Material parameter estimation with terahertz time-domain spectroscopy

TLDR

Terahertz time‑domain spectroscopy imaging offers unique modalities due to its broadband, sub‑picosecond, phase‑sensitive pulses, enabling simultaneous spectroscopic characterization and imaging, unlike conventional transmission methods that require known sample thickness. The study aims to develop a robust, real‑time algorithm for extracting material parameters from THz waveforms. The algorithm performs model‑based estimation using gradient‑descent search and total variation to simultaneously retrieve sample thickness and complex refractive index. The method’s limits were examined and its extracted optical parameters for several materials matched literature values. © 2001 Optical Society of America.

Abstract

Imaging systems based on terahertz (THz) time-domain spectroscopy offer a range of unique modalities owing to the broad bandwidth, subpicosecond duration, and phase-sensitive detection of the THz pulses. Furthermore, the possibility exists for combining spectroscopic characterization or identification with imaging because the radiation is broadband in nature. To achieve this, we require novel methods for real-time analysis of THz waveforms. This paper describes a robust algorithm for extracting material parameters from measured THz waveforms. Our algorithm simultaneously obtains both the thickness and the complex refractive index of an unknown sample under certain conditions. In contrast, most spectroscopic transmission measurements require knowledge of the samples thickness for an accurate determination of its optical parameters. Our approach relies on a model-based estimation, a gradient descent search, and the total variation measure. We explore the limits of this technique and compare the results with literature data for optical parameters of several different materials. 2001 Optical Society of America