Irnee D'Haenens

Bromberg:

This is Dr. Irnee D’Haenens at Hughes Research Laboratories on the 5th of February 1985, and we were talking about how he had just joined the Atomic Physics Department which Harold Lyons was head of and he was working under Theodore Maiman on solid state masers and he was just telling us a little bit about what the gaseous people were doing, making clocks and frequency standards, but we really want to, I guess, find out what kinds of things you people were doing in your solid state group. Was there just the two of you at this point?

D'Haenens:

No. There was, let’s see, there was Ted Maiman, Ray Hoskins, Ken Trigger and Ricardo Pastor, were the senior level people. Pastor was the materials man; at that point in time, was growing gadolinium ethyl sulfate as a solid state maser material.

Bromberg:

Yes, I was going to ask about that. Now that was just made in December. Now Bloembergen’s article came out around, I guess August ‘56, something like that, and the Bell people made their first maser at the end of December. So I am wondering whether you remember, at all, these discoveries and the impact that it made on your group, or what your group was doing.

D'Haenens:

Well, our group, let’s see if I can recall: Ray Hoskins was working on a pulsed maser scheme, where the pump was at x band and the system was pulse inverted, the magnetic field was increased to split the levels, and then it would oscillate at k band 24 gigahertz or thereabouts.

Bromberg:

Feher and Gordon had announced that in July of ‘56, I guess, at Bell Labs.

D'Haenens:

That’s right. At any rate, we were really in a position of playing catch up, because Lyons had just put the group together, the people, Maiman included, were either fresh out of school or maybe they had a couple of years of experience. Hoskins had done some spin resonance work at Dow Chemical back in Michigan; Ken Trigger had been doing spin resonance with one of the military labs, I don’t remember exactly where Pastor had been doing materials work, I think at the University of Chicago. So Lyons brought these people together as a nucleus for the solid state maser group. Pastor was then growing water soluble crystals, the gadolinium ethyl sulfate, he also prepared sodium in liquid ammonia for a very sharp spin resonance line, and Maiman was actually working on, I was working on, a cyclotron resonance experiment. We did cyclotron resonance in electrons which were generated thermionically, photoelectrically, so on and so forth, and studied the kinetics under high excitation. It turns out that under high excitation the cyclotron resonance goes non-linear and you can use it for harmonic frequency generation. The intent was to eventually be able to generate millimeter waves in semiconductors, specifically germanium.

Bromberg:

There is something you said at lunch that I would really like to get in here and that’s Maiman’s electronic background. I don’t know if you have said that elsewhere in print but I think that was an interesting comment.

D'Haenens:

Maiman, as a youngster, was fortunate in that his father was a Ph.D. electrical engineer. I can’t tell you where he did his undergraduate or graduate work, but he did work for about 40 years till retirement for Western Electric Company, and Ted told me that his father had told him that when he went to work he should not go to work for a big corporation because one does not get due credit for one’s accomplishments. And an example he used to illustrate with was, that he, Ted’s father, had developed the first dc to dc conversion using a mechanical chopper to make ac, a step up transformer, and subsequent rectification and felt that, had he been in a small company or out on his own, so that he would have been assigned the patent royalties, he could have been a very wealthy man. So that was one thing that Ted had implanted in him as a youngster, and the other thing was that he benefitted in the sense that he picked up electronics as a youngster. He had a small business going when he was, as I understand it, 12 or 13 years old, fixing neighborhood appliances, radios, so on and so forth. As a matter of fact, I recall him telling me that he and his father would compete in his early teenage years; they would compete in the design of audio circuits to see who could get the best frequency response, flat response from the low end of the spectrum to the high end of the spectrum. That’s something that he learned when most kids are out learning to shoot a basketball and steal apples from trees or whatever. So, Ted was really a unique combination. By infusion actually he learned all the electronic skills, and by education benefitted from doing his thesis under Willis Lamb, Nobel Laureate, and he was certainly at the right place at the right time with the right skills. To get back to what was going on at Hughes. We worked on the cyclotron resonance for probably a year and a half which took us to the end of ‘57 and I can’t be terribly specific about time, but it seems that in ‘58 Kikuchi and people at the University of Michigan used the paramagnetism of chromium in aluminum oxide, which is ruby, and demonstrated that they could make a very nice maser out of ruby as the active material. So we set up originally to duplicate their efforts, and then again, Ted’s feel for the electronics resulted in a compact and portable maser. The typical laboratory maser used a 12 inch Varian magnet which probably weighs 5,000 lbs, a large dewar which fit in between the pole pieces of the magnet, the fullup microwave plumbing; this certainly was not a portable, practical device. Ted developed techniques to match from standard 3 centimeter, 10 kmc, now GHz waveguide, into a ruby dielectrically loaded cavity, which was on the order of a centimeter by a centimeter by a third of a centimeter and fit very nicely between the poles of a little horseshoe magnet which probably weighed about 12 ounces, and dimensionally was maybe 2 1/2” by 2 ½”. The dielectric loaded cavity, magnet and modulation coils, everything fit very nicely into a liquid helium dewar and was a portable unit. Now that work was done under support by a then Signal Corps program for something on the order of a $100,000. That maser was delivered to Fort Belvoir, and I think they used it as the front end receiver in a weather mapping radar.

Bromberg:

Now it should be just about this time that the Townes-Schawlow paper came out and you didn’t mention right here so I just wonder if you happen to recall anything happening in this whole group in response to that paper.

D'Haenens:

There was a general excitement on getting from the microwave spectrum into the optical spectrum but initially, Ted had been aware of Wieder’s work. Wieder was at Westinghouse at the time and Wieder talked about making an optically pumped maser, using ruby. Ruby cooled to 78 degrees as a solid state light source and another ruby which would be pumped by the fluorescence from the first ruby as the maser. Using some optical selection rules one could in fact invert a couple of those Zeeman split levels, and make a maser or microwave amplifier in the second ruby. The results of the Wieder work, however, showed the quantum efficiency for ruby fluorescence to be the order of 1% or so, which turned out subsequently not to be applicable to the pink ruby. However, I have a personal opinion in this, and it is that Wieder wanted to get as much light out of that solid state light source as he could, and perhaps, ended up on the high side, concentration-wise. As you run the concentration up, you get crossrelaxation, you get pair spectroscopy, but most significantly I think, you get a reduction in quantum efficiency for the R line transition. You know, it leaks over to the pair states and comes back as the N lines, but he was measuring specifically the R line quantum efficiency. So it may have been a poor choice on Wieder’s part.

Bromberg:

You never have gotten in touch with him about that?

D'Haenens:

No. I have never gotten in touch with Wieder on that. And Maiman, how should I put it, Wieder followed Maiman at Stanford and used the apparatus which Maiman had developed for his thesis. Maiman measured the Lamb shift in helium, and then Wieder came along and measured the Lamb shift in neon using the apparatus that Maiman had built up. Maiman was very upset, because in his publication, Wieder did not acknowledge the fact that he used the apparatus which Maiman had built up. I guess there is no polite way to say it, but Maiman did not have much faith in Wieder, as an experimentalist. So when Wieder measured 1% quantum efficiency for ruby fluorescence, and it was accepted for publication in the literature, people in general, Schawlow specifically, believed it. But Maiman because of the past history with Wieder didn’t believe it, said, “We’re gonna measure it ourselves.”

Bromberg:

I see. So the situation was that he was following this and sort of talking to you about it. It was still the maser that you were doing at this point, the optically-pumped maser.

D'Haenens:

It was still the optically-pumped maser, and if you read through this^[1] you will find that he talks about using selection rules and maybe getting inversion down here, but by this point in time the Schawlow and Townes article is out, and he is becoming more and more convinced, particularly after having remeasured the quantum efficiency and having found it to be high, then in fact one should be able to invert the ruby system, that is the R-line excited state over the ground state of the ruby. Ok, this was written late ’59, and about then we also did a so-called microwave optical experiment, that is, the ground state in ruby is really split by about .38 wave numbers, which falls in the microwave region. And if one did a spin resonance experiment in the ground state, the signal that you got was proportional to the difference in those level populations, but more significantly if you did the experiment at room temperature with the temporal resolution on the order of milliseconds, these levels would relax and thermalize in microseconds or tenths of microseconds. So the point was that if you measured the microwave absorption, it was proportional to the total ground state population By applying an optical pulse which puts some of the population up into the excited state, you could see a change in the microwave absorption, which corresponded to the fact that we were removing some of that ground state population. The change in microwave absorption was such that it corresponded to the order of a 1 to 5% change in ground state population for coupling through an optical lightpipe, a quartz lightpipe. So, the idea was, that if you could increase the coupling of the light source into the ruby, you could obtain inversion. The obvious way of doing that was wrapping the light source around the ruby, and encasing the whole thing in a reflective enclosure, which was essentially the configuration of the first laser.

Bromberg:

Now someone has said to me, and I don’t know whether it is true or not, that these were things that were done after hours, on lunch periods and it was bootlegged.

D'Haenens:

No. It was done during working hours.

Bromberg:

I assumed from looking at the annual report that it was his project.

D'Haenens:

It was. Certainly.

Bromberg:

Ok. It was somebody who was in a different department.

D'Haenens:

I think it would have been fair to say it was done on a shoestring budget, but to say that it was bootlegged, I think is stretching the truth a bit.

Bromberg:

Is the shoestring budget fairly common in the kinds of experiments you were doing in that group or was it uncommon?

D'Haenens:

By the then standards, it was fairly common. Shoestring budget probably refers to: in comparison to today, or in comparison to the budgets that we had after the initial disclosure. Well I think I mentioned in the text of that,^[2] that we were shut down for the better part of a month, because we moved from the then site of the Research Lab, which was Building 12 in Culver City, to our present location in Malibu, and that occurred, oh, around the end of February or the beginning of March.

Bromberg:

Now, here you say there was only 2 weeks of downtime.

D'Haenens:

That is probably pretty close to correct.

Bromberg:

That’s what you remember?

D'Haenens:

Yes. When we got here, the laser experiments, the initial laser experiments, were done at this site, Malibu.

Bromberg:

I also heard somebody coming in, a photographer named Fred, coming with his own flash lamp. Is that an apocryphal story?

D'Haenens:

No. No it isn’t, but it was not Fred, and he was not a photographer; it was Leo Levitt, who was a member of the department. In addition to the Solid State Group and the Gaseous Group under Harold Lyons, there was a theoretical group of which Bob Hellwarth and Leo Levitt were prime members. Ted was looking for an intense light source while we were doing the microwave-optical experiments, and Leo Levitt had a small strobe unit in his office or brief case. We tried it, and it turned out that it was as good or better than any of the light sources that we had. So we started investigating the xenon strobe lights and of course the original lasers were pumped exclusively with flashlamps of that type.

Bromberg:

Now, is there anything that you think of in the actual discovery that isn’t in this little memoir that you wrote one and a half years ago or isn’t elsewhere that you have seen in print?

D'Haenens:

Well, the observation that I made to you over lunch, that I think that Maiman was at the right place at the right time and enjoyed a certain amount of serendipity; serendipity in the sense that Schawlow’s comment at the previous quantum electronics conference put people off of pink ruby, and his history with Wieder.

Bromberg:

I have always been interested in that conference^[3] to understand a little better its effect on the various people who took part and Maiman gave the paper there. Do you happen to remember when people came back from that conference? You didn’t go, did you?

D'Haenens:

No. I didn’t go. I think it was back in the Catskills.

Bromberg:

That’s right. Do you happen to remember anything of the response that people when they came back, whether there was any heightened excitement or I am sort of putting the idea in your head now. I don’t want to do that.

D'Haenens:

No, I do remember very well. When Ted came back he was terribly excited about the proposal for the optical maser, the Schawlow-Townes thing. I don’t think they had the full blown proposal in that, I think it was the first mention of the possibility of making an optical or infrared maser.

Bromberg:

And Schawlow gave a talk in fact.

D'Haenens:

As a matter of fact, Schawlow did say people were suggesting, how about this, how about that, and that’s when Schawlow said that the pink ruby would not work because of the low quantum efficiency with reference to Wieder’s result, and the fact that one had to obtain inversion over a ground state. He did suggest the N-line, that is the pair spectroscopy of ruby, of chromium in aluminum oxide, as being a likely candidate for a four level laser system, which subsequently Schawlow, and Wieder I might add, showed to be a viable laser material. After that conference it was all, how shall I put it, we had done a lot of work with ruby as evidenced by the paper that Maiman gave at that conference which was on ruby and high temperature maser operation, etc., and talked incidentally about the dielectrically-loaded wave guide, the smallness, and all of that. But after that conference, after his attendance at that conference, the emphasis was totally on the optical and/or microwave-optical…

Bromberg:

I see. So it was really a turning point in research direction.

D'Haenens:

Certainly, yes.

Bromberg:

I was just wondering if it is fair to say that laser work here really comes out of stimulus of that conference or was there really laser working going on before as opposed to maser. Of course, it is awfully hard to pin that down.

D'Haenens:

It is hard to pin that down. Maiman had followed what was going on. We had access to the Westinghouse reports, for example. And he was aware of what Wieder was doing. Of course, Wieder had published in the open literature, I think, by the time that conference was presented. And prior to the conference, Maiman had talked about doing an optically-pumped maser experiment. He measured the Lamb shift in He for Lamb in his thesis project at Stanford, and he felt that there was a distinct possibility of obtaining inversion in a couple of Zeeman split levels in helium and/or neon systems. And had things not worked out as they did, I am sure we would have gone back and looked at those as test systems to obtain a population inversion.

Bromberg:

Now when you were really in full swing there, you got a lot of groups working. Wieder’s work of course, but the people of Bell are working on lasers. I don’t know what you knew about Javan at that point because he was pretty secretive.

D'Haenens:

Well, Ted Maiman was pretty secretive also. Plus the fact that — how shall I put it — we didn’t have — we had no “critical mass.” We had Maiman, but he had all the tools.

Bromberg:

It was essentially Maiman and you.

D'Haenens:

That is correct. If you have a lot of people involved, one has to be very secretive, because as you know, word does tend to get out. But being on the West Coast, out of the East Coast establishment, it was not terribly difficult to keep things quiet, because it was a low budget operation and there weren’t that many people involved.

Bromberg:

What did you do when you got the thing to lase? Did you break out the champagne?

D'Haenens:

Well, that is a funny story in itself. It turns out that I am red color blind; I don’t see red. I am a protanope, which means I am short on red color receptors. The stand eye response is a bell shaped curve. My eye response is bell shaped on the blue side, but on the red side it drops at about .62 microns or 6200 angstroms. Actually what we were doing initially was looking photometrically at the temporal development of the output and we saw a shortened lifetime, which is an indication of lasing or stimulated emission. After making measurements of that type for several days, we decided to look at it, actually – we put up a white card to reflect some of the light. And what happened when we exceeded what our spectral and temporal measurements told us was a threshold, that is, where the output measured in the forward direction was increasing faster than linear with the energy input to the flashlamp. By then I think we had called in Ray Hoskins and Charlie Asawa to join Ted and myself, and I turned the thing below threshold and they looked and they all said, “Lot of red light.” Well I don’t see red light and to me it looked like a lot of white light. And then I exceeded threshold and they said, “Oh, look at that red light!” right in the forward direction, about the size of a collimated flashlight. And I didn’t see a thing, except a lot of white light. Subsequently, when we got some better rubies and had a little better control on the optical finishing of ends, the flatness, parallelism and so forth, we did the same experiment. Well they, with their super red sensitivity saturated, said, “Oh, can’t see any detail.” My red blindness was probably the equivalent of looking through optical density glasses, allowed me to distinguish some shape to the beam. I should indicate — you can’t tell by looking at this picture^[4] — but initially we coupled the light out by putting a small hole in an otherwise opaque silver endpiece — ideally the output characteristic of that kind of laser was sort of a doughnut shaped beam — well it turned out that there must have been a bad spot in that ruby or a jagged edge of the silver or something, and it did not give the doughnut shape beam but there was a section out of it, so my observation was that it looked like a horseshoe or a toilet seat or something like that. (They said) “Aw, go on, go on!” It turned out I had last laugh on them because when we put some attenuation in and took some photographs, sure enough, the output characteristic spatially, was horseshoe in shape.

Bromberg:

Did he know you were red color blind when you started on the ruby?

D'Haenens:

I didn’t know. I learned prior to the laser, while Charlie Asawa and I were doing some spectroscopy on ruby. The R lines, the two levels, actually this level is split, it is a doublet and is separated by some 14 angstroms or so, some 28 wave numbers. We were working with a small half meter Bausch and Lomb monochrometer, and trying to resolve the R lines. I recall looking into it after had made the adjustment and I said, “Charlie, I can’t resolve the R lines.” And he looked at it and he said, “Well of course you can’t; the slits are open too wide.” So I proceeded to follow his instructions and narrowed the slit width down. Well, of course, in addition to increasing the resolution or sensitivity of the spectrometer, you reduce the transmitted intensity. And I said, “Come on, Charlie. What happens is — the light goes out!” So he looked into it, and sure enough he convinced me after I did some hand chopping, that he, in fact, was seeing red light. So what we did, was we tracked across the spectrum and narrowed the slits down until we could just detect the presence of light. My eye response is skewed and it cuts at 6200 Angstroms, maybe not relative to the so called normal observer, but certainly relative to Charlie Asawa’s eye response. That was probably Fall of ’59 that we made the observation that I was indeed red color blind.

Bromberg:

Specific remembrance…?

D'Haenens:

Ok, well. The thing that I want to mention is kind of a personal impression, and incidentally I had occasion to confront Ted with that, probably within the last year, maybe six months. And there may be little recognition on his part that this was in fact the case. What I am talking about is the long period of time that elapsed between the submission of the original Phys. Rev. letter and the subsequent full up article which appeared in the Physical Review.^[5] Maiman’s theoretical paper and then the experimental paper, which was Maiman, et al., ourselves included. I think the reason that there was this long period of time was that Maiman — knowing his personality and the fact that he is very hesitant to talk about something unless he really knows it from all aspects — really wanted to figure out what the relaxation oscillations were all about. That was, however, not in the cards, not to be the case. And I think as I mentioned, it is ironic that to this day, I don’t think that anybody has a really good feel for what those oscillations are all about in any sort of detail. I think as time went by and other people started getting into the act, notably the Bell group, Collins and Schawlow with their publication, it became quite clear that we should go ahead and publish the full up experimental paper and his theoretical considerations, kind of avoiding the problem of the relaxation oscillations.

Bromberg:

Good, thank you.