In the semiconductor industry, infrared light can be used to characterize materials such as thin films and periodic trench structures. By measuring the reflectance of light from the surface of a semiconductor wafer, the index of refraction (n) and the extinction Coefficient (k) can be determined via the Forouhi-Bloomer dispersion equations. The reflectance from the infrared light can also be used to determine the critical dimension, depth, and sidewall angle of high aspect ratio trench structures.

Answer this question, if possible (if impossible, reply "unanswerable"): Along with critical dimension and depth, what can infrared light reflectance be used to determine in regard to index of refraction?
unanswerable