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Beam steering characteristics of highly directive photoconductive dipole phased array antenna for terahertz imaging application
摘要： In this paper, the beam-steering characteristics of photoconductive dipole phased array antenna configuration at 1.95 THz is presented. The proposed array antenna configuration with frequency selective surface favourably improves its gain and directivity which is useful to upsurge the imaging capabilities to address the deliberations such as limited depth-of-field (DoF) and size-weight-and-power of the THz source for imaging applications. These are important considerations for applications like stand-off imaging and surveillance of moving targets where the high angular resolution as well as extended DoF are the important parameters for successful detection of concealed explosives. The projected planar profile and compact highly directive (2 × 2) small-gap photoconductive dipole phased array antenna can be castoff for the exposure of concealed explosives such as RDX, TNT, and HMX which illustrate their substantial spectral absorption fingerprints in terahertz (1.4–2.2 THz) regime of the spectrum. A simple method of beam-steering has been explored based on phase controlled optical excitation of highly directive small-gap photoconductive dipole array antenna. Further, the effects of uniform progressive phase shift on the beam-steering of uniform linear array (along x-axis) as well as planar array (x-axis and y-axis) is investigated.
关键词： Terahertz frequency,Uniform current distribution,Photoconductive dipole antenna,Phased array,Frequency selective surface
更新于2025-09-23 15:23:52
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Wideband electrically-controlled Vernier frequency tuneable terahertz quantum cascade laser
摘要： Frequency tuning in terahertz frequency quantum cascade lasers is challenging because of low thermal and current tuning coefficients. Moreover, photonic designs like Vernier selection based sampled gratings, used in telecom lasers to tune emission frequency, are unsuitable due to the long terahertz wavelengths and will require impractically long cavities (>15 mm). Here, we report the first wideband frequency tuning from a monolithic device exploiting Vernier selection rules using a coupled-cavity laser with a defect engineered photonic lattice. A precisely positioned defect lattice allows us to engineer the free spectral range and finesse of one of the cavities, similar to a sampled grating but using shorter cavity lengths (<4mm). A coupled-cavity was used to tune the emission frequency. We achieve frequency tuning over 209 GHz, including mode-hop-free continuous tuning of ~6–21 GHz across six frequency bands, controlled through Stark shift, cavity-pulling, localized Joule heating and thermal effects.
关键词： quantum cascade laser,Terahertz,frequency tuning
更新于2025-09-23 15:21:01
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PERFORMANCE PREDICTION OF BUNDLE DOUBLE-WALLED CARBON NANOTUBE-COMPOSITE MATERIALS FOR DIPOLE ANTENNAS AT TERAHERTZ FREQUENCY RANGE
摘要： In this paper, the double-walled carbon nanotube composite material (DWCNTs-composite) and bundle of DWCNT-composite material (CB-DWCNTs) for antenna applications at terahertz frequency range are presented and investigated. The mathematical modeling and analysis of DWCNTs-composite material is presented for the purpose of modelling and simulation approach. The bundle of DWCNTs-composite material is constructed and designed, based on this modeling approach. The DWCNT-composite material consists of double-walled carbon nanotube coated by a thin jacket of another di?erent material. The dependency of the electrical conductivity of B-DWCNTs-composite on di?erent parameters is presented and investigated. The performance evaluation of B-DWCNTs-composite and CB-DWCNTs materials are presented based on their electromagnetic properties. For this purpose, the dipole antennas of these composite materials are designed and implemented using CST (MWS), where the cross sections of B-DWCNTs-composite and CB-DWCNT materials are circular geometry. Furthermore, comparative studies are performed to show the dependency of size and frequency of the DWCNT-composite material. The results obtained from the DWCNTs-composite and CB-DWCNTs dipole antennas are presented based on S11 parameters, resonant frequency, gain, bandwidth, and e?ciency.
关键词： terahertz frequency,dipole antennas,electromagnetic properties,composite material,double-walled carbon nanotube
更新于2025-09-23 15:19:57
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Electromagnetic-field analysis of diagonal-feedhorn antennas for terahertz-frequency quantum-cascade laser integration
摘要： we present an electromagnetic-field analysis of a terahertz-frequency quantum-cascade (THz QCL) integrated with a mechanically micro-machined waveguide cavity and diagonal feedhorn. A hybrid finite-element/Fourier transform approach enables analysis of both the near-field and far-field regions and is shown to agree well with experimental observations. The far-field antenna patterns show enhancement of the beam profile when compared with an unmounted QCL, in terms of beam divergence and side-lobe suppression ratio. Furthermore, we demonstrate integration of the QCL with dual diagonal feedhorns, enabling simultaneous access to both facets of the QCL, underpinning future integration with a satellite-based receiver and frequency-stabilization subsystem.
关键词： terahertz-frequency quantum-cascade laser,waveguide cavity,beam profile enhancement,electromagnetic-field analysis,diagonal feedhorn
更新于2025-09-16 10:30:52
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Excitation of Low-Frequency Surface Modes in the Plasma Layer Under the Action of Two-Frequency Laser Radiation
摘要： We construct the theory of generation of low-frequency surface eigenmodes in a rare?ed plasma layer under the action of two-frequency laser radiation. We show that a signi?cant increase in the energy of the plasma-layer low-frequency eigenmode occurs under resonance conditions, where the frequency of the mode coincides with the di?erence in laser frequencies. We establish that under the resonance conditions the energy ?ux density carried by the low-frequency eigenmode can be comparable to the laser-radiation intensity.
关键词： plasma layer,terahertz frequency range,two-frequency laser radiation,low-frequency surface eigenmode
更新于2025-09-12 10:27:22
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Theoretical and experimental studies of highly selective planar two-dimensional Bragg structures based on dielectric waveguides in the terahertz frequency range
摘要： Based on theoretical approach and three-dimensional modeling using the CST Microwave Studio code, planar dielectric two-dimensional Bragg structures in terahertz frequency range were developed and manufactured. Proof-of-principle electrodynamic experiments on the “cold” testing of these structures were carried out. It is shown that the experimental results are in good agreement with the theoretical predicts, including the existence of the highest Q mode inside the Bragg reflection band in the absence of periodicity defects.
关键词： CST Microwave Studio,Bragg reflection band,planar dielectric two-dimensional Bragg structures,terahertz frequency range,electrodynamic experiments
更新于2025-09-12 10:27:22
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Generation of THz radiation by photoconductive antennas on based thin films InGaAs and InGaAs/InAlAs.
摘要： Epitaxial low-temperature grown (LT) semiconductor arsenides (Al, Ga, In)As are widely used as materials for photoconductive antennas (PCA) generators and detectors of pulsed radiation in the terahertz (THz) frequency range [1–3]. It is the combination of subpicosecond carrier lifetime, relatively high mobility and high resistivity that makes LT-materials suitable for PCA applications. Lately, InGaAs has been investigated as a potential candidate for THz-PCA photoconductive material due to room-temperature band gap of 0.74 eV, which allows for 1.56 μm optical excitation with Er3+ fiber laser femtosecond pulses [4–6]. The low substrate temperatures result in a non-stoichiometric growth with the incorporation of excess arsenic in the crystal structure. The most common non-stoichiometry-related point defects in LT-arsenides are arsenic antisites with concentrations in the range 1017–1019 cm-3 depending on the substrate temperature and arsenic overpressure [7–10]. Antisite-related defect band in the semiconductor energy bandgap play a significant role in carrier dynamics. Fast non-radiative recombination of photogenerated electrons and holes through antisite centers results in sub-picosecond carrier lifetimes in LT-materials at optimized growth and annealing conditions [11, 12]. It is generally agreed that main traps of photo-excited electrons are ionized antisite defects [13–15]. A possible approach to increase the resistivity of LT-InGaAs is to employ LT-InGaAs/InAlAs superlattices [6,13,16,17]. LT-InAlAs layers have a higher dark resistivity as compared to LT-InGaAs and exhibit deep trap states that are situated energetically below the antisite defect levels of adjacent InGaAs layers that results in a reduction of residual carrier concentration. The Fig.1 shows the amplitude of THz radiation in time domain. It is seen that the signal from an InGaAs /InAlAs-based structure is 5-6 times higher due to a higher bias voltage, which is possible (without sample breakdown) due to higher sample resistance and lower dark current. Fig.2 shows a comparison of the Fourier amplitude according to the materials of the antennas LT-InGaAs/InAlAs and LT-InGaAs. It is seen that the spectrum of the LT-InGaAs / InAlAs sample is slightly wider in the range from 0.1 THz to 0.6 THz than that of the LT-InGaAs sample. We explain this effect by the difference between the characteristic relaxation times of electrons in the transition from the conduction band to the antisites. We determined the characteristic times of electron relaxation by the 'pump-probe' spectroscopy method. Fig.3 shows the dependence of the normalized transmission in time domain for the samples of LT-InGaAs and LT-InGaAs / InAlAs.We used 2-exponentional model for description experimental curves. On figures τ1 is an electron capture time (capture by charge AsGa defects) [18,19], τ2 is a recombination time of captured electrons and holes [17]. Due to the experimental fact that the characteristic relaxation times for the LT-InGaAs / InAlAs sample are less than for the LT-InGaAs, we observed the difference in the spectra for these samples. Summing up, it was found that THz generation is about 5-6 times more efficient in the case of LT-InGaAs/InAlAs superlattice than LT-InGaAs generation. It is found that due to the shorter electron relaxation time in the superlattice, the spectrum of these samples is wider in the range of 0.1-0.6 THz.
关键词： photoconductive antennas,InGaAs,THz radiation,terahertz frequency range,InGaAs/InAlAs,LT-materials
更新于2025-09-04 15:30:14