Experimental results in a uniform, supersonic, free-jet flow containing water vapor show that enhancement of OH concentration by focused UV photodissociation of H(2)O at 248 nm is an excellent tagging mechanism for velocity measurements. Two-dimensional images of OH fluorescence with a vidicon show a narrow initial enhanced OH zone along a straight line limited by the jet diameter. Fluorescence induced by a time-delayed pulsed dye laser documents the convection of this enhanced OH by the uniform core flow and reveals sharply stretched edge regions due to the shear layer with ambient air. The core flow velocity measurements are in agreement with predicted values.

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Population inversion has been generated through the mixing of CO2 or N2O into a supersonic N2 flow, vibrationally excited by thermal means. Gain at 10.6μ, corresponding to the 001 → 100 transition in CO2, equal to 0.8%/cm has been measured in this medium. Using an optical cavity, oriented transverse to the flow, up to 60-W cw laser power at 10.6μ from CO2 was extracted from a 5-cm length by 1.2-cm2 cross-section active volume. When N2O was substituted for CO2 in the mixing region, cw laser emission was demonstrated at 10.8μ, corresponding to the 001 → 100 transition in N2O.