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Oral History Transcript — Michael Bass

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Interview with Michael Bass
by Joan Lisa Bromberg at the University of Southern California;
29 May, 1985
 

Transcript

Dr. Bromberg:

Why don’t we just begin with these topics: The nonlinear optics work that you did at Michigan in the early years, then your period at Berkeley and then the Raytheon period. Those are really the three most important things I want to talk about, because we’re in many cases just interviewing up to the early seventies.

Dr. Bass:

OK, fine. Well, shall I just reminisce for a moment?

Bromberg:

Yes, and then I’ll be asking you some questions.

Bass:

OK. Let’s see, I arrive at the University of Michigan in the fall of 1960, as a beginning year graduate student. Peter Franken had arranged that he was the advisor to the first year graduate students, to (as I quote him) “identify students he would like to work with him.” OK, during the spring of that year, as I had the good fortune to have done tolerably well, he suggested I look around for things to do and told me about his own work, and during the summer of 1961, I worked with another graduate student setting up an optical system to look at some niobium balls that were to be suspended in a magnetic field, and to do some other experiments. The latter were a student’s start up experiments.

During that summer, Alan Hill was working on the frequency doubling experiment. That was on the fourth or fifth floor of Randall Hall, and the rest of Peter’s laboratories were in the second basement. So none of us really knew of what Alan was doing, because it was going on the fifth floor and we were “too” far away. Alan was a junior, an undergraduate at the time, and was doing a summer project. As far as he was concerned he was going back to take classes in the fall. By the end of the summer, that experiment was well established and they were doing things, but Alan was stopping and Peter was looking around for someone to work on this sort of thing. One of the things I did during the summer was to look around for work that I might be interested in doing, and I said, “Gee, that looks interesting, the stuff that Alan was doing,” and then it devolved on me as what I was to do.

The first thing that we went off to do, since by then ruby lasers at nitrogen temperature and room temperature were known to have different wavelngths, the first obvious thing to us was to mix the frequencies,[1] and to generate those frequencies, two different lasers, one at room temperature, one at nitrogen temperature, were put simultaneously through a nonlinear crystal in order to get out the harmonic of one, the harmonic of the other and the sum of the two.

Bromberg:

Now, you say the first obvious thing to you — let’s go a little bit more into the background of that, whether you remember any of the impetus or reasoning, because not everybody was doing that.

Bass:

At Michigan, having done the nonlinear optics and the demonstration of frequency doubling, we certainly had done more work on more efficient frequency doubling, and in fact the nonlinear crystal triglycine sulfate had been found, which had a larger nonlinear coefficient than quartz crystals that had been used before. What triglycine sulfate did not do, and this was rather a kind of an accident, it did not index-match very conveniently, and so, because we were looking for larger nonlinearities, by looking at different materials, we didn’t look for the index matching which the Bell group, Giordmaine and Kleinman, that whole group discovered.

Now, it was very interesting, with these nonlinear materials that we had been looking at, we had gone through quite a few and we had found that this one, triglycine sulfate, which had a large nonlinearity. We got better signals. And I’m not sure if it was that we did anything better, that the material was better, or that we weren’t doing the experiments better. We were using an old Hilger-Watts prism spectrometer to disperse the light, and we calculated that the second harmonic of the ruby at each of the wavelengths would be resolved (the room temperature wavelength and the nitrogen temperature wavelength). We calculated that those would be resolved. And then we decided, if those were resolved, we would be able to see something halfway in between which would be the sum of the two frequencies——that is, the adding process——I worked on that for a couple of months.

The problem that I was having was, I knew how I wanted to get both beams into the crystal at the same time, in the same place and going in the same direction, but the ruby rods in those days had silver coatings, and with any luck they might last 40 pulses. Now, there was no helium neon laser to align them with. You’d get about 30 or 40 pulses and the coatings would have fallen off and the system would stop lasing, or you’d run out of nitrogen and the alignment would shift. You could never quite get everything to work long enough to get any data.

Bromberg:

Now, the helium neon laser was invented by then, but I guess—

Bass:

Not the visible one.

Bromberg:

I see, you needed the visible one-—

Bass:

For doing alignments it would have been handy, and besides that, this was the fall of 1961. There were no commercial ones available.

Bromberg:

You were probably getting your rubies from Trion.

Bass:

Yes, everything was from Trion in those days. In fact I used to carry four or five rubies out to Trion for coating and then bring them back and do an experiment and run back and get them coated again and what have you.

Bromberg:

I see.

Bass:

One of my great disasters was the day I inadvertently stuck one in my shirt pocket, you know, in its box, and forgot about it. I bent over to pick something up and had it fall out and broke off a quarter of an inch of the ruby. Ever since then I’ve been able to tell my students, “If it’s in use and you break it, I don’t worry about it. It means you’ve been doing something. But don’t let it break through disuse.”

Anyway, the big breakthrough came on a day where I literally dragooned Franken into the lab to help me do this alignment. I knew what I had to do and I needed somebody to do the other half. There were two things and I couldn’t adjust them both by myself. All the data for that was taken in one afternoon. You know, to demonstrate frequency summing.[2] Well, the next day he (Franken) called Giordmaine, and Giordmaine said, “You know, we’ve also observed index matching,” and the two conversations went, they were both delighted with the results, but you know, we’d crossed—-the progress was going on in both places that quickly.

Bromberg:

By the way, I’m assuming that Franken worked with you the way you know most graduate student professors work, you’d go in and talk over with him what you were doing and go back in the lab, is that the way you two worked?

Bass:

Well, it was more like, he would come by every now and again, and try to find out what was happening, all right. Of course, you’ve got to remember, in the fall of the year he was teaching as well, and being very excited about what was going on, he was hard to get hold of. Yes, it wasn’t like I went in to see him. More often than not he came down to the lab to find out what we were doing, what I was doing, and the other students as well. There was an active program on crossover spectroscopy going on in those days. That was the funded work. This was really unfunded at that moment. It was a larger project funded by——I think it was the AEC.

Bromberg:

I see, so you got some of that money?

Bass:

——for crossover spectroscopy, and Peter kind of funneled some of that money into this nonlinear optics. Trion allowed the lasers be used, and you know, that was more or less how it was done. It was not something that Peter had thought about, gone out and gotten funding, brought the funding back and started the work. It was a program called the AEC Resonance Project, that was where all this crossover spectroscopy was being done by Jim Hobart, Steve Jarrett, Tom Stakr, Warren Moos, all the guys were in it.

Dick Sands and Peter Franken were mostly responsible for it, I guess C. Wilbur Peters was somehow involved but not directly, and Gaby Weinreich probably had some funding out of that program also, and what Peter was doing was using some of the AEC Resonance program to do nonlinear optics. So there was all this other work going on that Peter was responsible for at that time. This was just a small bit of the program at that moment. Anyway, I spent a little while, probably five or six months, fooling around with looking at the distribution of second harmonic light coming from various crystals, by focusing light into the crystal and looking at the UV light coming through a copper sulfate solution, and just photographing the pattern, and indeed I began to see rings, the way Kleinman and Giordmaine said they could see rings.

By this time the Bloembergen analysis relating the various coefficients had appeared. The coefficients of optical rectification and the Pockel’s coefficients were shown to be related through permuting the frequencies. If you look at the nonlinear terms, you could see that if you permuted the frequencies, the nonlinear coefficients remained the same, and so you could show certain equalities. We then decided by looking at the Pockel’s coefficients in different materials that it would be possible to measure the coefficients of optical rectification, which is the parallel process to frequency doubling. That became the subject of my thesis, which as concerned with measuring optical rectification.[3]

Bromberg:

There are a few names on this, there’s (Alan) Hill C. Wilbur Peters, Weinreich and Ward are all——

Bass:

Well, I skipped the arrival of John Ward. He was the postdoctoral student from Oxford. He came to work with Franken and I guess Franken had met him when he was in England. John arrived I think, in the spring of ‘62, and we worked together for quite a period there. As I remember, it was kind of interesting because he didn’t know much about lasers. Of course nobody knew much about lasers in those days, and more or less I wound up teaching John what I knew, and he went on of course from there.

Let’s see, the other names of course, you mentioned—- C. Wilbur Peters was a professor of physics at the University of Michigan. He is one of the very early researchers on fiber optics. In fact, the rumor has it that he actually held a patent on fiber optics devices from way back. It was in his laboratory that this experiment went on, with some of his equipment. He was kind of an infra—red person, by then.

Bromberg:

— more than he loaned the equipment?

Bass:

He was involved to an extent, providing some experimental guidance, as I recall, Weinreich is the person responsible for pointing out that the material had to lack an inversion center if you were going to see nonlinear effects of even orders. Franken conceived of the idea, And Alan Hill was a junior undergraduate student who did the first experiments.

Bromberg:

I’m looking at your papers though, not the frequency doubling one, the optical mixing, for example, Franken, Hill, Peters and Weinreich. It’s spelled Weinrich here?

Bass:

The “e” is left out. That’s right, those are misspelled, it’s Weinreich as I recall. And Ward of course was a post-doc. He arrived right about the time we did the first rectification.

Bromberg:

You mentioned the contact with the Bell group. What about the people at Ford, was that important?

Bass:

It was a very stimulating connection, in that (Robert) Terune and Maker with some regularity had visited with us. Peter would visit with them. I went over there later on in my career at Michigan, I went over to see Ford once. And I recall it’s kind of a rabbit warren. The walls seemed to move while you were standing there. You know, they had these movable walls and they were very proud of them, but you had the feeling that there was nothing permanent in the Ford Labs. But anyway, their work on the Raman effect, the stimulated scattering experiments that they were doing, was very stimulating, very exciting to us. It did not develop into a research direction for us.

It was of interest but it wasn’t a research direction, possible because, a kind of an interesting thing happened, and Peter was the one to say this, that when he got into nonlinear optics when he did the frequency doubling, in any other time in history he would have had a lifetime of research to do in all of these nonlinear processes. Within four years, all of the major things had been demonstrated, because there was this great mass of people waiting to work on the subject, all over the country, all over the world.

And there’s a lot of work that has gone on since, but that initial rush of things, Raman effects, stimulated Brouillin scattering, all the higher nonlinearities, index matching, the powder technique for evaluating nonlinearities——all that stuff was done by other people. Peter and the group at Michigan couldn’t keep up with it.

Bromberg:

Do you have any reflection now as to why that might have been, now that you know the physics game pretty well?

Bass:

I think it was an accurate statement to say that in the early 1960’s, when the laser was first developed, it wasn’t hard for everybody to have some kind of laser. That was relatively straightforward. Maiman’s design was easily copied. Not expensive either. It was not out of the range of anybody who had an electronics person who could make a power supply and someone else to polish something for him, to buy a flashlamp.

As a result, they were kind of sitting around trying to figure out what to do with these things, and with the publication of that PHYS REV Letter about second harmonic generation, the dam broke. People realized that there are two things lasers do that other light doesn’t do. It delivers a lot of light and it’s coherent. Now, coherent stuff is a lot more subtle than the fact that it delivers a lot of light. As a result, you’ve got high intensities and all of these nonlinear things become available.

Bloembergen and his group were ready to move in that direction and they moved beautifully. They did the analysis as well. Bloembergen, (Peter) Pershan, I guess it was (Jacques) Ducuing was visiting with them at the time, and (John) Armstrong—-that became a classic paper, because they got the analysis right. Of course, there was a factor of 2 mistake but that’s irrelevant.

Bromberg:

You say a factor—just for my own edification?

Bass:

I’d have to go back to my thesis to find it, but what it was was, they defined things in somewhat of a nonstandard fashion, and when I got my results, the optical rectification coefficient was so much and the electro—optical coefficient was so much, and they were different by a factor of 2. It turned out that it was in the definitions that Bloembergen and his group had used.

They had done really outstanding work, which gave the theoretical underpinning to this, and we (at Michigan) were really too small to get a hand in all of the stuff that was going on. After the couple of years, I graduated in ‘64, John Ward stayed for I think another year or so before he went back to Oxford for a couple of years, the so—to—speak laser group at Michigan kind of, you know, thinned out.

It didn’t really do much until John came back, by which time Peter I think was DARPA, and so it really never reached a real competitive position in later years. As Peter would say, the opening was there in the door and it filled up with people rushing through, before we could stick our foot through. Actually I just said that. Peter didn’t say that, I just said that.

Bromberg:

Did that interfere with your getting your thesis done, or create a certain kind of atmosphere?

Bass:

No, it was a very exciting atmosphere, in those days. Getting my thesis done was really spurred on by the work——it was not an interference, it was a stimulus. It was of course one of those things were I wished I were already done and could do other things I wanted to do. You know, as I wanted to do them, somebody else did them. It just meant that there’s a limited amount of time. For example, Q-switching, you know, when that paper came out of Hughes about how to Q-switch, that meant that the suffering I had done on how do you do rectifications, suddenly became clear, because you have a Q—switch laser, now you have a very clean simple pulse with a sufficient intensity to make this thing work, so that was essential. But that was (crosstalk)

Bromberg:

And then you built your own Q-switching apparatus?

Bass:

Well, with the people at Trion did. Basically, that was a really lousy Q—switch. It was a rotating mirror on the output end of the ruby laser. It was everything in reverse, it was the wrong direction——

Bromberg:

I thought they used a Pockel’s cell for their Q-switch.

Bass:

Not at the beginning. The first Q—switching was done with rotating mirrors. Then rotating prisms, and then finally you know, electro—optic devices.

Bromberg:

This Trion Connection is rather interesting. I knew that it was important for the original frequency doubling experiment, but I didn’t realize that it continued, that this association continued and facilitated the Michigan work right along.

Bass:

Oh yes, in fact, part of what I did was look at the nonlinear coefficients at 1 micron and at .69, the ruby wavelength. We had a neodymium glass laser from Trion. They actually provided a glass laser that produced two joules long pulse, again with a rotating Q—switch. It was also much more powerful than the ruby and began to damage things left and right. That I think may have triggered a lot of the research I did laser on. With my thesis, much of what I suffered with was laser damage. None of us understood how easy some of the nonlinearities were so we simple went for more and more intensity until we were working close to the breakdown level of the thing (the non linear medium).

Bromberg:

Was that something they just gave Franken as a kind of compensation for his consulting?

Bass:

That I don’t know. Whatever relations Peter had with Trion, I think they saw the work as marvelous publicity gimmick for them,that the papers, reports, referred to using Trion instruments, lasers and all that. They must have sold a few lasers by that means. Given the state of technology, they were probably pretty decent lasers but didn’t progress as fast as the rest of the industry. Of course, the elliptical cavity came along and Trion was still using helical flash lamps. You know, the linear lamps made life a lot easier. You could start talking about a little bit higher repetition rate. Cooling was more efficient. Lots of things got better that way.

Bromberg:

Were you able to go over to these other suppliers, like Raytheon is one I think of for the linear lamps, or did you just stick with Trion?

Bass:

Well, while I was at Michigan, we simply used Trion. It was basically local. I remember trying to build an etalon in order to make a mirror that would not damage in the glass laser. I spent a tolerable bit of time trying to make an interferometer, a little two place interferometer, by kind of squeezing two flat plates on an indium ring, to align them and to make that a reflector to take advantage of the Fresnel reflections, no coating, so it wouldn’t damage.

Unfortunately I never really got that to work properly, but had I done that, I would have observed what was observed later by a bunch of people in England, that when you restricted a laser to single frequency, the relaxation oscillation spikes were very regular, and then some other properties of lasers were to be seen.

But again, the difference in those experiments was timing. I was doing it in ‘63 with a mercury lamp as my light source for aligning these plates, and being low reflectivity plates, they were hard to align. When the group in England did it in ‘66 or so, ‘67, they used the helium neon laser for the alignment process. They could get it precisely aligned and stick it in.

Bromberg:

That whole business of the helium—neon and its use in alignment is something I guess I didn’t grasp sufficiently as a breakthrough.

Bass:

Oh, It’s incredible! In lining up those ruby lasers, I had an auto collimator. I guess it was, I think Bill Bridges, at the session at CLEO, showed a picture of what it looked like to look through an autocollimator.

Bromberg:

I wasn’t there.

Bass:

It brought back terribly unpleasant memories of what it was like. It was a really difficult situation. Using the alignment properties of the helium—neon laser is probably as valuable a tool in the business of lasers today as anything ever was. An inexpensive helium—neon laser just changed the possibilities by many orders of magnitude.

Bromberg:

That’s a really interesting point.

Bass:

I think if you ask me for the single most useful item in the laser business, I’d have to say it was the little helium—neon laser, in terms of making all sorts of other things possible. Complicated optical systems with 50 or 100 components delivering beams in all sorts of directions, could not be aligned in one’s lifetime without such things. It just wouldn’t be worth trying those experiments.

In fact, I remember, I was still at Michigan, so it must have been ‘63, ‘64, when Jim Hobart came from Spectra—Physics, and he had with him a little black box helium—neon laser that he was demonstrating, a little visible helium—neon, and he took it and banged it on the table to show how sturdy it was, and what impressed me no end was that this thing was small enough to be carried. All lasers before that had been immense and clumsy and had big power supplies and all that. This was it, it was——

Bromberg:

Some ruby lasers are little things.

Bass:

But the power supplies——the power supplies are the size of this file cabinet. And Jim was holding it in his hand. It was plugged into the wall, it was a box about a foot long, five inches high by four inches wide, and that was the whole laser. And it was really remarkable, It just blew my mind to think of the potential, how much faster I could have done what I’d been doing if I’d had it.

Bromberg:

Yes, I should think so. Was that an engineering triumph of Spectra—Physics that they made it so small? Or were all helium—neon lasers—of course I guess at Bell they were also working on very small ones, I know.

Bass:

Yes, everybody was trying to make things smaller. The several meter helium—neon laser, there was no way that was going to be of any use, and people felt getting them small was the thing. I think the breakthrough that I saw in the Spectra—Physics laser that Hobart had that day was that it was rugged, that you could carry around and it was still aligned, and it had in it the elements of a practical device. Now, it was a lot of money, even then, I think it was over $1200 or something, such that later on I think it was maybe three or four years later when Metrologic began to sell a helium—neon for $100, and that was a real breakthrough, because then it didn’t matter anymore. It was less than what triggered the bean counters to call it capital equipment. You know, as long as it was that low, nobody noticed it, and you could buy these things for your use. Any more than that and the capital equipment people would get all upset.

Bromberg:

Good. I don’t know if we’re finished talking about your graduate work. Are there more things we should talk about? Because the next question I wanted to ask you was, what kind of universe one graduated into if one was a laser man around ‘64?

Bass:

Well, let’s see——

Bromberg:

—who was fighting for you?

Bass:

OK, when I was nearing finishing, I interviewed at Bell Labs. I was kind of interested in going into the university world even then, so I interviewed at UC-La Jolla, San Diego, where the only thing related to lasers was some work that had been done on parametric oscillators, by Norman Kroll, and that was absolutely impenetrable. I remember Weinreich running around having to review that paper, just tearing his hair out, saying he couldn’t understand it.

Bromberg:

Franken said that he couldn’t understand it either.

Bass:

OK, he was asking Franken to look at it. Franken said no, maybe Mike would look at it. I shuddered to think of looking at the paper because I couldn’t understand it either. It was probably very good basic deep science but totally impenetrable. I couldn’t understand it. So I interviewed there and I interviewed with Erwin Hahn at Berkeley, who had a postdoctoral position and what they called a visiting assistant professorship. The visiting assistant professor is a UC system trick for bringing in young people who are not going to go on in the academic track, at the school, but who will be teaching while they’re there, so the title was visiting, and that was kind of fun.

I taught optics and I set up a senior year experimental laboratory, and that included a little laser project. Again, it was a little ruby laser in that lab. As I say, in those days ruby lasers were cheap to make. Anybody could do it. That was kind of a fun time, but the reason I went to Berkeley was that I wanted some more training and experience before lighting out in any other direction. The opportunity at Bell might have been a good one. I don’t know. I decided I wanted to go to California, not New Jersey. My family was from New Jersey. I wanted to try something else. It was cold in the winter and hot in the summer and all the things that I wasn’t so enamored of so I thought I’d try California. But then going to Berkeley, Erwin Hahn basically showed me an empty room and said, “You’re going to do work with coherent propagation of laser pulses.”

There were three students there, Lance Riley who is now a stock market analyst, Steve Miller, who I think is still at the NOSC[4] in San Diego, and Sam Mccall, who went to Bell Labs after he graduated, and continued in coherent propagation. Steve and Lance, I frankly don’t remember exactly what they did, but Sam was the one who carried through the issue of coherent propagation, and, you know, the so-called pi pulse, 2 pi pulse propagation business.

I arrived in Berkeley about the same day as Ron Shen, and we were the only people at Berkeley at the time who knew anything about lasers or quantum electronics, and I remember being grilled by Owen Chamber lain one day at lunch about what a hologram was, which I frankly didn’t know very much about. I was very unsure of what they were.

Bromberg:

—did you have any contact with Leith and Upatnieks when you were there in Michigan?

Bass:

No. They were on the North Campus. We didn’t see them. I didn’t know what they looked like. We knew of what they did. By the way, a guy I did see at Michigan was Kikuchi, Chihiro Kikuchi.

Bromberg:

How did he fit into the picture?

Bass:

He was just officially in nuclear engineering. He was the out-of—department member of my committee and was familiar with what rubies were all about. He was knowledgeable in rubies.

Bromberg:

He was also part of Trion.

Bass:

I guess so, again probably because he knew something about ruby. But no, we never saw much of the holographers. They were another world altogether. Also, you have to remember, the group at Michigan in the physics department, Franken’s group, in the laser business——it’s curious, it went uphill very rapidly, and then as I was finishing, that was about it, OK. Alan Hill did not go into graduate school. Peter wasn’t actively developing new programs in the laser business.

And things were running downhill toward the ‘64 time frame. Anyway, at Berkeley, as I say, Shen and I were the laser types who arrived at that time. There was also a group of people in Sumner Davis’s lab that was kind of traditional optics, spectroscopy stuff. And Erwin’s interest was kind of an open door to learn how to put together a whole laboratory from beginning to end. That’s what appealed to me about it. It was a lot of fun. While there, we were going to pass a laser beam through an electron beam, such that we would see light scattered from the electrons in the laser beam. Of course that didn’t work, but had we worked a little harder on it, we might have invented the free electron laser in 1965.

Bromberg:

Was that part of the plasma diagnostics that was going on?

Bass:

No, it was totally different. It started one day, I think it was Riley, myself and Miller were sitting around and having coffee and talking about what might happen if we did this and if we did that. I’ve forgotten whose experiment it was but it was an experiment where you sent a beam of electrons up above a grating, and the image charge oscillates with respect to the beam and you get radiation from that. All right, now we started talking about that, how a laser beam being an oscillating electric field might modulate a beam of electrons to radiate, and we tried looking for it.

We set up a little electron gun, a little electron beam chamber with a TV tube electron gun, and some turning magnets and all that and set it up, and we didn’t get anywhere. But that’s what life is like. Again, given enough time to play with that thing long enough, we might have invented the free electron laser way back then, but we didn’t. It was just some research that never got mentioned or published or anything else. It was something that didn’t lead us anywhere.

That didn’t mean it wasn’t going to lead someone else somewhere. The funny thing was, at Berkeley we had zero contact with the people at Livermore that were getting under way on the laser fusion programs. We had one tiny connection with the Rad Lab, and that was through a fellow who was trying to work on building a better argon ion laser, and-—

Bromberg:

What about Stanford? What about all these little industries? Spectra-Physics was there. Did you have much contact with these people?

Bass:

OK, yes. Well, again, remember that Hobart and I and Jarrett knew each other from graduate school days, so I would see them socially as well as going down there to see what they were doing. Hobart, when I taught optics at Berkeley, came and gave a demonstration of such fascinating things as interference patterns, scattering, diffraction, things that I would talk to the class about but here they could see it. He even showed them what coma in a lens was.

Bromberg:

What was it?

Bass:

Lens coma. If you have a lens that’s distorted, it will produce an image, instead of being a point, it will produce a kind of a comma shaped image.

Bromberg:

What about the research that you saw going on at Spectra—Physics in comparison with the research that one did at a university at that point? Was it just that they were making products?

Bass:

Yes, it was definitely product-oriented. They were very clear about what they had to do. Better coatings were essential. As far as the ion lasers were concerned, they were into the discharge dynamics. They were working in RF discharges. They were worrying about magnets and how to confine the plasma and how to keep the tubes from being ablated and what have you. But a lot of it was very much directed toward product development. And then of course, came the split to form Coherent, which, as I recall, was formed with DuPont money.

Bromberg:

I think so (crosstalk)

Bass:

DuPont wanted a white light laser or something, yes. That was an interesting moment.

Bromberg:

Oh? That’s a moment that you witnessed?

Bass:

Yes. It was kind of one of those strange feelings, that you know, looking back at it, you say, way didn’t I get in with them at that time? Well, there was no getting in. There wasn’t any room. It was too small, you know, to have any other involvement at that point. You know, it was just a couple of people who were from Spectra-Physics, who were not going to be Spectra-Physics, were going to be Coherent, and they were going to make a white light laser for people to do holography with.

Bromberg:

But you could have gotten into Spectra-Physics very possibly. Did that interest you?

Bass:

No. Not at all. I did want to do research. I felt that that I would enjoy. It probably wasn’t the most economically feasible thing I ever did, but at least I was happy doing that. I think that makes a big difference.

Bromberg:

What did Raytheon look like then from your point of view? Did they look as if they were more research—oriented and less product-oriented?

Bass:

In that time, yes. Well, 1966, Mary Weber was recruiting. He was a former student of Erwin Hahn’s. And he was at Berkeley recruiting, and spoke to me about coming to Raytheon and I was kind of interested in it, so I went and looked and it looked very interesting. I was also being recruited at that point by George Brinbaum who was then at Rockwell Science Center, Thousand Oaks, and Raytheon and RCA and Westinghouse, all of whom wanted me to work there, but Raytheon at that time, had a very good reputation in terms of doing research.

OK, they had a good staff. Think of the people who were on the staff of Raytheon in those days. There was Herman Statz who was in charge of the group, Frank Horrigan, Tom Deutsch, Mary Weber, let’s see — Dave Whitehouse, Perry Miles, Harry Barrett didn’t yet have his PhD, but he was at Raytheon at the time. He’s now professor at the University of Arizona at Tucson. Well, I’m just thinking of the laser types at Raytheon in those days.

Bromberg:

What size of a group are we talking about?

Bass:

Easily ten or twelve people. There was a fellow named Jerry Levine who was looking at semiconductor lasers. There was a guy Keimpe Andringa who was doing solid state optical pumped lasers, at the laser Advanced Development Center, but then came to research. His name is Keimpe, it’s a Dutch name. At any rate, all of that work was there, and all of that facility was there. There was a lot of equipment developed at Raytheon. Roy Paananen was doing argon ion lasers.

In fact, there is a very funny story about Paananen. He had a contract to develop a 100 watt argon ion laser, and for months and months and months he was suffering at 50,60,70 watts, whatever, he couldn’t really get 100 watts, with this great big immense thing, with half of the Charles River flowing through it and so on—and one of the technicians, a guy named Mike Seiden, went off and recalibrated the bolometer that Paananen had been using and discovered that there was a factor of 2 mistakes in calibration, that Paananen for five months had had over 100 watts coming out of that thing. One of the problems in the early days was that there was no good and reliable energy/power meters.

That’s another thing, Coherent makes a nice line of trustworthy meters, which tended to help out a great deal. The joke about Gillettes is true. People used to measure power in the number of Gillettes you would poke through with a pulsed laser, focused in such and such a way. Very simply, there weren’t any meters around that could handle these kinds of laser intensities.

Bromberg:

Also, this kind of relation between the experiments done and the state of equipment is an important part of the picture, and not always clear.

Bass:

Then I’m glad to be describing some of these things, because these were the kinds of things that we would suffer with. Any absolute measurement suffered tremendously from not knowing what the laser power was. The laser energy in the pulse. The wave form you could pretty well measure, if it wasn’t too fast, OK, so when mode—locking came along, the issue was really, how in the world could you measure the pulse wave form. And the beam distribution of these things?

Bromberg:

How did you measure the distribution?

Bass:

It was done rather poorly, mostly by photography, which meant that you had to depend on the linearity of film and on your developing process and such. Wavelengths that were not accessible to film were basically done by burning pieces of wood or pieces of unexposed polaroid film or whatever. There was not an electronic measurement technique until, I think, I’m kind of proud to say I was involved with it——I think myself, Frank Horrigan and Clarence Luck developed the use of the TV Vidicon to measure beam distributions for a YAG laser.

This was probably in ‘69 or ‘70. And that was developed into a very powerful technique. Nowadays you don’t necessarily use the TV Vidicon, you can use one of these linear detector arrays, but the recognition that a television scan line, when looked at electronically, was a recording of the spatial distribution of the beam made it possible to observe the beam distribution of the laser every pulse.

Bromberg:

Now, you mentioned two organizations at Raytheon, the Research Department that Statz’s group was located in, and the Laser Development Group?

Bass:

Something called LACD, Laser Advanced Development Center.

Bromberg:

What was that?

Bass:

Well. It was the group at Raytheon that was supposed to make and sell lasers. It was through that group that you would buy a laser if you bought from Raytheon. They would make the ruby lasers, the glass lasers, the argon ion lasers. Those were purchased from and made by that group. You’d purchase from them and they would make it.

Bromberg:

It was custom made stuff.

Bass:

Yes, as everything was then. There was no production line, except maybe in the optical polishing shop, that was also at the Laser Advanced Development Center. They were run by a man named Colin Bowness.

Bromberg:

Him I’ve met, briefly.

Bass:

He’s the inventor of the elliptical pump cavity. And he was the director of that center at Raytheon, along with Clarence Luck. Clarence was the associate director or some such thing, and they were supposed to turn the laser line into something that Raytheon would make a profit from.

Bromberg:

Now, what kind of relations subsisted between the Statz group and the Bowness group?

Bass:

It was actually fairly close. The research group was involved wherever appropriate in consulting with them on the development of new, more advanced systems and so forth and so on. For example, Paananen’s work on the 100 watt argon laser helped them with argon lasers, but what they didn’t understand, what really hurt Raytheon, was that you had a color center problem in the windows on argon lasers because of the UV discharge, and that was not clarified by Raytheon, and so Raytheon’s argon lasers never really held much of market. Spectra—Physics and Coherent solved those problems.

Bromberg:

You did some work on that, didn’t you?

Bass:

Yes, some work on color centers in various garnet materials.

Bromberg:

Was that kind of thing directly related to the argon?

Bass:

No. No. That was a funny——let me back up a moment. As an undergraduate, I had a summer NSF fellowship for working at Carnegie Tech or Carnegie Mellon as it is now called working for Professor Schmoluchowski on color center growth in lithium fluoride, and so when I was at Raytheon, I drew on that experience to recognize that the question of solarization that people were running around talking about what was really the growth of color centers in the laser materials. The little project that I did with Al Paladino was to look at the growth of color centers in these materials exposed to light from flashlamps, and that meant the UV light, because if we stuck a pyrex plate in between, the growth of color centers was inhibited.[5] So at least we identified the source of color center growth.

And what color centers did was, (A), they absorbed pump light and so the material would get hot, and (B), would take pump light out of the excitation process, and (C), it suggested that the crystal growers could do a better job, because color centers are present because of the vacancies in materials. The crystals weren’t perfect. And again, it was early in the day. The YAG laser was only developed in ‘65. This was ‘67 or so when we were looking at that. Paladino was growing yttrium gallium garnet as a host for neodymium and it just was a natural thing to see if it was more or less of a problem with color centers.

Bromberg:

Let’s go a little more paper by paper and get some feeling for how it came about. So that I can see which papers were stimulated by scientific work elsewhere, which papers might have been growing out of your interaction with the advanced Development group and so on. The color center work is the first thing on the list.

Bass:

That was just an easy thing to do when I first got there.

Bromberg:

Then you go right into dye laser work with Deutsch, what was that all about? How did that happen?

Bass:

Sorokin’s report came out and we got the IBM JOURNAL and there it was, and it just looked like an interesting thing to do.

Bromberg:

Raytheon wasn’t doing anything with dyes at that point?

Bass:

No, they didn’t then, and they probably as a company never wanted to. Raytheon never really understood that because it was tunable, the dye laser was of interest. Period. What exactly you would do with it later wasn’t important, any laser that was tunable was going to be important. In those days it still wasn’t tunable. That hadn’t been discovered yet.

Bromberg:

That’s right. So why were you interested?

Bass:

Purely scientifically. I couldn’t believe anything with as broad a spectral emission was actually laser light in the sense of being coherent and all the things laser light was supposed to be. In fact, it really isn’t, when it’s operating as a broad band source. And so I kind of had a suspicion that maybe it was really a narrow frequency that was sweeping and changing in time. Raytheon, one of the reasons I had gone there was because they were equipped. They had a 3/4 meter spectrometer, and there was a ruby laser sitting there not doing much, and so I could reproduce a lot of the Sorokin experiment, and took a look at the spectrum coming out, and indeed it was broad spectrum, it was all those things.

It also had channeled spectra in it, because of the parallel windows, which I should have recognized. I was getting the same energy but it was being redistributed in the spectrum which meant that it in fact precedes Soffer-MacFarland result, if only we’d known what it was. But nevertheless, what we really did which was of interest was to recognize that we could look at amplifying Raman—shifted light in a dye cell.

The reason that was kind of curious was that there was a question in those days about the wings of the Raman lines, and what we felt was it would be interesting if we could amplify that. So the first work with Deutsch was on the amplifier, and that proved to be so beautifully homogeneous in its broadening that it was kind of astounding, because the same dye that had a homogeneous amplification showed hole burning or inhomogeneous absorption, and that was an interesting thing.

Bromberg:

Now, just to go back for a moment, you say Raytheon wasn’t interested in this, but I assume Statz was supportive of this?

Bass:

No — I mean, one of the nice things about Raytheon in those days is that no one was caring specifically about justifying things, in the overall sense of “would it be of value to the company?” A year or so later I had to justify why we would continue working on dye lasers, and my answer was, it’s a tunable source of coherent light, it has to be of value. The statement then was, well, what good is a laser—pumped laser? And it’s the same thing. It’s a tunable source of light, it would be of value.

Bromberg:

They didn’t accept it? It seems so clear.

Bass:

No. No. It was fought tooth and nail. In fact, one of my biggest disappointments was being discouraged from the dye laser work. I mean, we did dye laser work because we got outside funding, but Raytheon really was regularly unwilling to put money into dye lasers.

Bromberg:

I really find that surprising too, but of course I’m looking at it with hindsight.

Bass:

Sure, so am I. In fact, some years later, I was consulting with Exxon as they were working on the isotope separation program, and I had all I could do to constrain myself from writing a letter to Raytheon saying, “I want you to watch this project because I want you to know I told you so.” You know, they had totally missed the boat on the possibilities of laser—driven chemistry, of all that, because they couldn’t understand why a tunable source was worth looking at. The military wasn’t interested in it for range finders or designators or what have you, and so wasn’t of any interest for Raytheon. It wasn’t of interest for laser radars so Raytheon didn’t have an interest.

Bromberg:

Raytheon’s contracts would be very much tied in with military?

Bass:

Yes. As the Seventies came to a close, Raytheon as a company was being more and more oriented to doing practical, for-the-company work.

Bromberg:

The seventies or the sixties?

Bass:

The sixties, excuse me. As the sixties were concluding and the seventies starting... I don’t know quite what was going on. Raytheon was being under somehow internally driven pressure to be doing research more oriented to the company needs, and they just didn’t understand that. By 1973, ‘74, let me just again jump ahead, there was a kind of an exodus out of the research division at Raytheon. From ‘73 to the end of ‘74, I left, Mary Weber left, Tom Deutsch left, Frank Horrigan left, Perry Miles left, Andringa left, Barrett left. Who else? Three more. Rafael Esposito went to Italy.

Oh gosh, a couple of other people left all at the same time. Anyway, there were about 11 people, I can’t remember all of them, but we actually had an alumni association going on for a while. We all felt the same thing. There was this pressure to do just what the company needed and somebody else was going to tell us what the company needed and we didn’t agree with it, and we didn’t want that kind of environment, and USC made me an offer I couldn’t refuse… But OK, let’s go back.

Bromberg:

Going back there, now whom do you approach for a contract? You said you had to finance the dye work on outside contracts.

Bass:

That was a very exciting bit of good luck. In Cambridge at the time was the NASA Engineering Research Center, I think that’s what they called it, and Horace Furumoto was on the staff there, and had an interest in dye lasers because he understood how to make fast flash lamps and things like that, and we got money through Horace, to do dye laser work. It wasn’t much but it was enough to do something useful. We also worked together with him and Harry Cecone on various flash lamp activities.

Purumoto is with Candella. Oh, and there was another fellow involved in this, a sort of technician whose name was Protopapa, Seifi Protopapa. Obviously an Eastern European name, but I don’t recall-—also, while doing dye laser work, we had a lot of fruitful interactions with the people at Kodak, Snavely and Peterson and that group, including Tuccio. We talked about the importance of helium-neons, and color meters that were reliable. The other major item that made this field move was the development of reasonably priced and compatible optical hardware. The Newport Corporation.

Bromberg:

Do they date back to the sixties?

Bass:

Late sixties, yes. That stuff was just invaluable. At Michigan, I was oriented to optical benches. OK. That meant Ealing benches, very well established stuff, Ealing optical benches. At Berkeley that’s what I would purchase because that’s where I was oriented, but also at Berkeley the machine shop was free and so you could get stuff designed and made to use. Everybody was oriented on optical benches because that’s how optics had been done before.

At Raytheon again it was optical benches, we all only knew that. But the advent of the optical table, starting out with the holographers basically looking at these very stable tables, they wanted granite blocks and so on, generated the optical table and the advent of optical hardware that you could buy and stick on and move and whatever, and it became much easier to do the work. That has made an immense difference in how the work gets done. The layout of an experiment is two dimensional now instead of one dimensional.

Bromberg:

That’s something I had not a clue to. Now I think I’ll try to follow it up a little and maybe—go there, talk to people there –

Bass:

I think you should. I think you should. I think they were the first but even if they weren’t, theirs is the stuff that you think of when you think about optical hardware and where it first developed from.

Bromberg:

Good.

Bass:

As long as you’re out here you ought to go over and see them.

Bromberg:

Probably not on this trip but probably on my next one.

Bass:

It was a major major contribution.....

Bromberg:

Something I wanted to go back to is, you talked about how you found, working with the amplifiers, with the dye lasers, that you got a homogeneously broadened line, but when they were working in another mode you were getting hole burning.

Bass:

Yes. For example, the dye cryptocianine is a very very effective saturable absorber Q—switch for a ruby laser, and by saturable absorption, it means the absorption goes from very large to very small, in a very short time, which can be described as a hole getting burned in the absorption spectrum. Now, that’s characteristic of inhomogeneous broadening. But as an amplifier, that dye shows all the characteristics of being highly homogeneously broadened.

Bromberg:

Now, are these things in contradiction?

Bass:

Well, it has to do with which state you’re looking at. In the emission process you’re looking at the properties of the excited state, when it’s an amplifier, and in the absorption you’re looking at the properties of the ground state. It was of the interest to try to understand why it was that these two were different, why they showed different properties, and I’m not sure that it ever got fully resolved, but it was so obvious as to warrant stating it, pointing it out. The fact that the emission is homogeneously broadened, is the reason why dye lasers are such efficient devices when frequency narrowed. You put in a grating, you narrow down the frequency, and you get the same output as if you didn’t narrow it. That’s due to the homogeneous nature of its broadening.

Bromberg:

Something else you were talking about off tape actually was that you were very much in contact with the Kodak people, Eastman Kodak, like Snavely and Tuccio.

Bass:

And Peterson.

Bromberg:

And Peterson. Were there other people in the dye laser world that you were seeing a lot of? What about the people in Europe like (Fritz) Schafer and so on?

Bass:

We had very little contact with the people in Europe. I remember the IQEC meeting in Miami, going up to Schafer and introducing myself, and having a funny feeling that he was not aware of what we had done, just as we weren’t aware of what he had done.

Bromberg:

You weren’t even reading the stuff?

Bass:

His stuff wasn’t readily available here, at least we hadn’t readily read it. OK, we hadn’t seen it. To our knowledge, dye lasers were invented by Sorokin. We didn’t even know who Schafer was or what he was doing. We did know of some of the papers. Yes, we knew of some of the dyes that he had studied, because we had looked at those dyes. But we didn’t know the history of Schafer’s contributions in Europe and the work that he had done. So it was not clear, you know, who he was and what he was about.

Bromberg:

I also think of Mary Spaeth at Hughes as being— What was the relation of your people to her?

Bass:

Of course I know Mary and enjoyed speaking with her and all that, but — we would read the papers. Spaeth and Bortfeld I guess worked together and we kept in touch with Soffer, Bernie Soff er was involved, and of course the connection with the Kodak group was more from the fact that Weber and I published some analysis of how dye lasers would work and what the analysis was, and they also published a long analysis of how dye lasers worked, indicating that they could run CW.

And Mary and I had also done that. We indicated in about two lines, using the rate equation for the triplet state, what the CW condition would be. It’s a two line step in our analysis, it’s a many line step in their analysis, and we had our analysis, it’s a many line step in their analysis, and we had long discussions with Snavely and Peterson as to which method gave more insightful analysis as to how you would get CW dye lasing. Taking nothing away from what they did, there’s a certain elegance to doing it in two lines as against doing it in 20, but there is some content in the longer derivation that is useful.

We had very good interactions. The other thing is that at Kodak, they had a great deal of knowledge about dyes, period, and that was a fascinating thing, to visit there and discover that they could actually, in a computer program, plot a multidimensional vector through dye space and identify dyes that would do various things. That was fascinating.

Bromberg:

What are the coordinates of dye space?

Bass:

Well, absorption and emission spectra wavelength.

Bromberg:

I see.

Bass:

Initial wavelength, lifetime, toxicity, solubility in water, methanol, ethanol, down the list. They catalogue all that stuff and they develop dyes, every day they develop many more dyes, you know. Again, some of this knowledge, some of this connection goes back to undergraduate work. I spent the summer between my junior and senior years as an undergraduate as a summer trainee at Kodak, and so I knew about their dye work. I was in the paper service division but I still knew that Kodak was a dye company, their color films totally depend on dyes. It’s not surprising to me that those guys were working on dye lasers. It was kind of obvious.

Bromberg:

I would like to say in terms of the Schafer question that, as you know, one of the things the laser history project cannot do is to go abroad and interview foreign workers, so I’m always very anxious to see, in terms of the Americans that we interview, what was going on in terms of the mutual influence or lack of influence with people abroad.

Bass:

Frankly, there wasn’t a lot of involvement with the European work on dye lasers. There were actually a number of Russian papers that I read very closely on dye lasers. Gosh, it’s so long ago, I can’t remember who the authors were, but they had reported on some dyes that worked at quite long wavelengths and I was very interested in that. When we wrote a review[6] on dye lasers, we sent letters to a number of different people in the Soviet Union asking for any recent publications they might have that would help us in this review, and got a couple that we had already seen. They just kind of didn’t respond. Of course the European journals that were in English, we were able to read and see, and again, as I say, the only difficulty in Schafer’s paper—why do I say Schafer and (Wolfgang) Kaiser together?

Bromberg:

Well, they’re both Germans.

Bass:

I think at one time they worked together. The only problem with Schafer’s role in the sequence of things was that we were unaware of it. We knew of his work, as we read it. We weren’t in any kind of direct contact. In those days, one didn’t go to Raytheon and ask for foreign travel money. It just was not done. So, you know, if there had been a conference in Europe, the idea of going would have been riot looked on with great favor. I remember going to a conference in Durham, North Carolina, on mode—locking, and finding Peter Sorokin at that conference and spending much of the time talking to him about dye lasers, while ostensibly it was a mode—locking conference.

The business with dye lasers was another one of those that I think took off faster than the inventors could keep up with it. Maybe they also chose to move on to other things, but if Sorokin had wanted to stay on dye laser work, it would have been hard for him to keep up with the hundred or so other people who were actively doing dye laser work. There were just too many people wanting to work on it.

Bromberg:

That whole thing is a kind of an interesting bit of sociology of science, because, I’ve heard other people say that at a certain point when a field gets too crowded or too competitive, they prefer to move to an unoccupied field, and it sound as if this kind of phenomenon came up several times in lasers. Something I want to talk about before we end is the laser damage work, and you alluded to that briefly early on.

Bass:

Yes. The very first nonlinear optics work that Hill was doing, you remember, they keep pointing out, they were very careful to filter out the flash that they would see when the material was damaged.

Bromberg:

Yes.

Bass:

Or breakdown. That would produce lots of blue and UV light that occurred at the same wavelength as the second harmonic. So it was to be avoided as much as possible, but it was there from the first day. There was a problem with laser damage, to the nonlinear crystal, because you were focused on it, but as I say, the silver coatings would eventually blow off the end of the rod, so we already had coating damage at that point. I kind of want to tell this story so I will tell it. If you look on that list of publications, you’ll see a paper by myself, Don Bua, another guy —

Bromberg:

— R. Mozzi I see and R.R. Monchamp.

Bass:

Right, concerning the nonlinear properties of organic dyes.

Bromberg:

Well, here’s one that says “Optical Second Harmonic Generation in Crystals of Organic Dyes.” [7]

Bass:

Right. Right. In that paper, there was about a four line allusion to the fact that one or two of these dye crystals was hard to damage. It withstood a fairly large flux of light. Martin Stickley from the Air Force Cambridge Research Lab called me up after seeing that, and asked if I would be interested in examining that issue further, the issue of damage on those materials, and that’s where it became an official activity. My study of laser damage started with that. And as I got into it, I discovered that there was this conference in Colorado that I had just missed, but that the next year there would be another one — this Boulder conference — and in getting ready for that, in doing some research with Stickley’s support, it became obvious that all the research that had gone before had done laser damage studies with multimode lasers.

It all was no more than a demonstration that there was a problem with laser damage. It was not useful in any way, shape or form, because the beam distribution wasn’t known and so the local intensity was an unknown quality. So the first thing that I was doing was to restrict the light to a Gaussian beam, so I could properly measure the distribution and know what the intensity was. And that first meeting, that’s what I did, I demonstrated that. At the second meeting, by then I had done a whole lot more work and discovered that the process was not threshold-like, that the process of laser damage really had a statistical nature that you had to take into account, otherwise you would delude yourself into thinking that you weren’t going to see laser damage.

That was one of the most exciting times. Those conferences were the way conferences ought to be, maybe 80 to 100 people, three days on one subject, no parallel sessions, all one session, and no one felt inhibited about asking questions and getting into the subject with the authors, with the presenters. It has gotten too big, as have all conferences. Really, one ought to take the laser damage conference and divide it into the coating damage work and the other damage work and separate it out, to get it back to that intimacy that it had at first.

Bromberg:

And everybody there was a contractor?

Bass:

Oh, it’s hard to say.

Bromberg:

They were classified conferences?

Bass:

There were two. Each year the group would go to Boulder for the open conference, and then afterwards there would be a classified conference at the Air Force base outside of Denver. It was kind of strange, because you would see viewgraphs or slides shown in Boulder with no axes labeled, they would just indicate trends, and you’d know that those same viewgraphs with the axes on them were going to be shown at the classified conference.

Bromberg:

Were you going to both?

Bass:

I never went to the classified section. I just went to the regular one. You knew what was going to happen. I mean, I spoke to these guys and I said, “Come on, you know a graph without axis labels is useless,” and they’d say “Yeah, but I can’t show you the labels, I can only tell you that there’s a trend here.” So it was fairly obvious what they were going to do. They would show the graph with the labels at the classified meeting.

Bromberg:

There was a group working here USC on laser damage, for example on windows. Did that have anything to do with your choosing USC? Hellwarth was already here working on it, and Marburger I guess.

Bass:

Yes, Hellwarth, Marburger, Larry DeShazer was involved a little bit. There were the people working on materials through the I R window program from DARPA, and yes, that certainly did help me decide to come here. It also is probably how they knew me, because they came looking for me. It was one of these DARPA sponsored workshops.

It was held in Hyannis or some place on Cape Cod near Hyannis, and Larry DeShazer came up to me and he was talking about what they were doing here, and I was telling him about this really neat student that was working with me from Harvard, Dave Fradon, and how he might be an appropriate guy to go off and be at USC, and DeShazer said, “Well, I wasn’t quite thinking of your student, I was thinking of you.” And that’s where it started. It went from there. That conversation was probably in the fall of ‘72 and it was in the spring of ‘73 that I came here.

Bromberg:

And then you became organizationally involved with the group here?

Bass:

Yes. Right. I came here as associate director of the Center for Laser Studies. There was a director, an associate director, one person and a secretary at that time. Maybe there were two people but I think only one was on the payroll, the other person wasn’t. It was an interesting time. We had some ups and downs. Got a benefit from Mal Stitch being around and not having other work to do and so associating with the Center for a while.

Bromberg:

Oh, I didn’t know that.

Bass:

He was here for about a year and some odd.

Bromberg:

I know he was in Korad just before that.

Bass:

I don’t know if he was bought out or got out or whatever, but when I got here Mal was looking around for something to do other than just be at home, so we got him an office and gave him a title and he spent about a year or so here, mostly consulting with various people, and generally being very useful. It was nice to have him around. The Center really got its first grant as of January ‘74. To work on yttrium vanadate as a laser host material, work for the Army Electronics Command in Fort Monmouth.

Neodymium in yttrium vanadate was looked at. It was very interesting work. If that material could be grown easily, it would be a very attractive laser material. It’s very hard to grow it, though. But nevertheless, that was the beginning. Some of our time was supported by the IR window project, the DARPA program, and that got me going in some areas. You know, that was one of the reasons I’d come. And also Marburger was good to have around. He went off into administration all too soon.

Bromberg:

Did he leave shortly after you came?

Bass:

No, Jack was department chairman in physics for a little while, then he went on to be dean of Letters, Arts and Sciences, and then went off to New York. We missed his involvement. He was a very powerful member of this group. Sergio Porto left not long after I got here, but helped me get started on the laser medical work. Sergio lent me an argon ion laser with which we did the laser treatment of gastric intestinal bleeding.

Bromberg:

I didn’t know that you were doing medical work importantly.

Bass:

In 1974, a paper appeared. You don’t have all of the pages of my bibliography. Actually, we have a patent on the use of the process of using fiber optics with lasers to irradiate and cauterize bleeding in the human body. “Access through openings natural and man—made.” Myself and Richard Dwyer. “Laser Induced Hemostasis in the Upper Intestinal Tract Using a Flexible Fiber optic Delivery System” (with R.M. Dwyer, B.J. Havenbock and 3. Cherlow) J. Am Med. Assoc. Feb. 4, 1975 also presented at 1974 Gordon Conference on Lasers in Medicine and Biology Meridan, NH June 1974.

In the Fall of 1973, Bob Hellwarth called me to say that he had somebody from the medical school who had called him about doing something, and would I speak to them? I said, sure. I’d only just got here and didn’t know what else to do, and so on. Then I get a phone call from a fellow named Richard Dwyer who was a fellow in gastroenterology in the USC gastroenterology department, working at the Los Angeles County Medical Center with a man named Jack Haverback who was chairman of that department, and what Dwyer asks is, he says, “I have a fiber optic endoscope where I can look inside the human body and see bleeding of ulcers and things like this.

Is it possible to irradiate a bleeding site with laser light and stop the bleeding?” I said, “Sure it is, and you probably could use a fiber optic.” He said, “Well, gee, could we just take the light and put it through the same bundle?” I said, “No, you’d burn the bundle up. We need to do it on a separate fiber.” He said, “That’s great, that’s great. Let’s get together and work on this next week.” I said, “Fine,” and we picked a day, and he showed up at the door with a surgical kit and four rats. He was meaning to really do the experiment right then and there. I quickly called up Sergio Porto, who I knew had an argon ion laser and would be able to let me borrow time on it for a period. We went over to Porto’s lab, and Dwyer anesthetized the rat, cut him open, made bleeding in his stomach and the bleeding stopped. He sewed up the rats, put them back, and I guess sacrificed them a week or so later, which was the normal procedure, and was delighted.

The bleeding had stopped, it had stayed stop, and that proved the principle. We knew we could do it. The next step was to get the laser light into a fiber, and deliver that fiber in the endoscope to a bleeding site in a larger animal, where you could demonstrate that it was feasible for humans. We had one of Porto’s post-docs at the time, a guy named Joel Cherlow who is now a radiologist at Long Beach Memorial Hospital, but Joel also has a PhD in physics working with us. Together we got this arrangement together where we could take the light from Porto’s argon laser, put it into a single fiber that we had gotten as a loan from a company in the Bay Area that did some laser things.

Bromberg:

Not Optics Technology? I think that was a big fiber optics group — or Kaptron whatever it is called.

Bass:

It might have been. It might be that. But they guy who was there, Chuck Enderby, is now with Spectra or something like that — no, he’s with Molectron now. Anyway, the issue really comes down to, we’d gotten a fiber which was a great big clumsy fat thing, and we taped with electrical insulating tape, to the outside of an endoscope, obtained permission to use an animal, use a dog—actually two dogs.

Brought them over to the laser lab, anesthetized the dog, inserted the endoscope in the dog the way you would in a human, created a bleeding site, then stuck in laser light with the fiber and stopped the bleeding. Yes, dogs tend to have blood that coagulates faster than humans, so the next dog, we gave a shot of heparin which makes them bleed more readily, and the same thing, we could make bleeding and we could stop bleeding. The next step was simply the scale of it, how much could we manage?

And with the argon laser, we could only do a bleeding artery of about a millimeter, because it was absorbed at too shallow a depth, so we used the neodymium YAG at one micron. It penetrates much more deeply, and with the neodymium YAG we could cauterize bleeding of a 5 millimeter artery. Well, we had already published our stuff. A group in Germany came along with Messerschmidt Company providing lasers, and really got going on the subject and began to develop actual hardware for it.

But indeed, ours was the first work on it. We also were the first ones to do humans. We did a human — that was the greatest day in my life. I mean, here was this guy, literally bleeding to death on the table in front of us, and we stopped the bleeding and he got better. It was one of those marvelous moments.

Bromberg:

I can imagine.

Bass:

— oh, I can’t say the greatest day, probably when my children were born was the greatest day, but still it was one of those marvelous experiences when you say: gee whiz, if I never did anything again, I’ve done something useful! In fact, this year is the tenth year of commercial laser treatment equipment, using fibers. There’s a big conference in Germany in October on the subject. They’ve invited us to give the keynote addresses.

Bromberg:

Nice.

Bass:

See, I get to go to Germany. I get to give a talk in Quebec & Toronto by way of going to Germany. But there are now probably 15,000 to 20,000 cases of gastrointestinal bleeding that have been treated that way, and more every day. It’s a common practice now. All sorts of things, pathologies in the bladder and a number of things in the uterus have been treated using laser irradiation. People are using lasers to remove cancers developing in the broncchia, and in the large passages of the lungs, to palliate patients so that they don’t die of asphyxiation. The cancer can’t be cured but they can open up the passageways so they can breathe. The next big thing is the use of laser fiber optics in clearing out your arterial placque. That is going to come.

Bromberg:

When do you think that will come?

Bass:

Well, a little company called Trimedyne now has permission for using a very flexible and tiny endoscope to allow you to view inside the arteries, you know, inside the veins and arteries, wherever they want to put it. That has a passageway in it for a fiber that could carry laser light. They’ve already in animals demonstrated the ability to clear placque in big arteries and things like this, and I think they have experimental permission to use it on humans now.

Anyway, they’re working with a bunch of people at Cedars Sinai and in New York at Columbia, I think it is, and of course there’s a whole crew of people wanting to use UV lasers to do that, but that’s another story. That hasn’t been developed yet. The issue there is to get fibers to carry the ultraviolet. But right now with the argon laser, it works, and again, you can see TV tapes that show you blockage and then show you green light going in, and the next thing you know there’s a hole in the blockage.


[1](with P.A. Franken, A.E. Hill, G.W. Peters, and G. Weinreich) “Optical Mixing,” Phys. Rev. Lett. 8 (1962), 18.

[2]”Optical Mixing,” with P.A. Franken, A.E. Hill, G.W. Peters and G. Weinreich, Phys. Rev. Letters 8 (1962) 18

[3](with P.A. Franken, J.F. Ward and G. Weinreich) “Optical Rectification “Phys. Rev. Lett. 9 (1962) 446. See Also Phys. Rev. 138 (1965) A 534

[4] Naval Ocean System Center

[5] With A. Paladino, “Color Centers in Yttrium-Gallium and Yttrium-Aluminum Garnet,” 3. App. Phys. 38 (1969) 2706

[6] Dye Lasers in Vol. 3 Laser Applications with M.J. Weber and T.F. Deutsch ed by A. de Maria

[7] Applied Phys. Letters 16 (1970), 244.