Reduction in Reflection Signal Losses in Complex Terahertz Optical Elements Through Tailored Oil Application

 Kaluza, Mateusz, Adrianna Nieradka, Mateusz Surma, Wojciech Krauze, and Agnieszka Siemion. "Reduction in Reflection Signal Losses in Complex Terahertz Optical Elements Through Tailored Oil Application." Applied Sciences 15, no. 20 (2025): 11167.

Abstract

In complex terahertz (THz) systems, multiple optical elements are often combined to achieve advanced functionalities. However, unwanted Fresnel reflections at their interfaces and between components lead to parasitic interference effects and signal losses. This study presents oil-based refractive-index-matching fillers integrated with additively manufactured assemblies to suppress Fresnel reflections and enhance overall optical system performance. The optical properties of 20 plant-based, synthetic, and mineral oils were investigated using terahertz time-domain spectroscopy (THz TDS). Furthermore, a multilayer structure was designed and experimentally verified, fabricated via fused deposition modeling (FDM) using highly transparent cyclic olefin copolymer (COC). The results demonstrate that the use of tailored oils reduces Fresnel reflection signal losses and also mitigates parasitic interference within the system, thereby improving the effective efficiency of the optical system. Additionally, THz TDS measurements on multilayer structures revealed that, in imaging configurations, the application of refractive-index-matched oils increases the signal gain by 2.33 times. These findings highlight the potential of oil-based index-matching fillers for imaging multilayered objects and mitigating delamination effects in optical elements.

see https://www.mdpi.com/2076-3417/15/20/11167

The first annual Showcase of the EPSRC NetworkPlus in Terahertz System

 📣 We are pleased to announce that the first annual Showcase of the EPSRC NetworkPlus in Terahertz Systems will take place in Leeds on 21st and 22nd April 2026 📣

The Showcase will bring together academics and representatives working in industry and non-academic research organisations for two days of engaging discussions on future prioritisation areas for THz science and technology across the UK and Europe. We will also provide information on our Flexible Fund, which will support researchers in exploring some of these opportunities through seedcorn projects. There will be plenty of opportunities for networking – including a poster session and conference dinner – and for helping to shape the future of the NetworkPlus.

For further details and to register your interest in attending the meeting, please see below 👇 The deadline for EOIs is Friday 30th January.

Using density changes to monitor blending with magnesium stearate by terahertz time-domain spectroscopy

Anuschek, Moritz, Thea Nilsson, Anne Linnet Skelbæk-Lorenzen, Thomas Kvistgaard Vilhelmsen, J. Axel Zeitler, and Jukka Rantanen. "Using density changes to monitor blending with magnesium stearate by terahertz time-domain spectroscopy." International Journal of Pharmaceutics 672 (2025): 125303.

Abstract

Magnesium stearate (MgSt) is among the most common excipients and the most common lubricant in solid oral products. It is primarily added to tablet formulations to ease ejection during tablet compression. While commonly present in low concentrations, the addition of MgSt substantially affects the final tablet properties. Its impact is further not only concentration dependent but also varies with exposure of the formulation to shear, which worst-case results in over-lubrication. The presented study investigated the applicability of terahertz time-domain spectroscopy (THz-TDS) to monitor the shear-induced blend densification of microcrystalline cellulose blended with MgSt over a range of concentrations (0.3, 0.7, and 1.0 %). The effect of shear was investigated by variation of blending times (5 – 20 min) in a diffusion blender. THz-TDS measurements of the powder blends were acquired in transmission by measuring directly through the mixing container. The refractive index at terahertz frequencies was found to be sufficiently sensitive to resolve the densification of the blend with increased blending times. Thus, THz-TDS blend density measurements can be used as a surrogate parameter to evaluate the total shear exposure of a blend. Considerations regarding implementation are discussed. In the context the approach was integrated with the well-described THz-TDS-based tablet porosity analysis into a unified model to monitor and predict the tensile strength. Including the THz-TDS measurement on the blend allowed for a more accurate description of the tensile strength, reducing the root mean squared error by over 40 % (0.33 MPa). The possibility of monitoring the density changes of a blend non-invasively makes THz-TDS a promising process analytical technology approach for controlling the total shear impact on lubricated blends and tablet quality.

see https://www.sciencedirect.com/science/article/pii/S0378517325001395

Terahertz non-destructive testing of thin self-lubricating bearing coating thickness based on SOMP sparse representation

 Huang, Yi, Hailiang Wang, Weiqiang Chen, Shuncong Zhong, Tingting Shi, Caihong Zhuang, Fuwei Sun, Yonglin Huang, and Zhenghao Zhang. "Terahertz non-destructive testing of thin self-lubricating bearing coating thickness based on SOMP sparse representation." Infrared Physics & Technology (2025): 106223.

Abstract

The thickness of aviation solid thin self-lubricating bearing coatings gradually decreases during wear, which leads to severe echo overlapping in terahertz non-destructive testing. This adversely affects the extraction of coating thickness information. In this paper, a thin coating thickness measurement method that integrates secondary orthogonal matching pursuit (SOMP) sparse representation with the time-of-flight (TOF) is proposed. The propagation characteristics of terahertz waves are firstly investigated, and the convolutional dictionary matrix is constructed based on the reference signal. Subsequently, a series of suboptimal atoms are selected by maximizing the inner product between the reflected signal and the column vector. On this basis, the optimal atoms are further identified using the minimum envelope entropy index to reconstruct the impulse response. The coating thickness is finally quantitatively calculated using the TOF method. The experiments demonstrate that this method can detect coatings thinner than 15 μm with a relative error below 5 %. This study is expected to provide an effective method for accurately measuring the thickness of thin self-lubricating bearing coatings.

see https://www.sciencedirect.com/science/article/abs/pii/S135044952500516X

Polarimetry terahertz imaging of human breast cancer surgical specimens

Gurjar, Nikita, Keith Bailey, and Magda El-Shenawee. "Polarimetry terahertz imaging of human breast cancer surgical specimens." Journal of Medical Imaging 11, no. 6 (2024): 065503-065503.

Abstract

Purpose
We investigate terahertz (THz) polarimetry imaging of seven human breast cancer surgical specimens. The goal is to enhance image contrast between adjacent tissue types of cancer, healthy collagen, and fat in excised breast tumors. Based on the biological perception of random growth of cancer and invasion of surrounding healthy tissues in the breast, we hypothesize that cancerous cells interact with the THz electric field in a different manner compared with healthy cells. This difference can be best captured using multiple polarizations instead of single polarization.
Approach
Time domain pulsed signals are experimentally collected from each pixel of the specimen in horizontal–horizontal, vertical–horizontal, vertical–vertical, and horizontal–vertical polarizations. The time domain pulses are transformed to the frequency domain to obtain the power spectra and 16 Mueller matrix images. The whole-slide pathology imaging was used to interpret and label all images.
Results
The results of the cross and co-polarization power spectrum images demonstrated a strong dependency on the tissue orientation with respect to the emitted and detected electric fields. At the 130-deg rotation angle of the scanned samples, the detector showed the strongest reflected signal in cross-polarization. Furthermore, the Mueller matrix images consistently demonstrated patterns in fresh and block tissues confirming the differentiation between tissue types in breast tumor specimens.
Conclusions
THz polarimetry imaging shows a potential for improving image contrast in excised tumor tissues compared with single polarization imaging. Cross-polarization signals demonstrated smaller amplitudes compared with co-polarized signals. However, averaging the signal during measurements has tremendously improved the image. Furthermore, in post-processing, averaging the frequency domain images and the Mueller matrix elements with respect to frequency has led to better image contrast. Some patterns in the Mueller matrix images were difficult to interpret leading to the necessity of more investigation of the Mueller matrix and its physiological interpretation of breast tumor tissues.

see https://www.spiedigitallibrary.org/journals/journal-of-medical-imaging/volume-11/issue-6/065503/Polarimetry-terahertz-imaging-of-human-breast-cancer-surgical-specimens/10.1117/1.JMI.11.6.065503.full

NetworkPlus in THz Systems Special Interest Group in Healthcare - Introductory Meeting

Hyper-Integrated CAD Database for One-Shot EOTPR Fault Localization in Heterogeneous Sip-on-Board Assemblies

 Bhattacherjee, Arpan, and Joy Liao. "Hyper-Integrated CAD Database for One-Shot EOTPR Fault Localization in Heterogeneous Sip-on-Board Assemblies." In International Symposium for Testing and Failure Analysis, vol. 85212, pp. 64-67. ASM International, 2025.

Abstract

The increasing complexity of datacenter accelerators and artificial intelligence (AI) inference systems has driven rapid adoption of sophisticated heterogeneous system-in-package (SiP) architectures. These advanced packages integrate multilayer printed circuit boards (PCBs), organic substrates, silicon interposers, and high-density integrated circuits, delivering significant performance improvements. However, these densely integrated architectures introduce substantial challenges for accurate and timely failure analysis (FA). Electro-Optical Terahertz Pulse Reflectometry (EOTPR), a non-destructive diagnostic method, offers superior fault localization compared to traditional techniques. Nonetheless, its practical implementation in complex SiP systems has been limited by fragmented CAD data and iterative manual analyses, significantly extending diagnostic timelines. This paper presents a novel “hyper-integrated” CAD database methodology, where disparate design datasets are automatically consolidated into a unified navigation database. This approach creates a static digital twin of the failing board-level device, enabling precise, “one-shot” fault localization using EOTPR. Experimental validation on advanced datacenter accelerator hardware demonstrates substantial improvements in diagnostic speed, accuracy, and efficiency, emphasizing the practical benefits of the hyper-integrated approach for state-of-the-art semiconductor failure analysis.

see https://dl.asminternational.org/istfa/proceedings/ISTFA2025/85212/64/35164

EOTPR Fine Pitch Probing for Die-to-Die Interconnect Failure Analysis

 Zee, Bernice, Wen Qiu, Aaron Wai Ken Lee, Jesse Alton, Thomas White, David Kim, and Martin Igarashi. "EOTPR Fine Pitch Probing for Die-to-Die Interconnect Failure Analysis." In International Symposium for Testing and Failure Analysis, vol. 85212, pp. 400-403. ASM International, 2025.

Abstract

Debug and physical failure analysis (PFA) of heterogeneously integrated semiconductor packages, particularly die-to-die (D2D) input/output (I/O) type fails, has become very challenging due to the lack of direct access to the I/Os from the package substrate to do static open/shorts fault isolation and limited test program granularity to determine which location along the D2D interconnect trace is failing. Thus, a suitable electrical fault isolation technique is required to ensure high success rate for root cause analysis. This paper discusses how EOTPR is used to isolate defects on a D2D interconnect trace of a chiplet advanced packaging using local silicon bridge with reasonable accuracy. Minimal sample preparation was needed to expose the I/O bumps for probing, thus minimizing the risk of artifacts that may cause the defect to be lost. A case study will demonstrate the successful application of the technique.

see https://dl.asminternational.org/istfa/proceedings/ISTFA2025/85212/400/35215

From powder to spectrum: A tutorial of terahertz transmission time-domain spectroscopy

 Zarrella, Salvatore, Elena Wanvig i Dot, J. Axel Zeitler, and Timothy M. Korter. "From powder to spectrum: A tutorial of terahertz transmission time-domain spectroscopy." International Journal of Pharmaceutics (2026): 126586.

Abstract

Terahertz time-domain spectroscopy (THz-TDS) is a non-destructive, high-resolution method that probes low-frequency vibrational modes and intermolecular interactions between the microwave and infrared regions inaccessible by other spectroscopic methods. The technique is established in the pharmaceutical sciences and is now spreading to other areas in need of an extensive understanding of material properties. Despite the growth in THz applications, measurements are still confined to specialized laboratories. This tutorial seeks to provide a practical standard operating procedure for taking transmission measurements of compacted powders and is designed for new users across disciplines. We describe sample preparation, spectrometer configuration, data acquisition, signal processing, quantitative analysis, and troubleshooting. Emphasis is placed on practical strategies such as selecting appropriate diluents, ensuring homogeneous sample mixing, optimizing pellet thickness, aligning the optical setup, and handling spectral artifacts like Fabry–Pérot etalons. Additionally, the tutorial guides users through data transformation using FFT and apodization techniques to extract accurate optical constants such as refractive index and absorption coefficients. By consolidating best practices and minimizing technical barriers, this resource aims to make THz spectroscopy more accessible and reproducible for researchers across disciplines.

see https://www.sciencedirect.com/science/article/pii/S0378517326000347

Ancient enamel plate characterized by Time domain spectro imaging

Mounaix, Patrick, Philip F. Taday, Frédéric Fauquet, Rémy Chapoulie, Aurélie Mounier, and A. Ben Amara. "Ancient enamel plate characterized by Time domain spectro imaging." In 2023 48th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE, 2023.

Abstract:

We report on further development of terahertz systems for measuring the thicknesses and the detection of fracture in art science. Analysis of time-domain data is described and the results of measurements made on ancient enamel plate are presented. We also show X-Ray images and hyperspectral visible and infrared images to identify the pigments used. We also test the Z tracker developed by Teraview Ltd and demonstrate the possibility to perform THz imaging on non-flat samples.

see https://ieeexplore.ieee.org/abstract/document/10299322

Dual-frequency liquid crystals as tunable materials for beam steering in terahertz photonics

Dual-frequency liquid crystals as tunable materials for beam steering in terahertz photonics

PHOTONICS LETTERS OF POLAND, VOL. 17 (4), 85-87 (2025) 

Oleksandra Gridyakina1 , Urszula Chodorow , Adrianna Nieradka , Agnieszka Siemion , Janusz Parka , Piotr Lesiak and Tomasz R. Woliński 

Abstract

Dual-frequency liquid crystal (LC) materials for tunable beam steering in the 0.1–3.5 THz range were investigated. Recent LC formulations exhibit a low loss tangent, high polarization coefficients, and significant dielectric and optical anisotropies, including suitably high birefringence for effective THz modulation. We have implemented this material in electrically tunable phase shifters and beam-steering elements, demonstrating their ability to operate with low absorption and controllable birefringence. The obtained characteristics suggest that dual frequency LCs could be used to create compact, efficient, and highly tunable THz photonic and sensing components. This study outlines the performance parameters relevant to practical THz devices and highlights their potential for reconfigurable photonic architectures.

… The measurements of DFLC optical properties were performed using a THz time domain spectroscopy (THzTDS) - the TeraView TeraPulse Lx Modular System at room temperature. To eliminate the adverse effects of atmospheric water vapor, the …