LIFETIME DETERMINATION FOR HIGH-LYING EXCITED-STATES USING Z-SCAN

We report a method of determining the lifetimes of the high-lying excited singlet states of dye molecules in solution. The method is based on the Z-scan technique and the observation of saturation of excited state absorption in dye solutions using laser pulses having Gaussian temporal and spatial distributions. This leads to the important finding that the use of laser pulses as long as tens of picosecond can resolve subpicosecond lifetimes. The method is demonstrated by measuring an upper excited singlet state lifetime of 900 fs using 30 ps full width at half maximum input pulses on a chloroaluminum phthalocyanine dye. (C) 1995 American Institute of Physics.