Basic experiments on measurement of salinity using a heterodyne double-pass interferometer

We propose a new method to measure the salinity of seawater using a heterodyne double-pass interferometer. Results of preliminary experiments show that the effect of the temperature was reduced by about one order of magnitude when compared with Michelson interferometer. The measured phase difference between pure water and 3.5 ‰ salt water of 182.0 degrees was slightly higher than that of the theoretically expected value of 176.0 degrees. The possible cause of this error is discussed in this paper.