Information obtained by investigating the aging process in passive CO<sub>2</sub> laser cells can be correlated with gaseous reactions that take place in active CO<sub>2</sub> laser tubes. The construction and operation of sealed off, passive cells facilitate the observation of gas mixtures under differing excitation conditions and electrode designs with a minimum expenditure of time and expense. The emission spectra in the visible region, recorded at intervals during operation, are used as indicators of the sequence of compositional changes in the original gas mixture. Additional information is gained by noting voltage changes. Data thus obtained from passive cells can be used for the possible extension of the lifetime of active lasers. Others have investigated long life, sealed off CO<sub>2</sub> lasers. A limited amount of information is available on passive systems.
J. W. Mellichamp and C. J. Bickart, "Visible Spectroscopy of the Aging Process in Passive N2–CO2–He–Xe Laser Cells," Appl. Spectrosc. 25, 97-99 (1971)