14 November 2003 Polarized stimulated emission depletion studies of two-photon excited states
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Stimulated emission depletion (STED) population and polarisation dynamics following two-photon excitation are investigated for rhodamine 6G in ethylene glycol. Time resolved fluorescence intensity and polarisation measurements were made using picosecond time-correlated single photon counting (TCSPC). Cross-sections for the stimulated transition were measured between 614nm (2.32x10-16 cm2) and 663.5nm (6.05x10-17 cm2), ground state vibrational lifetimes were found to vary between 314fs and 467fs. A collinear (180°) excitation-detection geometry was employed to investigate re-polarisation of the excited state array yielding fluorescence anisotropies above the two-photon limit. The circumvention of single-photon selection rules is demonstrated allowing the measurement of higher order parameters and correlation functions that are wholly inaccessible to 'conventional' (spontaneous) time resolved fluorescence techniques.
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Daven A. Armoogum, Richard J. Marsh, Angus J. Bain, "Polarized stimulated emission depletion studies of two-photon excited states", Proc. SPIE 5222, Nanocrystals, and Organic and Hybrid Nanomaterials, (14 November 2003); doi: 10.1117/12.505839; https://doi.org/10.1117/12.505839

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