A Lasting Light Show
The laser beam revolutionized medicine and industry
Charles Townes was distressed. It was 1951, a beautiful morning in Washington, D.C., and the physicist had awakened early to take a walk. He was in town for a conference devoted to a peculiarand frustratingeffect of quantum mechanics: The illusory particles that create light could clone themselves but were getting absorbed faster than they were created.
Townes sat down on a park bench and had an idea. "Thermodynamics says you can't get a certain amount of intensity out of molecules," says Townes, now 92 and still working at the University of California-Berkeley. "Suddenly I realized that thermodynamics didn't have to apply" if the atom was first heated by another source.
He ran back to his hotel to tell a colleague. In late 1957, in a lab at Columbia University, the first design for the laser was born. The invention would revolutionize industry, refine scientific measurements, and inspire 13 Nobel Prizes, including one for Townes. A vital tool in medicine, it would also find a tremendous market in reading data off CD-ROMs.
The principle that Townes was pondering reads like a bad physics joke. What happens when a photon meets an electron in an excited state? The answer had been proposed by Albert Einstein in 1917: Sometimes the collision produces a second photon, the fundamental particle of light that has the same color and direction as the original. Unlike the light from a bulb, which goes in many directions at many frequencies, this process, if repeated on a large scale, would create an orderly beam of light.
Microwaves. Building off of Einstein, and his own revelation in the park, Townes and his students created a device that could produce a stream of microwaves not visible to the eye. They named their invention "Microwaves Amplified by Stimulated Emission of Radiation"or maser.
Townes and others then turned to the problem of repeating the process for visible waves. Townes and his research partner, Arthur Schawlow, say they completed their design for an "optical maser" in late 1957. One of Townes's graduate students, Gordon Gould, also developed a model for optical light in 1957, coining the term "laser" by replacing the "microwave" in maser with "light." The original patent was awarded to Townes and Schawlow, but Gould challenged it in court, getting partial credit after a battle that lasted 30 years.
As Spencer Weart, the director of the Center for the History of Physics, notes, the laser proved that the photon-cloning effect was "not a weird theoretical thing but [that it] actually happens." Fifty years later, the laser is deeply integrated in industry, even as quantum mechanics continues to baffle us.