Abstract.
This paper presents experimental evidence that using the KrF excimer laser for quantitative laser-induced fluorescence (LIF) studies of the OH A-X (3,0) system is highly problematic if the effects of both photobleaching and photochemistry are not included for laser spectral irradiances greater than 20 MW/cm2 cm-1. Pump-probe and time-resolved measurements of the OH LIF signal in an atmospheric pressure, premixed CH4-air flame at low- and high-laser-spectral-irradiance conditions show that a significant amount of OH is produced from photofragments resulting from the simultaneous 2-photon predissociation of H2O molecules in the C-X system. A 5+2-level rate-equation model that includes the effects of both photobleaching and photochemical OH production is shown to satisfactorily predict the data using a single adjustable parameter given by the effective, spectrally integrated 2-photon cross-section of H2O near 248 nm. The time-integrated OH LIF signal was found to depend on both the laser spectral irradiance and the local concentration of H2O. Additionally, use of the KrF excimer laser for 2-line rotational thermometry can produce temperature errors as great as +550 K at high laser-pulse energies.
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Received: 21 August 2000 / Revised version: 30 October 2000 / Published online: 21 February 2001
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Nguyen, QV., Paul, P. Photochemical effects of KrF excimer excitation in laser-induced fluorescence measurements of OH in combustion environments . Appl Phys B 72, 497–505 (2001). https://doi.org/10.1007/s003400100521
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DOI: https://doi.org/10.1007/s003400100521