Fluorescence-detected pump-probe (F-PP) spectroscopy is a recently developed method to study excited-state dynamics. F-PP combines the temporal resolution of conventional transient absorption (TA) spectroscopy with the sensitivity of fluorescence detection. In this work, we demonstrate inherently phase-stable F-PP spectroscopy using 20 fs pulses to monitor the ultrafast Stokes shift dynamics of a solvated fluorophore (Y12). We observed a shift in the stimulated emission maximum with a time constant of 84 fs. In contrast to TA, F-PP provides a coherent artifact-free view of this process. Using quantitative signal background subtraction, as discussed in this work, F-PP uncovers the pure stimulated emission spectrum and its ultrafast dynamics. This signal isolation is a clear advantage over TA, where different contributions often overlap heavily. We compare results from F-PP and TA on an equal footing using the same excitation pulses, emphasizing the features and advantages of the F-PP technique.

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• Journal Article MeSH

Fluorescence lifetime imaging microscopy (FLIM) is a well-established technique with numerous imaging applications. Yet, one of the limitations of FLIM is that it only provides information about the emitting state. Here, we present an extension of FLIM by interferometric measurement of fluorescence excitation spectra. Interferometric Excitation Fluorescence Lifetime Imaging Microscopy (ixFLIM) reports on the correlation of the excitation spectra and emission lifetime, providing the correlation between the ground-state absorption and excited-state emission. As such, it extends the applicability of FLIM and removes some of its limitations. We introduce ixFLIM on progressively more complex systems, directly compare it to standard FLIM, and apply it to quantitative resonance energy transfer imaging from a single measurement.

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• Journal Article MeSH