Laser etched gratings on polymer layers for alignment of liquid crystals

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Abstract
Liquid crystal alignment layers are prepared using a noncontact method based on laser ablation. Nonpolarized light from a KrF excimer laser at 248 nm is exposed through a phase mask to etch gratings of period 1.1 μm onto polyimide alignment layers. Twisted nematic cells were prepared using one rubbed and one grating aligned surface, and azimuthal anchoring energies were found from measurements of the twist angles as a function of grating depth. The measured anchoring energies agree with those predicted from the minimization of elastic strain energy when the liquid crystal directors at the surface are aligned parallel to the groove of the grating. This suggests that topographical rather than epitaxial alignment is achieved.