[Illustration: _Nothing about lasers is more astonishing than their ability to produce holograms, under arrangements such as shown above. Two laser beams (of different colors) emerge from the curtain (rear). They are optically combined (left center) and the combined beam is then divided by prisms, mirrors and lenses so that part of it shines on the figurines (foreground) and part on the square holographic plate (right center). When the plate is developed (like an ordinary photographic film), it will seem to have only a dull gray surface until it is viewed with spatially coherent light (such as from a laser or a beam through a pinhole) shining through it. Then an amazing, multi-colored, three-dimensional image of the figurines will be visible. (See page 19 and Figure 13.)_] [Illustration: LASERS] By HAL HELLMAN INTRODUCTION The transistor burst upon the electronic scene in the 1950s. Almost overnight the size of new models of radios, television sets, and a host of other electronic devices shrank like deflating balloons. Suddenly the hard-of-hearing could carry their sound amplifiers in their ears. Teenagers could listen to favorite music wherever they went. Everywhere we turned the transistor was making its mark. There was even a proposal before Congress to require that every home have a transistor radio in case of emergency. The next development to fire the imagination of scientists and engineers was the laser—an instrument that produces an enormously intense pencil-thin beam of light. Most of us have heard so much about this invention it seems hard to believe that the first one was built only a few years ago. We were told that the laser was going to have an even greater effect on our lives than the transistor. It was going to replace everything from dentists’ drills to electric wires. The whole world, it seemed, eventually would be nothing but a gigantic collection of lasers that would do everything anyone wanted. Roads would be blazed through jungles at one sweep; our country would be safe once and for all from intercontinental ballistic missiles; cancer would be licked; computers would be small enough to carry in a purse; and so on and on. Yet for the first couple of years the laser seemed able to do nothing but blaze holes in razor blades for TV commercials. Somehow the device never seemed to emerge from the laboratory, prompting one cynic to call it “an invention in search of an application”.