Oral History Transcript — Dr. William Bridges
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William Bridges; January 28, 1985
ABSTRACT: University training at University of California, Berkeley, under John Whinnery and Charles Birdsall. The adaptation of the argon ion laser to an airborne reconnaissance system. Other laser researches are touched upon, including the gas dynamic laser and laser isotope separation. Relations between basic research and systems research at Hughes Aircraft Company. (See also the interview of W.B. Bridges by Richard Cunningham on file in the Laser History Project Archives).
Bromberg:I am speaking to Professor William Bridges in his office at Cal Tech in Pasadena. We are going to start in a little bit by trying to understand the kind of education. You were in the Berkeley electrical engineering department, is that so, from ‘56 to ‘62?
Bridges:Actually ‘52 through ‘62, I was an undergraduate at Berkeley ‘52 through ‘56 in electrical engineering, and then a graduate student from ‘56, formally through 1962. My Ph.D. is dated June 1962, but actually I left Berkeley in June ‘61 to work for Hughes Aircraft Company. Actually I signed in at the Hughes Aircraft Company in December, 1960. So I worked two weeks at Christmas vacation, and took a six month leave to get things squared away at Berkeley and then came down from Berkeley in June ‘61, finished writing my thesis in the evenings, and then it [Ph.D] was formally awarded in June ‘62.
Bromberg:I see. Well, the purpose of that question is to get some feeling of the background, the varying backgrounds of the people who went into lasers.
Bridges:Was I taught quantum mechanics? [Answer to a written question.] Yes, I took actually just one course in quantum mechanics. That was not my interest at all. My interest was “real” electrical engineering, and my thesis subject was involved in microwave tubes.
Bromberg:Were you a Whinnery student?
Bridges:I started off as a John R. Whinnery student for my Master’s degree. John was my Master’s thesis advisor, I was interested in noise in microwave tubes, how the noise processes actually worked in electron beams. I started to pick up on some work that John had done personally, years before, and it was the subject of my Master’s thesis.
[Break for phone call]And then after I got my Master’s degree in September 1957, I continued to work with John, I guess it was for two years while I was teaching at Berkeley as well. To be honest, I got so engrossed in teaching that I didn’t get a lot done on my own research for those two years, ‘58 and ’59. And then a friend of John’s came to Berkeley, first as a visitor and then as a permanent faculty member Charles Birdsall, and he and I hit it off very well, and in fact, while John went off on sabbatical for a year, Birdsall supervised all of John’s students. We hit it off so well that when John came back we agreed that I would switch to Ned Birdsall as a thesis advisor, and in fact I was Ned’s first Ph.D. student. [“Ned” is Charles K. Birdsall.] I started out with John Whinnery studying noise in electron beams but then Ned and I got off on a slightly different subject; the title of my thesis was “An Electron beam instability.” But having nothing to do with lasers or quantum electronics or quantum mechanics1 even. It was a totally classical microwave tube problem I guess.
Bromberg:What was the situation then? Tube noise was one of the forefronts of research I would guess?
Bridges:Yes, it had been. It was sort of the most challenging area of research, as long as microwave tubes were used in a receiving fashion. And people were very interested in noise. And in fact, some very important things had been done at Hughes by Mal Currie arid Don Forster. The tie there is that Currie was John Whinnery’s student and had done some good work at Berkeley, and then went on to Hughes, and he was working then with Don Forster. In fact, I think at the time they were working together, Don was also a graduate student of Roy Gould’s here at Cal Tech. And so it was a natural that when I got my Ph.D from Berkeley that I would consider Hughes as a good place to work in the microwave tube business, And I did, In fact, I joined the group that was then doing this work with low noise microwave tubes.
By that time Currie was associate lab director and Forster was the section head in the tube activity. So I would characterize my graduate background at Berkeley as in microwave tubes, definitely not in quantum electronics, In fact, I had summer jobs in 56 and 57 at Varian Associates, where I did work with an ammonia beam maser and I remember talking to John Whinnery about it, saying “Well, gee, that might be an interesting thesis area, maybe I should switch from microwave tubes to that?” And John was not particularly enthusiastic about it, I’m not quite sure why but it was a question of maybe, well, gee what would you propose to do? I mean, it has already been done. Here is this device. What more is there to do on it? And at that time, as a sort of young graduate student, I couldn’t think of an answer to that. And so we didn’t. [switch to maser research as my thesis topic.]
Bromberg:But now Yariv was already doing solid state masers.
Bridges:With John Whinnery, yes.
Bromberg:Did you have much interaction with him at this point?
Bridges:Well, Amnon also has a “tube” background, and he did his masters degree also in tubes, and then switched to masers. I’m trying to remember exactly when he made that switch, I think it was probably the year after I talked to Whinnery about getting out of it. [the tube business]. We used to have brown bag lunches almost on a daily basis in the tube lab. It was sort of a place where all the students congregated and shot the breeze, mostly about politics and all that. As a matter of fact, there were not usually a lot of technical discussions at lunch. So I saw Amnon on a pretty regular basis
Bromberg:Let me just say what I understand, do correct it if I’ve got it wrong. But you were really talking about ammonia beam masers, and he was coming in with the first solid state.
Bridges:Yes. Actually what Amnon’s research was doing was the answer to the question that John asked: “Well what do you propose to do? The ammonia maser is sort of already pretty much in hand. I don’t see anything that we could do with it.” And the answer to that is, “Yes that’s true, but here is another thing to work on.”
Bromberg:Did the ammonia beam maser stimulate your interest in quantum mechanics? You say you were not terribly…
Well, it was an interesting kind of thing, but my background really is engineering, and we sort of looked at the maser for these two summers at Varian. They were considering using it as a clock, I got off thinking about a much more engineering aspect of it, namely, the ammonia maser needs a vacuum pump. And in fact this particular contract at Varian was to develop an airborne ammonia maser. By the way this is an interesting side light on technology, but this whole business, the whole contract at Varian, was to make this airborne navigational system. And it was clear that you couldn’t use an oil diffusion pump in an airplane, because the oil has to slosh around at the bottom. And so the program there [at Varian] was to build a maser, but also to build a vacuum pump that you could put in an airplane.
Lou Hall, was considering the chemical getter pumps using titanium. And then how do you get a film of titanium, well you can evaporate it, or you can sputter it, and before he was over, Lou essentially rediscovered, or reinvented I don’t know exactly the proper term what is now called the Vacion® pump or the sputter pump, which [has become] a major industry. But that was done at Varian for the purposes of getting a pump to go on a [airborne] maser. Well, the maser disappeared into oblivion, but the pump remains a multimillion dollar a year business. And so, while we had a maser there, [at Varian] my project as a summer student was to work more with the vacuum pumps, and that was a fun thing to do.
But even after those summer jobs, I continued on in the microwave tube activity [at Berkeley], and came to work at Hughes because it was a microwave tube place, not because the laser had just been discovered. I mean, admittedly, that was the excitement around the [Hughes Research] Laboratories. But why I came there was to continue my work on low noise microwave tubes.
Bromberg:Now I just threw in a question there on the quantum electronics meeting at Berkeley, because you were right in Berkeley.
Bridges:No I didn’t go.
Bridges:In fact, I don’t know when that meeting was.
Bromberg:I think it was March [What year? 1961?]
Bridges:Oh, I was probably trying to figure out how to pack and leave in June . At that time, we had a second child on the way. That was the big stimulus to get out. Ann was two years old, almost two years old [actually 18 months], and Bruce was almost ready to be born . So time to leave-- get a job. That was the reason for leaving before actually having my thesis finished. Later, Birdsall said, “never again” would he let a student out without finishing it. It was too painful to do this manuscript by mail over the next year. And it was painful for me too, because I very quickly got out of the microwave electronics business and into the laser business at Hughes. And so I was doing something [else] during the day, and really writing my thesis in the evenings, or finishing my thesis in the evenings. That was difficult. Do you want to go on in historical sense?
Bridges:OK, some of it is already probably there in the manuscript.
Bromberg:There is no point doing it twice.
Bridges:Well I think I did a pretty good historical job for Cunningham. So maybe the best thing to do is go ahead and treat some of these questions. Because these are raised independently of what is on the Cunningham interview. Regarding classified research and how it affected us. In the earliest days, when we were working with the argon ion laser, not a lot of it was classified. It was not a high powered laser. But it was “military”. I mean, our work was very heavily biased by: “What can we do with this for military applications?” Hughes, if you haven’t already gotten the flavor, has in mind one customer. And that is the Department of Defense. It is nice to think about commercial diversification, it is nice to think about science, and all that kind of stuff. But when it comes right down to it, “Can you find a military customer for this breakthrough?” was always the question asked —— at least in this era at the research laboratories. And since I still have ties with them, I think it is true even today. Commercial application is just awfully hard to find a home within Hughes.
Bromberg:I have heard that even the helium neon business was started as a commercial application because they wanted to get experience that they could sell to the military. I don’t know if you happen to know that?
Bridges:You mean the helium neon product line or the research?
Bromberg:The product line.
The person you can really talk to about that is A. Stevens Halsted III. But I think it is not as clear cut as you just said. Some people, for example, Steve who was the department manager, [at Hughes Electronics Dynamics Division, beginning in 1969] really did want to make it a successful commercial venture. And eventually left his role as department manager when he decided it was just not going to really ever be an expanding commercial activity within Hughes. It is a personal opinion, but I think that Hughes when you come right down to it just doesn’t know or doesn’t care to deal with commercial customers. They have one customer that is just more important than that. And occasionally little commercial things get done, but when you come right down to it, the Department of Defense calls the shots.
And that was the case in my work there, I had worked in the laser business for a couple of years when the argon laser came along, but from that discovery in 1964 through about 1969 which I became Department Manager [at HRL], those years which are alluded to here, the very strong emphasis was on applications--and particularly military application. We really only identified one military application, that was this line scanning night reconnaissance system. And the company, at the Culver City organization, or what was then the R&D division, was very interested in making a system. By the way, this is a little out of order.
But one of your other questions her says that [in your study of] DTICs summaries that you were struck by the “systems emphasis of Hughes, as opposed to… “ that [emphasis is] real; that’s not an artifact of your DTIC system. Hughes is a systems company, and you never forget that when you work there. You may do the best device physics in the world, you may have the best device since peanut butter, but if it doesn’t fit into a Hughes system, it is probably not going to mature within the company, because systems are what they build. And devices are looked upon as a way of getting leverage in the systems business.
The ion laser is a perfectly good example of that. Here is a laser that is good for 50 million dollars or more in [annual] sales for Coherent [and] Spectra-Physics. Hughes wasn’t interested enough… They tried to bring it to the commercial market place; [and] did for a brief time, then just said, “Oh, well, this just isn’t our thing.” If it had found a home in a military system, if this line scanning reconnaissance system had continued to be successful, I am confident that Hughes would be a manufacturer of argon ion lasers today.
Bromberg:It would be nice to get a little feeling about the nitty gritty of how that process works. Here you make this laser, and it is pretty exciting, and you are elucidating the spectroscopy, now at this point does your supervisor go to R&D people and say, “We have this, do you think you can use it?” Or do the R&D people come to you? What the linkages?
In this particular situation, it was the people from the R&D division, let’s say the Aerospace Group, came to us, In the following sense, though: they did not invent this line scanning reconnaissance system idea; it had already been thought of by Perkin - Elmer Corporation and Perkin - Elmer had already built one with a helium neon laser in it. In fact, Perkin - Elmer had worked very hard to try to make a bigger and bigger red helium neon laser to fly in a system. And they actually made one that went up to all of a 100 milliwatts.
Well… and demonstrated it. In fact, I think that although it was a classified system there was a leak to Aviation Week, and even some pictures published as a result of Perkin Elmer system. The Hughes systems people were aware of the Perkin Elmer work, and they had looked at it and concluded that it just wasn’t ever going to be practical with that kind of laser in it. And therefore were uninterested in pursuing it as a system. And then when the argon ion laser came along with the potential of watts rather than milliwatts, when they heard that, suddenly that number clicked into their systems analysis and they said, “Whoa, this now practical.”… and then they came to us. They came to Malibu and said, “Hey look, we’ve been tracking this work at Perkin – Elmer. We’ve done the system calculations. We’ve concluded it isn’t practical with helium neon, but it would be practical with argon. The photo tubes are more sensitive in the blue, [and) you can also give us more power.
And it started off just months after the discovery of this thing - when Art [Arthur N. Chester] and I were still doing spectroscopy -- they wanted to know, can you give [us] a quarter of a watt laser that we can fly in an airplane? And we said, “Sure.” Not realizing how hard that was going to be.
Bromberg:Do you know, that seems extremely different from Bell because I can’t imagine somebody coming to the research people the research department at Bell -- and saying, “Well alright, you’ve invented this thing, now will you please give us a certain power level.” The research people would probably have said, that’s not what we’re interested in doing right now. So Hughes Is there a real difference?
Bridges:It’s very different, No… People come from the rest of the company, come to the Hughes Research Laboratories all the time, asking for a state-of-the—art device, if Hughes has in fact developed that state-of-the—art device. That was true of the ruby laser. Now the only thing that was really different with the ruby laser was that there was a group of people who left the research labs and went to the R&D division, and so they became their own producers.
Bromberg:Oh, I didn’t know that.
Yes. Stitch, Mal Stitch was one of the people. And when you interview George Smith he will go through that. That happened just before I got there, so I am really not the best person to talk about it. So that kind of thing would happen. I something became so important that the people from the research labs actually left to get it into production…But it was typical of having a break through at the research labs, that they would come and say, “Can you build us one?” And we did. We responded to it.
Now I don’t know that every department manager, every personality, or whatever would have responded with the same enthusiasm but my boss, Don Forster, and his boss, Mal Currie who was associate lab director, or actually I guess there was another level in there -- [Electron Device Physics Department Manager] George Brewer -- Curry, Brewer, Forster, and then me at the working level. We were all engineers. And our attitude was, OK, if this is the only way we can get you on the air. We responded to “The Hughes modes.” You get this new device, and then you use it as leverage to put together a multimillion dollar system. And that’s exactly what we did. So we spent the next five years in a very serious engineering effort to build practical argon ion lasers. Practical, and for airplanes. These were very rugged. I mean the kind of stuff we built then is still not available today in terms of milspec argon ion lasers. I dare say you would have trouble flying a Spectra-Physics or Coherent laser today.
Bromberg:And I’m understanding-- is this correct or not--that you enjoy this kind of problem too.
Sure, I considered myself an engineer. I still do. It wasn’t to say that it wasn’t hectic, and that it wasn’t frustrating not to be able to follow the science side of things, because as a device physicist, I also wanted to know, “How does this thing work?” And the only way to do that is to build experiments. And on the other hand we were working very hard to build full—up lasers that would work. In a way, however, the two are not contradictory. Because often when you are putting together scientific experiments, you don’t pay very much attention to the technology, and you put together very crude things, just to do the experiment.
On the other hand, if you can benefit from the technology from a development program, then some of your scientific experiments work a lot better, because you have got good technology to work with. And I think, in retrospect-- although it didn’t seem like it at the time we benefited a lot. By being forced into developing these improved products, we had better technology to do the scientific measurements. We could operate with more current, more power, better mirrors, better windows, because we were forced to do all those things for development. And it was the same guys, the same technical people, the same technicians and so the technology transfer was instantaneous.
Bridges:It’s just that it required a certain schizophrenic personality to work on both things simultaneously and keep your sanity, and your frustration level down.
Bromberg:Partly you spoke to that point when you here said that Forster very much encouraged this double…And I asked you here somewhere whether this was a common management policy or something idiosyncratic for him or what.
Well, I don’t know. My problem is that I worked for Don most of my technical career at Hughes, we moved up together. He was associate lab director when I was department manager. You know, we started from section head [Don) and staff member [me] and moved up, so I haven’t had a lot of experience with other managers. Don was a brilliant guy who understood systems, he understood devices, he was a dedicated company person. I don’t think he consciously thought he had a management style, or that he even worried about being a manager, but he was a good manager, and was very successful in a number of things that he managed, not just the laser work.
He had the millimeter wave tube work under him, which was a whole other story, but a very successful activity, technically. One that wasn’t published as well nor did the company benefit as much by it at the time, but an extraordinarily good activity. Plus raising six kids. Maybe you have to be well organized if you have six kids. I only have three, so I never had to be that well organized. No, Don was an extraordinarily good manager, and I don’t know that he consciously had this management style. He constantly pushed us into doing the development kinds of things for the company but he certainly encouraged us to write up things and present them at technical meetings as well, and to attend technical meetings.
Now the frustration, of course, was that you are always at technical meetings with your peers from other companies, like Bell Labs, who were working solely on the research side of things, and it was frustrating to go and compare noted because we knew we weren’t doing all we could. We knew we were doing the kind of things they were doing with about 30% of our effort, and the other 70% was getting a product out the door. So that was a frustration.
Bromberg:Of course there were two kinds of people at Bell Labs: there were the research people, and then there were people like Gene Gordon in development, and I always think of him being more like Hughes.
Bridges:In fact, most of our interactions in the ion laser era were really with division 20, with Gordon’s people, rather than division 10 which is more research. But Gordon’s group in that era was also able to do, I think, first class research as well. But you are right. They were more oriented towards actually getting things demonstrated and put in a useful form for internal use at Bell Laboratories.
Bromberg:OK. So there was this tension, and probably there were horrendous work weeks. Is that a correct inference?
Bridges:Oh, yes. There was one time when we were getting a tube ready to meet a flight test date, when we essentially put together a 24 hour effort with 3 teams of Ph.D.-plus-technician to essentially “mother” an ion laser that was being processed for a whole week of 24 hour days. That was not usually done in research, but in this case, the whole section was tapped for manpower. It failed too, by the way. The tube broke, ultimately, and we had to do something else instead to make the flight date.
Bromberg:In this case, when the R&D people come over to you and say, “Can you get a fourth of a watt, or a half of a watt, or whatever, do they just leave you then to work by yourself and report back, or do they actually work with you, or …
Well, in this particular case, the interaction happened on a bunch of different levels -- not all good. They were willing to supply some money out of their systems activity to cover a very small amount of our work, whereas a lot of it was being done on IR&D, and some was being done on direct Air Force funding. Actually, at that stage, we did not have any direct contract support, I think, in 1964. We already got a little money from the systems people to pursue this. No, the interaction was fairly regular, and in fact at one point, we actually had a department manager [the systems group] activity come up after hours and watch what we were doing. That got to be so nervewracking on the technicians that we had to essentially exclude him from the building. He was so desperate to see how the tubes were being built, and were they to make their flight test, that they made our guys nervous. We lost a tube, physically a tube when a technician was so nervous when this department manager was watching him, that the tube broke. And at that point, we said “No more. No visitors, even company people.” The pressure was so high at that point.
There was also a constant interacting on a specifications level. You know, they ask for a quarter of a watt, and we gave them that, two weeks later. Then they said, “Oh, that’s fine. How about a watt?” And we said, “Well, OK.” We succeeded in doing that, and then by this time they said, “Well, it would be nice if we could have two watts, because we have got some little inefficiencies here and there in the system.” And that’s when we started to interact back. And it turns out that some of the optical designers they had working on this systems, first of all, didn’t understand laser optics, Gaussian beam optics, and they were using classical optics analyses, which we had to explain to them was not the right way to do it.
And secondly, they had no concept of what doubling the laser power was going to cost them in size, weight, and development. And they were worried about, will this $500 filter cost us $1000 to make it that much better? And we kept saying, “If you can make it that much better, do it, that is so much cheaper than what we are doing.” So there was an interaction back and forth, trying to explain to them what we were doing so they would know how to set the specifications. And of course, as interested technical people, we sort of got involved in how this system really worked. And we started making suggestions, and interacting with those people—-both on an optical design level and a mechanical design level. I mean, we had a mechanical designer come up and initially design us a laser package that would have withstood atomic blasts. And we had to convince them that, no, it didn’t have to be that rugged, and so forth. So there was a technical interaction with engineering people.
Bromberg:Is there also an interaction with the manufacturing people. I mean, are there other interactions through the company?
Bridges:No, we were the manufacturing people in this case. We had zero interaction... The Hughes manufacturing people really are production people, and so at the research labs we didn’t really have any call to work with them. It is true that we did call on the microwave tube people in our Electron Dynamics Division to help us out on a few things, but since we ourselves were old microwave tube people, that was a natural tie. For example, doing metal—ceramic work, doing metalizing, brazing, that kind of thing we did. We asked them to help us in specific things.
Bromberg:Is there any other group that one should think about in terms of being a strongly interactive group? Are the contract writers, I mean is there a group that goes off to DOD, any other parts of the company?
Bridges:You are looking at them. The Research Labs staff members were responsible for their own technical interaction with the funding agencies. I wrote all the proposals that our group…Or I should say, our group wrote all the proposals. Nobody was exempt from contributing to proposals, and no one from on high assisted us. And that is the model at Hughes Research Laboratories, there is no separate marketing activity at all. The technical staff does their own marketing. , And they are expected to do it to the tune of about 50% of the support of the laboratory. About half the lab budget is direct contract support. Their other half is IR&D.
Bromberg:You must also be pretty much up to date on military requirements, on what the government…You read Aviation Week. Then I expect you would be talking to these guys?
Bridges:Yes, I still read Aviation Week. We were interested in government requirements, and we were constantly looking for government applications in addition to this line scanning reconnaissance thing. We answered a lot of funny little questions that would come in. Could it be used for this? Could it be used for that?
Bromberg:You said that the argon work was not largely secret. It was at a very low power level, and therefore this question about the effect on your research of doing partly classified work isn’t pertinent.
Bridges:What was pertinent was that the Hughes Aircraft Company was highly government oriented to build an argon laser that would fly in an airplane and deliver the best performance, and all that kind of stuff. So that was what motivated us, not just the general science of exploring things. Now we were self-motivated to do science but that was all. That kind of work was done in addition to and some times in conflict with-for time-the actual engineering of these things. That’s the argon work. There was later work, of course, that I was involved in, the early gas dynamic laser work, which was done as a subcontract to Avco. That was, of course, a project that was totally classified. That was such a big project it was like working in a totally classified community, so in a sense we were still publishing but only to this very small community.
Bromberg:And there, the only thing you felt was, for example when you went home to talk to your kids at night, you didn’t talk about that. But otherwise it resembled the other activities?
Bridges:Yes, The additional complexity there, of course, was working with another company as well as another division. Again, we worked cooperatively with the R&D division at Hughes Culver City but we were both then sub—contractors to Avco. It was a very interesting and sort of exciting interaction. It partly overlapped the ion laser work. We started with Avco I believe in 67 or 68, and that interaction continued through my tenure as department manager through 7l at least. Probably somewhat after that as well. Brornberg: And that would be, Ed Gerry?...
Bridges:Ed Gerry. Yes.
Bromberg:So that would be a bunch, I would guess, of very stimulating people?
Bridges:Oh, yes. It really was. And we had monthly meetings, usually either in Boston or Malibu and so there was a constant interaction. And again it was a very educational process, because everyone thought they knew what they were talking about, and in the course of talking we would find we did not, and have to go away and really think things through and then come back and explain it.
Bromberg:Was work on laser amplifiers for radar receivers, was that a big thing?
No, Not really. That was a little paper that we did as a result of having discovered and measured very high gain in a particular laser, in this case the neutral xenon gas laser, the neutral xenon gas laser at 3.5 microns. That was some work that I had done earlier and this was an attempt to find an application to push it. Would it work as a laser amplifier? So that was the question we asked. Would it have any practical value? And as a result, we looked into the question, and concluded: yes, in this particular case the gain was high enough so that if you really were going to make a laser system at 3.5 microns, you could consider using a low noise amplifier ahead of an infrared detector to improve its performance. And we published a little paper that showed under what conditions that would be an improvement.
This is another one of those interesting examples of what did we really do at Hughes. As a result of a contract we actually made a 3.5 micron oscillator, a 3.5 micron laser amplifier, and detector, and I hand-delivered them to Wright field Air Force Avionics Laboratory, set them up and demonstrated them for my contract monitor and left them there. That was a result of the contract. Now it turns out, that particular laser is not at all powerful, and the laser as an oscillator, the xenon oscillator, is not powerful enough to be a practical system. Had it been, it would have had this interesting effect that an amplifier would have been a big help, and we had the amplifier there.
Some people proposed using CO2 lasers as low noise amplifiers in systems, in fact the business we discussed at lunch with Vic Wong, in applying this phase conjugation technique to a C02 system required high gain, low noise preamplifier, which could only be made up using C02 lasers in this C02 laser system. And that was one of the reasons I didn’t think it was too practical, because I knew how hard it was going to be to build that kind of low noise amplifier. I had done it earlier with xenon. But generally speaking, the low noise amplifiers have never really found their way into systems.
Bromberg:I guess I always think of lasers as being high noise.
No, not true. Any basically quantum amplifier is sort of noisy compared to the microwave range. You sort of think of fluctuation noise as h2B in the optical regime, and kTB in the microwave regime. But you can have an ideal quantum amplifier, which is the lowest noise you are going to get. And compare that to the noise fluctuations in a detector without such an amplifier. And it turns out that the figure of merit for a detector is basically what is called the quantum efficiency. So if you have a detector with the quantum efficiency of 20% it is sort of 5 time noisier than ideal. The corresponding figure of merit in a laser amplifier is called the inversion ratio, which is just roughly N2/N1 in this case. And if you have a laser that is really well inverted as the xenon laser turned out to be, which we sort of measured, it can have a better noise performance than a detector with poor quantum efficiency.
And so if you put the two together, you end up being limited by the laser amplifier noise rather than the detector noise. Jerry Picus and I published a paper on how to make that improvement trade off, and gave the specific results for our xenon amplifier. But you need a laser with high inversion ratio, not high power, but high inversion ratio. And not many lasers have that. C02 is not bad; xenon was sort of anomalously good in that regard. So lasers as low noise amplifiers really haven’t found practical application.
Of course, lasers as high power amplifiers—that is an important use of lasers, I am no longer in the weapons laser business, but a lot of the earlier proposals really required that you start with an oscillator and build up through power amplifiers, rather than one big high-power oscillator. I donut know what the current approach is, but I would suspect both are viable alternatives. Just depending on the laser, whether it is a C02 gas dynamics laser or a hydrogen fluoride laser, or whatnot. The so-called master oscillator/power amplifier route is still one that can be important, and may be the way to go.
Bromberg:That’s something I just didn’t know.
Bridges:We did make a high powered laser amplifier at Hughes, not for weapons, but for radar. It was a one kilowatt average power amplifier. In the radar game you had to do that, because you need this very stable signal source, which you can only realize with a small low power oscillator, and then build it up to high power for transmission. We built the high power laser amplifier for a radar experiment at Rome Air Development Center.
Bromberg:Now, is that something you were involved in?
Bridges:Yes, I got involved in all these things in one way or another. That started out as a project that a technician and I had to get going, and then we hired another staff member to carry it on to fruition. In the early days there weren’t very many of us there, at the research labs.
Bromberg:How big was the research lab?
Oh, when I joined it was 450 people total. The gas laser activity in Forster’s department started with me——one person——and then in ‘63 we hired Peter Clark, who is now a big manager at TRW, and then followed by Steve Halsted in 1965, Howard in 1965. Steve and I did most of the work on the airborne ion laser. Neild Mercer was another young man who joined us from Yale shortly thereafter. Peter Clark gradually went into the C02 business: he was really our first C02 man. And then Mike Smith came, and this high power radar amplifier that I worked on--had designed—-he took it over and actually got the thing built.
This was again this business of “We have this device or devices,” and we were trying to find military applications. Well, the C02 laser, the minute it came along, we were already working on argon, we sort of jumped on the C02 and said, “Well what are the applications?” Well, radar is one. We quickly became part of a military-industrial C02 community, worrying about this problem, got a study contract first and then a hardware contract in competition with what was then the old TRG outfit, and Raytheon.
Three of us competitively were going to build three high power laser amplifiers or systems for the government. TRG went broke during that interval and went out of the laser business, and Raytheon and Hughes both finished successfully their activities. The Raytheon laser was installed at Lincoln Labs, I think it was the Mill Stone facility, and became part of a C02 laser radar, and the Hughes version was installed at Rome Air Development Center and became part of what was called the CORAL radar.
Bromberg:Now, I have heard about one competition between TRG and Hughes on a range—finder, that must have been a different, earlier one? Were you also involved in that?
Bridges:No. I was never involved in any of the solid state laser work beyond one little interaction at the research labs with Vikevtuhov and Jim Neeland, on some measurements on a early ruby laser. That was sort of a cooperative activity there. And then I never really got involved in solid state lasers again.
Bromberg:Question 11 is still outstanding. I don’t know whether it is an interesting question at all? [Parametric Studies of laser performance]
It seemed to us that this was really the appropriate way to go, and many people did this kind of activity. Similar measurements were being done almost simultaneously at Bell Labs, in Gene Gordon’s group, at Spectra-Physics, at Raytheon, and probably other companies. If you are trying to figure out how this device works, you have to know how things vary with parameters. So we wanted to know: how does it vary with bore diameter, for example, or current density, or gas pressure. Then you try to fit these into a physical model of what’s going on. So you play back and forth, theory and experiment. But the experiments really are these parametric studies. They also give you good design data. So if we are building a two watt laser and people come in and say “We’ve got to have a ten watt laser, how big is it going to be?”
We could tell them. So we very quickly got this information. These were largely done under Air Force sponsorship out of the Avionics Laboratory. And the resulting publication…It’s embarrassing because we always wanted to get around to publishing it. Its not in the archival literature, but we published about 600 pages of government reports which are classic best sellers. And we even refer to them. In fact I will point them out in my bibliography because they were very important publications, a judged not by me but by the people who have used them, all over.
In fact, it’s funny, even in this recent law suit Coherent vs. Spectra-Physics, over the Hobart & Mefferd patents, 1985 you find Xeroxes of those reports in somebody else’s lab notebook that they were using for design data. Essentially those have been very influential things; we never published them. That was the one thing. We never had time to sit down and contemplate and figure out what we were going to publish. Their interesting thing is that the Bell Labs people didn’t publish much either, and so all of these important parametric studies remain unpublished. We didn’t have time to do it, The Bell guys-Gordon, Labuda and Miller--didn’t either, Dick Miller ended up with a 200 page manuscript and 100 figures and no place to publish it, and then he got out of the business and it just died.
Bromberg:That’s very interesting. So that’s why I have never come across it.
Bridges:They’re government reports, yes. And by the way, if anything should go into the archives in addition to published things, there are about three government reports that really summarize the ion laser work that was done at Hughes in that interval by me, Steve Halsted and Neild Mercer. Those have become, as I say, classics among the people who care. But you have to get a copy. Or at least know that it exists.
Bromberg:Yes, you have to know that it exists.
Bridges:Actually Steve Halsted, even after we were both managers, we tried to decide that this stuff really needed to be published, and we contracted with Wiley to publish a book on ion lasers. It never got off the ground. Both of us were so busy, we never even got started on a manuscript. The only thing that came out of it was one publication called “Ion Laser Plasmas.” It was an invited paper for the IEEE, authored by myself and Halsted, Parker, and Chester, and it was hard to get all those busy people together to even do that review paper. I did most of the manuscript originally, and then shoveled it around. That was sort of the best we could do to summarize the work that had gone on over a long time and in a lot of different laboratories, largely our own. But the book never came out. What we should have done was slap hard covers on our government reports, or just issue them somehow that way. That would have been valuable at the time. I learned something there: never refer to something “to be Published” unless it has already been submitted. But the Bell people didn’t fare any better.
Bromberg:Is it an interesting question whether the argon ion laser was investigated as a high power laser?
Bridges:It depends what you mean by “high power.” For a CW visible laser, 10 watts is still high power, 20 watts is high power. For a weapons laser of course, it was never thought of as a weapons kind of laser.
Bromberg:Well, let’s go to question 14, because question 13 we really did. Suddenly, amidst everything in that interview with Cunningham, you talk about laser isotope separation. What kind of an enterprise was that on your Part?
Bridges:You know I was at Cal Tech as a visitor from ‘74 to ‘75, and prior to ‘74 at Hughes I was involved in these systems activities of the mechanical version of phase conjugation, which we called “adaptive optics”, and also some optical schemes for doing a photograph of satellites from the ground, you know getting rid of atmospheric distortion. I was project manager on two such activities. And when I came to Cal tech, and had a chance to think for a year, I realized I really didn’t want to go back to managing those projects. So I was looking for something else that would be interesting to do for me in the laboratory. It was a very selfishly motivated kind of thing. So I sat down and consciously thought of what would be interesting to do, what could I propose that would be…And so it came out of that. And I had, I think, a bit of inspiration on doing this isotope separation scheme. It is not profound, although the patent may issue actually this year, believe it or not. We have been fighting with the Patent Office, since 1976, when we filed. So we have an 8 year running battle on filing on the basic idea.
Bromberg:Is that because they won’t acknowledge its novelty?
Bridges:I think it is because they don’t understand…It is hard to say. We have had an almost laughable sequence of patent examiners. The first guy was I think, frankly, senile and retired, actually. And since then it has had vagaries…But by the time we finally convinced them that, look, here is the novelty and now you finally do understand it, then they decided to issue a patent. Unfortunately, I couldn’t interest Hughes really in funding it at a very high level. We sort of came to a negotiation, after I went back to the research labs, that they would let me work in the laboratory, and have fun on what I wanted to do about half—time if I would continue to work on some things of interest to Hughes systems. And so, I did for the next two years. And then I came here. And I tried to get some funding out of the Department of Energy for laser isotope separation and they were totally uninterested. Not only in this scheme, but in any scheme, I think.
Bromberg:That was about ‘78...
Bridges:That was ‘77—’78.
Bromberg:At the height of their lack of interest, I guess.
Well, they already had two warring factions with two competing schemes within the DOE. The last thing they wanted was a new scheme, I would think. And I guess the laser isotope separation thing was cooled off completely, because no one knows quite what to do with it if you had it, I guess. And by the way, it has been fun, though.
I had one graduate student try a version of the scheme. Unfortunately, we did not have any of the equipment to do the right thing. So we made a stab at the very crude thing. It did not work, as a matter of fact. We got a null result. But at least one student got his thesis on that--Andy Gabriel. He was my first graduate student. And I have had a couple of senior thesis projects that have been very educational for the student, but still have not resulted in net isotope separation, so I don’t know.
I am still bullish that one could do it. I still think the idea will work. I never made any claims that it was really going to be a practical, revolutionary kind of thing. I may try it again if I ever get the equipment all sorted out in my laboratory at one time and working. I might try it again with another student, Just as a sort of “for fun” thing. But it really started as a conscious effort to let me do something in the laboratory. And one of the things that came out of it was an interest in what is now called the “opto-galvanic effect.” I guess I am an independent discoverer of that, but the people at the Bureau of Standards published before I did. They had done it before I did. I did it independently, and about the time I was ready to publish, their publication came out, so I didn’t do my preliminary results. I waited and published a more extensive thing on my own measurements.
Again, not a new thing. When you look into it, it was known from the l920s that such an effect would take place. And it has been used in a lot of scientific applications, particularly in spectroscopy with lasers. Do you know who invited the term “opto—galvanic effect?”...I didn’t coin that, I don’t like that expression.
Bromberg:It sounds very much a 1920s term.
Bridges:Yes. I don’t know whether the 1920s people used that term either, but the Bureau of Standards people who published first said “opto—galvanic effect.” But basically, if you shine laser light on a plasma, and you tune it to an atomic resonance, you can perturb the processes in the plasma enough so that actually it changes the voltage across the gas discharge. So by shining laser light in, and modulating it, you can see that modulating on the voltage. It makes a dandy frequency—sensitive detector. In fact, if you now sweep the wavelength of the laser light, what you do is map out the absorption spectrum of the gas discharge. Just by looking at the voltage fluctuation across the discharge. It turns out that it is a very sensitive technique--surprisingly so. Which is why the Bureau people were interested in it. It is quite competitive with several other absorption spectroscopy techniques. And I have had some fun probing that. But never any funding, because it is sort of a scientific curiosity kind of thing.
Bromberg:And this is while you were still at Hughes?
Bridges:Yes. I discovered it while I was at Hughes trying to do this isotope separation thing. It sort of naturally comes out of that...
Bromberg:So you didn’t have funding because....in the Hughes context?
Bridges:Well I did have a little IR&D fund; that’s where I able to publish this one paper. But then coming to Cal Tech I didn’t get funding to pursue it. I have in fact bootlegged it with a couple of students, and they have had a lot of fun doing things, but there has been no formal funding to pursue it.
Bromberg:Now what was Hughes’s attitude toward patents? Of course I am going to ask Smith, I just wonder if you...
Bridges:Well, I think as a matter of fact, that you really ought to talk to George, because I think the attitude is now changing. In the past, I think Hughes did make a conscious effort to try to encourage people to file for patents. But, ultimately, they would look at it and say, in a lot of ways, “Does this patent have commercial applications?” Because so many of the people working on government type ideas, a lot of the patents would be for systems, or things, that would be of really only government interest, like reconnaissance systems, weapons systems. I have some like that. And the real question is, if the government owns them any way, and they are the only customer, why bother to patent it? And so a lot of Hughes patents were judged technically worthy, but simply not financially reasonable to pursue, and some things were not pursued. But if it had commercial interest, they would go after it and encourage patents. Largely, I think, towards the cross licensing mode with other big companies. The ion laser patent was sort of interesting because it was with small companies that they interacted, or smaller companies, not the giants.
Bromberg:Did you get involved with the companies that started to develop the ion laser?
Bridges:Yes. Right from the very beginning. At least I had a lot of conversations with Earl Bell at Spectra-Physics. I never thought about leaving to start my own ion laser company. I think I knew too much in the laboratory about how difficult these things are to work with. I once considered leaving Hughes with Steve Halsted to start a company, but it wasn’t going to make ion lasers. We were too smart for that.
Bromberg:What was it going to be?
Bridges:Oh, we were going to work with optical scanning. It came out of our interest in this reconnaissance system, which used a mechanical optical scanner. And we had an inquiry from a company that made scanners: Would we like to join them and start up an optical electronics division? And we pursued it in 1969, far enough to actually resign from Hughes.
Bridges:The resignation lasted a weekend, and…
Bromberg:The persuaded you to come back?
Bridges:That’s probably…Are these tapes confidential?
Bromberg:Well, why don’t you turn this off for a minute.
Bromberg:Another question I have been wanting to ask you is your relation to lasers in art? Was that an episode of any importance?
Bridges:No. Gee, I don’t think I had any.
Bromberg:I somehow think of you in terms of these experiments in technology and art group. You were not involved in that?
Bridges:No. I knew the guy, Billy Kluver, who was one of the functionaries. He and I were graduate students together at Berkeley. But, no. I had no involvement with the EAT people, other than to know of their existence.
Bromberg:OK, why don’t we get the...
Bridges:Updated bibliography. Oh, that’s not really important history, but this was also submitted to Applied Physics Letters, and I guess they adopted the attitude, “Well you’ve seen one ion laser, you’ve seen them all.” So they said, no they didn’t want to publish that it’s just the same old stuff. And so I turned around and published it as a correspondence in an IEEE proceedings, and the dates are rather different, but these were only one week apart essentially.
Bromberg:So there would be one on laser oscillation in singly ionized argon.+ and the one on laser action in singly ionized krypton and xenon.
Yes. Then this was really the major spectroscopic work.”
Note added: This "instability", which Birdsall and I discovered in a computer simulation of electron behavior is, 26 years later, alive and well, and going under the name "VIRCATOR" [for VIR tual CAThode oscillaTOR], a scheme for generating very high power microwave radiation.
Interview by Ricahrd Cunningham for Lasers & Applications, 9 November 1984, on deposit in the Laser History Project Archives.
Note added by WBB, July 1086, This was my feeling in Jan. '85 when the interview was given. Since then, General Motors has acquired Hughes and will likely change this single-minded dedication to military applications.
W.B. Bridges, "Ion Lasers: A Retrospective" Proc. Int'l Conf. on Lasers '81 Dec. 14-18, 1981.
W.B. Gridges and G.S. Picus, "Gas Laser Preamplifier Performance," App. Otics 3 (1964), 1189-1190.
W.B. Gridges and A.S. Halsted, "Gaseous ion Laser Research," Technical Report No. AFAL-TR-67-89, Husghes Research Laboratories, May 1969, (Final Report on Contract AF 33 (615)-3077) [AD 8148971]
William B. Bridges, Arthur N. Chester, A. Stevens Halted, and Jerald V. Parker, "Ion Laser Plasmas," Proc. IEEE 59 (1970).
The patent did finally issue.
William B. Bridges, "Gharacteristics of an Opto-Galvanic Effect in Cerium and Other Gas Discharge Plasmas," J. Opt. Soc. Am. 68 (1978), 352-360.
Let's just say that "Persons unknown" at Hughes persuased the company we were in canotact with that it would be highly unporfitable for them to hire us away from Hughes. Steve and I hold no grudges (now), since the Great Aerospace De[pression of 1970-73 would probably have killed our little effort anyway!
William B. Bridges, "Laser Action in Singly-Ionized Krypton and Xenon," Proc. IEEE 52 (1964) 843-844.
William B. Bridges, "Laser Oscillation in Singly Ionized Argon in the Visible Sprctrum," App. Phys. Lett 4 (1964), 1`28-130.
William B. Bridges, and A.N. Chester, "Visible and Ultraviolet Laser Oscillation at 118 Wavelengths in Ionized Neon, Argon, Krypton, Xenon, Oxygen, and Other Gasses", App. Optics 4 (1965) 573-580.