RefFIT is a data analysis program written by dr. Alexey Kuzmenko using the input and feedback from many colleagues over many years. It is designed to fit optical spectra, such as reflectivity, transmission, ellipsometry and Kerr and Faraday rotation using the Drude-Lorentz, Fano, Tauc-Lorentz and many other dielectric-function models. Currently the library includes more than 50 models. In addition to the rich model library, RefFIT allows you to apply a model-independent Kramers-Kronig analysis to virtually any type of optical spectra, using an original Kramers-Kronig constrained variational technique.

RefFIT has a powerful and fast fitting engine based on a modified Levenberg-Marquardt algorithm, a broad collection of proven physical models and a unique user-friendly interface. It allows you fitting manually or automatically several datasets of different type and using different models simultaneously while seeing on your screen precisely what you are doing.

Our users include physicists, material scientists, chemists, optics engineers, biologists and even computer-game designers. Also teachers use RefFIT in their courses: students can not only study the optical properties of materials, they themselves can play, model and fit as well.