Total internal reflection based sub-wavelength grating sensor for the determination of refractive index of liquids

In this work we present an optical refractive index sensor based on the Grating Light Reflection Spectroscopy (GLRS) method. The sensor consists of the finely spaced diffraction grating (sub micrometer region) that is in contact with the analyte (liquid or gas). Shining the polarized polychromatic light on the grating at the threshold angles of incidence and analysing the spectral response of the specular reflection we have observed steep changes of the reflection coefficient at certain wavelength values. We have shown that for the liquid analytes specular reflection spectra demonstrate double peak that can be used as one more parameter in the spectroscopic measurements. The detailed analysis of the spectral composition of the specular reflection illustrates ability of control of refractive index of analyte at least for two wavelengths at constant angle of incidence.

Research highlights▶ Refractive index sensor based on sub-wavelength period grating. ▶ Spectroscopic analysis of polarized polychromatic light reflected from the grating. ▶ Refractive index is obtained for two wavelengths at constant angle of incidence. ▶ Measurements at many angles of incidence defines dispersion curve of the analyte.