Page 89 - Tunable Lasers Handbook

70 Charles Freed

rotational quantum numbers J. even though adjacent levels seem almost
equally spaced in each of the vibrational modes. Correspondingly, the fre-
quency differences between adjacent lines in the P and R branches of the regu-
lar band 12C160, laser transitions will vary from less than 1 cm-1 (-30 GHz)
for high J number R lines to somewhat more than 2 cm-1 (-60 GHz) for high J
number P lines.
Further restrictions on allowed CO, lasing transitions are imposed by the
nuclear spin properties of the various oxygen isotopes. The spins in both 160 and
180 are zero, and symmetry considerations therefore preclude the existence of the
antisymmetric odd transitions in the regular bands of W160 2' 13C160,. lAC160,,
12C1802, 13C180,, and ll.C1802. However, in the mixed CO, isotopes where the two
oxygen atoms &e dissimillv isotopes, or when the nuclear-spin is finite (e.g., "O),
all rotational lasing transitions are allowed. We should emphasize, however, that dif-
ferent selection rules may apply for the other bands, such as sequence and hot bands
for example, that also can provide oscillating transitions in the CO, laser system.

3000

-
27

-
2500

-
2000 -I I
U -P (20)
W 20 i/; ! fl
5 J
z !O r(J
- !4 ,
1500
-:
4= I
0200
FERMI
RESONANCE

0000 v,
0 v2 v3
CO, GROUND STATE
FIGURE 3 Detailed vibrational-rotational energ level diagram for the (0001 j-[1000, 0200],,,,
regular band laser transitions. (After C. K. N. Patel.)