J-dependence of rotational relaxation in the CO200°1 vibrational level

Observations are presented on the
J
-dependence of rotational relaxation in the CO
2
00°1 vibrational level for mixtures of CO
2
, He, and N
2
. The experiment consists of injecting a saturating ∼2-ns pulse at the
P(20)
line in the 10.4-μ CO
2
band into a low-pressure CO
2
-laser amplifier while simultaneously monitoring the transient gain response of an overlapping weak probe beam in the 9.4-μ band restricted to operate on any of the transitions
P(10)
-
P(34)
. The data show that the decay times of the various
J
states in the CO
2
00°1 level get progressively longer for increasing or decreasing
J
value centered about the perturbed
J = 19
state. Such behavior may be expected to have a significant effect on the efficiency of energy extraction and pulse shapes in CO
2
amplifiers for nanosecond and, especially, subnanosecond laser pulses. An analysis using a coupled set of rate equations to describe the rotational level populations is presented in which consideration is given only to
\mid \DeltaJ \mid = 2
changes in collision. The analysis, when compared with the data, indicates that collisions in which
\mid \DeltaJ \mid
changes by more than two units must also be considered.