Science: Fantastic Red Spot

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It appeared as a mere spot of red light flashed last week on a screen. But scientists of Bell Telephone Laboratories at Murray Hill. N.J. are sure their new gadget, called a maser. from which the light came, will lead to astonishing things. The waves of red light moved exactly in step; other light is helter-skelter. The waves kept to the same razor-edged frequency; other light is a mixture of frequencies. They formed a slender pencil beam that hardly spread out at all. If they had marched to the moon—240,000 miles—they would have covered less than one twenty-fifth of its face.

The strange new light came from an optical maser (a word formed from the initials of Microwave Amplification by Stimulated Emission of Radiation). The optical maser is a long-predicted device that many famous laboratories have been racing to achieve, and may prove as important as the transistor, which, like the maser, is a solid-state device.* Existing masers generate or amplify radio microwaves with extreme efficiency, and they have revolutionized many branches of science, including accurate timekeeping and radio astronomy. But as soon as radio masers were in the bag, scientists began to dream about optical (visible light) masers.

Blood-Red Heart. Light and radio waves are both electromagnetic. But light waves are very much shorter and therefore have much higher frequency. They cannot be generated, tuned, filtered or amplified by the handy electronic apparatus used for radio waves. The new maser techniques promise, at least theoretically, to harness light waves just as radio waves have been harnessed.

The heart of the Bell optical maser is a rod of synthetic ruby ½ in. in diameter and 1½ in. long. It is chiefly aluminum oxide, but atoms of chromium replace a small amount of the aluminum, and these atoms cause the maser action.

Surrounding the ruby rod is a spiral flash tube rather like the tube of a photographer's strobe lamp. When a pulse of electricity passes through the tube, it gives a powerful burst of white (mixed) light, some of which strikes into the ruby rod. Certain wave lengths are absorbed by the chromium atoms, raising them momentarily to very high energy levels. They drop back down almost immediately, but instead of falling all the way, they accumulate at a level that still contains considerable energy. After the light flash has shone on the ruby rod for a few millionths of a second, a large number of the chromium atoms are perched on this intermediate level.

Then a sort of chain reaction happens. A few atoms drop spontaneously to the lowest energy level, emitting photons (units) of deep red light. The photons hit other chromium atoms, knocking them off their energy shelf and making them emit more photons of red light. The photons that move sideways escape from the rod, but a few of them hit its polished ends, which the scientists have covered with a thin film of silver that reflects nearly all of them back into the rod. This reflected light moves lengthwise between the two end mirrors, traversing .all of the ruby rod, knocking billions of chromium atoms off the energy shelf and releasing a vast amount of red light, all of whose waves are in step and all of which move parallel .to the sides of the rod. A few of those waves escape through the silver of one mirror, which is not quite thick enough to be totally opaque, and form the pencil beam of red maser light.