- 标题
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Enhancement of THz Generation by Two-Color TW Laser Pulses in a Low-Pressure Gas
摘要： We identify experimental conditions for efficient generation of THz pulses by high power near IR laser radiation: 2 TW, 30 fs, 800-nm laser pulses with their second harmonic were slightly focused in a low-pressure gas cell in such a way to avoid multiple filamentation and excessive ionization. This two-color scheme yields a microjoule level of THz pulses which is two orders of magnitude higher than the signal generated in the atmosphere of ambient air.
关键词： THz,Two-color,Plasma absorption,Terawatt,Chirp,Filament,Low pressure,Saturation
更新于2025-09-23 15:21:01
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Terahertz generation in quantum-cascade lasers through down-conversion optical nonlinearity: Design and modeling
摘要： In this paper, we propose an electrically driven optically excited laser structure for terahertz (THz) generation in quantum cascade lasers (QCLs) through frequency down-conversion optical nonlinearity. In our distinct design, both the pump and THz radiations are generated simultaneously by optical and electronic intersubband transitions (ISTs) between the quantized states within the conduction band of the same active region of a QCL. The modeling of laser bandstructure is achieved using a self-consistent solution of Schrodinger-Poisson equations, and the detailed analysis of electronic transport of the proposed structure is performed using the density matrix approach and energy-density balance equation that self-consistently consider the optical, electrical and thermal interactions in the structure. Additionally, the waveguide loss for the THz optical mode is considered using the bulk Drude model. Using a stationary solution of the density matrix equations, an expression for the THz intensity gain is derived as a function of pump field intensity, carrier distributions and quantum coherence contributions. Using the presented model, we analyze the steady-state and transient characteristics of the device for two different heatsink temperatures, 220 and 300 K. Simulation results show that the proposed structure has a potential to generate room-temperature THz radiation in QCLs.
关键词： Quantum-cascade laser (QCL),terahertz (THz) generation,down-conversion optical nonlinearity,density-matrix formalism
更新于2025-09-23 15:21:01
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Nonlinear Charge Transport in InGaAs Nanowires at Terahertz Frequencies
摘要： We probe the electron transport properties in the shell of GaAs/In0.2Ga0.8As core/shell nanowires at high electric fields using optical pump/THz probe spectroscopy with broadband THz pulses and peak electric fields up to 0.6 MV/cm. The plasmon resonance of the photoexcited charge carriers exhibits a systematic redshift and a suppression of its spectral weight for THz driving fields exceeding 0.4 MV/cm. This behavior is attributed to the intervalley electron scattering that results in the doubling of the average electron effective mass. Correspondingly, the electron mobility at the highest fields drops to about half of the original value. We demonstrate that the increase of the effective mass is nonuniform along the nanowires and takes place mainly in their middle part, leading to a spatially inhomogeneous carrier response. Our results quantify the nonlinear transport regime in GaAs-based nanowires and show their high potential for development of nanodevices operating at THz frequencies.
关键词： Localized Plasmon,Intervalley Scattering,Nanowire,Terahertz (THz)
更新于2025-09-23 15:21:01
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Ultrafast response of harmonic modelocked THz lasers
摘要： The use of fundamental modelocking to generate short terahertz (THz) pulses and THz frequency combs from semiconductor lasers has become a routine affair, using quantum cascade lasers (QCLs) as a gain medium. However, unlike classic laser diodes, no demonstrations of harmonic modelocking, active or passive, have been shown in THz QCLs, where multiple pulses per round trip are generated when the laser is modulated at the harmonics of the cavity’s fundamental round-trip frequency. Here, using time-resolved THz techniques, we show for the ?rst time harmonic injection and mode-locking in which THz QCLs are modulated at the harmonics of the round-trip frequency. We demonstrate the generation of the harmonic electrical beatnote within a QCL, its injection locking to an active modulation and its direct translation to harmonic pulse generation using the unique ultrafast nature of our approach. Finally, we show indications of self-starting harmonic emission, i.e., without external modulation, where the QCL operates exclusively on a harmonic (up to its 15th harmonic) of the round-trip frequency. This behaviour is supported by time-resolved simulations of induced gain and loss in the system and shows the importance of the electronic, as well as photonic, nature of QCLs. These results open up the prospect of passive harmonic modelocking and THz pulse generation, as well as the generation of low-noise microwave generation in the hundreds of GHz region.
关键词： harmonic modelocking,ultrafast response,THz QCLs,terahertz pulses,quantum cascade lasers
更新于2025-09-23 15:21:01
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Refractive Index Sensing Research on Multi-Fano-Based Plasmonic MDM Resonant System With Water-Based Dielectric
摘要： In this letter, we report initial experimental results which provide the foundation for low-terahertz (low-THz) radar imagery for outdoor unstructured scenarios as expected in automotive sensing. The requirements and speci?cations for a low-THz single imaging radar sensor are brie?y outlined. The imaging capabilities of frequency-modulated continuous-wave (FMCW) radar operating at 150 GHz are discussed. A comparison of experimental images of on-road and off- road scenarios made by a 150-GHz FMCW radar and a reference 30-GHz stepped-frequency radar is implemented, and their performance is analyzed.
关键词： low terahertz (low-THz),Imaging radar
更新于2025-09-23 15:21:01
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THz photodetector using sideband-modulated transport through surface states of a 3D topological insulator
摘要： The transport properties of the surface charge carriers of a three dimensional topological insulator under a terahertz (THz) field along with a resonant double barrier structure is theoretically analyzed within the framework of Floquet theory to explore the possibility of using such a device for photodetection purposes. We show that due to the contribution of elastic and inelastic scattering processes in the resulting transmission, side-bands are formed in the conductance spectrum. This side band formation is similar to the side-bands formation in cavity transmission spectra in an optical cavity and this information can be used to detect the frequency of unknown THz radiation. The dependence of the conductance on the bias voltage, the effect of THz radiation on resonances and the influence of zero energy points on the transmission spectrum are also discussed.
关键词： THz radiation,Floquet theory,surface states of topological insulators,side bands in transmission spectrum
更新于2025-09-23 15:21:01
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[IEEE 2019 Compound Semiconductor Week (CSW) - Nara, Japan (2019.5.19-2019.5.23)] 2019 Compound Semiconductor Week (CSW) - Breakdown of Pauli spin blockade by phonon irradiation in a GaAs double quantum dot
摘要： In this letter, we report initial experimental results which provide the foundation for low-terahertz (low-THz) radar imagery for outdoor unstructured scenarios as expected in automotive sensing. The requirements and speci?cations for a low-THz single imaging radar sensor are brie?y outlined. The imaging capabilities of frequency-modulated continuous-wave (FMCW) radar operating at 150 GHz are discussed. A comparison of experimental images of on-road and off- road scenarios made by a 150-GHz FMCW radar and a reference 30-GHz stepped-frequency radar is implemented, and their performance is analyzed.
关键词： low terahertz (low-THz),Imaging radar
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Shunt Resistance Relation to Power Loss due to Potential Induced Degradation in Crystalline Photovoltaic Cells
摘要： In this letter, we report initial experimental results which provide the foundation for low-terahertz (low-THz) radar imagery for outdoor unstructured scenarios as expected in automotive sensing. The requirements and speci?cations for a low-THz single imaging radar sensor are brie?y outlined. The imaging capabilities of frequency-modulated continuous-wave (FMCW) radar operating at 150 GHz are discussed. A comparison of experimental images of on-road and off- road scenarios made by a 150-GHz FMCW radar and a reference 30-GHz stepped-frequency radar is implemented, and their performance is analyzed.
关键词： low terahertz (low-THz),Imaging radar
更新于2025-09-23 15:21:01
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Optimization of PBG-Waveguides for Terahertz-Driven Electron Acceleration
摘要： The properties of 2-D photonic bandgap dielectric structures, also called photonic crystals, are numerically investigated to assist the design of waveguides for terahertz (THz)-driven linear electron acceleration. Given the broadband nature of the driving pulses in THz acceleration regimes, one design aim is to maximize the photonic bandgap width to allow propagation of the relevant frequencies within the photonic crystal linear defect waveguide. The proposed design is optimized to provide the best compromise between effective acceleration bandwidth and strong beam–wave interaction at the synchronism central frequency. Considerations on achieved acceleration bandwidth, accelerating voltage, and surface magnetic field are given to compare the proposed geometry to one of the main counterparts in the literature—the dielectric-lined waveguide.
关键词： Photonic crystals,terahertz (THz) electron acceleration,photonic-bandgap waveguides (PBG-Ws)
更新于2025-09-23 15:21:01
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Highly efficient surface-emitting semiconductor lasers exploiting quasi-crystalline distributed feedback photonic patterns
摘要： Quasi-crystal distributed feedback lasers do not require any form of mirror cavity to amplify and extract radiation. Once implemented on the top surface of a semiconductor laser, a quasi-crystal pattern can be used to tune both the radiation feedback and the extraction of highly radiative and high-quality-factor optical modes that do not have a defined symmetric or anti-symmetric nature. Therefore, this methodology offers the possibility to achieve efficient emission, combined with tailored spectra and controlled beam divergence. Here, we apply this concept to a one-dimensional quantum cascade wire laser. By lithographically patterning a series of air slits with different widths, following the Octonacci sequence, on the top metal layer of a double-metal quantum cascade laser operating at THz frequencies, we can vary the emission from single-frequency-mode to multimode over a 530-GHz bandwidth, achieving a maximum peak optical power of 240 mW (190 mW) in multimode (single-frequency-mode) lasers, with record slope efficiencies for multimode surface-emitting disordered THz lasers up to ≈570 mW/A at 78 K and ≈720 mW/A at 20 K and wall-plug efficiencies of η ≈ 1%.
关键词： quantum cascade laser,surface-emitting,Quasi-crystal,THz frequencies,Octonacci sequence,semiconductor lasers,distributed feedback
更新于2025-09-23 15:21:01