Creating A Population Inversion
As described above, a population inversion is required for laser operation, but cannot be achieved in our theoretical group of atoms with two energy-levels when they are in thermal equilibrium. In fact, any method by which the atoms are directly and continuously excited from the ground state to the excited state (such as optical absorption) will eventually reach equilibrium with the de-exciting processes of spontaneous and stimulated emission. At best, an equal population of the two states, N1 = N2 = N/2, can be achieved, resulting in optical transparency but no net optical gain.
Read more about this topic: Population Inversion
Famous quotes containing the words creating a, creating and/or population:
“If the child knows the rewards and punishments in advance and knows that his parents will stick to them, the parents can actually empathize with the child’s plight while, at the same time, creating a firm sense of structure.... Your child will sense your resolve and your empathywhether you do this with words or just a sense of warmth.”
—Stanley I. Greenspan (20th century)
“The principle goal of education in the schools should be creating men and women who are capable of doing new things, not simply repeating what other generations have done; men and women who are creative, inventive and discoverers, who can be critical and verify, and not accept, everything they are offered.”
—Jean Piaget (1896–1980)
“I think that cars today are almost the exact equivalent of the great Gothic cathedrals: I mean the supreme creation of an era, conceived with passion by unknown artists, and consumed in image if not in usage by a whole population which appropriates them as a purely magical object.”
—Roland Barthes (1915–1980)