THE SATURATION LIMIT TO PICOSECOND, INDUCED ABSORPTION IN DYES

The increase in transmission coefficient at high fluences, following low-fluence reverse saturable absorption (induced absorption), is demonstrated for the tricarbocyanine dye, HITCI. This novel effect is explained in terms of a modified three-level model of the singlet states. The absorption cross-section at 532 nm of the first excited state is determined to be 4.8 x 10(-16) cm2, 29 times that of the ground state. We find the lifetime of the first excited state to be 1.5 ns and that of the second excited state to be of the order of 8 ps.