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 (γ), the excited-state absorption cross section (σ_ex), the nonlinear refractive cross section (σ_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 γ value for [(CH₃-TXP)Cd]Cl is 6.9×10^-31 esu, which is 4 times as larger as that of SiNc. The nonlinearity of [(CH₃-TXP)Cd])Cl is predominantly electronic in origin with picosecond laser pulses. The excited-state absorption cross section (σ_ex) and the nonlinear refractive cross section (σ_r) obtained from the theoretical simulation and calculation of Z-scan results are 7.0×10^-17 cm² and 1.7×10^-17 cm², 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/cm². These data suggest that this complex and related complexes are a promising class of nonlinear optical materials.