Gain and fluorescence characteristics of flowing CO2laser systems

Single-pass gain has been measured for flowing CO
2
, CO
2
-N
2
, CO
2
-He, CO
2
-N
2
-He, and CO
2
-N
2
-H
2
mixes. The gain for CO
2
-N
2
mixes varies as d
^-0.9
, where
d
is the tube diameter. The diameter dependence of the gain is less pronounced for CO
2
- N
2
-He mixes; a peak gain of 4.7 dB/m was obtained in a 1/2 in diam tube. Fluorescence data indicate that the upper laser level population is saturated at 100 mA in all cases. The addition of He, H
2
, or O
2
depopulates the lower laser level; helium further increases the population of the upper laser level. The addition of CO increases the population of the upper laser level, probably by resonant transfer from the excited vibrational states of CO.