• Hologrambusiness presentation image by robert fori from Fotolia.com
  
  A hologram is a photograph or image of light wave interference. Because holograms are images with depth, they have the appearance of being real objects. A photograph or layer of emulsion captures the patterns of holographic light wave impressions. This article discusses the most commonly created types of holograms.
  
  

Laser Transmission

• A laser transmission hologram results when light from an object and reference beam interfere from the same side of the recording medium. Illuminated from the rear by laser light, these holograms bend the light passing through. Images of laser transmission holograms are sharp and the color of the illuminating laser.
  
  

Reflection

• Illuminated from the front, reflection holograms result from a point source of white incandescent light reflecting off the hologram to the viewer. Reflection holograms find applications in sunglasses and safety vests. Images with different characteristics result from the use of different film emulsions.
  
  

Transfer

• Using a holographic image from a "master" hologram as the object of another hologram creates a transfer hologram. Objects can appear to be in front of, behind or in the plane of the hologram.
  
  

Rainbow

• A rainbow hologram, viewed in incandescent light, displays 3-D images. It is a transfer transmission hologram, or a hologram of a hologram. A narrow horizontal slit masks the "master" hologram. The rainbow hologram distributes wavelengths of white light in all directions. As a result, the viewer sees only one wavelength. As the viewing angle changes, the color of the hologram changes. VISA cards, for example, have rainbow holograms in their logos.
  
  

Integral

• Creatives use a series of photographs to produce an integral hologram. Different shapes are possible for integral holograms. Displays can be flat, curved or cylindrical. Videos, technical presentations and scientific research may use integral holograms. Because each eye sees images from different narrow holograms, the resulting composite hologram is stereoscopic. A motion picture camera captures the images and a laser transfers them to holographic film.
  
  

Multiplex

• A multiplex hologram displays the optical illusion of depth created from 2-D images. It combines a large number of photographs onto a single hologram. Using these holograms, creatives can convert photographed objects into 3-D objects in motion. Viewers see the 3-D image in a slowly turning transparent cylinder. Multiplex holograms consist of a vast array of flat pictures of an object viewed from different angles. A composite 3-D multiplex hologram is the final product.
  
  

Animated

• Animated holograms use time-lapse photography in which the subject moves between exposures. Creatives transfer the time-lapse photos to a hologram through vertical slits. Tilting the hologram makes its subject appear to move.
  
  

Pseudocolor

• Puffing or swelling the photographic emulsion prior to photographic exposure creates pseudocolor holograms. Image color depends on the degree of swelling. When the swelling of the emulsion changes, the color changes as well, producing multiple colors within the image.
  
  

Computer Generated

• Computer users scan, design, enhance and create patterns and images for 2-D and 3-D holograms. These computer-generated holograms often depict objects that cannot exist in the real world. Employing computer-generated holography, manufacturers produce optical elements for scanning, splitting, focusing and controlling laser light in machines such as CD players.
  
  

Volume

• Spectroscopy, imaging and high-density data storage employ volume holograms, also known as "thick" holograms. The difference between their reference and object beams varies from 90 to 180 degrees. Recording the interference pattern of the two light beams creates 3-D volume holograms.
  
  

Plane

• A plane hologram is a transmission hologram in which the angle of difference between object and reference beams is less than 90 degrees. Most of the holographic information is within the 2-D plane of the emulsion. Because of their thin emulsions, plane holograms are also known as "thin" holograms. Plane holograms have uses in packaging.
  
  

Embossed

• Security applications use embossed holograms, which are difficult to counterfeit. Creation of a metal replica of a "master" hologram enables relief pattern printing onto plastic. Most passports and credit cards have an embossed hologram. Mass production of embossed holograms is inexpensive.