Who Really Invented the Laser?
by Mark W. Hibben
Of Patents and Precedence
I recently came across an article celebrating the 50th anniversary of the development of the laser, which made clear that not only do most technology writers know little about technology, they also know little about technology history. The article mentioned only one name in connection with the laser, the name of the researcher who built the first working prototype, Theodore Maiman. Maiman’s laser was even referred to as a “discovery”, as though he had just stumbled upon it while walking the dog. Maiman was a scientist working at the Hughes Research Laboratories in 1960 when he happened to win the race to build the first working laser, beating out a few other rivals. Maiman’s laser consisted of a glass flash lamp similar to what is used for flash photography coiled around a synthetic ruby rod from which the laser light emanated. There may have been discoveries associated with this first successful build, but the laser was an invention not a discovery, and Maiman is not even credited with being the inventor as far as the US Patent Office is concerned. Although, who actually invented the laser is a matter of some dispute, and this dispute, which dragged on in the courts for 28 years, points out the somewhat convoluted nature of American patent law and the interdependent and networked nature of modern technology research.
Before I delve into the history of laser technology development and the ensuing patent legal battle, I would like to describe briefly the essential elements of a laser. This will have a lot of bearing on the subsequent discussions about the laser as a patentable invention. Everyone knows that a laser produces a very bright beam of light that can propagate long distances without spreading very much, in contrast to a conventional light source like a flashlight or even an LED.
The red laser pointer that is used for presentations actually contains an LED, but there’s an additional technical component that converts the LED into a source of laser light. It’s the addition of this other technical component which leads to the unique properties of the laser beam in a very non-obvious way. In the diagram below I show the essential elements of a laser, the Gain medium and the Optical resonator. The Optical Gain Medium can provide optical amplification of light traveling through the medium, and can consist of a gas, liquid or solid. The Gain Medium must be “pumped” with some form of input energy: very bright light from a flashlamp as in the Maiman laser, or electrical current as in the LED. The Optical Resonator consists of mirrors at either end of the laser, supported by some structure that keeps the mirrors rigidly aligned.
Both the Gain Medium and the Optical Resonator are needed to make a laser, and both existed in various forms separately long before they were combined into the laser. In the example of the laser pointer, the LED serves as the Gain Medium, providing optical amplification of light that is passing through. If no light comes from the outside, the LED will just glow from its own spontaneous emission. The optical resonator bounces light waves back and forth between the mirrors. When the resonator is properly aligned, it serves as a kind of optical filter, only allowing certain wavelengths of light to build up in the resonator cavity.
When the Gain Medium and Optical Resonator are combined to make a laser, a wonderful synergy takes place. Nearly all the optical gain is now diverted into amplifying the light waves of the resonator, causing these waves to become very intense, but the waves are also all in phase and nearly monochromatic. Depending on the type of laser, the line width of the laser output, which is the range of optical wavelengths contained in the output, can be incredibly narrow, and is usually much narrower than the spectrum of the spontaneous emission of the Gain Medium, as illustrated qualitatively below.
Until the laser was developed, it had not been possible to produce light that was as bright and as spectrally pure, and it’s this combination of properties that make the laser uniquely useful. Because of the intense monochromatic nature of the laser beam, it can propagate long distances while still having high brightness, making it useful for laser target designators (used for laser guided munitions) and laser communications systems. Laser beams also enable fiber optic communications and optical data storage. All of these applications depend on the linewidth narrowing and intensification provided by the combination of optical Gain Medium and Optical Resonator in the laser.
Milestones in the History of Laser Development
I mentioned above that the critical components of the laser, the Gain Medium and the Optical Resonator already existed prior to their being combined in the invention of the laser. In fact, a type of laser based on electrical discharge through neon gas (as the Gain Medium), could have been built as early as the 1920’s, when neon signs first came into common usage.
The glow of a neon sign is just spontaneous emission. It wouldn’t have occurred to anyone to make a laser out of a neon sign because the conceptual underpinnings of the laser lie in quantum physics, which was just being developed at around that time. At this time, quantum physics was still controversial, with many physicists denying or disavowing it, even when they had made important contributions to quantum theory. Max Planck and Albert Einstein fall in this category. Both of these eminent physicists did essential theoretical and experimental work confirming the quantum nature of light. This is sometimes referred to as the “wave-particle duality” of light, but I really don’t like using the term particle at all. Suffice it to say that their work demonstrated that light beams transmit energy in quantized amounts given by a constant (named after Planck) multiplied by the frequency of the light. This quantized energy amount is really very small. A 100 W light bulb emits well over 10^20 such quanta of energy every second.
This quantum theory of light is absolutely essential to explain and analyze the way the Gain Medium works to amplify light. Einstein even won his Nobel Physics Prize not for Relativity, but for his experimental work that confirmed the theoretical supposition of the quantum nature of light made by Planck. In later life, both men disavowed their work, but the laser is a continuing testament to the validity and importance of the quantum theory of light.
At the heart of the concept of the Gain Medium is the concept of stimulated emission, first described theoretically by Einstein in a paper called “The Quantum Theory of Radiation” in 1917. In stimulated emission, light propagating through some medium stimulates the medium to emit light at exactly the same wavelength and phase as the propagating light, thus amplifying it. Stimulated emission only works if the quantum energy of the light (usually referred to as photon energy) matches a particular quantized energy state of the atoms or electrons of the gain medium. In nature, light amplification by stimulated emission doesn’t happen very often, but the laser Gain Medium is energized or “pumped” in such a way as to make stimulated emission a dominant effect, thus producing efficient optical amplification.
Thirty-six years would pass before amplification by stimulated emission would be actually demonstrated, by Charles Townes in the U.S. and Alexsandr Prokhorov in the U.S.S.R. These early systems operated at microwave frequencies and were called MASERs (Microwave Amplification by Stimulated Emission of Radiation).
Within a few years, both workers were beginning to consider whether the MASER concept could be applied to the amplification of light, electromagnetic waves at visible or infrared wavelengths. By 1957 Arthur Schawlow and Charles Townes began their research into “Optical MASERS” at Bell Labs. The following year they published their seminal paper “Infrared and Optical Masers” and filed a patent application for what would become Patent No. 2,929,922 MASERS AND MASER COMMUNICATIONS SYSTEM. Oddly, they were still referring to their device by the oxymoron “Optical Maser”. They had developed the first working theory of the laser, but not the term. By the time that their patent was granted in March 1960, working laser prototypes such as Maiman’s were mere weeks away from being realized. In 1964, Townes shared the Nobel Prize for Physics for his work on masers and lasers.
But did Schawlow and Townes invent the laser? On the basis of their patent and their paper I would be inclined to say yes. Their paper was especially prescient, although not particularly rigorous, in describing the linewidth narrowing properties of the laser that produce its monochromatic beam. However, a competing patent was filed in 1959 by a graduate student at Columbia University, Gordon Gould, who published a paper in the same year coining the term laser. Gould’s paper was titled, “The LASER, Light Amplification by Stimulated Emission of Radiation”. Gould had followed the work of Townes, who taught at Columbia, since the days of the maser in the 1950s, and there is no doubt that they exchanged ideas. Some accounts credit Gould with suggesting to Townes that the maser could be applied to amplification of visible light. Gould kept notarized notebooks that confirm that the idea for the laser and the acronym first occurred to him in 1957. Gould had filed his patent application after Schawlow and Townes, and Gould’s patent application was denied.
An IP Battle Royale
What followed was one of the most famous intellectual property battles in history, in which Gould and his employer Technical Research Group attempted to overturn the patent of Schawlow and Townes, which had been assigned to Bell Labs. This effort, which dragged on in some form until 1987, never succeeded in overturning the “Optical Maser” patent of Schawlow and Townes. However, in 1977 Gould’s legal challenge bore its first fruit when he was awarded Patent No. 4,053,845 OPTICALLY PUMPED LASER AMPLIFIERS. The patent contains a much lengthier technical description than the Schawlow and Townes patent, being full of not particularly germane facts about optics and spectroscopy, but beneath the verbiage, Gould’s patent is almost completely duplicative of the essentials of the Schawlow and Townes patent. Not only is there little new in Gould’s patent, he even omits any mention of the most important characteristic of lasers, their capability for almost perfectly monochromatic output, which was addressed in the Schawlow and Townes patent, albeit briefly. The linewidth narrowing result of combining the Gain Medium with the Optical Resonator is the truly non-obvious benefit that makes the laser patentable.
Why was Gould awarded the patent? To some extent, Gould was exploiting a prior court ruling that had constrained the applicability of the Optical Maser patent. Schawlow and Townes had presented the laser as part of a communications system in the patent, and the courts ruled that other potential uses for the laser such as laser machining (welding and cutting) were not covered.
Gould, on the other hand, had foreseen a broader range of applications for the laser which he had documented in his notebooks, and he discusses the laser machining application briefly in his patent. This difference in application may have been sufficient to justify legally the patent award to Gould, but one gets the impression that the courts were upholding his patent award as a way to redress the perceived wrong done to Gould for his not being included in the original Optical Maser patent. Gould would eventually become quite wealthy on the basis of the 1977 award and a subsequent 1987 patent.
Some authors have gone quite a bit further in portraying Gould as the aggrieved party. In LASER: The Inventor, the Nobel Laureate, and the Thirty-Year Patent War Nick Taylor portrays Gould as the true visionary and inventor of the laser who was exploited by the unscrupulous Townes. There’s probably some grain of truth in that. What graduate student hasn’t felt exploited by his professor at one time or another? This view of Gould has become popular in the tech media, but it ignores the realities of academic research.
Monetary rights to the laser patent were bound to be assigned to some other organization such as Bell Labs or Columbia no matter whose names were on the Patent, so there was no monetary incentive for Townes and Schawlow to deny Gould his due credit on the patent application. Almost certainly, Townes would have credited Gould if Gould had actually worked for Townes at Columbia on the optical maser, but there’s no evidence that Gould did. The exchanges of ideas were informal, as so often happens in academic research, and were probably productive for both men. Generally, in research, it’s considered good manners to credit such exchanges where appropriate. Here, Townes may have succumbed to vanity or mere competitiveness. For whatever reason, he decided that Gould’s contribution didn’t warrant inclusion on the patent application.
Who really invented the laser? I think the right answer is that many people made essential contributions to this invention, from Einstein to Prokhorov to Townes and Schawlow to Gould to Maiman. It’s not clear to me that any one of them could rightfully claim to be the inventor of the laser. In modern scientific research, all work is based on other prior work, just as the laser was derived from the maser. Given the open communication and collaborative networking which is considered essential for productive research, it is perhaps a shortcoming of the US patent system that patents are awarded on a first come, first served basis.