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New laser lines at 3.71 and 3.84 μm in hydrogen and lines at 4.52, 4.60, and 4.71 μm in deuterium excited by a pulsed electrical discharge have been obtained. The lines in hydrogen are assigned to the a 3Σ+g → c 3Πu triplet band, but the lines in deuterium have not yet been assigned. Direct electronic excitation from the ground state to the a 3Σ+g state is believed to be the excitation mechanism, and indicates that an excimer-type laser from the a 3Σ+g upper state to the dissociative b 3Σ+u state may be possible.

An experimental study of the breakdown of various gases under intense radiation of 10.6 μ was made, and a theoretical model for the development of gas breakdown is presented. The gases under investigation were He, Ne, Ar, O2, and air. The pressure range was from 0.3 to 13 atm and the focal diameter from 0.75 × 10−2 to 3.0 × 10−2 cm. It was found that for all gases studied, the threshold power density decreases as the focal volume increases and that it decreases as the pressure increases, in the pressure range considered. The rate of decrease with pressure was found to vary with different gases and focal volumes. This reduction of threshold with increased pressure is less sharp as the focal volumes become larger. The theoretical model is based on classical microwave cascade theory. The importance of loss terms other than the electron diffusion loss is discussed. The theoretical model predicts that even for large beams some loss terms are still important and the breakdown threshold is not completely time dominated. The threshold value is predicted to be higher than the one predicted based on a loss-free calculation.

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