We know that the spontaneous emissions are governed by the selection rules, both parity and the delta. J. The general aspect of stimulated emission tells us that a photon (not all?) depopulates the upper state and gives out an extra-photon with same features as the initial one, thus in total we have two identical photons. Do these depopulation mechanisms also follow the selection rule or are these intruder photons capable to de-excite the levels via forbidden transitions?
The rate of the stimulated emission is proportional to the square of the dipole matrix element, connecting upper and lower states of the emitting system (atom or molecule). Spontaneous emission rate is also proportional to this value, so the selection rules are the same.
Yes, the selection rules are the same. Think about the Einstein differential coefficients a and b and the relation between them.
I want to be more precise. Selection rules concern the states between which the transition could occur. Given an excited state and an external photon with an appropiate energy, in the majority of cases the depopulation is possible, so the textbooks (which?) could bre right.
If I understand well, the first case could correspond to Raman scattering (a second order process in the electron-photon interaction), which at its turn could be spontaneous , if sigma_1 is not present (in this case direction and polarization of the emitted photon are not fixed), or stimulated, if sigma_1 is present and then the emitted photon is identical with the one present.
The second case is spontaneous one photon emission I had in mind in the previous messages.
I think some time one case observe the excitation which are not allowed by selection rule. Let us take an example of case where a hybridization up-to some extent occurs between d-orbital and p-orbit, in this case the excitation can occur from d-orbit to s-orbit (d-s excitation is not allowed by selection rule) due to a hybridization of d-orbital with an orbit ( p-orbit ) from which excitation to s-orbital is allowed by selection rule.
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