Originally conceived to permit the high-throughput screening of optical meta-materials, the TRANK library is designed to use multiple amplitude based spectra such as transmittance, reflectance, absorptance for thin films and multilayered stacks to find the refractive index (n) and extinction coefficient (k) spectra. The software permits mixing of measurements from different films/stacks and illumination conditions to find the refractive indices of an unknown material. Additionally, we have implemented several (new) methods to avoid physically unrealistic complex branches which normally plague the fitting of the indices from amplitude based spectra.
The name is an acronym of transmittance, reflectance, absorptance to n and k.