Optically stabilized reflectors are demonstrated in this dissertation. These systems consist of a cholesteric liquid crystal with temperature sensitive helix pitch, in combination with a light absorbing dye. Light entering the liquid crystal is absorbed by the dye, generating heat which raises the temperature of the liquid crystal. The resulting change in the pitch length of the cholesteric causes an increase in its reflectivity, reducing the intensity of light absorbed by the dye. This negative feedback stabilizes the reflector for a given light intensity. The device provides a reflectivity which increases with increasing intensity of incident light. Two configurations of this device are demonstrated both in experimental measurements and in mathematical models. Additionally, a new kind of liquid crystal-polymer composite system is introduced. This system is made by dissolving 8% ~ 20% of acrylate monomers into thermotropic liquid crystals, and then photopolymerizing the homogeneous mixture. Electro-optical effects in nematic gels are studied. These nematic gels show different qualities from those of ordinary nematics and polymer stabilized liquid crystals. By using conoscopic method to measure the birefringence of this system under an electric field, certain gel properties can be understood. A piezoelectric effect in cholesteric gels is also demonstrated. When a shear stress is applied to a cholesteric gel in the direction perpendicular to its helical axis, a polarization can be induced in the direction perpendicular to both the stress and the helix. This experimental observation agrees with the theory proposed by Pelcovits and Meyer.
- Pub Date:
- May 1997
- Physics: Condensed Matter, Physics: Electricity and Magnetism, Physics: Optics