Definition

This is discovered by D Gabor. Holography is a technique which contains details of both amplitude and phase of light received from different parts of 3D object.

2D photography

Light reflected from an illuminated 3D object passes through a lens and a negative is made first and using it, a positive print is produced. Here the phase of light wave is not recorded. We get only a 2D picture of a 3D object. One cannot change the perspective of the image by viewing it from many angles or one cannot refocus the image.

Hologram

Here the intensities and phase of light wave (wave front construction) from a 3D object is recorded on a transparent photographic plate when viewed a 3D image is seen. This technique is called holography. The complete recording or hologram is developed, fixed and stored like ordinary photograph.

Holography  

Light is used in photography but lasers source is used in holography. This is optical recording of the object formed by the resulting interference pattern of mutually coherent component light beams. A 3D image is developed. Lens is not required during holography. Here records both intensity and phase variation.

Principle of Holography

Laser is a beam of light. When it scattered from an object allowed to superimpose on unobstructed coherent beam, interference fringes is produced in a photographic plate in front of the object. Before going to explain it we must know about constructive and destructive interference. If the superimposed light has zero phase difference constructive interference will occur, when the phase difference is 90 degree destructive interference is happened.

In holography a broad beam of laser splits into reference beam and object beam. The reference beam is directly fall on plate and object beam is illuminates the object, Part of the light scattered by the object travels towards the photographic plate. Due to Constructive interference of object beam and reference beam the intensity will increase. Where destructive interference occurs the intensity will decrease. The interference pattern shows the information about intensity and phase of scattered beam from the 3D object. The photographic plate carrying the interference pattern is called the hologram. This hologram can be reconstructed and viewed.

What we needed for Holography

  1. Sources of laser
  2. Beam splitter. An optically plane transparent plate to separate light from laser into reference beam and object beam.
  3. Mirror and lens to reflect and focus light from beam splitter.
  4. Photographic film or hologram. The amplitude and phase of the object beam is embedded in it.

Advantages of Hologram

The observer of the hologram can see the complete picture of the 3D object. All the visual properties of the original scene can be reproduced in a hologram. Every part of a hologram contains full information about the object. Several images can be recorded in a hologram.

Applications of Holography

It is influenced photography, microscopy, interferometers, acoustics etc. it is useful in medicine and technology. In microscopy hologram of moving biological specimen in a fluid can be made. Testing of materials with interferometer.