Mechanism of LCD Photoalignment

摘要

The mechanism of photo-alignment (PA) of azodye molecules is investigated. We show that PA takes place due to the pure reorientation of the molecular absorption oscillators perpendicular to the UV-light polarization. The model of the rotational diffusion of the azodye molecules in the field of polarized UV-light was used to explain the formation of the photo-induced order in azodye layers. We constructed a special experimental set-up, based on a photo-elastic modulator, that accurately measures of the phase retardation δ of thin film as a function of the exposure time t_(exp) and exposure power W (W/cm~2). The optical anisotropy was induced by a pump beam of Ar~+ laser (λ=457 nm). Fitting the experimental curves δ(t_(exp)) for different power values W, we can estimate the coefficient of rotational diffusion D and azodye dynamic order parameter S(t_(exp)).