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Oral History Transcript — Dr. Robert Hellwarth

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Interview with Dr. Robert Hellwarth
By Joan Bromberg
At Harborplace: Baltimore, Maryland
May 19, 1983

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Robert Hellwarth; May 19, 1983

ABSTRACT: T. H. Maiman’s work on the ruby laser. Brief remarks on Hellwarth’s invention of Q-switching and on the discovery and interpretation of the stimulated Raman Effect. A paraphrase of remarks.

Transcript

I held a Hughes postdoctoral fellowship while I was at California Institute of Technology '55-'56. The entire Hughes Fellowship program, Masters, Doctoral and Postdoctoral, was extensive, not limited to Cal Tech, One of the first of its kind, it has continued strongly to this day. It was the most generous fellowship I had found in applying. These were not limited to Cal Tech; such fellowships were widespread. Hughes fellows did not necessarily go on to work at Hughes as I did. I remember that Walter Gordy, a Howard Hughes distinguished lecturer, came up from Duke University to give a seminar we had a series of seminars at Hughes, organized by myself and others, to which outstanding scientists came, among them Feynman. I remember Gordy told us in his Southern accent, “I am delighted to be at Hughes, the only company in America which pays scientists a living’ wage.” At that time, the research staff wasn’t concentrated in one place, but was placed within the different divisions. Work was not preponderantly classified — I myself didn’t do classified work at Hughes with the single exception of Project Helsa (High Energy/Laser Systems Analysis) in the mid1960s. It was necessary, however, to have the lowest form of clearance, “confidential,” to work at Hughes, whatever your project. The Ruby Laser Arthur Schawlow had calculated that a ruby laser was impossible. But Ted Maiman knew the man on whose data Schawlow’s prediction was based and knew his work was sloppy. He was convinced he could make the ruby laser work; he was single-minded in this conviction. He was an experimentalist but with a good grasp of theory.

The equations here are not terribly difficult anyway, and Maiman had a good feeling for how the processes would go. Maiman had written up a proposal for work on the ruby laser, but he had been told by management to stick to microwaves — that Hughes was a microwave company. The proposal was therefore never submitted, and Maiman worked on his own. I remember that one day, at lunch time; I went to Maiman’s laboratory with Leo Levitt, now at the Harry Diamond Research Laboratories in Washington DC, who was a photographer. We used Leo’s flash bulb to irradiate Maiman’s laser and we watched the decay time of its fluorescence. We could tell from that that the quantum efficiency was much higher than the figure Schawlow was using. He went away and re-measured it much more carefully.

When Maiman made his laser, Bell Labs wasn’t anywhere close to one. Nor was Townes group, despite the undoubted fact that Townes had had many of the ideas. Maiman didn’t contribute much in terms of ideas, merely the idea that the ruby can be made to lase. But perhaps the greatest contributions come from the single-minded pursuit to success of ideas that others might let drop, from the vision and belief and courage to ignore the demands of job and smaller projects to go after the big one.

The competition afforded by Bell Labs was intense. Bell had splendid technical facilities. Javan, for example, had an exceptional technician working for him when he made his laser. Maiman, in contrast, didn’t have any resources at all behind him. In reading Maiman’s Nature article, therefore, you have to realize that he was holding back as much information as possible in order to safeguard himself. We thought that someone at Hughes must have leaked information to Bell, because the group at Bell made a ruby laser in a great hurry that duplicated Maiman’s entirely. The article this group published, RJ Collins et al., did not fairly represent the work done by Maiman. It belittled it. For a while, the notion was being spread that Bell had made the invention. Even an Encyclopedia Britannica article written at the time gives that impression.

It wasn’t simply that Bell was after the economic gain of having priority. There was a spirit at Bell, or perhaps an expectation, that everything should have been invented there. As a matter of fact, the reverse was true; Maiman’s invention facilitated Javan’s ability to get his laser to work. After Maiman’s invention, Hughes called a press conference. The management made it appear that it was they who deserved the credit. It was nowhere mentioned that Maiman had done this on his own, without their support. Maiman was very much in the background at that conference, and the management group was up front. Maiman, however, had had a father who had worked for a corporate research laboratory and was shabbily treated by them. He therefore stayed on at Hughes just long enough to work through the basic science and publishes the kind of work which would demonstrate his priority. He left Hughes about a year later.

There was a lot of disorientation at Hughes after the Maiman laser. For one thing, all the research groups were vying for the laser project. For another, there were recriminations once Maiman had left; questions came up as to who was responsible. During this time, the leadership of the laboratory turned over several times. I was thinking of quitting, but because I had a few weeks’ vacation coming, I went instead to a vacation and a quiet consideration of some offers I had had. I wanted to take the time to think through my future plans. It was Lester Van Atta, a traveling wave man, who kept together what laser group, was left during this period of shakeup. Somehow, he tracked me down to a cabin in New York. He telephoned me there and asked me to stay on at Hughes. The Q-switch and Stimulated Raman Emission I was not able to get management support for my Q-switch idea either.

About 4-5 months after I worked it out, I finally was able to get Fred McClung to run the experiment for me. In the general chaos of the post-Maiman-laser period, Fred’s work on a magnetic bubble experiment had been terminated. Before submitting my paper to the Berkeley QE conference, I sent the Q-switch to the patent department at Hughes, but the people there told me that it wasn’t worth patenting, that it wasn’t an important invention. Luckily, after the conference, I was able to get the application reconsidered and submitted hours under the deadline imposed by the public disclosure. (The rules have changed since.) Ray Kidder got wind of it and came down to the laboratory to talk to me about it. Afterwards, Kidder put in a proposal for laser fusion. I still have Kidder’s letter to me and a copy of his original proposal to DOD in my files. So, in a way, it was my work that stimulated the start of laser fusion at Lawrence Livermore Laboratory.

In contrast to the laser, where a number of teams had been already working, the stimulated Raman Effect was completely unexpected. Only Javan had had any inkling of this kind of effect before; he had suggested it for the microwave region, where, as a matter of fact, it is impossible to produce. I had not encountered this suggestion of Javan’s at the time I did my own work, nor had the optical analogue occurred to anyone else, including Javan. What happened is that Eric Woodbury and Ng at the Culver City facility discovered a strange emission from a ruby laser. Woodbury and Ng didn’t know the Raman Effect and hypothesized the emission was from ruby. I was in Colorado at the time and heard about it through a telephone conversation with Woodbury and McClung. I realized the emission could be due to Raman scattering from the Q-switch (nitrobenzene), but initial evidence was that it was probably not.(Refer to later tape for details.)

The first paper on the Raman Effect, which we sent to Physical Review Letters, was not initially accepted. It was not until George Smith, who was probably my boss at that time, talked to a Physical Review editor that they changed their position. George told him, “Look, this is an important paper.” We used to say in those days that you couldn’t get a paper into the Physical Review unless it was mediocre. There was quite a competition for a while between Culver City and Malibu over this effect — the rivalry taking the form of a feud over its naming. Culver City had called it the Woodbury effect when it first was noticed. Then, after they realized how it originated, they called it the Woodbury-Raman effect.

Meanwhile, we had had a meeting at Malibu to decide what it should be called. It was my idea, calling it “stimulated Raman scattering” that finally won out in the meeting. Early publications gave it one name or the other, depending on the originating group. History accepted my name.