Spectroscopic Ellipsometers are optical thin film measurement tools for determining film thickness and optical constants (n,k) of thin film structures. They are widely used in the microelectronics, display, photonics, photovoltaics, lighting, optical and functional coating, biotechnology industries. When compared with other optical metrology instruments the unique strength of spectroscopic ellipsometers are based on their highly precise and simple experimental measurements plus physical and material information derived from optical constants characterization.