Femtosecond nonlinear optical properties of alkoxy phthalocyanines at 800 nm studied using Z-Scan technique

We report our results on the nonlinear absorption, and its switching behavior, of two alkoxy phthalocyanines (a) 2,3,9,10,16,17,23,24-octakis-(heptyloxy) phthalocyanine (Pc1) and (b) 2,3,9,10,16,17,23,24-octakis-(heptyloxy) phthalocyanine zinc(II) (Pc2) studied at a wavelength of 800 nm with ∼100 fs pulses using the standard Z-scan technique. Both the molecules possessed negative nonlinear refractive index (n2) as revealed by signature of the closed aperture data. Magnitudes of the n2 evaluated were ∼1.26 × 10−13 esu for Pc1 and ∼1.68 × 10−13 esu for Pc2. Nonlinear absorption data of Pc1 obtained at a concentration of 5 × 10−4 M demonstrated complex behavior with switching from reverse saturable absorption (RSA) within saturable absorption (SA) at low peak intensities to SA in RSA at higher peak intensities. Pc2 data recorded at similar concentration exhibited saturable absorption type of behavior at lower peak intensities. The nonlinear absorption at higher intensities was again multifarious with switching over from SA to RSA. We discuss the complicated behavior of the nonlinear absorption and nonlinear optical performance of these molecules for their potential applications.