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What is difference between photography and holography? Explain holography technique to obtain 3-D image of an object.
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HOLOGRAPHY

• Holography is a technique of producing 3D images.
• In Holography, both intensity and phase of light waves are recorded.

PHOTOGRAPHY

• Photography is a technique of producing 2D image.
• In a photography, only intensity of light waves are recorded

TECHNIQUE TO OBTAIN 3D IMAGE USING HOLOGRAPHY TECHNIQUES.

• The advent of lasers has made the art of holography possible. Photography can be thought of as a new approach to the problem of generating images. An ordinary photograph represents a two dimensional recording of a three dimensional scene. The emulsion on the photographic plate is sensitive only to intensity variations. In this process the phase information carried by the electromagnetic wave scattered from the object is lost. Since only the intensity pattern is recorded, the 3D character of the object is lost.

• The principle behind the holograph is “During the recording process one superimposes on the scattered wave (emanating from the object) another coherent wave (called reference beam) of the same wavelength”. These two waves interfere in the plane of the recording medium and produce interference fringes. This is known as recording process.

• The interference fringes-characteristic of the object is formed. The recording medium records the intensity distribution in the interference pattern. This interference pattern has recorded in it not only the amplitude distribution but also the phase of the electromagnetic wave scattered from the object. Since the recorded intensity pattern has both the amplitude and phase recorded in it has been called “hologram” (Holos in Greek means whole).

• The holograms have little resemblance to the object. It has in it a coded form of a wavefront. The reproduction of the image is known as reconstruction in which a wave identical to the one used as reference wave is used. When hologram is illuminated by the reconstruction wave, two waves are produced. One wave appears to diverge from the object and provides the virtual image of the object. The second wave converges to form a second image which is real.