Stimulated emission depletion of two-photon excited states

Stimulated emission depletion of fluorescence (STED) from a two-photon excited molecular population is demonstrated for fluorescein in ethylene glycol and methanol. Time resolved fluorescence intensity and anisotropy measurements were made using picosecond time-correlated single photon counting (TCSPC). Pump–dump time delayed total fluorescence intensity measurements were used to characterise the response of the system and to provide additional data on the dump transition dynamics. Cross-sections for the stimulated transition in methanol and ethylene glycol were 1.4 and (3.6±1.0)×10−16 cm2, respectively, the corresponding ground state vibrational lifetimes were 636 and 717±99 fs.