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Lasers generate coherent light by amplifying light through stimulated emission in an excited gain medium.
A laser is a device that emits light through optical amplification based on stimulated emission of electromagnetic radiation. The term “laser” comes from “light amplification by stimulated emission of radiation.” Unlike ordinary light sources, lasers produce coherent light, which allows beams to be tightly focused, remain narrow over long distances, and have well-defined temporal and spectral properties. The optical amplification principle relies on exciting a gain medium so that it achieves population inversion (more particles in an excited state than in a lower-energy state). When a photon with the right energy passes through the medium, it can trigger stimulated emission: the medium emits a new photon that matches the incoming photon in wavelength, phase, and polarization direction. With sufficient pumping and an optical resonator (feedback via mirrors), stimulated emission repeats many times, causing the light intensity to grow until cavity losses and gain saturation balance. The minimum pump power needed to start sustained laser action is the lasing threshold.
Lasers generate coherent light by amplifying light through stimulated emission in an excited gain medium.
Population inversion in the gain medium enables stimulated emission to exceed absorption, producing net gain.
An optical cavity provides feedback so photons pass through the gain medium repeatedly, leading to exponential growth until gain saturation and cavity losses balance.
Laser action requires pumping above a lasing threshold; below it, gain cannot overcome resonator losses.
A device that emits light via optical amplification based on stimulated emission, producing coherent output.
The increase in optical power as light passes through a gain medium where stimulated emission dominates over absorption.
A process where an incoming photon triggers an excited atom or molecule to emit a second photon matching the original photon’s wavelength, phase, and polarization direction.
The material (gas, liquid, solid, or plasma) whose excited states allow stimulated emission to amplify passing light.
A condition where more particles occupy an excited energy state than a lower-energy state, enabling net amplification.
A feedback structure (typically mirrors) that causes light to circulate through the gain medium so one frequency and spatial mode dominate.
The minimum pump power required for the gain to overcome cavity losses and produce sustained laser output.
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