Hi all. I need a help about a stupid thing which is puzzling me! I'm studying a paper where it's described a classical excitation of a fluorophore from a ground state to an excited state.(adsbygoogle = window.adsbygoogle || []).push({});

See the attached image!

There are two laser beams which act on the sample, the first one which is an excitation laser (it runs the ##L_{0}## to ##L_{1}## transition) and a second laser beam called STED (yes the same of the "new" fancy way of getting super resolute images, I'm actually studying the theory of this super resolution technique).

Now the eqs are the classical Einstein like, but what I don't understand is (let's take for example the first one) why there's a factor like ##h_{exc}\sigma_{01} ( n_1- n_0)##. I would had expected something like "minus" a quantity which told me that the temporal variation of the ground state is diminished because of absorption. In fact the second term of the right hand side is of the form ##1/\tau_{vibr} * n_3## which is telling me that atoms are coming from the level ##L_3##.

Same reasoning applies for the other equations, but it would be great to have an understanding of just the first one, the other will be the same thing.

Thanks in advance and forgive me if my English is not so correct. I did my best.

Have a wonderful day everybody! Ciao

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# A problem with fluorescence

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