William Silfvast

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ORAL HISTORIES
William Silfvast

Photo credit: Bell Labs

Interviewed by
David Zierler
Interview date
Location
Teleconference
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Interview of William Silfvast by David Zierler on 2021 January 18,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/45382

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In this interview, David Zierler, Oral Historian for AIP, interviews William T. Silfvast, Professor Emeritus of Optics at the University of Central Florida. Silfvast recounts his childhood in Salt Lake City and he discusses his education at the University of Utah and a formative internship he spent at NASA Ames Laboratory. He describes his growing interests in lasers during graduate school at Utah working under the direction of Grant Fowles. Silfvast discusses his postdoctoral research as a NATO fellow at Oxford before he joined the Electronics Research Lab at Bell. He describes his major research work at Bell discovering new types of lasers, using optical detectors and photomultipliers for this research, and he explains his motivations in both basic research and the practical applications he saw for lasers in healthcare and in industry. Silfvast explains his decision to join the University of Central Florida where CREOL, the Center for Research and Education in Optics and Lasers was getting started. He recounts the enormous growth and success of the Center over the past thirty years, and he explains his motivations for writing Fundamentals of Lasers which is considered a standard text in the field. At the end of the interview, Silfvast reflects on his contributions to laser science, he provides an overview of all the ways lasers have become central to modern existence, and he explains how modern computing has revolutionized laser science and applications.     

Transcript

Zierler:

Okay. This is David Zierler, Oral Historian for the American Institute of Physics. It is January 18th, 2021. I'm delighted to be here with Professor William T. Silfvast. Bill, it's great to see you. Thank you so much for joining me.

Silfvast:

It's good to be here. Nice to see you, even though only on the screen.

Zierler:

That's right. Well, we're increasingly getting used to being in contact over Zoom. Isn't that right?

Silfvast:

Right.

Zierler:

To start, Bill, would you please tell me your most recent title and institutional affiliation?

Silfvast:

I'm an Emeritus Professor of Optics at the College of Optics at the University of Central Florida.

Zierler:

And when did you go emeritus?

Silfvast:

I went into retirement in 2000, a phased retirement. So, I was still involved half a year for the next five years, and then I was completely retired in 2005.

Zierler:

Now, in 2005, did you essentially stop being involved in research, or you've been active in certain ways since then?

Silfvast:

I didn't do any research after that. I gave up my lab and wrote the second edition of my textbook, Laser Fundamentals. Also decided there were other things to do in life.

Zierler:

When did you move to Oregon?

Silfvast:

We moved to Oregon in 2014. Happened to run into John Bjorkholm, a former colleague of mine at Bell Labs. He had moved to a large retirement community here called Rogue Valley Manor. We came to visit him and his wife, Mary, and we decided to move here. We were living in St. Helena in the Napa Valley, making wine in small amounts every year with some cousins, and having fun, but we decided this was the place for us at that point in our lives.

Zierler:

When did you get to California after Florida?

Silfvast:

Actually we decided when I was still fully active that we didn't want to retire in Florida, so we bought a house in St. Helena, California, in the Napa Valley, and loaned it out to others while I finished my full-time career in 2000. Then we drove back and forth across the country five times for the next five years to complete my one semester a year phased retirement program in Florida.

Zierler:

Bill, I was dismayed to see this past year that even Oregon wasn't spared from the fires. How did your community do during that ordeal?

Silfvast:

It came within about half a mile of us. It was very, very frightening. We were evacuated. It totally wiped out the two towns to the south of us, small towns. And the fire got very close to our complex. We're in a 70-acre complex on a hillside in southern Medford, and if the fire had crossed I-5, it would have come right up the hill to us. Fortunately, the wind did us a good job.

Zierler:

I'm glad to hear that. Well, Bill, let's talk about earlier times. Happier times. Let's start first with your parents. Tell me a little bit about them and where they're from.

Silfvast:

My father was born in Hanna, Wyoming, and grew up in a little town called Kemmerer, Wyoming. He only made it through the eighth grade because he quit school to help fund the family. He got a job at the railroad and worked his way up from there. Finally, he ended up going to Salt Lake City where he met my mother. My mother was from Butte, Montana, and also migrated to Salt Lake City. Her father was a barber, and better jobs were available in Salt Lake City than in Butte, Montana. So, that's how they met.

Zierler:

So, you're a true child of the west.

Silfvast:

Yes. My father's Finnish. His parents immigrated in the 1890s from Finland. My mother's heritage is English.

Zierler:

I was going to ask, Silfvast is a unique name. It's of Finnish origin?

Silfvast:

Yeah, Finnish — a little bit Swedish, but northern Finland.

Zierler:

Any idea what the name means, or what kind of labor it might entail?

Silfvast:

That's an interesting story, because Stig Stenholm, a well-known optical physicist, sent me an email once. He had switched from the University of Finland in Helsinki to the university in Stockholm. He said, "Bill, I'm intrigued by your name because my wife's parents have a little summer home in a village in northern Finland with that name." That's how I tracked down the heritage. My cousins and I went there expecting to find a fantastic village with signs of Silfvast, and Welcome, and visitor cards. There was nothing. We found one mailbox with the family name Silfvast. So, we were a little disappointed, but anyway, we got there.

Zierler:

And Bill, where did you grow up? What town did you grow up in?

Silfvast:

I grew up in Salt Lake City. I was born and raised there.

Zierler:

My first question with Salt Lake is how big was Mormonism in your environment?

Silfvast:

Huge. That's why I don't live there anymore, because I'm not a Mormon. And for example, in junior high and high school, all of the Mormons gathered before school at a Mormon facility nearby to start their day. Of course, if you weren't a Mormon, you weren't involved in any of that, so you missed — anyway, it was a feeling of being left out. Nobody meant it. None of my fellow classmates meant it, but it was certainly happening.

Zierler:

Feeling like an outsider was inescapable.

Silfvast:

Yeah.

Zierler:

What religious affiliations did your parents have?

Silfvast:

None. My father was a Mason and a Shriner, and my mother flirted around with various religious concepts, but that was about it.

Zierler:

And did you grow up in Salt Lake proper, or in the suburbs?

Silfvast:

Salt Lake proper.

Zierler:

And you went to public schools?

Silfvast:

I went to public schools, And it was always intended for me to go to college. I had two cousins that were about my age, and all our parents — none of them had graduated college, but all of them, made us feel that was the next step. You go to the university, which is what I did, but I wasn't ready for it. That's another story.

Zierler:

Bill, when did you start to get interested in science, and were big events like the space race or Sputnik, were those the kinds of things that captured your imagination as a boy?

Silfvast:

No, when I was about 12 or 13, I used to like to build things, so I decided I wanted to be a mechanical engineer. That gets us into another story, which I guess is appropriate to tell you now. I went to the University of Utah for two years in mechanical engineering. I also joined a fraternity and it was a mistake as far as getting an education was concerned. In fact, in the spring of my sophomore year, I was taking the optics portion of physics, and I only went to class once and flunked the course, which is my specialty now. Anyway, a fraternity brother had a summer internship at NASA at Ames in California the previous year, and he talked me into applying. So, I did, and I got accepted and went to California at Ames and spent the summer there working in the area of the 12-foot wind tunnel. That's when I met my wife, which is another intriguing story, because not only had my older fraternity brother convinced me to go to NASA, but I was assigned a younger fraternity brother from Los Altos, California, which was five miles from NASA, and that's when I met my wife. So, that was very fortunate.

Zierler:

What was your wife doing there?

Silfvast:

Well, she'd just graduated from high school and was planning on going to Cal Berkeley in the fall. We courted that summer. But the interesting story is that she started at Berkeley and I went back to Utah in mechanical engineering. At that point I was interested in aeronautical engineering because of being at NASA. I got a full-time job delivering groceries and that didn't agree with my schooling. I couldn't concentrate and went to visit her at Christmas in California. In the spring, I decided I didn't know what I was doing with mechanical engineering. I wasn't happy with it or school in general. So I quit school, went to California, and got a job at Lockheed, right next to NASA, working on the Polaris missile, where I worked for a year and a half.

Zierler:

Did you need a security clearance for that job?

Silfvast:

Yes, a confidential clearance. But that gets to the crux of the story. There was an older guy working in the materiel division with me. We scanned blueprints and ordered materials in advance for construction of Polaris test vehicles. Anyway, I was working with this older man, I think he was probably 30 or 40. But he was older to me at the time. Anyway, he talked to me about schooling and said, "Bill, what bothered you about mechanical engineering?" I said, "Well, they just threw a bunch of formulas at me. I had no idea where they came from, we were just supposed to memorize them." And he said, "Bill, you ought to go into physics. That way you’ll learn how those formulas were developed." I took that to heart. My wife and I were married the next summer. She had had two years at Cal, and I had had two and a half years at Utah. We went back to University of Utah because, with my bad grades I didn't want to apply anywhere else at that point. I entered the junior year physics program and my wife was in education at that time. We graduated together in '61, and I told her when we got married that we were just going to go back for two years to get our degrees, and come back to California and make lots of money. But I fell in love with physics. I took an optics class my senior year from Professor Frank Harris and decided that was what I loved.

Zierler:

Bill, what do you think was behind this amazing advice that you got when you confided that having a bunch of formulas thrown at you in mechanical engineering, it wasn't working for you? What do you think was behind that advice and what clicked about it for you?

Silfvast:

Well, obviously, he knew that physics was deriving those formulas, not memorizing them. He sensed that I wanted to know where they all came from and what the basis was for them, I guess. I'll continue with my story. So, I told my wife I loved physics, and wanted to apply for a teaching assistantship, and hopefully I could go on to graduate school. It was about that time I was working for Dr. Harris as a summer research assistant. But Dr. Harris decided to quit his job as a professor and go to California. So, I had to look around, and there was a professor named Dr. Grant Fowles, who was just starting to look into lasers. That was in the very early days of lasers. I approached him to see if I could get into his program and he said I could. That started my laser career. I was fascinated by optics and light.

Zierler:

Had you worked with masers at all up to that point?

Silfvast:

No, really nobody was doing masers that I knew of. Well, I guess, they were using masers. Charlie Townes and Jim Gordon invented the first masers, and they coined them optical masers, to keep them related closely to their masers. But that didn't last. Gordon Gould chose the word laser, and that stuck. Anyway, with Dr. Fowles, I got in line behind one other student who developed an ionized iodine laser, and I started talking to Fowles about a research program. He was interested in studying isotope shifts and hyperfine splitting in various species. That had been his career. So, he thought if you had a laser, you could more precisely define the isotope shifts and hyperfine splitting by having a narrower frequency defining each isotope. So, that intrigued him, and he suggested that if I wanted to do a research program, why don't we try making a laser in bismuth vapor, which had a single odd isotope and therefore ideal for studying hyperfine structure. So I started looking into bismuth. In order to get enough bismuth vapor pressure to make a laser you had to heat it. So, I was trying to figure out a way to make a laser system where I could heat bismuth as the laser medium, and yet still not have the vapor condense on the Brewster windows and coat them, so the beam couldn’t exit the laser tube. That's how my career started. I devised ways to do that. As a result, I have been called one of the fathers of metal vapor lasers, but bismuth started my career in that direction. It wasn't the Sputnik. That came later.

Zierler:

Bill, as you got your sea legs in physics as an undergraduate, and you developed an interest in optics, I'm curious if you ever thought about graduate programs beyond Utah.

Silfvast:

I mentioned I didn't dare apply because I didn't have the grades. I had flunked some courses before I quit school and went to Lockheed, so I didn't think I'd have a chance. So, I just decided to stay at Utah, and fortunately I did, because Grant Fowles and I started that whole new metal vapor laser program.

Zierler:

Yeah, and what was Grant working on prior to this? What was his previous research?

Silfvast:

He did isotope and hyperfine structure studies of various elements. He had gone to Berkeley for his PhD, and that was his interest. But our interest then switched to lasers.

Zierler:

Bill, would you say, was the lab and were Grant's research sensibilities more on the applied side, or more on the basic research side?

Silfvast:

Definitely basic. I have an interesting story. It's a digression to tell you though.

Zierler:

Please.

Silfvast:

I joined as a student member both the Optical Society of America and the American Physical Society. I tried to start a seminar series on optics in the physics department, and several of the senior professors poo-pooed it, thinking optics has nothing to do with physics. It amuses me now because at least half of the publications in physics involve lasers and optics. Anyway, I guess I must be a member of both APS and OSA for over 60 years now.

Zierler:

Bill, what do you think the initial feeling was about denigrating optics as not real physics? Where do you think that came from?

Silfvast:

I think the physicists at that point, this was back in 1961, '62, thought it was more about lenses and telescopes, and things like that. They never said that, but they kind of poo-pooed having an optics seminar in the physics department. It’s taken a while, but it’s changed.

Zierler:

Bill, how did you go about developing your thesis research?

Silfvast:

Oh, that was a story I should continue. I tried to get bismuth to work, to be able to do hyperfine structure splitting measurements. I developed an oven that heated the laser medium to the appropriate temperature. Bismuth had to be heated to about 300-400 degrees centigrade to get a decent vapor pressure. I worked for three months on bismuth, and I could never get a laser to work. I was getting very discouraged about the whole thing. I thought, well, I'll go over to the chemistry department and get another metal to try. I chose cadmium because it had a fairly high vapor pressure. It only had to be heated to about 250 degrees centigrade. I heated the tube, and out bursts this beautiful blue beam between the tube and the mirrors. No, it was a green beam at that point. A beautiful green beam, which just blew me away! I found Fowles at a meeting in the admin building. He came running to see it, and we were both blown away. It was an exciting time because no one had ever seen this sort of thing before. The laser mirrors were separated by about two meters, and the active medium was in the middle, but between the active medium and the mirrors you could see this beautiful green beam scattering off the dust in the air.

Zierler:

Was the central thrust of the research to see if the beam would work, or to see what the beam would do?

Silfvast:

The thrust of the research was to try to get bismuth to lase so that we could measure hyperfine splitting. But once we started having success, realizing no one had ever seen lasers like this before, I started getting other metals and putting them in. One of them was lead vapor. I had a pulser and was pulsing the lead gain medium with blue mirrors installed to form the laser cavity. These dielectric coated mirrors don't cover the whole spectrum. They just reflect very highly, nearly 100 percent, over a very narrow wavelength range, and I had mirrors on that would reflect the blue, because I thought there was a transition in lead that might lase in the blue. All of a sudden, we saw this red beam coming out of the end of the tube. We thought, how could we be getting a red beam when we were using blue mirrors? Well, it was the first really high gain laser. It occurred in lead vapor, and it had extremely high gain, which later is what I spent my year at Oxford working on, developing a way to measure that gain. But it started a whole new field of lasers which ended up with the copper vapor laser, which was used for isotope enrichment. The Israelis, in fact, developed that laser very extensively, and did isotope separation of uranium 235 using the copper vapor laser. The lead vapor laser, my thesis topic, was the forerunner of that copper vapor laser. So, not only did we discover some ion lasers including cadmium and zinc and several others, but we discovered this new kind of neutral lead laser that had very, very high gain. One of the highest gains of any laser. That started my thesis. I did a theory for my thesis on how that laser worked. So the discovery of that laser was an interesting story at that point. We went to Illinois to attend the Electron Device meeting of the IEEE where we presented our results of several new lasers, and we scooped Bell Labs. We were this little group at the University of Utah and had scooped Bell Labs! They approached us and wondered how we did it. So, I thought, maybe I might get a job at Bell Labs. When I finished my thesis, I interviewed Bell Labs at the University of Utah as part of the campus interview program and they never even sent me a reply. But I saw this ad for NATO post-doctoral fellowships in Europe sponsored by the National Science Foundation, and I thought, just for a lark, I'll apply for one. I got accepted, and that's how I went to Oxford. What's amusing is that all of a sudden, the fact that I was at Oxford, Bell Labs got interested in me. They never bothered with me at Utah. I was the same person, but it took going to Oxford to get me to Bell Labs.

Zierler:

Bill, I'll test your memory. Who was on your thesis committee?

Silfvast:

Grant Fowles, of course, and four others, one a professor in the math department, because I was awarded a minor in mathematics. I don’t remember all of their names.

Zierler:

And Bill, how parochial was your worldview in those years? Obviously, as a graduate student, you're hyper focused on your own work, but of course, there was a much broader world out there, even in your field, that was working on developing lasers. Were you aware what was going on at places like Bell Labs and other research university environments?

Silfvast:

We knew from attending the meeting in Illinois what was going on. And when we sent in our publication of the lead laser, which was a big breakthrough, apparently Bill Bennett, who was involved in developing the first gas laser at Bell Labs, got the paper to review. He had by then returned to Yale. It was in Applied Physics Letters. He got the paper to review for Applied Physics Letters and immediately called us, and said, "Can I come and visit you?" We were blown away that someone of his stature wanted to visit us. So he flew out to see our program. The bad part of that was we didn't know he was consulting with Gordon Gould at the time. So, he goes back to them, and they were working on manganese, a similar energy level arrangement as lead. They were trying to make a CW continuous manganese laser. Because of his visit to us, he told them, "Start pulsing your manganese," which they did, and immediately got the green manganese laser. We also had obtained results in manganese and were just writing up a publication when Fowles was asked to review the publication of manganese by Gordon Gould and Bill Bennett. So, they kind of scooped us. That taught me there's politics that goes on in research. Had he not come out, they still wouldn't have gotten the manganese to lase, and later the copper laser. We couldn’t do copper because my oven wouldn’t heat the vapor high enough. In my opinion it was not an ethical thing for Bennett to do, not telling us that he was doing competing research. And they filed a patent that almost completely ignored our results, even though they would have gotten nowhere without us and our results.

Zierler:

Bill, after you defended, what opportunities were available to you? Were you thinking about post docs? Did you think about any tenure line positions?

Silfvast:

All I wanted to do was teach. I wanted to be a professor. I applied to a couple of places in California. Let's see, I applied at UC Santa Cruz and UC Santa Barbara, but I also thought it'll be nice to interview on the east coast on my way to Oxford. I had interviews at GE, DuPont, I forgot who else, on the East Coast. But that was it. I had applied for the fellowship at Oxford, and my wife calls me at my lab at the university where I was doing research. This was in Salt Lake City. I had my PhD by then but I was doing a year post doc. She calls me and she says, "Honey, you got a letter in the mail from National Science Foundation." I said, "Is it thick or thin?" And she says, "It's thick." So, I knew I had won the NATO post-doctoral fellowship to go to Oxford. That was a pretty exciting time. You asked about how naive we were, though. Neither one of us had been east of Salt Lake City at that point. I'd tell people there was a log cabin in Salt Lake City that was 50 years old that they charged admission to. When we got to Oxford, the first night we stayed in a hotel because our flat wasn't available yet. I walked outside the nest morning, and printed on the wall was 1350, or some similar number. I just about freaked out to realize we’d just stayed in a building that was that old. It changed our whole lives. I mean, the theater and concerts we had access to — we made $7000 that year with the NATO fellowship. We were able to go to all of the good music and theater programs that came to Oxford from London. We traveled all over in England and Scotland with our two little boys, age 2 and 3, and it was an amazing year. I went there in August to work with Dr. John Sanders, a professor who had spent a year at Bell Labs working with Art Schawlow. In fact, he claimed he was the one who convinced Art that ruby wouldn't lase, which ruby, of course, was the first laser. Anyway, he said, "Bill, you're going to get a call from Bell Labs. You're going to get an offer." I couldn't believe it. John told me that Kumar Patel would be calling. So, in talking to my wife. I said, "You know, if I get offered a job, what's the minimum salary I should accept?" And we decided $11,000 would be the minimum. So, when I was talking to Kumar on the phone, he offers me a job, and I said, "How much would I get?" And he said, "$14,600." I just about fainted. Anyway, that was the story, and I went to Bell Labs. I will digress again. Looking back, you had to spend two years at Oxford to do a DPhil. I think I could have arranged with Kumar to let me go back there a few times during that year and stay in contact with John, and I could have earned a DPhil from Oxford, but I was having too much fun at Bell Labs at that point.

Zierler:

Bill, what was the research you were involved in at Oxford? What was the group you were a part of?

Silfvast:

It was a physics group, atomic physics. Some people were measuring isotope shifts. John Saunders, because he'd been at Bell Labs, had a student working on a laser in his lab. That's another interesting story. When I got there, John said, "Well, Bill, nobody can do anything in a year, so why don't you work with Brian Atkinson on his program? Maybe you could do something there." I said, "Really? I've got things I'd like to do if you'd let me set up a lab." He finally agreed, and he assigned me a PhD student, John Deech, to work with me and we set up a lab. In one month, we had a laser working, and in two months we had a metal vapor laser working. In five months, we had an Applied Physics Letter written. I'm sure that's what prompted John to talk to Bell Labs and say, "Maybe you might be interested in him."

Zierler:

Bill, to compare the instrumentation at a place like Oxford versus Utah, was it similar, or was it a totally different level?

Silfvast:

Pretty similar at that point. Probably the only sophisticated thing we had were photomultipliers. I'm trying to think of what else. We had an oscilloscope, and I had to make a special oven to heat the gain region. I had a very good glass blower, because most of my laser tube and vacuum system was with glass. Glass valves for the vacuum system and a glass diffusion pump. That sort of thing. It was not much different then, than what I had in Utah. But we did have a very good spectrograph. That was important.

Zierler:

And Bill, absent being surprised about this offer coming in from Bell Labs, was the assumption for you that you were going to go back and maintain your interest in teaching and being a university professor?

Silfvast:

Oh, the offer at Bell was for a two-year program, because I wasn't flown over there to interview. Thank God I wasn't, because I wasn't sophisticated enough to know how to do an interview at Bell Labs. I wouldn't have gotten the job. But they offered me what they called a limited term appointment. So I went there for two years with the idea of going from there to a university, and I stayed 23 years instead. It was such a fantastic place to do research. I got to play for 23 years. I could digress and talk about that if you want.

Zierler:

Absolutely. What year did you get to Bell Labs initially?

Silfvast:

1967.

Zierler:

1967.

Silfvast:

The Oxford fellowship was '66 to '67.

Zierler:

And what were your initial impressions when you got to the laboratory?

Silfvast:

I was in the Electronics Research laboratory in Holmdel — I don't know whether you're familiar with Holmdel. That’s where Penzias and Wilson measured the blackbody temperature of the universe and received the Nobel Prize. But initially, Murray Hill was the location of the research division. Bell Labs had about 20,000 people, with about 1,500 in their basic research division. Of those, 500-600 were PhDs, engineers and scientists, and the others were assistants. Each person got an assistant in their laboratory to work with them, and others were to keep the place running. Anyway, Kumar Patel had hired me in his department. Murray Hill got overcrowded in the research division, so they decided to move one of the laboratories of the Research Division to Holmdel, and that was the optics area. So, Kumar Patel was supposed to move from Murray Hill to Holmdel. When I got there, he’d decided he wanted to go back to Murray Hill, so he let me take his lab. The lab was already partially set up with optical benches, and so on. He didn't have any of the things I needed, but he said, "Go ahead and set up your lab. Buy anything you want. Money is not the object. Just buy what you need." I set my lab up, and I think within six months I had two lab benches of two different kinds of lasers running. It was pretty exciting. But there's that idea of just what was the management looking for, in terms of accomplishments? We were only required to submit a one paragraph summary of our results three times a year. No one ever told me what to do in 23 years. But there were 40 PhDs in my laboratory, and you knew you were ranked one through forty once a year, by your department heads and the director. So, that was the pressure. But I felt I was always in the top half. One year, I know I got ranked number one.

Zierler:

Bill, given the fact that money was no object, and you were at such an amazing industrial research environment, what was the process like for procuring the equipment? Was this all made in-house? Would you work with manufacturers? How did all of that work?

Silfvast:

We ordered anything we wanted from any manufacturer anywhere. I had spectrometers, fancy oscilloscopes, all kinds of technical equipment, anything I needed I could buy. It was an amazing experience at that point.

Zierler:

And this includes, sort of, the raw materials for something that you'd want to build on your own?

Silfvast:

Well, I would have somebody build it. I ordered mirrors from people up in Murray Hill, special dielectric mirrors. Things weren't that sophisticated at that point in time.

Zierler:

That's sort of my next question, which is, to what extent were technological limitations a part of your research reality? In other words, were there questions that you were after for which the available technology was not yet sufficient?

Silfvast:

Yes. The main thing was the speed of optical detectors. Photomultipliers at that point were limited. You could resolve light pulses down to a couple of nanoseconds time response. But I wanted to resolve optical pulses in the sub-nanosecond regime. It wasn't until later at Bell Labs that I was able to get a photodetector that would resolve in that time frame. I was looking at auto-ionizing emission, which was sub-nanosecond. It took a while to get there. I also had very the latest spectrometers.

Zierler:

In terms of that initial experiment that you were involved with at Bell Labs, did you see this as a new area of research, or was this essentially a continuation of what you had been doing at Oxford?

Silfvast:

It was a continuation of Oxford and University of Utah because it was a whole new field. When the Chinese made their first visit to America after Nixon opened things up with China, they sent a delegation of scientists to the USA. And when they came to Bell Labs, they were brought to my lab to see my lasers. That was pretty exciting for me. The interest in these new multiwavelength, colorful visible lasers, created a lot of interest at that time.

Zierler:

And clearly you had a reputation that was international at that point.

Silfvast:

My lab was on the top of the list for visiting at that time. I could tell you, looking a little further ahead, I had many Russian colleagues who started copying my work. At one meeting I was at, they told me they all thought I was the Thomas Edison of lasers, which was very flattering to me.

Zierler:

Bill, what were some of the things you were discovering in those early years about what lasers could and could not do?

Silfvast:

That's interesting. I was working with the blue helium cadmium laser, which was probably the most well-recognized laser I had discovered at that point. It was later made by three commercial companies for many, many years. I think it's still available with one company in Japan, but anyway, back to the blue laser. I got a call from a doctor in Philadelphia, at the Children's Hospital I think, named Tom Sisson. He said, "Bill, I'm very interested in using your blue laser to treat babies. Babies get jaundice, and we have to put a blue light on them to get rid of the jaundice. The blue light is absorbed by the yellow bilirubin distributed just under their skin." I went over to visit him and look at his system. He wanted to have one laser beam that could be sent along a row of baby cribs and put a mirror at the desired baby’s crib to irradiate that baby. I convinced him that although the blue laser light was wonderful, it was expensive compared to mercury lamps. So, that was one area. There were two areas, later in the early '70s, that a development area of Bell Labs had a need for a laser. They contacted me and they wanted to know if I could develop a compact ultraviolet laser, which also operated in cadmium vapor. They wanted to use it for a remote blackboard system, where they could use the laser to write and project, in real time, a lecture that someone was giving in one part of the country, that would be inscribed on a screen in another part of the country using the helium cadmium ultraviolet laser. So, I worked on developing that. I developed a compact laser maybe about 60 centimeters long that would fit into a suitcase. In fact, a version of that laser that I made is now on display at CREOL at the University of Central Florida. Anyway, they got excited about that, and I told them I think I could get a laser made that they could use. So, I contacted five laser companies and I wrote up a plan of how to make such a laser and we visited the five laser companies. We got to Spectra Physics and the guy there said, "Well, it can't be done." Then we went to Coherent Radiation next door, and they already had one running. Mark Dowley, who was the guy that made the laser at Coherent, quit and started Liconix, which was the first commercial helium cadmium laser. So, as far as the remote blackboard was concerned, they ended up doing it a different way and didn't end up using that laser. But at that same time, a fellow on another floor of Bell Labs was developing a printing machine, a copying machine. He wanted a laser, so I made a laser for him. He used it, and he made a copying machine that I actually went up and saw working. So, there were two places at Bell Labs where I helped them develop applications. Later this became very well-known. In my research division, everybody was coming to me wanting to know how I interfaced — by then the thing was how to interface basic research with development areas. They were coming to me asking me how I did it. That was the year I got number one in my laboratory. There were also other areas that I helped, mainly with the ultraviolet laser.

Zierler:

Bill, a similar question from your graduate research days, and that is, were you thinking at any point about the possible industrial applications for lasers, or were you always coming at it from the basic science approach?

Silfvast:

I could have quit Bell Labs and started a laser company, but I really wasn't interested. I was just interested in basic science. I know, from what I knew about myself that it wouldn't have worked. I just liked coming up with new ideas, and that's what I spent my whole career doing.

Zierler:

Did you trace the way that your research did inform commercial applications and companies that did build lasers based on what you were learning?

Silfvast:

Well, I was interfacing with the laser companies themselves. I communicated with Mark Dowley. And after I left Bell Labs I consulted for Liconix. Also, Omnichrome had me come out to California. I couldn't consult for money, but Bell Labs let me go out and talk to them about issues relating to their lasers.

Zierler:

Bill, what was the research culture like at Bell Labs? In other words, would you have opportunity to sort of just schmooze with other scientists who might not have even been involved in your research, just to bounce ideas off them?

Silfvast:

Good question. I have two answers. One is, in the research division you were not allowed to form groups. You had yourself and one assistant. Everybody was the same whether you were a hero or not. So, what you did is you collaborated. You knew what other people were doing, and you have an idea that might involve their specialty, and you collaborated and did experiments together, but you couldn't form groups. And it was never Dr. Silfvast, it was always Mr. There were no Dr. used at Bell Labs. It wasn't allowed. Also ,I remember when I first started, we were all going into the labs wearing jacket and tie, and my wife used to worry that my tie would get caught in the mechanical pump and strangle me. It's amazing how that culture changed over the years from what we wore then to later on.

Zierler:

What was advantageous to you about this research culture? Would you learn about what other people were doing, and in turn, was that useful for your research?

Silfvast:

Oh, yes. Two things related to that. First, I was up at Murray Hill all the time. Attending seminars up there, I got to know many of the researchers, and there were often seminars in our area. I should point out, the department I was in is where the whole fiber optics program of the world began. Somebody had heard that Corning had developed a low-loss fiber. One of my colleagues was encouraged to go up there and see if he could get a piece of fiber. He brought it down and people started doing experiments with it. It all happened right there. Peter Smith was called by the president of the research division, to see if he would work on developing how to splice a fiber since no one knew how to do that, and he agreed to work on it. But let me go back a little. When I got to Bell Labs, people were doing rain studies in 1967 in Holmdel, concerned about propagating lasers for communications in the atmosphere. They readily decided that wasn't going to work because you couldn't propagate the laser through rainfall. So, then, they started talking — this was in the late '60s — about running the laser beams through pipes underground, so they wouldn't be inhibited by rainfall. So, you'd have a whole series of pipes going all over the world. That was before the low-loss fiber was first discovered and that was the thought at that time. I should mention, another thing. The department I was in, I claimed I was the trainer of famous people. Do you know Bill Brinkman, or have you heard of Bill Brinkman?

Zierler:

I've heard the name, yes.

Silfvast:

Well, he was my department head. You heard of Steve Chu?

Zierler:

Of course.

Silfvast:

He was my department head. He was the head of the softball team, and he called me his veteran pitcher. Of course, Kumar Patel, and Paul Liao were also my department heads. So, I claimed to be the trainer of all these famous people.

Zierler:

Bill, of course, the environment at Bell Labs was famously not directed toward the bottom line. Bell Labs, obviously, was in a financial position where that was something that was never important, at least in the early years. Did you ever have a sense that it was good for your career that you could contribute research that might ultimately be profitable for Bell, or was that never the circumstance for you?

Silfvast:

It was only the small research division that didn’t work towards the bottom line. We were encouraged to have patents. I happen to have 30 patents, many of them from Bell Labs. But I realized later what was important to Bell Labs, about as important as anything, other than recognition of famous results, was that someone told me that Bell Labs licensing people would make available cross license patents with other companies. They might go to DuPont and say, "Our stack of patents is this high, and yours is this high, so we'll pay that ratio in licensing fees." And GE, also. So, I think that was an important point for Bell Labs to have all of these patents. There wasn't a whole lot of effort in the research division to take breakthroughs and incorporate them into new phone systems. It did happen but it wasn't a major effort at that time. That's why later when I had all these people asking me how I provided the development area with my laser, they wanted to know how I did it, because there wasn't a mechanism to do that in those early days.

Zierler:

What was the intellectual property process like when you had an idea that was patentable?

Silfvast:

Any paper we wrote had to go through patent to see if it might be a patentable idea. But at some point, I kind of got to know what was patentable and what wasn't. I got to be good friends with my patent attorney, Wil Wisner, at Bell Labs. He wasn't only mine, but he was the one I worked with. I got to know when things might be patentable, and I'd give him a call and say, "You might be interested in seeing this." As far as I know, progress during the year in the annual evaluation, patents didn't play a major role. They were more interested in publications and how good your new ideas were. I can say that Bell Labs was very good at evaluating people. I was in a laboratory that had five department heads and a laboratory director. Everybody in their department was in a different field than the department heads were, but they made it a point to find out from the outside world how good your research was, not from within Bell Labs. So those evaluations were pretty accurate. I don't know of any other place that went to that kind of effort, especially when I got to the university and realized how somebody in the university can get an offer from a publisher to write a book and make a big noise about that. No one ever checked outside of the university. I was chair of the physics department for three years so I know there were no efforts to check outside to see how valuable your research was. It was all done internally. The professors could build themselves up maybe more than they should have.

Zierler:

Bill, given the emphasis on publications over patents at Bell Labs, this is certainly a metric that sounds more like an academic environment than a for profit environment. So, my question is, to what extent were you connected with your academic colleagues? Were you reading the same journals? Were you presenting at the same conferences? Were you essentially working with academic colleagues as if you were in an academic environment yourself?

Silfvast:

I was in an academic environment. The Bell Labs research division was an academic environment. My colleagues were mostly university professors around the world.

Zierler:

Right. It was sort of like the best of both worlds because whereas your colleagues that were in university departments, they had to worry about research grants and things like that.

Silfvast:

Tell me about it. I left Bell Labs in 1990 and went to the University of Central Florida because I wanted to have a chance to become a professor. I went there as a full professor and found out you spend half your time teaching and supervising students. That's how I started writing my book, which I can tell you about at some point. It was a whole different story at the university. I realized I could never have done there what I did at Bell Labs. The things that I started I would never have gotten an NSF grant for, because I didn't have enough basis other than my own thoughts about it. I'd go into the lab and play around with things and have many successes, but that just couldn't happen at a university. They're just so tied up with teaching and writing proposals and they have very little time with students. And they do very little research themselves. They have students do it.

Zierler:

Bill, the story of the ultimate breakup of Bell Labs, and the impact that this had on the laboratory, and the basic research, of course, this story is well-known. I'm curious, if by the late 1980s, you had started to see the writing on the wall, or this was still too early?

Silfvast:

Oh, definitely. In fact, I can digress a little. My colleague, Obert Wood, and I were the first to propose using extreme ultraviolet, EUV, light to print microchips. I got a request from the Department of Energy to come up with an idea for an application of soft X-ray lasers in December 1986 which was the area I was working in at that point. I got together with Obert, and we came up with the idea of using reflective optics in that wavelength region since nothing transmits down there. So we thought of using a reflecting mask and a special mirror arrangement to print microchip patterns using extreme ultraviolet light. It turns out we were the first in America to propose that idea. So, we started working on that. A little later, Bill Brinkman, who was a director up at Murray Hill by that time, got in touch with one of his department heads, Rick Freeman and another colleague, and talked them into working in the EUV as well. He suggested we combine our efforts with Rick as the head of the group, which we did. Interestingly, that was one of the first collaboration efforts as a group that occurred in the research division of Bell Labs. This was in about 1988. Shortly after that, Rick came to me. He was busy with other research, so he asked me if I would be the group leader of this newly formed EUV lithography group. So, I organized the group, and we did the first imaging experiments out at Brookhaven, using the synchrotron as our light source. That was a major breakthrough. We scooped Stanford and Berkeley and University of Wisconsin on efforts to do sub-micron imaging in the extreme ultraviolet, which helped start the national program on EUV lithography. And I recently heard from the John Caruthers of Intel, who started the program there, that the version 12 of the Apple iPhone is now being printed by EUV lithography in Taipei. So, it took that long to come to fruition, but it's now happening. And that was exciting for Obert and me to be involved in the early stages of that program. I was involved in the light source portion of it, developing EUV light sources. It turns out that working in the extreme ultraviolet, lasers don't help you that much. The transition probabilities are so high in normal spontaneous emission that you don't need the extra power from lasers to be effective. So, there are very limited applications of extreme ultraviolet and soft X-ray lasers, because you can use normal spontaneous emission which is what we did to get as much light as we needed. In the visible, lasers make a huge difference, but not in the extreme ultraviolet.

Zierler:

Bill, would you say, given the fact that you were working on such a fundamental discovery, would you describe the discovery more as eureka moments that came in bursts of discovery, or was it more gradual?

Silfvast:

All of my laser discoveries were mostly eureka. I had various ideas, but making a laser, either it works, or it doesn't. I made several types of new lasers. I had a Russian colleague refer to me as the Thomas Edison of lasers. While at the University of Central Florida, I once asked my former colleague Obert Wood for a recommendation from him when I was being considered at the university for the Distinguished Researcher Award of the Year. He wrote a letter that said he thought I was the most creative of all the scientists at Bell Labs, which was very humbling to me.

Zierler:

Bill, what were some of the feedback mechanisms you would do during experiments to know if you were on the right track?

Silfvast:

I spent a good portion of my career developing new lasers and new kinds of lasers. And a laser, either works, or it doesn't. Of course, I tried different things. If it didn't work, I’d try something else.

Zierler:

And when you say, "does work," "does not work," what does it mean? what are the distinctions?

Silfvast:

Well, it means that the intensity of the emission you're looking at with the spectrometer increases by a factor of a hundred or a thousand instantaneously, or it doesn't. In the visible, you could see it sometimes, see the beam. But usually, it was looking through a spectrometer.

Zierler:

Bill, looking back at your long career at Bell Labs, what was your proudest moment?

Silfvast:

That's a good question. There were several. Certainly, one of my proudest was getting an offer at Bell Labs. I learned later that when hiring people, Bell Labs department heads depended on certain professors around the world to give them a recommend of their students, compared to the previous students of that professor. So, they had this mechanism to get input. They didn't want to take risks of hiring some bloke from the University of Utah, since they didn't know his professor, and didn't know how good he was. That's where John Sanders at Oxford helped me, because he had been at Bell Labs and knew the people there. Anyway, you asked me about other times. One was getting a selenium laser operating, which had 46 laser wavelengths in the visible. That was one I showed the Chinese. It made the cover of the February 1973 Scientific American when I was asked to write a Scientific American article. The cover photo shows many of those beams. That picture has been used a number of places, including Nico Bloomberg's article he wrote for American Scientist. Life Magazine also did a series on optics, and they had that photograph on the cover of one of their volumes. That was pretty exciting. Probably another exciting time would be in 1982 when I got the Guggenheim Fellowship to spend a year at Stanford. Steve Harris, a well-known professor there, encouraged me to apply. And maybe the most significant was in 2019 when, during the 60th anniversary of the laser, I was named one of 27 Laser Luminaires or Laser Pioneers for my work in metal vapor lasers. Some have mentioned me as the ‘father’ of metal vapor lasers and I am featured in a book written by Jeff Hecht titled ‘Laser Pioneers’, with my photo on the cover.

Zierler:

How did the Guggenheim Fellowship work? Was it site specific to Stanford, or could you take it wherever you wanted?

Silfvast:

It was site specific. I requested Stanford. Some people who get them can go anywhere they want to do their research. And my being awarded the fellowship is another interesting story. I got Art Schawlow (Nobel Laureate), a professor at Stanford and a friend, to write a recommendation for me for the Guggenheim Fellowship. You know him of course.

Zierler:

Of course.

Silfvast:

My wife calls me one day when I'm at Bell Labs and says, "Honey, I think you just got the Guggenheim Fellowship." I said, "Why?" "Because Art Schawlow just got the Nobel Prize." That turned out to be correct. I got the fellowship, and I suspect he played a role in that.

Zierler:

And what did you do for your year out in Palo Alto?

Silfvast:

I developed a new kind of gas laser. It was the first time anyone used extreme ultraviolet light as a broadband pump source to pump a laser. I did the very first experiment. I learned all of the physics from Steve Harris and I wanted to build that laser at Stanford, but he wouldn't let me do it. He didn’t want to interrupt his research program. I had talked about doing it to a couple students, and we just wanted to do a nighttime test of it, and he refused to let me do it. So, I went back to Bell Labs, spent a week there, and we set up the experiment and got it working. Some of his students were upset with him for not letting them participate in that breakthrough. And you did read the story about how my son got his computerized audio mixing board working by my connecting him with one of Steve Harris’s former students while I was there.

Zierler:

That's right.

Silfvast:

Well, none of that would have happened had I not had the Guggenheim Fellowship. I wouldn't have been with Steve, and I wouldn't have met his students, and all of that. So, I was thinking the other day, that my son started this whole new field, and it wouldn't have happened without the Guggenheim Fellowship. It's amazing how changes in events in one’s life can affect a lot of things.

Zierler:

Right. Bill, kind of a broad question, given how much interest there was commercially in the lasers and the research that you developed, were there any moments of satisfaction where you would see some of your research come to fruition that really benefited society, either technologically, or economically, or even the way that lasers are used for all kinds of health applications?

Silfvast:

Well, the helium cadmium laser became a commercial laser, and it was used in a number of areas. It was used in experiments that were the forerunner of 3D printing. That all started, it had a different name back then, but both my laser and the Argonne ion laser were the first lasers used to start that field. And the UV helium-cadmium laser was used for years to print the masters for CDs and DVDs. So, there were areas like cell sorting, where I could see that my lasers had an impact. Of course, also maybe negative impact when both Livermore and Israel started doing isotope separation using the copper vapor laser. But that's negative, that's to make bombs.

Zierler:

Bill, to go back to that question about the changing culture at Bell Labs, because of the impending breakup, in what ways, even at the relatively early juncture of the late 1980s, in what ways would you feel these changes underfoot? Were budgets shrinking? Were they hiring less people? How did that play out on a day to day basis?

Silfvast:

Thinking back on it, it's more that the department heads and the director started looking towards how they might help applications. There was pressure from above at AT&T to do that. Well, actually, it was Lucent Technologies by then, after the breakup had occurred, but there was pressure higher up to make what we discovered useful. That's how my colleague and I got over to doing EUV lithography and thinking about those kinds of things. That was around '87, '88. In fact, Obert and I did the first experiment on the first X-ray laser, which was a soft X-ray laser, at Livermore, but the experiment didn't work. The reason it didn't work is they hadn't characterized their laser beam well enough. They didn't know that there was a refraction in the plasma when they made it, and the beam was diverted out of the path where you'd normally think it was going. So, we aligned our system up as to where it was normally supposed to go, and the beam wasn't getting there. And we only got three shots. We went out there, spent a couple weeks setting up an experiment, and we got three shots on the X-ray laser for our experiment. So we didn't get much of a chance to try anything new. That was frustrating.

Zierler:

Bill, to look back on your decision-making, when it was time to move on from Bell Labs, how much of that motivation was about the fact that you saw where Bell Labs was headed, and how much was it that you had an opportunity to go back to your original interest of teaching and wanting to be a professor in a traditional university setting?

Silfvast:

Well, by then, I was driving out to Brookhaven from Bell Labs, doing experiments with groups, and doing organizing things rather than doing much experimenting myself. To tell you the truth, by then, I got tired of Bell Labs. I got tired of just going to try something else new, which I did for 23 years without anybody ever telling me what to do. I started thinking about universities, and we happened to go to the Optical Society meeting in Orlando, in October of '89. In fact, we were down there when the big San Francisco earthquake occurred. Anyway, a colleague of mine, Mike Bass, who had been at Southern California, USC, had become the Vice President of research at University of Central Florida, a fairly young, new university. Anyway, I met with him, and he said, "Bill, why don't you consider coming down here and being a professor”, and that alerted me. We spent the week looking around Orlando seeing if we wanted to live there, and later I also spent some time contacting other universities. I recall specifically talking to Stanford and Arizona and a couple of others. Anyway, we decided going to Florida would be lots of fun to help start a new laser center there. They were just organizing what they call CREOL, the Center for Research and Education in Optics and Lasers, which is now pretty well known, but then it was just in its infancy. They hired five of us senior people as full professors, which was a smart move for them. We all went there and helped start this new program. At that point I was ready to become a professor.

Zierler:

Bill, what was the impetus for the origins of CREOL? Where did the money come from? Where did all the energy and the political support come for the origins of CREOL?

Silfvast:

Well, MJ Soileau, who was then a director, had tried to start something similar in Texas, and it failed. He was interested in optics. In fact, he had spent some time with Grant Fowles, my previous professor, after I had left Utah, which we didn't know about until later. Anyway, he had the vision that funding might be available to develop new things in optics and lasers, and when he came to Florida, he started this new lab called CREOL, and convinced the legislature to fund faculty positions. They funded about ten or fifteen positions to start this new idea, and the basis for his argument to them was that it would help start industry up in Florida and make jobs other than in the entertainment industry. They went for it, and he started CREOL. He was skillful enough at that point to convince the legislature to fund it. It paid off. There are a large number of startup companies now that started in Florida as a result of that.

Zierler:

Now, was your appointment exclusively in CREOL?

Silfvast:

We didn't have a department then. I went there as a professor of physics and electrical engineering. I had a joint appointment. There was no optics department then, which there is now. Actually, there's a College of Optics now, which CREOL is a part of. But back then, about half of us that were at CREOL were members of the physics department and we comprised half of the physics department. They had fifteen people in other fields, and fifteen people from CREOL, and that comprised the entire physics department. The electrical engineering department was similar, although they were a much stronger department at that time. So, I had a joint appointment, full professor in both areas.

Zierler:

Did you take on graduate students right away?

Silfvast:

Immediately. In fact, my younger son was at that point going to University of Arizona. His friend was getting a master's degree, and I talked him into coming out to CREOL, and he was my first graduate student. I fairly quickly had two more, and at one point I had more female graduate students than male, which I'm proud of. When I first went there, I was staying for the first few months — my wife was still in New Jersey — I was staying at motel nearby, and this black couple across the way, I got chatting with them, and it turned out they were from Trinidad, and she had obtained a PhD in physics from Trinidad. I can't remember why she came to Orlando, but she couldn't get a job. Her thesis was in timber physics, and nobody was interested in that. I guess, being a black woman probably played a role there too. She couldn't get a job, and I called Larry at NSF, a friend that I knew, and talked him into providing her with a fellowship to spend a year with me in my lab, and I would re-train her, which I did. And she immediately got a job teaching up at Grand Valley State University in Michigan, and she's now back in Florida where she wanted to be. Anyway, I got her into the system.

Zierler:

Oh, wow. Bill, how much of the research lab was already built up for you at CREOL, and how much was it sort of a repeat like at Bell Labs where you had to build this up from scratch?

Silfvast:

When I went to CREOL, CREOL was over in the research park since there was no room at the university. That was where business startups of various kinds began. One of them was the Navy who had a research lab there, and they had this huge building. In the beginning, we occupied the top floor of that building. We weren't even on the university campus for the first two years. And then the legislature was finally convinced to build a building that was called CREOL, and we moved there after about two years and got to set up our labs there. But I initially set up lab space in the naval research building for two years.

Zierler:

Was it obvious to you that CREOL was going to be such a big success and experience such rapid growth?

Silfvast:

It was the plan. There was nothing obvious about it. It was the motivation of all five of us that went there. We didn't want to just do more research. We wanted to help start a new program. Our competitors were the University of Rochester, which had the School of Optics, and the University of Arizona, which had the Optical Science Center. We were the new kid on the block, and it was our goal to get at least equal to them, which we have long since achieved. CREOL is well known in the field of optics all over the world now.

Zierler:

Bill, given that you finally had the opportunity to pursue your interest in teaching, what were some of your favorite courses to teach undergraduates?

Silfvast:

Initially I had to teach some physics classes, and I taught mechanics and modern physics, which were the two areas I loved the most. But I didn't teach the first year. That was my agreement with them. My second year I agreed to teach, and I asked to teach a laser course. I had been thinking about writing a book about lasers when I was still at Bell Labs. In fact, for 15 years I taught the introduction to lasers class to non-scientists at the big CLEO Laser Conference, the largest laser conference in the world, I would get salespeople and marketing people, those kinds of people. And while doing that, I had the idea of writing a text/reference book about lasers. There were four or five books out by then, and I didn't like the way any of them were arranged. I used my ideas in teaching that course at the CLEO Conference to get an idea of how to teach various aspects of lasers, because lasers involve physics, they involve engineering, they involve optical configurations, cavities. They involve all kinds of areas, and I'd noticed in all the books that were written, people just jumped into one area and started writing their book about it. It wasn't logical to me. So, the second year I was at CREOL, I thought I would start writing my book. I was teaching my laser class and I wrote a chapter a week to present the rough draft to the students. I told them later, I said, "Because you suffered through reading my rough drafts, you all get a free copy of the book when it's published." Well, I finally, after maybe a year and a half or so, got the first draft of the book written. I didn't want to do what a lot of guys did. A lot of guys were corralled by publishers to write a book, and then they committed to that publisher to write that book. I instead decided I was going to write the book and then I was going to put it out to a bunch of publishers. So, I had five publishers that were bidding to publish my book. I ended up going with Cambridge University Press, which I'm very pleased with. My first edition was published in '96, and I wrote a second edition while I was out on phase retirement and published it in 2004. It still sells. I still get $1000 royalties every year. In fact, last year, the royalties went up. That's after sixteen years of the second edition. The success of it is that it started with the basic principles. It's called Fundamentals of Lasers. A lot of professors around the country use it as their physics course in optics because it covers all the basic things. Spontaneous emission, and line shape, line width, and so on. So, I'm very proud of that book. A colleague of mine at Livermore once told me, "Bill, as much recognized as you are with your research, you'll be remembered more by your book."

Zierler:

Although, you couldn't have written the book without the research.

Silfvast:

No, of course not.

Zierler:

Bill, who is the book geared toward? Who is the audience that most benefits from this book?

Silfvast:

In some schools, it could be a senior division physics class, or a first-year graduate course. It's not a highly sophisticated book like Tony Siegman's laser book. That would be the follow-up to my book if anybody wanted to go into it further. It's just simple ideas developed in physics. Each area of physics that’s related to lasers is explained. And then I go into all of the different kinds of lasers. I talk about gas lasers, plasma lasers, solid state lasers, liquid lasers, dye lasers, and semiconductor lasers. I take each of those subjects and go into them separately, so it covers the whole field. And then, in the end, I have a summary of the characteristics of all these kinds of lasers. I finish up with a chapter on non-linear optics. So, it covers pretty much the whole field.

Zierler:

In terms of prerequisites, or an assumed knowledge level, what are some of the things that you think readers of this book already know, and what are some things where you feel like you need to explain things right down to the basics?

Silfvast:

They need to know calculus, and they need to know wave theory. They need to know how to write an exponential wave equation. And they’d need to know simple differential equations.

Zierler:

Was this something that you theoretically could have written during your days at Bell, or you wanted to be within a university environment and with a certain removal from the research at Bell before you wrote the book?

Silfvast:

I couldn't have taken the time to write it at Bell, but all my ideas on how I had to write the book were pretty much there by the time I went to CREOL. So, I knew what I needed to do, and I just said, "I've got to start doing it." I remember going to MJ, our director, at the end of that year for a review, and I guess I had been spending maybe more time writing the book than getting success in my research at that early stage. I remember him saying, "What have you accomplished?" I said, "Well, I wrote a book." And he said sort of negatively, "Well, everybody's writing a book." It was later that he put my book on display in a case out in the lobby, but not at that point. He didn't think I was serious.

Zierler:

Bill, what prompted the second edition in 2004? Was it technological developments mostly?

Silfvast:

Technological and some errors I made in the first edition. Not blatant errors, but descriptions and so on, that I did in a hurry and realized later weren't quite accurate. But mostly it was getting new kinds of lasers into the book. I thought of writing a third edition, but I looked the field over and very little in the way of basic concepts had occurred that wasn't already in my book. I guess that's why it has survived for so long.

Zierler:

So, that's to say that the field has not really developed that much since the second edition.

Silfvast:

Well, it's like saying mechanics hasn't developed that much either since Newton. You kind of get to the point where there's not much more — there's certainly a lot in making various kinds of lasers, and how to package them, and how to miniaturize them. Of course, that's the big thing in lasers now. It's all semiconductors or LED pumping sources, and solid-state lasers, the two prominent fields now. Gas lasers still are around but they're too inefficient and too large. The solid state and semiconductor lasers have pretty well taken over. But it took a while.

Zierler:

Bill, when you say that you decided on a phased retirement, what were some of the things that you took out of your portfolio, and what are the things that you wanted to still be involved in?

Silfvast:

Well, I was kind of getting tired of research. I was thinking about doing other things. I thought there was a lot more in life. At that point, I'd spent 40 years or so in a laboratory. I thought there were a lot of other things to do, and we decided — this was around 1997 — that we didn't want to retire in Florida, so we narrowed it down. My wife was from Los Altos, which is right near Stanford. I don't know that you're familiar with that town. I had been out there and spent two years working at Lockheed there. So, we decided California was where we wanted to retire. We chose either Carmel Valley or Grass Valley or St. Helena. We finally narrowed it down to St. Helena, and we actually bought a house there in 1997 but I didn't retire until 2000, but we decided that's where we wanted to be in the long term, and we were fortunate enough to be able to afford to do that. So, I continued on at CREOL, but our goal was to get to California. The university offered a phased retirement program that you could spend one semester a year for the next five years if you retired, but you had to do it before you were 63, and you had to have ten years of experience. Well, when I turned 63, I had been there just one month over ten years. So, I qualified in both cases, and I applied for phase retirement. That allowed me to go back one semester of the year, of my option, any one of the semesters for five years, and have full salary for that semester. That was attractive to me. Of course, when I retired from Bell Labs, I had a retirement package as well. So, financially, we were never better off than at that point. So we drove back and forth from St. Helena, California, once a year for five years, and had a blast doing that. We knew all the good restaurants on the way and had a lot of fun doing that driving.

Zierler:

Well, Bill, now that we've worked our way right up the time of your retirement from your active research career, I'd like to ask one broadly retrospective question about your career, for the last part of our talk. The first is, what have you found are some of the most basic public misconceptions about lasers? In other words, everybody's heard about lasers, but very few people really know what they are, where they came from, and what they're used for.

Silfvast:

Most people think of lasers as a beam. I used to ask, when I gave talks to the public, which I did around the country several times, "How many people have a laser?" No hands went up. I said, "How many people have a CD player?" Everybody's hand went up. I said, "You own a laser." The biggest application of lasers in 1977 — I was pretty good friends with a lot of the laser companies — the biggest application of lasers in 1977, you'd never guess. Sewer pipe alignment. And Spectra Physics developed a laser for construction companies, to level a field or to give the orthogonal positions of the corner of the house, so you’d get everything orthogonal. They had a 3-beam laser pointing in three orthogonal directions. The guy at Spectra Physics told me they sold that laser for $3500, and he said, "80% of that cost was for the salesperson to go out and spend two or three days teaching them how to use it. It wasn't the cost of building the laser." But people thought of it mainly as a beam. Of course, it's now used in your eye. I got to know Dr. Tom Lesperance in New York City, an ophthalmologist, who did the first application of lasers in medicine. He used it to irradiate the blood vessels in people's eyes who had diabetes. They tended to get little blood vessels scattered through their vitreous. He used an Argonne laser, which transmitted through the retina, and it would be absorbed by the blood vessels that were floating around, using the blue laser. We had conferences up in New Hampshire called Gordon Research Conferences on different subjects such as Lasers, Biology and lasers, Lasers in Medicine, all kinds of things. We'd get people from all disciplines coming to those conferences. Very casual, in the summer, out in the woods. We'd have presentations and very informal discussions which were very, very fruitful for the whole field. It still goes on in other fields, but for lasers in that area, it was very useful. I forget now what the question was you asked me. I got sidetracked.

Zierler:

The question about people generally hearing about lasers.

Silfvast:

Oh, yes. Lasers are used to irradiate various cancers, both inside the body and outside. The copper vapor laser was used to do cancers. They put a dye in your blood that was absorbed by the green laser, and then irradiate that through the skin. That was for surface types of cancers. I don't think people in general think about lasers used for communications, but of course, they are used there to generate the signals in fiber optics. I'm trying to think of what other areas people might be familiar with lasers. As opposed to hearing about them, actually being familiar with them. I think, probably, medicine is the biggest area where people hear about them, possibly mostly for eye stuff, but also for cancers. But the biggest area is in manufacturing, drilling, heat-treating, cutting, etc.

Zierler:

Bill, after your many decades in the lab, did you have any close calls in terms of safety?

Silfvast:

I didn't, but my assistant that worked for me, one day was operating a dye laser, and he thought he blocked the laser. You'd have mirrors, and then the cavity would be in the middle. So, there'd be an airspace in between. He was lining up something in the laser amplifier, and he reached up with his hand to block the beam while looking down the laser tube. His hand dropped, and he got irradiated in his retina. It blew out the fovea of one of his eyes and he lost his vision in that eye. It was a very sad time for me, and especially for him, but he continued on working. I got him a fellowship at Stanford, and he later got a PhD there and had a very successful career. But that was the worst thing, and it didn't happen to me. It happened to him. The closest thing that happened to me probably was not getting my tie caught in the mechanical pump.

Zierler:

To your wife's great relief. Bill, have you been active in the Optical Society of America, and in what ways has the OSA been useful for your career and those of your colleagues?

Silfvast:

I was very, very active. First of all, I started being involved at the CLEO Conference. I was on the board of that conference for a couple of years. Then, I ran for the OSA board, and was elected to that board. I also was involved in their conferences. We had technical groups covering all areas of optics, and heads of those groups would gather to plan the annual meeting and come up with a program. I decided to organize them into five divisions, with a division head for each category, which still exist today. One of them was lasers and one was biological optics, and so on. I was the one that organized that. I was also on the executive part of the board, there were five of us, for a couple years. And I co-chaired the |CLEO conference one year. I also got involved in organizing some meetings with IEEE, and two other colleagues and I organized some ultraviolet laser meetings in Santa Barbara, which we held every other year for about 12 years, including the time I was at CREOL. They were very successful, very casual meetings, like the Gordon Conferences, to translate research information to industry. About half of them were industry people and half were scientists and engineers. That was pretty rewarding to organize those conferences.

Zierler:

To go back to that amazing earlier conversation, back in undergraduate and graduate days where there was sort of a suspicion that optics and lasers was not "real physics". Of course, today, that's obviously not true. Reflecting over the course of your career, in what ways has your research been useful more broadly in physics? How have lasers advanced physics that might not have ever been possible without this research?

Silfvast:

Well, mainly, it was making my lasers that I developed available for researchers in the lab. When I was at CREOL, there must have been five or six helium cadmium lasers in various research labs being used for experiments in optics, in various phases of optics. Mostly in solid state optics, but I don't know that I directly got a field started. I'm trying to think. But indirectly, it helped in a lot of fields. I was more interested in the atomic physics side of lasers. A lot of people were more interested in the wave part of it, describing nonlinear optics, and all of that. I was more interested in the physics, and the atomic and molecular physics side of it. The research I did sort of followed along those lines. I published a number of papers in that area.

Zierler:

Bill, you've been involved in research in so many different kinds of lasers: recombination lasers, metal vapor lasers, laser plasmas. I wonder, what areas of research have seen the most growth over a sustained period of time, and what areas in laser research were finished? Essentially, this is what you needed to know and there wasn't that much development thereafter.

Silfvast:

Well, I would say, gas lasers, of course, were the big starting lasers, other than ruby, which didn't last very long. Solid state lasers started off very slowly. The field early was dominated by gas lasers, I would say, through the '80s. By then, mainly, Peter Molton started the titanium sapphire laser, and it was pumped by LEDs. That laser started taking over because it was broadly tunable, so you could make lasers at any wavelength. Gas lasers, earlier, you had to use the wavelength that they worked at, and we developed a broad spectrum of them. Neodymium was the first solid state laser but it was ti sapphire that made the real breakthrough, because you could tune it over the visible spectrum, and that offered a lot of wavelengths to do all kinds of experiments. But now semiconductor lasers have taken over. Especially, more recently developing the green and the blue wavelengths. Many people in those early days thought you could never make a blue or a green semiconductor laser because of the arrangement of the energy levels. But then there were breakthroughs, and they learned how to combine various elements and make new compounds, new semiconductors, that allowed them to make green and blue lasers. Now they're even working toward the ultraviolet. They're going to have trouble there, but green and blue — you can get lasers across the entire spectrum now. The trouble with diode lasers is they're so small, you can't make very pure beams with them. You need a large cavity. I don't know whether you're familiar with that, but you need a large cavity to develop the modes of a laser, such as the single mode laser operating on a single cavity mode, for example. You can't do that in a little semiconductor laser. So, you develop a bigger, quality beam laser, and then you use the semiconductor laser to amplify that beam to give you a more powerful beam. Or, you can have a powerful multimode beam, but it's not very pure. It's a has a much broader wavelength spread, which has many applications. In machining, for most applications they don't care if it's not a pure beam. You don't care about the purity of the wavelength. You care about the purity of the beam itself, to focus it, but not about the wavelength.

Zierler:

Bill, a very broad question, given that you started your academic career really being at the beginning of the creation of lasers and laser research. That is, if you can reflect back all the way to the early 1960s and then fast forward to today, what were some of the mysteries surrounding laser research, and what is truly understood now as a result of the research you and your colleagues have been involved in, and what are some things that really remain to be understood, that are ongoing question marks in the field?

Silfvast:

In the field of lasers?

Zierler:

Yes.

Silfvast:

I would think one area is the development of extremely short wavelength lasers, and hard X-ray lasers, and so on. Lasers are pretty well understood. The atomic physics is known, and the wave mechanics of making single mode lasers and so on, cavity properties — a famous paper Jim Gordon first described how you could make single mode cavities using end mirrors, following some of the work he and Charles Townes did in his thesis on masers. He was able to do the math to show that you could make a stable mode of a laser beam. That was done very early on, in 1959, I think. So, that part was understood. The atomic physics, a lot of it was understood. As far as physics is concerned, I'm trying to think. Of course, studying isotope shifts and things like that were breakthroughs. A lot of physics came out of the development of semiconductor lasers, and working with them. A lot of new physics of semiconductors. Making new materials was a new area. A lot of work in solid state crystals came as a result of making semiconductor lasers. I'm trying to think. In terms of atomic physics, other than isotope measurements, I don't think a lot of basic physics came about from that. Just the lasers themselves and how to produce population inversions.

Zierler:

Bill, in what ways have computers been useful for your research over the course of your career?

Silfvast:

Well, early on, we didn't have them. I remember doing Fortran at the University of Utah, putting in punch cards into a very large computer. I got one of the first IBM little computers in 1982 while at Bell, one of their first little PCs. I used that to model plasmas. I developed models that I used while at Stanford, that helped me formulate that new laser I described that I had to go back to Bell Labs to make. Anyway, I took my computer, my little IBM, out to Stanford and used that to model the lasers. I'm trying to think of what else. I did a lot of modeling with the lasers at that time in the '80s. Of course, in the '90s, let's see if I did anything. Probably not a whole lot. I was busy writing my book at CREOL and probably not doing a lot of theory. I had students doing experiments, trying to make new kinds of lasers, and so on. But there was still a goal to make ultraviolet and extreme ultraviolet and vacuum ultraviolet lasers. There still weren’t many achievements in that area. But that's when I got into EUV light sources, other than lasers, for lithography and followed that field the rest of my career. I contributed a fair bit to that area. I spent a year and a half, while I was still full-time at Florida on sabbatical leave at Sandia Labs in California helping to work on those sources for micro lithography. That was fun. I left Tuesday morning every week for a year and a half and drive from St. Helena to Livermore where I rented a room for two nights. I then worked there for three days at Sandia, and drove back to St. Helena on Thursday.

Zierler:

Well, Bill, for my last question, looking forward, using the powers of extrapolation over your many decades in laser research, where do you see the field headed? What are some of the exciting developments that remain for the future of laser research, and perhaps, what advice might you give young people interested in pursuing a career in this area? What are some of the kinds of things you think they'd focus on?

Silfvast:

Well, of course, the big areas are, as I mentioned — X-ray lasers, that's difficult area to get funding in. It takes big machines to make those work. But the biggest area in the last 20 years, I would say, is developing ultrashort pulses. They've gone from nanosecond to picosecond to femtosecond to attosecond lasers. People have developed those, and the idea is to develop such lasers with a high enough repetition rate or power to do exciting science experiments. So, lasers have become more of a tool, but people are still developing means to make very short pulses. You can do all kinds of biological experiments because the biological lifetimes are so short. They're sub-picosecond, femtosecond timeframes. So, you can excite a state and then look at it decay in that time frame. It can give you a lot of information about the science of atoms and molecules, solids, and semiconductors.

Zierler:

Well, Bill, it's been an absolute pleasure spending this time with you. I'm so grateful that I had the opportunity to interview you and get your perspective and insights over the course of your long and engaging career. Thank you so much for spending this time with me. I really appreciate it.