Third-order nonlinear optical properties of an expanded porphyrin cadmium complex

The third-order nonlinear optical properties of a pentaazadentate porphyrin-like cadmium complex, [(DBP-APPC)Cd]Cl, have been investigated using 40-ps and 5-ns laser pulses at 532 nm. The molecular second-order hyperpolarizability of this complex is 9.7x10(-31) esu, and the nonlinearity is predominantly electronic in origin with picosecond laser pulses. Temporal response of the nonlinear process is composed of at least two components with different time responses and shows a strong fluence dependence that indicates the participation of excited states in the nonlinear process. Nonlinear absorption measurements demonstrate that this complex shows strong reverse saturable absorption for nanosecond laser pulses, but exhibits a transformation from reverse saturable absorption to saturable absorption at high fluence for picosecond pulses. These results suggest that [(DBP-APPC)Cd]Cl is a very promising candidate for optical limiting of nanosecond laser pulses. (C) 2000 American Institute of Physics. [S0003-6951(00)02638-3].