Nelly: An Open-Source Package for Complex Refractive Index Extraction for Terahertz Spectroscopy on Layered Samples

As researchers have begun to apply THz spectroscopy to increasingly novel materials and THz spectrometers have become more widely available, the need has arisen for data workup techniques that both avoid approximations and are accessible to a wide range of researchers. Here, we present Nelly, a software package that uses a tree-based algorithm to perform complex refractive index extraction for any layered sample geometry without invoking approximations. It is provided as a MATLAB library and graphical user interface (GUI) for ease of use. We have tested it using CST simulations to verify that it gives accurate results for various sample geometries.