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

Planar fluorescence images of OH were obtained in a continuous-flow, e lectrically heated, high enthalpy, hydrogen-air combustion tunnel, usi ng a tunable KrF laser. These images were compared to previously recor ded fluorescence images produced using a doubled-dye laser under simil ar conditions. For the detection configuration used, the images of dou bled-dye laser-induced fluorescence demonstrated a severe distortion a s a result of laser beam absorption and fluorescence trapping. By cont rast, images of the fluorescence induced by the tunabie KrF laser reta ined the symmetry properties of the flow. Based on signal-to-noise rat io measurements, the yield of the fluorescence obtained with the doubl ed-dye laser is considerably larger than the fluorescence yield induce d by the KrF laser. The measurement uncertainties in the present facil ity of OH fluorescence induced by the KrF laser were primarily control led by photon-statistical noise. Based on these results, tunable KrF l aser 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 p ath is greater than 10(16) cm/cm3.