Page 292 - Tunable Lasers Handbook

252 Norman P. Barnes

Pump
Manifold
Phonon Upper
Laser
Manifold

FIGURE 1 2 Four-level laser energy-level diagram.

-..
Phonon
Upper
Laser
Manifold

1

- - - - - - - Virtual
Vibronic
Phonon State
Ground *

operation. A four-level laser, depicted in Fig. 12, has a ground manifold, a pump
manifold, and an upper laser manifold, similar to the three-level laser. However,
in contrast to the three-level system, there is a fourth manifold, the lower laser
manifold, in which the lower laser level resides. As with the three-level laser,
lasing occurs between a level in the upper laser manifold to a level in the lower