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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) - THz Properties of Fe and Ti Oxides Nanoparticles Obtained by Pulsed Laser Ablation
摘要： We present Dielectric properties of Fe and Ti oxides nanoparticles (NPs) measured by THz-TDS. The NPs were obtained via ns pulsed laser ablation (PLA) of the metals in air and water and were annealed at different temperatures. In the paper, we exhibit the dependence of absorption spectra on NPs structure: from magnetite to hematite for Fe, and from anatase to rutile for Ti. The prospects for their use as materials for the THz photonics are discussed.
关键词： THz-TDS,Fe and Ti oxides nanoparticles,THz photonics,dielectric properties,pulsed laser ablation
更新于2025-09-12 10:27:22
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A 230-GHz High-Power and Wideband Coupled Standing Wave VCO in 65-nm CMOS
摘要： This article presents a 230-GHz wideband harmonic voltage-controlled oscillator (VCO) with large output power based on a compact and low-loss structure of coupled standing wave oscillators. In order to boost the output power, oscillators are coupled together without adding extra passive loss to the circuit. Transistors with inductive drain impedances provide the necessary negative resistance to the oscillators while simultaneously acting as active variable capacitors for frequency tuning and generate the desired second-harmonic power through their nonlinearities. Transmission lines at the drains are responsible for creating the inductive impedance as well as coupling adjacent oscillators and routing and combining the output power. Therefore, the circuit has a compact structure that minimizes passive losses. A varactor-less frequency tuning scheme is used and allows for wideband operation without sacrificing the output power. In addition to oscillator coupling and minimizing the losses, the output power has been boosted by engineering the harmonic impedance that is seen by the transistors in the circuit. The prototype chip was implemented in a 65-nm CMOS process. The output power of the VCO covers 219–238 GHz frequency band (8.35% tuning range) and delivers 3.4-dBm maximum output power. The minimum measured phase noise is ?105.8 dBc/Hz (at 10-MHz offset) while consuming 195 mW from a 1.5-V supply.
关键词： standing wave,low-loss,THz,wideband,frequency tuning,Compact structure,millimeter-wave (mm-Wave),voltage-controlled oscillator (VCO),mm-wave/terahertz (THz) power generation,harmonic oscillator,varactor-less
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) - 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) - Inhomogeneous Broadening of a Polaritonic Mode in the Ultrastrong Coupling Regime
摘要： Ultrastrong coupling (USC) regime has been an intriguing research topic in cavity quantum electrodynamics (QED) experiments due to its capability to modify the ground and the excited states of a coupled system[1-3]. We investigate the USC of Landau level (LL) transitions in a two dimensional electron gas to teraherz (THz) metasurfaces using THz time domain spectroscopy. Complementary THz split ring resonator (cSRR) arrays are used as metasurfaces[4]. A higher coupling rate can be achieved by reducing the capacitive gap of the resonator due to the increased vacuum ?eld ?uctuations. However, our results indicate that this reduction introduces an inhomogenous broadening of the upper polariton branch below a threshold gap width.
关键词： complementary split ring resonator,Ultrastrong coupling,Landau level transitions,THz time domain spectroscopy,THz metasurfaces
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) - THz Time-Domain Reflection Spectroscopy of KTiOPO <sub/>4</sub>
摘要： Terahertz (THz) radiation has been of increasing interest in the last decades, for security, manufacturing, quality control, medical and security imaging applications. The field requires more efficient and affordable sources and nonlinear upconversion schemes point in this direction. KTiOPO, (KTP) is a well-established material for nonlinear optical applications in the visible and near-IR region thanks to its large transparency, high nonlinear coefficient and damage threshold. Its reasonably low absorption [1, 2] and strong polariton resonances [1] show promise for efficient IR to THz upconversion and Wu et al. [2] recently demonstrated its superiority to LiNbO3 and LiTaO3 in a back to back experiment. However, the complex refractive index needs to be measured before further power scaling is realistic. Terahertz time-domain spectroscopy (TTDS) allows for direct extraction of both the phase and amplitude of the THz electric field and grants the possibility of extracting the optical parameters n and α. In this work, we report on THz time-domain reflection spectroscopy of flux grown KTP from 0.5 to 7 THz at room temperature. The THz-TDS setup used air-filament plasma for generation of the THz radiation and the Pockel's effect in 300um thick GaP for detection. The a and b-axis of a KTP crystal were probed using an HDPE polarizer and rotation of the sample. The geometry of the setup is based on the work of Pashkin et al. [3], where the THz was focused onto the GaP crystal after the 25x15x0.5mm3 sample. Fig.1 shows the refractive index and the absorption coefficient from left to right, respectively. Blue and red color depict the two axes of the KTP crystal. Errors are estimated to: ?n < ±0.025 and ?α <±5 cm?1 (0.5?3THz), ?n < ±0.05 and ?α < ±25 cm?1 (3?5THz), ?n < ±0.1 and ?α < ±50 cm?1 (5?6THz), ?n < ± 0.25 and ?α < ±150 cm?1 (6?7THz). The accuracy in frequency was ≈ 90 GHz or 2 cm?1, limited by the scan time of 11ps. To the best of our knowledge, the convoluted frequency dependent nature of the refractive index has not been measured by direct time-resolved THz measurement before. Earlier spectroscopic studies of KTP have either lacked the possibility of directly extracting the complex refractive index [4] or been limited by absorption of the transmitted signal due to the strong resonances of KTP, limiting the bandwidth to about 2.5 THz [5]. In the regions where the bandwidth of this and older studies overlap, the measurements are similar, giving credibility to both measurements over the whole bandwidth. Besides, the measured resonances in Fig.1 can be related to IR active phonon modes, as seen in, e.g. [6]. This study will be of utmost importance when constructing new devices for optical to THz conversion. We also report a possible new phonon mode at 1.4 THz.
关键词： absorption coefficient,KTiOPO4,refractive index,THz time-domain spectroscopy,Terahertz
更新于2025-09-12 10:27:22
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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) - Optoelectronic Properties of Tin-Based Hybrid Metal Halide Perovskite Thin Films for Photovoltaics
摘要： Due to their exceptional optoelectronic properties, hybrid metal halide perovskites films have shown extraordinary success as active layers in solar cells. One potential drawback of hybrid perovskites, however, is that the highest performing devices are currently based around toxic, lead-containing materials. Tin is a promising replacement for lead, p-doping in tin-based materials has prevented them from achieving the efficiencies of their lead-based analogues. Using optical-pump/THz-probe spectroscopy and THz time-domain spectroscopy, we compare the intrinsic and extrinsic optoelectronic properties formamidinium tin triiodide thin films and comment on the fundamental limits to charge transport.
关键词： tin-based hybrid metal halide perovskite,optoelectronic properties,photovoltaics,THz spectroscopy
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Miramar Beach, FL, USA (2019.8.19-2019.8.21)] 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Non-Reciprocal Graphene Gratings Based on Spatiotemporal Modulation
摘要： This paper presents a nonreciprocal grating based on graphene strips on top of a dielectric substrate for THz frequencies. Nonreciprocity is achieved by applying a directional temporal modulation with different phases to different graphene strips of the grating. Quite importantly, only three distinct modulation regions are necessary to achieve strong nonreciprocity, relaxing the fabrication requirements. Simulation results show very large isolation with moderate insertion loss for realistic parameters for graphene, making the proposed structure suitable for practical applications at THz frequencies.
关键词： spatiotemporal modulation,graphene,THz frequencies,nonreciprocal grating
更新于2025-09-12 10:27:22
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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) - Numerical Study of CO Laser Down-Conversion into the THz Range With ZnGeP <sub/>2</sub> crystal
摘要： Difference frequency generation of rotational-vibrational lines of nonselective CO laser in ZnGeP2 crystal was numerically studied. It was shown that a great number of difference frequency lines can densely cover spectral range from 50 to 1000 (cid:2)m and even up to 5000 (cid:2)m. An influence of ZnGeP2 crystal absorption on THz generation was studied.
关键词： THz generation,CO laser,difference frequency generation,ZnGeP2 crystal
更新于2025-09-12 10:27:22
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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) - Effect of DC Electric Field on the Emitted THz Signal of Antenna-Coupled Spintronic Emitters
摘要： We study the impact of an external electric DC field on antenna-coupled spintronic THz emitters driven by a 90 fs, 1550 nm laser oscillator. Simultaneous application of external electric and magnetic field shows a quadratic decrease in peak-peak THz pulse with increase in the bias voltage. We ascribe this decrease to Joule heating caused by the DC current flowing through the spintronic material.
关键词： spintronic emitters,Joule heating,DC electric field,THz
更新于2025-09-12 10:27:22
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Terahertz Dielectric Spectroscopic Analysis of Polypropylene Aging Caused by Exposure to Ultraviolet Radiation
摘要： Terahertz dielectric spectroscopy is shown to be an effective tool for bench-marking ultraviolet aging of polypropylene. In this, thin-film polypropylene samples exposed to standard artificial ultraviolet radiation in accelerated aging from 1 day to 30 days are closely monitored by a terahertz time-domain spectroscopy system and analyzed using an effective data processing method. It is found that the terahertz absorption of the polypropylene samples is generally weak and the terahertz dielectric constant varies slightly though discernibly during the aging process, with the refractive index decreasing slightly with increasing length of ultraviolet exposure. Nonetheless, the rate of variation of the polypropylene refractive index with increasing terahertz frequency exhibits a drastic inflection around the 15-days aging point and the rate changes suddenly from positive value to negative value. Based on this prominent and consistent THz dielectric spectroscopic feature of the aging process, an efficient judging criterion is established to distinguish the early-term, mid-term, and late-term phases as well as the degree of polypropylene ultraviolet aging, corresponding to the fundamental transformation of the polymer material from a nonpolar to a polar substance at a critical level of oxidation induced by ultraviolet radiation.
关键词： ultraviolet aging,polypropylene,THz dielectric spectroscopy
更新于2025-09-12 10:27:22