Photons are emitted. Light waves bounce back and forth between the mirrors on the resonator. Output mirror reflects part of the light and outputs the rest. Gas Lasers Collision of atoms results in a resonant collision. Excited and unexcited atoms collide.
Population inversion occurs, and amplification results.
Schematic of a CW Gas Laser . D Semiconductor Lasers Electric current passing through the diode produces light emission. Electrons and holes combine at the p-n junction. Schematic of a Semiconductor Laser D Dye Lasers Liquid laser that consists of an organic dye molecule dissolved in a solvent. Dye is excited by a flashlamp or other laser.