ABSTRACT
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 (Δε>0) the refractive index was found to decrease continuously with increasing field. In a system with Δε>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.