Electron-radiation temperature measurements in a sealed-off CO2laser system

Measurements of the noise temperature in the
L
band were used to investigate the effect of several constituents of the gas mixture on the discharge properties of the CO
2
laser. Addition of He and H
2
O to the discharge gives no significant change in the temperature. By contrast, addition of 4-torr N
2
to 2-torr CO
2
increases the noise temperature from 1.3 to 1.5 eV. Increase of the current in an optimum CO
2
-N
2
-He-H
2
O mixture leaves the temperature nearly constant (1.5 eV). This result deviates from that of Tyte and Sage, who found an anomalous rise of noise temperature with increasing current. Within the 5 percent experimental error the radiation temperature does not depend on laser action. A comparison of the present results with those of probe measurements is given. It is concluded that He has practically no influence on the average electron energy, which in turn controls the vibrational excitation. This and the observed behavior of the output power as a function of the partial He pressure give strong evidence that the major role played by He is cooling the gas in the discharge.