Hologram and Holography in a Nutshell

What is meant by hologram?


A hologram in simple words is a 3D (Three dimensional) picture. This picture, when properly illuminated returns a 3D image. You know that the computer monitor screen, which you are watching right now, is 2D or two dimensional. The two dimensions are (1) length or left to right, and (2) width or top to bottom. In 3D, it has an added dimension; depth or forward to backward. Cubes and books are classic examples of 3D while normal photographs and papers are representatives of 2D. 

 

hologram 2


Suppose that you are taking a photograph by keeping a small cube behind a bigger cube. It is impossible to capture the image of small cube as normal photographs are 2D. But in 3D, you will be able to capture the image of small cube too. You might have seen 3D movies wherein you are require to wear specially designed spectacles. But for viewing a hologram in 3D, no special equipment is required.


How is a hologram made? 


A traditional photograph captures information about size, shape, brightness and contrast of the object. By using unique properties of laser, the depth information is additionally captured in a hologram.  Laser light plays an important role in creation of hologram and due to this, holography was once called laser photography. 

 

hologram 1
 

Light which is responsible for sense of sight is an electromagnetic radiation visible to human eye. The white light contains seven colors. A 3D object reflects light in a complicated pattern which also is in 3D. To record this pattern, the light must be highly directional and must be of one color. Light with these features is called coherent light. Normal light being a combination of different colors of different wavelengths is not suitable for this purpose. Light from laser is monochromatic (one color) and light waves leave the laser in an orderly manner. Hence laser light is best suited for creating holograms. 
 

A hologram is printed on a set of ultra-thin curved silver plates. The hologram is actually the interference pattern of two original images. To capture the image, the laser light is split into two different beams. One beam gets reflected off of the object and reaches the silver plate while the other beam reaches directly. The two beams meet at the film causing the interference pattern of bright and dark lines. This pattern becomes the hologram. 
 

What is holography? Who are the major contributors?
 

Holography is the process of recording and play back of hologram. 
 

The first 3D images were created by Leith and Upatnieks , researchers of  University of Michigan. This was in the early 60’s following invention of laser. Around this time, Yuri Dennisyuk of erstwhile Soviet Union also succeeded in creating holograms viewable using ordinary white light. 
 

Dr. Dennis Gabor of the Imperial College of London is credited with the invention of holography. In 1971, he was awarded Nobel Prize in physics for this invention. 
 

Presently different types of holograms like reflection hologram, transmission hologram, multichannel hologram, volume hologram,  dot matrix hologram, embossed hologram, etc are in use. 
 

A type of hologram widely in use due to its capability of mass copying is rainbow hologram. This hologram finds application in credit cards to prevent counterfeiting. This was developed by Benton. 
 

What are the applications of holograms?
 

Holograms are widely used in art, science and technology. Holograms find applications on driving licenses, credit cards and even on clothing to prevent counterfeiting. Computer generated holograms enables engineers to locate defects in their products. 


•    Interferogram holography is used for testing purposes to find out defects in automobiles, artificial bones and joints, machines, equipments, aircraft tyres etc.
•    Holography cat scans support doctors in diagnosis.
•    Attractive colorful holograms are used in consumer packaging to attract attention. 
•     Holographic lenses are used to improve vision.
•    Holograms are used to depict images of people, objects, art work etc. 


As of now, holography provides most accurate depiction of 3D images. 


 John CS

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