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Tunable plasmon-induced transparency and slow light in terahertz chipscale semiconductor plasmonic waveguides
摘要： We numerically propose the plasmon-induced transparency (PIT) and slow light effect based on terahertz (THz) chipscale plasmonic semiconductor-insulator-semiconductor (SIS) waveguide system. Via the coupling between two stub resonators, PIT is introduced due to the destructive interference, which can be theoretically described by the transmission-line Method (TLM). Meanwhile, the strong dispersion within the transparent window will lead to the slow light effect. Via tuning the geometric parameters, the profile of PIT as well as group delay line can be arbitrarily tailored. Moreover, active control of both PIT and slow light can be realized by changing the ambient temperature. Especially, by integrating monolayer graphene into the structure, PIT and slow light can also be electrically modulated via applying voltage. This work provides geometrical, thermal and electrical approaches to manipulate THz transmission and group delay in subwavelength scale, and can find potential applications as filters, sensors, modulators and active optical delay lines in THz ultracompact circuits.
关键词： graphene,plasmon-induced transparency,slow light,terahertz,plasmonic waveguide
更新于2025-09-23 15:19:57
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Metasurfaces for Terahertz Wavefront Modulation: a Review
摘要： Metasurface is an artificial material composed of a series of subwavelength structure units and has unique electromagnetic characteristics. Based on the ability of manipulating the phase, amplitude, and polarization of electromagnetic wave, various kinds of metasurfaces are designed to realize wavefront manipulations, such as beam focusing, beam steering, vector beams generating, and holographic imaging. This paper reviews the design methods of metasurfaces for wavefront modulation and evolution of the metasurfaces designed for wavefront manipulation in the terahertz (THz) region. The metasurfaces can be divided into two categories: passive and active metasurfaces. For the passive metasurfaces, the single-functional metasurfaces, multifunctional metasurfaces, and high diffraction efficient metasurfaces designed for various THz wavefront shaping, such as focusing, imaging, and special beams generating, are reviewed. For the active metasurfaces, the metasurfaces with fixed structure and all-optical metasurfaces without fixed structure for THz wavefront modulation are summarized. Furthermore, a comparison on the performance of different kinds of metasurfaces for THz wavefront modulation is presented and the development direction and challenges of the THz wavefront modulation metasurfaces in the future are discussed.
关键词： Active metasurface,Wavefront modulation,Terahertz,Passive metasurface
更新于2025-09-23 15:19:57
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Extremely high-intensity operation of a THz free-electron laser using an electron beam with a higher bunch charge
摘要： A higher intensity THz beam is generated with a free-electron laser (FEL) based on the L-band (1.3 GHz) electron linac at Osaka University by increasing the electron bunch charge four times higher from 1 nC in the conventional mode (the 108 MHz mode) to 4 nC in the new mode (the 27 MHz mode). This is realized by expanding the electron bunch intervals four times longer with the grid pulser of the electron gun, generating a series of 5 ns pulses at a repetition frequency of 27 MHz (the 48th subharmonic of 1.3 GHz), whereas the beam loading of the linac remains unchanged. The energy of an FEL macropulse comprised of many micropulses is measured in the 27 MHz mode to be approximately 28.5 mJ at a maximum of around 65 μm or 4.6 THz compared with the maximum macropulse energy of 13 mJ in the 108 MHz mode. The maximum micropulse energy in the 27 MHz mode is approximately 260 μJ using 110 micropulses, which is estimated by a macropulse duration of 4 μs and micropulse intervals of 36.9 ns. The micropulse energy is nearly 10 times higher than the micropulse energies in the conventional mode and in other FELs in the same wavelength or frequency region.
关键词： Free-electron laser (FEL),Terahertz (THz),Electron beam,High charge
更新于2025-09-23 15:19:57
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Optical external efficiency of terahertz quantum cascade laser based on ??erenkov difference frequency generation
摘要： In this paper, we consider terahertz sources based on ?erenkov di?erence frequency generation in a dual-wavelength mid-infrared quantum cascade laser and calculate analytically the optical external e±ciency of the out-going terahertz wave. The mid-infrared pumps operate simultaneously and have a common upper level. For short cavity lengths and low terahertz losses in the substrate, we ˉnd that implementation of the ?erenkov emission scheme in terahertz di?erence frequency generation quantum cascade lasers improves the optical external e±ciency dramatically. The maximum value of the latter is close to 19%, but is only attainable if the laser exhibits negligible mid-infrared transmission losses.
关键词： phased matching,Terahertz quantum cascade laser,optical external e±ciency,?erenkov,di?erence frequency generation
更新于2025-09-23 15:19:57
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The Antibody-Free Recognition of Cancer Cells Using Plasmonic Biosensor Platforms with the Anisotropic Resonant Metasurfaces
摘要： It is vital and promising for portable and disposable biosensing devices to achieve on-site detection and analysis of cancer cells. Although traditional labelling techniques provide an accurate quantitative measurement, the complicated cell staining and high-cost measurements limit its further development. Here, we demonstrate a non-immune biosensing technology. The plasmonic biosensors which is based on anisotropic resonant split ring resonators in terahertz range successfully realize the antibody-free recognition of cancer cells. The dependences of Δf and fitted phase slope (FPS) on the cancer cell concentration at different polarizations give new perspective in hexagonal radar maps. The results indicate that the lung cancer cell A549 and liver cancer cell HepG2 can be distinguished and determined simply based on the enclosed shapes in the radar maps without any antibody introduction. The minimum concentration of identification reduces as low as 1×104 cells/ml and such identification can be kept valid in a large range of cell concentration, ranging from 104 to 105. The construction of two-dimensional extinction intensity cards of corresponding cancer cells based on the wavelet transform method also supplies corresponding information for the antibody-free recognition and determination of two cancer cells. Our plasmonic MBs show a great potential in the determination and recognition of label-free cancer cells, being an alternative to non-immune biosensing technology.
关键词： terahertz,antibody-free biosensing,cancer cells,metasurfaces,continuous wavelet transform
更新于2025-09-23 15:19:57
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Photon-driven broadband emission and frequency comb RF injection locking in THz quantum cascade lasers
摘要： We present homogeneous quantum cascade lasers (QCLs) emitting around 3 THz which display bandwidths up to 950 GHz with a single stable beatnote. Devices are spontaneously operating in a harmonic comb state, and when in a dense mode regime they can be injection locked at the cavity roundtrip frequency with very small RF powers down to -55 dBm. When operated in the electrically unstable region of negative differential resistance, the device displays ultra-broadband operation exceeding 1.83 THz (?f /f = 50%) with high phase noise, exhibiting self-sustained, periodic voltage oscillations. The low CW threshold (115 A· cm?2) and broadband comb operation (?f /f = 25%) make these sources extremely appealing for on-chip frequency comb applications.
关键词： quantum cascade laser,terahertz,domain formation,injection locking,frequency comb
更新于2025-09-23 15:19:57
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Widea??Bandgap Organic Crystals: Enhanced Opticala??toa??Terahertz Nonlinear Frequency Conversion at Neara??Infrared Pumping
摘要： Enhanced terahertz (THz) wave generation is demonstrated in nonlinear organic crystals through refractive index engineering, which improves phase matching characteristics substantially. Unlike conventional low-bandgap nonlinear organic crystals, the newly designed benzimidazolium-based HMI (2-(4-hydroxy-3-methoxystyryl)-1,3-dimethyl-1H-benzoimidazol-3-ium) chromophore possesses a relatively wide bandgap. This reduces the optical group index in the near-infrared, allowing better phase matching with the generated THz waves, and leads to high optical-to-THz conversion. A unique feature of the HMI-based crystals, compared to conventional wide-bandgap aniline-based crystals, is their remarkably larger macroscopic optical nonlinearity, a one order of magnitude higher diagonal component in macroscopic nonlinear susceptibility than NPP ((1-(4-nitrophenyl)pyrrolidin-2-yl)methanol) crystals. The HMI-based crystals also exhibit much higher thermal stability, with a melting temperature Tm above 250 °C, versus aniline-based crystals (116 °C for NPP). With pumping at the technologically important wavelength of 800 nm, the proposed HMI-based crystals boost high optical-to-THz conversion efficiency, comparable to benchmark low-bandgap quinolinium crystals with state-of-the-art macroscopic nonlinearity. This performance is due to the excellent phase matching enabled by decreasing optical group indices in the near-infrared through wide-bandgap chromophores. The proposed wide-bandgap design is a promising way to control the refractive index of various nonlinear organic materials for enhanced frequency conversion processes.
关键词： organic crystals,terahertz,refractive index engineering,phase matching,nonlinear optics
更新于2025-09-23 15:19:57
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Terahertz Spectroscopy of Thermal Radiation from AlGaN/GaN Heterostructure on Sapphire at Low Temperatures
摘要： Terahertz spectroscopy of thermal radiation from electrically pumped AlGaN/GaN structures on sapphire substrate was investigated in this work. Comparison of experimental THz spectroscopy results to theoretical spectra calculations shows that thermal radiation of the sample lattice is the main mechanism causing the emission above T = 155 K, and it is mainly influenced by sapphire substrate. Here, the emission was attributed to the radiative electron transitions in shallow impurities and nitrogen vacancies as well as to radiative decay of longitudinal optical phonons (387 cm?1) in sapphire substrate. We have successfully demonstrated that THz emission spectroscopy can be used to define the temperature at which thermal emission from AlGaN/GaN HEMT structures dominates the emission spectrum.
关键词： terahertz spectroscopy,AlGaN/GaN heterostructure,electroluminescence,thermal radiation
更新于2025-09-23 15:19:57
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Free-Standing Complementary Asymmetric Metasurface for Terahertz Sensing Applications
摘要： We designed and tested a highly sensitive metasurface device based on free-standing complementary asymmetric split-ring resonators at terahertz frequencies. It is utilized for sensing a galactose film. We characterized the device using the induced red shift of a Fano resonance observed in the THz transmission. The sensor has a high sensitivity of 91.7 GHz/RIU due to a significant interaction between the galactose overlayer and the metasurface.
关键词： terahertz,asymmetric split-ring resonators,sensing,free-standing
更新于2025-09-23 15:19:57
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[IEEE 2019 International Conference on Smart Systems and Inventive Technology (ICSSIT) - Tirunelveli, India (2019.11.27-2019.11.29)] 2019 International Conference on Smart Systems and Inventive Technology (ICSSIT) - Power Quality Enhancement of a Photovoltaic Based Micro Grid System Using Optimized Fuzzy Controller with SAPF
摘要： We investigate terahertz quantum cascade lasers with a dense array of active micropillars forming the gain medium. Depending on the size of these pillars relative to the emission wavelength different optical regimes are identified. For pillar dimensions on the order of the emission wavelength, a photonic crystal resonator is created. Single mode emission is observed at high symmetry points of the photonic band structure. The selection mechanism of the favored laser mode is studied by analyzing the gain enhancement effect for eigenmodes with a low group velocity and a large mode confinement of the electric field energy in the micropillars. Subwavelength micropillar arrays constitute a photonic metamaterial, which can be described using an effective medium approximation. Similar to a bulk laser ridge, the array forms a Fabry–Pérot resonator that is defined by the boundaries of the array. From the longitudinal mode spacing, we derive an effective group index of the pillar medium. Limitations in terms of minimum filling factors and waveguide losses for the realization of subwavelength micropillar and nanowire array terahertz quantum cascade lasers are investigated.
关键词： optical metamaterials,terahertz,optical waveguides,Photonic crystals,quantum cascade lasers
更新于2025-09-23 15:19:57