A hologram is like a three-dimensional photograph. Photographs show only two dimensions: height and width. Holograms show three dimensions: height, width, and depth. By moving from side to side, a viewer can see the front and the sides of an object shown in a hologram. The process of making holograms is called holography.

How holograms are made and viewed

Holograms are created with lasers. A single beam of light from a laser is split into two beams by a special mirror. One of the beams shines onto a piece of photographic film. This beam is called the reference beam. The second beam shines on the object to be holographed. The light from this beam reflects off the object onto the film. This beam is called the object beam. The reference beam and the object beam overlap and create a pattern of lines on the film. The pattern does not look like the object, but it contains a record of what the object looks like.

To view the hologram, the film must first be developed. Then a laser is used to light up the film. The laser light makes the pattern on the film appear as a three-dimensional image of the original object.

Uses

Holograms have many uses. Architects can use holograms to see how their designs will look in three dimensions. Doctors can study holograms of a patient's body before performing surgery. Museums can make holograms of artifacts that are too valuable or too fragile to handle.

Because holograms are difficult to copy, they help to prevent people from making illegal copies of important cards and documents. Holograms are commonly found on credit cards, driver's licenses, and paper money.

History

Dennis Gabor, a Hungarian scientist, invented holography in 1948. Early holograms were very small and difficult to see. The light sources available at the time were not strong enough to produce a quality image. The invention of lasers in the 1960s allowed holograms to become larger and brighter. Gabor won a Nobel prize in 1971 for his invention of holography.