Liquid refractometry by the rainbow method

Abstract

A new method for measuring the refractive index of liquid, proposed in a previous paper [Appl. Opt. 36, 5552–5556 (1997)], has been developed. The minimum deviation of a laser beam deflected by a liquid-filled cylindrical cell was calculated by use of geometric optics. These theoretical results were compared with experimental results, with excellent agreement. As a result, the unknown refractive index of a liquid could be obtained by use of a computer calculation to give a best fit. The computer calculation showed that the sensitivity of the refractometer increases with the cell-wall thickness until total reflection takes place. A small refractive-index difference can be detected within a precision of 1 × 10^-6 by use of a metal-oxide semiconductor linear image sensor. We show how to calibrate the refractometer with pure water at 3.98 °C.