Laser stands for "light amplification by stimulated emission of radiation". Aside from the cutting applications of lasers, they are used for joining, heat treating, inspection, and free form manufacturing. Laser cutting differs from other laser machining processes since it requires higher power densities but shorter interaction times.
Lasers are generated by a high-intensity light source inside a reflective laser cavity, that contains a laser rod that generates the radiation. The light source stimulates the laser rod's atoms as they absorb wavelengths of light from the light source. Light is composed of small bundles of photons that strike the lasting media atoms energizes them. The photon's energized atoms, give off two more photons with the same wavelength, direction, and phase, called stimulated emission. The new photons stimulate other energized atoms producing more photons, causing a cascade of excitations.
The photons move perpendicular to parallel mirrors located on the ends of the laser rod but stay within the laser rod. One mirror is transmissive, enabling the partial escape of light from the cavity. This escaping stream of coherent, monochromatic light is the laser beam used to cut the material. Another set of mirrors or fiber-optics direct light into a lens that focuses the light into the material.
The three main types of lasers used for cutting, are CO₂, Nd-YAG (Neodymium Yttrium-Aluminum-Garnet) lasers, and fiber-optic lasers. They differ in the materials used to generate the laser beam.