| 单词 | quantum theory of radiation |
| 释义 | quantum theory of radiation The study of the emission and absorption of photons of electromagnetic radiation by atomic systems using quantum mechanics. Photons are emitted by atoms when a transition occurs from an excited state to ground state. If an atom is exposed to external electromagnetic radiation a transition can occur from the ground state to an excited state by absorption of a photon. An excited atom can lose the energy it has gained by stimulated emission (see laser). However, an atom can also emit a photon in the absence of external electromagnetic radiation, a process called spontaneous emission. The quantum theory of radiation was initiated by Einstein in 1916–17, as an extension of Planck's radiation law. The theory is quantified by the Einstein coefficients. The quantum theory of radiation is the basis of the theory behind the operation of lasers and masers |
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