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We develop the method of determining the threshold voltages of a cholesteric-nematic transition which is based on the analysis of conoscopic images. To improve the measurement accuracy of the threshold voltages and to eliminate the effect of a radiation wavelength, we propose a new method which also could be efficiently used to study the influence of surface conditions on the liquid crystal texture and to obtain the additional information about the liquid crystal texture in the process of cholesteric-nematic transition. [ABSTRACT FROM AUTHOR]

In this article the investigation of the cholesteric-nematic transition in thin layers of nematic-cholesteric mixtures is carried out. Nematic-cholesteric mixtures based on a nematic matrix MLC-1 with a low concentration (up to 2%) of an optically active dopant were the object of this investigation. The dependencies of threshold voltages of focal-conic deformation and forward cholesteric-nematic transition for different thicknesses of a liquid-crystal layer are obtained. It was demonstrated that the twist effect in induced cholesterics can be considered as a simple case of a cholesteric-nematic effect in thin liquid-crystal layers. [ABSTRACT FROM AUTHOR]