Since ancient times, people believed that rays of light carry grand and mysterious powers. Interest in radiation redoubled around the start of the 20th century with the discovery of radio, X-rays and radioactivity. A whole spectrum of radiation opened up, with wavelengths longer or shorter than light. What amazing new uses might be discovered for use in medicine, communications, scientific research — or warfare?
Radio was soon put to use, but the same techniques could not be used with radiation of shorter wavelengths. A method for amplifying light had its origins in an idea Einstein developed in 1916. Looking deeply into the new theory of quantum physics, he predicted that rays could stimulate atoms to emit more rays of the same wavelength. But engineers had little notion how to manipulate atoms, and for decades the idea seemed a theoretical curiosity of no practical interest.
Scientists and engineers pushed radio techniques to ever shorter wavelengths. In the 1930s some hoped they were on the verge of creating a “death ray.” That turned out to be unworkable, but the effort led to something better — radar. By 1940, ingenious devices could generate rays with wavelengths of a centimeter or less. They were swiftly pressed into service to detect enemy airplanes.
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By the start of the 20th century, scientists understood that light rays could be thought of as electro- magnetic waves — similar to radio waves, but with much shorter wavelengths. A spectrum chart shows various forms of electromagnetic radiation. The only difference between one ray and another is the length of its wave. (We can also say the frequency is different, the frequency being the number of waves that pass a point each second as the ray moves through space.) The spectrum is drawn so that the wavelength is reduced by a large factor at each major division. Thus visible light rays are 1/100,000 the length of "microwave" rays commonly used for radar. Rays with shorter wavelengths can carry more information and more energy.
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Scientists boasted that radar had won the war and the atomic bomb had ended it. What might physicists create next? As the Cold War against the Soviet Union got underway, the US government poured ever larger funds into basic and applied research. Detecting not only military but civilian applications, corporations and entrepreneurs heaped their own money on the pile. Industrial and university laboratories proliferated. It was from this fertile soil that the laser would grow.
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Already in the 1930s scientists could have built a laser. They had the optical techniques and theoretical knowledge — but nothing pushed these together. The push came around 1950 from an unexpected direction. Short-wavelength radio waves, called microwaves, could make a cluster of atoms vibrate in revealing ways (a technique called microwave spectroscopy). Radar equipment left over from World War II was reworked to provide the radiation. Many of the world’s top physicists were thinking about ways to study systems of molecules by bathing them with radiation.
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Charles Townes of Columbia University had studied molecules as a physicist in the 1930s, and during the war he had worked on radar as an electronics engineer. The Office of Naval Research pressed him and other physicists to put their heads together and invent a way to make powerful beams of radiation at ever shorter wavelengths. In 1951 he found a solution. Under the right conditions — say, inside a resonating cavity like the ones used to generate radar waves — the right kind of collection of molecules might generate radiation all on its own. He was applying an engineer’s insights to a physicist’s atomic systems. Townes gave the problem to Herbert Zeiger, a postdoctoral student, and James P. Gordon, a graduate student. By 1954 they had the device working. Townes called it a MASER, for "Microwave Amplification by Stimulated Emission of Radiation."
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Townes had predicted a remarkable and useful property for the radiation from the device: it would be at a single frequency, as pure as a note from a tuning fork. And so it was. The high degree of order in such radiation would give the maser, and later the laser, important practical uses.
Townes was not alone in his line of thought. Joseph Weber of the University of Maryland expressed similar ideas independently in 1952. And Robert H. Dicke of Princeton worked toward the same goal along a different path. Neither tried to build a device. In Moscow, A.M. Prokhorov and N.G. Basov were thinking in the same direction, and they built a maser in 1955.
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Physicists had been working for generations toward controlling ever shorter wavelengths. After radio (meters) and radar (centimeters, then millimeters), the logical next step would be far-infrared waves. Masers had been modestly useful, more for scientific research than for military or industrial applications. Only a few scientists thought an infrared maser might be important and pondered how to make one. Infrared rays could not be manipulated like radar, and indeed were hard to manage at all.
Townes thought about the problems intensively. One day in 1957, studying the equations for amplifying radiation, he realized that it would be easier to make it happen with very short waves than with far-infrared waves. He could leap across the far-infrared region to the long-familiar techniques for manipulating ordinary light. Townes talked it over with his colleague, friend and brother-in-law Arthur Schawlow.
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Schawlow found the key — put the atoms you wanted to stimulate in a long, narrow cavity with mirrors at each end. The rays would shuttle back and forth inside so that there would be more chances for stimulating atoms to radiate. One of the mirrors would be only partly silvered so that some of the rays could leak out. This arrangement (the Fabry-Pérot etalon) was familiar to generations of optics researchers.
The same arrangement meanwhile occurred to Gordon Gould, a graduate student at Columbia University who had discussed the problem with Townes. For his thesis research, Gould had already been working with "pumping" atoms to higher energy states so they would emit light. As Gould elaborated his ideas and speculated about all the things you could do with a concentrated beam of light, he realized that he was onto something far beyond the much-discussed "infrared maser." In his notebook he confidently named the yet-to-be-invented device a LASER (for Light Amplification by Stimulated Emission of Radiation).
Gould, Schawlow and Townes now understood how to build a laser — in principle. To actually build one would require more ideas and a lot of work. Some of the ideas were already in hand. Other physicists in several countries, aiming to build better masers, had worked out various ingenious schemes to pump energy into atoms and molecules in gases and solid crystals. In a way they, too, were inventors of the laser. So were many others clear back to Einstein.
In 1957 Townes talked over some ideas about pumping light-energy into atoms with Gordon Gould, a graduate student who had been thinking along similar lines. Worried that he might be scooped, Gould wrote down his ideas for the record. He developed many more ideas of how lasers could be built and used, and in April 1959 he filed patent applications with his employer, the high-tech research firm TRG. Nine months earlier Schawlow and Townes had applied for a patent on behalf of Bell Laboratories, which employed Schawlow on staff and Townes as a consultant.
When the Bell patent was granted, Gould sued, claiming he was first to conceive the device. Legal battles raged for the next thirty years. If Gould’s patents were valid, everyone who built or used a laser would owe him money—and the longer the patents were undecided, the more valuable they became as the laser industry grew. In 1987 Gould and his backers began to win settlements. One of the greatest patent wars in history was over.
The historical question of how to assign credit for inventing the laser remains controversial. Most of the ideas were patented by someone, but that tells little about how the ideas actually arose and spread among scientists.
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The race was on! When Schawlow and Townes published their ideas in 1958, physicists everywhere realized that an "optical maser" could be built. Teams at half a dozen laboratories set out, each hoping to be the first to succeed.
Columbia University: Schawlow left it to Townes to make the first attempt. Townes decided to start with potassium gas, since its properties were well understood. But one of these properties is that it is corrosive. The gas attacked the seals on Townes’s glass tubes and darkened the glass.
TRG Corporation: When Schawlow and Townes published their work, Gould told his employers that he was working along the same lines. They got funding for a project from the US Department of Defense. The project was classified "secret," and Gould was barred from working on it because he had briefly participated in a Marxist study group during the war.
Westinghouse Research Laboratories: Masers were being made not just from gas but from crystals — synthetic ruby, for one example. Perhaps a crystal might be stimulated to emit visible light. Irwin Wieder and collaborators tried pumping energy into a ruby using a tungsten lamp. The system was hopelessly inefficient — they couldn’t get nearly enough energy into the atoms to make a laser.
IBM: At IBM’s Thomas J. Watson Research Center, Peter Sorokin realized that you didn’t need mirrors if you used a crystal with the right properties. He had a calcium fluoride crystal polished to have square sides. A ray striking an edge at a 45-degree angle would be reflected toward the next edge and continue to go round and round the inside. A trace of uranium atoms sprinkled through the crystal could act like a gas in a cavity. But they couldn't get laser action, that is, amplification of light.
Bell Labs: Bell Labs had a good supply of rubies for maser research, and Schawlow decided to try that route. Meanwhile, Ali Javan, a former student of Townes, tried another route. Like Townes, Javan preferred the simple medium of a gas, and he settled on a combination of helium and neon in a long glass tube. An electric discharge through the gas would energize the helium, and collisions would transfer that energy to the neon. They too couldn't get laser action.
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Hughes Laboratories: Theodore Maiman made calculations and measurements that convinced him Wieder was wrong in saying it was impossible to pump much energy into a ruby. Even so, you would need an extraordinarily bright energy source. One day, Maiman realized the source did not have to shine continuously, which was what Schawlow and others were trying. A flash lamp would do. Scouring manufacturers’ catalogs, he found a very bright lamp with a helical shape. Just right, he thought, for fitting a ruby inside. He assembled the components with the aid of an assistant, Irnee d’Haenens, and on May 16, 1960 they observed pulses of red light. It was the world’s first laser.
Other teams moved quickly when they heard of Maiman's work. Within a couple of weeks of the press conference that announced the discovery in July, groups at Bell Labs and TRG had bought flashlamps like the one shown in Maiman's publicity photo, reproduced his device and studied it in detail. Schawlow, who had joined the Bell group, with his technician George Devlin made a laser out of a different type of ruby crystal. Wieder with Lynn Sarles independently got the same result. When Sorokin heard of Maiman’s achievement, he realized that he had been too pessimistic. He and Mirek Stevenson had their calcium fluoride crystals recut into cylinders silvered at their ends, and got laser action from them in November. The input power required was less than 1 percent of that needed for the ruby laser. Back at Bell Labs, Ali Javan with Donald Herriott and William Bennett continued on their original path, and in December produced a continuous beam of infrared rays — the first gas laser. Altogether, by the end of 1960 three quite different types of laser had been demonstrated.
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Fifty years after the first laser, there are few people in modern society who have not been affected by the invention.
Revolutionizing Communications: In the 1980’s telecommunication systems relied on bulky copper cable, which was at the limits of its signal-carrying capacity and had filled the duct space under city streets with no room for expansion. Laser light beamed through a single strand of glass optical fiber, thinner than a human hair, can carry more than half a million telephone conversations, or thousands of computer connections and TV channels. Without fiber optics the internet that brings you this exhibit would not exist.
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Improving Commerce, Industry and Entertainment: One of the earliest uses of lasers was in surveying. For example, to tunnel under the English Channel, separate tunnels were started from the English and French sides of the Channel. Laser surveying brought the two together with a misalignment of only a few inches over 15 miles. Today, supermarket checkout scanners, CDs, DVDs, laser holograms for security on credit cards, and laser printers are just a few of the countless consumer products that rely on lasers. Industrial lasers cut, drill and weld materials ranging from paper and cloth to diamonds and exotic alloys, far more efficiently and precisely than metal tools.
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Pain free Surgery: Used in millions of medical procedures every year, lasers reduce the need for general anesthesia. The heat of the beam cauterizes tissue as it cuts, resulting in almost bloodless surgery and fewer infections. For example, detached retinas cause blindness in thousand of people each year. If caught early, a laser can "weld" the retina back in place before permanent damage results. Optical fibers can also deliver laser beams inside the body to reduce the need for more invasive surgery.
Advancing Science: Before any other application, lasers were used for scientific research. At first, like masers, they were used to study atomic physics and chemistry. But uses were soon found in many fields. For example, focused laser beams are used as "optical tweezers" to manipulate biological samples such as red blood cells and microorganisms. Five researchers have shared Nobel Prizes for using lasers to cool and trap atoms and to create a strange new state of matter (the Bose Einstein condensate) that probes the most fundamental physics. Over the long run, none of the uses of lasers is likely to be more important than their help in making new discoveries, with unforeseeable uses of their own.
Everyday Lasers: From cat toys to computer mice, lasers play important (and fun) roles in our daily lives. The average red laser pointers, for example, are great tools for presentations and giving your cat some exercise. But did you know high grade laser pointers, preferably green, can be used in astronomy? Brighter and easier to see, a well-powered green laser can be used to point out planets and constellations in the night sky. The primary reason a green laser stands out so well, is because it delivers at least 5 milliwatts of power.
Laser pointers have also taken on a political role in recent history. At a 2019 Chilean protest, a coordinated effort using hundreds of common laser pointers resulted in the take down of a surveillance drone.
Pop Culture and Not-So-Fiction Science-Fiction: After the invention of the laser, science fiction audiences witnessed a boom in laser-inspired weapons. In 1977, “Star Wars Episode IV, A New Hope,” fans saw the Death Star use laser power to destroy an entire planet. In some early episodes of Star Trek, such as “The Cage” and “Where No Man Has Gone Before,” the laser pistol was the weapon of choice. In “Goldfinger” (1964), James Bond must escape death by laser beam, and in “Tron” (1982), the laser beam acts as a transporter for main protagonist, Kevin Flynn to enter a digital world.
Currently, these weapons remain in the world of research and development, but several countries are working on how to harness lasers for defense. For example, beams of light are used in military applications for targeting and passive surveillance.
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