LASER

(The inventor, the Nobel laureate and the thirty-year patent war.)

By Nick Taylor

Simon and Schuster, 2000. 303 pages, $27.50

In 1999, I reviewed a book, A Beautiful Mind, about a friend of mine, the mathematician John Nash.1 Now I have the opportunity to review a book about another friend of mine, the physicist Gordon Gould. John, as everybody knows by now, won the Nobel Prize for economics in 1994. Gordon deserved a Nobel Prize, for inventing the laser, but had to be satisfied with becoming a multi-millionaire when he finally won his thirty-year-long patent war in 1988. The fascinating story of the invention initially conceived by Gould while he was a graduate student at Columbia and the long fight for recognition are admirably told in this well-written book. The author, Nick Taylor, has written a number of similar books including a biography of John Glenn.

The book begins with a description of Gould's childhood, first in Pittsburgh and then, from ages 12, in Scarsdale, New York. He was considered a science whiz in high school, but also had time for outside activities, singing in his church choir, playing the flute in the high-school band and orchestra and running track. Even while he was in junior high, Gould was a tinkerer, repairing his neighbors' radios for example, and otherwise showing an inventive flair.

Although he was offered a scholarship to MIT, financial considerations made it necessary for Gordon to enroll in Union College in Schenectady, 2 in 1937 (where I, 17 years later, served on the adjunct physics faculty). Here Gordon's interest in optics, to serve him so well several years later, was first engendered. When he graduated in 1941 he entered graduate school at Yale because it had a well-known program in spectroscopy.

Gordon did receive a master's degree from Yale, and embarked on a Ph.D. program, but World War II had begun by now, and in April 1944, he went to work for the Manhattan Project. Unlike so many others who were sent to places like Oak Ridge, Los Alamos and Hanford Gordon actually worked in Manhattan, at Broadway and 137th St.., on problems involving uranium separation. He soon acquired a female roommate in his Greenwich Village pad, Glen Fuldwider, who later became his first wife and who introduced Gordon to communism, something which was to cause him considerable trouble a few years later.

After the war Gordon worked in the optical industry for several years but finally, in 1949, enrolled in the Ph.D. program in physics at Columbia University. It was the same year that I enrolled in the Ph.D. program at Duke, but Gordon was nine years older than I was (and, mirabile dictu, still is). I.I. Rabi was the grand old man of the Columbia physics department in those days, but Charles Townes (who with his brother-in-law Arthur Schawlow invented the maser) was the up-and-coming young star. When the first working model of a maser was produced in 1954 Gordon was trying to carry out his Ph.D. research under the direction of Nobel laureate Polykarp Kusch (who shared the 1955 prize with Willis Lamb) He was trying to measure the hyperfine splitting of the metastable energy levels of thallium.

At about the same time Gordon began to fear that his experiment wasn't going anywhere, he ran into trouble with the New York City Board of Education which was investigating possible communist infiltration into the school system. Gordon, when called on to testify, admitted to having been a communist, but he refused to name names. For this he lost his teaching job at City College, which he depended on to augment his minuscule assistantship pay from Columbia. He managed to stay in graduate school by first moving in with, and later marrying, his new girl friend, Ruth Francis Hill. Then came a breakthrough in his research: he found that by using optical pumping, a technique only recently invented by Alfred Kastler, he could get the necessary population of excited thallium atoms to enable him to carry out his measurements

But this was the beginning of he end for Gordon's Ph.D. aspirations. It was now 1957, and Gordon had been a post-masters student at Columbia since 1949. He never did get his Ph.D. because he got the brilliant idea of using optical pumping to created a population inversion (in those early days we used to call it "negative temperature.") and began to devote full time to his new ideas, ignoring his Ph.D. research.3 (He formally left graduate school a year later.) Gordon had told Townes about these ideas, and in fact had gotten him to sign the laboratory notebook in which they had been outlined. Gordon at once figured out that population inversion would enable him to construct a maser of any material, whereas the original Townes et. al. device was restricted to ammonia vapor. Then came the breakthrough--he realized that a cavity with partially silvered mirrors at the ends and transparent sides would trap a beam of photons all traveling in the same direction. (The transparent sides are important; not only do they allow stray photons to escape, but the provide the ingress for the light which pumps the lasing material. Gordon actually lost a patent court case for not having stated explicitly that the sides of the laser needed to be transparent.) If in addition the material within the cavity was pumped to "negative temperatures," then as the beam reflected back and forth the photons would stimulate emission of other photons coherent with each other, producing what we now call a laser beam.

Since I feel that the concept of coherence is one of the least understood aspect of physics, let me put in my two cents' worth. (The best discussion of this point has been given by Feynman.4) In superposing quantum states, one adds the amplitudes when there are no possibilities, even in principle, of distinguishing the states. Examples are two-slit diffraction or elastic scattering of neutrons by a crystal lattice. When the sum of amplitudes is squared to give a probability, interference terms arise. We call this diffraction. In stimulated emission, photon 1 impinges on an atom, and stimulates the emission of photon 2, so now there are two photons. There is no way, even in principle, of determining which photon went in and which was "stimulated." So these two photons are indistinguishable, and in particular they have precisely the same frequency. We say that they are coherent. As the "chain reaction" in the laser continues, each photon stimulates more photons, but all of the photons are coherent because coherence is transitive, that is if 1 is coherent with 2 and 2 is coherent with 3, then 1 and 3 are also coherent with each other.5

An example of incoherence is nonelastic neutron scattering, say spin-flip (even with no change in energy). In principle, one could go into the lattice and determine which atom had flipped its spin and thus distinguish outgoing neutrons from each other. (This example is given in Ref. 4). Thus probabilities add rather than amplitudes, and so the diffraction pattern is lost. As Feynman stresses, this idea of coherence and addition of amplitudes is a (mysterious) empirical law of nature, one which has never been explained in macroscopic terms.

So population inversion provided the coherent photons (like an amplifier), and the mirrored cavity got them all moving together (like an oscillator). Gordon immediately visualized the possible applications, for example as weapons, distance-measuring equipment (and even extra-terrestrial distances have in fact been measured very precisely by laser beams).6 In eye surgery, a laser beam of the proper frequency does not interact with the cornea, but delivers heat to the retina. (Hasn't everybody seen the elementary physics demonstration, in which balloons of different colors are inflated one inside the other. A laser beam passes through the outer balloon and bursts only the inner balloon.) Gordon applied for patents, eventually on the amplifier, the oscillator, and various applications.

In 1957, Gordon wrote up many of the concepts inadequately outlined above, and has his notebook notarized, on every page. I am privileged to have been given a copy of the first page, dedicated to me by Gordon. (A photo of this page also appears in the book.) Here is what it says:

Some rough calculations on the feasibility of a LASER;7 Light

Amplification by Stimulated Emission of Radiation.

Consider a tube terminated by optically flat partially reflecting parallel mirrors. The mirrors might be silvered or multilayer interference reflectors. The latter are almost loss less and may have high reflectance depending on the number of layers. A practical achievement is 98% in the visible for a 7-layer reflector. (Here there is a reference to the book of O.S. Heavens, "Optical Properties of Thin Solid Films.") Flats with a lesser tolerance than 1/100 ? are not available, so if a resonant system is desired, higher reflectances would not be useful. However, for a nonresonant system, the 99.4% reflectances, which are possible, might be useful.

Consider a plane standing wave in the tube. There is the effect of a closed cavity: since the wavelength is small, the diffraction and hence the lateral loss is negligible.

This was dated Nov. 13, 1957 and notarized by Jack Gould. The coincidence that the notary and Gordon had the same last name, even though they were not related, later caused trouble in the patent litigation. Gordon then got a job working for a new company called TRG, of which Ray Aaronson was an employee.8 Gordon began his work at TRG trying to build a laser and applying for government contracts to support the research. These contracts eventually arrived, but a problem now rose. . Owing to the obvious weapons potential of the laser the contracts were classified, and Gordon, due to his communist background, could not get clearance. So he sat in a separate building and was not even allowed to read his own notebooks! Gordon also couldn't read his own patent applications, which for a couple of years were classified secret.

Many other groups, such as Bell Labs, Hughes Aircraft and Westinghouse were working on the lasers, and patents were issued. For example, Townes and Schawlow were issued a patent for "Masers and maser communication systems." (Townes for years insisted on calling the laser an "optical maser.") And by this time, TRG, Bell Labs, and Hughes had all produced lasers of some description; Hughes' device was the celebrated ruby laser. TRG's first successful laser, an optically pumped cesium cell, fired in 1962.

It was not too long after this (1967) that TRG was bought by Control Data Corporation, and a number of TRG's employees, including Gordon and Ray Aaronson, took positions at Brooklyn Polytech. This school was trying to exploit, in a big way, the possibility of government contracts. Gordon was successful in obtaining grant support for some time through his friend and former fellow-graduate student at Columbia, the late Peter Franken.9 Peter, who was a colleague of mine at the University of Michigan during the early 60's, had moved to Washington to work at ARPA (Advanced Research Projects Agency, a hush-hush branch of the US government). He always supported Gordon, both with grants, at TRG and Brooklyn Poly, and as a witness in some of the patent litigation. However when Peter left ARPA oin1968 the grant support dried up, and so did Gordon's job at Brooklyn Poly.

Much of the rest of he book deals in detail with Gordon's long and bitter fight to validate his patent applications. This involved filing (unsuccessful) interference claims against the Townes-Schawlow patent as well as suing the Patent Office in Federal Court when his own previously issued patents were disallowed. Then Patent Office acted in a strange manner throughout all these battles, almost it seemed with prejudice. However Gordon was finally vindicated in court, in 1988, when a jury awarded him a patent for the gas-discharge laser. (Some 80 per cent of he lasers in commercial operation are of this type, so even though Gordon had bargained away a large percentage of his future royalties in return for financial backing during the legal proceedings, he became a very wealthy man.)

Today Gordon at the age of 80 is sufficiently vigorous and healthy to enjoy his money. He lives in Breckenridge, CO (my summer home) with his present wife, Marilyn Appel, whom he met when they were both working at TRG. (He and Ruth split up in 1962, partially over his affair with TRG's security officer, whom he evidently got to know well during his unsuccessful attempts to obtain his clearance.) Marilyn and Gordon got together soon after, and she stuck by him, through thick and thin, through good times and bad, even studying law at one time in order to help him in his legal battles. I got to know Marilyn before I met Gordon, because we both sang in the local choral society. They live in a magnificent home, with views of the continental divide. Inside are a full-size swimming pool and specially built rosewood Bösendorfer piano which sees yeoman service during the many chamber music evenings Gordon and Marilyn sponsor. Breckenridge has become a summer music Mecca, with two symphonyorchestras in residence in addition to all the chamber music. This is in no small part a result of Gordon's and Marilyn's extensive financial and moral support.

Laser tells an incredible story, and I wish that the whole scientific world would read it Then Gordon, would get the much-merited recognition from his scientific colleagues which has so far eluded him because his story is not yet well known.

NOTES:

  1. TTSP 28, 315 (1999)
  2. In addition to the MIT scholarship, Gordon had received a New York State scholarship, awarded for attaining high rank in high school. However, the New York State scholarship could only be used at a New York school.
  3. In fact the patent Gordon as finally awarded was for lasers in which the population inversion was achieved by atomic collisions rather than pumping.
  4. Richard P. Feynman, Lectures in Physics, Vol. III, Quantum Mechanics. Addison-Wesley, Reading, MA (1965). Chapter 3.
  5. In coherent states it is really meaningless to speak of individual photons. One speaks of "n-photon states," but there is no implication that the photons exist as individual entities. Such states are called "coherent states" and have been studied by a number of techniques, including the Wigner transform. Cf. P.F. Zweifel, TTSP 22, 459 (1993).
  6. The distance to the moon was measured by reflecting laser light from a special retroreflector placed there by an astronaut. The retroreflector was another of Gordon's inventions.
7. This is the first time the word "laser" was ever used.
  1. At about the same time Ray arranged for me to get a job offer from TRG, but I decided to give acadaemia a whirl and went to the University of Michigan instead.
  2. Peter was a founder of the field on nonlinear optics, an area of research made possible by the high intensities available in laser beams. Actually, the technically correct term would be "semi-linear" optics, since photons don't collide. Rather the optical properties of the medium depend on the electric fields, i.e. on the intensity of the light. This is always the case, but absent lasers the fields are too small for this effect to be observable. Cf. R. Illner, H. Lange, B. Toomire ad P.F. Zweifel, Math. Meth. Appl Sci. 20, 177 (1998).