Spontaneous emission

Quantum mechanical state change

Spontaneous emission is the process in which a quantum mechanical system (such as a molecule, an atom or a subatomic particle) transitions from an excited energy state to a lower energy state (e.g., its ground state) and emits a quantized amount of energy in the form of a photon into a field that was previously devoid of radiation. Lasers start via spontaneous emission, then during continuous operation work by stimulated emission. Albert Einstein discussed spontaneous emission in a series of papers starting in 1916, which first predicted the phenomenon of stimulated emission and introduced the Einstein Coefficients.

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