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LASERS (Light Amplification by Stimulated Emission of Radiation): Any
of several devices that emit highly amplified and coherent radiation
of one or more discrete frequencies. One of the most common lasers
makes use of atoms in a metastable energy state that, as they decay to
a lower energy level, stimulate others to decay, resulting in a
cascade of emitted radiation.
[Source: The American Heritage® Dictionary of the English Language,
Fourth Edition]
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