Dealing with saturation of the laser-induced fluorescence signal: An application to lead atoms

This work provides a theoretical basis for a partially saturated regime of laser-induced fluorescence (LIF). The partially saturated LIF regime, where the dependence of the fluorescence signal on the laser-power is non-linear, benefits from higher signal-to-noise ratio at the cost of more complex measurement evaluation when compared to the typically used linear regime. Starting from a well-established three-level model, and considering a realistic temporal and spatial profile of the laser pulse, approximate formulas were found that describe the dependence of fluorescence signal on laser pulse energy in commonly used experimental arrangements. These formulas can be used to determine absolute concentration from partially saturated LIF measurements. This method was applied to the atomic lead measurement and to the study of the decomposition of lead hydride in various versions of flames. (c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.