Large third-order optical nonlinearity and optical limiting in symmetric and unsymmetrical phthalocyanines studied using Z-scan

The third-order nonlinear optical and optical limiting properties of 2,3,9,10,16,17,23,24-octakis-(heptyloxy)-phthalocyanine, 2,3,9,10,16,17,23,24-octakis-(heptyloxy)-phthalocyanine zinc(II) (symmetric) and 2(3)-(butane-1,4-dioic acid)-9(10),16(17),23(24)-tri tert-butyl phthalocyanine zinc(II) (unsymmetrical) have been investigated using a continuous wave laser at 633 rim. We have employed the Z-scan technique to evaluate the sign and magnitude of nonlinear refractive index and the nonlinear absorption coefficient. Optical limiting based on nonlinear refraction was performed and limiting thresholds were estimated for all the three samples. The magnitude of the third-order nonlinearities measured were one of the highest reported in the cw regime rill date. Unsymmetrical phthalocyanine had better limiting characteristics and its nonlinear coefficients were comparatively high. Results of the nonlinear optical studies performed with these organic dyes doped in Poly(methylmethacrylate) are also presented. Our studies indicate that these phthalocyanines are potential candidates for optical limiting applications in low power cw regime. (c) 2007 Elsevier B.V. All rights reserved.