population inversion

American  

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.

---

population inversion Scientific  

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.

2. See also stimulated emission

---

Etymology

Origin of population inversion

First recorded in 1960–65

Example Sentences

A population inversion is necessary for there to be a net production rather than a net absorption of the photons.

From Textbooks • Aug. 12, 2015

Helium-neon lasers often have continuous output, because the population inversion can be maintained even while lasing occurs.

From Textbooks • Aug. 12, 2015

A large percentage of the original pumping energy is dissipated in other forms, but a population inversion must be achieved.

From Textbooks • Aug. 12, 2015

A population inversion in neon is achieved, allowing lasing by the neon to occur.

From Textbooks • Aug. 12, 2015

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 Scientific American • Oct. 9, 2012