Difference beween holography and photography

Last time I have discussed about the holography and written that it is a two stage process. The first stage is recording of hologram in the form of interference pattern and in the second stage, the hologram acts as a diffraction grating for the reconstruction beam and the image of the object is reconstructed for the  hologram.

Do you know what is the difference between hologram and photograph? If no, then let us discuss:

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Recording and reconstruction process in holography

Last time I have discussed the basic definition of holography and hologram. Today I will discuss the process with the help of which hologram is formed or complete picture is recorded:

1. Recording of the hologram.

The recording of hologram  is based on the  phenomenon of interference.  It requires a laser source, a plane  mirror or beam splitter, an object and a photographic plate. A laser beam from the laser source is incident on a plane mirror or beam splitter. As the name suggests, the function of the beam splitter is to split the laser beam. One part of splitted beam, after reflection from the beam splitter, strikes on the photographic plate. This  beam is called reference beam. While other part of splitted beam  (transmitted from beam splitter) strikes on the photographic plate after suffering reflection from the various points of object. This beam is  called object beam.

The object beam reflected from the object interferes with the reference beam when both the beams reach the photographic plate. The superposition of these two beams produces an interference pattern (in the form of dark and bright fringes) and this pattern is recorded on the photographic plate. The photographic plate with a recorded interference pattern is called a hologram. The photographic plate is also known as the Gabor zone plate in honor of Denis Gabor who developed the phenomenon of holography.

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Holography

The word holography originates from the Greek  words “holos” (complete) and “graphos” (writing). Thus, it is the technique to record the complete picture of an object. The technique was  proposed by Gabor in 1947.

An ordinary photograph records the two dimensional image of the picture because it records only the amplitude or intensity distribution. But in holography technique, both, the intensity as well as phase of the light wave is recorded.

In holography, the light  waves reflected from an object is  recorded. These light  waves  consist of intensity and phase  and the record is called a hologram. The hologram has no resemblance to the original object but it contains all the information about the object in a optical  code. Continue reading “Holography”

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