Abstract
The temperature gradients of refractive indices, and , of three nematic liquid crystals (E7, E44, and E48) are analysed at different wavelengths. For the temperature gradient of , there exists a crossover temperature, Tco. The wavelength dependence of the crossover temperature is reported. The dispersion behaviour of , the birefringence in the crystalline state or at T = 0 K, is also tested.