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12 September 2007 Tuning of a cholesteric filter having a negative dielectric anisotropy
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We have studied the tunability of the reflection notch of a cholesteric filter containing a negative dielectric anisotropy LC in a planar alignment. For this purpose, we studied physical, optical and electro-optical characteristics of mixtures containing chiral dopant S811 and the negative dielectric anisotropy liquid crystal ZLI-2806. Interestingly, smectic A phases were seen at room temperature for S811 loadings >20% by weight of ZLI-2806. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) studies confirmed the formation of a cholesteric phase above room temperature. A phase diagram was constructed by varying S811from 9-50% by weight in the mixture. Reflection notchs were not seen at room temperature for compositions of S811 >20%. On heating, the selective reflection notch of the cholesteric phase appeared and blue shifted with temperature. Various methods of tuning the reflection notch were examined. Thermal tuning from 2200 nm to 450 nm was observed over the temperature range 23 to 55° C. Application of a DC field led to electrical tuning (~50 nm) of the notch. The notch was also tuned (>500 nm) optically by exposing a dye doped cholesteric cell to laser lines at either 532 or 647 nm.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Lalgudi V. Natarajan, Jeremy M. Wofford, Vincent P. Tondiglia, Richard L. Sutherland, Stephen A. Siwecki, Hilmar Koerner, Richard A. Vaia, and Timothy J. Bunning "Tuning of a cholesteric filter having a negative dielectric anisotropy", Proc. SPIE 6654, Liquid Crystals XI, 66540A (12 September 2007);

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