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The Study of Refractive Indices of Liquid Crystal Mixtures

In the present study the ordinary refractive indices of Nematic liquid crystal (LC), Cholesteric liquid crystal and their mixtures were measured by multiple wavelength refractometer in the visible range with temperature range from 20°C to 80°C. As the wavelength increases, the refractive indices may decrease. As the temperature increases, the refractive index may decrease. The ordinary refractive index decreases or increases depending on the crossover temperature of the Liquid Crystal employed. The wavelength- and the temperature-dependent refractive indices are fundamentally interesting and practically important for optimizing the display performances and other photonic devices employing LCs. We also tried to investigate factors affecting the temperature gradient of ordinary refractive index (dno/dT).Liquid crystal should exhibit a large temperature gradient refractive index to reduce the required laser intensity for triggering the nonlinear optical effects. The two crucial parameters for achieving large dno/dT are high birefringence and low clearing point. However, these two requirements are often conflicting each other. The temperature at which dno/dT = 0 is called the cross-over temperature To. If Tc, the clearing temperature of liquid crystal material is much higher than the room temperature then the cross-over temperature would be relatively high and dno / dT < 0 at room temperature. From all the investigations it is observed that the values of refractive index change with temperature, wavelengths as well as with the mixture. Some of the liquid crystal mixtures show excellent index matching property.