Bruning et al. developed the first phase-shifting interferometer (PSI) in the 1970s. The PSI technique is used to determine the diffusion field in the area of interest in real-time as it hashigh spatial and time resolution. We know in a dilute solution; the refractive index varies linearly with the concentration of the solute . The interferometer measures this refractive index change, which is then used to obtain the concentration profile and subsequently the diffusion coefficient. The PSI scans the interference fringes, leading to the development of a detailed pattern of the observation region. A local profile is generated between two neighboring fringes on an atomic level.