Holography

Holography

The word holography originates from the Greek words "holos" (complete) & "graphos" (writing). Thus it is the technique to record the complete picture of an object. The technique was proposed by Dennis Gabor in 1948 for which he received Nobel prize in 1971. Holography is also called as lensless photography.

In normal photography only the intensity of light (reflected from object) is recorded but in holography the intensity of light as well as phase of light is recorded; the record is called hologram. By holography we get a 3-dimensional image.

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Holography consists of two processes –

(i) Recording of hologram.                  (ii) Reconstructing of image.

Recording of hologram 

It is based on the phenomenon of Interference. A laser beam from the laser source is incident on beam splitter. As the name suggests, the function of the beam splitter is to split the laser beam. One part of split beam, after reflection from the beam splitter strikes on the photographic plate. This beam is called reference beam. While other part of split beam strikes on the photographic plate after suffering reflection from the various points of object. This beam is called object beam. The object beam and reference beam interferes. The super position of these two beams produces an interference pattern & this pattern is recorded on the photographic plate.

Reconstruction of image

It is based on the principle of diffraction. In the reconstruction process, the hologram is illuminated by laser beam. The hologram act as a diffraction grating. The laser beam will undergo the phenomenon of diffraction during the passes through the holograms which produces real as well as virtual image of the object. 

 Rainbow holograms 

 With advancement in technology it has been possible to construct holograms that could be reconstructed using white light. Such holograms are termed as rainbow holograms. The holograms which is pasted on several products like books, debit cards, calculators etc are examples of rainbow holograms.

         If we move rainbow holograms horizontally we get 3-D image of recorded object but if we move it vertically we get different color only (VIBGYOR) instead of 3-D image which looks like rainbow that's why the name is rainbow hologram.