Basic experiments on measurement of salinity using a heterodyne Michelson interferometer

In order to develop a new optical method to measure the refractive index of seawater having longterm stability, we propose to use a heterodyne Michelson interferometer. We made a prototype, and measured the difference of refractive index of pure water and 3⁰/₀₀ saline water in order to evaluate the possibility of the proposed method. The result coincided with the theoretically expected value within an accuracy of ±1.6×10^-5. In this paper we present the outline and the results of basic experiments, and discuss the feasibility of the proposed method.