Femtosecond, broadband nonlinear optical studies of a zinc porphyrin and zinc phthalocyanine

Broadband (700-950 nm) third order nonlinear optical (NLO) properties of porphyrin (ZnTPP) and phthalocyanine (TPA-ZnPc) molecules in solution form have been studied using the Z-scan technique with femtosecond, MHz pulses. Two-photon, three-photon absorption coefficients along with the third-order NLO susceptibility (χ3) and their optical limiting thresholds are estimated from the theoretical fits to experimental data. Closed aperture Z-scan data provided the information on the sign and magnitude of nonlinear refractive indices (n2) at different wavelengths. Our results clearly suggest that these molecules possess the potential for applications such as optical limiting and biological imaging at high repetition rates.