A hologram is a type of three-dimensional image that gives the appearance as a real object as the image has depth. The best way to think of a hologram is to visualize them as impressions on light waves. The patterns of light wave impressions are photographed or captured in the layer of emulsion. In other words, a hologram is an image or photograph of light wave interference. It is to be noted that not all 3D images are holograms and neither a hologram is required to be 3D. In technical terms, a hologram is the captured intensity and phase information which is produced by the interference or interconnection of two or more beams of light. People often consider a hologram as some type of a three-dimensional photograph. However, the only thing common between photography and holography is the use of a photographic film. The important difference is the way the image is produced in both the cases. A photographic image is produced by a camera lens and it is described almost accurately using a simple geometric or ray model for the behavior of light. On the other hand, the holographic image is formed depending on diffraction and interference, which are wave phenomena.

Types of Hologram

Let us now discuss in details the various types of holograms produced under different processes and methods. These holograms are:

• Reflection Hologram: It forms an image by reflected light. Click here to know more ....
  
  
• Transmission Hologram: It forms an image from the light that passes through the holographic emulsion. Click here to know more ....
  
  
• Embossed Holograms: The most commonly used hologram. Click here to know more ....
  
  
• Integral Hologram: A type of hologram formed from series of photographs of an object. Click here to know more ....
  
  
• Rainbow Holograms: A popular type of hologram, viewed in white light. Click here to know more ....
  
  
• Computer Generated Holograms: Computers are used to create images and patterns for developing holograms. Click here to know more ....
  
  
• Multiplex Hologram: It is a type of hologram produced by combining a large number of photographs. Click here to know more ....
  
  
• Stereogram: An optical illusion of depth created from flat, two-dimensional image. Click here to know more ....
  
  
• Volume Holograms: A hologram in which the angle difference between the object beam and reference beam is greater than 90 degrees. Click here to know more ....
  
  
• Plane Holograms: A hologram in which the angle difference between the object beam and reference beam is less than 90 degrees. Click here to know more ....

Properties of Holograms

Holograms have some very interesting properties such as follows:

• Distributed information: The information in a hologram is always distributed. If it is cut into pieces, each piece contains enough information to reconstruct the entire scene.
  
  
• Image projection: Under certain cases, merely shining or lighting a laser through the hologram projects an image on to a screen.
  
  
• Viewing directly with a point source: A hologram reconstruction shows exactly the same light wavefronts to our eyes that we receive with the real object, using a point source of illumination. The hologram is not distinguished from the physical object.

Hologram: Application

Holography and hologram products are now widely used in various applications. One of the most common application of holography is in security maintenance. Spreading from the research laboratory to industry, holography today finds wider employment in communication and various engineering problems. It is used in computer technology to store numerous quantities of information. Another important application area is bar-code readers in shops, warehouses, libraries etc. Holograms are today considered as the best promotional media. Every type of industry can use the Holographic products to enhance their brands in the market and make them genuine and authenticated brands. Holograms are used for attractive product packaging, security applications, fancy gifts, 3-D art etc. New technology aircraft, automobiles, etc. also make use of holograms.

How is a hologram made?

A laser beam is divided into two beams: The reference beam and the object beam.


Using a lens or curved mirror, the width of the reference beam is increased conically and aimed directly at the film plate. The width of the object beam is also increased and aimed at the object which reflects some of the light on the holographic film-plate. The two beams form an interference pattern on the film by crossing each other. This leads to the forming of the hologram. To create a hologram, laser light is needed because it is made of coherent waves.

Projection of a hologram and types of hologram-A diagrammatic representation