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Concept

Stimulated emission

A stylized depiction of an atom with a central nucleus emitting light rays outward, symbolizing stimulated emission, a fundamental concept in laser physics.

The quantum process at the heart of every laser. An atom sitting in an excited state can be coaxed into releasing its stored energy early when struck by a photon of exactly the right wavelength. The new photon comes out matched to the trigger: same frequency, same phase, same direction. Einstein predicted the effect in 1917 from thermodynamic arguments alone, decades before any device exploited it.

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