population inversion

noun

Physics.

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.

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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Word History and Origins

Origin of population inversion¹

First recorded in 1960–65

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Example Sentences

Examples have not been reviewed.

Working to enable the precursor of the laser — the maser — he found a practical way to generate a population inversion, an unusual situation in which more members of a physical system exist at a higher energy level than at a lower one.

From

Population inversion is a prerequisite for lasers, and Bloembergen's scheme, three-level pumping, enabled the development and widespread adoption of the laser.

From

Lasers ordinarily require a population inversion, a condition in which atoms in an excited state outnumber those in the ground state; the excited atoms emit laser photons as they drop to the ground state.

From

population genetics population parameter

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