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 ␦ of thin film as a function of the exposure time t exp and exposure power W ͑W/cm 2 ͒. A good agreement with experiment was observed. Fitting the experimental curves ␦͑t exp ͒ for different power values W, we can estimate the coefficient of rotational diffusion D, azo-dye order parameter S͑t exp ͒, and other parameters of the rotational diffusion model.

The photoinduced alignment of ferroelectric liquid crystals (FLCs) onto photochemically stable azo-dye films was studied. The alignment quality of FLC display cells depends mainly on the difference between the FLC surface energy and the aligning substrates surface energy; however, the structure and thickness of FLC layers are also important. The effect of the thickness of photoaligning azodye layer on the alignment quality and multiplex operation of passively addressed FLC display cells has been investigated. An optimal (about 3-5 nm) azo-dye layer thickness that provides both the highest multiplex operation steadiness and the best contrast ratio of the FLC display cells was found. The photoaligned FLC display cells showed the contrast ratio CR > 500 : 1 at the wavelength ¼ 0:63 mm both in surface stabilized and deformed helix FLC electrooptical modes.

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