What is an Ellipsometer?
Ellipsometry is an optical technique for measuring the thickness and optical properties of extremely thin films, or layers, of material. The measurable properties are the refractive index, or how much light is bent, and the level of light absorption, called the absorption coefficient. An ellipsometer is a device used to perform these measurements. Ellipsometers work by shining a well-defined source of light on a material and capturing the reflection. Modern ellipsometers use lasers, typically Helium-Neon lasers, as the source. The ellipsometer beam first goes through a polarizer so that only light orientated in a known direction is allowed to pass. It then goes through a device called a compensator, which elliptically polarizes the light beam. The remaining light is then bounced off the material under study. The analysis is dependent on Snell’s Law; when a beam of light strikes a material, some will reflect immediately, and some will pass through to the far side of the material before
