130_notes.dvi

He Ne

(2p)

(2p) (3s)

(2p) (4s)

(2p) (5s)

(2p) (3p)

2 S

1 S

1

0

2 S^3

1

1

0

5

5

5

5

6

collision

collision

visible laser

IR laser

Another way to get the population inversion is just the use of a metastable state as in a ruby laser.
A normal light sorce can excite a higher excited state which decays to a metastable excited state.
The metastable state will have a much larger population than in equilibrium.

A laser with a beam coming out if it would be made in a cavity with a half silvered mirror so that
the radiation can build up inside the cavity, but some of the radiation leaks out to make the beam.

high

voltage