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| (a) Simplified illustration of TDS. The different colors correspond to different delay-line positions. These positions correspond to different time points in (b). (b) Measured THz time-domain signal. (c) Fast Fourier transformation (FFT) of the signal in the frequency domain. The upper panel shows the unwrapped phase of the complex Fourier transform and the lower shows the amplitude. |
Terahertz time-domain spectroscopy (THz-TDS) is a powerful technique for material’s characterization and process control. It has been used for contact-free conductivity measurements of metals, semiconductors, 2D materials, and superconductors. Furthermore, THz-TDS has been used to identify chemical components such as amino acids, peptides, pharmaceuticals, and explosives, which makes it particularly valuable for fundamental science, security, and medical applications. This tutorial is intended for a reader completely new to the field of THz-TDS and presents a basic understanding of THz-TDS. Hundreds of articles and many books can be consulted after reading this tutorial. We explore the basic concepts of TDS and discuss the relationship between temporal and frequency domain information. We illustrate how THz radiation can be generated and detected, and we discuss common noise sources and limitations for THz-TDS. This tutorial concludes by discussing some common experimental scenarios and explains how THz-TDS measurements can be used to identify materials, determine complex refractive indices (phase delay and absorption), and extract conductivity.
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