Third-order optical nonlinearities and optical limiting of octa-octyloxy metallo-phthalocyanine for ps pulses in toluene

The third-order nonlinear optical properties of the octa-octyloxy metallo-phthalocyanines (C8H(17)O)(8) PcZn (PcZn) (C8H17O)g PcNi (PeNi) and (C8H17O)(8) PcPb (PePb) were studied by Z-scan using 35 ps laser pulses at 532 run in toluene. The excited singlet absorption cross-sections sigma(ex) of 2.7x10(-17) cm(2) (PcZn) 8.2x10(-18) cm(2) (PcNi) and 3.4x10(-18) cm (PcPb) were obtained by the simulation of experimental data using a multi-level model and the corresponding nonlinear refractive index n(2)=-7.9x10(-13) esu I -5.5x10(-13) esu, and -1.6x10(-12) eSU were also obtained respectively. The optical-limiting performances of this kind of molecules at 532 nm for 35 ps pulses have been investigated, and the limiting mechanism is the reverse saturable absorption of excited singlet states. The limiting thresholds at T/T-0 = 0.5 were measured to be 60, 80 and 130 mJ/cm(2) for (PcZn), (PcNi) and (PePb) respectively. When the incident fluence reached 0.5 J/cm(2), the corresponding transmitted fluences were 40, 80 and 150 mJ/cm(2) for (PcZn), (PcNi) and (PePb) respectively, in which the transmitted fluences of PcZn and PcNi were much lower than that of C-60 (140 mJ/cm(2)) under the same condition. These data suggest that the octa-octyloxy metallo-phthalocyanines are a kind of promising optical limiting materials.