holography

Holography is a technique that records and reconstructs the light field scattered from an object to produce a three-dimensional image, or hologram. Unlike ordinary photography, which records only intensity, holography captures both amplitude and phase information of light, enabling the reconstruction of near-true light waves when the hologram is illuminated by a reference beam.

Principle and process: Holography typically uses a coherent light source such as a laser. The object is illuminated, and the light scattered from it interferes with a reference beam on a photosensitive recording medium. The resulting interference pattern stores the phase and amplitude information. When later illuminated with light similar to the reference beam, the hologram diffracts light to recreate the original wavefront, producing a three-dimensional image with parallax and depth cues.

History: Holography was invented by Dennis Gabor in 1947 as a method to improve electron microscopy; practical realizations required lasers and were developed in the 1960s by researchers including Emmett Leith and Juris Upatnieks. Since then, holography has diversified into numerous recording materials and digital techniques.

Techniques and formats: Transmission holograms are viewed with a transmitted beam, while reflection holograms are viewed with light reflecting off the hologram. Off-axis and in-line geometries describe how the reference beam is arranged. Digital holography records holograms with electronic sensors and reconstructs them numerically. Holographic interferometry uses holographic methods to measure small deformations and displacements.

Applications: Uses include holographic data storage, security and anti-counterfeiting holograms, three-dimensional displays and virtual imaging, optical metrology and microscopy, and art. Digital holography enables quantitative phase imaging and flexible post-processing.