Characterization of the third-order nonlinearity of [(CH3-TXP)Cd]Cl

The third-order nonlinear optical properties of a methyl substituted Texaphyrin, [(CH3-TXP)Cd]Cl, were studied by degenerate four wave mixing (DFWM) and Z-scan techniques using 40 ps laser pulses at 532 nm. The molecular second-order hyperpolarizability (gamma), the excited-state absorption cross section (sigma(ex)), the nonlinear refractive cross section (sigma(r)), and the optical limiting performances at both nanosecond and picosecond time scales have been determined. We have also studied the third-order nonlinearity of SiNc, one of the most promising optical limiting materials in literature, for comparison. The gamma value for [(CH3TXP)Cd]Cl is 6.9x10(-31) esu, which is 4 times as larger as that of SiNc. The nonlinearity of [(CH3TXP)Cd]Cl is predominantly electronic in origin with picosecond laser pulses. The excited-state absorption cross section (sigma(ex)) and the nonlinear refractive cross section (sigma(1)) obtained from the theoretical simulation and calculation of Z-scan results are 7.0x10(-17) cm(2) and 1.7x10(-17) cm(2), respectively. The complex shows strong optical limiting performance via reverse saturable absorption for 5 ns laser pulses. The nonlinear absorption of this molecule for 40 ps laser pulses exhibits a transition from reverse saturable absorption to saturable absorption when the fluence is higher than 0.3 J/cm(2). These data suggest that this complex and related complexes are a promising class of nonlinear optical materials.