Accurate laser-based characterization of liquid refractive index for advanced undergraduate laboratories

This paper presents a compact, low-cost optical setup designed for measuring refractive indices of liquid samples. The system employs a tilted transparent quartz cuvette placed on a rotating stage, where a small angular offset between the laser beam and the cuvette induces a lateral displacement of the transmitted beam. By quantifying this displacement, the refractive index of liquids (water and 1-propanol in this paper) is determined with minimal optical complexity. The laser beam displacement is accurately quantified by the knife-edge technique. Key physical quantities, including beam displacement and refractive index, are derived through an optical ray transfer matrix. Students typically obtain accuracy of three significant figures after the decimal point. Experimental results demonstrate agreement with theoretical models, validating the method's precision for applications in materials science, biochemical sensing, or quality control. Considering the simplicity, affordability, and versatility of this device, the setup integrates practical optical experiments with fundamental optical principles, making it well-suited for both research and educational environments.