Search Results (37)

This study presents the design and development of electromagnetic dipole magnets for use as beam dumps and spectrometers in the MIR and THz free-electron laser (FEL) beamlines at the PBP-CMU Electron Linac Laboratory (PCELL). The magnets were optimized to achieve a 60-degree bending angle for electron beams with energies up to 30 MeV, without requiring water cooling. Using CST EM Studio for 3D magnetic field simulations and ASTRA for particle tracking, the THz dipole (with 414 turns) and MIR dipole (with 600 turns) generated magnetic fields of 0.1739 T and 0.2588 T, respectively, while both operating at currents below 10 A. Performance analysis confirmed effective beam deflection, with the THz dipole showing that it was capable of handling beam energies up to 20 MeV and the MIR dipole could handle up to 30 MeV. The energy measurement at the spectrometer screen position was simulated, taking into account transverse beam size, fringe fields, and space charge effects, using ASTRA. The energy resolution, defined as the ratio of energy uncertainty to the mean energy, was evaluated for selected cases. For beam energies of 16 MeV and 25 MeV, resolutions of 0.2% and 0.5% were achieved with transverse beam sizes of 1 mm and 4 mm, respectively. All evaluated cases maintained energy resolutions below 1%, confirming the spectrometer’s suitability for high-precision beam diagnostics. Furthermore, the relationship between the initial and measured energy spread errors, taking into account a camera resolution of 0.1 mm/pixel, was evaluated. Simulations across various beam energies (10–16 MeV for the THz dipole and 20–25 MeV for the MIR dipole) confirmed that the measurement error in energy spread decreases with smaller RMS transverse beam sizes. This trend was consistent across all tested energies and magnet configurations. To ensure accurate energy spread measurements, a small initial beam size is recommended. Specifically, for beams with a narrow initial energy spread, a transverse beam size below 1 mm is essential. Full article

The present study explores a multi-analytical non-invasive approach based on the application of terahertz continuous wave (THz-CW) spectroscopy for the non-invasive characterization of historically produced synthetic copper silicate pigments. For the first time, Han Blue, Han Purple and Egyptian Blue were examined within the THz spectral region using a compact and portable THz-CW spectrometer. The three pigments exhibit distinct absorption features, which facilitate the differentiation of molecular structures within the same chemical and mineralogical category. Moreover, the same compound was analyzed using Energy Dispersive X-Ray Fluorescence (ED-XRF) to determine its elemental composition, alongside Fiber Optics Reflectance Spectroscopy (FORS) in the range 350–2500 nm, providing crucial insights into its optical properties and molecular structure. To the best of the authors’ knowledge, the present study presents the first spectra for these copper silicates at these wavelengths, thereby expanding the shortwave infrared spectral database of Cultural Heritage materials. This synergistic approach enables a comprehensive characterization, offering a deeper understanding of the compounds’ chemical nature and paving the way for potential applications in the Cultural Heritage domain. Furthermore, the findings underscore the potential of THz-CW spectroscopy as an innovative and effective tool for Cultural Heritage research, providing a non-destructive method to investigate artistic materials. Full article

Waste recycling is critical for the development of smart cities. Local authorities are responsible for the disposal of waste plastics, but the extent of material recycling is insufficient, and much of the waste generated is incinerated. This conflicts with the trend of decarbonisation. Of particular note are the effects of the COVID-19 pandemic, during and after which large quantities of waste plastics, such as plastic containers and packaging, were generated. In order to develop a sustainable smart city, we need an effective scheme where we can separate materials before they are taken to the local authorities and recyclers. In other words, if material identification can be performed at the place of disposal, the burden on recyclers can be reduced, and a smart city can be created. In this study, we developed and demonstrated smart material identification equipment for waste plastic materials made of PET, PS, PP, and PE using GaP THz and sub-THz wavelengths. As basic information, we used a GaP terahertz spectrometer to sweep frequencies from 0.5 THz to 7 THz and measure the spectrum, and the transmittance rate was measured using the sub-THz device. The sub-THz device used a specific frequency below 0.14 THz. This is a smaller, more carriable, and less expensive semiconductor electronic device than the GaP. Moreover, the sub-terahertz device used in the development of this equipment is compact, harmless to the human body, and can be used in public environments. As a result, smart equipment was developed and tested in places such as supermarkets, office entrances, and canteens. The identification of materials can facilitate material recycling. In this study, we found that measuring devices designed to identify the PET and PS components of transparent containers and packaging plastics, and the PP and PE components of PET bottle caps, could effectively identify molecular weights, demonstrating new possibilities for waste management and recycling systems in smart cities. With the ability to collect and analyse data, these devices can be powerful tools for pre-sorting. Full article

A standard measuring gas cell used in absorption spectrometers is a cylinder enclosed by two transparent windows. The Fabry–Perot effects caused by multiple reflections of terahertz waves between these windows produce significant variations in the transmitted radiation intensity. Therefore, the Fabry–Perot effects should be taken into account to correctly measure absorption spectra in Bouguer law-based absorption spectroscopy. One approach to reducing the Fabry–Perot effects is based on inserting an additional external movable window with the standard measuring gas cell. This was proposed and numerically analyzed in our previous work. This paper is aimed at the experimental validation of this method when using amplitude modulation (AM) spectroscopy. Also, a comparison of the efficiency of reducing the Fabry–Perot effects using this method is experimentally compared to frequency modulation spectroscopy. The latter was shown to effectively reduce the Fabry–Perot effects compared to AM spectroscopy with the standard measuring gas cell, and the use of the external movable window was shown to further improve the elimination of Fabry–Perot effects. Full article

As artificially engineered subwavelength periodic structures, terahertz (THz) metasurface devices exhibit an equivalent dielectric constant and dispersion relation akin to those of natural materials with specific THz absorption peaks, describable using the Lorentz model. Traditional verification methods typically involve testing structural arrays using reflected and transmitted optical paths. However, directly detecting the dielectric constant of individual units has remained a significant challenge. In this study, we employed a THz time-domain spectrometer-based scattering-type scanning near-field optical microscope (THz-TDS s-SNOM) to investigate the near-field nanoscale spectrum and resonant mode distribution of a single-metal double-gap split-ring resonator (DSRR) and rectangular antenna. The findings reveal that they exhibit a dispersion relation similar to that of natural materials in specific polarization directions, indicating that units of THz metasurface can be analogous to those of molecular structures in materials. This microscopic analysis of the dispersion relation of artificial structures offers new insights into the working mechanisms of THz metasurfaces. Full article

Space exploration presents vast prospects for scientific, industrial, and economic progress. This paper introduces the MeSat mission as a pioneering approach to Mars exploration. The MeSat aims to deepen our understanding of Martian conditions and resources by employing an optimized Earth-to-Mars trajectory, enabling a comprehensive study of the Martian atmosphere and surface. The mission comprises a cargo microsatellite hosting three 6U CubeSats and two 3U CubeSats, deployed into four separate Mars orbits to form a constellation. Each CubeSat carries distinct payloads: a THz radiometer for Martian water vapor atmospheric observation, a high-resolution surface camera, a high-tech spectrometer, and a Fourier transform spectrometer (FTS) for wind speed readings. This paper includes the majority of the key parameters; however, we focus our discussion more on two aspects of this pioneering mission: the first aspect contains the proposal of four distinct payloads for the study of Mars’ atmosphere and the second aspect proposes an optimal mission design algorithm that analyzes a fuel-efficient low-thrust trajectory from Earth to Mars. Regarding the payloads, the THz radiometer requires a specific design; hence, we explain this payload in more depth; the rest of the payloads, we suggest utilizing commercially available elements for the cost-effective manufacture of a whole system. For mission trajectory optimization, the study employs a dual-step hybrid optimization algorithm (PSO-homotopy) to analyze fuel-efficient low-thrust trajectories from Earth to Mars, incorporating the ephemeris dynamics model to account for gravitational perturbations in the entire Solar System. In practical mission design, crucial factors like hyperbolic excess velocity, diverse opportunities for Earth launch and Mars rendezvous, varied propulsion systems, and time of flight (TOF) play vital roles in trajectory optimization. In summary, for the MeSat mission, we propose a comprehensive Mars environmental mission design. We consider all aspects of the mission from trajectory design to engineering detail design, since we would like to inspire future Mars missions with a complete report. Full article

Airborne dust plays an active role in determining the thermal structure and chemical composition of the present-day atmosphere of Mars and possibly the planet’s climate evolution over time through radiative–convective and cloud microphysics processes. Thus, accurate measurements of the distribution and variability of dust are required. Observations from the Mars Global Surveyor/Thermal Emission Spectrometer Mars Mars Reconnaissance Orbiter/Mars Climate Sounder and Mars Express/Fourier Transform Spectrometer and the Curiosity Rover have limited capability to measure dust. We show that spacecraft occultation of the Martian atmosphere at far-infrared frequencies between 1 and 10 THz can provide the needed global and temporal data on atmospheric dust by providing co-located measurements of temperature and dust opacity from the top of the atmosphere all the way down to the surface. In addition, spacecraft occultation by a small-satellite constellation could provide global measurements of the development of dust storms. Full article

The linear accelerator system of the PBP-CMU Electron Linac Laboratory has been designed with the aim of generating free-electron lasers (FELs) in the mid-infrared (MIR) and terahertz (THz) regions. The quality of the radiation is strongly dependent on the properties of the electron beam. Among the important beam parameters, the electron beam energy and energy spread are particularly important. To accurately measure the electron beam energy, the first dipole magnet in the bunch compressor system and the downstream screen station are employed as an energy spectrometer. The A Space Charge Tracking Algorithm (ASTRA) software is used for the design and optimization of this system. Simulation results demonstrate that the developed spectrometer is capable of accurately measuring the energy within the 5–25 MeV range. The screen station system is designed and constructed to have the ability to capture a beam size with a resolution of 0.1 mm per pixel. This resolution is achieved with a screen-to-camera distance of 1.2 m, which proves sufficient for precise energy measurement. The systematic error in energy measurement is found to be less than 10%, with a minimum energy spread of 0.4% achievable when the horizontal beam size remains below 3 mm. Full article

Spectroscopy in the terahertz (THz) band has been discussed as a promising tool for identifying substances such as mold in food, narcotics, or explosive materials. Other than the technological limitations, the most important difficulty is the presence of water vapor in the atmosphere, which affects THz measurements. In this paper, we present a systematic approach to the challenging subject of remote identification. We start with a brief analysis of the technical capabilities of the THz components and report the choice of devices for designing an experimental setup for reflection spectroscopy. We follow with the presentation of the transmission THz spectrometer working in an open atmosphere. Research conducted on the transmission configuration provides findings that are implemented in the experimental setup working in a reflective configuration. The final phase is an experiment providing data measured in the reflection configuration with the presence of water vapor, allowing the use of spectra in the identification of the measured samples. Full article

Terahertz photonic integrated circuits are becoming popular in ultrafast on-chip signal generation and processing. They outperform assemblies of electronic devices making use of metallic waveguides in term of both fabrication complexity and system losses. In this study, we report on a nearly all-dielectric hot electron bolometer mixer compatible with the technology of integrated Si photonic crystals. The developed on-chip power distribution networks ensure input losses of 2.4 dB and far-field radiation patterns with a gain of 12.1 dB and a side lobe level below −11 dB. The mixer is designed for spectral measurements at 2.7 THz. It can be used either as a part of an on-chip spectrometer or as a standalone device. Full article

THz-Time domain spectroscopic imaging is demonstrated combining a robotic scanning method with continuous signal acquisition and holographic reconstruction of the object to improve the imaging resolution. We apply the method to a metallic Siemens star in order to quantify resolution and to wood samples to demonstrate the technique on a non-metallic object with an unknown structure. Full article

Nowadays, physicochemical methods of analysis are used in medical diagnostics. One can identify metabolites characteristic of a particular disease. The compilation of a metabolic profile will facilitate the diagnosis of diseases, evaluate their stage and etiology, and predict treatment. The goal of the study is to analyze the metabolite composition of the ear-nose-throat (ENT) tissues by high-resolution THz spectroscopy based on nonstationary effects and compare metabolites formed during the thermal decomposition of relatively healthy mucosa, polyps, and cysts. Studies were performed with the spectrometers operating from 118 to 178 GHz. The chemical compounds were identified using online catalogs. In all samples, there are such substances as methanol, propanediol, acetaldehyde, acetonitrile, butyronitrile, methyl mercaptan, azole, ethylene sulfide, carbon sulfide, and sulfur dioxide. In the spectrum of relatively healthy mucosa, the number of absorption lines of these substances is much less than in the spectrum of the polyps and cysts, which indicates their lower concentration. In the products of the polyps and cysts, acetone, hydroxyacetone, dihydroxyacetone, propionitrile, acrylonitrile, aminopropionitrile, hydroxyacetonitrile, aminoacetonitrile, methylbutironitrile, propanal, glycolaldehyde, lactaldehyde, and malone dialdehyde appear. The products of cysts’ thermal decomposition also contain acetic and acrylic acids. High-resolution THz spectroscopy has been shown to be promising for detecting disease metabolites in ENT tissues. Full article

Graphene-based metamaterials have been widely applied in optoelectronic devices, optical modulators, and chemical sensors due to the outstanding tunability and optical response in the terahertz (THz) region. Here, tunable THz metamaterial absorbers based on patterned graphene are designed, fabricated, and modulated. The proposed metamaterial absorbers are constructed by the top layer of patterned graphene arrays and the aluminum (Al) film separated by polyimide (PI). The different THz absorption spectra can be acquired by changing the patterns of graphene. In order to verify the simulation results, a series of tests were conducted by THz time-domain spectrometer (THz-TDS) systems. The proposed absorbers are able to be insensitive to the angle of the incident wave. Besides, chemical doping is applied to turn the Fermi level of graphene and the absorption performance is promoted with the increase of the Fermi level. The experimental results have been demonstrated to have associated resonant peaks with the simulation results. The aim of this paper is to exhibit a systematic study on graphene-based THz metamaterial absorbers, including the simulation and experiments. By comparing the simulation and experimental results, it is useful to clarify the relevant theories and manufacturing processes. The work will provide a further step in the development of high-performance terahertz devices, including tunable absorbers, sensors, and electro-optic switches. Full article

Conventional black box machine learning (ML) algorithms for gas-phase species identification from THz frequency region absorption spectra have been reported in the literature. While the robust classification performance of such ML models is promising, the black box nature of these ML tools limits their interpretability and acceptance in application. Here, a one-dimensional convolutional neural network (CNN), VOC-Net, is developed and demonstrated for the classification of absorption spectra for volatile organic compounds (VOCs) in the THz frequency range, specifically from 220 to 330 GHz where prior experimental data is available. VOC-Net is trained and validated against simulated spectra, and also demonstrated and tested against experimental spectra. The performance of VOC-Net is examined by the consideration of confusion matrices and receiver-operator-characteristic (ROC) curves. The model is shown to be 99+% accurate for the classification of simulated spectra and 97% accurate for the classification of noisy experimental spectra. The model’s internal logic is examined using the Gradient-weighted Class Activation Mapping (Grad-CAM) method, which provides a visual and interpretable explanation of the model’s decision making process with respect to the important distinguishing spectral features. Full article

Gas sensing for dimethyl sulfoxide (DMSO) based on rotational absorption spectroscopy is demonstrated in the 220–330 GHz frequency range using a robust electronic THz-wave spectrometer. DMSO is a flammable liquid commonly used as a solvent in the food and pharmaceutical industries, materials synthesis, and manufacturing. DMSO is a hazard to human health and the work environment; hence, remote gas sensing for DMSO environmental and process monitoring is desired. Absorption measurements were carried out for pure DMSO at 297 K and 0.4 Torr (53 Pa). DMSO was shown to have a unique rotational fingerprint with a series of repeating absorption bands. The frequencies of transitions observed in the present study were found to be in good agreement with spectral simulations carried out based on rotational parameters derived in prior work. Newly, intensities of the rotational absorption lines were experimentally observed and reported for DMSO in this study. Measured intensities for major absorption lines were found in very good agreement with relative line intensities estimated by quantum mechanical calculations. The sensor developed here exhibited a detection limit of 1.3 × 10¹⁵–2.6 × 10¹⁵ DMSO molecules/cm³ per meter of absorption path length, with the potential for greater sensitivity with signal-to-noise improvements. The study illustrates the potential of all electronic THz-wave systems for miniaturized remote gas sensors. Full article