Question

What is holography? Differentiate between holography and photography.

Answer 1

1. 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 photography represents a two dimensional recording of three dimensional scene.
2. The emulsion of the photographic plate is sensitive to only 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.
3. The principal behind holography is “During the recording process one superimposes on the scattered wave another coherent wave of same wavelength.”
4. These two waves interfere in the plane of the recording medium and produce interference fringes. This is known s recording process. The interference fringes characteristic of light of object is formed. The recording medium records the intensity distribution in the interference pattern.
5. The interference pattern is recorded in it not only the amplitude distribution but also the phase of the electromagnetic waves scattered from the object. Since the recorded intensity pattern has both the amplitude and the phase recorded in it has been called “HOLOGRAM”.
6. The hologram has little resemblance to the object. It has in it a coded form of a wavefront. The reproduction the image is known as reconstruction in which a wave identical to the one used as reference wave is used.
7. When hologram is illuminated by the reconstruction wave, two waves are produced. One wave appeared 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.