==Method of operation==
*Elliptically polarized light is reflected from the measurement sample and is analyzed in p- and s- vector components.
**p- polarized light is in the plane of incidence
*Since ellipsometry measures both intensity and phase information, thickness and optical constants can be extracted. [[Spectroscopic reflectometry]] only measures reflected intensity vs. wavelength and is only capable of extracting film thickness by using a fixed set of optical constants for the thin film material in a material file stored on the tool.