Radial gain profiles in CO2laser discharges

Measurements of the gain of the P(20), 10.6 μ, transition of CO
2
have been made in a flowing He, N
2
, CO
2
amplifier. Both small-signal and saturated gain conditions were investigated as a function of radial position. At low discharge currents, the radial small-signal gain profile followed a J
0
Bessel function distribution as predicted from the electron density distribution, while at higher currents, the gain was nearly constant across the tube diameter. Further increases in the current produced a lower gain on the tube axis than near the tube wall. This spatial behavior of the small-signal gain with discharge current can be understood following the theoretical models of Gordietz et al. or more recently of Wiegand et al. The theory indicates the small-signal gain behavior is largely explained by the increase of axial gas temperature with discharge current. Gain measurements at signal levels high enough to cause gain saturation indicate the gain is harder to saturate on the tube axis than near the tube wall. An analysis of the experimental data shows that the gain-saturation parameter increases with current density.