# Neon energy levels in He-Ne laser

## Main Question or Discussion Point

Neon is the lasing element in He-Ne laser. The lasing transition(632.8nm) is from 3s to 2p. In the energy level diagram there is one 1.15μm transition from 2s to 2p. But we studied that 2s orbital have lower energy than 2p then how it is possible, in the energy diagram, 2s level have higher energy than 2p level and one transition of 2s to 2p?
http://en.wikipedia.org/wiki/Helium–neon_laser#mediaviewer/File:Hene-2.png

Related Other Physics Topics News on Phys.org
Quantum Defect
Homework Helper
Gold Member
Neon is the lasing element in He-Ne laser. The lasing transition(632.8nm) is from 3s to 2p. In the energy level diagram there is one 1.15μm transition from 2s to 2p. But we studied that 2s orbital have lower energy than 2p then how it is possible, in the energy diagram, 2s level have higher energy than 2p level and one transition of 2s to 2p?
http://en.wikipedia.org/wiki/Helium–neon_laser#mediaviewer/File:Hene-2.png
The notation in the diagram you reference is called Paschen notation. The labels are numberings of excited states, by energy. The "2S" does not refer to a "2s" hydrogen-like wave fundtion. Look at the reference given on the wikipage for a discussion of what nominal electron configurations correspond to the different Paschen notation labels.

http://archive.today/pwve [Broken]

Remember too that in multi-electron atoms, the kind of electron configurations that you learn to write as a beginning student (e.g. 1s^2 for He) are all approximations to the truth.

Last edited by a moderator:
The notation in the diagram you reference is called Paschen notation. The labels are numberings of excited states, by energy. The "2S" does not refer to a "2s" hydrogen-like wave fundtion. Look at the reference given on the wikipage for a discussion of what nominal electron configurations correspond to the different Paschen notation labels.

http://archive.today/pwve [Broken]

Remember too that in multi-electron atoms, the kind of electron configurations that you learn to write as a beginning student (e.g. 1s^2 for He) are all approximations to the truth.

Thank you

Last edited by a moderator:
Andy Resnick
how it is possible, in the energy diagram, 2s level have higher energy than 2p level and one transition of 2s to 2p?
http://en.wikipedia.org/wiki/Helium–neon_laser#mediaviewer/Fileene-2.png
Recall that Neon has more than 1 electron: the notation used in the level diagram is a not literally the same as for hydrogen:

http://archive.today/pwve [Broken]

As you can see, the 2P level corresponds to the outermost 3p electron, while the 2S state corresponds to the outermost 4s electron, which has a higher energy than the 3p electron.

Last edited by a moderator:
Thank you, now it is in phase with what I learned!!!