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population inversion

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noun Physics.
  1. a condition of matter in which more electrons are in a high energy state than in a lower energy state, as is required for the operation of a laser.
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Origin of population inversion

First recorded in 1960–65
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

population inversion in Science

population inversion

  1. The condition of having enough excited or high-energy states distributed throughout a substance to sustain a chain-reaction of stimulated emission. Lasers, for example, need a constant power source that maintains population inversion in order to generate radiation continuously, since each stimulated emission reduces the population of high-energy states. See also stimulated emission.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.