Laser is an acronym for “Light Amplification by Stimulated Emission of Radiation.” A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term “laser” originated as an acronym for “light amplification by stimulated emission of radiation.”In its simplest form, a laser consists of a gain medium (the active region) and two mirrors that form an optical cavity. The gain medium is typically pumped with electrical current or light from another laser to produce population inversion, in which the number of electrons in the upper energy level exceeds the number in the lower energy level.
This condition allows spontaneous emission to occur, which produces coherent light—a beam consisting of waves with identical frequencies, amplitudes, and phases—that travels parallel to each other in phase unison. When this coherent light strikes one of the mirrors surrounding the gain medium, it reflects back into the cavity and passes throught the gain medium again; this process is known as resonant feedback.