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Old 31st August 2014, 05:30 PM   #17
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Originally Posted by wogoga View Post
Population inversion essentially means that the majority of atoms/ molecules are in an excited state. This concept is not necessarily useful in the case of thermal radiation, where instead of discrete energy states a continuous velocity distribution of the atoms/ molecules is the driving force of photon emission. So you cannot conclude from the inadequacy of population inversion in thermal radiation to non-involvement of stimulated emission.
Still wrong. Thermal emission applies even to systems with discrete energy levels. It does not produce a blackbody spectrum in such a case, but that's irrelevant.

But no matter. The point, which eludes you, is that stimulated emission (which produces coherence in lasers) is essentially irrelevant for thermal emissions. Thermal emission is always, always, dominated by spontaneous emission, which is why it's always incoherent.
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