Nonlinear absorption in metallo-porphyrin-like

Nonlinear absorption at 532 nm in a series of metallo-porphyrin-like compounds using 8 ns and 23 ps laser pulses is reported. The experiments show that for picosecond pulses, reverse saturable absorption occurs only at low fluences, and saturable absorption occurs at high fluences, for nanosecond pulses, only reverse saturable absorption occurs. The density matrix equations of motion for a six-level model are deduced to explain these nonlinear absorption effects, and numerical results calculated by the model agree well with the experimental results.