PLANAR KRF LASER-INDUCED OH FLUORESCENCE IMAGING IN A SUPERSONIC COMBUSTION TUNNEL

Planar fluorescence images of OH were obtained in a continuous-flow, electrically heated, high enthalpy, hydrogen-air combustion tunnel, using a tunable KrF laser. These images were compared to previously recorded fluorescence images produced using a doubled-dye laser under similar conditions. For the detection configuration used, the images of doubled-dye laser-induced fluorescence demonstrated a severe distortion as a result of laser beam absorption and fluorescence trapping. By contrast, images of the fluorescence induced by the tunabie KrF laser retained the symmetry properties of the flow. Based on signal-to-noise ratio measurements, the yield of the fluorescence obtained with the doubled-dye laser is considerably larger than the fluorescence yield induced by the KrF laser. The measurement uncertainties in the present facility of OH fluorescence induced by the KrF laser were primarily controlled by photon-statistical noise. Based on these results, tunable KrF laser systems are recommended for quantitative OH imaging in facilities where the product of the optical path length for either fluorescence excitation or collection and the average OH concentration along that path is greater than 10(16) cm/cm3.