Oral History Transcript — Dr. Anthony DeMaria
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Anthony DeMaria; April 13, 1984
ABSTRACT: Research and education, 1956 to ca. 1970. Establishment of the electromagnetics group at United Aircraft Research Center, 1958. Inauguration of laser research after the SchawlowóTownes paper appeared. Modulating laser output. Modelocking investigations. Laser work on fusion and gas-dynamic CO2 lasers by other United Technologies groups.
DeMaria:In 1956 I graduated from the University of Connecticut with a Bachelorís in Engineering. I had worked my way through college, and being married, I accepted a job before going on for my Masterís. I went to work for a place called Anderson Laboratories, which is still in existence. At that time they were situated in West Hartford, Connecticut, and they were a manufacturer of RF and microwave delay lines for military radar systems, and the delay lines used acoustics for getting the time delays. Acoustic waves traveled 50,000 times to 100,000 times slower than electromagnetic radiation in free space so very long delays for radar applications in very small compact packages could be obtained. In one year I felt that I had probably learned about 75-80% of what I felt was important to me or of interest to me in acoustics, so I began looking around for other employment.
Bromberg:Were you already in a Masterís Degree at this time? Was this just an interim?
DeMaria:That was an interim. After I left Anderson Labs, I went to Hamilton Standard which was at that time a division of United Aircraft, which is now United Technologies Corporation.
DeMaria:[The Electronics Department of] Hamilton Standard was in Broad Brook3 Connecticut. The major plant was out in Windsor Locks, where it is now. And there I worked in magnetics and interfacing transistors and magnetics devices. How to make magnetic amplifiers, magnetic switching devices, high frequency transformers and isolation transformers for transistor amplifiers and thatís when I began my Masterís studies on a part-time basis during the evenings, first at the University of Connecticut, and later on completed my studies at the Hartford Graduate Center which is affiliated with the Rennselaer Polytechnical Institute, and that culminated in a Masterís Degree in 1960. So I worked at Hamilton for one year and then I had an opportunity to transfer to what they called the newly formed Missile and Space Division. United Aircraft was going to try to enter the space and missile business at that time (which was not successful) and so they borrowed talents from many organizations throughout the corporation and centralized their efforts to get into that business. The man that I was working for at the time was Lee Antes. He and management agreed that if UAC was going to successfully enter the space and missile business they needed to have a research activity. So instead of transferring to the missile and space division, Lee Antes and his staff, which I was part of at that time, came to the Research Center of United Aircraft Corporation here in East Hartford, Connecticut, in the summer of 1958.
Bromberg:Now this was already in existence, this Research Center?
DeMaria:The Research Laboratories, as it was then called, was in existence since 1929 or so. This corporation has had a long commitment to a centralized research center. At that time most of the research work here was dedicated towards jet engines, piston engines, propellers, helicopters, aerodynamics, fluid-dynamics, combustion, metallurgy, those sorts of technologies. There were no programs in physics, electro-optics, optics, microwaves, electronics, etc., because the corporation had few products associated with these technologies at that time.
Bromberg:And this group that Antes had, what did they call it?
DeMaria:They called it the Electromagnetic Research Group or Section. I donít remember whether it was a group or a section. We came here the summer of Ď58. About a year after I went to Hamilton Standard. For the first year, I worked on trying to detect low frequency electromagnetic radiation emitted from rocket exhaust as a way of trying to detect the launching of missiles. I also performed paper studies on techniques of how to realize three-color infrared systems. We also worked on high temperature electronic devices for jet engine applications. We looked at parametric amplifiers which were of considerable research interest at that time as were Esaki Tunnel diodes for microwave oscillators. So we were flirting around with a lot of different technologies. I also did a study on how to detect very very low frequency electromagnetic radiation propagating through seawater for communicating with and detecting submarines. In retrospect, the topics we looked at were very much in vogue.
Bromberg:Sounds as if there were lots of different topics. Was it a big group?
DeMaria:No. It was a very small and young group. We were launching new activities within the Research Center and it was a very stimulating time. There were a lot of things to do. We were the first staff members here with electrical engineering background and there was one physicist amongst the group. For the first part of my employment, for about three or four months here, I took the opportunity to complete a manual that I was writing for Hamilton on how to design magnetic devices, transformers, magnetic amplifiers and things like that. So I had essentially one year of acoustic experience, one year of magnetic design and transistor circuit experience, and then there were these areas of involvement in system studies involving new technologies. For a young man it was a very exciting period, because one developed a way of looking at problems in a very inventive, broad-scope kind of a way which I found very helpful later on as a researcher. I had to develop an ability of looking over a new problem quickly to determine what were the important aspects of the problem and then try to address those specific aspects of the problems. How to sort these things out in your mind was important training for me at the time.
Bromberg:Is that something you do by literature search, or is it something you do right on the bench with your hands or what, when you say that?
DeMaria:It was all that. I first learned to do a literature search to try to get a big picture. And then after I got the big picture, I tried to concentrate on what I thought were the important problems. Then I would get more specific and I would begin to think up experiments to perform in order to better understand those problem areas with the hope that I could make a contribution to the advancement of the state of the art. That training was very helpful to me at the time. Itís the sort of experience one obtains in graduate school, but I learned it while working here with a B.S. degree.
Bromberg:I might just say that we are very interested in the styles of work that people have and for this kind of material it would be interesting to know.
DeMaria:I donít know how other people work. Itís a topic I havenít had much of a discussion with other researchers about. We were young and immature and not very experienced, there werenít any people here at the Research Center that could guide us in the fields I mentioned. We were breaking new ground and we werenít in a mature, well-established group within the Research Center. So Iím sure we did a lot of foolish things. We had to fend for ourselves and sort these things out.
Bromberg:Are there any other names that I should have besides Antes that you interacted with at this point? That you think might be useful?
DeMaria:There was a very outstanding young man who was a technician at that time who assisted me in performing some of these experiments, and reduce them to practice. The technician was Gordon Barnard. He and I published some early work in lasers and acoustics. It was very difficult getting permission from management to make him an author for he did not have a college degree. He was a very hard working, sharp young man and together we were able to perform experiments in the area of lasers and come up with some publishable results at a time when the field was moving very quickly. He is now at Martin- Marietta in Florida and he has been there a long time. There was another man by the name of Val Gates, who was a man I admired very much. He was more senior than I was. He went to MIT and was a very good engineer. We got along very well. He went to EG&G late in 1958.
Bromberg:You were working with Gates on specific experiments?
DeMaria:We worked together at Hamilton in the Component Group. He was my immediate supervisor under Antes at Hamilton. He launched me on this problem of working on magnetic devices. I read so much about the field that I was asked to write a design manual by Hamilton Standardís management. It was a design manual on how to design various magnetic devices for Hamiltonís use at that time. I guess it was in use at Hamilton up until 1978 or 1979. So it had some longevity. I once thought of publishing it as a book but I never got around to it because of my laser research interest that developed about 1959. Those were the two outstanding people I remember. The other three members of the group did not impress me technically very much. They have since left the technical field. About 1959 I got very very excited about lasers. I read the paper of Schawlow and Townes. Page 1949, in the Physical Review of 1958, it came out, and it really captured my imagination. At that time I only had a bachelorís degree. I was taking graduate courses during the evenings. I really didnít have enough background to comprehend much of the content of that paper, because I was trained in electrical engineering. You know the transistor was the major research interest of most electronic engineers at the time. I was trained at the University of Connecticut where the research specialty was controls at the time. So I was not exposed much to applied physics-type courses.
Bromberg:The maser was familiar to you?
DeMaria:No. I also had to learn about masers on my own. Just the concept of having an optical device that could generate optical waves that had all the characteristics of radio waves, and microwaves was extremely exciting to ma. I just fell in love with the field. At that time it was called the optical maser so I read all that I could about the maser work that Charlie Townes and Nico Bloembergen did in the microwave regime and I learned a lot about subject matters that I had no training in. I was self-taught at first and later I began taking graduate courses in physics.
Bromberg:Now you were right here at RPI extension at that time. You were taking physics then through them?
DeMaria:Yes. They didnít have a physics department at that time. They had a masterís in engineering science. I took as many of the courses in physics as I could get there. I had taken a few other graduate courses at the University of Connecticut in electrical engineering and transferred them to RPI Hartford Graduate Center. In June 1960 I did get my M.S. degree at the RPI Hartford Graduate Center in Science. And in the late 1960s, the first laser was operated by Maiman. Now prior to that time, I was trying to make a laser here at UTRC. You know after I got introduced to the Schawlow/Townes paper I read voraciously. I put in hours and hours on weekends and evenings just catching up on technical subjects that I needed to learn. Then in early 1960 I began thinking, ďOK Iíve read as much as I could. What are some of the specific areas that I am going to do research in? What am I going to contribute to this field?Ē I was the only one at UTRC attempting to do work in lasers at the time. There were two people in management who encouraged me to work in the field. Together, we had many interesting technical discussions on how a laser could work.
Bromberg:Now this is before Maiman? And the ďweĒ isÖ?
DeMaria:At the time there was a man here by the name of John Hawkes, who was an ex-professor. He was a retired professor I think from Columbia, and he came to work here as part of the personnel department. The reason for his employment was that the corporation was going to broaden the research activity of the Research Center because the corporation was going to change and he was brought in to recruit researchers in physics. The corporation was going to broaden its horizons. It was going to get into electronics and military electronic systems, missile work, etc. The other person was Henry Hoadley.
Bromberg:Like Bell Labs?
DeMaria:I am not aware that Bell Labs was the model management was trying to follow or not follow at the time. The model was probably the General Electric Research Center. Anyway, the idea was to broaden the technology base of the Research Center. And when I came here there was Wes Kuhrt, who was at that time head of Research Programs. There was another man parallel to him by the name of Henry Hoadley, an outstanding man also. Iíll say more about him later. And these two gentlemen guided R&D throughout the whole lab and they reported to the Director of Research who was John Lee. Another very outstanding man. John Lee is still alive and retired. Wes Kuhrt became Director of the Research Center after John Lee retired. He hired Russ Meyerand, who became Director of the Research Center after him. Wes Kuhrt went on to become the President of Sikorsky Aircraft and after that he became Sr. Vice President of Technologies for the corporation which then was renamed as United Technologies Corporation. Henry Hoadley was a very unusual guy. He had enormous patience. He was trained as an engineer but he really wanted to know the physics of problems, what made things work on a real detailed scale. I enjoyed him immensely. Henry was an outstanding individual. From my standpoint, he really formed most of my professional values because he was a very generous, gracious, kind, considerate individual and really had an exceptional research mentality for looking at problems.
Bromberg:Does that mean that you didnít have a lot of pressure to develop things or that the pressure changed at this point? I mean some laboratories give their researchers a lot of freedom and some give a lot of pressure to produce products.
DeMaria:We had a lot of freedom, because at that time the corporation was trying to grow the Research Center toward establishing a reputation of research excellence in technical fields new to the corporation. In the l960s there was a tremendous national technical renaissance or let me call it ďintellectual welfareĒ throughout the whole country. It was a glorious decade. And the lab grew enormously. It probably grew to four times its size from the first time I came here. All these new additions were built when Wes Kuhrt was Director of Research. We had a man in the Corporate office by the name of Earl Martin as Vice Chairman of United Aircraft. He pushed for the expansion of the Research Center into the mode that it is today.
Bromberg:Just to get this historically in perspective, from the very time you came here, Antesí group came here, there was this sense of freedom or did it come in a little later or what?
DeMaria:No. It came right from the very beginning. And I think that if anything happened, it was because of that freedom. We really had the decision to do what we thought was important. At that time my laboratory was my hobby shop. Coming to work in the morning was my hobby. I never considered it a job. It really wasnít. We had endless meetings with Henry Hoadley and John Hawkes and we were learning together. John Hawkes had a good physics background. He was in the personnel department trying to help us hire very competent staff in physics and expand our horizons. Our group was run like a small Bell Labs-type philosophy, if you wish. I really did not know how the rest of the Research Center was run at the time.
Bromberg:So here you were in Ď59-Ď60 in the lab trying to do something in lasers and you were talking to these people.
DeMaria:Yes, We knew about Charlie Townes and his work at Columbia. It was the center of maser activity. It was also the center for trying to develop an optical maser. So we hired one of his grad students as a consultant. His name was Patrick Thaddeus. He would visit us once a month. From Mr. Thaddeus we learned that Charlie Townes and his students were trying to realize an optical maser by optical pumping the alkali metals, such as cesium, potassium and rubidium, and things like that. These materials were very hard to handle. At the same time Russ Meyerand came to UTRC from MIT and he started a large plasma program here at the Research Center. A whole bunch of plasma researchers came on board at that time. John Hawkes, Henry Hoadley, and I decided that we were going to follow in the research footsteps of Charlie Townes and his students. And so I learned about optical pumping schemes, about radio frequency and microwave discharges for pumping alkali metals such as cesium. I also learned to calculate radiation strengths, transition probabilities, write rate equations for quantum transitions, etc., on my own. I had to worry about the contaminants. I had to worry about windows, mirrors and all those sorts of experimental things that appear trivial now, but were difficult technologies back then, especially with materials such as cesium. We were making reasonable progress and doing a lot of spectroscopy which was all new to me. I guess those were my Ph.D. graduate years; I was like a Ph.D. student at a university, except at a university one was under the tutelage of an expert and here I was feeling my own way. John Hawkes had not been in a laboratory for 25 years at the time. Henry Hoadley was trained as an aerodynamic engineer and neither had time to spend in the laboratory because of their administration duties. And then about the late 1960ísÖ
Bromberg:What impression, by the way, did Maiman make as he came into view at this point?
DeMaria:Well, then Maiman came out and reported the operation of the first optical maser or laser at the end of 1960.
DeMaria:Was it July? I read about it in Nature a little later than July. I remember that when I first got my hands on the first publication that had any detail about the ruby laser it was the paper by Arthur Schawlow and staff from Bell Labs which came out at the end of 1960 in Physical Review Letters. The Maiman results we heard about in July were in the New York Times, I believe. When we obtained a copy of the paper that appeared in Nature, there was indication of laser action, but very little detail. So the Maiman Nature paper didnít give me much help in building my first laser. But then of course, the Schawlow paper came out with a lot of detail in the Physical Review Letters in late Ď60 and so we really just took a look at what he did and said, ďthatís pretty straightforward, you know, and itís pretty well spelled out,Ē and so we built one and got it operating within a few months. And so because of just sheer drive, we had a ruby laser operating here in the early part of Ď61. I think it was February or something like that.
Bromberg:Within this time, there was the Columbia University first Quantum Electronics Conference published and the lasers at IBM. Did any of these things make an impression on you?
DeMaria:Oh yes. They came in this period. I was too junior a staff member to attend the Columbia Quantum Electronics Conference. No one attended from UTRC at that time. Maybe Iím going into too much detail for you.
Bromberg:No. I want detail and thatís why I keep asking questions.
DeMaria:That comes up to our first publication. We had a ruby laser operating and like everybody else we were puzzled because the ruby laser didnít put out a continuous wave. It put out these spikes of random heights, pulse widths, and time intervals. A lot of people had written papers on these random spikes and their possible causes. I learned about acoustics at Anderson Labs. I had read that if you take light and pass it through ultrasonic waves you could make a phase grating and get a doppler shift imposed on the light waves. And if you generate a long wavelength, time varying refractive index gradient you can take a light beam and scan it by the refractive gradient effect. You can take a low frequency sound wave or generate an acoustic shock and you can deflect the light beam instantaneously. So my idea was to insert an acoustic cell inside the ruby laser and exert control on the output of the laser. My thought was analogous to putting the third grid in a vacuum tube to control the electron flow. The acoustic cell was going to control the photon flow within the laser or that was my thought process.
Bromberg:I see. Was this even before Q-switching?
Bromberg:Was this to get control by this acoustic method?
DeMaria:Yes. Now there was a paper written by Pershan and Bloembergen that examined all the techniques for modulating laser radiation. It was published in the Proceedings of the Columbia Quantum Electronics Conference. We did not know of the paper because I did not attend that conference. Since the Proceedings was in book form, it was expensive so we did not have a copy. They went through a discussion of the electro-optic effect and the acoustic-optics effect, etc., in that paper.
Bromberg:They talked about acoustics?
DeMaria:Yes, they did discuss it. At that time I wasnít aware of their paper. We had already started our work. But they did mention acoustics as one of the various techniques useful for modulating lasers which was not surprising because acoustic modulation of light was known for a long time prior to the laser. Theirs was an overview type of paper and they never did any work on the devices discussed in the paper for active modulation applications. So I published my first paper in 1962. There was another man here at the time who got a masterís degree from Trinity. He was good in optics. His name was Ron Gagosz. He was a co-author on that early paper. So Gordon Barnard, Ron Gagosz and I formed a team. We synchronized the random output pulses of the ruby laser to the electrical signal we were using to drive the acoustic waves and we published the results in the Proceedings of the IRE in 1962.
Bromberg:Now you didnít expect synchrony then?
DeMaria:Yes we did. We got exactly what we had expected.
Bromberg:How did you come to expect it? I mean, you purposely synchronized the round trip time?
DeMaria:I believe you are thinking about the work we did in 1965 concerned with mode-locking lasers to obtain picosecond pulses. The acoustic work I am discussing now has nothing to do with the picosecond laser pulse work of 1965 and later. What I am discussing now is the work we did to Q-switch, modulate, scan, and frequency translate a laser beam with acoustic waves that occupied my research interest from 1961 to 1964. Having been trained as an undergraduate in electrical engineering, I understood electronic oscillators. Electronic oscillators used electron flow, either in a solid for transistors or in a vacuum for vacuum tubes. A laser is a comparable oscillator analogy; except here we have a photon stream, a light beam, and if somehow you can control that photon flow between the laserís mirror, you can exert control on the laserís output. It was an obvious analogy to me at the time. How were we going to do it? Well, the people at Hughes began working on electro-optics devices; i.e., the Kerr cells and Pockel cells. They did Q-switching. We were also doing Q-switching and modulation but we were using acoustic waves. And we obtained early patents on the use of acoustic devices for use in lasers.
Bromberg:I was kind of interested in the sense I got from skimming some of your papers that there was an engineering tradition which is rather different from the physics point of view.
DeMaria:Thatís right. Almost everybody at that time came into the field with a physics background. Eventually the EEís got into it. One now finds that most of the researchers that were working on lasers in the early days on lasers are now in electrical engineering departments or applied physics departments of universities because lasers are devices. Itís not an electronic device, itís a quantum-electronic device, and engineers were going to eventually use them and work with them. So I was stimulated from an engineerís point of view almost entirely throughout my career.
Bromberg:Thereís some name that crops up here, Suprynowicz. Is that an important name?
DeMaria:Yes. Vincent Suprynowicz came to UTRC about 1961. He was hired into UTRC as part of our Instrumentation Laboratory and then in 1962 or 1963 he became a supervisor of the Electromagnetics, Physics Group of which I was a member. But thatís getting ahead of the story.
Bromberg:I donít want to do that.
DeMaria:But going back to the acoustic area, so we did this gating at the hundreds of kilocycle rates. The second paper was on Q-switching. It came out after the basic concept of Q-switching was published by the Hughes Group. In our first paper we were turning the laser off and on in synchronous with the electrical signals driving the relatively low frequency acoustic waves and obtaining very regular pulsating outputs. The ruby laser pulses we were obtaining were narrower and also exhibited much higher peak power. We were getting Q-switching but didnít appreciate the concept as Q-switching as was done by the people at Hughes at that time. And then we did the Q-switching work with the generating of acoustic shock waves in acoustic cells inserted into the feedback cavity of a ruby laser and obtained our first laser contract at UTRC with the Army at Fort Monmouth, NJ, who of course was interested in rangefinders.
Bromberg:I would like to ask you about that. As you did this work, who in the company was picking up on it? What kind of excitement, what kind of interests were you creating?
DeMaria:Well at that time, the group I was in was a basic research group. I will use the term intellectual welfare even though it now hurts, but thatís really the philosophy that we had at the time. The group was funded by the divisions of the corporation without much representation by the divisions on the nature of our work. We were doing long-range research and the divisions paid for it and there wasnít too much concern in that one group about being relevant to the divisions per se. That hope was that perhaps out of this basic research some new products would result, leading to some expansion of the core business of the corporation. Since the laser was such a revolutionary device at that time (it was of great interest to Wall Street, the scientific community, the media and so forth), so it was considered a good area of research. So [our work] wasnít directed toward a specific application. I should point out that I did the first hole drilling laser work within the Corporation in 1961 and the first welding work with lasers in 1962. The research results were published in Physikaliche Blatter in West Germany on 19 January 1963. At the time material working with lasers did not interest me very much.
Bromberg:Then you say that something happened with this range finding business?
DeMaria:I realized that the government was funding good research for lasers. I reasoned that getting government research funding in competition with other researchers in the country was a good way of testing oneself. How do you test yourself to see how good you are? One way is to get your research published. Another way is to compete for research money that somebody else is also trying to get. Itís a way of competing and so that appealed to me. So without management encouragement I went out and got the first government research contract in lasers in this laboratory in 1963. It was concerned with Q-switching a laser for rangefinder applications. Our contract was a backup to the rotating prism and the Pockel cell Q-switching work being performed by the Army.
Bromberg:So tell me about that. Letís not let that go. Thatís the kind of thing that you donít get in published papers. As I said we are trying to get this whole context. How did you get that?
DeMaria:The engineering community, not the physics community, got interested about the use of acoustic waves to control the output of lasers. The Army was interested in range-finding and based on our work, acoustic waves were considered a good alternate technique for Q-switching at the time. There was a man by the name of Reg Preli who was hired in to perform marketing to the government. He transferred from Hamilton Standard to the Research Center about 1962. I knew him at Hamilton. There he had responsibility for preliminary design. He was a remarkable man. He looked around UTRC and found out what the researchers were interested in. He would then make contacts with the government and say: ďLook, we have some guys at the Lab who are working in this area. Do you have any interest in funding part of their research?Ē And when he found somebody in the government that had an interest in that area, he would introduce us to them, and we would make a presentation to them about the research we were doing with the hope that a research contract would result.
Bromberg:So thatís what happened with this? He brought you down to Washington?
DeMaria:No, he took me down to Port Monmouth, New Jersey. The Army Signal Corps who had the rangefinder responsibility for the Army. So we got a contract and we worked on the ultrasonic control of lasers up until about early 1965. It was the first laser contract obtained by the corporation.
Bromberg:And that was the first military contract you were working on?
DeMaria:That was the first military contract I worked one. It was also the first research contract that Reg Preli or I obtained for UTRC.
Bromberg:The other work was all on United Aircraft money?
DeMaria:Yes and no. We did also obtain a Navy contract utilizing acoustic waves to nonmechanically deflect or scan a laser beam in 1963 for obtaining images. It was also obtained by Reg Preli and I working as a team.
Bromberg:Now, that masterís degree. Was there a thesis that we ought to talk about?
DeMaria:Yes, there was a thesis and I did it in late 1958 to early 1959 time period. It was a theoretical thesis concerned with the use of the Gudermannian function to approximate the magnetization curve of magnetic material. The formulations were used to treat the behavior of devices based on two superposed perpendicular magnetic fields. I gave my first paper at a conference in 1963 and I was very flattered, because you have to remember that I come from an immigrant family. My mother canít read or write, my dad only had three years of schooling, so publishing papers and making presentations were very exciting for me. My English diction is not good now, but you should have heard it them. I have a revealing story concerning my diction. John Lee was Director of Research up to 1964 or 1965. I was at a retirement party for Wes Kuhrt and John Lee was also there. John Lee was about 77 years old at the time of the party. My wife was with me and he knew her and he came over to her and said: ďI remember you. I want to tell you about this young man of yours. You know when he first came to work with us we had a research advisory committee meeting and we asked him to give a talk about his laser acousto-optics research. He got up there and he demonstrated such excitement and enthusiasm about this work, but he broke into the worst Brooklynese accent we ever heard. You should be proud of him though because he has overcome it, or almost overcome it.Ē I never heard that story before that time. It does reveal much about my early days.
Bromberg:You were really the first scientist in the family? The first person going into this kind of field?
DeMaria:I was probably the first person that ever got equivalent to a high school, let alone a college, education in the family. I was the oldest of three children. OK, thatís enough of that.
Bromberg:OK, so we have you on this Signal Corps contract.
DeMaria:So we had this Signal Corps contract that was very successful because it established the field that is now referred to as laser acousto-optics. Then I took a leave of absence. I was taking courses during the evenings for a Ph.D. at the University of Connecticut in the electrical engineering department. I took a leave of absence and went to the University of Connecticut for nine months during the winter of 1963 and the spring of 1964 and took all their physics courses required for a Ph.D. in physics. I already had all the EE courses required for a Ph.D. in EE. I began performing my Ph.D. thesis during the summer of 1964 at UTRC on the subject of ďEffect of Periodic Refractive Index Perturbations on Laser Oscillations.Ē It also was concerned with my attempts to generate ultra short laser pulses by mode-locking glass lasers with acoustic cells.
Bromberg:Letís talk a little bit about that. Was there anybody at UConn or any activity that was important for what you did next?
After I got my masterís degree, I was publishing papers on my laser research. I got very interested in learning more about subject matters in which I had a poor background in order to become a better researcher. I was faced with a decision whether to stay in this area or go away to graduate school. My wife, Katherine, and I talked about it. I had a daughter, Karla, at that time, so it was not going to be easy to go away to graduate school. About that time I read a paper that was published jointly by a professor at the University of Connecticut with William Shockley, in the Journal of Applied Physics. The professor at the University of Connecticut was Professor M. Malahy. And I asked myself why should I go away to graduate school. Hereís a guy near UTRC that is publishing with a Nobel Prize winner. Perhaps I can do a thesis on lasers with him while continuing my employment and work at UTRC. So I contacted him and I began my course work at the University of Connecticut. I had almost taken all the courses required for a Ph.D. at the University of Connecticut in EE.
Since they had no one on their [electrical engineering] staff who knew anything about lasers, they felt that they should have members of the physics department serve on my thesis advisory committee, which was logical. [The physicists] serving on my advisory committee also had no experience with lasers but physicists considered lasers an area of physics at that time. So my advisory committee members were composed of half EEs and half physicists. My EE advisors felt that I should have all the course work required for a Ph.D. in EE because I was doing the work in the EE department and the physics advisors thought that I should have all the course work required for a Ph.D. in physics because I was doing my thesis on lasers. [Since] there werenít any staff members working on lasers at UConn and they knew I had already published four or five papers in the field, I represented an opportunity for the university to gain some experience with lasers. So an arrangement was worked out where I would take nine months of physics course work on campus and I would do my thesis at the Research Center where I had all the equipment required to do state-of-the-art experiments. It was a nice arrangement for all concerned.
DeMaria:It was a very unique arrangement and it has not been done very often since. So I ended up taking all the courses for the Ph.D. in EE and all the courses for the Ph.D. in Physics. I took nine months leave of absence to take the physics courses. Not only did I have all the physics background I felt I required for a good understanding of lasers, but I also had all this electronic background. I could easily appreciate the working of oscillators, amplifiers, and modulation and detection devices. Background in both physics and electronic engineering helped me immensely in my laser research from then on. It has also helped me in my present position as Assistant Director of Research for Electronics and Electro-Optics Technology. I am now equally interested in compound semiconductor devices as I am in laser devices.
Bromberg:Then when you came back after the nine months, is that when you started your thesis?
DeMaria:Yes. When I came back here I started doing my thesis in the summer of 1964. My thesis was going to treat what happens to the operating characteristics of a laser if you put a periodic refractive index medium inside the optical feedback path of the laser. And the way to generate that periodic refractive index perturbation within the laser was with acoustic waves. During the course of that thesis I put together a mathematical summary of the acousto-optical experiments I had done previously. During the thesis performances I became very interested in a phenomena that was called mode-locking. I should talk about that.
Bromberg:Weíll want to talk about that. This is after the Polytechnic 1963 Symposium? I noticed that you gave a paper there.
Yes, the paper was titled, ďUltrasonic Control of Lasers,Ē and it was given in April 1963. In Ď64 I went to an Electron Devices Research Conference held at Cornell University. At the conference, Hargrove, Fork, and Pollack of Bell Labs gave a talk on their experiment in which they put an acoustic cell inside the feedback path of a Helium-Neon laser and referenced the acousto-optics work that I had done. At the time, they were only the second research group to utilize acousto-optics devices inside a laser. They modulated their acoustic device at the same frequency as the axial mode separation frequency of the laser and they observed that the laser emitted a continuous train of short pulses. They called the effect mode-locking. The laser research community became excited because the periodic pulses were very narrow and the noise quality of the laser was improved. The acoustic cell which we had pioneered at UTRC was the only optical device at the time, that had sufficiently low optical loss that it could be inserted into a Helium-Neon laser. The He-Ne laser had very little gain so if you inserted anything with loss into it, it would cease oscillating. So I listened to that paper and decided to do the experiment with a glass: Nd3+ laser because the line width was 180 angstrom wide. I thus reasoned that pulses down to 10-13 seconds in duration could be thus generated. I mentioned my plans at the meeting to Amnon Yariv who was at Bell Labs at that time.
Soon after that, he went to Cal Tech and has been contributing immensely to semiconductor laser, nonlinear optical devices, etc., technology since then. I also mentioned it to Adrian Korpel who was at Zenith at the time working under Robert Adler. I got Korpel interested in acoustic waves and he wrote a lot of very beautiful papers in acoustics and lasers after that. He is now at the University of Iowa and still publishing very good work. I listened to the Hargrove, Fork and Pollack paper and decided to do the experiments in a glass laser where you have 180 angstrom line width. As I stated earlier I reasoned that I could generate pulses lasting only 10-13 seconds. It would be the shortest event ever generated by mankind. I reasoned that once I had an optical pulse that shorts I could make all kinds of measurements in a time regime which was previously unaccessible to scientists.
Bromberg:In other words it was at this meeting that you had this idea?
DeMaria:Yes. It was not a revolutionary idea. I was going to use acoustic waves to mode-lock a glass laser. These other researchers at Bell Labs had already used acoustic waves to mode-lock a Helium-Neon laser. So my idea was only a natural extension of their work.
Bromberg:Of course you were very familiar with these glass lasers.
DeMaria:Yes, as well as ruby lasers. I had worked with both of them. The glass laser was invented by Eli Snitzer at American Optical Research Center which was close to UTRC. Only one hour away by car. So that idea was part of my thesis at the University of Connecticut. Generating ultra short laser pulses with glass lasers and acousto-optics cells, I published the results in Applied Physics Letters in January 1966.
Bromberg:Anybody you were working with on this, by the way?
DeMaria:Yes, at that time I began working with Carl Ferrar who I met as a graduate student at UConn. He and I graduated together in 1965. Carl is still here also. Ron Gagosz also was still working with us at that time. Edward Danielson joined our staff in 1964. In the summer of 1964, I was made group leader. The group was situated within the Physics Department, headed by Hal Taylor. The Physics Department was formed in 1963 or there about.
Bromberg:So these guys were in your group?
DeMaria:Yes, they were working for me at that time. I had a small group of about three staff members. All of the staff members had masterís or bachelorís degrees; Carl Ferrar received his Ph.D. in 1965.
Bromberg:Did you call this a laser group?
DeMaria:It was called the Electromagentics Group of the Physics Department. Its research emphasis was all on lasers at that time. From 1966 on we resorted to hiring only Ph.D.s for our research staff.
Bromberg:I would like to know a little bit about [how] you worked with these people. Did you all do everything together, or did you divide up the work? Would one perform one particular phase and others would perform another particular phase?
DeMaria:The way that worked was as follows: the management of the lab [had the philosophy] that the Physics Department was going to be a very small fraction of the lab. Consequently one could hire the very best talent one could hire and turn them loose to do what they wanted to within reason. The manager of the Physics Department had to be an administration/financial-type manager and did not have to worry about technical matters. Hal Taylor handled the financial and administration paperwork and left us technically alone. So we were the basic physics group. The Lab at that time had set up a basic research advisory committee that was headed by Frederick Seitz who was a solid state physicist. During this period of the Research Center, Wes Kuhrt was Director of Research and Russ Meyer and was chief scientist. During the 1960ís, the Research Center grew by a multiple of three to four times. [The committee] made recommendations on how one should run a physics research activity. Since the committeeís experience was with basic research performed at a university, the management techniques used to run the Physics Department were patterned after the techniques used in universities. Everyone was expected to have their own research project but also expected to collaborate and help others when appropriate. Everyone (i.e., all three staff members plus me) within the Electromagnetics Group was working on the application of acoustics to lasers. When I took the year off to go to UConn, they were performing on my contract work here.
Bromberg:You were still on Signal Corps [money] at this time?
DeMaria:Yes, up to late 1965. I would come to UTRC one day a week as a part-time consultant while on my leave of absence. UTRC paid me one-fifth of my salary. In this way, I kept the contract going with Ed Danielson doing the day-to-day work on the contract. There was another man by the name of Dave Flinchbaugh. Dave got his Ph.D. in the summer of 1964 in atomic physics. He also performed some portion of the Army Signal Corps contract as well as his own research interest.
Bromberg:And that was your thesis? I mean you actually did a thesis on this contract?
DeMaria:At that time that contract was specifically on Q-switching lasers with acoustic waves. My thesis was more of a generic investigation concerned with the generation of refractive index perturbation whose periodic perturbations lengths were larger than, equal to, or much smaller than the light beams diameter. The mode-locking of a glass laser constituted one third of my thesis. Based on the thesis work, a laser mode locking contract was obtained from the Office of Naval Research in 1966 and lasted until 1972.
Bromberg:Was this an ONR contract?
DeMaria:The ultra short laser pulse contract was with ONR. There was also a Naval Systems Command contract that was concerned with the nonmechanical scanning of a laser beam with acoustic waves which Reg Preli and I sold. Since the work to be performed on the Naval Systems Command was a development effort rather than a research effort, the contract was transferred to the Instrumentation Department headed by Dec Wingfield. The work on the contract was performed by Robert Erf. Robert Erf later changed his field to holography and edited several books in the field. So we were at the point where in 1964 I was doing my thesis. I was interested in mode-locking a glass laser. Carl Ferrar, Ed Danielson and I collaborated on the initial experiment of mode-locking a glass laser and published it in Applied Physics Letters in January 1966. We generated pulses shorter than we could measure, but it was pretty obvious to us at the time that the glass laser had such high gain and the amount of modulation index we could get with the acoustic device was not sufficient to get the shortest pulse possible out of the glass laser. And I was about ready to give up on that idea, until another man came to me by the name of Hans Heynau. Hans Heynau had a bachelorís degree in physics and was working in the Instrumentation Department under another engineer called Al Penney. Hansí function in the Instrumentation Department was to build special instruments for other researchers to use. Somebody within UTRC wanted a Q-switched glass laser for a plasma generation experiment. Hans Heynau was using a well-known passive Q-switch dye that everybody in the laser field was purchasing from Kodak at the time. This dye was known to be a good passive Q-switch for Nd3+:glass lasers. The dye was called a saturable absorber. Passive Q-switching with these saturable absorbers was generally well known at the time. Hans came to me for help. He said, ďYou know Iím working on glass lasers using this Kodak dye to Q-switch but I have a problem. The guy that Iím building this laser for wants a nice smooth pulse but I keep getting these modulations on these Q-switched pulses.Ē Hans was not getting the sharp spikes normally associated with mode-locking. He had amplitude modulation on the Q-switched pulsed envelope that was equal to the axial mode frequency spacing interval. His detector was not optimized for a fast response. His detector was so slow that he couldnít see the spikes. As I looked at his oscilloscope trace pictures, I realized what was going on for I had read the paper of C. Cutler and knew of the work of Hargrove, Pork, and Pollack. I, thus, realized that the Kodak saturable absorber dye was playing the same role as Cutlers microwave expander circuit that he used to mode-lock a travelling wave tube feedback circuit in the mid-1950ís. I also made the connection between the Cutler work and the laser mode-locking work.
Bromberg:Had you just reed it or years ago?
DeMaria:Cutlerís paper was published in Ď55. I had read it back in late 1958 when I was reading about microwaves and all those sorts of things. He had generated short pulses with a microwave travelling wave tube and what he called an expander electronic circuit. The electronic circuits function was that when one passed a pulse through it, the low amplitude portions of the pulse would get attenuated more than the high amplitudes portion of the pulse. So in essence every time the pulse passed through the expander circuit, the pulse would become sharper and sharper. The saturable absorber was equivalent to his expander. The laser with a fast relaxing saturable absorber was the optical analog of what Cutler had done in 1955 or of the laser mode-locking with an acoustic modulator in 1964. I went to the library, looked up Cutlerís 1955 article and sure enough, there it was. I could have taken his block diagram and substituted it for Hansí laser system. It was the same thing. Except instead of having mirrors, Cutler had a microwave waveguide feedback loop. Instead of a travelling wave tube, Hans had a glass laser, which was the amplifier, and Cutlerís expander circuit was Hansí saturable absorber. We began working on the glass laser saturable absorber passive Q-switch and mode-locking equipment immediately. We used Brewster angles on the glass rod, placed the Kodak dye at Brewsterís angle near one of the mirrors, redesigned the detector and electronics for faster speeds, etc. We got pulse so short we could not measure them by any electronic means available at the time. Hans Heynau, Dave Stetser, who joined my staff early in 1965, and I published the finding in Applied Physics Letters in April 1966. The paper opened up the field of picosecond laser pulses which is still very active today.
Bromberg:By the way, just for a little background for me, was mode locking very familiar to engineers in the microwave region or what?
DeMaria:No. Just to Cutler, and he never called it mode-locking. The concept never found applications in the microwave region. Mickey Gilden, Tom Reeder and I also published a paper on mode-locking a surface acoustic wave oscillator at 300 MHz in the late l970s. The concept has proven to be important only in the optical region as of this time.
Bromberg:What about Lambís paper. A lot of people say to me that Lambís paper in early 1964, Willis Lamb, which had a little bit about self-mode-locking, made a big impression on them. Was that something you remember?
DeMaria:I knew Willis Lamb because we hired Marlan Scully about that time as a consultant to teach us Lambís laser theory. Scully was Willis Lambís student at Yale and he introduced me to Prof. Lamb. Marlan would come up and give us lectures on the Lamb theory. The Lamb theory was very elegant but it really never was useful to us. In my opinion, the really important contribution from Lambís laser theory was the Lamb dip which gave the homogeneous line width. That very important scientific contribution came out of his paper. The mode-locking aspect of Lambís work was never that evident to me. The fact that nonlinearities within the laser medium could cause self-mode-locking in laser systems was also an important scientific contribution by Lambís theory but self-mode-locking by these nonlinearities has not lead to usage in any application to date. In l964 we also had Willis Lamb give a seminar at UTRC on his theory but the theory was so complex that it didnít prove to be useful to engineers working in the field. It does provide a great theoretical foundation for understanding the behavior of laser devices in great detail.
Bromberg:I wondered about the reaction of people.
DeMaria:The discovery of the Lamb dip was beautiful for spectroscopy. I had another ONR contract later that was directed toward studying the Lamb dip in Argon ion lasers through the use of acoustic waves to obtain tunable laser radiation by means of the Doppler off-set and thus tune through an argon-ion laser gain profile to measure the actual line width of the argon-ion. Bob Beringer of ONR funded that work. It was good work but it wasnít really outstanding. It was one of those papers; a scientific contribution, but it didnít impact us or anybody else. So we were familiar with Lambís work. The Lamb dip was very important from a basic physics standpoint, I donít want to minimize that. The fact that one could obtain natural line widths out of a lasers output radiation was a major spectroscopic contribution and it first came out of Lambís theory and not out of experiments, contrary to the majority of case for outstanding technical contributions coming out of the laser field. It didnít influence us much because we werenít working in that direction.
Bromberg:I guess what I was doing there was fishing for things about mode-locking that might have been fed into your work or might have been interesting.
DeMaria:Lambís work did not have much of a practical effect on mode-locking and the generation of pico- and subpicosecond pulses. If you put nonlinearities in Lambís equations, they provide self-mode-locking results. And indeed after Lambís work was published, researchers at Bell Labs who were working with mode-locking Be-Ne gas lasers, did indeed find that occasionally the Helium-neon laser did emit pulses by a self-mode-locking effect. I skipped over Ali Javan and his gas laser work, and Peter Sorokin and his work with solid state and dye lasers and many others.
Bromberg:Were you pretty much in touch with them?
DeMaria:I knew them from meeting them at conferences. They really didnít influence the work that I was doing, except that I followed their work religiously. Anything that was published on lasers I reed and studied.
Bromberg:OK, so one should understand that you really followed the whole field, engineering and physics.
DeMaria:Yes, I followed the whole field. The field was small then and it was easy to follow the entire field. Itís no longer possible today. I got to know nearly all the laser researchers well, such as Bill Bridges, Peter Franken, Charlie Townes, Arthur Schawlow, Eli Snitzer, Ali Javan, Peter Sorokin, Tony Siegman, Bob Hellwarth, Nico Bloembergen, etc.
Bromberg:What about people at Raytheon, such as Statz?
DeMaria:You mean the team of Statz, Tang, and Demars. I never really knew Demars, but Statz and Tang I know very well. Tang is up at Cornell. I spent three weeks with him in Mainland China in 1982. I read with great interest their work on spatial hole burning in homogeneous broaden ruby as an explanation of multiple axial mode oscillators and random pulsations in ruby lasers. I published a paper on the use of a streak camera in Applied Optics in August 1963 concerning the study of spatial hole burning. Itís not a paper I am proud of. I donít really think they made much of a contribution to mode-locking per se, but their spatial hole burning contribution was very important. Steve Harris of Stanford University made major contributions in FM mode-locking with the researchers at Sylvania. Early in the 1970ís the Raytheon Research Center dropped their work on lasers and focused their attention predominantly on microwave/millimeter-wave device research. All their laser researchers left, Statz remained and I understand he has focused his attention on compound semiconductor microwave device research.
Bromberg:I think that my question is, now given these people, their contributions, who were you most interactive with?
DeMaria:I wasnít interactive with the Raytheon researchers. I was in contact with Steve Harris because he had this beautiful idea of FM modulation of a laser and then feeding the FM modulated laser radiation through a separate FM modulator with opposite phase and thus getting a single frequency output which was very inventive and extremely clever. Hasnít gone anywhere, but at the time it was very inventive. Steve Harris also did some beautiful acoustic work associated with a tunable optical filter. He has since been trying to generate very short wavelength laser radiation. I believe, Steve was a young graduate at Stanford about the time he was doing the early research. As a matter of fact, Steve Harris is going to receive the Davies Medal at RPI a week from this coming Monday. He is going to be the fourth Davies award winner. He received his undergraduate degree at RPI. RPI gave me the first Davies medal about four years ago, so Iím going to be looking forward to seeing him again.
Bromberg:Thatís right here?
DeMaria:No, up in Troy, NY. At the main campus. So I was familiar with the ideas of Chap Cutler. All the history concerned with our early picosecond laser work was written up in that Citation Classic because they asked me to review it there. Based on Cutlerís paper and my conversation with Hans Heynau, the connection was made. Then we performed refined experiments with faster detectors built by Hans Heynau and Al Penney and we noted that these pulses were very very short and we published the results in 1966. We had completed the experiments in the fall of 1965. We held off publishing the paper sooner because we wanted to present a paper at the International Quantum Electronics Conference in Phoenix in the spring of 1966. Only unpublished research results could be presented at the conference. The paper packed the room to standing room only. The Russian scientists at the conference were very interested. I had long conversations with Bosov of the U.S.S.R. at the meeting. Bill Condell of ONR asked me to send him a proposal right after hearing my paper at the conference. The work was sponsored with Advance Project Research Agency (ARPA) funds.
Bromberg:I was wondering what it was like when you gave the paper.
DeMaria:The room was filled to overflow capacity. People were very interested in picosecond pulses with gigawatts of peak power. The concept for their generation was so simple as was the experimental arrangement. Researchers began thinking of measurements they could make for the first time on picosecond time scale. Soon after, I visited Mike Herscher at the University of Rochester. He informed me that he observed in ruby lasers similar short pulses, but he never really put the whole thing together. Bob Collins and Hans Mocker were also doing experiments with ruby lasers utilizing Schott glass as a saturable Q-switch in which they noticed short pulses. They published their results about one-half year before our publication. They never made the connection to mode-locking either. They never developed the understanding of the passive absorber. Even though Bob Collins came from Bell Labs, he never made the connection to Chap Cutlers work. These two publications never caught the imaginations of researchers because the data wasnít explained. They never realized that ultra short laser pulses could be generated by such a technique. Mike Herscher had the result and he went to great lengths to eliminate it. He didnít want short pulses so he got rid of them. We saw the result and explained it and pointed out potential applications. We explained the narrowing mechanism for generating the pulses, the various fast relaxation requirements of the dye, the connection to Chap Cutlers work and the analogy between the two, and provided data on how it worked.
Bromberg:I didnít realize that at all. Just reading the papers you never get that sense of who was really making a splash.
DeMaria:When Collins paper was published, our paper was already submitted to the Quantum Electronics Program Committee for presentation at the 1966 Quantum Electronics Conference. And they had a rule, they still have the same rule, that you could not publish research results before the conference and have a paper on the same data presented at the conference. So we held off. Bob Collins and Hans Mocker of Honeywell (who was his student) werenít looking for mode-locking as I understand it. If you read their paper, they essentially stated that they inserted a Schott glass passive Q-switch inside a ruby laser and hereís what we saw. There was no interpretation or explanation of what was happening. I looked at the paper with great interest, when it came out. Our paper was already submitted so I didnít know about their work when writing our paper, therefore I couldnít reference it. They didnít know about our work so they couldnít reference our work either. Our paper explained the concept so clearly based on Cutlerís work, that everybody caught it and from then on the field just took off. And the field grew and grew. ďHow do you measure such short events? My God, 10-12 seconds is the approximate time it takes light to travel the thickness of a sheet of paper. We measured the spectrum of the laser under such mode-locked conditions, found that the spectrum actually got wider, just the way Cutler said it should.Ē Then we measured the pulses by the two-photon absorption technique illustrated in this photograph on the wall here. The person in the photograph is Mike Mack. Bill Glenn of our group later used the second harmonic technique to measure the pulse widths to greater accuracy.
Bromberg:In the photograph, (Iím telling the tape of the photograph) on the wall there?
DeMaria:The two-photon absorption technique for measuring ultra short laser pulses was first performed by researchers at Bell Labs. I think that it was Joe Giordmaine, but Iím not sure. I have to go back and review it. The two-photon technique requires one to split a light beam into two beams and send them in opposite overlapping directions through the two-photon absorption dye cell. Each light pulse makes a streak through the dye. When the two pulses overlap a brighter portion of the streak appears. The widths of this brighter portion of the streak gives a measurement of the pulse if the proper contrast ratio is met.
Bromberg:Now what youíre pointing to in this photograph, the beams are going in opposite directions. What is that?
DeMaria:The little bright spot there is the overlapping region of two optical pulses travelling in opposite direction. When you photograph it, know the velocity of light, and measure the length of the spot you can calculate the time duration of the pulse if the proper contrast ratio is obtained.
Bromberg:Now tell me, did this work make any difference here at U.A.C.? Did you get any new contracts or new organization of your group or what?
DeMaria:At that time, the group had grown into two groups. One for basic research and one for applied laser research. Bill Glenn was hired at the time, as was Brian Tracey and Mike Mack.
Bromberg:As a result of the laser research work?
DeMaria:Yes. Carl Ferrar was here. Dave Stetser had joined our group a little earlier. Mike Brienza was head of our Applied Laser Group activity. He worked mostly on laser acoustic delay lines and YAG lasers later on. Bill Glenn ran the Laser Physics Group.
Bromberg:But they werenít brought in because of the short pulses research program?
DeMaria:No. They were brought in to work on lasers. Brian Tracey came in about that time. Most of the new members joined our group because of our work on picosecond laser pulses. They wanted to perform research in the field. There was Brian Tracey, Bill Glenn, Mike Mack and Mike Brienza, as well as Dave Stetser and Carl Ferrar. The others had moved on to other places. Mike Brienza transferred to the Norden Division of United Aircraft Corporation to get them into the laser business. They all published a lot of papers in many different areas of lasers while they were here.
Bromberg:Sounds as if the group got much larger from when we last looked at the group. About how big was it?
DeMaria:At that time we had only about eight people. And we had a basic research group and an applied laser group. Mike Brienza had the Applied Laser group and Bill Glenn had the basic group.
Bromberg:Now somewhere around this time period you got a Project Defender contract? Was that anything to do with short pulses?
DeMaria:As soon as we gave that paper at the 1966 International Quantum Electronics Conferences Bill Condell of ONR requested a proposal on the subject. So we worked on an ONR contract from 1967 to about 1972 on picosecond laser pulses. I was the principal investigator. It was part of Project Defender. It was a DARPA program. Project Defender was directed toward funding basic research in lasers of all types to see where the field was going to lead to. Our contract was administered out of Bob Beringerís ONR office in Pasadena. Those reports have all the technology discussed in greater detail than we have published anywhere else.
Bromberg:I see, so that would be a good source for people to examine.
DeMaria:Yes, and they are somewhere in those three bookcases. I kept a lot of our old reports. This bookcase contains the proposals and this bookcase contains the report. Only unclassified ones, of course.
Bromberg:That is a lot of proposals.
DeMaria:I didnít write all of those. In the early days (1963 to 1970) I had a hand in writing all of them, but then as the group grew, I kept the important ones that the staff wrote and stored them here. This shelf here and whatís in here contain the earlier ones. I guess they are all in there. These here date from 1971 on. These are the ones before the 70ís. Before 1970, there was the first Army program on acoustics and that program set the technology base for everything that was done in the acousto-optics field from that time on. There are now small companies who sell acoustic cells for lasers and we have a lot of the basic patents, but we never exercise them because they are all small business, 10-15 million dollars gross sales per year. And then we went into the picosecond pulses and that was Project Defender. We got the line scanner for imaging using acoustic waves. We had another contract to measure the Lamb dip in the argon ion laser. But you know that was good science but it never really had any national or international impact. And then we had a program with Martin Stickley from the AF Cambridge Research Center to do some other short pulse work. The two short pulse [contracts] that we had were the Project Defender and the Martin Stickley contracts and we had a total of $250K to $300K a year for something like five or six years.
Bromberg:And all this time you werenít involved with the application of short pulses? Why do I get the feeling that you might have been involved with laser fusion?
DeMaria:Oh, let me tell you about that. I was giving a lot of presentations around 1967 to 1969 on applications of picosecond pulses. One application I addressed was the generation of very hot plasmas. Russ Meyerand had joined UTRCs staff as a plasma physicist and he was studying gas breakdown with Q-switched ruby and glass lasers for controlled fusion applications. He did the first definitive experiment of gas breakdown with lasers and showed the significance of the importance of such experiments for the generation of very dense plasmas. Russ Meyerand had joined UTRCs staff as a plasma physicist and he was studying gas breakdown with Q-switched ruby and glass lasers for controlled fusion applications. Russ served as Chief Scientist under Wes Kuhrt and he then became Director of Research when Wes Kuhrt transferred as a Vice President of Engineering to Sikorsky Aircraft. Sikorsky is another one of our Divisions. So I became familiar with the importance of lasers for the generation of hot plasmas. Since Russ had a M.S. in Nuclear engineering, as well as a Ph.D. in plasma physics, he was also interested in nuclear energy. I had utilized a technique developed by Hans Heynau and Al Penney to select a single pulse out of a mode-locked train of pulses by means of a Marx-bank high voltage pulser which was used to switch a kerr cell in a time shorter than the round trip time of the laser pulse bouncing back and forth between the two laser mirrors in 1966. I then passed this single pulse through a 75 cm long glass rod amplifier and amplified the pulse up to energies of 1.8 J. The paper was published in October 1967 in the Journal of Applied Physics. This paper got the Atomic Energy Commission interested in ultra short laser pulses for controlled thermonuclear research. I also referred to this possibility in many of my presentations as well as in my Proceedings of the IEEE review paper on Picosecond Laser Pulses published in January, 1969. First let me finish the other part of the story. After we generated these pulses, how were we going to measure them? Bill Glenn took the lead in our group on how to perform measurements on the picosecond pulses, with optical time delays and nonlinear second harmonic effect and found that the pulses became longer later on in the pulse train.
Bromberg:[The paper on] optical delay lines that I see here?
No. The paper entitled, ďTime Evolution of Picosecond Laser Pulses.Ē Bill Glenn was the first to report on the use optical delay lines and second harmonic generation for the absolute measurement of the time duration picosecond laser pulses, if I am not mistaken. In October 1967, researchers at Bell Labs came up with this two-photon absorption way of measuring the pulses and they had a very complicated dye that gave weak fluorescence. At that time, we were playing with rhodamine 6-G pumped with a mode-locked ruby laser. So we knew the spectrum of rhodamine 6-G well. It had a strong absorption at the second harmonic of the Nd3+ ion in a glass host. I suggested to Bill Glenn to use rhodamine 6-G as a two-photon absorber/fluorescence to measure the mode-locked glass laser pulses. So he did the experiment and we submitted it for publication and it got turned down because of the prior Bell Labs publication. Rhodamine 6-G has now been established as the standard technique for measuring picosecond pulses at 1.06 micron wavelength.
Then there was a lot of controversy about what researchers were actually measuring utilizing the two-photon fluorescence technique. Some researchers at Bell Labs caused a lot of confusion. They stated at a conference that a ruby laser emitted short pulses naturally and it was not necessary to mode-lock it. Researchers at the time did not understand the fine points of the two-photon measurement process until Hans Weber at Bell Labs came up with the factor of 3 contrast requirement in the photograph to truly measure accurately the pulse widths with the two-photon fluorescence technique. Bill Glenn was on the same path. It was very good work by both researchers. And so that put that controversy to rest. And then Brian Tracey made his important contribution. We were measuring these short pulses emitted by glass lasers and found by all the techniques we had that they were 10-12 long. Theory said they should be 10-13 sec. long. Having read Cutlerís papers I concluded that dispersion was causing the pulses to chirp. A chirp is familiar to radar engineers as a signal whose frequency is varying with time. And I tried to do an experiment to detect this chirp and was unsuccessful because the dispersion I was using to counteract the laser dispersion was reinforcing it instead. Joe Giordmaine of Bell Labs also became interested in optical dispersion and optical chirping. There was an Air Force-sponsored summer conference that Harlan Scully ran in Arizona with Steve Jacobs, both from the University of Arizona at the time. At that conference, I talked about chirping caused by the lasers dispersion and postulated that it was responsible for not realizing the factor-of-l0 shorter pulses that we were supposed to obtain. Since I had no data, just the analysis performed by Cutler in 1955, they didnít believe it. That was the first time those physicists had heard about an optical chirp.
Bromberg:Is that something that came out of [your] electrical engineering background too?
Bromberg:That was already familiar to you?
DeMaria:It was already known in microwave radars. And Chap Cutler, who was a microwave engineer and worked on radars during WWII, published the theory as well as experimental proof that dispersions caused chirping in mode-locked oscillators in 1955.
Bromberg:Were you in touch with him by the way?
DeMaria:I didnít meet him until two years ago. He showed up at my summer home one day. It turned out he was raised in Connecticut. I spent six months with him at Cal Tech during 1982 to 1983. Then Brian Tracey had the idea of cascading two prisms to obtain adjustable dispersion with a slope opposite to the dispersion existing in the laser. It was a great idea.
Bromberg:He came from Bloembergenís Groups didnít he?
DeMaria:Yes. He got his Ph.D. from Nico Bloembergen an outstanding scientist at Harvard. Brian Tracey had the idea [of] tandem gratings which gave the appropriate dispersion slope which was needed to eliminate the laser dispersion and obtained pulses of 4x10-13 pulses in time duration. He was a very unique inventive person. He did the experiment with the tandem grating and published his results in 1968 or 1969 in the He was the first to measure an optical chip and to perform optical pulse compression as far as I know.
Bromberg:And that was done right here?
Yes. I believe Brian Tracey made a major contribution to optics. All of a sudden, he was able to get down to an order of magnitude shorter pulse than what we were able to generate prior to that time. I think he went down to 0.4 picoseconds, which was the record until many years later when Shank and Ippen of Bell Labs went down to even shorter widths using dye lasers. Today, their record is down to about 10-15 seconds, or a femto second. I tried to hire Chuck Shank and Ippen when they graduated from Berkeley under John Whinnery. They decided to go to Bell Labs instead. Ippen is now on the MIT faculty. They both have made outstanding contributions. Brian Traceyís work was done on the Project Defender contract that I discussed previously. George Lamb was also here working in the Theoretical Physics group. He was a theoretical physicist and he became interested in self-induced optical transparency with short pulses. Erwin Hahn at the University of California at Berkeley was working on this new phenomena at the time.
He had previously pioneered photon echoes. We were in close touch with Hahn. We became very interested in nonlinear optical effects utilizing short pulses. George Lamb developed some elegant equations by the use of a number of mathematical transformations which gave closed-form solutions describing self-induced optical transparency, photon echos, etc. He submitted his paper to the Physical Review Letters and it was turned down by the reviewer because the reviewer felt the work was mathematics and not physics. The reviewer felt that physicists had computers to solve such problems and did not have to resort to such complicated mathematics any more. The reviewer turned out to be Willis Lamb who was at Yale at the time. Incidentally, George Lamb has no family relation to Willis Lamb. Anyway, they worked out their differences and the paper got published. Georgeís work was also sponsored by that Project Defender contract. Based on this work, George got a Full Professor position in both the Mathematics and Physics departments of the University of Arizona. He is still there today. His theoretical research performed at UTRC has become a classic in applied mathematics and is now considered important in understanding all forms of nonlinear wave propagations. As I stated previously, about that time I was going around the country giving invited presentations on picosecond laser pulses and stating that an important experiment to do was to take one short pulse and amplify it to high energies.
We knew the Army had huge glass laser rods resulting from an Army-sponsored program at American Optical for the development of high energy glass lasers for the Army weapon program at Huntsville. The work was classified at the time because they were investigating glass laser rods for laser weapons applications. They had these huge long glass rods which could generate a lot of laser pulse energy. So they gave me some of those rods and a $65K contract and I brought them back to UTRC and assembled a big laser amplifier pumped from a 200,000 Joule capacitor bank that was formally used to generate acoustic shocks for shock tube experiments at UTRC. I took one of those short pulses and I passed it through a 75 cm long rod and amplified it to 1.8 J. My idea was to get a lot of energy in one very short laser pulse and by focusing it on material, one could pump in energy much faster than the material could expand. Consequently, I reasoned that I could get around the cooling process resulting from the material expansion and thus generate very hot plasmas. I kept telling people this was a possible approach to controlled fusion.
Bromberg:Now were you already in touch with the fusion people? What was going on?
DeMaria:There was a fusion program with lasers going on here at UTRC funded by the AEC. Russ Meyerand was running it and later it was conducted by Alan Haught. They purchased conventional glass lasers from American Optical for this research. They were using laser pulses of 10 to 20 nanoseconds time duration as was everyone else.
Bromberg:Was that a DoD project?
At that time, it was funded by the Atomic Energy Commission and later on by the Department of Energy. Everyone believed at the time that the temperature of the gas researchers could obtain was limited by how short a laser pulse they could generate from their lasers because the gas was expanding faster than the Q-switch laser pulse was adding energy. And so my idea was that if one had a short enough laser pulse, perhaps one could put in energy faster than the gas was cooled by expansion. Consequently, one could get it much, much hotter. So I went around the country, not knowing what I was talking about really, because I wasnít trained in plasma or nuclear physics. It caught a lot of peopleís interest in the nuclear energy field. Of course at the time, I did not realize that the pulse compression concept was really one of the basic concepts for the hydrogen bomb.
They used an atomic bomb to generate the pulse compression required to ignite the fusion process. So, there is the possibility that the laser controlled fusion program got started seriously perhaps as a result of our work. Since I did not have a Q clearance, I really did not know what was going on. I learned of this thought process when Edward Teller gave an invited paper at an International Quantum Electronics Conference in Canada some years later. Later on I heard through the grapevine that some earlier calculations revealed that only a few hundred Joules of energy from a picosecond laser were believed to be sufficient to replace the atomic bomb in the fusion process. I was told later that these earlier calculations caused much concern. As the calculations were refined, the energy increased as well as the pulse widths. It was then reported that approximately 0.1 nanosec was later believed to be the optimum pulse length. It is now my understanding that the energy requirements have scaled up to a high enough level so as to push the realization of laser controlled fusion way out into the future.
Bromberg:Did Meyerand pick that up and transfer it to wherever it was going on here?
DeMaria:Well, he picked it up but he couldnít get any appreciable funding because the Atomic Energy Commission was very classified on such matters and I did not have a need to know. The government was also dedicated toward doing all that type of research work in the national labs, so we had an unclassified program at UTRC directed toward controlled fusion funded by DoE. The only program that Alan Haught could get funded was to use the laser to ignite a particle and then use a magnetic field to confine it and study the trapped plasma ball. KMS tired to compete with the national labs on controlled fusion. The result was that they almost went bankrupt. Exxon tried to compete against the National Labs in the laser isotope separation field and they also had to drop out.
DeMaria:Look what happened to the Laser Energic Lab at the University of Rochester. They made some beautiful contributions to efficient second harmonic generation for laser fusion and have received very little funding. You canít compete with the national labs. They have huge programs, huge organizations, an inside track for obtaining funding, and they have very competent researchers. So I was very bitter about the national labs for a long time. We did the first pulse selection out of a train with a Marx-bank. We have the basic patent on the concept. The technique has been used enthusiastically by all the national labs. We did the first pioneering work here at UTRC and never got research support from them. They would always offer me a job to go work for them, but no funding.
Bromberg:Now let me just ask you something else. Among the applications you mentioned, besides CTF, you mentioned high speed photography, radar, optical communications, optical data processing and scientific instrumentation. I was just wondering whether you actually made connection with any of these applications.
DeMaria:Well, we published a paper in the generation of microwave acoustics with lasers. I believe that was the first Controlled Thermonuclear Fusion publication on microwave acoustic generation with lasers. There was some prior work with E-beams and ruby lasers for the generation of acoustic impulses in materials by R. White when he was at GE. And then he went to Berkeley. We did some work in ranging with picosecond pulses. Trying to range very accurately. We were in close touch for a while with the people who were trying to do the moon ranging experiments. Trying to measure the position between the earth and the moon very accurately and to measure continental drifts.
Bromberg:Who are they?
DeMaria:Carroll Alley at that time was the man we interacted with at the University of Maryland. He was taking part in putting the program together. We talked a lot with them but they were short of money and they were essentially doing the work and we were feeding them some laser technology information. And I think they did try an experiment. What actually happens is that the atmosphere distorts the laser beam and you lose the benefits of the short pulse capability anyway. Consequently, time averaging with nanosecond pulses provides the best technique to perform the experiment.
DeMaria:We did work in mode-locking dye lasers by pumping them with short pulses from ruby lasers and published the results in January 1968. This was the first mode-locked pumping of a dye laser. Bill Glenn and I have a patent on the concept. What researchers finally did in the late 1970ís was take an argon ion laser mode-locked it, and then used that to pump the dye lasers. And thatís what made picosecond pulses very useful scientifically. This provided wavelength tunable picosecond pulse laser sources with a continuous pulse train output which was well behaved and provided a continuous pulse train. Ben Snavely at Kodak made the very important contribution of being the first to obtain cw operation of a dye laser by using an argon ion laser to pump the dye laser and presto, he obtained continuous tunable visible radiation. Ippen and Shank used that technique with the modification of mode-locking the Ar ion laser, the mode-locked pumped source provided a mode-locked dye laser output as we reported in 1968 except theirs was continuous. This was an important exception. We were the first to take a mode-locked ruby laser to pump a dye laser, thereby also mode-locking the dye laser. We published it soon after Snavely published his paper. But we use second harmonic glass lasers as well as ruby lasers and in retrospect, those passively mode-locked and Q-switched laser sources were very erratic and not very useful for scientific usage. Shank and Ippen came along. They generated very repeatable continuous trains of pulses whose wavelength could be selected by tipping a grating comprising a part of the feedback optical cavity. It worked beautiful, and so the scientists began to use them. The chemists are having a field day with these mode-locked dye lasers. So are the biophysicists. Shank and Ippen later added a passive absorber into the dye lasers and used the CW-Argon ion lasers to pump it. They got down to even shorter pulses, very reproducibly, so their contribution was very important and was really responsible for the field continuing to grow and finally becoming practical as a scientific tool.
Bromberg:I just want to make sure that I understand this. When you were going to Livermore or wherever you might have gone and talked about short pulses, you wanted a contract, but you wanted a contract for more basic research on short pulses. Or did you want a contract for Meyerandís group or what?
DeMaria:I was interested in a contract to perform basic research on short pulses. Meyerand and Haught would have liked a contract in the use of laser pulses for controlled fusion. Now this was coming close to the end of the beautiful decade of the 60ís when funding for science was relatively plentiful and intellectual welfare for researchers was locked upon with a smile. But the 1960ís were beginning to dray to a close. The 70ís was a decade when funding for research took a nosedive, if you remember.
DeMaria:UTRC got out of the laser fusion work because we couldnít get any funding. In retrospect, I donít think it was right for us to obtain such funding. The field has not developed into a business. Controlled fusion was 20 years away then. It is still 20 years away from realization now probably. Why should an industrial lab like ours duplicate the long-term research role of the National Labs in this field? But at that time, I was young and motivated by doing research in my field of interest. I got captured by the publication game. It was a means of getting satisfaction from your research. When youíre making important contributions to your field of sciences, you are treated like a star by the research community. You go to conferences and other researchers recognize you. You get invited to give presentations all over the world, etc. Youíre riding high when you are productive. It was probably immaturity at that time. But the young spirit keeps pointing out to you all the contributions one could make to your field. A lot of ego and selfishness was probably involved at the time. All in all, I did believe it was positive though.
Bromberg:Well, did you begin to get word from on high? I mean, how did the change begin to percolate down?
DeMaria:The change began to percolate down when the funding level wasnít increasing. Inflation was coming on. Our budget was remaining constant. All of a sudden I had to worry about research funding. How was I going to feed the staff? I had to become more of a manager. Basic research was not looked upon with as much favor as in the past. Relevance and applied research was more the order of the day.
Bromberg:But you were getting money from Project Defender and so on?
DeMaria:But that wasnít enough. Project Defender paid for approximately three or four researchers.
Bromberg:I see. So you had a lot more people.
DeMaria:I had about eight researchers. Even prior to that period, Project Defender wasnít picking up all the expenses. The corporation was always contributing funding to the area. What we did on in-house money, we would treat separately. At that time, ONR contracts to industry were more like grants. Our group was operating more like the philosophy of a university department. So the government money began to stay constant. The in-house money stayed constant. Inflation went up. The overhead went up because of new capital equipment so we were beginning to be strapped for funding. So the reality of the 1970ís came in. I had to mature in the financial thought process. I had to think mere like a manager with responsibility for peopleís jobs and to serve the need of the Corporation rather than science. I had to dedicate less and less of my time to science and more and more on how to find funds by being relevant to the divisions, that sort of thing. And that was the time I had to make a decision whether to stay here or go to a university. Many researchers in industry had to make the same decision at that time. It was also a time that moving to a university was not very easy because they were having similar funding problems. Enrollments in engineering and science were decreasing during that period. Fortunately for me, it would not have been difficult because I had published quite a bit and I was reasonably well-known in the laser field. I had what I considered very good university offers and, but that is another story. My decision was to stay and I have never regretted the decision.
Bromberg:What year are we talking about?
DeMaria:The early 70ís. In 1969, this laboratory had a cut in work force of approximately 30%. In spite of the basic research nature of my groups work, I lost only one staff member at that time due to the lay off. In retrospect, I was treated very well.
Bromberg:As I turned over the tape you were just saying that in Ď72-Ď73 the need to decide whether or not you wanted to go the university came. With you deciding to stay here.
Well, there was one place in 1969 Ö I had the opportunity to go to Berkeley. John Whinnery and I had a lot of discussions. That was at the peak of my picosecond laser pulse research effort. I gave it a lot of thought at the time. I looked at what I could accomplish at a university and what I could accomplish in research at UTEC and I concluded that I could probably perform more research faster here at UTRC. So I decided to stay at that time, with the hope that I could go back later. Another opportunity came about 1973. I had an offer to become the Director of the Institute of Optics. And I was ready to go. But it would have made my wife and daughter very unhappy to leave the Hartford area where we were very happy. They would have gone along with my decision but it was obvious to me that they would have been unhappy and so I decided to stay again. There were also opportunities to join the staff of the Optical Science Center of the University of Arizona not to mention offers from industry. The offers from industry were always for management-type positions in profit organizations. But I never made decisions concerning employment strongly based on money. The technical aspects of the work and family considerations were always the most important to me.
About 1968 the high energy laser program became very important within UTRC and I think it is important to go into that. Much of that work was classified at the time. Consequently, one may not have heard about it. Most of the researchers in that community do not publish so their contributions are not as apparent to researchers outside the classified community. So I like to credit some of these researchers at UTRC if I can. I need to go back to 1966. We have an outstanding plasma group here, which was started by Russ Meyerand. About 1966, a bunch of people like Ed Pinsley, Ed Larry, Russ Meyerand, Bob Bullis, George McLafferty, Bill Nighan, Clyde Brown, etc., were working on CO2 lasers. Patel at Bell Labs had published his papers on CO2 lasers and everybody thought that you could get a maximum of 100 watts of output per meter of discharged length. That was believed to be the upper limit. Researchers at UTRC knew the behavior of the CO2 and N2 molecules very well. We had a lot of aerodynamicists, fluid dynamicists and what have you, and they began working on fast flow CO2 lasers. And in 1967 when I and my staff hit our stride on picosecond pulses, there was a lot of classified government work ongoing in electrical discharge, fast flow CO2 lasers here at UTRC. Several thousands of watts per meter length were routinely obtainable. Based on the recommendation of the Research Advisory Committee, management made a decision not to interfere with our work on picosecond laser pulses even though the high power CO2 laser program had a considerable amount of funds and required people with laser expertise.
Bromberg:I see. So this was a whole other group.
A whole other group. I never worked in that time frame on high power lasers, even though it was a big program at UTRC. So our major push in CO2 high power lasers was conducted by these people that I mentioned. Since the program was large, it required considerable amounts of managing and teamwork. Consequently, there wasnít really one individual that I can point to as spearheading the effort. Collectively these people were all contributing to the program. The basic concept was to move the gas very fast and thereby cool it. The thing that happens with CO2 lasers is that as you put more and more electrical power into the gas to get more and more power out of the gas, the gas gets hot and the laser power output drops. For high power, one requires a large volume. The gas in the center of the discharge takes a long time to hit the walls of the container to get cool so the gas heats up and the power drops. To obtain more power at the time, researchers resorted to making CO2 laser tubes longer and longer.
Scaling up the length of the discharge, researchers reached 200 foot long tubes to get 1,000 watts of average output power. UTRCís concept was to flow the gas very fast and take away the heat. And so they obtained 1,000 watts in one meter of discharge length in about 1967 or so. So they got large programs from DARPA, the Al Weapons Lab, etc., to push high power electric discharge CO2 lasers. About this same time, there was Kantrowitz at AVCO. He knew the properties of CO2 and N2 molecules well because of his research at Cornell. He was an aerodynamicist, so he knew about nozzles, etc. He came up with the gas dynamic laser concept and they built a little one that worked very well. We heard rumors of his results so some of the people here jumped on the idea because they quickly understood the concept. We were already working on fast flows. And there was Ed Pinsley, Russ Meyerand, Ed Larry, Bill Nighan, who were experienced in molecular kinetic relaxations research. There was Bob Bullis, Walt Wiegand, Clyde Brown, Casper Ultee, Jack Hinchen, Jack Davis, all these people got interested in the gas dynamic laser concept and jumped on it. Since the AVCO program was treated as proprietary to AVCO very little information leaked out concerning the details of their approach. Consequently, the researchers at UTRC almost started at the beginning. They were armed only with the information that AVCO had made a gas dynamic laser work.
Bromberg:You didnít have need to know here?
DeMaria:It was not a question of a need to know, AVCO rightly prevented the government from releasing the information. It was their prerogative and they knew how to play the R&D funding game very well. And rightly so. Now we had a lot of facilities here at United Aircraft Research Labs for conducting gas dynamic type of research. We had wind tunnels, gas handling equipment such as big pumps, compressors, etc. So our staff went after it and pushed real hard. They spent a lot of corporate money. Russ Meyerand was so interested in high power lasers that for a period of time he had almost 80% of the corporate funds coming into the Research Center directed toward high power laser research. So my little group was doing the basic laser work with a lot of visibility in the laser community, but it was a small effort in comparison to what was going on in the high energy lasers within the laboratory.
Bromberg:Was there much interaction that was interesting between the groups in conversation?
We were working on solid state lasers and the applications of picosecond pulses to physics and these guys were working on the application of aerodynamics technique to high power CO2 lasers. Consequently, at first there was little interaction because our experimental techniques were so different. In 1969, I began to realize that I had to find funding to support my staff. I became interested in CO2 lasers. In 1969, I was given two additional groups. One was directed toward finding applications for CO2 laser in laser radars and for supporting the high power laser people with special optics; i.e., unstable resonators, etc. It was headed by Carl Buczek. The other group was to be a basic research group in gas laser physics. It was headed by David C. Smith. I wanted to make sure that these researchers contributions got recognized. So Kantrowitz and his staff had the idea of the gas dynamic laser first in the U.S. No question about it. I read the translated paper that Prokhorav and his student published in 1965. Before that Basov published an analytical paper but it was useless. Abe Hertzberg also published a paper in the U.S. in 1963 that received much attention after AVCOís work, but his concept never worked either. Prokhoravís paper stated it all quite clearly. It was dated about the same time that the results of AVCOís work began to leak out but we didnít get a copy of Prokhoravís paper until it came out in translated form about one year later.
So it didnít come out in translated form until mid-1966 and that was the last paper that Russia had published on gas dynamic lasers that I know of for a long, long time. George McCafferty was the high energy laser program manager at UTRC at the time. He knew Dick Mulready in our Pratt & Whitney Division very well. He got Mulready interested in the gas dynamic laser concept. Dick Mulready, with inputs from researchers at UTRC, put together a large gas dynamic laser at the Pratt & Whitney Government Products Division in Florida and it worked like a charm. They built it in a few months and it held the free world record for the highest laser power output for a long time. The numbers may still be classified. United Technologies, as we are now called, won all the major DoD contracts in gas dynamic lasers. A lot of contributions were made here. Ed Pinsley transferred from UTRC to Pratt & Whitney in Florida to run the engineering effort on the gas dynamic lasers. Ed Sziklas also transferred a few years later to perform the development of optical codes for the program. In the early l970s, Bob Frieberg from my staff transferred to Florida to run their optics group. When it became apparent that the gas dynamic laser was not going to be put into the military inventory the DoD began to transfer their research attention to the HF and DF chemical lasers. One of the reasons why the gas dynamic laser was not going to be put into production was because the atmosphere effects limited its usefulness when operated in the earthís atmosphere and the energy output per mass of laser fuel was considered too low.
The energy output per mass of fuel was higher for chemical lasers. This was the reason for DoDís interest in chemical lasers. Pratt & Whitney had to make a decision whether to redirect their energies toward chemical laser weapon programs, or get out of the laser weapon business. Since it appeared reasonable that the chemical laser weapon concept was going to suffer in the same way as the gas dynamic laser weapon systems from atmospheric effects, Pratt & Whitney decided to drop out of the laser weapon business in the mid-1970ís. In retrospect, it was a wise choice in my opinion. They invested their engineering resources into the Fó100 engineering program and it proved to be a wise business decision. The hope for laser weapons amounting to anything now is in the SDI program where the atmosphere is not a limitation. Unfortunately, there are other severe limitations for the SDI application. Only time will tell if laser weapons will ever play an important role in military applications besides use as rangefinders, target designators, etc. Dave Smith and his group became outstanding experts on propagation effects in the atmosphere. They performed nearly all of the definitive lab experiments concerned with thermoblooming, convective cooling, atmospheric optical breakdown effects, etc. Since there was considerable interest in chemical lasers amongst UTRC staff members, Pratt & Whitneyís decision to get out of the laser weapon business was taken hard by some of our staff members. Richard Meinzer of UTRC was the first to operate a purely combustion driven HF chemical laser. Wayne Burwell (who became the Director of Research after Russ Meyerand was promoted to Vice President of Technology of UTC upon Wes Kuhrtís retirement) and Richard Meinzer have a basic patent on the combustion driven HF chemical laser system. Dick Meinzer is still in chemical laser research here at UTRC today. Wayne Burwell also ran a successful chemical laser program for naval electro-optical countermeasure applications.
It is my understanding that the AF personnel considered the chemical laser staff members at UTRC to be the best in the country at that period of time. Unfortunately, we did not have the extensive facilities in place required for high power chemical laser work as we had for the gas dynamic laser. Rocketdyne and TRW had such facilities already in place and it was thus easier for them to enter the field. It would have been too costly for our corporation to duplicate such facilities. Rocketdyne and TRW are presently still the big players in the chemical laser arena. Another major contribution by UTRCs staff to the high energy laser research area was the gas dynamic window. It was invented by George Hausmann, a propulsion engineer who was responsible for advanced projects and government marketing. It eliminated the need for solid state windows in high energy lasers. All high power lasers have utilized the gas dynamic window concept to date. The laser weapon field has always been fickle. Every few years DoD jumped on a new approach. First there was ruby. Since they could not grow ruby crystal large enough, DoD migrated to glass lasers where size was not considered a problem. Thermal optical distortion finally killed the hope of developing solid state laser weapons by the middle of 1960. Then everyone jumped on the CO2 gas dynamic laser bandwagon to be followed by the electron-beam pumped CO2 lasers and then by the chemical lasers. For a while, the interest was in excimer lasers, now free-electron lasers and nuclear pumped X-ray lasers for possible space applications. These last three should keep laser researchers working for a long time. When Pratt & Whitney dropped out of the laser weapons program, their optics group was transferred to UTRC to manage in case UTC should want to re-enter the laser weapons arena again in the future.
They numbered about 50 staff members at the time. Today they number approximately 350 staff members and still growing rapidly because of the SDI program. Their interests are in high energy optics, adaptive optics, optical phased arrays, laser beam management systems, etc. Jim Pearson now heads the activity after Robert Frieberg left to join TRW. The group is now called the Optics and Applied Technology Lab (OATL). The plan is to grow OATL to a sufficient size so they can be self-supporting and then transfer OATL to the Defense and Space Systems of UTC as one of their profit centers. Carl Buczek and his staff transferred their interest to CO2 laser radar for tactical applications such as obstacle and terrain avoidance, Doppler navigation, 2-D and 3-D imaging. The Norden Systems and Sikorsky Aircraft divisions of UTC cause this technology to be relevant to UTC because their product lines are radars and helicopters, respectively. The laser radar group has had many pioneering accomplishments, such as the first 2-D range gated images performed with a repetitively Q-switched laser in a heterodyne laser radar system, the first coherent laser radar flown in a helicopter and successfully detected 1/8 diameter wire obstacles at a mile away, measuring depths of targets to less than one foot, etc. The laser radar activity at UTRC is now headed by Bernie Silverman and Leon Newman, We have high hopes that it will develop into a product line for UTC. In 1969, there was a conference in Washington called the Conference on Laser Engineering and Application, CLEA. That was the first time that people began talking in the open about high power CO2 lasers with fast flow. There was a paper by Raytheon, by Sylvania, and by somebody in France. They were talking about 1,000 watts per meter of discharge length. In our classified work, we were already up to about 10,000 watts per meter of discharge length with electric discharge length fast flow CO2 laser at the time but we could not discuss our work. Eventually the electric discharge lasers got declassified and we talked about it. At that time, I wrote that review paper that you may have seen. Itís on the history, physics, and application of CO2 lasers, and it was published in the Proceedings of the IEEE and itís only devoted to fast flow CO2 lasers, and many of the references are listed there. At that time, discussion of the gas dynamic laser work was still not allowed. The only thing that isnít in there is that we had 10,000 watts in 1969. We began utilizing the electric discharge CO2 lasers in materials cutting, welding, hole drilling in the late 1960ís. Ed Pinsley was very interested in that application. The activity has been very successful. It is now headed by Jeff Carstens and has made important contributions to Pratt & Whitney in the manufacturing of jet engines.
DeMaria:The purpose of the UTRC laser material working program was directed more for applications within the corporation. Jeff Carstens and his staff have delivered high power CO2 lasers to AT&T, automotive manufacturers, European companies, etc., but selling outside UTC was not and is not the major purpose of the program. After Pratt & Whitney went on and won all major programs in the gas dynamic laser field; interest in the electrical discharge CO2 lasers dropped for laser weapon applications. And so, our high power electric discharge CO2 laser work got directed into material working such as cutting, welding, heat treating, drilling for aerospace applications. AVCO at that time, having lost the Airborne Laser Lab program on the gas dynamic laser, redirected their efforts toward the electron beam-initiated CO2 laser. This was another very important contribution. They made two major outstanding contributions to high energy laser technology. Jack Daugherty and his staff worked on that concept which contained new plasma physics. Ejecting electron beams into gas discharge lasers was new. Then along came the TEA lasers developed by the Canadians. I published a paper on TEA lasers with Dave Smith which gave the first parametric performance behavior of TEA published in the open literature at the time. I published a paper on chemical lasers also about that time.
Bromberg:I was going to ask you about that. There was a high energy iodine laser in there. Now how did that get in? Ultee was a name that I have never seen before.
DeMaria:Casper Ultee is still here. Heís a physical chemist so he has published in the chemical laser field. In 1966, remember, I had this big glass laser amplifier. It had a 200,000 Joules capacitor bank to energize it that I salvaged when a shock tube was dismantled. In 1964 Jerome Kasper and George Pimentel of Berkeley published their paper on the operation of the first photodissociation laser. I invited Kasper to UTRC to give a seminar. He gave a seminar on his photodissociated iodine laser research. He and I talked and I realize that I had all the equipment to operate a real big iodine laser and it shouldnít be very expensive. I took a big aluminum pipe, placed windows on each end. I went to the wind tunnel and picked up these big mirrors that we used for studying air flow around models in blow down tunnels and used them as the laser mirrors. I had these one-meter-long flash-lamps I picked up from my Army contract for large glass laser amplifiers and used them to pump the iodine laser. It worked so well that I got 60J from that iodine laser with no trouble at all. I forgot to tell you what happened with those single amplified pulses from the large glass laser amplifier. We had so much energy in those short pulses that the ends of the laser amplifier rod blew out. The optical electric field was so high that the glass material got ripped apart and so the ends of the amplifier would be destroyed after each shot. My standard joke at the time was that since the laser rods cost $10,000 and I was destroying them in 10-12 seconds, I was thus spending money at the rate of 1016 dollars per second.
Bromberg:Was the damage problem an important problem to overcome?
DeMaria:We noted there was considerable interest in the damage problem, especially in the optical self-focusing effects that were causing long bubble tracks of damaged glass in the amplifier if the pulse energy got too large. Of course, what Lawrence Radiation Labs did was to go to large disks instead of rods to reduce the optical density. They got around the damaged problem with the disk amplifiers.
Bromberg:I see. So it actually contributed to it in a way? The damage itself contributed to the understanding?
DeMaria:Well, we were not doing research in optical damage in any serious way. Other researchers did the serious research on optical damaging effects. Going back to the iodine laser paper. That paper was the result of only a few weeks of work. The paper turned out to be important because it encouraged West German researchers to conduct their national controlled fusion program with iodine lasers.
Bromberg:Now this whole thing interests me. I would like to talk a little bit about your methods of working and just the idea that you could go down and get some salvage material and perform an experiment within a few weeks is kind of interesting to me. Iím just a historian. I donít do experiments. So I like to be able to get the feeling of the nitty-gritty way in which people do experiments.
DeMaria:Well. That was a one-and-only experiment. Casper Ultee was a physical chemist. I didnít know much about chemistry. And so I asked him to collaborate with me. He did very little of the experiment, but I asked him a lot of questions and solicited his opinions a lot while performing those experiments. I made some calculations and I would ask him to check them to make sure I was not going in the wrong direction or interpreting the data wrong. Because so much of the experimental equipment was around, one had to only overcome inertia to do the experiment.
Bromberg:But was it often a seminar talk like this that would set you off and you would go off and do something?
DeMaria:The answer is more of a yes. It was nice in those days. The laser field was young and almost anything that one tried was considered new and would contribute to the state-of-the-art of laser technology. The important thing was to be willing to try things and do them fast because the field was moving at a fast pace. One had to have a competitive spirit and work hard.
Bromberg:In other words, you donít have that same kind of freedom of motion anymore?
DeMaria:The laser is older now. The easy discoveries have been already made. One has to work harder and longer on a problem nowadays. We also have a lot more relevance to the corporation so we pick experiments with a different philosophy these days. As I stated earlier, my laboratory was my hobby shop. I really mean that. There were a lot of facilities here for performing good laser research. I always made sure I had an exceptional technician to work with. If the facilities were here, all I had to do was creatively arrange the equipment to do something creative. At the time, I always had more experiments in mind than I had time to perform.
Bromberg:I see. The technician, is that something that makes a big difference?
Bromberg:Tell me a little about that.
Well you see at universities you have the professor who is really the Lord of the manor or over his fiefdom. He has to worry about research funds to pay his postdoctoral and his graduate students and to buy equipment. University researchers have often stated to me that we in industry have to worry about research money, but they do not have to. In addition, they have the freedom to do the research they want while we have to do research relevant to the corporation that funds us so we do have a similar freedom. These are half truths. They have to worry about research funding as much or more than we in industry do. If they do not have funding, they cannot pay their postdoc or graduate students or buy equipment to operate their experiments. They have as much freedom in selecting research topics as long as their government sponsors are willing to fund the research they want to perform. So they have to be relevant to the needs of their contract monitors. They also talk about the risk of layoff in industry. The claim is the university researchers do not have to worry about staff cuts because the faculty has tenure in a university.
What they forget is that the postdocs and graduate students have no tenure. When the professorsí research funding gets cut off, they are in serious trouble. So I think there is not that much of a difference between a good industrial laboratory and a good research university. In industry, we canít use our researchers like some professors use graduate students because our researchers are considered professionals. Grad students are considered to be training to become professionals. In industry, we work very close with technicians. In my organization, we try to assign one technician per researcher so the researcher can concentrate on doing the more advanced work such as calculations, developing concepts, etc., and have the technician do the daily nitty-gritty, nuts and bolts-type of things. So if you have technicians who are very good, they are worth their weight in gold. We tend to always run at lent one technician with one experimentalist whenever possible. Some industrial research organizations are assigned a manpower ceiling. I have found that such organizations tend to hire as many Ph.D.ís as they can and cut back on technicians and supporting staff. Consequently, what you end up with is a lot of Ph.D.ís paid high wages, but doing mostly technician work. My policy has always been not to do this. It is important to make researchers productive and enjoy their work. Having good and plentiful technicians around help in accomplishing this.
Bromberg:Do technicians get considerably less on the market than the Ph.D.?
DeMaria:Well, a Ph.D. has eight to ten years of college training. A technician has high school [plus] maybe two years of advanced training; but on the other hand, if heís good, he can make things happen quickly in the lab.
Bromberg:There is one other thing I would like to fill in here. I would like to get a feel for the way in which you work theoretically. I remember in the survey article that you referred me to on picosecond pulses, for the IEEE, you spoke not only about the experimental work, but about the theory having been evolved over the past few years and there was the Cutler analogy, there was the self-consistent method of talking about the way in which the light was passing through the various elements in the circuit, the amplifier, and so on. What do you see as your own way of handling theoretical analysis?
I am not particularly strong in theory. I published one theoretical paper and that paper was written while I was recuperating from a back operation. I guess a Willis Lamb or Nicolaas Bloembergen would rightly consider that paper as an analytical paper and not a theoretical paper. Some of the engineers around here think it is a theoretical paper. The paper treated stagger tuning to create broad band optical amplifiers. But most of my work has been experimental. I guess my strong points have been in the experimental area. If you are an experimentalist working in a newly emerging area like laser research was in the 1960ís, there are so many experiments that could be done that havenít been done before. The most important attribute to have under such conditions is to be fast on your feet and to have little inertia. Once a field is mature, one has to work harder and longer in making contributions to advance the state-of-the-art. In the earlier days, I had a lot of reading and a lot of catching up to do because of my lack of advanced education at the time. In spite of this limitation, I was able to make some contribution because I was fortunate to come into the laser field early. I came into the exciting field of lasers at the very beginning when the modern giants of science and physics were also involved. The Charlie Townes and Art Schawlow and Nico Bloembergen and the Peter Franken and the Peter Sorokin, and Willis Lamb and on and on. The large research organization such as IBM, Bell Labs, MIT, Hughes, RCA, GE, MIT, Stanford, Yale, Harvard, etc., were also heavily involved in laser research. It was a very new area. All one had to do was be nimble on ones feet and have a lot of drive and not be afraid to try things. I honestly believe that it was almost impossible not to discover something worthwhile even if you went about it in a reckless manner. As a field matures, it becomes more difficult to approach a research problem with such a philosophy.
Itís important for people who want to make a contribution to enter new fields of research. In my youth, I was really driven not to be a parasite in the technical field. I wanted to contribute something to science or technology. Maybe it was because of my family background, but I was just so enchanted when I went through my graduate courses. I was reading and studying the result that other researchers had dedicated their lives to accomplish. As a result, I felt I was getting a free ride on their work. I felt it was my obligation to also do something to pay them back, to make my contribution to science. Thoughts such as these drove me throughout the whole 60ís. Fortunately, I was in an organization that allowed me to do it; fostered that kind of thinking, in a way. In retrospect, it was easy and it was enjoyable. There are similar areas of opportunities like that today like biophysics, astronomy, genetics, compound semiconductors, etc., to name a few. And so I think in science you have to be a risk-taker, you have to throw away the shackles, you canít be confined. And once you have an attitude like that and you have good people around you, itís catchy. The spirit catches on and everybody tends to work in that way. Anyway, that is the way it worked for our Group here at UTRC in the 1960ís and up to the mid-1970ís. I see the same spirit in effect now in our laser radar programs, in our fiber-optics sensor and integrated optics programs. This is a great source of pleasure to me. Iíve always felt bad that after the 60ís, research funding during the 70ís became so tight.
Research funding has loosened up again in the 1980ís. The younger staff members in the 1970ís didnít have the opportunities that I had in the 60ís. But, there are fields that are as exciting as the lasers. You know the laser will be 25 years old in 1985. It is getting matured. A lot of the original contributors are dying off. There are still interesting things to do in the area but you have to work a little harder at it now. Discoveries are coming slower. A new researcher entering the field has to read 25 years of history before deciding what research problem to tackle or he or she will repeat what others have done before. Now is the time for entrepreneurs and engineers to enter the laser field and do their thing; to build major industries and new products utilizing the laser. It is happening! Just take a look at fiber-optics telecommunications, laser printers, video and audio disks, optical data disks, medical instrumentation, bar code readers, etc.
"Ultrasonic Feedback Modulation of an Optical Maser Oscillator,Ē Proc. IRE 50 (1962), 1522.
"Ultrasonic Ė Refraction Shutter for Optical Maser Oscillators,Ē Journ. Of Applied Physics, 34 (1963), 453.
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"Optical Spectra of Ultrashort Optical Pulses Generated by Mode-Locked Glass: Nd Lasers,Ē Applied Physics Letters, 9, p. 118 (1966).
DeMaria, A. J.; R. Gagosz, H. A. Heynau, A. W. Penney, Jr., and G. R. Wisner; ďGeneration and Amplification of a Subnanosecond Laser Pulse,Ē Journal of Applied Physics, 38, pp. 2693-2695 (May 1967).
Glenn, W. H.; M. J. Brienza; ďTime Evaluation of Picosecond Optical Pulses,Ē Applied Physics Letters, 10, pp. 221-223 (April 1967).
Controlled Thermonuclear Fusion
W. H. Glenn; Brienza, M. J.; DeMaria, A. J. ; ďMode-Locking of an Organic Dye Laser,Ē Appl. Phys. Letters, 12, pp. 54-56, January 1968.
"Review of CW High-Power CO2 Lasers,Ē Proc. IEEE, 61, pp. 731-748 (1973).
"Review of CW High-Power CO2 Lasers,Ē Proc. IEEE, 61, pp. 731-748 (1973).
"Linear Wide-Bandwidth Optical Amplifiers by Staggered Tuning,Ē J.O.S.A., 54, pp. 467 (1968).