Holography is a 3-D photographic technique based on laser light.
When photographing an object in a conventional manner, one records the amplitude of lightwaves emitted by an object. When making a hologram, one records both the amplitude and phase of emitted waves, reconstructing the parallax and the object in depth.
Holograms are typically performed by laser. The laser emits a beam of coherent light :
- monochromatic (all photons have the same frequency or color)
- directional (spatial coherence)
- in phase (temporal coherence)
To record a hologram, two beams of coherent light produced by laser are interfered on a photographic emulsion (plate).
While the first beam is directed onto the plate, the second one is directed onto the object scattering the light received in the line of the holographic plate.
The intersection of two beams generates an interference pattern which contains information about the shape of the object and its position in space.
Holography - Record
The holographic plate is illuminated by laser at the same angle as the reference beam to enable the reconstruction of the hologram. The object is reconstructed in three dimensions with respect to the volume of light.
Holography - Reconstruction
Applications
Holography has a variety of applications :
Holographic imaging is used in museology (holograms of rare or fragile objects).
Embossed holograms have become popular for purposes, like advertisement, protection against any forms of manipulation (credit cards, official documents).
Holographic interferometry is used for measurement or industrial control. Conventional optics are replaced by holographic optics.
Head up display, holographic mirrors (fighter aircraft, automobile).
Information storage.
Courtesy of LSP
