Optical constants of azopolymer PAZO thin films in the spectral range 320 - 800 nm
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2018-04-05
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Abstract
Azobenzene containing polymers (azopolymers) have been investigated for a number of applications - holographic data storage, polarization optical elements, diffractive gratings, etc. Herein we report on the optical characteristics of films obtained from the commercially available water soluble azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt). Thin films were deposited by spin coating and their thickness was determined by a Talystep precision profilometer. The FTIR spectra of PAZO were measured between 3000 cm-1 and 500 cm-1. For the first time, to the best of our knowledge, we evaluated the PAZO complex refractive index continuously in a broad spectral range (320 - 800 nm) based on transmission and reflection spectrophotometric data. The wavelength dependence of the complex refractive index of organic dyes layers cannot be readily described with dispersion models used for crystals, metals or semiconductors. This is why we used a derivative approach on a wavelength-by-wavelength basis to solve a set of two nonlinear equations with two unknowns - the real and imaginary parts of the refractive index. The determination of the optical constants of PAZO films is effective and robust.