Linear and third-order optical characterisation of polyDPCHD

Abstract

We report here on linear and non-linear optical characterisation of the polydiacetylene poly[1,6-bis(3,6-dipalmitoyl- N-carbazolyl)-2,4-hexadiyne] (polyDPCHD). Thin films (14 and 32 nm) of good optical quality have been obtained by deposition of the monomer from chloroform solutions on glass by standard spin-coating technique, followed by thermal polymerisation at 115 °C. Complex index of refraction of a thin film deposited on a 1 mm thick fused silica substrate has been determined in the spectral range from 270 to 1700 nm by ellipsometry. Third-order optical susceptibility ( χ (3)) has been measured by Third Harmonic Generation (THG) technique on a thin polyDPCHD film deposited on a 160 μm thick BK7 substrate in the spectral range from 1000 to 1900 nm, using the Maker fringes method. The χ (3) dispersion shows the typical resonant behaviour due to multi-photon processes and is strictly related to the absorption spectra in the visible range. Values of χ (3) of the order of magnitude of 10 −11 esu have been obtained. A comparison between linear and non-linear optical properties of polyDPCHD and poly[1,6-bis(3,6-dihexaedcyl- N-carbazolyl)-2,4-hexadiyne] polyDCHD-HS will be presented.