How to determine the complex refractive index from infrared reflectance spectroscopy

A new theoretical methodology enabling the determination of the complex refractive index has been developed and explored; it only requires to use a classical set-up to control the incident angle, without the need for a polarizer. As a proof of concept, this new methodology has been successfully applied to investigate the optical properties of amorphous silica in the mid-infrared spectral range and validated by comparison with a standard routine based on polarization state of the light. This work thus makes it possible to determine the complex refractive index of an isotropic material by a reflectance measurement without needing to control the polarization of light. The refractive index can be measured with a relative uncertainty close to $$10^{-3}$$ over a wide range of wavelengths, as needed for a growing number of optical applications. Therefore, this new technique is cost effective and permits the accurate assessment of the refractive index in the whole infrared range.