A novel frequency domain fluorescence technique for determination of triplet decay times

Frequency domain fluorescence measurement using two diode lasers with amplitude modulation in the kHz range yields a signal component at the sum frequency. This intermodulation phenomenon was observed in an aqueous solution of haematoporphyrin (HP) and could be related to triplet state population kinetics. This indirect measurement technique may allow triplet decay time measurement during photodynamic therapy (PDT) enabling monitoring of the type II phototoxic damage rate.

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