Velocity dependence of the gain of a CO2laser

Measurements of the small signal gain and saturation intensity of a CO
2
-N
2
-He laser are made as a function of gas flow velocity over the range from
\sim 0-10
m/s. The small signal gain increases and the saturation intensity decreases with increased gas velocity. For intermediate flow velocities with a gas transit time in the laser of a second, the gain also depends on the direction of propagation of the amplified beam with respect to the gas flow. The directional dependence is due to an axial gradient in the saturation intensity. The transit time of the gas in the 2.5-m amplifier spans the time required for appreciable generation of CO by dissociation of the CO
2
and the variation of the laser gain with velocity is attributed to the effects of CO on the inversion of the laser medium.