THz Measurement Systems

Abstract

The terahertz (THz) frequency region is often defined as the last unexplored area of the electromagnetic spectrum. Over the past few years, the full access has been the objective of intense research efforts. Progress in this area has played an important role in opening up the possibility of using THz electromagnetic radiation (T-waves) in science and in realworld applications. T-waves are not perceptible by the human eye, are not ionizing, and have the ability to cross many non-conducting materials such as paper, fabrics, wood, plastic, and organic tissues. Moreover, the use of THz radiation allows non-destructive analysis of the materials under investigation both by study of their "fingerprint" via spectroscopic measurements and by high-resolution spatial imaging operations, exploiting the see-through capability of T-waves. Such technology can be applied in diverse areas, spanning from biology to chemical, pharmaceutical, environmental sciences, etc. In this chapter, we will present the typical architecture of measurement systems based on the THz technology, detailing what are the parameters that define their performance, the measurement methods, and the related errors and uncertainty, and focusing at the end on the use of time-domain spectroscopy for the evaluation of different material properties in this specific frequency region.

Terahertz Spectroscopy of Amorphous WSe2 and MoSe2 Thin Films

“…Routine procedures for the retrieval of the complex electrodynamic parameters of a single or a multilayer sample have been settled for years and goes under the name of the transfer function (TF) model [ 28 , 29 ]. Specifically, when the electromagnetic signal passes through a film having thickness t deposited on a dielectric substrate, the transfer function in the frequency domain can be written as [ 17 ]: where represents the Fabry–Perot factor [ 29 ].…”

“…Subscripts a , s , and f in the complex refractive index refers to air, the substrate, and the TMD film respectively. Equation (1) suggests that and affect the modulus and phase of transmission in such a way that a specific numerical algorithm has to be applied [ 28 ]. Specifically, this algorithm, called the total variation technique (TVT) extracts the refractive index of the sample by minimizing the difference between the experimental and theoretical transmission curve [ 28 ].…”

“…Equation (1) suggests that and affect the modulus and phase of transmission in such a way that a specific numerical algorithm has to be applied [ 28 ]. Specifically, this algorithm, called the total variation technique (TVT) extracts the refractive index of the sample by minimizing the difference between the experimental and theoretical transmission curve [ 28 ]. We first extracted the refractive index of the substrate by employing the simple expression of the transfer function for a single layer [ 29 ].…”

Morphological, Structural, and Charge Transfer Properties of F-Doped ZnO: A Spectroscopic Investigation

“…Since σ r = ε 0 ωε i (see below), the uncertainty on conductivity is worth Δσ r ≅ ε 0 ω Δε i ≅ ± 6%. The complex dielectric function ε̃ s /ε 0 = ε r + iε i of each pellet is easily obtained through the relations ε r = n s 2 – k s 2 and ε i = 2 n s k s , with ε 0 as vacuum permittivity.…”

AI-Powered Terahertz VLSI Testing Technology for Ensuring Hardware Security and Reliability

“…Terahertz imaging technology can be an ideal approach for defect detection because several materials have unique spectral fingerprinting characteristics in the terahertz spectral region. Utilizing the advantages provided by terahertz systems it is feasible to perform authentication [16], non-destructive inspection [17]- [21], laser terahertz emission spectroscopy (LTEM) [22], [23] for VLSI testing, terahertz time-domain reflectometry (THz-TDR) [24], terahertz scanning near-field optical microscope (THz-SNOM) and terahertz scanning tunneling microscope (THz-STM) [25], [26], large scale integrated circuit (LSIC) inspection [27], 3D imaging [28]- [30], quality control [31]- [35], airport security [36]- [40], art investigations [41], tomography [29], [42]- [44], biomedical diagnosis and imaging [45]- [47], material characterization [48]- [53], thickness measurements [54], [55], and holography [56], [57].…”