Hi Masoud,

if you have no background, this open access article seems to give a good overview of the required algorithms for the extraction of the relative permittivity and loss constant:

Article Data Extraction from Terahertz Time Domain Spectroscopy Measurements

Usually, most research institutions with TDS systems also have the scripts and are able to post process the raw data after the measurements.

If this is not your case, I found an open source code written in Python:

https://github.com/THzbiophotonics/Fit-TDS

The code is explained in the following paper:

Article THz-TDS Time-Trace Analysis for the Extraction of Material a...

I hope it helps!

Perhaps you can also have a look at :

https://www.chem.uci.edu/~dmitryf/manuals/Fundamentals/Thor.pdf

Article Time domain dielectric spectroscopy: An advanced measuring system

The simplest way to extract material properties like refractive index, absorption coefficient and conductivity is using "TDS spectrum Viewer software". Here, I am attaching the link where instructions to install the software are given clearly. We can import the time domain data directly into it. The software easily performs the FFT of the time domain data and shows the refractive index and absorption coefficient.

Link for TDS spectrum viewer:

http://www2.riken.jp/lab/THz-img/hoshina/software_e.html

The best way to extract is using matlab or origin pro from the equations "

P. S. Sindhu, D. Prasad, S. Peli, N. Mitra, and P. Datta, Journal of Molecular Structure 1184,

1114 (2019). "

Hope this helps.