Page 269 - Tunable Lasers Handbook

6 Transition Metal Solid-state Losers 229

a tZ

FIGURE 3 Transition metal atom undergoing absorption of a photon. (a) Transition metal atom
in ground level before absorption. (b) Transition metal atom in excited level irnmediaiely aftzr absorp-
tion. (c) Transition metal atom in excited level. Nearest neighbors vibrating around new positions.

changes in the strength of the crystal field can substantially shift the position of
the energy levels.
In lanthanide series lasers, electrons in the 4f subshell participate in the las-
ing process. Lanthanide series atoms that have demonstrated lasing appear in
the sixth row of the periodic table of the elements. The electronic configuration
of these atoms, shown in Fig. 4, has all of the subshells of the first three shells
filled; that is, Is, 2s, and 2p, as well as 3s, 3p, and 3d are filled. In addition, the
4s, 4p, and 4d subshells and the 5s and 5p subshells are filled. The next two
electrons added to this structure go into the 6s subshell before the 4f subshell
begins to fill. When incorporated into a laser material, the lanthanide atoms