Abstract
It is shown that the technique of intermodulated fluorescence can effectively correct for scattering problems in analytical flame fluorescence spectroscopy. When two laser beams, amplitude-modulated at different frequencies f1 and f2 and counterpropagated colinearly throughout an atomizer, are tuned to the absorption transition of the element of interest, non-linear mixing of the fluorescence signal results, due to saturation effects. By extraction of the signal at the sum or difference frequency, f2 ± f2, the linear scattering component of the spectrum can be essentially eliminated. This has been demonstrated for a sodium solution nebulized in a premixed, laminar, argon-oxygen-hydrogen flame. Because the modulation signal can be observed only at the intersection volume between the two beams, this technique constitutes a powerful tool for spatially resolved combustion diagnostics.
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