Determination of optical birefringence of S-benzylisothiouronium chloride and S-benzylisothiouronium nitrate using Cauchy's two term model by the channelled spectrum method

The channelled spectrum method was used for measuring the birefringence of anisotropic organic single crystals S-benzylisothiouronium chloride (SBTC) and S-benzylisothiouronium nitrate (SBTN). Crystals of uniform thickness were placed between crossed polarizers and illuminated with a tungsten source. The resulting pattern was analyzed to deduce the birefringence and its dispersion across the visible spectrum. Cauchy's two term formula was applied to fit the experimental data. The Cauchy's coefficients A and B were obtained by solving the linear equations using MATLAB®. The wavelength dispersion of birefringence was calculated.