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Polarized THz Emission from In-Plane Dipoles in Monolayer Tungsten Disulfide by Linear and Circular Optical Rectification
摘要： Recent advances in the development of polarized terahertz (THz) emission from nanomaterials have not only opened up a new “TeraNano” interdiscipline but also provided a new tool for nonlinear optical process research. Herein, THz radiation mechanism of monolayer tungsten disulfide (WS2) is first investigated by both linear and circular polarization laser excitations at room temperature. The results reveal that polarized THz emission is dominated by the optical rectification based on in-plane nonlinear dipoles, which is totally different from that of bulk WS2. The mechanism is verified by the azimuthal angle and pump polarization angle dependence of THz emission in both experiment and theory. Furthermore, controllably elliptically polarized THz emission is observed with the maximum ellipticity of ≈0.52 based on nonresonant nonlinear process under the circularly polarized excitation. A clear understanding of THz radiation mechanism of 2D materials will facilitate further design, optimization, and polarization control of integrable 2D THz optoelectronics.
关键词： THz radiation,monolayer WS2,in-plane nonlinear dipoles,optical rectification,elliptically polarized THz emission
更新于2025-09-23 15:23:52
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Resonant Enhancement of THz Radiation Through Vertically Aligned Carbon Nanotubes Array by Applying Wiggler Magnetic Field
摘要： The present analysis develops a novel theory of terahertz radiation generation by beating of two laser beams, incident obliquely on the array of vertically aligned carbon nanotubes (CNTs) in the presence of an external wiggler magnetic field. The array of CNTs behaves as nanoantenna to generate THz radiations. The incident lasers exert a ponderomotive force on the electrons of the CNTs to produce nonlinear oscillatory velocity, which beats with the applied wiggler magnetic field. This beating produces a nonlinear current at (ω2 ? ω1, k2 ? k1 + k0) which acts as an antenna to produce the THz radiation. We observe that when the beat frequency (ω2 ? ω1) lies near the effective plasmon frequency of the CNTs, strong THz radiation is produced due to a resonant interaction of the laser with CNT electrons. The externally applied wiggler magnetic field enhances the efficiency of THz radiation of nanoantenna by providing the necessary momentum to the generated THz radiation. We explore the impact of radius and length of nanotubes on the efficiency of THz generation. The generated THz power is enhanced at an optimum angle of incidence of lasers with an array of CNTs.
关键词： THz radiation,Carbon nanotubes,Antenna theory,Wiggler magnetic field,Plasma,Nanotechnology
更新于2025-09-23 15:23:52
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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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All-carbon THz components based on laser-treated diamond
摘要： We report on fs laser structuring and graphitization of diamond and experimental characterization of its THz response. A full characterization of graphitized, conductive layer generated by laser irradiation is carried out by performing scanning-electron microscopy, Raman spectroscopy and electrical measurements. The transmittance of the laser textured diamond samples, both with the graphitic overlayer and after selective oxidizing etching, is analyzed in the (0.25 ÷ 6.0) THz spectral range. A significant selective absorption of the graphitized overlayer towards polarized THz radiation is demonstrated, which is associated to the formation of graphitic laser induced periodic surface structures. This anisotropy allows conceiving compact passive metasurfaces based on conductive/dielectric patterns on the diamond plate surface for the development of robust, lightweight and broadband THz optical components.
关键词： graphitic laser induced periodic surface structures,graphitization,electrical measurements,fs laser structuring,THz response,transmittance,THz optical components,polarized THz radiation,conductive layer,diamond,Raman spectroscopy,metasurfaces
更新于2025-09-23 15:19:57
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Thermostimulated THz Radiation Emission of GaAs at Surface Plasmon-Phonon Polariton Frequencies
摘要： The THz radiation reflection, absorption and emission spectra of conductive n-GaAs/air surface are considered. The influence of thermostimulated surface plasmon-phonon (SPP) polariton oscillations on THz radiation reflection, absorption and emission of high conductivity GaAs polished plates with electron density n = 7·1017 cm–3 and 4·1018 cm–3 and thickness of 350 μm is studied experimentally. The frequencies of thermostimulated transverse and longitudinal optical phonons and SPP oscillations, which characterize a heated lattice state, were determined. It is found that the heated highly doped interface layer (GaAs/air) emits the THz radiation at selected frequencies of SPP oscillations in the (7 – 8) THz and (10 – 15) THz ranges. It is shown that thermal heating of the GaAs/air interface enhances the absorption of the incident THz radiation. The huge decrease of the incident radiation reflectivity at the SPP frequencies with an increase of GaAs temperature is observed experimentally.
关键词： surface plasmon-phonon polaritons,black-body radiation,GaAs,thermostimulated THz radiation emission
更新于2025-09-19 17:15:36
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Influence of exciton energy on intersubband transition of chirped superlattice GaAs/AlGaAs quantum cascade laser
摘要： The influence of exciton energy on intersubband transition was simulated for a chirped supperlattice quantum cascade laser of GaAs/AlxGa1-xAs. Exciton energy was modelled as a function of QW width for alloys of various percentages of constituent elements. The results showed that the exciton energy decreased proportionally with increasing QW width. Models were also generated to study exciton energy as a function of the percent alloy contents of AlxGa1-xAs barriers for QWs of various widths. Exciton energy showed characteristics of higher discrete energy when QW width was narrower. Transition energy was also simulated from 1e and 2e to the 1s exciton state as functions of applied electric field at various QW widths. Our simulation results showed that the transition energy from 2e to the 1s exciton state increased proportionally to the increasing strength of the electric field. This transition energy was indicative of THz range radiation.
关键词： percent alloy contents,chirped superlattice quantum cascade laser,aluminum arsenide monolayer,THz radiation,transition energy
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Enhancing THz Emission using a Shallow-Bounce Configuration
摘要： THz radiation promises to revolutionise applications in fields from security and counter terrorism, to medicine and agriculture. In the drive to develop robust, powerful and frequency-tunable THz laser sources, systems based on the stimulated polariton scattering (SPS) process, derived from solid state architectures, are arguably at the forefront. Within the realm of THz-SPS lasers, there are significant opportunities to enhance the performance of these systems, through careful consideration of the system architecture. It is well known that SPS-active crystals are inherently highly absorbing in the THz frequency range. This presents a dilemma in that while these crystals are capable of optically generating THz radiation, they are also the greatest cause of THz loss within these systems. This has led to system architectures/designs such as the surface-emitting configuration, which place the THz generation region as close to the emitting surface as possible. While this design has proven effective, it is but one consideration in maximising the possible THz power emitted from these systems. Of great relevance is the overall generation volume, its proximity to the emitting surface, and how this evolves with THz frequency tuning. Here, we report both computational modelling and experimental results contrasting the use of a new, novel, shallow-bounce architecture, in comparison to conventional linear and surface-emitting designs; the architecture of each is shown in Fig. 1. The shallow bounce system is shown schematically in Fig. 2. The system comprises a diode-end-pumped 0.3 at. % Nd:YVO4 laser crystal generating a fundamental field at 1342 nm. A flat end-mirror (M1), an x-cut 5 at. % MgO:LiNbO3 SPS crystal (HC Photonics Corp.) and a concave high reflectivity (HR) mirror (M2, radius of curvature (ROC) = 1000 mm) defined the ends of the fundamental resonator. The MgO:LiNbO3 crystal had dimensions of 5×5×20 mm3, and was AR coated on both end surfaces (R < 0.2 % at 1340 – 1380 nm at normal incidence). The system was Q-switched to achieve pulsed operation at a repetition rate of 5 kHz. A separate pair of HR mirrors (M3 and M4, ROC = 1000 mm; R = 99.9 % from 1340 – 1380 nm) were used to construct a 95 mm-long resonator which oscillated and bounced the Stokes field at the same TIR surface position as the fundamental field. Two high-resistivity Si-prisms with angles of 33°/33°/114° (dimensions 6×6×10 mm3) were placed in close proximity to the Teflon-coated polished x-z surface of the MgO:LiNbO3 crystal. These prisms extracted two THz beams at angles of ~ ± 30°relative to the TIR surface. The bounce angle of the fundamental field is 84.5 o (to the crystal normal), in comparison to 65 o which is typical in surface-emitting configurations. The shallow-bounce system generated dual-beam THz emission (with similar output powers and beam profiles) with a total, maximum average power of 67.5 (cid:541)(cid:58) for an incident CW pump power of 15.1 W. Notably, the frequency-tuning range was broad, covering the range 1.05 – 2.89 THz. High emission is maintained throughout this tuning range, especially in comparison to that achieved from linear and surface-emitting geometries, the details of which will be elucidated and discussed in this paper.
关键词： stimulated polariton scattering,THz-SPS lasers,shallow-bounce architecture,THz radiation,SPS
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Dual-Wavelength Y-Branch DBR-RW Diode Laser at 785 nm with Adjustable Spectral Distance from 0 up to 1.6 nm
摘要： For several applications compact light sources are requested providing two stabilised wavelengths with a narrow linewidth. Applications are shifted excitation Raman difference spectroscopy (SERDS) which separates the Raman lines from disturbing background signals such as ambient daylight or fluorescence or concentration measurements using absorption spectroscopy. Moreover, two slightly different wavelengths are needed for the difference frequency generation into THz radiation. Beside the narrowing and stabilization of the emission wavelength using an internal grating, heater elements above the implemented grating can be used to adjust the spectral distance to meet the demands for the above-mentioned applications. In this contribution, dual-wavelength Y-branch DBR-RW diode lasers emitting at 785 nm with on-chip implemented resistor heaters close to the DBR gratings similar to [1] will be presented. In contrast to the already presented work the heaters are controlled individually and thus the emission wavelength of each laser cavity can be tuned via temperature for each DBR grating separately. This enables the device to provide a flexible spectral distance of the two emission wavelengths in common laser operation of both cavities and fast alteration between both laser lines as recently demonstrated in [2]. The total length of the devices is 3 mm. Two 500 μm long 10th order passive DBR gratings, a 2 mm long S-bend shaped Y-branch coupler section and a 500 μm RW output section form the two laser resonators. The on-chip resistor heater elements are separately controllable as well the two S-bend shaped RW branches and the output RW section. The grating periods are chosen to generate two slightly different emission wavelengths with a spectral distance of 0.6 nm, i.e. 10 cm-1, suitable for SERDS. After a description of the device, electro-optical and spectral properties will be discussed with respect to the above- mentioned applications. In Fig. 1 the power-current characteristic for such dual-wavelength diode lasers is shown. Here the current IY in the Y-coupler was 0 mA, the current Iout in the RW output section was 35 mA and the heatsink temperature is 25°C. Lasing starts for both cavities at about 30 mA with a slope efficiency of 0.6 W/A. An optical output power of more than 200 mW was measured at an injection current of 400 mA. For an output power of 100 mW the spectral tuning with the individual heater elements is shown in Fig. 2 and Fig 3. Here, a flexible spectral range between 0 and 1.6 nm can be obtained while the emission of both branches shows single mode operation with a narrow bandwidth below 11 pm.
关键词： adjustable spectral distance,dual-wavelength,785 nm,Y-branch DBR-RW diode laser,absorption spectroscopy,THz radiation,SERDS
更新于2025-09-12 10:27:22
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An advanced approach to control the electro-optical properties of LT-GaAs-based terahertz photoconductive antenna
摘要： This work reports on an advanced approach to the design of THz photoconductive antenna (PCA). The LT-GaAs thin films used for the PCA fabrication were synthesized by MBE method on GaAs (100) substrate by adjusting the As pressure, As/Ga fluxes ratio, growth/annealing temperatures and annealing time. These parameters crucially affect electro-optical properties of the PCA samples as evidenced by the THz radiation power and time-domain spectroscopy measurements. The annealing temperature of 670 °C was found to be optimal for constructing a PCA possessing high amplitude of the THz radiation over the spectral range up to 1 THz at the resonance of 0.1 THz. The comparison of this PCA with the reference ZnTe crystal reveals a 2-fold increase in THz power. Furthermore, this antenna attains a 1.5-, 3-, and 2-fold increase in THz power, photocurrent efficiency, and actuating dc BV, as compared with the commercial ZOMEGA antenna. These results pave the way towards the creation of highly efficient LT-GaAs-based PCAs.
关键词： THz-antenna,Terahertz (THz) radiation,Photoconductive antenna (PCA),Low temperature-grown gallium arsenide (LT-GaAs),THz-spectroscopy
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP) - Bochum, Germany (2019.7.16-2019.7.18)] 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP) - Pulse-resolved Data Acquisition System for THz Pump Laser Probe Experiments at TELBE using Super-radiant Terahertz Sources
摘要： the terahertz (THz) frequency range lies between the frequency range of radio and infrared. The development of suitable detectors, detection techniques, and sources for this frequency range has much interest over the past decade. THz pulses of sufficient strength that act as an excitation of dynamics in the matter have only been available, due to the development in 4th generation superconducting radiofrequency (SRF) technology. In the THz pump laser probe experiments the electric or magnetic field in the THz pump pulse acts as the excitation of dynamics in the matter. Ultra-short laser pulses then probe this dynamic in turn. In this contribution, we will outline the pulse-resolved data acquisition scheme of the TELBE user facility based on the characterization of a new class of accelerator-based light sources, which provide a unique combination of high pulse energies and high repetition rates.
关键词： Superradiant Terahertz Sources,Data Acquisition System,THz Radiation Detection Techniques,THz pump Laser Probe Experiments
更新于2025-09-11 14:15:04