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Articoli di riviste sul tema "THZ FREQUENCY"

Autore: Grafiati

Pubblicato: 11 settembre 2023

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1

Gu, Qun Jane, Zhiwei Xu, Heng-Yu Jian, Bo Pan, Xiaojing Xu, Mau-Chung Frank Chang, Wei Liu e Harold Fetterman. "CMOS THz Generator With Frequency Selective Negative Resistance Tank". IEEE Transactions on Terahertz Science and Technology 2, n. 2 (marzo 2012): 193–202. http://dx.doi.org/10.1109/tthz.2011.2181922.

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2

Kleine-Ostmann, Thomas, Christian Jastrow, Kai Baaske, Bernd Heinen, Michael Schwerdtfeger, Uwe Karst, Henning Hintzsche, Helga Stopper, Martin Koch e Thorsten Schrader. "Field Exposure and Dosimetry in the THz Frequency Range". IEEE Transactions on Terahertz Science and Technology 4, n. 1 (gennaio 2014): 12–25. http://dx.doi.org/10.1109/tthz.2013.2293115.

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3

Yablokov, Anton A., Vladimir A. Anfertev, Leonid S. Revin, Vladimir Yu Balakirev, Mariya B. Chernyaeva, Elena G. Domracheva, Aleksey V. Illyuk, Sergey I. Pripolzin e Vladimir L. Vaks. "Two-Frequency THz Spectroscopy for Analytical and Dynamical Research". IEEE Transactions on Terahertz Science and Technology 5, n. 5 (settembre 2015): 845–51. http://dx.doi.org/10.1109/tthz.2015.2463114.

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4

Consolino, Luigi, Malik Nafa, Michele De Regis, Francesco Cappelli, Saverio Bartalini, Akio Ito, Masahiro Hitaka et al. "Direct Observation of Terahertz Frequency Comb Generation in Difference-Frequency Quantum Cascade Lasers". Applied Sciences 11, n. 4 (4 febbraio 2021): 1416. http://dx.doi.org/10.3390/app11041416.

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Terahertz quantum cascade laser sources based on intra-cavity difference frequency generation from mid-IR devices are an important asset for applications in rotational molecular spectroscopy and sensing, being the only electrically pumped device able to operate in the 0.6–6 THz range without the need of bulky and expensive liquid helium cooling. Here we present comb operation obtained by intra-cavity mixing of a distributed feedback laser at λ = 6.5 μm and a Fabry–Pérot device at around λ = 6.9 μm. The resulting ultra-broadband THz emission extends from 1.8 to 3.3 THz, with a total output power of 8 μW at 78 K. The THz emission has been characterized by multi-heterodyne detection with a primary frequency standard referenced THz comb, obtained by optical rectification of near infrared pulses. The down-converted beatnotes, simultaneously acquired, confirm an equally spaced THz emission down to 1 MHz accuracy. In the future, this setup can be used for Fourier transform based evaluation of the phase relation among the emitted THz modes, paving the way to room-temperature, compact, and field-deployable metrological grade THz frequency combs.

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5

Jarzab, Przemysław P., Kacper Nowak e Edward F. Plinski. "Frequency aspects of the THz photomixer". Optics Communications 285, n. 6 (marzo 2012): 1308–13. http://dx.doi.org/10.1016/j.optcom.2011.09.053.

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6

Zhang, Xiao Yu, Zhong Xin Zheng, Xin Xing Li, Ren Bing Tan, Zhi Peng Zhang, Yu Zhou, Jian Dong Sun, Bao Shun Zhang e Hua Qin. "Terahertz Filter Based on Frequency Selective Surfaces". Advanced Materials Research 571 (settembre 2012): 362–66. http://dx.doi.org/10.4028/www.scientific.net/amr.571.362.

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Terahertz filters based on the frequency selective surfaces (FSS) structure have been modeled and fabricated on the sapphire substrate. The terahertz (THz) transmission properties are investigated using a THz time-domain spectroscopy (THz-TDS) system. The designed two FSS-based THz filters exhibit the THz electromagnetic wave transmission and reflection characteristics, respectively, showing about 70% change of THz transmission at the frequency of 1.3 THz. It is suggested that the THz filtering effect results from the resonance behavior between THz plane-wave and resonant elements of designed metallic FSS structures. The agreement between experiments and simulations indicate that the designed THz filter show a great potential application for high-speed THz modulator.

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7

Yashchyshyn, Yevhen, e Konrad Godziszewski. "A New Method for Dielectric Characterization in Sub-THz Frequency Range". IEEE Transactions on Terahertz Science and Technology 8, n. 1 (gennaio 2018): 19–26. http://dx.doi.org/10.1109/tthz.2017.2771309.

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8

Dickie, Raymond, Robert Cahill, Vincent Fusco, Harold S. Gamble e Neil Mitchell. "THz Frequency Selective Surface Filters for Earth Observation Remote Sensing Instruments". IEEE Transactions on Terahertz Science and Technology 1, n. 2 (novembre 2011): 450–61. http://dx.doi.org/10.1109/tthz.2011.2129470.

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9

Liu, Weilin, Jiejun Zhang, Maxime Rioux, Jeff Viens, Younes Messaddeq e Jianping Yao. "Frequency Tunable Continuous THz Wave Generation in a Periodically Poled Fiber". IEEE Transactions on Terahertz Science and Technology 5, n. 3 (maggio 2015): 470–77. http://dx.doi.org/10.1109/tthz.2015.2412381.

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10

Nazarov, Maxim, O. P. Cherkasova e A. P. Shkurinov. "Spectroscopy of solutions in the low frequency extended THz frequency range". EPJ Web of Conferences 195 (2018): 10008. http://dx.doi.org/10.1051/epjconf/201819510008.

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11

Durand, E., T. Saitoh, M. Kourogi e M. Ohtsu. "0.4-THz frequency offset locking between two optical frequency combs". IEEE Photonics Technology Letters 8, n. 1 (gennaio 1996): 163–65. http://dx.doi.org/10.1109/68.475813.

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12

Xia Zuxue, 夏祖学, 刘发林 Liu Falin, 邓. 琥. Deng Hu, 陈俊学 Chen Junxue e 刘泉澄 Liu Quancheng. "Frequency adjustable THz microstructured photoconductive antennas". Infrared and Laser Engineering 47, n. 5 (2018): 520002. http://dx.doi.org/10.3788/irla201847.0520002.

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13

Yin, H., L. Zhang, Y. Yin, J. Zhao, G. Shu, W. He, A. W. Cross e A. D. R. Phelps. "Pseudospark excited sub-THz frequency sources". EPJ Web of Conferences 149 (2017): 05015. http://dx.doi.org/10.1051/epjconf/201714905015.

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14

Trofimov, Vyacheslav A., Nan-Nan Wang, Jing-Hui Qiu e Svetlana A. Varentsova. "Spurious Absorption Frequency Appearance Due to Frequency Conversion Processes in Pulsed THz TDS Problems". Sensors 20, n. 7 (27 marzo 2020): 1859. http://dx.doi.org/10.3390/s20071859.

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The appearance of the spurious absorption frequencies caused by the frequency conversion process at the broadband THz pulse propagation in a medium is theoretically and experimentally discussed. The spurious absorption frequencies appear due to both the frequency doubling and generation of waves with sum or difference frequency. Such generation might occur because of the nonlinear response of a medium or its non-instantaneous response. This phenomenon is confirmed by the results of a few physical experiments provided with the THz CW signals and broadband THz pulses that are transmitted through the ordinary or dangerous substances. A high correlation between the time-dependent spectral intensities for the basic frequency and generated frequencies is demonstrated while using the computer simulation results. This feature of the frequency conversion might be used for the detection and identification of a substance.

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15

Xie Jing, 谢静, 谭佐军 Tan Zuojun, 陈阳 Chen Yang, 石舒宁 Shi Shuning e 陈璐 Chen Lu. "THz time-frequency analysis with Hilbert-Huang transform". High Power Laser and Particle Beams 26, n. 7 (2014): 73103. http://dx.doi.org/10.3788/hplpb20142607.73103.

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16

WOOLARD, DWIGHT, PEIJI ZHAO, CHRISTOPHER RUTHERGLEN, ZHEN YU, PETER BURKE, STEVEN BRUECK e ANDREAS STINTZ. "NANOSCALE IMAGING TECHNOLOGY FOR THz-FREQUENCY TRANSMISSION MICROSCOPY". International Journal of High Speed Electronics and Systems 18, n. 01 (marzo 2008): 205–22. http://dx.doi.org/10.1142/s012915640800528x.

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A novel nanoscale-engineering methodology is presented that has potential for the first-time development of a microscope-system capable of collecting terahertz (THz) frequency spectroscopic signatures from microscopic biological (bio) structures. This unique THz transmission microscopy approach is motivated by prior studies on bio-materials and bio-agents (e.g., DNA, RNA and bacterial spores) that have produced spectral features within the THz frequency regime (i.e., ~ 300 GHz to 1000 GHz) that appear to be representative of the internal structure and characteristics of the constituent bio-molecules. The suggested THz transmission microscopy is a fundamentally new technological approach that seeks to avoid the limitations that exist in traditional experiments (i.e., that must average over large numbers of microscopic molecules) by prescribing a viable technique whereby the THz frequency signatures may be collected from individual bio-molecules and/or microscopic biological constructs. Specifically, it is possible to envision the development of a “nanoscale imaging array” that possesses the characteristics necessary (e.g., sub-wavelength resolution) for successfully performing “THz-frequency microscopy.”

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17

Indrisiunas, Simonas, Evaldas Svirplys, Heiko Richter, Andrzej Urbanowicz, Gediminas Raciukaitis, Till Hagelschuer, Heinz-Wilhelm Hubers e Irmantas Kasalynas. "Laser-Ablated Silicon in the Frequency Range From 0.1 to 4.7 THz". IEEE Transactions on Terahertz Science and Technology 9, n. 6 (novembre 2019): 581–86. http://dx.doi.org/10.1109/tthz.2019.2939554.

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18

Li, Xiang, Xiaoming Liu, Yasir Alfadhl, Kevin Ronald, Wenlong He, Adrian Cross e Xiaodong Chen. "A Dual-Frequency Quasi-Optical Output System for a THz Gyro-Multiplier". IEEE Transactions on Terahertz Science and Technology 6, n. 5 (settembre 2016): 674–81. http://dx.doi.org/10.1109/tthz.2016.2581982.

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19

Udomariyasap, Pongputhai, Suthichai Noppanakeepong e Nithiroth Pornsuwancharoen. "High Frequency Generation Based-On Nonlinear Micro Ring Resonator for Frequency Band Enhancement". Advanced Materials Research 979 (giugno 2014): 508–11. http://dx.doi.org/10.4028/www.scientific.net/amr.979.508.

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Propose the simulation of THz carrier frequencies using the small device and a Gaussian beam propagating within the device system. We found that the generated output power with the high frequency can be achieved. This consisted of a serial nonlinear micro ring resonator system for generating pulse and signal filter by Add/Drop filter, a technology optical communication by the micro ring resonator which generates the THz frequency multiple, whereas channel capacity in term of multi frequency bands can be provided by optical Add/Drop multiplexing. The increase in the number of channel capacity can be obtained by the increase in frequency density, while the security was introduced by the specific frequency filter, which was operated by the central operator. The optical micro ring resonators for THz frequency generation and enhancement are reviewed. The advantage of proposed system can be implemented by using the simultaneous optical communication system.

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20

Puc, Uroš, Andreja Abina, Anton Jeglič, Aleksander Zidanšek, Irmantas Kašalynas, Rimvydas Venckevičius e Gintaras Valušis. "Spectroscopic Analysis of Melatonin in the Terahertz Frequency Range". Sensors 18, n. 12 (23 novembre 2018): 4098. http://dx.doi.org/10.3390/s18124098.

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There is a need for fast and reliable quality and authenticity control tools of pharmaceutical ingredients. Among others, hormone containing drugs and foods are subject to scrutiny. In this study, terahertz (THz) spectroscopy and THz imaging are applied for the first time to analyze melatonin and its pharmaceutical product Circadin. Melatonin is a hormone found naturally in the human body, which is responsible for the regulation of sleep-wake cycles. In the THz frequency region between 1.5 THz and 4.5 THz, characteristic melatonin spectral features at 3.21 THz, and a weaker one at 4.20 THz, are observed allowing for a quantitative analysis within the final products. Spectroscopic THz imaging of different concentrations of Circadin and melatonin as an active pharmaceutical ingredient in prepared pellets is also performed, which permits spatial recognition of these different substances. These results indicate that THz spectroscopy and imaging can be an indispensable tool, complementing Raman and Fourier transform infrared spectroscopies, in order to provide quality control of dietary supplements and other pharmaceutical products.

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21

Saha, Bishwadeep, Sebastien Fregonese, Anjan Chakravorty, Soumya Ranjan Panda e Thomas Zimmer. "Sub-THz and THz SiGe HBT Electrical Compact Modeling". Electronics 10, n. 12 (10 giugno 2021): 1397. http://dx.doi.org/10.3390/electronics10121397.

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From the perspectives of characterized data, calibrated TCAD simulations and compact modeling, we present a deeper investigation of the very high frequency behavior of state-of-the-art sub-THz silicon germanium heterojunction bipolar transistors (SiGe HBTs) fabricated with 55-nm BiCMOS process technology from STMicroelectronics. The TCAD simulation platform is appropriately calibrated with the measurements in order to aid the extraction of a few selected high-frequency (HF) parameters of the state-of-the-art compact model HICUM, which are otherwise difficult to extract from traditionally prepared test-structures. Physics-based strategies of extracting the HF parameters are elaborately presented followed by a sensitivity study to see the effects of the variations of HF parameters on certain frequency-dependent characteristics until 500 GHz. Finally, the deployed HICUM model is evaluated against the measured s-parameters of the investigated SiGe HBT until 500 GHz.

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22

Shipilo, Daniil E., Nikolay A. Panov, Irina A. Nikolaeva, Alexander A. Ushakov, Pavel A. Chizhov, Kseniia A. Mamaeva, Vladimir V. Bukin, Sergey V. Garnov e Olga G. Kosareva. "Low-Frequency Content of THz Emission from Two-Color Femtosecond Filament". Photonics 9, n. 1 (29 dicembre 2021): 17. http://dx.doi.org/10.3390/photonics9010017.

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We experimentally investigate the low-frequency (below 1 THz) spectral content of broadband terahertz (THz) emission from two-color femtosecond filament formed by the 2.7-mJ, 40-fs, 800+400-nm pulse focused into air. For incoherent detection, we screened the Golay cell by the bandpass filters and measured the THz angular distributions at the selected frequencies ν=0.5, 1, 2 and 3 THz. The measured distributions of THz fluence were integrated over the forward hemisphere taking into account the transmittance of the filters, thus providing the estimation of spectral power at the frequencies studied. The spectral power decreases monotonically with the frequency increasing from 0.5 to 3 THz, thus showing that the maximum of THz spectrum is attained at ν≤0.5 THz. The THz waveform measured by electro-optical sampling (EOS) based on ZnTe crystal and transformed into the spectral domain shows that there exists the local maximum of the THz spectral power at ν≈1 THz. This disagrees with monotonic decrease of THz spectral power obtained from the filter-based measurements. We have introduced the correction to the spectral power reconstructed from EOS measurements. This correction takes into account different focal spot size for different THz frequencies contained in the broadband electromagnetic pulse. The corrected EOS spectral power is in semi-quantitative agreement with the one measured by a set of filters.

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23

Zeng Bangze, 曾邦泽, 梁美彦 Liang Meiyan, 赵跃进 Zhao Yuejin e 张存林 Zhang Cunlin. "0.2 THz stepped frequency inverse synthetics aperture radar imaging". High Power Laser and Particle Beams 25, n. 6 (2013): 1601–4. http://dx.doi.org/10.3788/hplpb20132506.1601.

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24

Minamide, Hiroaki, e Hiromasa Ito. "Development of frequency-agile monochromatic THz-wave parametric oscillators". Review of Laser Engineering 35, Supplement (2007): 34–35. http://dx.doi.org/10.2184/lsj.35.34.

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25

LEI, Lei, Di-Wei LIU e Yang YAN. "Continuous frequency tunable 0.42 THz coaxial gyrotron". Journal of Infrared and Millimeter Waves 32, n. 6 (2013): 559. http://dx.doi.org/10.3724/sp.j.1010.2013.00559.

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26

Lu, Yalin, Weili Zhang e Min Qiu. "Metamaterials, Plasmonics, and THz Frequency Photonic Components". Active and Passive Electronic Components 2007 (2007): 1–2. http://dx.doi.org/10.1155/2007/80839.

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27

Bray, C., A. Cuisset, F. Hindle, JF Lampin e G. Mouret. "Frequency comb for THz metrology and spectroscopy". EPJ Web of Conferences 195 (2018): 02014. http://dx.doi.org/10.1051/epjconf/201819502014.

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28

Vitiello, Miriam Serena. "Bi-dimensional materials for THz frequency nanodevices". Photoniques, n. 101 (marzo 2020): 39–46. http://dx.doi.org/10.1051/photon/202010139.

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Abstract (sommario):

Although artificial semiconductor heterostructures have long been the core material system for the generation, detection and manipulation of carriers, at TeraHertz (THz) frequencies, the discovery of graphene and the related intriguing abilities have triggered an unprecedented interest in inorganic two-dimensional (2D) materials, as black phosphorus and boron nitride, amongst many others. They offer a unique platform for developing efficient devices, without the need of lattice matching, and with a variety of physical properties, that can be engineered from scratch, exploiting the material structures, the layer thickness or their inherent anisotropy.

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29

Li, Min, Shuai Yuan e Heping Zeng. "THz Frequency Modulation by Filamentary Plasma Grating". IEEE Journal of Selected Topics in Quantum Electronics 23, n. 4 (luglio 2017): 1–4. http://dx.doi.org/10.1109/jstqe.2017.2652063.

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30

Ni, Y. C., e C. O. Weiss. "Simple frequency measurement chain to 30 THz". Applied Physics B Photophysics and Laser Chemistry 50, n. 5 (maggio 1990): 381–83. http://dx.doi.org/10.1007/bf00325090.

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31

Liu, Jianjun, e Zhi Hong. "Mechanically tunable dual frequency THz metamaterial filter". Optics Communications 426 (novembre 2018): 598–601. http://dx.doi.org/10.1016/j.optcom.2018.06.019.

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32

Montofre, Daniel Arturo, Rocio Molina, Andrey Khudchenko, Ronald Hesper, Andrey M. Baryshev, Nicolas Reyes e Fausto Patricio Mena. "High-Performance Smooth-Walled Horn Antennas for THz Frequency Range: Design and Evaluation". IEEE Transactions on Terahertz Science and Technology 9, n. 6 (novembre 2019): 587–97. http://dx.doi.org/10.1109/tthz.2019.2938985.

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33

Arzi, Khaled, Safumi Suzuki, Andreas Rennings, Daniel Erni, Nils Weimann, Masahiro Asada e Werner Prost. "Subharmonic Injection Locking for Phase and Frequency Control of RTD-Based THz Oscillator". IEEE Transactions on Terahertz Science and Technology 10, n. 2 (marzo 2020): 221–24. http://dx.doi.org/10.1109/tthz.2019.2959411.

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34

Cazzoli, Gabriele, Cristina Puzzarini, Giovanni Buffa e Ottavio Tarrini. "Pressure-broadening in the THz frequency region: The 1.113 THz line of water". Journal of Quantitative Spectroscopy and Radiative Transfer 109, n. 9 (giugno 2008): 1563–74. http://dx.doi.org/10.1016/j.jqsrt.2007.11.003.

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35

Volkov, O. Y., I. N. Duzhikov, R. A. Khabibullin, A. N. Baranov e Y. Y. Divin. "Subterahertz difference-frequency generation in terahertz quantum cascade lasers". Applied Physics Letters 121, n. 26 (26 dicembre 2022): 263504. http://dx.doi.org/10.1063/5.0135562.

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We have detected subterahertz spectral lines in the emission of free-running GaAs/AlGaAs quantum cascade lasers (QCLs) operating around 3 THz. We have found that the power W( fd) of an individual sub-THz line at the frequency fd is directly proportional to a power product W( fi) × W( fk) of the corresponding pair of THz lines having the frequency difference fi − fk = fd. The established one-to-one correspondence of each sub-THz line to pair combinations of THz lines proves the nonlinear mechanism of difference-frequency generation (DFG) in the QCL active region. The conversion efficiencies W( fi − fk)/[ W( fi) × W( fk)] estimated from the experimental data are about 4 × 10−3 and 5 × 10−5 W−1 for the sub-THz lines found at 132 and 310 GHz, correspondingly. Considering nonlinear polarization of QCL active regions as the reason for DFG, we have evaluated the following values of the second-order nonlinear susceptibility χ(2)(132 GHz) ≅ 7 × 105 pm/V and χ(2)(310 GHz) ≅ 4 × 104 pm/V from the experimental data. The obtained results pave the way for the use of THz QCLs as sources of sub-THz radiation.

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36

Kourogi, M., B. Widiyatmoko e M. Ohtsu. "3.17-THz frequency-difference measurement between lasers using two optical frequency combs". IEEE Photonics Technology Letters 8, n. 4 (aprile 1996): 560–62. http://dx.doi.org/10.1109/68.491226.

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37

Fu, Shu-Fang, Sheng Zhou, Hong Liang e Xuan-Zhang Wang. "Phase-matched sum frequency generation of antiferromagnetic film in THz frequency field". Journal of Magnetism and Magnetic Materials 346 (novembre 2013): 178–85. http://dx.doi.org/10.1016/j.jmmm.2013.07.026.

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38

Torkhov, Nikolay, Valeriy Vertegel, Mikhail Tkachenko e Aleksandr Manko. "Optimization of the Planar Schottky Diode Structure in THz Range". Infocommunications and Radio Technologies 6, n. 2 (23 agosto 2023): 194–200. http://dx.doi.org/10.29039/2587-9936.2023.06.2.16.

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Optimization of the structure of a planar Schottky diode with a whisker and an air anode lead allowed to obtain 198 GHz bandwidth (fractional bandwidth of 16.5 %) at a central frequency of ~1200 GHz and reduce insertion losses of 3.4 dB at a noise temperature of ~3300 K.

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Honjo, Minoru, Koji Suizu, Masaki Yamaguchi e Tomofumi Ikari. "Distance Measurement of a Frequency-Shifted Sub-Terahertz Wave Source". Photonics 9, n. 3 (24 febbraio 2022): 128. http://dx.doi.org/10.3390/photonics9030128.

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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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Kontar, E. P., G. G. Motorina, N. L. S. Jeffrey, Y. T. Tsap, G. D. Fleishman e A. V. Stepanov. "Frequency rising sub-THz emission from solar flare ribbons". Astronomy & Astrophysics 620 (dicembre 2018): A95. http://dx.doi.org/10.1051/0004-6361/201834124.

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Observations of solar flares at sub-THz frequencies (millimetre and sub-millimetre wavelengths) over the last two decades often show a spectral component rising with frequency. Unlike a typical gyrosynchrotron spectrum decreasing with frequency or a weak thermal component from hot coronal plasma, the observations can demonstrate a high flux level (up to ∼104 solar flux units at 0.4 THz) and fast variability on sub-second timescales. Although, many models have been put forward to explain the puzzling observations, none of them has clear observational support. Here we propose a scenario to explain the intriguing sub-THz observations. We show that the model, based on free-free emission from the plasma of flare ribbons at temperatures 104 − 106 K, is consistent with all existing observations of frequency-rising sub-THz flare emission. The model provides a temperature diagnostic of the flaring chromosphere and suggests fast heating and cooling of the dense transition region plasma.

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41

Brekhov, Kirill, Vladislav Bilyk, Andrey Ovchinnikov, Oleg Chefonov, Vladimir Mukhortov e Elena Mishina. "Resonant Excitation of the Ferroelectric Soft Mode by a Narrow-Band THz Pulse". Nanomaterials 13, n. 13 (28 giugno 2023): 1961. http://dx.doi.org/10.3390/nano13131961.

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This study investigates the impact of narrow-band terahertz pulses on the ferroelectric order parameter in Ba0.8Sr0.2TiO3 films on various substrates. THz radiation in the range of 1–2 THz with the pulse width of about 0.15 THz was separated from a broadband pulse with the interference technique. The 375 nm thick BST film on a MgO (001) substrate exhibits enhanced THz-induced second harmonic generation when excited by THz pulses with a central frequency of 1.6 THz, due to the resonant excitation of the soft phonon mode. Conversely, the BST film on a Si (001) substrate shows no enhancement, due to its polycrystalline state. The 800 nm thick BST film on a MgO (111) substrate demonstrates the maximum of a second harmonic generation signal when excited by THz pulses at 1.8 THz, which is close to the soft mode frequency for the (111) orientation. Notably, the frequency spectrum of the BST/MgO (111) film reveals peaks at both the fundamental and doubled frequencies, and their intensities depend, respectively, linearly and quadratically on the THz pulse electric field strength.

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Yadav, Chandan, Marina Deng, Sebastien Fregonese, Marco Cabbia, Magali De Matos, Bernard Plano e Thomas Zimmer. "Importance and Requirement of Frequency Band Specific RF Probes EM Models in Sub-THz and THz Measurements up to 500 GHz". IEEE Transactions on Terahertz Science and Technology 10, n. 5 (settembre 2020): 558–63. http://dx.doi.org/10.1109/tthz.2020.3004517.

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43

Li, Yinwei, Li Ding, Qibin Zheng, Yiming Zhu e Jialian Sheng. "A Novel High-Frequency Vibration Error Estimation and Compensation Algorithm for THz-SAR Imaging Based on Local FrFT". Sensors 20, n. 9 (7 maggio 2020): 2669. http://dx.doi.org/10.3390/s20092669.

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Compared with microwave synthetic aperture radar (SAR), terahertz SAR (THz-SAR) is easier to achieve ultrahigh-resolution image due to its higher frequency and shorter wavelength. However, higher carrier frequency makes THz-SAR image quality very sensitive to high-frequency vibration error of motion platform. Therefore, this paper proposes a novel high-frequency vibration error estimation and compensation algorithm for THz-SAR imaging based on local fractional Fourier transform (LFrFT). Firstly, the high-frequency vibration error of the motion platform is modeled as a simple harmonic motion and THz-SAR echo signal received in each range pixel can be considered as a sinusoidal frequency modulation (SFM) signal. A novel algorithm for the parameter estimation of the SFM signal based on LFrFT is proposed. The instantaneous chirp rate of the SFM signal is estimated by determining the matched order of LFrFT in a sliding small-time window and the vibration acceleration is obtained. Hence, the vibration frequency can be estimated by the spectrum analysis of estimated vibration acceleration. With the estimated vibration acceleration and vibration frequency, the SFM signal is reconstructed. Then, the corresponding THz-SAR imaging algorithm is proposed to estimate and compensate the phase error caused by the high-frequency vibration error of the motion platform and realize high-frequency vibration error estimation and compensation for THz-SAR imaging. Finally, the effectiveness of the novel algorithm proposed in this paper is demonstrated by simulation results.

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44

Zhang, Jinnan, Shijie Tao, Xin Yan, Xia Zhang, Jinxuan Guo e Zhiqiang Wen. "Dual-Frequency Polarized Reconfigurable Terahertz Antenna Based on Graphene Metasurface and TOPAS". Micromachines 12, n. 9 (9 settembre 2021): 1088. http://dx.doi.org/10.3390/mi12091088.

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A hybrid dual-frequency polarized reconfigurable terahertz antenna is designed and studied. Graphene and TOPAS are employed as the polarization conversion metasurface and dielectric substrate, respectively, enabling tunable polarization conversion and circular polarization. TOPAS is a good substrate material for broadband THz components due to its low absorption. By adjusting the chemical potential of graphene between 0 eV and 0.5 eV, the polarization state in the band of 1 THz (0.76–1.02 THz) and 2.5 THz (2.43–2.6 THz) can be reconstructed. Thanks to the multilayer graphene structure and low absorption TOPAS, the graphene metasurface exhibits a broad bandwidth of 0.26 and 0.17 THz, respectively, in the band of 1 THz and 2.5 THz. The working state of the circularly polarized antenna and linearly polarized antenna can be switched in the bands around 1 THz (0.7–0.75 THz, 0.96–1.04 THz) and 2.5 THz (2.42–2.52 THz), respectively, without changing the physical geometry. Moreover, the graphene antenna, metasurface, and hybrid structure are tested, respectively, to verify that the components do not interfere with each other in performance. The hybrid antenna shows great potential in tunable terahertz devices and related applications.

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45

Hossain, I., M. Samsuzzaman, M. S. J. Singh, B. B. Bais e M. T. Islam. "Numerical investigation of polarization-insensitive multiband metamaterial for terahertz solar absorber". Digest Journal of Nanomaterials and Biostructures 16, n. 2 (2021): 593–600. http://dx.doi.org/10.15251/djnb.2021.162.593.

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This study presents a nanostructured multiband metamaterial absorber for the optical regime application. The proposed structure is exhibited 0° to 90° polarization insensitivity and up to 45° angular stability with more than 90% peak absorption in between 300 THz800 THz frequency range. Proposed MMA structure is acquired perfect absorption of 99.99% at 571THz, 99.50% at 488.26 THz, 99.32% at 598 THz frequency by adjusting geometrical parameters. Due to perfect impedance matching with plasmonic resonance characteristics, these structures achieved an average absorption of 95.30%, 91.96%, 97.25%, 97.65%, 91%,90%,90.23% in between (337.5 THz-346.5 THz), (471 THz-478 THz), (497.5 THz-505 THz), (519 THz-530.5 THz), 564.5 THz-577 THz), (604 THz-673 THz), (686 THz-708 THz), respectively. The near field pattern of proposed MMA is used to explain the absorption mechanism at resonance frequency point and the geometric parameters are explored and analyzed to demonstrate the performance of the proposed structure. Moreover, CST-HFSS interference is validated the simulation data with the help of the finite element method (FEM). Polarization insensitivity and wide angular stability in terahertz (THz) frequency regime make this structure suitable for the application of magnetic resonance imaging (MRI), color images, thermal imaging and solar cell applications like exploitation of solar energy.

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46

Aly, Arafa H., Walied Sabra e Hussein A. Elsayed. "Cutoff frequency in metamaterials photonic crystals within Terahertz frequencies". International Journal of Modern Physics B 31, n. 15 (14 marzo 2017): 1750123. http://dx.doi.org/10.1142/s0217979217501235.

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By employing the characteristics matrix method, we have investigated the transmission properties of one-dimensional dielectric–semiconductor metamaterial photonic crystals (PC) at Terahertz (THz) range theoretically. The numerical results show the appearance of cutoff frequency within THz range. Furthermore, the thicknesses of the constituents materials and the filling factor have a significant effect on the cutoff frequency. The proposed structure may be useful in many applications, particularly in THz frequency regions.

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47

Przewłoka, Aleksandra, Serguei Smirnov, Irina Nefedova, Aleksandra Krajewska, Igor S. Nefedov, Petr S. Demchenko, Dmitry V. Zykov et al. "Characterization of Silver Nanowire Layers in the Terahertz Frequency Range". Materials 14, n. 23 (2 dicembre 2021): 7399. http://dx.doi.org/10.3390/ma14237399.

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Thin layers of silver nanowires are commonly studied for transparent electronics. However, reports of their terahertz (THz) properties are scarce. Here, we present the electrical and optical properties of thin silver nanowire layers with increasing densities at THz frequencies. We demonstrate that the absorbance, transmittance and reflectance of the metal nanowire layers in the frequency range of 0.2 THz to 1.3 THz is non-monotonic and depends on the nanowire dimensions and filling factor. We also present and validate a theoretical approach describing well the experimental results and allowing the fitting of the THz response of the nanowire layers by a Drude–Smith model of conductivity. Our results pave the way toward the application of silver nanowires as a prospective material for transparent and conductive coatings, and printable antennas operating in the terahertz range—significant for future wireless communication devices.

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48

Criado, A. R., C. de Dios, E. Prior, G. H. Dohler, S. Preu, S. Malzer, H. Lu, A. C. Gossard e P. Acedo. "Continuous-Wave Sub-THz Photonic Generation With Ultra-Narrow Linewidth, Ultra-High Resolution, Full Frequency Range Coverage and High Long-Term Frequency Stability". IEEE Transactions on Terahertz Science and Technology 3, n. 4 (luglio 2013): 461–71. http://dx.doi.org/10.1109/tthz.2013.2260374.

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49

Ceraso, Arianna, Sen Mou, Andrea Rubano e Domenico Paparo. "Coherent THz Hyper-Raman: Spectroscopy and Application in THz Detection". Materials 12, n. 23 (23 novembre 2019): 3870. http://dx.doi.org/10.3390/ma12233870.

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Abstract (sommario):

Recently we have demonstrated a new nonlinear optical effect in the THz interval of frequencies. The latter is based on the use of femtosecond optical pulses and intense, sub-ps, broadband terahertz (THz) pulses to generate a THz-optical four- and five-wave mixing in the investigated material. The spectrum of the generated signal is resolved in time and wavelength and displays two pronounced frequency sidebands, Stokes and anti-Stokes, close to the optical second harmonic central frequency 2 ω L , where ω L is the optical central frequency of the fundamental beam, thus resembling the spectrum of standard hyper-Raman scattering, and hence we named this effect ‘THz hyper-Raman’—THYR. We applied this technique to several crystalline materials, including α-quartz and gallium selenide. In the first material, we find that the THYR technique brings spectroscopic information on a large variety of low-energy excitations that include polaritons and phonons far from the Γ-point, which are difficult to study with standard optical techniques. In the second example, we show that this new tool offers some advantages in detecting ultra-broadband THz pulses. In this paper we review these two recent results, showing the potentialities of this new THz technique.

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50

Trofimov, Vyacheslav A., Dmitry M. Kharitonov, Mikhail V. Fedotov e Yongqiang Yang. "Frequency Down-Conversion of Optical Pulse to the Far Infrared and THz Frequency Ranges Due to the Cascading Process in a Medium with a Quadratic Nonlinear Response". Applied Sciences 12, n. 8 (12 aprile 2022): 3891. http://dx.doi.org/10.3390/app12083891.

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Difference-frequency generation is a well-known method of obtaining IR and THz radiation. It has many practical applications, such as sensing, optical metrology, diagnostics, detection and identification of substances, etc. One of the generation methods is based on the three-wave interaction in a medium with second-order nonlinear susceptibility. In this study, we investigated a special case of the frequency down-conversion into IR and THz ranges of the frequencies: the frequencies of interacting waves were multiple. We analyzed theoretically two cases of three-wave interactions: amplification of the infrared (or THz) radiation (incident weak intensity of a wave at this frequency) and a wave generation with the difference-frequency (incident zero-value intensity at this frequency). The amplification efficiency could achieve 75% and the maximal frequency conversion efficiency is about 25%. The computer simulation results made for the femtosecond pulse interaction in a crystal with the wavelength 4, 10, and 24 μm demonstrates applicability of such a scheme for the frequency down-conversion. This scheme of the THz radiation generation is a perspective tool for its application in the screening system for the detection and identification of substances.

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