Smartphone-based system for measuring liquid refractive index

Abstract

The liquid refractive index is one of the important optical parameters reflecting the properties of solution. A simple scheme based on shading effect for measuring liquid refractive index is presented. When a light beam passes through the liquid, the total reflection occurs at the interface with the air to produce a shading effect, forming a circular shading pattern, and its radius is related to the refractive index of the liquid. Based on this principle, a liquid refractive index measurement system based on smartphone is built. A rectangle colorimetric dish with tested liquid is illuminated by He-Ne laser. A white stickable label paper is attached to one side of colorimetric dish. Then the circular shading pattern displayed on label paper can be recorded by smartphone. A smartphone data processing program was developed to calculate the liquid refractive index from the image taken by smartphone. System calibration and smartphone shooting parameters are discussed in detail. The refractive index measurement experiments of sucrose solution and sodium chloride solution with different concentrations demonstrate the feasibility and effectiveness of the proposed method.