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Simulations of some physical parameters of homologous series of nBT and nCHBT at 0.3–20.0 THz
摘要： In this work, the terahertz (THz) absorption of homologous series of isothiocyanobiphenyls (nBT) and 4-(trans-4?-n-alkylcyclohexyl)isothiocyanato-benzene (nCHBT) are simulated by using the density functional theory (DFT) method. Numerical results show that absorption of the tested nematic liquid crystals (NLCs) varies up to 0.04 in the broad range of 0.3–20.0 THz and takes maximum value in the range of 9–14 THz. In addition, the values of molecular polarisabilities (αo, αe) increase with the increase in the number of carbon atoms in the alkyl chain, while refractive indices (no, ne) decreases. The calculated birefringence (Δn) values for nCHBT are approximately twice as large as the birefringence value for nBT. It is crucial to examine these series of nematic liquid crystals at THz frequencies due to the role of soft matter in various switchable THz components.
关键词： Numerical calculations,refractive index,terahertz radiation,birefringence,nematic liquid crystals
更新于2025-09-23 15:22:29
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The coherent THz Smith-Purcell radiation from a three-dimensional open holes array structure
摘要： Coherent Smith-Purcell radiation from multiple electron beam excitation in a three-dimensional open holes array structure has been proposed. The electron beam passes through the holes, which can be coupled with each other to enhance surface wave fields, so that the multiple electron beam injection can interact with the surface wave field efficiently. And the Smith-Purcell radiation will be enhanced due to an increasement in dipole oscillations occurring when the electrons pass through the holes. Therefore, a high beam-wave interaction efficiency is yielded and very strong coherent terahertz radiation can be generated. This multi-beam system is expected to provide a favorable way to excite the coherent Smith-Purcell radiation, which would be used to generate terahertz radiation.
关键词： terahertz radiation,open holes array structure,Smith-Purcell radiation,electron beam
更新于2025-09-23 15:21:01
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Terahertz Photoconductivity in Graphene in a Magnetic Field
摘要： The terahertz photoconductivity in epitaxial graphene grown on SiC substrates is investigated in a magnetic field. The magnetic-field dependence of the photoresponse signal amplitude is examined at different electron densities, bias currents, and terahertz radiation intensities. The experimental results are explained well by a photoconductivity mechanism based on the heating of electrons by terahertz radiation. A strong increase in the photoconductivity signal with increasing magnetic field caused by an increase in the relaxation time due to the suppression of electron-electron scattering is observed.
关键词： terahertz radiation,photoconductivity,magnetic field,graphene
更新于2025-09-23 15:21:01
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Self-focused amplitude modulated super Gaussian laser beam in plasma and THz radiation with high efficiency
摘要： Based on self- focusing of an amplitude modulated super Gaussian laser beam in preformed ripple density plasma, one scheme can be proposed for generating terahertz (THz) radiation at the modulation frequency when pondermotive nonlinearity is operative. The eikonal in paraxial ray approximation (PRA) along with higher order terms in the expansion of the dielectric function have been taken into account. Intensity variation in the direction transverse to the propagated laser causes a pondermotive force which generates transient transverse nonlinear current. At the modulation frequency, the mentioned current drives radiation in THz domain. Therefore, comparing to simple PRA, inclusion of terms with higher order enhances beam self-focusing, THz radiation field and, efficiency. In addition, the degree of the self-focusing is reduced in higher laser beam orders and has changed by the modulation index and the time. Here, by considering higher order paraxial ray approximation and optimizing laser beam and ripple density, plasma parameters are investigated and the efficiency of THz radiation reaches up to 6.5%. This method can be applied for the efficient types of THz radiation.
关键词： Efficiency,Self-focusing,Terahertz radiation,Super Gaussian beam,Amplitude modulated
更新于2025-09-23 15:21:01
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[IEEE 2018 11th UK-Europe-China Workshop on Millimeter Waves and Terahertz Technologies (UCMMT) - HangZhou, China (2018.9.5-2018.9.7)] 2018 11th UK-Europe-China Workshop on Millimeter Waves and Terahertz Technologies (UCMMT) - Dispersion Characteristics of Surface Plasmon Polaritons of Graphene Loaded Three Dimensional Dielectric Gratings
摘要： Graphene has been used widely in optical and electronic devices due to its extraordinary electromagnetic characteristics. Recent theories and experiments prove that (SPPS) and graphene support surface plasmon polariton transform it into Terahertz (THz) radiation. In this paper, a dispersion and electric amplitude equations of SPPS of graphene loaded on the three dimensional dielectric gratings excited by parallel moving electron beam are derived by solving the Maxwell’s equations. The numerical results show that the frequency of amplified electric amplitude are same as the frequency point where electron beam and dispersion curve meet, which demonstrate theoretical analysis are right. The influence of dielectric gratings width is considered. It is found that the cutoff frequency occurs and rises on the dispersion curve as the width narrowing. The working point frequency is also higher compared with infinite width dielectric gratings. The SPPS of graphene loaded the three dimensional dielectric gratings whose work point is under cutoff frequency can’t be excited, even though it can be tuned. The numerical results show the electric amplitude becomes greater with width increasing.
关键词： Terahertz Radiation,Graphene,Electron Beam,Dielectric Gratings,Surface Plasmon Polariton
更新于2025-09-23 15:21:01
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Vacuum Arc Plasma Heated by Sub-Terahertz Radiation as a Source of Extreme Ultraviolet Light
摘要： This paper presents the results of the ?rst experimental studies of the interaction of a powerful sub-terahertz radiation with expanding highly inhomogeneous plasma of vacuum arc discharge. The tantalum plasma of a vacuum arc discharge additionally heated by the focused sub-terahertz radiation of a gyrotron, the radiation power is up to 250 kW, and the wavelength is 1.2 mm. Characteristics of the light emission in the extreme ultraviolet range are presented.
关键词： gyrotron,vacuum arc plasma,Extreme ultraviolet light,sub-terahertz radiation
更新于2025-09-23 15:21:01
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - N ovoFEL as Source of Powerful Ultramonochromatic Tunable Terahertz Radiation
摘要： Laser nature of a continuous pulse-periodical radiation of the Novosibirsk free-electron laser (NovoFEL) appears in a good coherency of its pulses and very narrow synchronized longitudinal modes. Filtration of one of the modes by a system of three resonance Fabry-Perot interferometers allows to create laser source with monochromaticity which is sufficient for typical high-resolution THz spectroscopy (δf/f ≤ 5·10-8, δf ≤ 0.1 MHz). Features of the source compared to other alternative devices are a wide tuning range (1.5-3 THz) and much more high output power (up to 50-100 mW).
关键词： high-resolution spectroscopy,Fabry-Perot interferometers,monochromaticity,NovoFEL,terahertz radiation
更新于2025-09-23 15:21:01
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State-of-the-Art of Studies of the Effect of Terahertz Radiation on Living Biological Systems
摘要： The appearance of modern sources and detectors of terahertz radiation (1011–1013 Hz) stimulated the rapid development of practical applications for radiation in this frequency range. Therefore, the question of the safety of terahertz radiation for living objects was sharply raised. In this review, we present an analysis of research on this issue published from 2010 to the present. A brief description of the most significant works performed before 2010 is given. Particular attention is paid to the sources of terahertz radiation used in the studies and the results of experimental work on the study of possible bioeffects when such radiation is applied to both individual cell lines and microorganisms and animals generally.
关键词： cell lines,biological systems,bioeffects,safety,animals,terahertz radiation,microorganisms
更新于2025-09-23 15:21:01
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Arrays of Carbon Nanotubes in a Field of Continuous Laser Radiation
摘要： A numerical analysis of the phase-matching conditions during the incidence of one or two counterpropagating laser beams on an ordered array of single-walled carbon nanotubes (CNTs) is performed. The conditions for the generation of slow surface plasmon waves of the terahertz (THz) and far infrared range propagating along the nanotubes of the irradiated array are determined. It is shown that the plasmon frequency can be controlled by changing the angle of incidence of laser radiation on the structure under study. Thus, it is possible to fulfill the condition of longitudinal resonance, in which each array nanotube is a dipole antenna radiating at the plasmon frequency. In this case, the array forms a system of a large number of in-phase emitters, which allows increasing the efficiency of conversion of laser radiation into THz radiation in comparison with a single nanoantenna.
关键词： phase-matching conditions,terahertz radiation,carbon nanotubes,laser radiation,plasmon waves
更新于2025-09-23 15:19:57
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Generation of kinetic Alfv??n wave and whistler waves by parametric decay of high power laser in lasera??plasma interaction
摘要： In this paper, we report theoretical modeling for parametric decay instability of the high-intensity elliptically polarized laser beam [pump wave, (x0)]. A wave–wave interaction model is investigated, based on the decay of the high-intensity elliptically polarized laser (x0) into an oblique whistler wave (OWW, ex1T) and a kinetic Alfv(cid:2)en wave (KAW, ex2T). The importance of oblique whistler waves (OWWs, ex1T) and kinetic Alfv(cid:2)en waves (KAWs, ex2T) similar to solar wind spectra [Chatterjee et al., Nat. Commun. 8, 15970 (2017)] has been pointed out, as a means to understand the turbulent magnetic ?eld ampli?cation, implicating electron and ion dynamics [Chatterjee et al., Nat. Commun. 8, 15970 (2017); Tzeferacos et al., Nat. Commun. 9, 591 (2018); Meinecke et al., Proc. Natl. Acad. Sci. 112, 8211 (2015); Mondal et al., Proc. Natl. Acad. Sci. 109, 8011 (2012); Romagnani et al., Phys. Rev. Lett. 122, 025001 (2019); Perri et al., Phys. Rev. Lett. 109, 191101 (2012); and Adak et al., Phys. Rev. Lett. 114, 115001 (2015)]. In the nonlinear stage, the decay instability is expected to attain the turbulent state, via a cascade process or ?lamentation/modulation instability (oscillating two stream instability). Therefore, in the present paper, we have considered the ?rst part of this research, namely, the beating mechanism ex2 ? x0 (cid:2) x1T, induced due to the nonlinear interaction of elliptically polarized laser velocity and oblique whistler wave density perturbation. The nonlinear saturation will be conferred in future investigations. Besides turbulence, the relevance of the present work to terahertz radiation generation [Singh et al., Europhys. Lett. 104, 35002 (2013); Dewan et al., Phys. Plasmas 25, 103105 (2018); Singh et al., Phys. Plasmas 18, 022304 (2011); M. Singh and R. P. Sharma, Contrib. Plasma Phys. 53(7), 540–548 (2013); Adak et al., Phys. Rev. Lett. 114, 115001 (2015); G. Brodin and L. Sten?o, Contrib. Plasma Phys. 54, 623 (2014); L. Sten?o, Phys. Scr. T50, 15–19 (1994); Li et al., Phys. Rev. E 84, 036405 (2011); L. Sten?o, Phys. Scr. T107, 262 (2004); and R. Boyd, Nonlinear Optics, 3rd ed. (Elsevier, 2008), Chap. 2] and fast ignition laser fusion [Kumar et al., arXiv:1804.02200 (2018)] by ion heating has been emphasized. The coef?cients for the nonlinear coupling pertaining to this parametric decay process and the growth rate of the decay instability are investigated.
关键词： high-intensity elliptically polarized laser beam,terahertz radiation,oblique whistler wave,kinetic Alfv(cid:2)en wave,parametric decay instability,fast ignition laser fusion
更新于2025-09-23 15:19:57