Understanding Laser Principles and Applications

Laser terminology and related terms

Laser terminology covers the vocabulary used to describe how lasers work and how different laser devices are classified. The word “laser” originated as an acronym for “light amplification by stimulated emission of radiation.” The related earlier device is the “maser” (microwave amplification by stimulated emission of radiation), and devices operating at microwave or lower radio frequencies are generally called masers, while higher-frequency devices are called lasers. In practice, the field also uses verbs such as “to lase” (to give off coherent light) and “lasing” (when a laser is operating). The terms laser and maser are also used for naturally occurring coherent emissions, such as astrophysical masers and atom lasers. Key related concepts include coherence (spatial and temporal), which distinguishes laser light from incoherent sources and enables tight focusing, narrow beams over distance, and narrow frequency spectra. Fundamental processes use “stimulated emission,” where an incoming photon triggers an excited atom or molecule to emit an identical photon (matching wavelength, phase, and polarization), enabling amplification and a chain reaction when many particles are in suitable excited states (often described via “population inversion” and an “active laser medium”). Laser design terminology commonly refers to the “gain medium,” “pumping” (energy supplied to excite the medium), and “optical cavity” or “resonator” (feedback elements such as mirrors), along with the “output coupler” and the “lasing threshold” (minimum pump power needed for laser action).

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Coherence as the defining laser property

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