Simultaneous determination of the spatial variation in the pretilt angle and thickness of a liquid crystal cell using the crystal rotation method

Abstract

The large optical nonlinearity of dye-doped nematic liquid crystals makes them promising materials for various photonics applications such as dynamic holography, image processing and adaptive optics. Studies of the nonlinear optical properties of liquid crystals are performed to better evaluate their suitability for these applications.
The correct measurement of the geometrical properties of LCs (e.g. thickness) is important in the proper interpretation of results from studies of the nonlinear optical properties of liquid crystals. In information processing, any thickness difference can result in high noise level or false processing. Another important geometrical property is the pretilt angle. This is the average tilt of the LC molecules with respect to the surface for samples aligned by rubbing polyimide layers on the glass substrates.
Various techniques such as magnetic null method, capacitance method and crystal rotation method have been used to determine the pretilt angle. Interferometric techniques can be used to determine the thickness of materials. However, interferometric measurement is not so simple due to the birefringence of liquid crystals. In this research, the thickness and pretilt angles of liquid crystal cells are both determined using the crystal rotation method.