Gain Medium

A laser is a coherent and highly directional radiation source. LASER stands for "Light Amplification by Stimulated Emission of Radiation".


A laser consists of at least three components:

  1. A gain medium that can amplify light that passes through it.
  2. An energy pump source to create a population inversion in the gain medium.
  3. Two mirrors that form a resonator cavity.

The gain medium can be solid, liquid, or gas and the pump source can be an electrical discharge, a flashlamp, or another laser. The specific components of a laser vary depending on the gain medium and whether the laser is operated continuously (cw) or pulsed. Einstein A and B coefficients used to describe optical transitions and the rate equations are used to describe the dynamics of lasers, avoiding esoteric quantum calculations.

Please select one of the Applets below for Gain Medium:

Einstein A & B Coefficients Gain Mechanism:
Photons Emission and Absorption Energy System Applet
2-Level Gain Medium
  3-Level Gain Medium
  4-Level Gain Medium