Mapping the changes in the optical properties of azobenzene films due to photoisomerization

•Noticeable changes of ellipsometry parameters during the glass transition temperature.•Spin coating preparation of poly(disperse Red 1 methacrylate) azobenzene (PDRM) films.•The absorption band of the PDRM films slightly decreases with temperature.•The photo isomerization of the PDRM films depends on the polarization of laser used. We used spectroscopic ellipsometry to study the dielectric function of an azobenzene polymer called Poly(disperse Red 1 methacrylate) (PDRM) as it underwent a photoisomerization process. The polymer films were fabricated by dissolving PDRM in tetrahydrofuran, and by spin coating films on silicon substrates. After fabricating the films, we used UV-VIS spectroscopic ellipsometry to determine the index of refraction, extinction coefficient and the thickness of each film. Using a heating cell coupled to the ellipsometer, we obtained temperature dependent ellipsometry data from 34 ℃ to 180 ℃, spanning a spectral region between 300 nm and 1500 nm. Using the raw data, we determined that the glass transition temperature of PDRM was 85 ℃ ± 3 ℃. Employing a three-oscillator model, we deduced the temperature dependent dielectric functions of PDRM films. Subsequently, the films were photoisomerized at two polarizations using a visible laser. For the horizontal polarization, there is nearly a 15% a change in the extinction coefficient as the PDRM films undergo a photoisomerization process.