Electric Field Induced Variation of the Refractive Index in Cholesteric Blue Phases

To study the electric field induced deformation of blue phases in greater detail the variation of the refractive index δn for light propagating in field direction was investigated. In a system with positive dielectric anisotropy (Δe>0) the refractive index was found to decrease continuously with increasing field. In a system with Δe>0 the opposite behaviour was observed. The time constant of this effect is in the range of a few milliseconds, whereas that of the shift of the wavelength of selectively reflected light at maximum intensity was found to be larger by about three orders of magnitude. A simple model is proposed to describe the field induced deformation of blue phases.