Knowra Helium–neon laser Helium–neon laser A gas laser in which an electrical discharge excites helium atoms that transfer energy to neon atoms, producing coherent light. Its best-known output is red light at 632.8 nanometers.
Population inversion : A condition in which more particles occupy an excited energy state than a lower one, enabling optical amplification. The discharge and helium-to-neon transfer create the excited neon population needed for laser gain.
Gas discharge : An electrical current carried through an ionized gas by electrons and ions. The discharge supplies energetic electrons that excite helium atoms in the laser tube.
Laser interferometry : Measurement methods that use interference between coherent light beams to detect changes in distance, motion, or optical path. The stable wavelength supports precise fringe-based measurements.
Ruby laser : A solid-state laser that uses chromium-doped sapphire as its gain medium, typically producing pulsed red light. It is an early solid-state alternative, unlike the continuously operated gas-discharge helium–neon laser.
Resonant energy transfer : Energy transfer between systems whose energy-level differences closely match. Excited helium atoms transfer energy efficiently to neon because their relevant energy levels are closely matched.
Metastable state : An excited atomic or molecular state that persists unusually long because direct decay is unlikely. Long-lived helium states allow collisions to transfer substantial energy to neon.
Holography : A method of recording and reconstructing optical wavefronts, often to produce three-dimensional images. Its coherent red beam can illuminate holographic recording setups.
Argon-ion laser : A gas laser that uses ionized argon to produce strong blue and green output lines. It offers prominent blue-green wavelengths but requires a different ionized-gas gain process.
Stimulated emission : The emission of a photon triggered by an incoming photon, producing a second photon with matching frequency, phase, and direction. Stimulated emission amplifies the red light generated by excited neon atoms.
Laser gain medium : The material in a laser that amplifies light through stimulated emission. The helium–neon gas mixture is the gain medium, with neon providing the laser transitions.
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