Laser-Induced Fluorescence

Laser-induced fluorescence (LIF) is a powerful technique that is routinely used in combustion research laboratories for sensitive, spatially resolved detection of minor species. The quantitative application of the technique in flames, however, can be precluded by a lack of a predictive understanding of the signal-generation process in these complex environments. For example, changes in collisional conditions in the flame affect the laser-molecule interaction by modifying spectral line shapes and population distributions during the laser pulse. LIF measurements are also particularly sensitive to collisional electronic energy transfer (quenching) rates, which can dramatically vary with changes in the collisional conditions, resulting in a strong dependence of the fluorescence yield on local conditions. Consequently, quantitative measurements require accounting for dependence of the laser diagnostic signal on changes in collisional conditions in the flame. Furthermore, the intense laser pulses used to generate measurable fluorescence signals can cause photochemical interferences. Scientists at the CRF study these collisional and photochemical processes that are relevant to fluorescence-based detection of important radical species.