1
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Ghosh M, Deb SB, Acharyya A, Biswas A, Inokawa H, Satoh H, Banerjee A, Seteikin AY, Samusev IG. Edge-Terminated AlGaN/GaN/AlGaN Multi-Quantum Well Impact Avalanche Transit Time Sources for Terahertz Wave Generation. NANOMATERIALS (BASEL, SWITZERLAND) 2024; 14:873. [PMID: 38786828 PMCID: PMC11123759 DOI: 10.3390/nano14100873] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2024] [Revised: 05/14/2024] [Accepted: 05/14/2024] [Indexed: 05/25/2024]
Abstract
In our pursuit of high-power terahertz (THz) wave generation, we propose innovative edge-terminated single-drift region (SDR) multi-quantum well (MQW) impact avalanche transit time (IMPATT) structures based on the AlxGa1-xN/GaN/AlxGa1-xN material system, with a fixed aluminum mole fraction of x = 0.3. Two distinct MQW diode configurations, namely p+-n junction-based and Schottky barrier diode structures, were investigated for their THz potential. To enhance reverse breakdown characteristics, we propose employing mesa etching and nitrogen ion implantation for edge termination, mitigating issues related to premature and soft breakdown. The THz performance is comprehensively evaluated through steady-state and high-frequency characterizations using a self-consistent quantum drift-diffusion (SCQDD) model. Our proposed Al0.3Ga0.7N/GaN/Al0.3Ga0.7N MQW diodes, as well as GaN-based single-drift region (SDR) and 3C-SiC/Si/3C-SiC MQW-based double-drift region (DDR) IMPATT diodes, are simulated. The Schottky barrier in the proposed diodes significantly reduces device series resistance, enhancing peak continuous wave power output to approximately 300 mW and DC to THz conversion efficiency to nearly 13% at 1.0 THz. Noise performance analysis reveals that MQW structures within the avalanche zone mitigate noise and improve overall performance. Benchmarking against state-of-the-art THz sources establishes the superiority of our proposed THz sources, highlighting their potential for advancing THz technology and its applications.
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Affiliation(s)
- Monisha Ghosh
- Department of Electronics and Communication Engineering, Supreme Knowledge Foundation Group of Institutions, Mankundu, Chandannagar 712139, India;
- Department of Mining Engineering, Kazi Nazrul University, Asansol 713340, India;
| | - Shilpi Bhattacharya Deb
- Department of Electrical Engineering, RCC Institute of Information Technology (RCCIIT), Canal Road, Beliaghata, Kolkata 700015, India;
| | - Aritra Acharyya
- Department of Electronics and Communication Engineering, Cooch Behar Government Engineering College, Harinchawra, Ghughumari, Cooch Behar 736170, India;
| | - Arindam Biswas
- Department of Mining Engineering, Kazi Nazrul University, Asansol 713340, India;
- Centre for IoT and AI Integration with Education-Industry-Agriculture, Kazi Nazrul University, Asansol 713340, India
| | - Hiroshi Inokawa
- Research Institute of Electronics, Shizuoka University, Hamamatsu 4328011, Japan;
| | - Hiroaki Satoh
- Research Institute of Electronics, Shizuoka University, Hamamatsu 4328011, Japan;
| | - Amit Banerjee
- Microsystem Design-Integration Lab, Physics Department, Bidhan Chandra College, Asansol 713303, India
| | - Alexey Y. Seteikin
- Computation Biophysics Group, Amur State University, Blagoveshchensk 675027, Russia;
- Research and Education Center for Fundamental and Applied Photonics & Nanophotonics, Immanuel Kant Baltic Federal University, Kaliningrad 236000, Russia
| | - Ilia G. Samusev
- Research and Education Center for Fundamental and Applied Photonics & Nanophotonics, Immanuel Kant Baltic Federal University, Kaliningrad 236000, Russia
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2
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Farzin P, Hajiahmadi MJ, Soleimani M. Multi-channel polarization manipulation based on graphene for encryption communication. Sci Rep 2024; 14:11155. [PMID: 38750175 PMCID: PMC11096339 DOI: 10.1038/s41598-024-61323-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2024] [Accepted: 05/03/2024] [Indexed: 05/18/2024] Open
Abstract
Wave-based cryptography, at the vanguard of advancing technologies in advanced information science, is essential for establishing a diverse array of secure cryptographic platforms. The realization of these platforms hinges on the intelligent application of multiplexing techniques, seamlessly combined with appropriate metasurface technology. Nevertheless, existing multi-channel encryption technologies based on metasurfaces face challenges related to information leakage during partial channel decoding processes. In this paper, we present a reprogrammable metasurface for polarization modulation. This metasurface not only allows for the arbitrary customization of linearly polarized reflected waves but also enables real-time amplitude modulation. Here, relying on polarization amplitude control, a fully secure communication protocol is developed precisely in the terahertz (THz) spectrum to achieve real-time information encryption based on polarization modulation metasurfaces where access to information is highly restricted. The proposed metasurface employs the double random phase encryption (DRPE) algorithm for information encryption. It transmits the encrypted data through different polarization channels using two graphene nanoribbons, exclusively controlled by external biasing conditions. Various encryption scenarios have been outlined to fortify information protection against potential eavesdroppers. The simulated results show that this unique technology for hiding images by manipulating the polarization of the reflected wave provides new opportunities for various applications, including encryption, THz communications, THz secure data storage, and imaging.
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Affiliation(s)
- Parsa Farzin
- School of Electrical Engineering, Iran University of Science and Technology, Tehran, 1684613114, Iran
| | - Mohammad Javad Hajiahmadi
- School of Electrical Engineering, Iran University of Science and Technology, Tehran, 1684613114, Iran.
| | - Mohammad Soleimani
- School of Electrical Engineering, Iran University of Science and Technology, Tehran, 1684613114, Iran
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3
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Yang Z, Li D, Chen L, Qiu F, Yan S, Tang M, Wang C, Wang L, Luo Y, Sun F, Han J, Fan C, Li J, Wang H. Near-Field Terahertz Morphological Reconstruction Nanoscopy for Subsurface Imaging of Protein Layers. ACS NANO 2024; 18:10104-10112. [PMID: 38527229 DOI: 10.1021/acsnano.3c12776] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/27/2024]
Abstract
Protein layers formed on solid surfaces have important applications in various fields. High-resolution characterization of the morphological structures of protein forms in the process of developing protein layers has significant implications for the control of the layer's quality as well as for the evaluation of the layer's performance. However, it remains challenging to precisely characterize all possible morphological structures of protein in various forms, including individuals, networks, and layers involved in the formation of protein layers with currently available methods. Here, we report a terahertz (THz) morphological reconstruction nanoscopy (THz-MRN), which can reveal the nanoscale three-dimensional structural information on a protein sample from its THz near-field image by exploiting an extended finite dipole model for a thin sample. THz-MRN allows for both surface imaging and subsurface imaging with a vertical resolution of ∼0.5 nm, enabling the characterization of various forms of proteins at the single-molecule level. We demonstrate the imaging and morphological reconstruction of single immunoglobulin G (IgG) molecules, their networks, a monolayer, and a heterogeneous double layer comprising an IgG monolayer and a horseradish peroxidase-conjugated anti-IgG layer. The established THz-MRN presents a useful approach for the label-free and nondestructive study of the formation of protein layers.
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Affiliation(s)
- Zhongbo Yang
- Center of Super-Resolution Optics and Chongqing Engineering Research Center of High-Resolution and Three-Dimensional Dynamic Imaging Technology, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
- Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
| | - Dandan Li
- Center of Super-Resolution Optics and Chongqing Engineering Research Center of High-Resolution and Three-Dimensional Dynamic Imaging Technology, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
| | - Ligang Chen
- Center of Super-Resolution Optics and Chongqing Engineering Research Center of High-Resolution and Three-Dimensional Dynamic Imaging Technology, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
- Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
| | - Fucheng Qiu
- Center of Super-Resolution Optics and Chongqing Engineering Research Center of High-Resolution and Three-Dimensional Dynamic Imaging Technology, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
- Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
| | - Shihan Yan
- Center of Super-Resolution Optics and Chongqing Engineering Research Center of High-Resolution and Three-Dimensional Dynamic Imaging Technology, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
- Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
| | - Mingjie Tang
- Center of Super-Resolution Optics and Chongqing Engineering Research Center of High-Resolution and Three-Dimensional Dynamic Imaging Technology, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
- Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
| | - Chunlei Wang
- Institute of Materiobiology, Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China
| | - Lihua Wang
- Institute of Materiobiology, Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China
| | - Yang Luo
- Center of Smart Laboratory and Molecular Medicine, School of Medicine, Chongqing University, Chongqing 400044, China
| | - Fei Sun
- Center for Biological Imaging, Core Facilities for Protein Science, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Jiaguang Han
- Guangxi Key Laboratory of Optoelectronic Information Processing, School of Optoelectronic Engineering, Guilin University of Electronic Technology, Guilin 541004, China
| | - Chunhai Fan
- School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules and National Center for Translational Medicine, Shanghai Jiao Tong University, Shanghai 200024, China
| | - Jiang Li
- Institute of Materiobiology, Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China
| | - Huabin Wang
- Center of Super-Resolution Optics and Chongqing Engineering Research Center of High-Resolution and Three-Dimensional Dynamic Imaging Technology, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
- Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
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4
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Báez-Chorro MA, Vidal B. Particle Size Inversion from Spectrally Resolved Full-Field Forward Scattering. Anal Chem 2023; 95:15994-16003. [PMID: 37847094 PMCID: PMC10620756 DOI: 10.1021/acs.analchem.3c03178] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Accepted: 10/03/2023] [Indexed: 10/18/2023]
Abstract
Ensemble particle sizing has traditionally relied on inversion of extinction measurements for the characterization of the particle size distribution (PSD) in particulate media. However, particulate media induce complex phase changes that contain valuable information about their structure. Here, we propose the use of coherent detection to derive particle size distributions in inhomogeneous samples from light scattering. This is achieved by exploiting THz waves, which allow for both extinction and refractive index information to be directly retrieved. A modified version of the iterative Twomey method is presented in order to take into account this information. Additionally, by using a forward model based on the Waterman-Truell formula for the complex refractive index, samples with absorption in both the matrix medium and the particulate phase can be measured. The inversion needs neither a priori assumptions nor constraints regarding the PSD shape. Numerical simulations show that this full-field approach reduces the error of the inversion process potentially up to 65% compared with inversion using only extinction data. Experimental validation of the technique is provided by measuring calibrated spherical glass particles inside a PTFE matrix and retrieving the PSD in the case of monodisperse and polydisperse samples showing an enhancement of up to 32% in comparison to inversion from extinction data.
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Affiliation(s)
- Miguel A. Báez-Chorro
- Nanophotonics Technology Center, Universitat Politècnica de València, Valencia 46022, Spain
| | - Borja Vidal
- Nanophotonics Technology Center, Universitat Politècnica de València, Valencia 46022, Spain
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5
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Li J, Li X, Yardimci NT, Hu J, Li Y, Chen J, Hung YC, Jarrahi M, Ozcan A. Rapid sensing of hidden objects and defects using a single-pixel diffractive terahertz sensor. Nat Commun 2023; 14:6791. [PMID: 37880258 PMCID: PMC10600253 DOI: 10.1038/s41467-023-42554-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2023] [Accepted: 10/13/2023] [Indexed: 10/27/2023] Open
Abstract
Terahertz waves offer advantages for nondestructive detection of hidden objects/defects in materials, as they can penetrate most optically-opaque materials. However, existing terahertz inspection systems face throughput and accuracy restrictions due to their limited imaging speed and resolution. Furthermore, machine-vision-based systems using large-pixel-count imaging encounter bottlenecks due to their data storage, transmission and processing requirements. Here, we report a diffractive sensor that rapidly detects hidden defects/objects within a 3D sample using a single-pixel terahertz detector, eliminating sample scanning or image formation/processing. Leveraging deep-learning-optimized diffractive layers, this diffractive sensor can all-optically probe the 3D structural information of samples by outputting a spectrum, directly indicating the presence/absence of hidden structures or defects. We experimentally validated this framework using a single-pixel terahertz time-domain spectroscopy set-up and 3D-printed diffractive layers, successfully detecting unknown hidden defects inside silicon samples. This technique is valuable for applications including security screening, biomedical sensing and industrial quality control.
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Affiliation(s)
- Jingxi Li
- Electrical and Computer Engineering Department, University of California, Los Angeles, CA, 90095, USA
- Bioengineering Department, University of California, Los Angeles, CA, 90095, USA
- California NanoSystems Institute (CNSI), University of California, Los Angeles, CA, 90095, USA
| | - Xurong Li
- Electrical and Computer Engineering Department, University of California, Los Angeles, CA, 90095, USA
- California NanoSystems Institute (CNSI), University of California, Los Angeles, CA, 90095, USA
| | - Nezih T Yardimci
- Electrical and Computer Engineering Department, University of California, Los Angeles, CA, 90095, USA
- California NanoSystems Institute (CNSI), University of California, Los Angeles, CA, 90095, USA
| | - Jingtian Hu
- Electrical and Computer Engineering Department, University of California, Los Angeles, CA, 90095, USA
- Bioengineering Department, University of California, Los Angeles, CA, 90095, USA
- California NanoSystems Institute (CNSI), University of California, Los Angeles, CA, 90095, USA
| | - Yuhang Li
- Electrical and Computer Engineering Department, University of California, Los Angeles, CA, 90095, USA
- Bioengineering Department, University of California, Los Angeles, CA, 90095, USA
- California NanoSystems Institute (CNSI), University of California, Los Angeles, CA, 90095, USA
| | - Junjie Chen
- Physics & Astronomy Department, University of California, Los Angeles, CA, 90095, USA
| | - Yi-Chun Hung
- Electrical and Computer Engineering Department, University of California, Los Angeles, CA, 90095, USA
| | - Mona Jarrahi
- Electrical and Computer Engineering Department, University of California, Los Angeles, CA, 90095, USA
- California NanoSystems Institute (CNSI), University of California, Los Angeles, CA, 90095, USA
| | - Aydogan Ozcan
- Electrical and Computer Engineering Department, University of California, Los Angeles, CA, 90095, USA.
- Bioengineering Department, University of California, Los Angeles, CA, 90095, USA.
- California NanoSystems Institute (CNSI), University of California, Los Angeles, CA, 90095, USA.
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6
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Nie H, Hao F, Wang L, Guo Q, Chen H, Ren J, Wang K, Dang W, Liang X, Ma W. Application of Terahertz Nondestructive Testing Technology in the Detection of Polyethylene Pipe Defects. ACS OMEGA 2023; 8:27323-27332. [PMID: 37546631 PMCID: PMC10398680 DOI: 10.1021/acsomega.3c02701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Accepted: 07/12/2023] [Indexed: 08/08/2023]
Abstract
At present, polyethylene pipeline is widely used in urban gas projects, but a relatively mature and reliable nondestructive testing technology has not been formed. Therefore, it is urgent to develop a new nondestructive testing technology to meet the increasing demand for inspection of non-metallic pipes. The terahertz testing technology and related equipment have played an increasingly important role in the nondestructive testing of many nonmetallic structures, but they have not been applied to polyethylene (PE) pipes. In this work, terahertz time-domain spectroscopy was used to detect prefabricated defects inside the PE pipe specimens. The results show that the terahertz nondestructive testing technology can be used to detect common defects in nonblack PE pipes with a detection error of less than 10%. Higher-power terahertz devices can detect defects in black PE pipe, while lower-power terahertz devices cannot. Because the black PE pipe contains carbon and has a strong absorption of terahertz waves. The penetration of lower-power terahertz devices to the black PE pipe is not enough, resulting in a low resolution of the imaging. The results of this work may promote the progress of the nondestructive testing technology of nonmetallic pipelines.
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Affiliation(s)
- Hailiang Nie
- Institute
of Safety Assessment and Integrity, State Key Laboratory for Performance
and Structure Safety of Petroleum Tubular Goods and Equipment Materials, Tubular Goods Research Center of CNPC, Xi’an 710077, China
| | - Fengdan Hao
- China
Promotion Association for Special Equipment Safety and Energy-Saving, Beijing 100029, China
| | - Litao Wang
- The
Third Oil Transportation Department of Changqing Oilfield Branch of
China National Petroleum Corporation, Ningxia 750006, China
| | - Qiang Guo
- Shaanxi
City Gas Industry Development Co., LTD., Xi’an 710000, China
| | - Hongda Chen
- Institute
of Safety Assessment and Integrity, State Key Laboratory for Performance
and Structure Safety of Petroleum Tubular Goods and Equipment Materials, Tubular Goods Research Center of CNPC, Xi’an 710077, China
| | - Junjie Ren
- Institute
of Safety Assessment and Integrity, State Key Laboratory for Performance
and Structure Safety of Petroleum Tubular Goods and Equipment Materials, Tubular Goods Research Center of CNPC, Xi’an 710077, China
| | - Ke Wang
- Institute
of Safety Assessment and Integrity, State Key Laboratory for Performance
and Structure Safety of Petroleum Tubular Goods and Equipment Materials, Tubular Goods Research Center of CNPC, Xi’an 710077, China
| | - Wei Dang
- Institute
of Safety Assessment and Integrity, State Key Laboratory for Performance
and Structure Safety of Petroleum Tubular Goods and Equipment Materials, Tubular Goods Research Center of CNPC, Xi’an 710077, China
| | - Xiaobin Liang
- Institute
of Safety Assessment and Integrity, State Key Laboratory for Performance
and Structure Safety of Petroleum Tubular Goods and Equipment Materials, Tubular Goods Research Center of CNPC, Xi’an 710077, China
| | - Weifeng Ma
- Institute
of Safety Assessment and Integrity, State Key Laboratory for Performance
and Structure Safety of Petroleum Tubular Goods and Equipment Materials, Tubular Goods Research Center of CNPC, Xi’an 710077, China
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Kucheryavenko AS, Zhelnov VA, Melikyants DG, Chernomyrdin NV, Lebedev SP, Bukin VV, Garnov SV, Kurlov VN, Zaytsev KI, Katyba GM. Super-resolution THz endoscope based on a hollow-core sapphire waveguide and a solid immersion lens. OPTICS EXPRESS 2023; 31:13366-13373. [PMID: 37157475 DOI: 10.1364/oe.484650] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
To address a challenging problem of super-resolution terahertz (THz) endoscopy, in this paper, an antiresonant hollow-core waveguide was coupled with a sapphire solid immersion lens (SIL), aimed at subwavelength confinement of guided mode. The waveguide is formed by a polytetrafluoroethylene (PTFE)-coated sapphire tube, the geometry of which was optimized to ensure high optical performance. SIL was judiciously designed, fabricated of bulk sapphire crystal, and then mounted at the output waveguide end. Study of the field intensity distributions at the shadow side of the waveguide-SIL system revealed the focal spot diameter of ≃0.2λ at the wavelength of λ = 500 μm. It agrees with numerical predictions, overcomes the Abbe diffraction limit, and justifies super-resolution capabilities of our endoscope.
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8
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Peng S, Lu X, Tang L, Chang X, Yan J, Shi Q, Chen K, Li J, Du L, Huang W. Thermal and mechanical THz modulation of flexible all-dielectric metamaterial. OPTICS EXPRESS 2023; 31:2644-2653. [PMID: 36785273 DOI: 10.1364/oe.481264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Accepted: 12/13/2022] [Indexed: 06/18/2023]
Abstract
The implementation of Terahertz (THz) modulation is critical for applications in high-speed wireless communications, security screening and so on. Therefore, it is particularly significant to obtain THz wave modulation devices with stable and flexible performance, easy manipulation of the modulation method, and multi-functionality. Here, we propose a flexible all-dielectric metamaterial by embedding zirconia (ZrO2) microspheres into a vanadium dioxide/polydimethylsiloxane (VO2/PDMS) composite, which can achieve thermal and mechanical tuning of THz wave transmission. When the temperature of the ZrO2/VO2/PDMS metamaterial increases, VO2 changes from the insulating phase to the metallic phase, and the 1st (at 0.304 THz) and 2nd (at 0.414 THz) order magnetic resonances exhibit the tunability of 20 GHz and 15 GHz, respectively. When stretched, the 1st and 2nd order magnetic resonances show the tunability of 12 GHz and 10 GHz, respectively. In the meantime, there are accompanying changes in transmittance at the resonances. The ZrO2/VO2/PDMS all-dielectric metamaterial presented in this work provides an alternative strategy for developing actively tunable, flexible, and versatile THz devices. In addition, it has the merits of simple preparation and low cost, promising large-area and rapid preparation of meta-arrays.
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Shukoor MA, Bini TS, Kunju N, Dey S. Wideband dual-polarized linear-circular and linear-cross angular stable THz reflective polarizer based on a modified square loop FSS. APPLIED OPTICS 2022; 61:6476-6482. [PMID: 36255870 DOI: 10.1364/ao.462466] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2022] [Accepted: 07/03/2022] [Indexed: 06/16/2023]
Abstract
A simple wideband reflective type linear-cross and linear-circular polarization converter for terahertz (THz) applications is proposed in this paper. The top frequency selective surface (FSS) consists of a thin gold coated figure of eight square loop with the connected strip line corners on a thin grounded polyamide dielectric substrate. For the y/x-polarized incidence, the design exhibits linear-circular conversion with an axial ratio (≤3dB) from 0.49-0.50, 0.60-0.83, 1.16-1.62, and 1.81-1.85 THz with 2.02%, 32.17%, 33.09%, and 2.19% fractional bandwidth (FBW), respectively. In addition, it also performs the linear-cross conversion with a minimum 90% polarization conversion ratio (PCR) from 0.53-0.56, 0.92-1.07, and 1.69-1.75 THz having 5.50%, 15.08%, and 3.49% FBW, respectively. Multiple plasmonic resonances are the reason behind different polarization conversions and are confirmed with surface current distribution profiles of the FSS and ground. The metasurface's performance is stable up to 45° for both transverse electric (TE) and transverse magnetic (TM) oblique incidences. The polarizer's unit cell architecture is compact with structural dimensions of 0.121×0.121×0.041λL3, where λL is the lowest operating frequency's free-space wavelength. The authors believe this design is compact, with angular stable multi-band multi-conversion ability that will significantly impact the THz applications in real time.
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10
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Miriya Thanthrige USKP, Jung P, Sezgin A. Deep Unfolding of Iteratively Reweighted ADMM for Wireless RF Sensing. SENSORS (BASEL, SWITZERLAND) 2022; 22:3065. [PMID: 35459049 PMCID: PMC9028850 DOI: 10.3390/s22083065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Revised: 03/31/2022] [Accepted: 04/13/2022] [Indexed: 06/14/2023]
Abstract
We address the detection of material defects, which are inside a layered material structure using compressive sensing-based multiple-input and multiple-output (MIMO) wireless radar. Here, strong clutter due to the reflection of the layered structure's surface often makes the detection of the defects challenging. Thus, sophisticated signal separation methods are required for improved defect detection. In many scenarios, the number of defects that we are interested in is limited, and the signaling response of the layered structure can be modeled as a low-rank structure. Therefore, we propose joint rank and sparsity minimization for defect detection. In particular, we propose a non-convex approach based on the iteratively reweighted nuclear and ℓ1-norm (a double-reweighted approach) to obtain a higher accuracy compared to the conventional nuclear norm and ℓ1-norm minimization. To this end, an iterative algorithm is designed to estimate the low-rank and sparse contributions. Further, we propose deep learning-based parameter tuning of the algorithm (i.e., algorithm unfolding) to improve the accuracy and the speed of convergence of the algorithm. Our numerical results show that the proposed approach outperforms the conventional approaches in terms of mean squared errors of the recovered low-rank and sparse components and the speed of convergence.
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Affiliation(s)
| | - Peter Jung
- Institute of Communications and Information Theory, Technical University Berlin, 10587 Berlin, Germany;
- Data Science in Earth Observation, Technical University of Munich, 82024 Munich, Germany
| | - Aydin Sezgin
- Institute of Digital Communication Systems, Ruhr University Bochum, 44801 Bochum, Germany;
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11
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THz Time-Domain Ellipsometer for Material Characterization and Paint Quality Control with More Than 5 THz Bandwidth. APPLIED SCIENCES-BASEL 2022. [DOI: 10.3390/app12083744] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
Quality control of car body paint in the automotive industry is a promising industrial application of terahertz technology. Terahertz time-domain spectroscopy in reflection geometry enables accurate, fast, and nondestructive measurement of individual layer thicknesses of multi-layer coatings. For high precision thickness measurements, the frequency dependent complex refractive index of all layers must be calibrated very accurately. THz time-domain ellipsometry is self-referencing and provides reliable, frequency resolved material properties with high signal-to-noise ratio. The method is characterized by a high sensitivity to optical material properties and layer thicknesses. We present characterization results in the frequency range 0.1–6 THz for typical automotive paints and different substrates such as polypropylene (PP), which features a high material anisotropy. We demonstrate that the broadband material properties derived from ellipsometry allow for inline thickness measurements of multi-layer car body paints with high accuracy.
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12
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Nondestructive Evaluation of Thermal Barrier Coatings Thickness Using Terahertz Technique Combined with PCA–GA–ELM Algorithm. COATINGS 2022. [DOI: 10.3390/coatings12030390] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Thermal barrier coatings (TBCs) are usually used in high temperature and harsh environment, resulting in thinning or even spalling off. Hence, it is vital to detect the thickness of the TBCs. In this study, a hybrid machine learning model combined with terahertz time-domain spectroscopy technology was designed to predict the thickness of TBCs. The terahertz signals were obtained from the samples prepared in laboratory and actual turbine blade. The principal component analysis (PCA) method was used to decrease the data dimensions. Finally, an extreme learning machine (ELM) was proposed to establish the thickness of TBCs prediction model. Genetic algorithm (GA) was selected to optimize the model to make it more accurate. The results showed that the root correlation coefficient (R2) exceeded 0.97 and the errors (root mean square error and mean absolute percentage error) were less than 2.57. This study proposes that terahertz time-domain technology combined with PCA–GA–ELM model is accurate and feasible for evaluating the thickness of the TBCs.
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13
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Abstract
In this paper, we report the development of a frequency-shifted (FS) terahertz (THz) wave source for the non-destructive inspection of buildings. Currently, terahertz-time domain spectroscopy (THz-TDS) is the mainstream method for non-destructive inspection using THz waves. However, THz-TDS is limited by its measurement range and difficulties encountered when there is a strong frequency dependence in the absorption characteristics and refractive index of the measurement target. To address these issues, we developed a novel non-destructive approach for inspection applications using frequency-shifted THz waves. Our system uses a frequency-shifted feedback (FSF) laser as the pump light source to generate FS-THz waves; this allowed us to obtain precise distance measurements of objects over a broad range of distances. We tested a prototype FS-THz system and confirmed successful measurement of spatial distances inside a building material.
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14
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Abstract
Proteins play a key role in living organisms. The study of proteins and their dynamics provides information about their functionality, catalysis and potential alterations towards pathological diseases. Several techniques are used for studying protein dynamics, e.g., magnetic resonance, fluorescence imaging techniques, mid-infrared spectroscopy and biochemical assays. Spectroscopic analysis, based on the use of terahertz (THz) radiation with frequencies between 0.1 and 15 THz (3–500 cm−1), was underestimated by the biochemical community. In recent years, however, the potential of THz spectroscopy in the analysis of both simple structures, such as polypeptide molecules, and complex structures, such as protein complexes, has been demonstrated. The THz absorption spectrum provides some information on proteins: for small molecules the THz spectrum is dominated by individual modes related to the presence of hydrogen bonds. For peptides, the spectral information concerns their secondary structure, while for complex proteins such as globular proteins and viral glycoproteins, spectra also provide information on collective modes. In this short review, we discuss the results obtained by THz spectroscopy in the protein dynamics investigations. In particular, we will illustrate advantages and applications of THz spectroscopy, pointing out the complementary information it may provide.
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15
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Minamide H, Nawata K, Moriguchi Y, Takida Y, Notake T. Injection-seeded terahertz-wave parametric generator with timing stabilized excitation for nondestructive testing applications. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:093002. [PMID: 34598517 DOI: 10.1063/5.0057040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Accepted: 09/01/2021] [Indexed: 06/13/2023]
Abstract
An injection-seeded terahertz (THz)-wave parametric generator (is-TPG) with a footprint the size of an A3 paper is presented. We improved the measurement performance of the is-TPG source for nondestructive inspection applications. A high pulse repetition rate up to 70 kHz and a low pulse timing jitter of a few tens of picoseconds, which is approximately one ten-thousandth of the conventional is-TPG, were achieved. THz waves exhibited excellent performance with a maximum average output power of 20 µW, a monochromatic spectrum linewidth of ∼20 GHz, and a frequency tuning range of 1.7-3.0 THz. This was achieved by designing the entire system configuration from the pump laser source to THz-wave generation. A new double-pass all-solid-state optical amplifier was developed with a high gain and low noise using an externally pulse-modulated laser diode (LD) as the master oscillator source. An achromatic optical injection system was developed for the is-TPG with a 40% reduction in the conventional path length. They were housed in a single enclosure in two layers. LDs and optical fiber amplifiers could be rack-mounted, and the outputs were delivered to the housing via optical fibers. The developed THz-wave source performed nondestructive imaging of a human hair sample fixed with Scotch tape on a test pattern in an envelope by irradiating 2.1 THz waves. A clearly recognizable THz-wave image of an enclosed hair with a spatial resolution close to the THz wavelength was obtained.
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Affiliation(s)
- Hiroaki Minamide
- RIKEN Center for Advanced Photonics (RAP), RIKEN, Aoba-ku, Sendai 980-0845, Japan
| | - Kouji Nawata
- RIKEN Center for Advanced Photonics (RAP), RIKEN, Aoba-ku, Sendai 980-0845, Japan
| | - Yoshikiyo Moriguchi
- RIKEN Center for Advanced Photonics (RAP), RIKEN, Aoba-ku, Sendai 980-0845, Japan
| | - Yuma Takida
- RIKEN Center for Advanced Photonics (RAP), RIKEN, Aoba-ku, Sendai 980-0845, Japan
| | - Takashi Notake
- RIKEN Center for Advanced Photonics (RAP), RIKEN, Aoba-ku, Sendai 980-0845, Japan
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16
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Luo W, Jiang P, Xu Q, Cao L, Jones A, Li K, Copner N, Gong Y. Terahertz Sensor via Ultralow-Loss Dispersion-Flattened Polymer Optical Fiber: Design and Analysis. MATERIALS (BASEL, SWITZERLAND) 2021; 14:4921. [PMID: 34501010 PMCID: PMC8434055 DOI: 10.3390/ma14174921] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Revised: 08/18/2021] [Accepted: 08/23/2021] [Indexed: 11/28/2022]
Abstract
A novel cyclic olefin copolymer (COC)-based polymer optical fiber (POF) with a rectangular porous core is designed for terahertz (THz) sensing by the finite element method. The numerical simulations showed an ultrahigh relative sensitivity of 89.73% of the x-polarization mode at a frequency of 1.2 THz and under optimum design conditions. In addition to this, they showed an ultralow confinement loss of 2.18 × 10-12 cm-1, a high birefringence of 1.91 × 10-3, a numerical aperture of 0.33, and an effective mode area of 1.65 × 105 μm2 was obtained for optimum design conditions. Moreover, the range dispersion variation was within 0.7 ± 0.41 ps/THz/cm, with the frequency range of 1.0-1.4 THz. Compared with the traditional sensor, the late-model sensor will have application value in THz sensing and communication.
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Affiliation(s)
- Wanli Luo
- College of Physics and Optoelectronic Technology, Baoji University of Arts and Sciences, Baoji 721016, China; (W.L.); (P.J.); (L.C.)
- Engineering Technology Research Center for Ultrafast Optics and Advanced Material of Baoji, Baoji 721016, China
| | - Peng Jiang
- College of Physics and Optoelectronic Technology, Baoji University of Arts and Sciences, Baoji 721016, China; (W.L.); (P.J.); (L.C.)
- Engineering Technology Research Center for Ultrafast Optics and Advanced Material of Baoji, Baoji 721016, China
| | - Qiang Xu
- College of Physics and Optoelectronic Technology, Baoji University of Arts and Sciences, Baoji 721016, China; (W.L.); (P.J.); (L.C.)
- Engineering Technology Research Center for Ultrafast Optics and Advanced Material of Baoji, Baoji 721016, China
- Wireless and Optoelectronics Research and Innovation Centre, Faculty of Computing, Engineering and Science, University of South Wales, Cardiff CF37 1DL, UK; (A.J.); (N.C.)
| | - Lei Cao
- College of Physics and Optoelectronic Technology, Baoji University of Arts and Sciences, Baoji 721016, China; (W.L.); (P.J.); (L.C.)
| | - Adam Jones
- Wireless and Optoelectronics Research and Innovation Centre, Faculty of Computing, Engineering and Science, University of South Wales, Cardiff CF37 1DL, UK; (A.J.); (N.C.)
| | - Kang Li
- Wireless and Optoelectronics Research and Innovation Centre, Faculty of Computing, Engineering and Science, University of South Wales, Cardiff CF37 1DL, UK; (A.J.); (N.C.)
| | - Nigel Copner
- Wireless and Optoelectronics Research and Innovation Centre, Faculty of Computing, Engineering and Science, University of South Wales, Cardiff CF37 1DL, UK; (A.J.); (N.C.)
| | - Yongkang Gong
- School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, UK;
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17
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Boursier Niutta C, Tridello A, Paolino DS, Belingardi G. Residual Properties in Damaged Laminated Composites through Nondestructive Testing: A Review. MATERIALS (BASEL, SWITZERLAND) 2021; 14:4513. [PMID: 34443035 PMCID: PMC8401990 DOI: 10.3390/ma14164513] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 07/31/2021] [Accepted: 08/03/2021] [Indexed: 11/16/2022]
Abstract
The development of damage tolerance strategies in the design of composite structures constitutes a major challenge for the widespread application of composite materials. Damage tolerance approaches require a proper combination of material behavior description and nondestructive techniques. In contrast to metals, strength degradation approaches, i.e., the residual strength in presence of cracks, are not straightforwardly enforceable in composites. The nonhomogeneous nature of such materials gives rise to several failure mechanisms and, therefore, the definition of an ultimate load carrying capacity is ambiguous. Nondestructive techniques are thus increasingly required, where the damage severity is quantified not only in terms of damage extension, but also in terms of material response of the damaged region. Based on different approaches, many nondestructive techniques have been proposed in the literature, which are able to provide a quantitative description of the material state. In the present paper, a review of such nondestructive techniques for laminated composites is presented. The main objective is to analyze the damage indexes related to each method and to point out their significance with respect to the residual mechanical performances, as a result of the working principle of each retained technique. A possible guide for future research on this subject is thus outlined.
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Affiliation(s)
- Carlo Boursier Niutta
- Department of Mechanical and Aerospace Engineering, Politecnico di Torino, 10129 Turin, Italy; (A.T.); (D.S.P.); (G.B.)
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18
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Zhai M, Locquet A, Jung M, Woo D, Citrin DS. Characterization of nanoporous Al 2O 3 films at terahertz frequencies. OPTICS LETTERS 2020; 45:4092-4095. [PMID: 32667362 DOI: 10.1364/ol.390129] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Accepted: 05/27/2020] [Indexed: 05/27/2023]
Abstract
Terahertz birefringence in nanoporous Al2O3 films grown on Al substrates is characterized nondestructively by polarization-resolved terahertz spectroscopy. Sparse deconvolution is used to find the film thicknesses from the data, showing good agreement with the values measured directly by destructive cross-sectional field-emission scanning electron microscopy.
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19
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Jiang Y, Ge H, Zhang Y. Quantitative analysis of wheat maltose by combined terahertz spectroscopy and imaging based on Boosting ensemble learning. Food Chem 2020; 307:125533. [DOI: 10.1016/j.foodchem.2019.125533] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Revised: 06/02/2019] [Accepted: 09/12/2019] [Indexed: 12/01/2022]
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20
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Guo Y, Ling F, Li H, Zhou S, Ji J, Yao J. Super-resolution reconstruction for terahertz imaging based on sub-pixel gradient field transform. APPLIED OPTICS 2019; 58:6244-6250. [PMID: 31503766 DOI: 10.1364/ao.58.006244] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2019] [Accepted: 07/10/2019] [Indexed: 06/10/2023]
Abstract
This paper presents the gradient-guided image super-resolution reconstruction for terahertz imaging to improve the image quality, taking advantage of super-resolution reconstruction based on adaptive super-pixel gradient field transform. Moreover, spatial entropy-based enhancement and a bilateral filter are introduced to ensure better performance of the reconstruction. Furthermore, we compare the performance of reconstruction operated on terahertz images with frequencies of 0.1 THz, 0.3 THz, 0.5 THz, and 0.7 THz. Experimental results demonstrate that this method successfully improves the image quality and reconstruct high-resolution images from low-resolution images with the peak signal-to-noise ratio and structural similarity index improved. In addition, the signal frequency and intensity are demonstrated to affect the performance of reconstruction.
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21
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Kulya M, Semenova V, Gorodetsky A, Bespalov VG, Petrov NV. Spatio-temporal and spatiospectral metrology of terahertz broadband uniformly topologically charged vortex beams. APPLIED OPTICS 2019; 58:A90-A100. [PMID: 30873965 DOI: 10.1364/ao.58.000a90] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Accepted: 11/10/2018] [Indexed: 06/09/2023]
Abstract
A comprehensive characterization of the diffraction properties of terahertz (THz) pulsed broadband vortex beams consisting of several electromagnetic field oscillations requires state-of-the-art techniques for studying the evolution of a wavefront as it propagates. For this purpose, we have applied the capabilities offered by THz pulse time domain holography. Accurate metrological study of pulsed single-period THz field propagation allowed us to reveal the spatio-temporal and spatiospectral couplings in broadband uniformly topologically charged vortex beams. Here, we reveal dynamics of such beam propagation in a free space as well as in the experiment with edge diffraction with 50% blocking of the beam focal waist. In this study, we compare the dynamics of freely propagating and edge-diffracted THz vortex. Despite the fact that in the amplitude representation one can observe the emergence of strong asymmetry, analysis of the spectral trajectory of the singular point at some distance from the obstacle and the visualization of phase distribution for individual spectral components testify to the conservation of transverse energy circulation. Similar to the edge diffraction of monochromatic optical vortices, it can be interpreted as self-reconstruction of vortex properties. The given term has not previously been used for the case of pulsed broadband THz beams, to the best of our knowledge.
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22
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Balbekin NS, Kulya MS, Belashov AV, Gorodetsky A, Petrov NV. Increasing the resolution of the reconstructed image in terahertz pulse time-domain holography. Sci Rep 2019; 9:180. [PMID: 30655553 PMCID: PMC6336780 DOI: 10.1038/s41598-018-36642-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 11/22/2018] [Indexed: 12/19/2022] Open
Abstract
In this paper, we present a novel numerical approach for increasing the resolution of retrieved images of objects after their diffraction patterns are recorded via terahertz pulse time-domain holography (THz PTDH). THz PTDH allows for spectrally resolved imaging with high spatial resolution and does not require the fine alignment of complex optics in the THz path. The proposed data post-processing method opens up the possibility to reconstruct holograms recorded with spatially restricted THz detectors, and overcome the diffraction limit even for the lower-frequency spectral components. The method involves an iterative procedure of backward-forward wavefront propagation to simulate the field distribution beyond the initially recorded hologram area. We show significant improvement in both the object reconstruction and contrast across the whole spectrum, with qualitative resolution enhancement at lower frequency spectral components.
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Affiliation(s)
| | | | | | - Andrei Gorodetsky
- ITMO University, Saint-Petersburg, 197101, Russia
- Department of Chemistry, Imperial College London, London, SW7 2AZ, UK
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23
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Poulin C, Zerrad M, Triki M, Guille A, Antonini T, Amra C. Terahertz transmission imaging of inhomogeneous polymer multilayers: theory and experiment. APPLIED OPTICS 2018; 57:10380-10389. [PMID: 30645381 DOI: 10.1364/ao.57.010380] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Accepted: 11/12/2018] [Indexed: 06/09/2023]
Abstract
We extend an interferential multilayer model used in optics in the terahertz domain to be able to simulate the mapping of the transmissivity of a multilayer structure of polymers. In particular, we are interested in extracting the thickness gradient of a glue layer within an assembly of polymers. We developed an iterative procedure which we validated by terahertz imaging.
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24
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Crystal structure, thermal, luminescent and terahertz time domain spectroscopy of magnesium N-phthaloyl-β-alaninate: A combined experimental and theoretical study. J Mol Struct 2018. [DOI: 10.1016/j.molstruc.2018.05.063] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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25
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Schemmel P, Moore AJ. Monitoring stress changes in carbon fiber reinforced polymer composites with GHz radiation. APPLIED OPTICS 2017; 56:6405-6409. [PMID: 29047841 DOI: 10.1364/ao.56.006405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 05/16/2017] [Indexed: 06/07/2023]
Abstract
We performed proof of concept experiments to demonstrate that the reflected power of GHz illumination from the surface of carbon fiber reinforced polymer (CFRP) composites is linearly related to the stress in the material. We introduce a stress coefficient to describe the change in normalized power with applied stress, analogous to the stress-optic coefficient, because the effect is attributed to changes in the refractive index of the effective medium comprising the polymer matrix and carbon fibers. Stress coefficients of -0.549±0.134/GPa and -0.154±0.024/GPa were measured for two different composite materials, both linear in the measurement range of 40 MPa and 100 Mpa, respectively. This technique opens up the possibility of non-destructive evaluation of stresses in CFRP components for quality assurance in manufacturing and in structural health monitoring of in-service aerospace and automotive parts.
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26
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Funaki C, Toyouchi T, Hoshina H, Ozaki Y, Sato H. Terahertz Imaging of the Distribution of Crystallinity and Crystalline Orientation in a Poly(ɛ-caprolactone) Film. APPLIED SPECTROSCOPY 2017; 71:1537-1542. [PMID: 28145737 DOI: 10.1177/0003702816684838] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The distribution of crystallinity and the crystalline orientation of a poly(ɛ-caprolactone) (PCL) film have been studied using terahertz (THz) imaging. Terahertz images were developed by using the intensity ratio of the two spectral peaks at 1.42 and 2.03 THz that are assigned to the crystalline modes parallel and perpendicular to the c-axis (I⊥/I ||) of the PCL film. The obtained THz images show that the distribution of crystallinity and crystalline orientation vary considerably between the different regions in the PCL film, even though this inhomogeneity is not visible in the corresponding optical image. Our results clearly illustrate that THz imaging is a promising technique to characterize the physical properties of semi-crystalline polymers.
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Affiliation(s)
- Chihiro Funaki
- 1 Graduate School of Human Development and Environment, Kobe University, Japan
| | - Takuya Toyouchi
- 1 Graduate School of Human Development and Environment, Kobe University, Japan
| | | | - Yukihiro Ozaki
- 3 Department of Chemistry, Kwansei Gakuin University, Hyogo, Japan
| | - Harumi Sato
- 1 Graduate School of Human Development and Environment, Kobe University, Japan
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27
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Chernomyrdin NV, Frolov ME, Lebedev SP, Reshetov IV, Spektor IE, Tolstoguzov VL, Karasik VE, Khorokhorov AM, Koshelev KI, Schadko AO, Yurchenko SO, Zaytsev KI. Wide-aperture aspherical lens for high-resolution terahertz imaging. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2017; 88:014703. [PMID: 28147664 DOI: 10.1063/1.4973764] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
In this paper, we introduce wide-aperture aspherical lens for high-resolution terahertz (THz) imaging. The lens has been designed and analyzed by numerical methods of geometrical optics and electrodynamics. It has been made of high-density polyethylene by shaping at computer-controlled lathe and characterized using a continuous-wave THz imaging setup based on a backward-wave oscillator and Golay detector. The concept of image contrast has been implemented to estimate image quality. According to the experimental data, the lens allows resolving two points spaced at 0.95λ distance with a contrast of 15%. To highlight high resolution in the THz images, the wide-aperture lens has been employed for studying printed electronic circuit board containing sub-wavelength-scale elements. The observed results justify the high efficiency of the proposed lens design.
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Affiliation(s)
- Nikita V Chernomyrdin
- Bauman Moscow State Technical University, 2nd Baumanskaya St. 5, Moscow 105005, Russia
| | - Maxim E Frolov
- Bauman Moscow State Technical University, 2nd Baumanskaya St. 5, Moscow 105005, Russia
| | - Sergey P Lebedev
- A.M. Prokhorov General Physics Institute of the Russian Academy of Sciences, Vavilova St. 38, Moscow 119991, Russia
| | - Igor V Reshetov
- I.M. Sechenov First Moscow State Medical University, Bolshaya Pirogovskaya St. 2-4, Moscow 119991, Russia
| | - Igor E Spektor
- A.M. Prokhorov General Physics Institute of the Russian Academy of Sciences, Vavilova St. 38, Moscow 119991, Russia
| | - Viktor L Tolstoguzov
- Bauman Moscow State Technical University, 2nd Baumanskaya St. 5, Moscow 105005, Russia
| | - Valeriy E Karasik
- Bauman Moscow State Technical University, 2nd Baumanskaya St. 5, Moscow 105005, Russia
| | - Alexei M Khorokhorov
- Bauman Moscow State Technical University, 2nd Baumanskaya St. 5, Moscow 105005, Russia
| | - Kirill I Koshelev
- Bauman Moscow State Technical University, 2nd Baumanskaya St. 5, Moscow 105005, Russia
| | - Aleksander O Schadko
- Bauman Moscow State Technical University, 2nd Baumanskaya St. 5, Moscow 105005, Russia
| | - Stanislav O Yurchenko
- Bauman Moscow State Technical University, 2nd Baumanskaya St. 5, Moscow 105005, Russia
| | - Kirill I Zaytsev
- Bauman Moscow State Technical University, 2nd Baumanskaya St. 5, Moscow 105005, Russia
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28
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Sommer S, Probst T, Kraus E, Baudrit B, Town GE, Koch M. Cure monitoring of two-component epoxy adhesives by terahertz time-domain spectroscopy. POLYMER SCIENCE SERIES B 2016. [DOI: 10.1134/s1560090416060154] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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29
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Ge H, Jiang Y, Lian F, Zhang Y, Xia S. Quantitative determination of aflatoxin B1 concentration in acetonitrile by chemometric methods using terahertz spectroscopy. Food Chem 2016; 209:286-92. [DOI: 10.1016/j.foodchem.2016.04.070] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Revised: 03/27/2016] [Accepted: 04/18/2016] [Indexed: 10/21/2022]
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30
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Redo-Sanchez A, Heshmat B, Aghasi A, Naqvi S, Zhang M, Romberg J, Raskar R. Terahertz time-gated spectral imaging for content extraction through layered structures. Nat Commun 2016; 7:12665. [PMID: 27610926 PMCID: PMC5023963 DOI: 10.1038/ncomms12665] [Citation(s) in RCA: 103] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 07/20/2016] [Indexed: 12/04/2022] Open
Abstract
Spatial resolution, spectral contrast and occlusion are three major bottlenecks for non-invasive inspection of complex samples with current imaging technologies. We exploit the sub-picosecond time resolution along with spectral resolution provided by terahertz time-domain spectroscopy to computationally extract occluding content from layers whose thicknesses are wavelength comparable. The method uses the statistics of the reflected terahertz electric field at subwavelength gaps to lock into each layer position and then uses a time-gated spectral kurtosis to tune to highest spectral contrast of the content on that specific layer. To demonstrate, occluding textual content was successfully extracted from a packed stack of paper pages down to nine pages without human supervision. The method provides over an order of magnitude enhancement in the signal contrast and can impact inspection of structural defects in wooden objects, plastic components, composites, drugs and especially cultural artefacts with subwavelength or wavelength comparable layers.
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Affiliation(s)
- Albert Redo-Sanchez
- Department of Media arts and Sciences, MIT Media Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Barmak Heshmat
- Department of Media arts and Sciences, MIT Media Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Alireza Aghasi
- Department of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
| | - Salman Naqvi
- Department of Media arts and Sciences, MIT Media Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Mingjie Zhang
- Department of Media arts and Sciences, MIT Media Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Automation, Tsinghua University, Beijing 100084, China
| | - Justin Romberg
- Department of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
| | - Ramesh Raskar
- Department of Media arts and Sciences, MIT Media Lab, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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31
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Dolganova IN, Zaytsev KI, Metelkina AA, Yurchenko SO. The active-passive continuous-wave terahertz imaging system. ACTA ACUST UNITED AC 2016. [DOI: 10.1088/1742-6596/735/1/012075] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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32
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Schemmel P, Diederich G, Moore AJ. Direct stress optic coefficients for YTZP ceramic and PTFE at GHz frequencies. OPTICS EXPRESS 2016; 24:8110-8119. [PMID: 27137250 DOI: 10.1364/oe.24.008110] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report the first measurement of the direct stress optic coefficient for yttria-partially stabilized zirconia (YTZP) ceramic, using illumination between 260 and 380 GHz with applied stresses up to 27 MPa. YTZP exhibited a linear change in refractive index as a function of stress across the entire applied stress domain. A direct stress optic coefficient was also measured for polytetrafluoroethylene (PTFE). PTFE showed viscoelastic behavior at stress values above 4.5 MPa. These results open the way for quantitative sub-surface stress measurements in structural ceramics and ceramic coating systems at GHz and THz frequencies.
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33
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Tang HH, Liu PK. Terahertz far-field superresolution imaging through spoof surface plasmons illumination. OPTICS LETTERS 2015; 40:5822-5825. [PMID: 26670521 DOI: 10.1364/ol.40.005822] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The applications of terahertz (THz) imaging are always restricted by the low resolution. We introduce here a new way to realize far-field superresolution imaging at THz frequency. Assisted by a new spoof surface plasmons (SSP) probe illumination, the images of two subwavelength separated slits can be reconstructed by a single shot. Although only 0.06λ resolution is numerically demonstrated at 0.3 THz, the resolution potentially can be further enhanced by scaling down the size of the SSP probe. Deep subwavelength focusing is also achieved by the SSP probe. Our work may open a new avenue for SSP-based superresolution at longer wavelengths.
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34
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Rämer JM, von Freymann G. Terahertz waveform generation for S 21-parameter measurements using a fiber-coupled optical pulse shaper. OPTICS EXPRESS 2015; 23:30872-30877. [PMID: 26698720 DOI: 10.1364/oe.23.030872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A THz time-domain spectroscopy-based vector network analyzer for S21-parameter measurements is presented providing THz waveforms as input signal for waveguide-coupled devices under test. We integrate an optical pulse shaper into the emitter arm and fiber-couple the photoconductive antennas to allow for flexible usage. The pulse-shaping capabilities are demonstrated by realizing all 5 bit combinations of a 0.5 THz signal. Furthermore, we can set the center wavelength of the resulting THz spectrum. Finally, we apply the shaped THz waveforms to test the response of a low-noise amplifier.
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Dolganova IN, Zaytsev KI, Metelkina AA, Karasik VE, Yurchenko SO. A hybrid continuous-wave terahertz imaging system. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:113704. [PMID: 26628141 DOI: 10.1063/1.4935495] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A hybrid (active-passive mode) terahertz (THz) imaging system and an algorithm for imaging synthesis are proposed to enhance the THz image quality. The concept of image contrast is used to compare active and passive THz imaging. Combining the measurement of the self-emitted radiation of the object with the back-scattered source radiation measurement, it becomes possible to use the THz image to retrieve maximum information about the object. The experimental results confirm the advantages of hybrid THz imaging systems, which can be generalized for a wide range of applications in the material sciences, chemical physics, bio-systems, etc.
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Affiliation(s)
- Irina N Dolganova
- Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005, Russia
| | - Kirill I Zaytsev
- Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005, Russia
| | - Anna A Metelkina
- Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005, Russia
| | - Valeriy E Karasik
- Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005, Russia
| | - Stanislav O Yurchenko
- Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow 105005, Russia
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Zhang L, Wu T, Zhao J, Zhang C, Zhang XC. Bi-directional terahertz-to-infrared emission from metal-coated nanostructures upon femtosecond laser irradiation. OPTICS EXPRESS 2015; 23:25202-25208. [PMID: 26406717 DOI: 10.1364/oe.23.025202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report on the investigation of bi-directional terahertz-to-infrared (THz-to-IR) radiation from a metal film coated on a substrate with randomly ordered pore arrays by irradiation of femtosecond laser pulses. THz-to-IR radiation was observed both for front-side excitation (laser incident on the metal surface) and for rear-side excitation (laser incident on the substrate). In both cases, the radiation was observed both in the propagation direction of the laser beam and in the reverse direction. Considering these findings, we propose a thermal emission mechanism based on the production of surface plasmons, either delocalized (through phase-matched excitation) or localized (through surface roughness) at the air/metal and metal/substrate interfaces.
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Zhang L, Mu K, Zhao J, Wu T, Wang H, Zhang C, Zhang XC. Intense thermal terahertz-to-infrared emission from random metallic nanostructures under femtosecond laser irradiation. OPTICS EXPRESS 2015; 23:14211-14218. [PMID: 26072788 DOI: 10.1364/oe.23.014211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report intense (~10 mW), ultra-broadband (~150 THz wide), terahertz-to-infrared, Gaussian-wavefront emission from nanopore-structured metallic thin films under femtosecond laser pulse irradiation. The proposed underlying mechanism is thermal radiation. The nanostructures of the metal film are produced by random holes in the substrate. Under pulse-train femtosecond laser irradiation, we found dramatically enhanced optical absorption, with an absorptivity that was equal to as much as 95% of the metallic surface nanostructure, due to both an antireflection mechanism and dissipation of excited surface plasmon polaritons into the metal surface.
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Balbekin N, Kulya M, Rogov P, Petrov N. The Modeling Peculiarities of Diffractive Propagation of the Broadband Terahertz Two-dimensional Field. ACTA ACUST UNITED AC 2015. [DOI: 10.1016/j.phpro.2015.09.120] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Dietz RJB, Vieweg N, Puppe T, Zach A, Globisch B, Göbel T, Leisching P, Schell M. All fiber-coupled THz-TDS system with kHz measurement rate based on electronically controlled optical sampling. OPTICS LETTERS 2014; 39:6482-6485. [PMID: 25490499 DOI: 10.1364/ol.39.006482] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We demonstrate a completely fiber-coupled terahertz (THz) time-domain spectrometer (TDS) system based on electronically controlled optical sampling with two erbium-doped femtosecond fiber lasers at a central wavelength of 1560 nm. The system employs optimized InGaAs/InAlAs photoconductive antennas for THz generation and detection. With this system, we achieve measurement rates of up to 8 kHz and up to 180 ps scan range. We further achieve 2 THz spectral bandwidth and a dynamic range of 76 dB at only 500 ms measurement time.
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Bulgarevich DS, Watanabe M, Shiwa M, Niehues G, Nishizawa S, Tani M. A polarization-sensitive 4-contact detector for terahertz time-domain spectroscopy. OPTICS EXPRESS 2014; 22:10332-10340. [PMID: 24921735 DOI: 10.1364/oe.22.010332] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
A light polarization angle-sensitive photoconductive detector for terahertz time-domain spectroscopy is computer-modeled, microfabricated, and tested. The experimental results show good agreement with the linear angular response for an ideal detector. The detector's frequency, angular, and crosstalk responses are discussed in the context of theoretical and experimental considerations.
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Zaytsev KI, Fokina IN, Fedorov AK, Yurchenko SO. Sensing of phase transition in medium with terahertz pulsed spectroscopy. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/1742-6596/486/1/012024] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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42
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Yakovlev EV, Zaytsev KI, Fokina IN, Karasik VE, Yurchenko SO. Nondestructive testing of polymer composite materials using THz radiation. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/1742-6596/486/1/012008] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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43
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Dai J, Zhang XC. Terahertz wave generation from thin metal films excited by asymmetrical optical fields. OPTICS LETTERS 2014; 39:777-780. [PMID: 24562204 DOI: 10.1364/ol.39.000777] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We experimentally demonstrated terahertz (THz) wave emission from thin metal (gold) films excited by asymmetrical optical fields synthesized using an in-line phase compensator. By driving the electrons in thin metal films asymmetrically, THz wave emission is observed at normal incidence of two-color pump beams. Coherent control of THz wave emission from metal films suggests that a mechanism similar to that of the air-plasma THz source excited by two-color laser fields can be used to describe the generation processes.
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Theurer M, Göbel T, Stanze D, Troppenz U, Soares F, Grote N, Schell M. Photonic-integrated circuit for continuous-wave THz generation. OPTICS LETTERS 2013; 38:3724-3726. [PMID: 24081036 DOI: 10.1364/ol.38.003724] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We demonstrate a photonic-integrated circuit for continuous-wave (cw) terahertz (THz) generation. By comprising two lasers and an optical phase modulator on a single chip, the full control of the THz signal is enabled via a unique bidirectional operation technique. Integrated heaters allow for continuous tuning of the THz frequency over 570 GHz. Applied to a coherent cw THz photomixing system operated at 1.5 μm optical wavelength, we reach a signal-to-noise ratio of 44 dB at 1.25 THz, which is identical to the performance of a standard system based on discrete components.
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Li L, Song W, Wang Z, Wang S, He M, Han J, Cong L. Active modulation of refractive index by stress in the terahertz frequency range. APPLIED OPTICS 2013; 52:6364-6368. [PMID: 24085099 DOI: 10.1364/ao.52.006364] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 08/07/2013] [Indexed: 06/02/2023]
Abstract
Experimental tests are presented to investigate the stress effect on terahertz (THz) waves with a THz time-domain spectroscopy system. Through the Jones matrix method, an experimental principle is derived according to the experimental system. Experimental results indicate the linear relationship between a polytetrafluoroethylene refractive index and applied stress. The result can be applied to the active modulation of a refractive index or phase of a THz wave.
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Yim JH, Jeong H, Irfan M, Lee EH, Song JD, Jho YD. Directional terahertz emission from corrugated InAs structures. OPTICS EXPRESS 2013; 21:19709-19717. [PMID: 24105518 DOI: 10.1364/oe.21.019709] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The terahertz (THz) radiation from transient dipoles, formed by distinct diffusion coefficients between oppositely charged carriers as often observed in low band gap semiconductors, propagates with an anisotropic amplitude distribution perpendicular to the dipole axis along the diffusive motion. By directionally adjusting the electronic diffusion, we conceptualize groove-patterned THz emitters based on (100) InAs thin films and demonstrate the unidirectional radiation. Line-of-sight emission along the surface-normal direction is greatly enhanced in a distributed asymmetric trapezoid with its period similar to the electronic diffusion length of InAs. This directional enhancement is in clear contrast to the constant emission amplitude along the lateral direction, regardless of pattern scale, which manifests the role of groove patterns as microscale reflectors in laterally corrugating the carrier density. In contrast to the rather limited nonlinearity in (100) plane, the azimuthal angle dependence of the THz field amplitude in corrugated samples shows a combined effect of diffusive transport and second-order nonlinearity, whose compositional contributions varies in different structures.
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Acharyya A, Banerjee JP. Prospects of IMPATT devices based on wide bandgap semiconductors as potential terahertz sources. APPLIED NANOSCIENCE 2012. [DOI: 10.1007/s13204-012-0172-y] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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48
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Fiorino ST, Deibel JA, Grice PM, Novak MH, Spinoza J, Owens L, Ganti S. A technique to measure optical properties of brownout clouds for modeling terahertz propagation. APPLIED OPTICS 2012; 51:3605-3613. [PMID: 22695600 DOI: 10.1364/ao.51.003605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2012] [Accepted: 03/23/2012] [Indexed: 06/01/2023]
Abstract
Brownout, the loss of visibility caused by dust resultant of helicopter downwash, is a factor in the large majority of military helicopter accidents. As terahertz radiation readily propagates through the associated dust aerosols and is attenuated by atmospheric water vapor within short distances, it can provide low-profile imaging that improves effective pilot visibility. In order to model this application of terahertz imaging, it is necessary to determine the optical properties of obscurants at these frequencies. We present here a method of empirical calculation and experimental measurement of the complex refractive index of the obscuring aerosols. Results derived from terahertz time-domain spectral measurements are incorporated into the AFIT CDE Laser Environmental Effects Definition and Reference (LEEDR) software.
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Affiliation(s)
- Steven T Fiorino
- Center for Directed Energy, Air Force Institute of Technology, 2950 Hobson Way, Wright-Patterson Air Force Base, Ohio 45433-7765, USA.
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Wietzke S, Jansen C, Reuter M, Jung T, Kraft D, Chatterjee S, Fischer B, Koch M. Terahertz spectroscopy on polymers: A review of morphological studies. J Mol Struct 2011. [DOI: 10.1016/j.molstruc.2011.07.036] [Citation(s) in RCA: 160] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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50
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Scheller M, Dürrschmidt SF, Stecher M, Koch M. Terahertz quasi-time-domain spectroscopy imaging. APPLIED OPTICS 2011; 50:1884-8. [PMID: 21532669 DOI: 10.1364/ao.50.001884] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
We demonstrate terahertz (THz) imaging with a quasi-time-domain spectrometer. This type of THz system is inexpensive, compact, and relatively easy to set up. Beating the simultaneously emitted equidistant modes of a compact diode laser allows for analysis of samples at multiple frequencies with a single measurement. Thus, this technique merges the potential of terahertz time-domain spectrometers with the simplicity of continuous wave lasers. Multiple imaging applications and stability issues are discussed.
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Affiliation(s)
- Maik Scheller
- Fachbereich Physik, Philipps Universität Marburg, Renthof 5, 35032 Marburg, Germany. ‐marburg.de
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