Feodor Oestreicher

Observation of Electro-Optical Effects in Blue Phase Systems

Abstract The blue phases of two cholesteric systems are studied under the influence of an electric field. The wavelength of maximum absorption due to the selective reflection of circularly polarized light of both blue phase I (BP I) and blue phase II (BP II) turns out to be shifted to longer wavelengths with increasing electric field. In addition to that, a phase transition from BP II to BP I is observed for one of the systems used. Under favorable conditions, brilliant color changes from blue to red are observed in the reflected light.

Determination of the Cholesteric Screw Sense

Abstract If a cholesteric liquid crystal is placed between a glass plate with planar alignment and a spherical lens with concentric surface alignment, a double spiral disclination line appears. The spiral rotation sense depends on the helix screw sense of the cholesteric phase and the radial distance between the disclination lines on the pitch magnitude. A theoretical calculation of the form of the spiral disclination lines is given and compared with experimental results.