Spatially Resolved Optical and Electro-Optic Properties of Electroclinic Liquid Crystals
NAVAL RESEARCH LAB WASHINGTON DC OPTICAL SCIENCES DIV
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Chiral smectic A Sm A liquid crystals are of increasing interest because of their potential for fast analog electrooptic modulation. Chiral smectic A liquid crystals, when viewed between crossed polarizers, exhibit distinctive periodic stripe domains due to a voltage dependent deformation of the bookshelf geometry. These stripe domains reduce the contrast ratio of electrooptic devices employing these materials. This paper describes a novel optical technique to probe spatial variations in the optical properties of liquid crystals with micron resolution. The effect of the stripe formation on the electrooptic properties of a electroclinic Sm A liquid crystal, denoted as KN125, is investigated. The electric field induced stripe domains were experimentally characterized by measuring the transmission of KN125, interposed between crossed polarizers. A sharply focussed visible CW laser beam was translated across the sample with one-micron resolution. A quasi periodic modulation of the transmission due to stripe deformation of the bookshelf geometry was observed. Measurements performed within a single stripe and between adjacent stripes permitted an independent determination of the true optical tilt angle and that of the stripe deformation. The electric field dependence of the optical tilt angle for the KN125 liquid crystal is reported.
- Electrooptical and Optoelectronic Devices