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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 pai...
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PLASTICS

Plastics are synthetic (man-made) materials that can be easily shaped and moulded. Most plastics are polymers . The structure of polymer molecules gives plastic different properties. Long chains of molecules that slide over each other easily make flexible plastics such as polythene. Tangled chains make rigid plastics such as melamine. Typically plastics are made by joining carbon and hydrogen atoms. These form ethane molecules, which can be joined to make a plastic called polythene. Many plastics are made from liquids and gases that are extracted from crude oil. Thermoplastics are soft and easily moulded when warm but set solid when cool. They are used to make bottles and drainpipes and can be melted again. Thermoset plastics , which cannot be re-melted once set, are used to make telephones and pan handles. Blow moulding involves using compressed air to push a tube of plastic into a mould. Vacuum moulding involves using a vacuum to suck a sheet of plastic into a mould. Extrusion...
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LASERS

Laser light is a bright artificial light. It creates an intense beam that can punch a hole in steel. A laser beam is so straight and narrow that it can hit a mirror on the Moon. The name ' LASER ' stands for L ight A mplification by S timulated E mission of R adiation. Laser light is even brighter for its size than the Sun. Laser light is the only known 'coherent' source of light. This means the light waves are not only all the same wavelength (colour), but they are also perfectly in step. Inside a laser is a tube filled with gases, such as helium and neon, and a liquid or solid crystal such as ruby. Lasers work by bouncing photons (bursts of light) up and down the tube until they are all travelling together. Lasing begins when a spark excites atoms in the lasing material. The excited atoms emit photons. When the photons hit other atoms, they fire off photons too. Identical photons bounce backwards and forwards between mirrors at either end of the laser. Gas lasers...
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