Dispersion of the complex cubic nonlinearity in two-photon absorbing organic and organometallic chromophores

Abstract

There is much interest in nonlinear absorbing chromophores for applications in photonics, nanophotonics and biophotonics. We have performed studies of dispersion of the nonlinear absorption cross sections and the refractive nonlinearities of organic and organometallic nonlinear chromophores using the technique of Z-scan, with a tunable amplified femtosecond laser system. Z-scan is less sensitive than the popular technique of two-photon induced fluorescence but has advantages of being suitable for non-fluorescent substances and providing information on both absorptive and refractive nonlinearities. We have analysed the experimental results in terms of simple models and using the Kramers-Kronig transformation as shown in this paper for Coumarine 307 and an organometallic dendrimer. The dispersion curves are often dominated by two-photon resonances but inclusion of other nonlinear mechanisms seems to be necessary for better understanding of their features.