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Charge and dielectric response to terahertz pulses in the charge-ordered phase of
摘要： We investigated the dielectric properties of the charge-ordered phase of α-(BEDT-TTF)2I3 using exact numerical calculations of an extended Hubbard model. The electronic contribution to the electric polarization (electronic polarization) ˉP of the charge-ordered ground state is obtained by directly calculating the current when transfer integrals were changed adiabatically from symmetric integrals to integrals for the charge-ordered phase without inversion symmetry. The angle of ˉP from the positive b axis is 36?, which is consistent with experimental results and previous theoretical results based on density-functional theory. Furthermore, we numerically calculated the dynamics induced by terahertz- (THz-) pulse excitation. Both the THz-pulse-induced variation of the electronic polarization magnitude and that of the charge disproportionation that shows the charge-order amplitude are largest when the electric field of the THz pulse and ˉP have almost the same direction. This originates from the charge transfer through bond b2(cid:3) being dominant in both the adiabatic flow of the current and the THz-pulse excitation. These results reproduce important features of the experimental results of THz-pulse-induced dynamics.
关键词： charge-ordered phase,ferroelectricity,extended Hubbard model,THz-pulse excitation,electronic polarization
更新于2025-09-23 15:21:01
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Spectral efficiency optimization for intelligent reflecting surface aided multi-input multi-output terahertz system
摘要： Intelligent reflecting surface (IRS) is considered as a promising application in terahertz (THz) communications since it is able to enhance the THz communication with no additional power consumptions. In this letter, we consider a downlink multi-input multi-output system, where a base station (BS) communicates to a user with the aid of the IRS. Our goal is to optimize the spectral efficiency by designing discrete phase-shifts at the IRS and the precoder at the BS, which is an intractable nonconvex optimization problem. To solve it, we approximate the problem into another form where we maximize the sum of path gains by designing the phase-shifts of the IRS, and we propose a cross-entropy based algorithm to search the optimal IRS phase-shifts matrix. After that, we use the classical singular value decomposition and water-filling solution to design the optimal precoder.
关键词： terahertz (THz) communication,intelligent reflecting surface (IRS),spectral efficiency
更新于2025-09-23 15:21:01
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Low-Terahertz Transparent Graphene-Based Absorber
摘要： A new, transparent, metal-free absorber, based on the use of multilayer graphene/dielectric laminates (GLs), is proposed for applications in the low-terahertz frequency range. The designed absorber has a total thickness of around 70 μm and consists of a front matching dielectric layer followed by a GL, a dielectric spacer and a back GL. The laminates are periodic structures constituted of graphene sheets separated by 50-nm-thick polyethylene terephthalate (PET) interlayers, while the matching layer and the spacer are one-quarter-wavelength thick and made of PET. The GLs are modeled as homogeneous-equivalent single layers (ESLs) characterized by their sheet resistances Rs. An innovative analytical method is proposed in order to select Rs values optimizing the electromagnetic wave absorption either in low-gigahertz or low-terahertz frequency range. The frequency spectra of the absorption, reflection and transmission coefficients are computed in the range up to 4 THz by using different values of Rs. Then, realistic Rs values of chemically doped graphene monolayers over PET substrates are considered. The designed absorbers are characterized by an absorption coefficient with a peak value of about 0.8 at the first resonant frequency of 1.1 THz, and a 1.4 THz bandwidth centered at 1.5 THz with reflection coefficient below - 10 dB. Moreover, the optical transmittance of the proposed absorbers are computed by means of the optical matrix theory and it is found to be greater than 86% in all the visible ranges.
关键词： absorption,reflection and transmission performance up to 4 THz,low-terahertz transparent absorber,transmission line approach,graphene-polyethylene terephthalate laminate,laminate effective medium model,optical transmittance in the visible range
更新于2025-09-23 15:21:01
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Engineering of high quality factor THz metasurfaces by femtosecond laser ablation
摘要： We report on the realization of high Q metasurfaces operating in the THz frequency range by femtosecond laser ablation applied to a nanometric metallic layer over a silicon substrate. Two different fabrication methods are used to develop periodic patterns whose basic elements are in form of an array of through-holes or metallic islands. The response of the resulting structures is characterized using a time-domain spectrometer in the frequency range 0.3–1.5 THz. The experimental findings are compared with the predictions of full wave electromagnetic simulations. The fairly good agreement between simulation predictions and experimental findings evidences that the proposed approach can offer a facile way to the elaboration of THz metasurfaces.
关键词： Femtosecond laser ablation,THz,High quality factor,Metasurfaces
更新于2025-09-23 15:21:01
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A novel star shape photonic crystal fiber for low loss terahertz pulse propagation
摘要： An extremely low loss circle-based star shape photonic crystal fiber (CS-PCF) has been proposed for terahertz (THz) spectrum. A dielectric material TOPAS has been used for constructing the proposed model. Some important parameters for the proposed waveguide have been investigated a wide THz spectrum ranging from 0.5 to 2.50 THz. The simulation result exhibits an extremely-low material loss of 0.01607 cm-1 and a large effective area of 1.386 × 106 μm2 at 1.0 THz frequency with 55% core porosity. In addition, the proposed structure establishes comparatively higher core power fraction maintaining lower scattering loss about 1.235 × 10-15 dB/cm and 91.97% of bulk absorption material loss at the same operating frequency. From the above results, it is anticipated that proposed CS-PCF model of the THz waveguide will make the conventional communication very effective over the current designs.
关键词： Effective material Loss,Scattering Loss,Power Fraction,THz Application,Single Mode Fiber
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) - Lasing and saturation of CAEP THz FEL facility
摘要： A high power THz free electron laser (FEL) facility is under construction at China Academy of Engineering Physics (CAEP) since October, 2011. The radiation frequency of the FEL facility is designed in range of 1~3 THz and the average output power is about 10 W. First lasing of the CAEP THz FEL (CTFEL) facility was obtained in August 29, 2017. Then the saturation operation is observed in September 20, 2017. The radiation frequency is sequentially as 1.99THz, 2.41THz and 2.92THz. And the average output power is larger than 10 W; the largest output power is about 20W. The peak power of micro-pulse is larger than 0.5MW. The optical resonator of CTFEL is optimized to ensure wavelength tunable in a wide range and high power operation. In this paper, the main designed and present status of the facility is given.
关键词： free electron laser,lasing,CAEP,saturation,FEL,THz
更新于2025-09-23 15:21:01
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The upGREAT dual frequency heterodyne arrays for SOFIA
摘要： We present the performance of the upGREAT heterodyne array receivers on the SOFIA telescope after several years of operations. This instrument is a multi-pixel high resolution (R&107) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receivers use 7-pixel subarrays configured in a hexagonal layout around a central pixel. The low frequency array receiver (LFA) has 2x7 pixels (dual polarization), and presently covers the 1.83-2.06 THz frequency range, which allows to observe the [CII] and [OI] lines at 158μm and 145μm wavelengths. The high frequency array (HFA) covers the [OI] line at 63μm and is equipped with one polarization at the moment (7 pixels, which can be upgraded in the near future with a second polarization array). The 4.7 THz array has successfully flown using two separate quantum-cascade laser local oscillators from two different groups. NASA completed the development, integration and testing of a dual-channel closed-cycle cryocooler system, with two independently operable He compressors, aboard SOFIA in early 2017 and since then, both arrays can be operated in parallel using a frequency separating dichroic mirror. This configuration is now the prime GREAT configuration and has been added to SOFIA’s instrument suite since observing cycle 6.
关键词： SOFIA (GREAT),high resolution spectroscopy,THz astronomy,airborne
更新于2025-09-23 15:21:01
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Influence of Reactive Ion Etching on THz Transmission and Reflection Properties of NiCr Film Deposited on a Dielectric Substrate
摘要： Enhanced terahertz (THz) absorption of NiCr film deposited on a dielectric substrate has been proven by applying a reactive ion etching (RIE) treatment to the dielectric film. Nano-scale nickel-chromium (NiCr) thin films are deposited on RIE treated silicon dioxide (SiO2) dielectric substrates to study the transmission and reflection characteristics. Experimental results suggest that both transmission and reflection of NiCr film are weakened by the RIE treatment. The most significant decrease of transmission is observed in (1 ~ 4) THz while that of reflection occurs in (1.7 ~ 2.5) THz band. The decrease of both transmission and reflection is more significant for NiCr film with higher thickness. The RIE treatment, which induces a roughened surface of SiO2 substrate and increases the effective surface area of NiCr film, enhances the absorption and weakens the transmission and reflection of THz radiation.
关键词： NiCr thin film,transmission,RIE,THz,reflection,absorption
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) - Turning THz Communications into Reality: Status on Technology, Standardization and Regulation
摘要： Already a couple of years ago THz communications have not only become an attractive new research area on channel modeling but also triggered a couple of projects heading to develop appropriate technological solutions to enable the set-up of hardware demonstrators. Also discussions and activities in standardization and regulation already took off. In October 2017, IEEE published Std. IEEE 802.15.3d-2017 the worldwide first wireless communications standard operating in the 300 GHz frequency band. In parallel to the standardization process activities at the ITU-R level targeting on the provision of an appropriate regulatory framework at the World Radio Conference 2019 (WRC-2019) via a dedicated agenda item have taken off. This paper provides a brief overview on the current status of the development of THz Communication systems focusing on recent results on advanced channel characterization at 300 GHz, hardware demonstrators operating in this frequency range, the past and current activities at IEEE 802 and the WRC 2019 preparations.
关键词： channel modeling,standardization,THz communications,regulation,hardware demonstrators
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) - Tuneable Optical Frequency Comb Generator for THz Spectroscopy
摘要： We present an optical frequency comb generator with a record span of 3.8 THz suitable for high resolution THz spectroscopy, based on a single phase modulator system. The line spacing, exactly referenced to a microwave synthesizer, can be continuously tuned from 17.5 GHz to 20 GHz overcoming the limitation otherwise imposed by the free spectral range of the fibre loop, making the system capable of generating a continuously tuneable electrical signal from 122.5 GHz to >2.7 THz. The system noise has been measured up to a record frequency of 300 GHz, and shown to be limited by the multiplied phase noise of the reference synthesizer.
关键词： THz spectroscopy,tuneable,heterodyne signal,phase modulator,optical frequency comb generator
更新于2025-09-23 15:21:01