Hi! I wanted to check if I have got the correct interpretation of stimulated vs spontaneous emission.(adsbygoogle = window.adsbygoogle || []).push({});

It seems like stimulated emission is defined as a process for which an excited atom/electron spontaneously relaxes down to a lower energy level.

Stimulated emission on the other hand seems to be defined as the emission of a photon from at atom/electron due to the interaction of that atom/electron with a surrounding electromagnetic field.

However, now I'm reading some quantum optics where the electromagnetic field is quantized.

1) Here the author considers initial and final states of the form [itex]|i\rangle = |A, 0\rangle, \quad |f\rangle = |B, 1_{\vec{k}, a}\rangle [/itex] where A and B is the initial and final states of the atom and 0 and [itex]1_{\vec{k}, a}[/itex] are the initial and final number of photons in the electromagnetic field (wave vector [itex]\vec{k}[/itex] and polarization [itex]a[/itex]). One calculates the amplitude for this process to happen through the lowest order interaction term in the hamiltonian.

2) The other type of initial and final states which is considered is of the form [itex]|i\rangle = |A, n_{\vec k ,a}\rangle, \quad |f\rangle = |B, n_{\vec{k}, a} + 1\rangle [/itex].

It seems like the author defines 1) to be spontaneous emission. I.e emission of a photon into a vacuum mode, while he defines 2) to be stimulated emission, i.e. emission into a mode which is already populated. However both these processes involve interactions with the electromagnetic field rendering my previous understanding wrong.

So what is stimulated and spontaneous emission? Is spontaneous emission an interaction with an electromagnetic ground state (vacuum)? Or is there no electromagnetic field at all?

If there is an interaction, the process is not really spontaneous is it?

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# Spontaneous vs Stimulated Emission

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