Holography

Holography is the process by which three-dimensional visual information is recorded on a high contrast, very fine grain film. A hologram refers to the flat “picture” that displays a multi-dimensional image under proper illumination. Unlike a photograph, a holographic image has “parallax” (the ability to see a scene from many angles) and depth to give the image a real life quality. And, unlike a regular photograph, a hologram records the image’s diffraction pattern, not the actual image. This is achieved by creating an interference pattern between two wavelengths of light that are in phase. The object that is being recorded must by illuminated by a coherent light source such as a laser.

The quality of a hologram is dependent upon numerous factors including exposure time, laser linewidth, frequency stability, power stability and pointing stability. Minimizing the exposure time is generally desirable since this reduces the effects of the environment
(e.g., vibration). Ample illumination power is a good solution. Narrow laser linewidths/long coherence lengths are essential when there are large pathlength differences. Variation in the laser frequency during holographic recording shifts the interference pattern and smears the hologram. The need for power and pointing stability is obvious.

Holography is also used as a tool in the medical, semiconductor and photonics industries.