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24 October 2000 Characterization of optical devices based on liquid crystals embedded in porous thin films
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Porous, chiral thin films with controlled microstructure fabricated by glancing angle deposition (GLAD) exhibit unique optical properties. The observed optical activity and circular birefringence in these films have been compared to those of cholesteric (or chiral) liquid crystals. Porous GLAD films have been previously demonstrated as alignment 'backbone' structures for liquid crystals (LC) embedded in the pores of the films, leading to a new class of composite optical materials. GLAD films with chiral, or 'helical,' microstructure have been found to impose a chiral nematic-like molecular ordering in non-chiral nematic liquid crystals. The addition of nematic LCs to the films was found to enhance significantly the chiral optic response compared to that of the film alone. Recently, we demonstrated electro-optic switching of the LC component in optical devices based on GLAD-LC composites. In an unaddressed state, the GLAD film induces chiral nematic-like alignment in the embedded LC, with the GLAD film controlling pitch and handedness of the aligned LC. In an addressed state, the LC molecules align parallel to the field and by index matching, the chiral optic response of the device vanishes. In this work, we present extensive optical characterization of the GLAD-LC composite materials including measurements of optical rotation and circular dichroism, switching behavior, and analysis of structure- property relationships.
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Jeremy C. Sit, Scott R. Kennedy, Dick J. Broer, and Michael J. Brett "Characterization of optical devices based on liquid crystals embedded in porous thin films", Proc. SPIE 4107, Liquid Crystals IV, (24 October 2000);

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