Basic_Terms_in_Holography

2.2 Basic Terms in Holography

The prospective method of optical information recording, the so-called holography is the total recording about a wave, i.e. the recording of its amplitude and phase. It practically means that with the aid of holography it is possible to record solid objects reflecting the light as well as solid transparent objects three-dimensionally, in contrast to the photography or cine-camera recordings that are able to record the three-dimensional objects only two-dimensionally. Optical holography is based on the interference of coherent light.

Holography is not to be understood in terms of the geometric optics where the light is manipulated as if it were composed of discreet elements (photons). Holography requires the light to be regarded as a wave motion. During the reflection and refraction of the light a camera uses the light′s intensity, but not its phase. To display the objects on the holography principle the wave character of light is applied. This method does not need lenses but its essential condition is that the object must be illuminated by coherent beam whose individual parts have time-constant phase difference. The incident light is dispersed on the surface of the object and, if incident on the photographic plate it causes the blackening in the emulsion corresponding to the resultant amplitude of light vibrations in the relevant location. The final amplitude is the result of beam activity dispersed on all points of the body that interfere in consequence of the "ideal" coherence. Such record on the photographic plate gives information about intensity and phase of the beams dispersed all over the body (Ennos, Virdee, 1982).