The chain-length dependences of static third-order hyperpolarizabilities γ<sub>STAT</sub> of the homologous series of thiacyanines, of their <i>meso</i>-nitrogen-substituted derivatives, and of simple bis(dimethylamino)methine dyes are determined from nondegenerate four-wave mixing dispersion curves. We determined nearly the same very rapid increase of γ<sub>STAT</sub> with growing numbers of π electrons of the chain (γ<sub>STAT</sub>∝−<i>N</i><sup>8±2</sup>) for both the thiacyanine and the bis(dimethylamino)methine series, an alternating influence of <i>meso</i>-nitrogen substitution for even and for odd double bonds of the chain, and a saturation of the hyperpolarizability for the longest thiacyanine (thiatricarbocyanine). We discuss our results, taking into account semiempirical quantum chemical calculations.
© 1998 Optical Society of America
(120.6710) Instrumentation, measurement, and metrology : Susceptibility
(190.0190) Nonlinear optics : Nonlinear optics
(190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing
(190.4710) Nonlinear optics : Optical nonlinearities in organic materials
W. Werncke, M. Pfeiffer, A. Lau, W. Grahn, H.-H. Johannes, and L. Dähne, "Alternation and saturation effects in the chain-length dependences of the third-order hyperpolarizabilities of cyanines," J. Opt. Soc. Am. B 15, 863-870 (1998)