Heterostructure thickness measurement is an important quality control step after deposition. It can work together with the in-situ real -time thickness control  or instead of it.  Heterosctructure filmstack ,typically, consists of repeated alternating layers of low and high reflective index material, e.g. Al oxide  and Zn oxide. Double layer can be repeated 10s or 100s of times – typically from 60x to 200x. They are widely used for filters, anti-reflection coatings and other applications. One of these applications is LED and semiconductor laser: heterostructure filmstack, in this case, is used to concentrate light radiation in the narrow wavelength range.  Frequently, optical constants of the constituent materials are measured separately and only thickness is measured in the actual heterosctucture. Unfortunately, it is not always possible because materials in heterostructure may have different optical properties. It is possible , however, to measure both thickness and optical constants assuming that all the same material layers have identical properties.