Ellipsometry is an optical measurement techniques that uses reflection from (or transmission through) the surface of a thin film or stack of films to determine the complex refractive index of a given layer. A polarizer is used to vary between s- and p-polarized incident light and an analyser and photodetector are used to measure the changes in polarization. By monitoring the changes in ratio of reflected or transmitted intensities of the two polarizations for each wavelength, the full complex refractive index can be recovered by fitting the measured data to fundamental physical models such as the Drude-Lorentz for metals. This is a very useful process when investigating a material with an unknown refractive index or determining the thickness of a sample with known optical properties.

The Woollam V-VASE Ellipsometer is fully-automated, mounted on a rotating stage that allows for angles of incidence between 15⁰ and 90⁰ (0.01⁰ accuracy) with a detection range spanning from the ultraviolet to near infrared (240-1700nm) selected using a monochromator. Equipped with a rotating analyser, the equipment can reliably measure a diverse range of materials including dielectrics, semiconductors, metals and polymers. With the vertical-mount, this system is capable of both reflection and transmission measurements. Shown below are the ellipsometric measurements of aluminium fitted to a Drude-Lorenz model showing both the intraband and interband absorption behaviour.