas Bloembergen, once you people there at Bell became aware of what he had done?
Scovil:OK, well, maybe I can answer that last one, first. Bloembergen, I believe, contacted people at Bell, probably Kompfner, regarding his idea.
Bromberg:He said that Hogan who was at Harvard sort of put Bell in touch with him.
Scovil:Well, maybe that was the way it was. I don't know the details. I wasn't involved. But I believe that Bloembergen was interested in having somebody file patent, you know, money to do that, and that there was some suggestion that we might file patents for a right to use, or something of that sort. I'm not sure of the details. But Bloembergen came to the lab, gave a talk on his proposal, and it was perfectly clear that it was essentially the same as mine. I had written an internal memorandum on the subject.
Bromberg:Do you have that?
Scovil:I presume it's in the file somewhere.
Bromberg:I would like very much at some point to find out what you've got that should be saved, and that certainly sounds like something that should be saved.
Scovil:OK. Well, I wrote a memorandum, and I also prepared a paper for PHYS REV detailing the proposal in shorter language. But when Bloembergen came here, it was quite clear that he had the same idea, that in fact he had certainly had it before I did. So I did not send my paper in for publication. Instead, I told him that I would withdraw may paper, since it's clear that he was first, but that we would race to be first to get it in operation. I believe he was working on some copper compound, I forget what it was, but I worked on gadolinium ethyl sulfate.
Bromberg:Yes, they wanted to make a 21 centimeter.
Scovil:Yes, well, everyone was interested in 21 centimeters. At that time.
Bromberg:I see. You also were, then.
Scovil:Well, I think the whole world was, because that's the hydrogen line in radio astronomy.
Bromberg:Were there other applications that were also especially interesting to you at that point?
Scovil:Well, we had very considerable interest in them for military applications. In fact, most of the masers we built went into military applications.
Bromberg:Of course that was just the time when missiles were really being developed very rapidly, I guess.
Scovil:That's right, and Bell was concerned with anti-missile development.
Bromberg:So even though you were at Murray Hill, and I always thing of Whippany as the missile place, Murray Hill was also with their eye on these military things, is that right?
Scovil:Oh yes. At that time, quite a large fraction of the people at Murray Hill were associated with military projects. Primarily unclassified.
Bromberg:Stuff like communications?
Scovil:Yes, and radar.
Bromberg:What were the surprises, as you went on to do this? Were there any? The paper you published had to do with using rather dilute cerium.
Bromberg:Was that a surprise?
Scovil:Well, it was and it wasn't. In my original memo I suggested the use of a dopant such as cerium to speed up a relaxation. At the time, I felt that this was a bit of a refinement. I didn't know whether or not it would be really necessary in practice. What happened is that when we grew the material, there was cerium in there accidentally. It was not pure. So we just automatically made use of the cerium. Since it was already present.
Bromberg:Then you went on to do some considerable study of that cerium, didn't you?
Scovil:Not a great deal, no. I believe we did virtually all of our work in about three days. I was working with Feher at the time. Well, see, I'd offered them cerium for my thesis. In fact, I worked in the whole rare group of the ethyl sulfates. So, no, I wasn't interested in cerium per se, but George Feher and I did a few days of work detailing relaxation times and so on, and there is a companion paper to our one on the maser detailing that. The same issue.
Bromberg:Yes, that's the one I looked at and assumed
Scovil:There were the two. But we did all that in a couple of days.
Bromberg:Well, when you got this amplifier going, what happened? Did that change research programs very much at Bell?
Scovil:Well, yes, it did. It certainly changed mine.
Bromberg:What happened then?
Scovil:At that time, as I say, I was working as a single person. I teamed up with Feher. At that point, we decided to go into the maser development business in a serious way. That Bell did. I was based around me, and we built up initially small group and it eventually became an entire department. thing we did then of significance, I think, was to develop concept of the traveling wave maser. Cavity masers, which people were working on, are simply not stable enough for, practically applications, at least a lot of practical applications, so we developed the traveling wave maser. I Initially we used gadolinium ethyl sulfate salts as a material, because it was available and we knew about it. It was clear that that was not a practical material and we later substituted ruby for it.
Bromberg:When was that, about? That was after the Kikuchi and so on work?
Scovil:Let's see, it was essentially at the same time. Joe Guesic had been working at Ohio State, and he worked at Ohio State, and he worked on ruby for his thesis. I hired him.
Bromberg:With that in mind?
Scovil:Yes. So Joe came here. He was very helpful, of course, in helping us get the ruby going. But so was Kikuchi and of course we relied heavily on Linde for material, and indeed, we spent large sums of money getting the material developed. Now, there are some other aspects of traveling wave masers, other than just that material. There is the slow wave structure itself, and that was developed in my group. I'd say Bob DeGrasse whom we had also just recently hired was the primary inventor of that structure. He was the electrical engineer who proposed that structure, and it became essentially, you know, the standard structure throughout the whole industry. Another aspect of it was that we needed a non-reciprocal device, an isolator in the structure, and it was fortunate that at the time, we had contacts with a couple of fellows down at that is, Ed Spencer and Connie LeCraw -- and in fact, we hired them too. They brought with them the technique for making small garnet spheres. They knew a great deal about those. We adapted that technique. In fact, they helped us do it. We used that as the non-reciprocal device.
Bromberg:Is there any crossover here between what's going on with transistors and transistor crystal growing and that stuff, and this maser stuff, or is it not?
Scovil:No, it was quite independent.
Bromberg:I'd like to find out the name of this department, just ln case we ever look for records, this department that grew out of this maser work.
Scovil:I'll have to take a look. You know, we change names around here so often. I think at one time it was called the Maser Department, but I'd have to take a look at it.
Bromberg:Now, you went on to a radio telescope program also, didn't you?
Scovil:Yes, we did. But the first practical application that we had was for military radar. And indeed, quite a large number of masers were built for these applications. That was in conjunction with our friends over in Whippany. They were the customers, if you like. And along with that, we teamed up with A.D. Little and Air Products. They developed the refrigeration system for radar systems.
Bromberg:These were all going to be ground based radars?
Scovil:They were all ground-based radar. Now, with that sort of as a background, this technology was not pretty good. In fact, it had to be for these phased array systems. And I teamed up with DeGrasse and Dave Hogg down at Holmdel and Ed Ohm, because those fellows had been working on antennas. They were of course very familiar with the horn reflector antenna, which presumably was a very low noise antenna. Hogg had worked on the calculations of high noise and so DeGrasse and I went down there with our maser and gear, tied it in to their antennas, and we measured the sky noise.
Bromberg:Was this also a Bell project?
Scovil:This was a Bell project, that's right. This was by far and away the most sensitive antenna-receiver combination ever developed at that time, and we measured the sky noise quite accurately. It's interesting that at that time, we were missing a couple of degrees. It was a little noisier than we thought, and we had all sorts of arguments about that. De Grasse and I'd blame the other boys' antennas and their feeds, and they said we didn't know how to measure the maser noise and all the rest of it. So we never did resolve that missing couple of degrees.
Bromberg:Now, did Pensias and Wilson do it independently of your group?
Scovil:Well, we published a paper on ultranoise receiver and our missing couple of degrees was in there, but we didn't make a big fuss about it, because we thought we'd goofed, you see! Now, Pensias and Wilson were hired as radio astronomers at Holmdel, and now, you'll have to ask Wilson or Penzias about this -- certainly one advantage they had at Holmdel was the possibility of these low noise receivers, and the low noise antennas. Oh, incidentally, after we developed the low noise receiver there, then that was followed fairly quickly by Project Echo. You remember, the satellite communication system?
Scovil:The big balloon? For that, we built a fairly larger horn reflector antenna at Holmdel. We put a maser in it, and signals were transmitted from the West Coast to the East Coast. That was again followed by Telstar, which was a very large installation. There was one up in Maine, I guess it is, and over in France, and those both used our masers as well.
Bromberg:I guess I'm surprised when so many of the projects you're talking about were so applied, either to radar or to these communications satellites, that Bell also gave you the time to do this pure radio astronomy measurement right in the middle of things. Is that the way things usually worked?
Scovil:Well, this wasn't so much astronomy measurement as it was a question of measuring the sky noise, and of course a measurement of that noise was fairly critical, because it would confirm that indeed it made sense to do satellite communications with these systems.
Scovil:Otherwise it was pure theoretical speculation, and you like to have confirmation when you're spending all this money. After that, then Penzias and Wilson arrive, and they began to make use of the antennas and the masers down at Holmdel for radio astronomy purposes, and amongst other things they became interested in these missing few degrees. They measured it much more precisely than we did. Of course, I think at that time, and you'll have to ask them about it, I think some theoretical work was done on Big Bang suggesting that there would be a missing few degrees, and at that stage of the game, they published.
Bromberg:That's right, that was the interaction with Dicke, I guess.
Scovil:That's right, with Dicke. So, I think that was the sequence there. Now at about this time two things happened, almost of a political nature. One of them was the big phased array radar system -- the mono pulse radar systems with which we'd been concerned were replaced by big phased array systems, and masers were no longer appropriate for that, so our main military application disappeared.
Bromberg:OK, that's interesting.
Scovil:Now, the other thing that happened is that we were legislated out of the satellite communication business by the formation of COMSAT.
Bromberg:I don't remember the dates on either of these things, so maybe --
Scovil:OK, maybe we can check that, but with the formation of COMSAT, AT&T clearly was no longer going to be the one and only in the satellite communications business. And with the advent of phased array radar, the masers were no longer particularly practical there. So we phased out. We stopped work.
Bromberg:Now, I don't know your subsequent career, what did you do after that? Did you go on to lasers?
Scovil:Yes, we did. The lasers were a pretty obvious frequency extension, so we did work on lasers, like neodymium: YAG for example was developed by my group. We did things of that sort.
Good. I'm very grateful to you for taking the time to talk with me today.
Rudi Kompfner was Director of Electronics Research