Holography

Photography is the process of recording illuminated three dimensional objects in a two dimensional light sensitive surface, called photographic film. the light reflected by the objects in the scene are focused onto the surface of the film by suitable image forming devices, which can be a simple lens or a combination of lenses. The film simply records the amplitude of light reflected by the object. Hence we cannot record the depth of the object in photography and the basic technique remains unchanged even today.

A different technique of recording an object with its three dimensional image is developed by Dennis Gabor, a British scientist in 1948. This technique is known as holography., a term derived from greek words holos and graphs. The technique assumed practical proposition and really demonstrated us potential only after invention of laser in 1960.

Basic principle

Holography is based on principles of recording amplitude and phase of light scattered from different points of object. The phase recording helps to record depth of the object. This is achieved in a unique way by recording the interference pattern produced by light waves scattered by the object with the light waves from parent source. The recorded interference pattern as known as hologram. The three dimensional image is recreated by wavefronts reconstruction method that is by diffraction grating method. The need for highly coherent light source to produce stable interference pattern delayed the practical development of optical holography till advent of laser.