Angstrom Advanced  PHE-102 series is a variable angle spectroscopic ellipsometer operating in the spectral range 250 - 1100nm, 250-1700nm or 250-2100nm. In the PHE-102 ellipsometer a broad band white light source is used to illuminate the sample spot. The layer stack imparts a change in state of polarization to the light and is reflected back through the analyzer and into the detector; where it is measured under the ellipsometric parameters of Psi and Delta. The spectral dependence of the refractive index, dielectric constants of the materials and other parameters under measurement are determined by comparing the measured data to a theoretical model, which defines the layer structure in detail.