Comparison of excitation techniques for quantitative fluorescence imaging of reacting flows

Abstract

To determine the quantitative limitations of fluorescence imaging of OH, various systematic and random errors associated with three excitation approaches are analyzed. The three laser pumping schemes, 1) dye laser excitation of the A2Σ+←X2Π (1,0) band, 2) KrF laser excitation of the predissociative (3,0) band, and 3) saturated pumping of the (0,0) band with a XeCl laser, are compared to find which method minimizes the overall error. The approaches are compared by calculating shot-noise limited random errors and systematic deviations between the standard scaling equations and solutions to a time-dependent five-level rate equation model of the population densities. The model is used to address saturation and depletion (bleaching) effects. Dye laser excitation has the lowest overall error for single-shot imaging in turbulent hydrocarbon-air and hydrogenair flames. XeCl pumping produces the strongest signals, with evidence of strong saturation and ground state depletion effects. KrF pumping of the weakly absorbing and predissociative (3,0) band shows potential for quantitative imaging, when frame averaging is used. © 1993 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.