Estimation of refractive index of crystal plate from Haidinger fringes

We proposed and realized an accurate method for measuring the refractive index and physical thickness of a transparent wafer by analyzing the Haidinger fringes. Simply, we took transmitted Haidinger fringes caused by multiple reflections at the back and rear surfaces of the wafer, which worked as a Fabry-Perot eatlon. The refractive index was determined by analyzing the interferogram obtained in terms of an incidence angle at a single-shot. Based on the proposed method, the absolute value of the refractive index of a LiNbO₃ wafer was estimated with an overall uncertainty of 10^-4.