Chumbak [CPS] IN

Thursday, April 16, 2020

HOLOGRAPHY

Hologram


A hologram is a physical recording of an interference pattern which uses diffraction to reproduce a three-dimensional light field, resulting in an image which retains the depth, parallax, and other properties of the original scene. Holography is the science and practice of making holograms. A hologram is a photographic recording of a light field rather than an image formed by a lens. The holographic medium, i.e., the object produced by a holographic process (which itself may be referred to as a hologram) is usually unintelligible when viewed under diffuse ambient light. It is an encoding of the light field as an interference pattern of variations in the opacity, density or surface profile of the photographic medium. When suitably lit, the interference pattern diffracts the light into an accurate reproduction of the original light field, and the objects that were in it exhibit visual depth cues such as parallax and perspective that change realistically with the relative position of the observer. That is, the view of the image from different angles represents the subject viewed from similar angles. In this sense, holograms do not simply produce the illusion of depth but are truly three-dimensional images.


In its pure form, holography requires the use of laser light for illuminating the subject and for viewing the finished hologram. A microscopic level of detail throughout the recorded scene can be reproduced. In common practice, however, major image quality compromises are made to eliminate the need for laser illumination to view the hologram, and in some cases, to make it. Holographic portraiture often resorts to a non-holographic intermediate imaging procedure, to avoid the hazardous high-powered pulsed lasers otherwise needed to optically "freeze" moving subjects as perfectly as the extremely motion-intolerant holographic recording process requires. Holograms can now also be entirely computer-generated to show objects or scenes that never existed.

Process

When the two laser beams reach the recording medium, their light waves intersect and interfere with each other. It is this interference pattern that is imprinted on the recording medium. The pattern itself is seemingly random, as it represents the way in which the scene's light interfered with the original light source  but not the original light source itself. 
The interference pattern can be considered an encoded version of the scene, requiring a particular key  the original light source  in order to view its contents.
This missing key is provided later by shining a laser, identical to the one used to record the hologram, onto the developed film. When this beam illuminates the hologram, it is diffracted by the hologram's surface pattern. This produces a light field identical to the one originally produced by the scene and scattered onto the hologram.

Items required

To make a hologram, the following are required:
  • An object
  • Part of the laser beam to be directed so that it illuminates the object (the object beam) and another part so that it illuminates the recording medium directly (the reference beam), enabling the reference beam and the light which is scattered from the object onto the recording medium to form an interference pattern
  • A recording medium which converts this interference pattern into an optical element which modifies either the amplitude or the phase of an incident light beam according to the intensity of the interference pattern.
  • A laser beam that produces coherent light with one wavelength.
  • An environment which provides sufficient mechanical and thermal stability that the interference pattern is stable during the time in which the interference pattern is recorded

Applications

  1. Art
    German Circus using Holography
  2. Data Storage
  3. Dynamic Holography
  4. Holographic Interferometry
  5. Interferometric microscopy
  6. Sensors or Biosensors
  7. Security
  8. Electrical & Electronic Products
  9. Credit Cards
  10. Entertainment




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