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Oral History Transcript — Dr. Eric Woodbury

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Interview with Dr. Eric Woodbury
By Joan Bromberg
November 14, 1985

 
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Dr. Eric Woodbury; November 14, 1985

ABSTRACT: Narrative account of Woodbury's work at Hughes Aircraft Company (1951-1981) focusing on the design and development of the laser rangefinder in Carver's group, changes in the company structure that fostered the project, George Smith's Research Laboratory, contract work with McClung for Franford Arsenal and ARPA, Air Force contract work with W.K. Ng leading to discovery of stimulated Raman scattering, Second and Third International Quantum Electronics Conferences (1961, 1963), the first Mark II Colidar and other applications, licensing arrangements and production.

Transcript

A word of caution to the reader. This memoir covers a period of time that began more than 30 years ago. Although some of it is based upon notes made at the time most of it is reconstructed from memory. Further, my impression of what happened often depends upon what I remember being said by others who may remember things differently. Nevertheless, I believe that the general tone is correct and that these notes will be useful to anyone interested in the period. Woodbury: I joined Hughes Aircraft Company's Guided Missile Laboratory in 1951 after obtaining a Ph.D. in the Kellogg Radiation Laboratory at the California Institute of Technology. Hughes was growing rapidly under the direction of Simon Ramon and Dean Wooldridge, but by 1954 their relations with Howard Hughes became strained and they left to form a company which later became TRW. Hughes Aircraft was left in a state of flux for about a year, at the end of which L. A. Hyland was induced to leave Bendix and become the General Manager. At this time Hughes Aircraft was essentially a single product company: missiles and radar fire-control systems for air defense interceptor aircraft. This was not a stable situation and Hyland recognized the need to diversify. To this end he made major changes in the company structure over the next few years.

One of these changes was a major reorganization of the missile group, which in 1960 resulted in the consolidation of the missile electronics and the radar electronics activities into one laboratory under the direction of F. R. Carver. Carver understood the spirit of diversification that was in the air and set about looking for new projects. One of these came from H. A. Rosen, who with D. D. Williams and T. Hudspeth conceived a practical design for synchronous communication satellites. They were able to obtain significant funding from Hyland to build a prototype. The story of their success has been well told elsewhere.

Another new technical direction undertaken by Carver, and the one of interest here, was the result of developments at the Hughes Research Laboratory (which had only recently moved from the central company facility at Culver City to new quarters located in the hills above Malibu). T. H. Maiman invented the ruby laser through experiments performed in the spring of 1960 at the Research Laboratory. At almost the same time M. L. Stitch, then a staff member of the Research Laboratories, became dissatisfied with his position and was induced by Carver to join Carver's laboratory. Stitch had been working on cesium clocks with Harold Lyons. Carver gave Stitch the charter to determine which of these technologies, atomic clocks or lasers, offered the best opportunity for development (this is my understanding of what happened but the matter should be checked with either Stitch or Carver). Stitch decided, and Carver agreed, that a promising effort would be to develop a laser rangefinder. Such a device had obvious application and would also complement the microwave radar effort which made up the bulk of the work in the laboratory. (It is worth mentioning that prior to the invention of the laser rangefinder, engineers at Frankford Arsenal had built an active optical rangefinder which employed a spark-gap for the light source and a large mirror for recollimation. Because of the large mirror size and the broad spectral range of the spark-gap light source which precluded the use of spectral filtering to reduce the interference caused by sunlight, this design remained a laboratory demonstration.)

In the fall of 1960 Stitch received a modest sum to pursue the rangefinder project; I donít know the amount, but judging from the number of people it could not have been more than 10-15 thousand dollars. He immediately picked up James Morse, a mathematician by training but actually a hardware engineer of considerable intuitive ability, borrowed an optical expert and system analyst, Frank Meyer, from the infrared laboratory, and obtained the temporary services of a machinist and went to work. In December 1960 the Missile Electronics Department was dissolved. The department had become part of Carver's Laboratory at the beginning of the year as mentioned above (incidentally, for a few years during this period Hughes did not have a unified missile operation even though it was heavily engaged in missile work — the work was scattered over several groups — then in the early 60's a new missile division was put in place in Canoga Park where it remains to this day).

I had been head of a small low budget group doing fundamental research in missile electronics. With the department gone I was left without portfolio and joined Stitch's operation on 1 January 1961. By this time Stitch, Morse and Meyer had designed the bits and pieces for a laser rangefinder but needed someone to put them together. I had been trained as a physicist and in those days physicists in industry (except in research laboratories) were considered generalists, and I became the system coordinator. Our "competition" was a group led by George Smith at the Research Laboratory who were also assembling a laser rangefinder. It may seem unusual that this could happen; two groups within the same company working on identical projects.

Actually the objectives were completely different. The Research Laboratory's project was designed to demonstrate the efficacy of laser rangefinding. Once that was done they would not, under their charter, engineer the device for production. As a consequence they used standard laboratory test equipment to the greatest extent possible. Our effort, on the other hand, was intended to illustrate that a laser rangefinder could be designed as a practical field device which could be manufactured for a reasonable cost. Our objective was to interest customers and get contracts. In fact, neither group had practical designs, but both were effectively promoted by Smith and Stitch. (Smith and Stitch both have excellent market sense; although Smith is analytic, while Stitch is intuitive.)

The optical system for the receiver in our experiment consisted of an 8" amateur's reflecting telescope manufactured by a Long Beach company. The detector was a 2" diameter photomultiplier tube of the sort I had used during my thesis work, but with a new cathode design that was much more sensitive at the red wavelength of the ruby laser. The optics for the transmitter was made by revamping the optics for an infrared star-tracker built by the infrared laboratories. If you should see a picture of our rangefinder (many were published in the flurry of publicity which followed) you will notice a wire grid in front of the transmitter. This was used to scatter a small amount of the transmitted light to a second photomultiplier whose output then served as the master synchronizing pulse for the echo position measuring scheme. Our laser was similar to the original Maiman laser, a ruby centered in a spiral flashlamp. The rubies were small, one quarter inch in diameter and an inch or so long, and of rather poor optical quality. All of our rubies came from Adolf Mellor, an agent for Swiss manufacturers of synthetic ruby intended for use as watch bearings (where, of course, the optical quality was of no concern). Mellor would come with his sample case like a peddler of pots and pans. We would look at a distant object through a proffered ruby and if the image was recognizable we bought the ruby on the spot.

During January 1961 Morse was trying to get a laser to work, Meyer was working on the optics and the system analysis while I concentrated on the electronics, getting the phototubes working, solving shielding problems and generally integrating the system. We were racing Smith's group for no particular reason other than the glory of being first, but the competition kept both groups moving at full speed. And both groups succeeded in bringing rangefinders into operation the last weekend of January 1961. There has been an argument ever since as to which was first. The resolution turns on the meaning of 'operation.' I am inclined to consider the entire weekend as a single point in time. After all, simultaneous discovery is probably the best solution to a priority problem.

An important technical point should be mentioned. Q-switching had not yet been invented. Without Q-switching the output of a ruby laser is a series of irregular pulses extending over a period of several hundred microseconds. For this reason we measured range by comparing the traces on a dual beam oscilloscope produced by the photomomultipliers which sensed the transmitted signal and the received echo. We experimented extensively with the system during the spring and summer of 1961. Although our peak powers were only about 1 KW (as contrasted with today's 1 MW) we had a large receiving aperture and sensitive receiver with a narrowband optical filter. These, when combined with a transmitted beam whose divergence was about one milliradian which in turn permitted a correspondingly small receiver fieldstop, resulted in range measurements out to 7-8 miles. Favorite targets were the high rise buildings along Wilshire Blvd. in Westwood and the tower of the Mormon Temple also on Wilshire Blvd. Safety considerations prohibit the use of such targets today but our beam, fortunately, was of such low energy and poor divergence that no one was harmed.

Our original rangefinders were not practical because of the complex pulse structure of the ruby laser. There was no reasonable way we could replace the subjective comparison of oscilloscope traces by a precise automated measurement. Although techniques could be imagined that would do the task, they would be difficult and expensive to implement even with today's advances in digital data processing. Nevertheless, our only real competitor at the time, the TRG Corporation on Long Island, was working on such a scheme as we found when we demonstrated our rather large and unwieldy system at the 1961 WESCON meeting in San Francisco. I remember their spokesman denigrating our work as primitive. But they had no demonstration, and the data processing scheme they were attempting to develop became unnecessary because Q-switching had been invented. We all recognized from the beginning that what was needed was a method for getting single pulses of high power and narrow width. With single well defined pulses range determination would be easy. Any of the usual radar electronic methods would work. Morse and I had an idea for making single pulses by using two flashlamps in a scheme Stitch named the hair-trigger mode. Our idea is documented in my notebook dated May 1961 and we later received a patent for the idea. A prototype worked, but not well, a single large pulse would be produced as expected but it was always accompanied by a lot of garbage.

This matter received a lot of attention at the Second Quantum Electronics Conference held in Berkeley (I think in February 1961). Key participants were R. W. Hellwarth, then at the Hughes Research Laboratories now at the University of Southern California, and representatives from the Bell Telephone Laboratories (BTL). The basic idea was to keep the laser from oscillating until a very large population inversion could be produced. BTL proposed a rotating disc with a hole. Hellwarth proposed a method — ultimately implemented by F. McClung — which used a nitrobenzene Kerr cell. The cells were manufactured by a small firm, Kappa Scientific, which had developed them as part of a fast camera shutter for atomic bomb test instrumentation. One of the disadvantages of the Kerr cell was the need for very high voltage, 30-40 KV, which ultimately made them impractical for many systems. This problem was resolved by a group at the Ft. Monmouth Signal Corps Laboratories under M. Mirachi, which included Robert Godwin (now at Livermore) and Robert Benson (now at Hughes). Their Q-switch consisted of a rotating mirror, an idea derived from the BTL rotating disk. The rotating mirror Q-switch was used in all early rangefinders that were produced in quantity. The different methods came to fruition almost simultaneously and the word of each success propagated through the compact laser community very rapidly.

We actually had Q-switching by the time of the WESCON meeting, McClung's nitrobenzene switch was finished, but it had not been incorporated in a rangefinder. That same summer we received a study contract from Frankford Arsenal to design a military rangefinder that could be used for artillery spotting. We produced a design incorporating a nitrobenzene Kerr cell and a really neat optical system, but by the time we finished the study in the fall it was already out of date. My notebooks for this period indicate a concern with the question, "How does the optical system work?" I was not acquainted with Gaussian optical analysis at the time (it had not entered the body of common knowledge), and I could not reconcile geometric analysis with what was obviously happening. A notebook entry for 4 December 1961 shows that I was also beginning to study the details of operation of the nitrobenzene Q-switch. This is important for the work which later lead to the discovery of stimulated Raman scattering in 1962.

In February 1962 McClung and I worked together for a short time on an unfunded project that could be considered a forerunner of today's SDI or StarWars. I think the project was called BAMBI (but that may have been later) and that it was sponsored by the Advanced Projects Research Agency (ARPA). Our effort involved the interaction of laser beams with matter and we did the work because HRL was one of the few places that had a working high power Q-switched laser. But McClung needed a special polarizing prism and I happened to have one. So we got together working around the clock for several days measuring the impulse delivered by the laser pulse to various samples. The impulse was measured with an acoustic transducer borrowed from the Stanford Research Institute. I cite this effort for several reasons. It shows the close cooperation that existed in the early days between our group and the group at HRL (in spite of our occasional competitive moments). It also shows the cooperation which existed between government agencies and industry, cooperation which I suspect may be less today with the controls that have come into place over the years to correct abuses. And finally it shows Stitch's never-lagging effort to seek out joint experiments that might ultimately lead to contracts.

About this time we received a contract from the Air Force to build and study laser amplifiers, particularly for the single pulses generated by Q-switched lasers. W. K. Ng and I were the principle investigators. J. Geusic at BTL had published a paper describing similar work and we were attempting to extend his results to higher powers. I was in charge, but Ng's careful work was essential to our discovery of stimulated Raman scattering. By April the experiments were in full swing but we had a problem. The calibrations of our various detectors did not agree despite a great deal of effort to trace back to NBS standards. We were using photomultipliers connected in both the multiplier mode for pulse shape analysis and the diode mode for energy determination. The amount of neutral density attenuation needed to bring the signals to acceptable levels was different in the two modes. The attenuators were ordinary Kodak gelatin neutral density filters purchased from local camera stores. Eventually we realized what had happened. The filters were not actually neutral; they were intended for photographic use with visible light and had less than the indicated attenuation for infrared radiation. With this information in hand we deduced that our system must be producing infrared radiation in addition to the normal radiation in the red expected for a ruby laser.

We did not have much in the way of instrumentation to test our hypothesis but we were able to convert an old Beckman spectrophotometer into a monochrometer which was then used to laboriously search the near infrared region 10 Angstroms at a time. We were about to quit the search, having seen nothing, when at a wavelength of 7670 Angstroms there was a large response. Further tests showed the new radiation to be monochromatic and collimated, the usual tests for laser action in those days (we had no way to test coherence directly). We immediately sent a letter to the Proceedings of the IEEE. I fix the date in July 1962 because I remember being certain that we had stumbled onto something new and exciting as I walked through the deserted plant on the 4th of July after a particularly good day of experiments. Some research laboratory people happened to be working (I've forgotten why) on another experiment in the laboratory where Ng and I were set up.

They mentioned our results to others at the Research Laboratory upon which I got a call from McClung. We told him of the contents of the IEEE letter and of our search for the underlying cause. McClung and others immediately reproduced our results and then conducted several other experiments for which they were equipped and we were not (and we also had to finish work on the Air Force contract). We did not know we were getting Raman scattering. That suggestion came from the Research Laboratory, I think from Gisela Eckhardt. In any event she and I were eventually given credit for the discovery. Other than the IEEE letter the first publication was the transcript of the talk we gave at the Third International Quantum Electronics Conference held in Paris in February 1963. Immediately following our talk a paper on the same topic was given by Zeiger and Tannenwald of Lincoln Laboratories. I do not remember who actually gave the talk but I will never forget his opening statement which was essentially this, "You've just heard how Woodbury and Ng found stimulated Raman scattering when they weren't looking for it; now I'm going to tell you how we looked for it and didn't find it."

We got a three year contract from the Army Research Agency to study stimulated Raman scattering but the work was done by M. Geller and D. P. Bortfeld as my assignments become more and more directed toward the practical problems of making laser rangefinders. As a consequence I find very little material in my notebooks that relates directly to stimulated Raman scattering (see pages 36-45 of notebook 4). Today a group such as the one I was in would probably not be allowed to bid on a research contract, but at that time we were willing to do anything for anybody who could pay. Our group grew rapidly. By early 1963 there were 63 people under Stitch, as against 3 of us in January 1961. We had obtained a number of laser study contracts (experimental in nature) but nothing for laser rangefinders which we knew should be our main product line. We had expected a follow-on contract from Frankford Arsenal, but the Signal Corps work convinced the Army that they could do the development in-house. So we asked for and received a modest amount of company money to keep the effort going.

We built our first practical rangefinder, the Mark II Colidar, in 1962, finishing it up in flurry of activity at about the time of the Christmas break. I do not remember whether this was one of the many times when our best work was done over a holiday period, but it could well have been. The Mark II was configured as a two barreled shotgun, one barrel containing the receiver and the other the transmitter. The laser was Q-switched by a rotating reflector, following the lead of the Signal Corps. The power supply and other electronics were housed in a box mounted on a Boy Scout backpack. Our rotating mirror was driven by a torsion spring which was loaded by a cocking arrangement like that found on air guns rather than by a motor. The Mark II worked exceptionally well and one of our engineers, Rod Smith, took it all over the United States and Europe giving demonstrations and looking for contracts. By June 1963, I was assistant manager of the department. Stitch didn't like routine, neither do I, but unfortunately I have a knack for it and that is what I did. In retrospect, I wish that I had not been drafted into management.

I believe that one of the weaknesses of the aerospace industry, and perhaps much of the rest of industry, is the unspoken rule that advancement must be along the managerial path to be meaningful. There are notable exceptions to this rule at Hughes, but they are just that, notable exceptions. There must be a way to organize and run research and development organizations that will take advantage of and reward those with other than managerial talent.

We began to get one-of-kind contracts for laser rangefinder prototypes. The first came from Europe and ultimately resulted in licensing arrangements that proved quite profitable to the Company. Two that come to mind immediately were with the firms of Barr and Stroud in Scotland and with Electro in Germany. Except for the Barr and Stroud artillery rangefinder, all of the contracts were for rangefinders for use in aiming tank cannons. In addition to Germany (through Electro), we built prototypes for Sweden, Switzerland, Israel and Japan. The market was not going to be for artillery spotting as we had originally thought but for tank gun laying. These were all experimental units with no production and our future was beginning to look dim. The company leaders began to lose interest. Then we got a big break. The US Army had a design competition for a rangefinder and fire control system for the M60A2 tank and we won the competition. There were two other competitors, TRG, and, I think, either Westinghouse or RCA. The M60A2 contract was for a few hundred systems. This was the first time we were in the factory with a laser system and the experience proved invaluable. The M60A2 tank itself was never particularly successful but the fire control system was, and we later received a contract to retrofit the fire control system of the older M60Al tank with a modified version of the A2 rangefinder and fire control system. Hughes has since built thousands of these Al systems (now called the A3) and just this year (1985) received another large production contract.

After this we always had contracts and the group grew steadily. Although there have been many reorganizations which tend to blur the genetic lines, it is fair to say that several thousand Hughes employees can trace their current jobs to the effort begun by Stitch and Carver in 1960. Stitch left Hughes in 1968 to join Korad, the company which T. H. Maiman had formed when he left the Research Laboratory shortly after the invention of the laser. From 1968 until 1976 I concentrated my efforts on the engineering of rangefinders and related devices such as target illuminators.

For a year or so after Stitch left, Walter Sooy led the other half of the operation, which dealt with high power lasers and the problems of pointing and tracking for systems which employed them. Then Sooy accepted a position at the Naval Research Laboratory and his place was taken by Eugene Peressini. From 1976 until I retired from Hughes in 1981 I was Chief Scientist of first the Laser Systems Division and then the Electro-Optical Engineering Division which became an umbrella organization for both infrared and laser operations in the Aerospace Groups of the Company. This work was interesting and rewarding but not nearly as exciting as the early 60's when a few of us were instrumental in building a new technology for which there were no rules; we found our way as we went.