The refractive index is an important material parameter, not only for optical applications. In mixtures, the refractive index can be used to determine the concentration of the components. Non-contact optical methods are particularly advantageous in the life sciences, as they eliminate the need for sampling and the risk of contamination.
In the completed research project, a new optical sensor was developed for the high-precision determination of refractive index changes, which can be used to determine concentrations using the examples of “ethanol in water” and “water content in dimethyl sulfoxide (DMSO)”. In addition, the result should also be suitable for applications in a flow cell, so that applications without sampling can be addressed in the future. The measuring principle is based on laser excitation and the correlation of speckle patterns, which are detected using image sensors. For this purpose, deterministic, i.e., specially calculated, optical diffusers made of chemically resistant quartz glass or fused silica were developed.
The graph shows a correlation matrix (correlation coefficient of the images color-coded) for 15 measurements of different ethanol concentrations in deionized water (zero vol.% ethanol [first 5 measurements]; 7.41 vol.% ethanol [second 5 measurements]; 10.71 vol.% ethanol [third 5 measurements]) for a measurement setup with the novel refractive index sensor with a deterministic diffuser made of fused silica.
The research and development work described was funded by the German Federal Ministry for Economic Affairs and Energy (BMWE) as part of the “New Refractive Index Sensor” (NBZ) research project.
Funding code: 49MF220065
