Liquid Crystal Alignment on the Patterns Produced by Nonlinear Laser Lithography

Liquid crystal (LC) based devices such as displays, spatial light modulators (SLM) and different switchable phase masks constitute the main part of the graphic information display and light control. Mechanical rubbing and photo-alignment are the most widely used industrial technologies to create anisotropic surfaces for these devices. Recently, nonlinear laser lithography (NLL) was introduced as a fast, cost effective method for large area nano-grating fabrication based on laser-induced periodic surface structuring [1]. Here we report on alignment of nematic LC on NLL treated Ti film deposited on glass for the first time. We demonstrate controllable changes of azimuthal anchoring energy (AAE) depending on processing and additional coating parameters. To create the large area of structured Ti layers we used the experimental scheme of the NLL method, as described in [2]. The setup consists of a home-made femtosecond fiber laser system (up to 1.8 μJ pulse energy at 1 MHz repetition rate), galvanometer-scanner and motorized 3D-translation stage. The samples were 300 nm Ti films deposited on glass. 5×5 mm ² zones were structured by raster scanning of the laser beam over the surface with different parameters. To measure the twist angle and further calculate the AAE we have made combined twist LC cells. LC cells consisted of the tested and reference substrates where the last one was a glass substrate coated with a polyimide PI2555 and processed by the rubbing technique. The first type of the tested substrate was coated with Ti layer and further processed by the NLL method. The second type of the tested substrate was additionally coated with ODAPI. The twist angle was measured by using the combined twist LC cell method. Later, the AAE was calculated from the obtained twist angles of different samples. Fig. 1 (a-c) demonstrates dependencies of the measured twist angles and calculated AAE for different samples. We obtain controllable changes of the anchoring energy in the range between 2×10 ^-6 J/m ² to 10 ^-4 J/m ² . The highest AAE 10 ^-4 J/m ² is obtained for the samples which are processed by NLL with post-coating by ODAPI.