New dendrimer molecules with a record high intrinsic two-photon absorption cross-section

Abstract

Summary form only given. Two-photon absorption (TPA) is a third-order nonlinear optical process, in which two photons are absorbed simultaneously such that the energy of the photons adds up to the energy of the molecule's excited state. TPA has important applications in three-dimensional optical data storage, photolithography, scanning fluorescence microscopy, optical power limiting, etc. These applications exploit the fact that the rate of TPA has a quadratic dependence on the illuminating laser intensity. In particular, TPA allows confining absorption to a small diffraction-limited volume. This effect has been used recently for micro-fabrication of photonic band gap materials, tapered optical wave-guides and micro-electromechanical devices. A majority of known organic molecules have a very small nonlinear absorption cross-section, typically /spl sigma//sub 2//spl sim/1 GM (1 GM=10/sup -50/ cm/sup 4/s photon/sup -1/ molecule/sup -1/), which is insufficient for most proposed applications. An increase in /spl sigma//sub 2/ value has been achieved by using molecular design elements such as extension of /spl pi/-conjugation length of the molecule and by introduction of electron-donating (D) and electron-accepting (A) groups at the opposite ends of a linear molecule. In this paper we present results on measurement of two-photon absorption properties of a new class of macro-molecules with even higher intrinsic /spl sigma//sub 2/. These molecules are synthesized by using a strong D-A-D type two-photon absorbing chromophore 4,4'-bis(diphenylamino)stilbene as a building block for a much larger nanometer-size dendrimer structure.