Measurement of Optical Properties of Aqueous Lithium Bromide Solutions with and without Surfactant for Potential Use in Interferometric Analysis of Absorption Systems

The refractive indices of aqueous lithium bromide (LiBr–H₂O) solutions were measured over a wide range of mass fractions, from 0 to 0.62 kg/kg (62%), at seven wavelengths between 436.1 and 655 nm. Measurements were conducted over a temperature range of 296.15 to 320.15 K, with 1 K increments, using a commercial refractometer. In total, 3485 refractive index measurements were recorded, covering 35 compositions at 25 temperatures for each of the seven wavelengths. A parametrization model was proposed to unify the data set. The wavelength dependence of the refractive indices was further analyzed by using the Cauchy dispersion relation, from which three main coefficients were determined to predict n(λ) for arbitrary wavelengths. Additionally, the optical contrast factors ∂n/∂T and ∂n/∂w were determined from the parametrized data. The effect of the surfactant (1-octanol) on the refractive index and contrast factors was carefully analyzed.