Gordon Gould v. Arthur L. Schawlow and Charles H. Townes

Gould1 appeals from the decision of the Board of Patent Interferences which awarded priority of invention of the subject matter set forth in four counts to the senior party, Sehawlow and Townes (Sehawlow).2 After reviewing a voluminous record in light of appellant’s allegations of reversible error, but finding none, we affirm that decision.

The invention relates to an apparatus for light amplification by stimulated emission of radiation, better known by the acronym “laser.”

It appears that amplification of electromagnetic radiation by stimulated emission of radiation was first realized on a practical basis by devices3 operating in the microwave frequency range. The laser is described in the record as an extension of the maser principle to optical wavelengths, i. e. infrared, visible and ultraviolet light. No matter in what portion of the electromagnetic spectrum it is designed to operate, it appears that the heart of a maser-like device is a *910working medium, generally a gas or solid, containing atoms or molecules which have one or more sets of energy levels. Unlike the situation ordinarily prevailing in a volume of matter at equilibrium, where the lower energy states of the material will be more heavily populated with atoms or molecules than the higher energy levels, the laser working medium contains material in which a higher energy level is populated by a significantly greater number of atoms than is a lower energy level of the material. A working medium in such a non-equilibrium condition is said to have an “inverted population” or “negative, temperature.” The means used to excite or “pump” the working medium to create an inverted population of atoms or molecules may comprise a source of electromagnetic energy, for example, a strong light of suitable wavelength directed at the working medium.

The record also shows that a medium in which a population inversion exists may be stimulated to emit its stored energy by wave energy (microwave energy in a “maser” and light energy in a “laser”) of the frequency corresponding to the energy separation of the inverted pair of energy levels, thus amplifying the stimulating signal. In marked contrast to white light from the sun or an electric light bulb, which consists of a whole spectrum of colors and which is emitted in a random, non-directional manner when excited atoms spontaneously return to a lower energy level, the light radiation emerging from the laser device here under conditions of stimulated emission is both “temporally coherent” (a term used to describe the monochromatic nature of the emitted light) and “spatially coherent” (a term used to describe the tendency of the emergent light to undergo little divergence or spreading).

The counts of the interference relate to a laser comprising an active medium with the requisite energy level characteristics, means for pumping that medium, and a cavity resonator to enhance the laser operation. The cavity employed in microwave masers which characteristically has dimensions of the order of one wavelength, e. g. 1-100 centimeters, cannot be conveniently employed in light amplifiers because of the shortness (10-5 — 10-2 cm) of light wavelengths. Rather, a cavity is utilized which has dimensions on the order of thousands or more of light wavelengths. Typically, the cavity defined by the counts is formed by a pair of spaced, plane, parallel optical reflectors, at least one of which is partially transparent, and side members through which pumping energy is admitted and some of the spontaneous and undesired stimulated emission, deviating in its travel from an axis perpendicular to the reflecting end plates, is allowed to escape. The laser employing a pair of opposed reflectors is now termed a Fabry-Perot laser, since the structure involved is reminiscent of the so-called Fabry-Perot interferometer used by physicists for a number of years. The desired output beam of the laser is built up or amplified by repeated passes back and forth along the axis perpendicular to the reflecting end plates, ultimately passing out of the cavity through the partially transparent end reflecting mem- , ber in coherent form.

With the advent of devices capable of amplifying radiation other than microwaves, the term “maser” has assumed a more general meaning — molecular amplification by stimulated emission of radiation. The Schawlow patent uses the expression “optical maser” to denote an apparatus performing the function of the “laser.” As a consequence, the counts employ the expression “maser.” Count 1, to which we have added numerals keyed to Fig. 2 of the Schawlow patent reproduced below, is representative:

1. A maser generator comprising a chamber [14] having end reflective parallel members [16, 17] and side members [15], a negative temperature medium disposed within said chamber, and means [20] arranged about said chamber for pumping said medium, *911said side members being transparent to the pumping energy and transparent to or absorptive of other energy radiated thereat.

Some controversy has arisen in the parties’ briefs and at oral argument as to the various forms of laser devices within the scope of the counts. We find it unnecessary to treat that issue for reasons which will become evident later in this opinion, and will proceed on the assumption that the counts are as broad as Gould asserts.

Both Schawlow and Gould rely on their filing dates of July 30, 1958, and April 6, 1959, respectively, for constructive reduction to practice of the subject matter in interference, neither party alleging an actual reduction to practice prior to those dates. Under such circumstances it is, of course, well established interference law that the junior party, here Gould, must prove by a preponderance of the evidence (1) conception of the invention prior to July 30, 1958,4 and (2) reasonable diligence in reducing it to practice commencing from a time just prior to July 30, 1958, to his filing date of April 6, 1959. 35 U.S.C. § 102(g). The board found that Gould had failed to prove either conception or diligence. We shall consider those issues separately.

Conception

In attempting to discharge his burden of proof, Gould relies primarily on his own testimony coupled with Exhibit 1, which is a bound notebook identified as notebook #1. Pages 1 to 9, the only pages relevant here, were witnessed November 13, 1957, by a notary public. The notary testified that, while he did not read the contents of that notebook and would not have understood them had he tried to do so, “those pages were full” at the time he signed on the margins. The board, but for two “insignificant exceptions” relating to additions Gould admitted making after the date of notarization, accepted Exhibit 1 as a “genuine and authentic document existing substantially as when notarized.” However, the board held that pages 1 to 9 of Exhibit 1 did not disclose “an operative embodiment of the subject matter of the counts,” stating:

* * * jn particular, the notebook No. 1 does not specifically indicate how the pump light is to be applied to the active medium nor that the sides of the cavity are transparent to the laser light. Gould himself testified that *912the disclosure of the Notebook No. 1 does not explicitly show a laser with “side members being transparent to the pumping energy and transparent to or absorptive of other energy radiated thereat” although he did indicate his belief that it was obvious that such was the construction of the side members of the apparatus of Figure 1 of the disclosure. * * * Although it is urged that one skilled in the art would realize that the walls of the tube illustrated on page 1 of Notebook No. 1 were non-reflective and, specifically, were transparent to both pumping and laser light we are not prepared to accept this unsubstantiated conclusion.

Set forth below are the drawing and associated text in Gould’s notebook which he relies on to establish conception:

Some rough calculations on the feasibility of a LASER: Light Amplification by Stimulated Emission of Radiation conceive a tube terminated by optically flat

partially reflecting parallel mirrors. The mirrors might be silvered or multilayer interference reflectors. The latter are almost lossless and may have high reflectance depending on the number of layers. A practical achievement is 98% in the visible for a 7-layer reflector. * * *

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:

If the tube contains an excess of atoms in a higher electronic state, a plane travelling wave may grow by inducing transitions in the atoms, which must add energy to the wave * * *.

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There are several possibilities for excitation:

A. Optical excitation from an external discharge. * * *

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the narrow beam

B. The (coherent) beam of light would emerge from the partially transmitting mirrors as a wave which was plane to within a fraction of wavelength, that is the beam would have an angular divergence 10-5 or better. At a distance of one kilometer the beam would have broadened ✓v 1 centimeter. Thus the beam could travel long distances essentially unweakened. Application to communication, radar etc. are obvious. * * *

It is true, as the board noted, that Gould has conceded that his notebook disclosure does not state “in so many words” that the side walls of the contemplated device are “transparent to the pumping energy and transparent to or absorptive of other energy radiated thereat,” as count 1 requires. However, Gould submits that “even a relatively untrained layman” should be able to understand that the disclosed apparatus meets the terms of the co