Quantitative interferometric measurements of the refractive index and its applications

Abstract

Optical interferometry is a non-contact method used for the imaging and measurement of the optical properties of small or large objects with nanoscale accuracy. Interferometers are essential optical systems in engineering and medical science and are generally used to measure refractive index changes, cell pathology and shape irregularities. The ability to provide quantitative, non-invasive measurements makes interferometers suitable candidates for the study of living cells in vivo and in vitro applications. In this study, a simple interferometric system capable of providing precise measurements of the refractive indices of transparent and semi-transparent mediums was designed and developed based on the Mach-Zehnder arrangement. During the development phase, the system was used to take precise measurements of the contrast factors of the three hydrocarbon components 1,2,3,4-Tetrtahydronaphtalenene (THN), Isobutylbenzen (IBB), and Dodecane (nC12), prepared in the laboratory. The results were also compared with the corresponding results obtained using the Abbemat refractometer. The results were in agreement with those obtained from both techniques as well as the results obtained from the literature, confirming the accuracy of the measurements obtained with the new system with deviations of ± 2.50×10-3. Blood analysis is a routine procedure used in medical diagnostics to confirm a patient’s condition. Measuring the optical properties of blood is difficult due to the non-homogenous nature of the blood itself. In addition, there is a lot of variation in the refractive indices reported in the literature. These are the reasons that motivated this research to develop an empirical model that can be used to predict the refractive index of human blood as a function of concentration, temperature and wavelength. The experimental measurements were conducted on mimicking phantom, that shows better stability compared to human blood, using the Abbemat Refractometer. The values obtained using the model was in substantial agreement with those obtained experimentally with standard deviations of ± 2.33×10-3. Once the accuracy of the interferometric system was confirmed, the system was used to study the refractive index and morphology of human red blood cells. The results of the analysis confirmed the system’s ability to determine refractive index and/or blood hematocrit values with appropriate clinical accuracy.