Atomic transition - What does this notation mean?

[octol]

Hello all, I've been reading about laser cooling, and when they speak of tuning the laser to a atomic transition, they write this (for example) as
"The laser cooling was performed on the D_2 transition (3S_{1/2} \rightarrow 3 P_{3/2})".

But what do they mean by that notation? I'm clueless as what it is supposed to mean as it doesn't look like the spectroscopic notation (i.e the number 3 is NOT in superscript).

Jon

 

[Astronuc]

I believe that the 3 is the principal quantum number, S and P are related to the suborbtial or azimuthal quantum number, and 1/2 and 3/2 are (IIRC) the total electronic angular quantum momentum numbers which parameterize the total angular momentum of a given electron, by combining its orbital angular momentum and its intrinsic angular momentum (i.e., its spin).

Has one studied the quantum numbers of atomic electrons?

 

[octol]

ok so the
3 S_{1/2} \rightarrow 3 P_{3/2}
means the same as for a normal transition, except that this is in the case of a composite system? i.e the transition is L=0 to L=1 and J=1/2 to J=3/2.

What is then meant by D_2? And how does this relate to the above?