Liquid refractometer based on interferometric fringe projection

Measurement of the refractive index of liquids is of great importance in ap plications such as the control of adulteration of liquids and pollution mon itoring. We present and discuss a fringe projection technique for measuring the index of refraction of transparent liquid materials. In the proposed t echnique a fringe pattern produced by a reflective grating interferometer i s imaged by a lens before passing through a cell containing the liquid samp le under test. The interference pattern consists of a family of parallel st raight fringes that are digitized by a CCD array. The focal shift, which is induced by the liquid sample, produces changes in the spatial frequency of the projected pattern. Spatial frequency of the fringe pattern is analysed by means of a one-dimensional Fourier transform and phase demodulation pro cedure. The principle of the proposed fringe projection refractometer relie s on a comparative measurements of the refractive index of the sample under test with respect to a reference liquid, The method is simple and can be e asily interpreted geometrically. (C) 2000 Elsevier Science B.V. All rights reserved.