He-Ne lasers

[djef]

hallo all,
I was wondering the following thing: when using a He-Ne laser, you pump some energy in the system to get the He excited, but why only the He atoms?

If you pump energy in the systems, wouldnt the Ne atoms get excited too ? (and I am not speaking about them getting excites because the collisions with the He atoms).


Is this simply because it takes less energy to get the He atoms excited then the Ne atoms (though , the difference is very very small)

[Dr Lots-o'watts]

Perhaps some of the Ne atoms do get excited by themselves, but not sufficiently so as to have a constant population inversion. It is the many surrounding excited He atoms that allow the population inversion to be sufficient for continuous stimulated emission to occur.

[Andy Resnick]

He-Ne lasers are interesting, and more complicated than the typical 'laser' diagram- which is odd considering how common they are.

A key step is the collision of He and Ne atoms to transfer energy- the He atoms are excited, collide with Ne atoms, and the Ne atoms produce the laser line:

http://en.wikipedia.org/wiki/Helium-neon_laser