THz-TDS time-trace analysis for the extraction of material and metamaterial parameters

TL;DR

This paper introduces Fit@TDS, an open-source software that uses time-trace fitting in terahertz spectroscopy to accurately extract material and metamaterial parameters, even in noisy conditions.

Contribution

The paper presents a novel method for fitting time-trace data directly to retrieve material and metamaterial parameters, improving robustness over traditional frequency domain methods.

Findings

Successful extraction of refractive index from noisy data

Reliable retrieval of resonance parameters of metasurfaces

Effective analysis of real samples like silicon, lactose, and gold metasurfaces

Abstract

We report on a method and an associated open source software, Fit@TDS, working on an average personal computer. The method is based on the fitting of a time-trace data of a terahertz time-domain-spectroscopy system enabling the retrieval of the refractive index of a dielectric sample and the resonance parameters of a metasurface (quality factor, absorption losses, etc.). The software includes commonly used methods where the refractive index is extracted from frequency domain data. However, these methods are limited, for instance in case of a high noise level or when an absorption peak saturates the absorption spectrum bringing the signal to the noise level. Our software allows to use a new method where the refractive indices are directly fitted from the time-trace. The idea is to model a material or a metamaterial through parametric physical models (Drude-Lorentz model and time-domain coupled mode theory) and to implement the subsequent refractive index in the propagation model to simulate the time-trace. Then, an optimization algorithm is used to retrieve the parameters of the model corresponding to the studied material/metamaterial. In this paper, we explain the method and test it on fictitious samples to probe the feasibility and reliability of the proposed model. Finally, we used Fit@TDS on real samples of high resistivity silicon, lactose and gold metasurface on quartz to show the capacity of our method