Oral History Transcript — Drs. Peter E. Tannenwald and H. J. Zeiger[an error occurred while processing this directive]
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Interview with Drs. Peter E. Tannenwald and H. J. Zeiger
Peter E. Tannenwald and H. J. Zeiger
ABSTRACT: Notes on a conversation with Tannenwald and Zeiger on their interests in new concepts to generate coherent radiation, Zeiger's paper on the Raman maser (1962), knowledge of related work, the 1963 paper on origin of type 2 Raman scattering.
At the time this research was done, the Solid State Division at Lincoln Laboratory was headed by Benjamin Lax. Lax wished to model the Division after Bell Laboratories. Consequently it was very much oriented towards research. The funding was largely from the Air Force on a block grant basis. No proposals needed to be submitted. There was a great deal of flexibility.
After the laser was announced, Lax saw this area as a promising field of research and strongly encouraged laser research within the Division. Tannenwald, who had been working on magnetic resonance and Zeiger were both intrigued by the exciting developments and began to think of new concepts to generate coherent radiation. The work was not directed towards a particular application. Rather, the Division wished to help open up the full spectrum of possibilities for the new field, with the conviction that applications would follow in due course. It is the case; however, that Tannenwald at this time was very much interested in the generation of sub-millimeter waves. That was therefore, one of the app1ications in the forefront of their minds, and this fact is reflected in the first discussion on the Raman maser, authored by Zeiger, that appears in the Solid State Divisionís quarterly report for mid-1962. (It should be noted that the Solid State Progress Reports in which their results are chronicled had a considerable circulation.)
There was a general process of looking into the various areas where research might turn up coherent sources on the part of the Division members who now attacked the laser field. Raman masers were attractive candidates because they might give a flexible method of shifting to new frequencies. Opening up the full frequency spectrum was a cardinal goal at the time.
The first report on the project was written in May or June of 1962, the second probably in August or September. As the reports show, they were not yet aware of the Hughes work. Probably they first learned of it from the article by Eckhardt et al. in The Physical Review, because they subscribed to that journa1. It may be that someone pointed the article out to them. They were unlikely to have seen it in IEEE Proceedings because they were not IEEE members and did not receive the Proceedings.
Zeiger and Tannenwald did not have much contact with the Hughes group. Zeiger had a friendly, but cursory meeting with them at the conference in Paris in February 1963. One sequence of events, however, which did put them in touch with other researchers, began, in their recollection, after February 1963, when the military got excited about Raman lasers as a possible source of high power for beam weapons. IDA, including Townes and William Culver, and ONR were both involved. The important person at ONR was Fred Quelle. He had a scheme for using Raman scattering as a pump for a system which included many lasers and a single output. A series of meetings resulted at which Tannenwald and Zeiger met, among others, Bloembergen, Townes, Fred McClung, and Terhune.
They had no appreciable interaction with Bloembergen on the subject of SRS other than this. They had somewhat more contact with Townes. At one point, he sent a group of his graduate students out to look over their setup in preparation for outfitting his own laboratory for nonlinear optics experiments. Later on, a good deal of interaction took place with Stoicheff, who in the meantime had come to spend a year at M.I.T.
Their 1963 paper on stimulated Raman scattering related their observations back to a dispersion curve in nitrobenzene, which demonstrated some peculiar effects, different from what was predicted by a simple theory. People were not too happy about this. Garmire and Townes got results which matched the simple theory. The Garmire-Townes type of result was subsequently termed type 1 scattering whereas the Zeiger-Tannenwald results were type 2. It has never been exactly clear what went on.
There were lively debates on these subjects at the meeting in Puerto Rico in the summer of 1965. Filaments were discussed, as the possible cause of type 2 Raman scattering. After every session, and after other seminars, people like Szöke, Kelley, Bloembergen, Townes, and Stoicheff argued over the meaning of the results.
At Lincoln Laboratory a significant result was the first experiment on pumping a Raman laser at 90° to the beam. This was thought by a number of people (Quelle, Culver) to be an advantageous configuration in order to obtain a high-purity, high-power laser.
The physics of stimulated Raman scattering was a subject which caused a stir for a while, but it then quieted down, and the subject is no longer much discussed as a basic research topic. However, stimulated Raman scattering in liquids, gases, and solids is routinely used today to obtain coherent sources of radiation at many different wavelengths.