Diffusion model of photoaligning in azo-dye layers

Abstract

The model of the rotational diffusion of the azo-dye molecules under the action of polarized uv light was used to explain the formation of the photoinduced order in azo-dye layers. We consider both the approximations of negligible and strong molecular interaction during the process of the reorientation under the field of a polarized light. We constructed an experimental setup, based on a photoelastic modulator, that allows accurate in situ measurements of the phase retardation $\delta$ of thin film as a function of the exposure time $t_{\exp }$ and exposure power $W(\mathrm{W}∕{\mathrm{cm}}^2)$. A good agreement with experiment was observed. Fitting the experimental curves $\delta \left(t_{\exp }\right)$ for different power values $W$, we can estimate the coefficient of rotational diffusion $D$, azo-dye order parameter $S\left(t_{\exp }\right)$, and other parameters of the rotational diffusion model.