HOLOGRAMS

• Holograms are three-dimensional photographic images made with laser lights.
• The idea of holograms was suggested by Hungarian-born British physicist Dennis Gabor in 1947. The idea could not be tried until laser light became available.
• The first holograms were made by Emmet Leith and Juris Upatnieks in Michigan, USA in 1963 and by Yuri Denisyuk in the Soviet Union.
• To make a hologram, the beam from a laser light is split in two. One part of the beam is reflected off the subject onto a photographic plate. The other, called the reference beam, shines directly onto the plate.
• The interference between light waves in the reflected beam and light waves in the reference beam creates the hologram in complex microscopic stripes on the plate.
• Some holograms only show up when laser light is shone throught them.
• Some holograms work in ordinary light, such as those used in credit cards to stop counterfeiting.
• Holograms are used to detect defects in engines and aeroplanes, and forgeries in paintings by comparing two holograms made under slightly different conditions.
• Huge amounts of digital data can be stored in holograms in a crystal.
• In 1993 10,000 pages of data were stored in a lithium nobate crystal measuring just 1cm across.