The influence of oxygen on CO-laser performance

Additions of a few parts per thousand of oxygen to a CO-He mixture change drastically the laser output power, the axial field in the positive column, and the slope of the E-I curve of the discharge. The intensity of the spectrum of vibrational transitions of the CO molecule increases when oxygen is added; the increase is especially pronounced for transitions from higher (nu exceeding 7) levels. The most prominent feature in the visible spectrum is the disappearance of the C2-Swan bands with the addition of oxygen. The populations of CO vibrational levels were derived from the IR spectra; they increse by more than an order of magnitude for nu exceeding 7. The electron energy distribution was derived from measured E/N and the Boltzmann equation. Oxygen affects the Boltzmann equation (and thus the electron energy-distribution function) through the change in E/N, which is in turn determined by ionization and deionization processes. The fractional power transfer from electrons increases to vibrational levels and decreases to electronic levels.