Population inversion

Definition

Population inversion occurs when more atoms or molecules in a system are in an excited state than in the ground state. This condition is essential for the operation of lasers.

5 Must Know Facts For Your Next Test

1. Population inversion is a prerequisite for laser action.
2. Achieving population inversion requires an external energy source, such as optical pumping or electrical discharge.
3. In a three-level laser system, population inversion occurs between the second and third energy levels.
4. In a four-level laser system, the fourth level quickly depopulates to help maintain population inversion.
5. Population inversion can be described mathematically using the Boltzmann distribution.

Review Questions

• Why is population inversion necessary for laser operation?
• What methods can be used to achieve population inversion?
• How does a four-level laser system differ from a three-level system in terms of maintaining population inversion?

Related terms

Laser: A device that emits light through optical amplification based on the stimulated emission of electromagnetic radiation.

Stimulated Emission: The process by which an incoming photon causes an excited atom or molecule to drop to a lower energy state, releasing a photon identical to the incoming one.

Optical Pumping: A method used to achieve population inversion by using light (photons) to raise electrons from a lower energy level to a higher one.