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Terahertz Spectroscopy: Instruments, Methods, and Application
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Terahertz Spectroscopy: Instruments, Methods, and Application

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: closed (30 November 2023) | Viewed by 13257

Special Issue Editors

Dr. Vladimir L. Vaks

E-Mail Website
Guest Editor
Institute for Physics of Microstructures, Russian Academy of Sciences, Kstovo 603087, Russia
Interests: instruments and methods of terahertz spectroscopy
Prof. Dr. Valery P. Koshelets

E-Mail Website
Guest Editor
Kotelnikov Institute of Radioengineering and Electronics (IRE), Russian Academy of Sciences, Moscow 125009, Russia
Interests: instruments and methods of terahertz spectroscopy; SIS devices
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Alexei N. Baranov

E-Mail Website
Guest Editor
Institute of Electronics and Systems (IES), University of Montpellier, 34000 Montpellier, France
Interests: laser diodes; quantum cascade lasers; semiconductor lasers

Special Issue Information

Dear Colleagues,

This Special Issue is devoted to the development of Terahertz Spectroscopy Instruments and Methods and their Applications (TS) to various research fields. However, taking into account that a validation of a supposition is usually realized via a cross-check, the use of combined approaches is also welcomed.

Regardless, the authors should demonstrate that the part of TS is predominant in their works, and it is directed toward the implementation of new ideas. In our opinion, the participation of leading scientists is important to guide the reader and new users toward world learning at terahertz. In this way, it will be necessary to develop new approaches to the creation of THz radiation sources, THz detectors, and new schemes of THz spectrometers. This can be useful in the development of new methods of investigations in astrophysics, biology, medicine, ecology, agriculture, etc. These topics are the sectors at the core of this Special Issue.

Particularly welcome will be works that validate, at the experimental level, preliminary numerical simulations. In situ applications are considered on the same level as laboratory measurements, although we imagine that case studies will not be the majority of the published papers. With respect to the future generations of researchers and diagnosticians, TS as a non-destructive, non-invasive, and non-intrusive method useful to analyze spectroscopic data coming from analysis of samples of human tissues, liquids, etc. and other materials, and of various processes, is of particular importance.

Dr. Vladimir L. Vaks
Prof. Dr. Valery P. Koshelets
Prof. Dr. Alexei N. Baranov
Guest Editors

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Keywords

  • terahertz spectroscopy
  • terahertz radiation sources
  • terahertz detectors
  • applications of terahertz spectroscopy

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Related Special Issue

Published Papers (7 papers)

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Research

10 pages, 2951 KiB  
Communication
Superconducting Electronic–Photonic Platform for HEB-Based Terahertz Spectrometers
by Alexander Shurakov, Ivan Belikov, Anatoliy Prikhodko, Margarita Ershova and Gregory Goltsman
Appl. Sci. 2023, 13(10), 5892; https://doi.org/10.3390/app13105892 - 10 May 2023
Cited by 2 | Viewed by 1736
Abstract
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 [...] Read more.
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
(This article belongs to the Special Issue Terahertz Spectroscopy: Instruments, Methods, and Application)
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16 pages, 1855 KiB  
Article
Terahertz Absorption Spectroscopy in Bicrystal Josephson Junctions Formed from Mutually Tilted c-Axes YBa2Cu3O7−x Films
by Yuriy Divin
Appl. Sci. 2023, 13(9), 5766; https://doi.org/10.3390/app13095766 - 7 May 2023
Viewed by 1397
Abstract
Spectral analysis of terahertz (THz) and sub-THz emission from quantum cascade lasers has been recently demonstrated using conventional YBa2Cu3O7−x bicrystal Josephson junctions made from c-axes thin films. Josephson frequencies of alternative bicrystal junctions made from YBa2 [...] Read more.
Spectral analysis of terahertz (THz) and sub-THz emission from quantum cascade lasers has been recently demonstrated using conventional YBa2Cu3O7−x bicrystal Josephson junctions made from c-axes thin films. Josephson frequencies of alternative bicrystal junctions made from YBa2Cu3O7−x films with mutually tilted c-axes extend further into the THz range. However, these THz oscillations can weaken due to new absorption channels in the junction environment. Here, using Josephson admittance spectroscopy, THz losses in YBa2Cu3O7−x bicrystal junctions with mutually tilted c-axes are studied. Absorption maximizes at a reproducible set of THz frequencies close to those of collective modes in bulk YBa2Cu3O7−x recovered by Fourier spectroscopy. Annealing junctions in atomic oxygen reduces the losses at frequencies of 2.7 and 3.6 THz, while the losses increase at frequencies of 2.3 and 4.6 THz. Thus, as a THz spectrum analyzer, YBa2Cu3O7−x bicrystal junctions require post-fabrication correction of the oxygen content. In addition, the fine structure of the absorption spectrum appears at frequencies near 4.6 THz. Significant absorption near 2.3 THz may be due to effects associated with the second Josephson harmonic or second-order nonlinearity of the susceptibility in YBa2Cu3O7−x. This work paves the way towards probing collective modes in high-Tc materials in situ using the Josephson oscillations. Full article
(This article belongs to the Special Issue Terahertz Spectroscopy: Instruments, Methods, and Application)
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17 pages, 4796 KiB  
Article
Terahertz Time-Domain Spectroscopy of Glioma Patient Blood Plasma: Diagnosis and Treatment
by Olga Cherkasova, Denis Vrazhnov, Anastasia Knyazkova, Maria Konnikova, Evgeny Stupak, Vadim Glotov, Vyacheslav Stupak, Nazar Nikolaev, Andrey Paulish, Yan Peng, Yury Kistenev and Alexander Shkurinov
Appl. Sci. 2023, 13(9), 5434; https://doi.org/10.3390/app13095434 - 27 Apr 2023
Cited by 4 | Viewed by 2274
Abstract
Gliomas, one of the most severe malignant tumors of the central nervous system, have a high mortality rate and an increased risk of recurrence. Therefore, early glioma diagnosis and the control of treatment have great significance. The blood plasma samples of glioma patients, [...] Read more.
Gliomas, one of the most severe malignant tumors of the central nervous system, have a high mortality rate and an increased risk of recurrence. Therefore, early glioma diagnosis and the control of treatment have great significance. The blood plasma samples of glioma patients, patients with skull craniectomy defects, and healthy donors were studied using terahertz time-domain spectroscopy (THz-TDS). An analysis of experimental THz data was performed by machine learning (ML). The ML pipeline included (i) THz spectra smoothing using the Savitzky–Golay filter, (ii) dimension reduction with principal component analysis and t-distribution stochastic neighborhood embedding methods; (iii) data separability analyzed using Support Vector Machine (SVM), Random Forest (RF), and Extreme Gradient Boosting (XGBoost). The ML models’ performance was evaluated by a k-fold cross validation technique using ROC-AUC, sensitivity, and specificity metrics. It was shown that tree-based ensemble methods work more accurately than SVM. RF and XGBoost provided a better differentiation of the group of patients with glioma from healthy donors and patients with skull craniectomy defects. THz-TDS combined with ML was shown to make it possible to separate the blood plasma of patients before and after tumor removal surgery (AUC = 0.92). Thus, the applicability of THz-TDS and ML for the diagnosis of glioma and treatment monitoring has been shown. Full article
(This article belongs to the Special Issue Terahertz Spectroscopy: Instruments, Methods, and Application)
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8 pages, 774 KiB  
Communication
Compact High-Tc Superconducting Terahertz Emitter with Tunable Frequency from 0.15 to 1 THz
by Hancong Sun, Shixian Chen, Yong-Lei Wang, Guozhu Sun, Jian Chen, Takeshi Hatano, Valery P. Koshelets, Dieter Koelle, Reinhold Kleiner, Huabing Wang and Peiheng Wu
Appl. Sci. 2023, 13(6), 3469; https://doi.org/10.3390/app13063469 - 8 Mar 2023
Cited by 8 | Viewed by 2245
Abstract
A compact cryogenic terahertz emitter is highly desired for applications in terahertz astronomy with a broad frequency range of emissions and relatively high emission power. In this paper, we report on a terahertz emitter based on Bi2Sr2CaCu2O [...] Read more.
A compact cryogenic terahertz emitter is highly desired for applications in terahertz astronomy with a broad frequency range of emissions and relatively high emission power. In this paper, we report on a terahertz emitter based on Bi2Sr2CaCu2O8 + δ (BSCCO) intrinsic Josephson junctions, with a frequency range from 0.15 to 1.01 THz. The emitter is a square gold-BSCCO-gold mesa on a sapphire substrate fabricated by a simple and efficient method. The highest emission power of 5.62 μW at 0.35 THz was observed at 50 K. A record low emission frequency of 0.15 THz was achieved at 85 K, extending the applicability of BSCCO terahertz emitters in the low-frequency range. Full article
(This article belongs to the Special Issue Terahertz Spectroscopy: Instruments, Methods, and Application)
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14 pages, 4255 KiB  
Article
Detection of Terahertz Frequencies in S-Doped GaSe Crystals Using Laser Pulses at Telecom Wavelengths
by Olesya N. Shevchenko, Sergey L. Mikerin, Konstantin A. Kokh and Nazar A. Nikolaev
Appl. Sci. 2023, 13(4), 2045; https://doi.org/10.3390/app13042045 - 4 Feb 2023
Cited by 4 | Viewed by 1774
Abstract
Nonlinear optical crystals of gallium selenide are efficient up- and downconverters of infrared and terahertz frequencies. Their nonlinear properties have been investigated at wavelengths within the main transparency window. However, insufficient attention has been paid to studies at the telecommunication wavelength, especially for [...] Read more.
Nonlinear optical crystals of gallium selenide are efficient up- and downconverters of infrared and terahertz frequencies. Their nonlinear properties have been investigated at wavelengths within the main transparency window. However, insufficient attention has been paid to studies at the telecommunication wavelength, especially for sulfur-doped crystals. Closing this gap, we report on the optical and electro-optical properties of GaSe(1–x)Sx crystals (where x = 0, 0.03, 0.12, 0.16, and 0.22). For this purpose, the refractive indexes of the ordinary waves at terahertz frequencies and at a wavelength of 1.55 μm have been measured. The detection efficiency of the subterahertz waves in the crystals was studied using Er-fiber laser pulses and compared with that of GaAs, the etalon electro-optical crystal, at this wavelength. This allows us to estimate the dependence of the electro-optic coefficient r22 of GaSe(1–x)Sx on the sulfur concentration. It was shown that the sample with x = 0.12 has the largest value of the electro-optical coefficient r22 = 1.26 pm/V and provides the highest detection efficiency among the samples. The potential of employing S-doped GaSe crystals as nonlinear optical converters for photonic devices operating at telecom wavelengths is discussed. Full article
(This article belongs to the Special Issue Terahertz Spectroscopy: Instruments, Methods, and Application)
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10 pages, 5347 KiB  
Article
Novel Approaches in the Diagnostics of Ear-Nose-Throat Diseases Using High-Resolution THz Spectroscopy
by Vladimir Vaks, Vladimir Anfertev, Andrey Ayzenshtadt, Maria Chernyaeva, Elena Domracheva, Kseniya Glushkova, Roman Larin and Maria Shakhova
Appl. Sci. 2023, 13(3), 1573; https://doi.org/10.3390/app13031573 - 26 Jan 2023
Cited by 4 | Viewed by 1467
Abstract
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 [...] Read more.
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
(This article belongs to the Special Issue Terahertz Spectroscopy: Instruments, Methods, and Application)
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6 pages, 930 KiB  
Article
Towards Watt-Level THz Sources for High-Resolution Spectroscopy Based on 5th-Harmonic Multiplication in Gyrotrons
by Grigory Denisov, Irina Zotova, Ilya Zheleznov, Andrey Malkin, Alexander Sergeev, Roman Rozental and Mikhail Glyavin
Appl. Sci. 2022, 12(22), 11370; https://doi.org/10.3390/app122211370 - 9 Nov 2022
Cited by 5 | Viewed by 1278
Abstract
We propose the concept of high-power THz radiation sources based on five-fold frequency multiplication in gyrotrons intended for plasma applications. The efficient excitation at the 5th cyclotron harmonic is due to the specific property of the eigenmodes of cylindrical waveguides, as a result [...] Read more.
We propose the concept of high-power THz radiation sources based on five-fold frequency multiplication in gyrotrons intended for plasma applications. The efficient excitation at the 5th cyclotron harmonic is due to the specific property of the eigenmodes of cylindrical waveguides, as a result of which, the conditions of simultaneous electrodynamic resonance at two selected TE modes are satisfied asymptotically with very high accuracy. Previously, we have verified this principle in experiments with a low-frequency kilowatt-level gyrotron in which, due to the low-density spectrum, the operating mode is excited with no competition from parasitic oscillations. The novel concept is a development of this idea applied to the systems with a denser spectrum, which is inevitable in higher frequency and power devices. Simulations within the averaged time-domain model demonstrate that, despite the mode competition, it is possible to excite Watt-level 1.25 THz 5th cyclotron harmonic in a recently developed sub-MW 0.25 THz gyrotron with TE19,8 operating mode. The obtained results open a possibility for implementation of radiation sources with output power/frequency combination, practically inaccessible using other THz generation methods and highly sought for a number of applications, including high-resolution molecular spectroscopy. Full article
(This article belongs to the Special Issue Terahertz Spectroscopy: Instruments, Methods, and Application)
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