Stepped-Up

One of the prizes that has dangled just out of reach of the scientists is a method of amplifying light: i.e., increasing the brilliance of a dim "picture." It can be done in the innards of electron tubes, but only in ways that are unsatisfactory. The ideal is a system that will brighten an optical image--with all its lights and shadows--just as sound is strengthened by a public-address apparatus.

This week Dr. F. E. Williams and D. A. Cusano of General Electric's Research Laboratory demonstrated the first major step toward licking the problem. On a round screen four inches in diameter they projected in ultraviolet light the image of an ordinary photographic slide. It made a yellowish picture (of three G. E. scientists) that was almost too dim to be seen. Then Cusano fed electric current to terminals on the screen. As the voltage gradually increased, the image brightened until it was clearly visible. No contrast or detail of the original was lost. The strength of the light falling on the screen had remained the same; the increase in brightness was due to energy supplied by the electric current.

The trick is done by a zinc sulphide "phosphor" (a substance that glows when light strikes it) sandwiched between two conducting films, one of them transparent. When an electric voltage is applied across the films, the phosphor takes energy from it and uses it to increase by "electroluminescence" the brightness of the light image.

The G.E. scientists warn that the new system is still young, but they suspect that it has great possibilities. One possibility: "picture-on-the-wall" television. A faint image projected by a small TV set would be amplified by electric current supplied to a flat screen. Other possibilities are in photography (taking pictures with very dim light) and in devices for "seeing in the dark."

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