Why don't electron go into the next orbit during stimulated emission?

[.::Ash::.]

Why don't electrons go into the next orbit during stimulated emission?

Hey all,
I was studying stimulated emission in lasers and I had a doubt regarding the same.
When the electron collides with another which is in an excited state, why doesn't the electron, which gets collided, move into the next orbit? Why does it radiate a photon and goes into the ground state?

It would be great if someone could explain it to me in simple terms.

Thank you.

 

[Simon Bridge]

Welcome to PF;
The "simple terms" answer is: "it just does" - the trigger is the particular frequency of the stimulating photon.
See: http://hyperphysics.phy-astr.gsu.edu/hbase/mod5.html
Basically: it is a property of photons that they like to travel together in bunches.

It's probably not very useful to think of the effects in terms of collisions though.

If the incoming photon had the same energy as the gap to the next higher energy level, then the electron would, indeed, go there. But atomic energy levels are not evenly spaced like rungs on a ladder - they get closer together as you get higher. If the incoming photon has the same energy as the gap between the excited level and the ground state, then you get stimulated emission.

Also see: http://www.aps.org/publications/apsnews/200508/history.cfm