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The Laser at (About) 40

First ruby laser
Image: Laser Stars
FIRST LASER, based on a crystal of ruby encased in a flash tube, was built by Theodore Maiman at Hughes Aircraft in 1960.
If you accept Bell Labs' version, the laser has just passed its 40th anniversary. They mark as the seminal event the publication in the December 1958 Physical Review of a paper describing the principles of amplifying light by Arthur L. Schawlow, a former research associate at Columbia University who was then a Bell Labs researcher, and Charles H. Townes, a professor at Columbia University and consultant to Bell Labs. At the same time, the two applied for a patent on the optical device proposed in their paper. They called their invention an optical maser--basing the name on an earlier technique for amplifying microwaves.

But there is more to the story. The Bell Labs patent wasn't issued until 1960. And the race to build the first working laser--a ruby crystal that emitted pulses of light at 0.69 microns--was won that same year by Theodore Maiman of Hughes Aircraft Co. Meanwhile, a graduate student at Columbia University named Gordon Gould had scribbled down ideas for a laser in 1957. Gould had his notebook, in which he coined the term laser, notarized. But he didn't apply for patents because he believed he had to build a working model first. By the time he did file in 1959, the Bell Labs application was already being considered by the Patent Office. Only after 20 years of bitter litigation did Gould win several key patents, beginning in 1977.

But whatever the official date, the work of these four laser pioneers sparked a technological revolution. In just four decades, the laser has become so commonplace that few people even realize that laser, now used as a noun, had its beginning as an acronym for "light amplification by stimulated emission of radiation."

In their paper, Townes and Schawlow presented the idea of arranging mirrors at each end of a cavity containing a gas or substance that could be excited to emit light. The mirrors would bounce the light back and forth so that all the photons would be moving in one direction. The size of the mirrors and the cavity could be adjusted to produce one frequency of light.

Theodore Maiman was one reader of the article who decided to see if he could test the idea by building a working laser. He selected a crystal of ruby and coated each end with a silver mirror. One mirror was thinner so that some of the light could escape as a beam. The ruby was surrounded by a flash tube to provide the energy to stimulate the atoms in the crystal. The entire assembly was encased in a polished aluminum tube. It worked.

When the team at Bell Labs heard of Maiman's success, they dispatched Amnon Yariv, one of their colleagues who was vacationing in San Diego, to rush to Maiman's lab in Malibu. He returned with the bad (good) news. The laser now existed as more than a theory proposed by Albert Einstein's in 1917. Chagrined but not defeated, the researchers at Bell Labs soon bested Hughes with a laser that ran continuously, rather than in pulses (they replaced the flash lamp with an arc lamp).

Laser principles
ANIMATION from Bell Labs shows how a beam of laser light is triggered in a rod of ruby crystal by a flash of light.

The contentious genesis of the laser did almost nothing to slow the rapid pace of its development and commercialization. Patent piled on patent, Bell Labs and others churned out a steady stream of innovations that continues unabated today. The importance did not pass unnoticed. In fewer than six years from the publication of the Schawlow-Townes paper, the 1964 Nobel Prize in Physics was shared by Townes and by Nicolay Gennadiyevich Basov and Aleksandr Mikhailovich Prokhorov of the Lebedev Institute in Moscow for their early work in masers ("microwave amplification by stimulated emission of radiation") and the subsequent development of the optical maser, or laser.


Charles H. Townes
CHARLES TOWNES

Arthur L. Schawlow

Theodore Maiman


Gordon Gould

Although Schawlow was not named in the 1964 prize, his contribution as a collaborator with Townes was acknowledged in the presentation speech. (Schawlow won his laurels in 1981 when he shared the Nobel Prize in Physics for his "contribution to the development of laser spectroscopy.")

What the 1964 Nobel committee failed to note was the vast potential for practical applications of the laser, emphasizing instead its opening of "new possibilities for studying the interaction of radiation and matter." That, of course was very true. A recent example is the 1997 Nobel in Physics to Steven Chu of Stanford University for his use of laser light to trap and cool atoms to nearly absolute zero.

But today, lasers--from semiconductor devices as tiny as grains of sand to experimental giants the size of buildings--are used in hundreds of applications, from cutting and welding metal to repairing damage to delicate tissue of the eyes. They are at the heart of many scientific instruments and are guiding surveyors and sighting weapons. With their light guided through threads of glass, they have revolutionized communications. Lasers scan bar codes at the supermarket and record sound on compact disks.

It's already getting hard to imagine what life was like without them. So, happy 40th--give or take a few months.

RELATED READING:

OPTICAL MASERS, Arthur L. Schawlow, Scientific American, June 1961

ADVANCES IN OPTICAL MASERS, Arthur L. Schawlow, Scientific American, July 1963

THE PRESSURE OF LASER LIGHT, Arthur Ashkin, Scientific American, February 1972

LASER TRAPPING OF NEUTRAL PARTICLES Steven Chu, Scientific American, February 1992.


Images: LUCENT TECHNOLOGIES (Townes and Schalow, laser animation), LASER STARS (Maiman, ruby laser), MIT LEMELSON INVENTION DIMENSION (Gould)
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