Light and lasers
A laser - 'Light Amplification by Stimulated Emission of Radiation' - produces an intense narrow beam of light. The light from a laser is monochromatic (a single colour).
Some lasers are capable of heating materials. This makes them useful in surgery and for cutting metals and other industrial materials.
A typical laser beam might only spread out by 1 m when shone onto a surface 1 km away. As light also travels in straight lines, this makes lasers useful for guiding weapons to their targets, and for laser light shows.
The light waves have a low divergence (they spread out very little). They are coherent, which means that they are:
When light waves are in the same phase, their crests all line up, as do their troughs.
Laser beams are used to read information from CDs in CD players. The shiny surface of a CD contains billions of microscopic pits in a spiral track. The pattern of pits contains digital information. The laser light is reflected off the surface of the CD as the disk spins, and is detected by:
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