Measurements of UV photoionization parameters for TEA CO2gas lasers are presented. Electron density and ionization decay times are given as a function of pressure for several gases and gas mixtures. Penetration depth of ionizing radiation in the gases is determined. The effect of selected additives on photoionization is demonstrated. The results show that a significant enhancement in electron density can be achieved. The -band microwave interferometer data provide additional insight into the mechanisms involved and further substantiate the effectiveness of the technique in high-powered CO2laser design.