Optical Kossel line study of an aligned monodomain sample of a cholesteric phase: Temperature evolution of the Kossel diagram

Abstract

In the preceding paper, the optical Kossel diagram of an aligned monodomain sample of a cholesteric phase was studied. The Kossel diagram reported was a single annular broad ring containing fine detail which depended on the polarization conditions of the incident light. With crossed polarizers there was a pattern of four spiral arms and a central more intense band. The pattern was shown to be consistent with the analytical treatment of the selective reflection of light by the cholesteric phase of Oldano et al. This paper extends the investigation to explore the way in which the appearance of the Kossel ring changes with the temperature and hence the pitch of the sample. Measurements of key positions on the Kossel rings and the features contained within them are shown to be in good agreement with theory. The measurement of the pitch of the cholesteric phase from the Kossel diagrams is also described.