When CO2-laser pulses of ∼50 ns duration and intensity of ∼100–500 MW/cm2 are incident upon NixP1−x surfaces in oxygen-containing atmospheres, distinctive ’’ripple’’ patterns are etched into the surfaces. The ripple wave fronts are normal to the E field and vary in spacing from ∼λlaser at normal incidence to ∼0.5λlaser for π polarization at grazing incidence.

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Observation of the visible fluorescence of the SiF radical in SiF4 gas irradiated by the pulsed output of a CO2 laser leads to the conclusion that the molecules are dissociated into electronically excited fragments by the action of the intense laser field. A clear distinction is observed between the fluorescence produced through this process and that associated with thermalization of the incident energy.

In gases which absorb CO2 laser radiation, luminescence, consisting largely of the molecular spectra of dissociation products, precedes the occurence of breakdown. Temporal, spatial, and spectral characteristics of this radiation and also of the sparks produced in a number of gases have been studied.

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