Trigger the emission of light by an atomic electron

[afcsimoes]

What does trigger the phenomenon of an atomic electron losing energy through the issue of a photon?
(I know how an atomic electron absorbs light and changes to a more energetic level but I never read an explanation cause-effect of the inverse)

 

[blue_leaf77]

Stimulated emission?

 

[afcsimoes]

Stimulated emission?

Yes but not only. I think also in the natural expontaneous emission, like the emissions of a radioactive nucleous.

 

[blue_leaf77]

When a photon comes, it actually couples the electron sitting in a certain level with other levels which are separated from the initial level by about the same amount of energy as the energy of the incoming photon. The result of this coupling may end up as an up transition (absorption where the photon get absorbed) or down transition (stimulated emission where the electron goes down to a lower level emitting another photon of the same energy). Whether the electron will undergo absorption or stimulated emission is determined by the transition probability between the initial level and the other level.
As for spontaneous emission, the proper treatment of this event can be done using quantum electrodynamics (QED). It has to do with zero point energy, when you go deeper in QED you will find that vacuum is not really nothing. By quantizing electromagnetic field, it has been found that the absence of photon doesn't mean the energy is zero, I would say it's almost like the case with quantum harmonic oscillator.

 

[afcsimoes]

I liked your answer. Than you.

 

[afcsimoes]

To Blue_Leaf77 attention, please:
In Classic Physics are there some explanation to the spontanity of those phenomenons?

 

[blue_leaf77]

Not even in classical physics. Even semi-classical treatment of the interaction between EM field and atom cannot satisfactorily explain spontaneous emission. Well there is this so-called Einstein A coefficient which is related to the probability of spontaneous emission and which was invented before the birth QED (I think), but I would say that the treatment was more empirical.