Refractive index calculation from echo interference in pulsed terahertz spectroscopy

A method for calculating the average refractive index of a sample using transmission terahertz time-domain spectroscopy in a single measurement is presented. The refractive index is derived from the analysis of the frequency-domain interference caused by Fabry-Pérot reflections in the sample through the discrete Fourier transform of the spectrum module. This approach is simple and fast (not requiring a reference measurement), improves sensitivity over direct time-domain analysis and allows the derivation of the refractive index in a specific frequency window. The method can also be used to identify unwanted reflections in the experimental setup.