An acronym of Light Amplification by Stimulated Emission of Radiation. A laser is a cavity that has mirrors at the ends and is filled with lasable material such as crystal, glass, liquid, gas, or dye. These materials must have atoms, ions, or molecules capable of being excited to a metastable state by light, electric discharge, or other stimulus. The transition from this metastable state back to the normal ground state is accompanied by the emission of photons which form a coherent beam.

The hardware and options available for lasers, such as secondary gases, Brewster windows, Q-switches, and electronic shutters.

An indication of the beam hazard level of a laser or laser system during normal operation or the determination (typically established by its AEL) thereof.
Laser Classifications are cited in Accessible Emission Limit (AEL).

Laser-beam traversal of metal to harden quenching process producing the maximum hardness for most metals.

The buildup of the coherent wave between laser cavity end mirrors. In CW mode, the wave bounding back and forth between mirrors transmits a fraction of its energy on each trip; in pulsed operation, emission happens instantaneously.