Determination of refractive indices for liquid crystals using a double transmission technique

We report a new, to the best of our knowledge, approach to determine the refractive indices (RIs) of liquid crystal (LC) systems by considering a double transmission phenomenon of a light beam within the LC medium and the principle of the wedged-cell refractometer. This modified system delivers better spatial resolution of refracted beams in terms of well-resolved spots, compared to the single transmission of a beam in the conventional thin-prism method. The deviation angle obtained in this method is found to be comparatively greater than that of the thin-prism method. The higher values of deviation angle are described using a theoretical model and further experimentally demonstrated for the 5CB nematic LC compound. The variation of the principal RIs (n_o, n_e), and hence the birefringence (Δn) with temperature as well as electric field is investigated for both transmission methods. A relative comparison is carried out between the simulated and standard values obtained from literature. The present technique provides a higher spatial beam resolution to determine the RIs and birefringence of LC systems, which can be very advantageous for different modern photonic applications based on beam shaping and steering.