Holography, << huh LAWG ruh fee, >> is a method for storing and displaying a three-dimensional image, usually on a photographic plate or another light-sensitive material. The exposed plate is called a hologram. Some credit cards contain holograms to prevent counterfeiting. In addition, holograms appear in advertising displays, in artwork, and in jewelry. Holography may be used to detect flaws in tires, lenses, airplane wings, and other products.
Holography involves two basic steps: (1) creating a hologram and (2) illuminating the hologram to display the image. During the first step, a beam of laser light is reflected off a subject and onto a light-sensitive material, such as a photographic plate. Another laser beam, called the reference beam, also shines on the plate. Where these two light beams cross on the plate, they make a complex, microscopic pattern of bright and dark stripes (see Interference ). In the second step, a light beam traveling in the same direction as did the reference beam illuminates the hologram. The hologram changes the direction of light waves in this beam so that the waves appear to come from the original illuminated subject. The resulting three-dimensional image seems to hover in space. Illuminating the hologram with white light, such as sunlight, produces an image containing rainbowlike bands of color. Using a beam of a single color, such as a laser beam, avoids this effect.
Dennis Gabor, a Hungarian-born engineer, invented holography in 1947. For this work, Gabor won the 1971 Nobel Prize in physics.
