WHAT’S SO SPECIAL ABOUT COHERENT LIGHT?

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So desirable are the qualities of coherent light that the complicated filtering process described above has actually been used. For example, one British experimenter, Dennis Gabor, used it in the 1940s in an attempt to make a better microscope. But so great was the effort, and so meager the resulting light, that this project was abandoned. In the course of Dr. Gabor’s experiments, however, he did manage to make a special kind of picture, using coherent light, which he called a hologram. He derived the name from two Greek words meaning a whole picture. We shall see why in a moment. Ordinary black and white photographs merely record darks and lights, or the intensity of the illumination, thereby providing a scale of grays, nothing more. But because waves of coherent light consistently maintain their relative spacing, they can be used to record additional information, namely the distance from objects.