The simulation initializes with multiple excited atoms (orange particles) randomly colliding with each other and the inner walls of a laser cavity. A Light waves spontaneously appears to simulate the process of stimulated emission from an external energy source (not illustrated in this widget). The wave propagates back and forth through the laser cavity. The intensity increases at each pass, forming more waves, but some of the light is passed through the partially reflecting mirror (output mirror) on the right side of the laser cavity. Eventually the laser reaches an equilibrium state where the cavity is filled with oscillating waves and pumping a continuous flow of light through the mirror. Use the slider to control the speed of the simulation.