Oral History Transcript — Dr. Nicholaas Bloembergen
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Nicolaas Bloembergen; March 22, 1977
ABSTRACT: In this interview, Nicolaas Bloembergen discusses the history of the Harvard University physics department. Topics discussed include: Otto Oldenberg; Abraham Pais; Edward M. Purcell; nuclear magnetic radiance; Julian Schwinger; University of Leiden; Harvard University Division of Engineering and Applied Physics; Eli Yablonovitch.
Sopka:This is Katherine Sopka speaking. Iím visiting today, March 22, 1977 with Professor Nicholaas Bloembergen in his office in Pierce Hall. In the interest of compiling a history of the Physics Department in recent decades, Professor Bloembergen has kindly consented to share with me today his recollections and perspectives on developments within the department, since he first served as an Assistant in Physics in 1946. Professor Bloembergen, perhaps we can best begin by asking you to comment on your pre-Harvard background and upon the circumstances surrounding your coming to Harvard in 1946.
Bloembergen:Yes, I came to Harvard in Ď46, fairly early in the year, because I always wanted to do my thesis at another location than where I did my formal course studies. I had obtained my so-called Doctoral, which is more than a Masters here — itís about equivalent to passing the qualifying exam, and to go on for thesis research. And in Holland that meant I could do my thesis research anywhere and submit my thesis at any Dutch university to get the Doctorate. So, when I started my studies I had thought of Germany and Switzerland, but clearly after the War and the German Occupation, that was out. Switzerland and England were the only countries that werenít completely devastated by the war theatre, but they hardly were in a position to accept foreign students because they had so many problems to cope with in their own reconstruction and with all the refugees, and whatnot. So at the strong encouragement of my relatives, I just wrote a few letters to American Universities I had heard of rather at random, having read, or rather, glanced through some Physical Reviews in the library from pre-war days. I wrote to Harvard University to be admitted as a student, also to the University of Chicago, and the University of California at Berkeley. I never got a response from Chicago — I did get a letter of regret from Berkeley, reminding me that the war in Japan was still going on, this was June and July of Ď45. Of course in Europe, you werenít aware of those other problems — for us, the war was just over. The Harvard Chairman of the Physics Department, Otto Oldenberg wrote back a very nice letter asking me to submit more materials, and then they would process my application. Then there were other roadblocks. It turned out that I was admitted, but the funding was a problem, and although my father was willing to put up the Dutch equivalent, the restrictions on exchange of currency were enormous, and it would require a very special permit to convert guilders into dollars in those days. What it involved were special trips to the Hague and Amsterdam in cattle cars, because the railroads were in a deplorable situation after the German Occupation, and there were trains maybe once a day. There was a long series of cattle cars in which people stood up to travel from one city to the next. The argument I used to get my permit was that I was among about 20 Dutch students on a list of the Department of Education in Holland — The Ministry of Education, to have first preference to go ahead.
Sopka:How old were you at that time?
Bloembergen:I was twenty-five, I was born in 1920. I was with Abraham Pais who later came to Princeton, the two recommended Physics students. At that time funds in the U.S., such as from the Rockefeller Foundations and other foundations, were only given in the Humanities and perhaps the Social Sciences, but the Natural Sciences, as I later learned, were considered...too sensitive, from the point of view of the National Security, so that the U.S. government would not encourage people to come in the sciences. So my argument was then, look, the Ministry of Education in The Hague considered me qualified to go, I have been admitted as a private student, my father is willing to put up the money, so the least you can do is give me a permit. That worked. And there was only one bank, the main national bank, in Amsterdam, that could handle that transaction in those peculiar days of pre-Marshall aid. So, I came with a permit to convert 5,000 guilders into $1,800 — which was just enough for a year at Harvard in those days. And the man asked, ďWho are you?Ē, and I said, ďWell, Iím a student.Ē But the reason he asked, he said, was because theyíd only had a few professors, and they could convert $500 because they would go for...maybe a couple of weeks. And then there were some tulip bulbs dealers, and they were the only people who could commercially bring in some dollars, so they got a permit too. So I was the first permit of over $1,000. I had to travel on a Liberty Freighter, which went back in ballast...they brought grain to Rotterdam, and that was a very slow trip of 18 days or more. We landed in Philadelphia rather than New York because there was a port strike going on. So I took the train up to Boston, and I arrived on the scene...Professor Oldenberg received me, and then I looked around to see where I could do my thesis work. Of course, it so happened that Professor Purcell had just discovered experimentally, nuclear magnetic resonance. And I was a little bit aware of it since I had an earlier interest in magnetism with Professor Gorter in Leyden. This subject appealed to me and I saw the challenge, so I asked to work with him and became his first graduate student. Then after a year and a half, I had done all my thesis work and I was very fortunate that both Purcell and Pound were very busy during the first eight months, finishing up writing the History of the MIT Radiation Laboratory and I was able to learn a great deal and had to do all the work in the laboratory essentially on my own. It was good for learning the intricacies and for catching up on the topic in general — it was a very stimulating time.
Sopka:Had you been able at home to do much laboratory work during those war years?
Bloembergen:Well, some from 1941-43 (the University was closed in early Ď43) and from Ď43 to Ď45 I had done absolutely nothing in the laboratory. So I was way behind... I was a pre-war vintage physicist in those days, although I was well prepared in the basics of classical mechanics and electromagnetism...statistical mechanics. But behind in Quantum Mechanics — I had to learn that. I took a course with Professor Schwinger to catch up. I taught Quantum Mechanics to myself at home after the University was closed, reading H.A. Kramerís text book ďQuantum Theorie des Electrons und der StrahlingĒ by the light of a kerosene lamp, but there was no kerosene in it, just some heavy oil, and the lamp had to be cleaned every hour.
Sopka:At what point in your growing-up years did you decide on a career in Physics?
Bloembergen:Well, that was about when I was 18, just after graduation, because I found it very challenging. I think one of the most challenging things — thatís why I took it. I like Mathematics but not as much as to become a pure mathematician, so I chose Physics right away as a student starting as a freshman. I had already one or two publications before Ď42; I was already initiated by more advanced graduate students in the physics lab of the University of Utrecht. So in about a year I had enough for a thesis, and although they encouraged me to take general exams here and get the PhD at Harvard, I decided to go back because I didnít have the funds. That would have meant spending several months passing exams, and in Holland you donít have to pass any exams, so I went back. I could become a post-doc in Leyden at the Kamerlenjoh-Onnes Lab, which was sort of attractive, to apply magnetic resonance techniques at very low temperatures which very soon became a very big field of research. But before I returned, I was already interviewed by the Senior Fellows of the Society of Fellows because both Professor Van Vleck who was Chairman of the Department and Professor Purcell decided I had a good chance to become a Junior Fellow. And sure enough, after a year in Holland I was elected to The Society of Fellows and I decided to return after a very fruitful stay of a year and a half in Leyden. Well, I donít know where we should go from here. I came back to Harvard as a Junior Fellow and became Associate Professor in Ď51. That was tenure in those days — I jumped from the Society of Fellows right into tenure.
Sopka:As a Junior Fellow, were you working independently or were you again working with people like Professor Purcell and Professor Pound?
Bloembergen:No, I decided to try my hand at other things. I wanted to learn about microwaves and I worked in what was known as the Vanserg Building, a wooden building in which during the war years Professor Van Vleck and Chaffee had worked, which you have already probably recorded. They had microwave equipment there and I did microwave magnetic resonance in ferromagnetic materials and then I used the last part of my Society of Fellows period learning nuclear physics, and I worked for a year or more at the Cyclotron. In retrospect, that may have been a mistake, but it certainly broadened my outlook. I realized that the pastures in experimental solid state physics were greener and more adapted to my style, and Purcellís style of small individual things rather than working with a team and a big machine. So I returned to magnetic resonance after I had worked in the Cyclotron.
Sopka:You were a Junior Fellow within the Physics Department...?
Bloembergen:No, Junior Fellows are in the University, and the work in the Vanserg Building was really with Professor Chaffee. I think he was jointly Physics and Applied Physics as it was then called, so I didnít work in the Physics Department at that time. Of course when I went to the Cyclotron building, that was back in Physics. I worked there with Van Heerder and Professor Ramsey was Director at that time I believe, or was it Livingston...?
Sopka:No, it was Ramsey who was then Director of the Nuclear Program at Harvard in its various parts. When you were appointed an Associate Professor in Ď51, was that within the Division of Engineering and Applied Science?
Bloembergen:That was in the Division...the Physics Department said they were worry but at that time at most they could offer me was Assistant Professorship, and I said in that case I ought to go to Chicago where they also had an Assistant Professorship that was considerably higher paying and much more of a challenge. So, then I got tenured right away in the Division of Engineering and Applied Physics...Van Vleck became the Dean, and of course that was a period of rapid growth in the Division. In a way, it was nice — I was completely independent of Professor Purcell, who might otherwise have dominated the scene, although not by his design but because of his outstanding stature. I think it was better for a young man to branch out...so thatís what happened. In that sense I did not contribute further to the history of the Physics Department, although I always kept very close contact with many members of the Department, especially Purcell, Pound, Ramsey, Van Vleck, and to a lesser extent with the others.
Sopka:Well actually, itís not possible to view the Physics Department in isolation because there are so many interconnections both of programs and people, with the Division in particular.
Bloembergen:In my view, what was decided really, basically was to use the money of the Gordon McKay Endowment in Mechanical Engineering but, as a result of the Vannevar Bush Report, Mechanical Engineering would start with solid state physics and related subjects. So they were built up in those days in the Division and I think that freed the limited funds of the Physics Department to expand into high energy physics and nuclear physics where there was a very pressing need, and so they decided to emphasize those frontiers, whereas solid state physics and in particular magnetic resonance and some related things were developed more in the Division...which is a fair division of labor.
Sopka:Have the students who have worked with you then been entirely from the Division or have you also supervised others?
Bloembergen:Oh no, Iíve supervised many students from Physics. I donít know how many but I would guess about one-third out of about 45 or 46 — fifteen or so came from Physics. They did their thesis in by lab, but formally got their PhD degrees in Physics. We have this system of collaboration between the Departments. There really is very little distinction in certain areas, requirements are very similar.
Sopka:I realize that itís almost impossible to compare life in the Harvard Physics Department or in the Division with the situation in Europe, but I wonder if you have any perspective on science in Europe as you knew it growing up, and now the way it is all over the world, and in particular at Harvard.
Bloembergen:Nowadays in Europe, things are more like the Departments here. When I had left it was a system where there was one chair, and there was a Professor and he was director of the lab and everybody else was way below him. In fact, there was at that time no room for me. I might very well have ended up in Holland again if their offers had come a little earlier and with a little more, but as it was, it was too little too late. So then in Holland and other western European countries the big spurt in science really came at the end of the 50s and all during the 60s. But of course, in this country it exploded immediately right after the war... but they had this delay due to economic reconstruction in the countries. And now they have many chairs, many professorships in Physics, and so on, and labs as big as ours and probably better equipped at this time than ours.
Sopka:Have you spent much time in Europe...either in Holland or elsewhere?
Bloembergen:Well I think traditionally, the Rumford Professor of Physics went to a physicist who had an interest and active participation in practical applications of physics as well, probably in the image of Rumford himself. And I understand it, itís the second oldest endowed chair in the United States in the Natural Sciences, but you as a historian can correct me if that is not so.
Sopka:I wouldnít want to make a statement earlier than my period of expertise.
Bloembergen:Well, if you are a historian you could check up on it.
Sopka:I could certainly check up on it...
Bloembergen:Well my predecessors as far as I know them included G.W. Pierce. I heard a Physics Colloquium by G.W. Pierce...he had already retired at the time but he was interested in the sound of crickets, and ran a tape at different speeds so you could hear the sound that crickets made. Of course, he was famous in classical electronics. Then Professor Chaffee who was well known for his work in high power tripodes (?) and vacuum tubes held the Chair. I believe he was in both the Physics Department and the Applied Physics Department.
Sopka:Yes, he was.
Bloembergen:Well, of course with the reorganization all that was changed. The people who formerly had combined appointments, like Professor Hunt in acoustics, then became members of the Division of Engineering and Applied Physics, and Professor Hunt held the Rumford Chair before me. Professor Hunt was in acoustics, and Iím sort of in lasers and optics now — quantum electronics.
Sopka:Do you want to make any comment about your present research interest and activity?
Bloembergen:Well, itís a very exciting field. It has a very large activity all over the world; I enjoy my international travels because of it and the high level of scientific effort in many countries. I find that makes it a very exciting field. It was sort of a natural development for me, although there are other paths and other people came into it in different ways. I started with nuclear magnetic resonance, went on to microwave resonance, that led to the solid state mass which is described in that article. It had a big impact because the pumping scheme to get inverted populations and negative temperatures as first discussed by Purcell and Pound in the Physics Department in nuclear magnetic resonances (where it had no practical significance), really led to masers which are still used as low noise amplifiers in our deep space receiving antennas in the trans-Atlantic communication link via Telstar. Receiving stations use the masers, and some of the big radio telescopes use them. Then, that same mechanism of establishing inverted populations was used in all lasers. So I decided to get into optics — I wish I had had the idea myself to apply lasers to optic first, but I didnít. But I went in and I used the lasers to study the properties of matter at very highlight intensities, which is the field of non-linear optics. I think we are one of the leading universities and laboratories in that area, since we came in at the very beginning.
Sopka:And yet, is it a field in which you can work, not completely independently, but at least not as part of a large team with complicated funding procedures?
Bloembergen:Small groups...the equipment is very modest by present day standards, and students can work almost by themselves, on the individual experiments or sometimes they team up in twoís and threeís. But itís a small, individual project.
Sopka:Itís nice to know there are fields like that for people who simply arenít psychologically attuned to working in large groups, and doing a lot of traveling as it turns out now people in high energy physics around here must do.
Bloembergen:Very recently, one of my colleagues, Professor Yablonovitch did a research paper on a very exciting new topic which is multiphoton disassociation of poly-atomic molecules with some undergraduates, and the research project led to published results. Itís a very, very simple table-top experiment, and it just shows you that small scale experiments can still be done and lead to research at the frontiers of Physics.
Sopka:Thatís nice to know! Do you have any general perspective on the Physics Department or Physics at Harvard that you want to comment on?
Bloembergen:Well, I always felt that, probably by necessity they had to, in order to stay in the competition, emphasize too much the high energy physics field...at the detriment of atomic and solid-state physics. Now they had to financially, and they could argue also that solid-state physics is done in the Division. But I think it slants the flavor and outlook of the Department when you split up Physics that way. And I am very happy to see now, in the 70s that they are coming back from this course — which I really did not think was in the best interests of the Physics Department. They are coming back from this course for the very important and practical reasons, that of course itís very much harder for students in high energy physics to find jobs. People begin to realize that interesting physical questions still exist, in what were the more classical aspects of the field, such as electromagnetism and radiation problems, fluid mechanics, statistical mechanics and phase transitions. Now all these are again studied with new intensity.
Sopka:Presumably, not only are there interesting questions, but there also are employment possibilities in terms of their practical applications.
Bloembergen:So, the students themselves shift away — they see the handwriting on the wall, and so the department had to accommodate that too. But I think what will happen is that the Division may well then de-emphasize solid state physics in the future because Physics is re-appropriating it.
Sopka:In your own work have you always had a blend of experimental and theoretical concerns?
Bloembergen:Thatís correct, and I like to operate that way. I consider myself an experimental physicist first, but I like to combine experiment and theory. I think that makes for a very useful and also interesting combination because it means you can pick your experimental topics with theoretical insight. Also, if you find something new and unexpected you can work out the theory, at least in rudimentary form...I find that fascinating.
Sopka:It gives you more of a total picture of your own work than if you were relying on others for the theoretical developments and following along.
Bloembergen:So, I still get students both from Physics and the Division and I personally always kept bridges and contacts open, and I enjoy it.
Sopka:Well there seems to be a very good feeling between the two entities, one the Department and the other the Division — at the present time certainly.
Bloembergen:In retrospect, from a historical point of view, it may have been a blessing in disguise that there was not room for me in the Physics Department, because it forced me to find my own way and go my own way, without too much close contact with Purcell, and other very famous people. I could show that I could make it on my own (chuckle).
Sopka:You have not had to take on administrative responsibilities at any point within your career?
Bloembergen:No, I was never forced to, and I think nobody is forced to, if he lets it be known that he isnít very keen on doing it — then, he may escape (laughter).
Sopka:It allows you to pursue your own work. I guess the reason that sometimes one is forced into taking administrative positions is because you just feel that...somebody has to do it, and maybe you could do it a little bit better than some of the other people who might be appointed there, or something like that.
Bloembergen:Well, I probably let it be known that I probably couldnít do it better than anybody else (laughter).
Sopka:Well I thank you very much for telling me these things, and I appreciate your calling to my attention these reports. Iíll make a note of them at the end of the tape — of their existence, so that if theyíre used sometime later...
Bloembergen:You can take some personal notes out of it...especially in the early part, it has more to do with the Physics Department.
Sopka:Yes. Well, in setting up these oral history tapes they do like to know something about the background — the personality of the person, as well as the specific commitments right now.
Bloembergen:Of course, I forgot to mention that many of my colleagues and myself as well are regularly teaching in the Physics Department...you know that.
Sopka:I knew that you do teach courses. Are there any courses that you particularly enjoy teaching?
Bloembergen:Well yah, I enjoy teaching the electromagnetic theory course, Physics 232 a and b. I taught these last years, and I will teach 232a again next fall. I enjoy that...I also taught the intermediate electromagnetic course, Physics 131, 132 — now itís called 153.
Sopka:Have you ever had elementary courses assigned to you?
Bloembergen:Not in Physics.
Sopka:Well, again I thank you, and unless you have some further comment...
Bloembergen:No, but after reading those papers, if you have any further questions please donít hesitate to call me.
Well, thatís very kind.