Optical response of azopolymer (PAZO) layers doped with TiO2 nanoparticles

In this paper we analyze the optical response of azopolymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido] -1,2-ethan-ediyl, sodium salt]), shortly denoted as PAZO. The photoinduced birefringence of this material has a potential for polarization holographic recording. We consider thin PAZO layers with embedded TiO2 spherical particles. This is a numeric simulation motivated by the search of photoinduced birefringence enhancement in azopolymer layers. The scattering of a single particle in the dye-polymer matrix is calculated using the exact vector Maxwell equations. The particles are treated as ensemble of non-aggregated spheres with normal distribution of sizes, characterized by the mean radius <r> and standard deviation sigma = <r>/ 4. Multiple scattering by individual particles is ignored. The refractive index of the PAZO matrix at 442 nm has a complex value (due to absorption) as we have determined it from experimental spectrophotometric data. The 442 nm wavelength is commonly used for recording polarization holographic gratings in azopolymer materials. Embedded TiO2 spheres with mean radius from 10 to 80 nm are considered. The angular dependences of all the scattering matrix elements, which describe the optical response of the composite layers, are estimated.