The transmission measurement of two intense picosecond pulses (wavelength A t = 527 nm) separated by 10 ns is applied to extract the quantum yield of triplet formation <£ T , the S l singlet excited state absorption cross-section

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The absolute S,-state excited-state absorption cross-section spectrum of eosin Y in methanol has been determined by picosecond second harmonic Nd:glass laser excitation and time-delayed picosecond light continuum probing (probing wavelength region from 400 to 980 nm).

The absolute triplet-triplet absorption cross-section spectrum a T (X) of eosin Y in methanol at room temperature is determined in the wavelength region from 400 to 1000 nm and at 308 and 1054 nm. The triplet state is populated by XeCl excimer laser excitation to a singlet state and subsequent intersystem crossing. The triplet level population is determined by numerical simulation of the pump pulse absorption dynamics. The triplet-triplet absorption is probed with picosecond spectral light continua which are generated in a D 2 0 sample by a synchronized mode-locked Nd:glass laser. The decay of the triplet level population is studied by delayed picosecond light continua probing. Second order rate constants of hQ* =* i.l X10 9 dm 3 mol~l s~l for oxygen quenching, fc&> = i.3x 10 9 dm 3 mol~l s~l for triplet-triplet annihilation, and k$ ss4x 10 8 dm 3 mol~l s" 1 for triplet-singlet concentration quenching have been determined.

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