Device for measuring the refractive index of transparent liquids based on a sectoral diffractive sensor element

Subject of study. A device for measuring the refractive index (RI) of transparent liquids has been developed; its operating principle is based on the use of a sectoral diffractive sensor element. Aim of study. The aim of this study is to develop a diffractometric device for measuring the RI of transparent liquids over a wide range of values using a statically installed diffractive sensor element with a diffraction pattern recording unit. Method. In the proposed approach, a diffractive grating immersed in the liquid under study is illuminated with laser radiation, and the angular positions of the diffraction orders are measured to determine the RI of the liquid. To extend the range of measurable values of the RI without loss of accuracy, a single grating is replaced by the sectoral diffractive sensor element developed in this study, which comprises a set of diffractive gratings with different periods and angular orientations. Main results. A diffractometric device for measuring the RI of transparent liquids has been successfully developed. Its distinguishing feature is the use of a sectoral diffractive sensor element consisting of four diffractive gratings with different periods and angular orientations. An experimental prototype is fabricated, which enables RI measurements of transparent liquids in the range of 1.3200–1.7200 at a wavelength of 639 nm. Practical significance. The proposed concept of a diffractometric device for measuring the RI of transparent liquids allows simplifying the design of these types of devices, reduces their cost, and improves both the speed and accuracy of the measurements performed.