Imagining Ray Devices

Follow the Dream

In the War of the Worlds (1898)...

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 (see sidebar). 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.

The Radiation Spectrum Picture of a diagram of the electromagnetic spectrum

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.

Follow the Money

When the Soviet Union launched...

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. Scenting 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.

Listen: Charles Townes recalls how physicists' war work brought postwar research funding