What is hologram?

A hologram is a pattern recorded on a photographic plate or film using laser illumination without the use of a lens. The method used for producing a hologram is called ‘holography’. It was invented by Denis Gabor in 1948. The method consists of two steps. In the first step, a hologram is produced and in the second step, a three-dimensional image of the original scene is re-created from it. A system of mirrors is employed to split a laser beam into two. One beam illuminates the object or scene to be made into a hologram and then the scattered beam falls on the photographic film or plate. The other ‘reference’ beams falls on the film or plate directly. But before these two beams strike the film or plate, they interfere with each other and form a complex pattern of light and dark areas which gets recorded on the film or plate. This is the hologram of the object or scene.

To reproduce the scene in three dimensions, a laser beam is directed at the hologram in the same direction as the original reference beam. Even a portion of the hologram can reproduce the entire original reference scene, though with diminished details. Techniques are now available for producing holograms which can be seen in white light. Holography finds applications in industry and research. For instance, it is employed to check flaws in aircraft wings, tyres, and lenses. Holograms are also being used on valuable documents such as Voter’s identity cards and credit cards as an anti-forgery measure.