Other Methods of Creating A Population Inversion
Stimulated emission was first observed in the microwave region of the electromagnetic spectrum, giving rise to the acronym MASER for Microwave Amplification by Stimulated Emission of Radiation. In the microwave region, the Boltzmann distribution of molecules among energy states is such that, at room temperature all states are populated almost equally.
To create a population inversion under these conditions, it is necessary to selectively remove some atoms or molecules from the system based on differences in properties. For instance, in a hydrogen Maser, the well-known "21cm wave" transition in atomic hydrogen, where the lone electron flips its spin state from parallel to the nuclear spin to antiparallel, can be used to create a population inversion because the parallel state has a magnetic moment and the antiparallel state does not. A strong inhomogeneous magnetic field will separate out atoms in the higher energy state from a beam of mixed state atoms. The separated population represents a population inversion which can exhibit stimulated emissions.
Read more about this topic: Population Inversion
Famous quotes containing the words methods, creating and/or population:
“The greatest part of our faults are more excusable than the methods that are commonly taken to conceal them.”
—François, Duc De La Rochefoucauld (16131680)
“There are characters which are continually creating collisions and nodes for themselves in dramas which nobody is prepared to act with them. Their susceptibilities will clash against objects that remain innocently quiet.”
—George Eliot [Mary Ann (or Marian)
“What happened at Hiroshima was not only that a scientific breakthrough ... had occurred and that a great part of the population of a city had been burned to death, but that the problem of the relation of the triumphs of modern science to the human purposes of man had been explicitly defined.”
—Archibald MacLeish (18921982)