Dual scanning interferometric technique for measurements of the temperature and concentration dependence of the refractive index of liquids

Abstract

A novel laser interferometric technique for measuring the variation of the refractive index with concentration and temperature is presented. The technique is based on the principle of ‘absolute scale’ accomplished with a Michelson interferometer. The linear motion of the scanning mirror allows simple extraction of the optical path change inside the Fabry–Perot interferometer. The measurement of the relative positions of the interference maxima reduces the sensitivity of the system to intensity noise and drift of the laser source. The sensitivity to the changes of the refractive index is of the order of 1 × 10−7 for a 20 mm optical path.