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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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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Optical Generation of High-power Terahertz Pulses for Tunable Wave Source
摘要： High-power terahertz pulse generation and its polarization and frequency control by optical rectification with nonlinear organic crystals were studied. Terahertz pulses up to 730 nJ/pulse was generated from a DAST crystal pumped by 250 μJ femotosecond laser pulses with a central wavelength of 1500 nm. The terahertz peak electric field is estimated as 860 kV/cm if we focus the terahertz beam to φ=300 μm spot, which is expected to nonlinear material control application. We proposed the high-power terahertz polarization pulse shaping using the double stacked nonlinear organic crystals excited with tailored pump pulses. Through the terahertz modulation of pump pulses, the waveform shaping of the high-power terahertz pulses are expected, which leads to selective excitation of molecules or spin waves.
关键词： optical rectification,terahertz pulses,nonlinear organic crystals,polarization control,DAST crystal
更新于2025-09-23 15:21:01
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Nonlinear optical rectification and electronic structure in asymmetric coupled quantum wires
摘要： Asymmetric coupled quantum wires provide the possibility for realizing obvious nonlinear optical rectification due to breaking the inversion symmetry. Here, we investigated nonlinear optical rectification (NOR) and electronic states in asymmetric coupled quantum wires (ACQWs). We find that the NOR max value of the ACQWs exhibits double peak structure with the increase of the geometrical asymmetry (i.e. the left wire radius deviating from the right wire radius), thus offering a direction for achieving remarkable NORS. In the double peak structure, the max value is one to two orders of magnitude larger than the min value. Furthermore, we find that the tunneling effect with respect to the ground state is reduced with the increase of the geometrical asymmetry, while the tunneling effect with respect to the first-excited state is firstly reduced, subsequently enhanced and then reduced with the increase of the geometrical asymmetry. Such coupling pictures elucidate the double peak structure in the NOR max value of the ACQWs. Our work enriches our understanding for the NOR and quantum states of the ACQWs, thereby laying the groundwork for the design and optimization of nonlinear nano-optical devices based on asymmetric coupled quantum wires such as THz radiation sources and infrared photo-detectors.
关键词： Asymmetric coupled quantum wires,Electronic structure,Nonlinear optical rectification
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) - High Conversion Efficiency in a System “Nonlinear-Optical Crystal Partially Filling the Cross Section of a Rectangular Waveguide”
摘要： It is shown that terahertz radiation (0.1-3 THz) can be effectively generated via optical rectification of femtosecond laser pulses in a system of a “nonlinear-optical crystal partially filling the cross section of a rectangular metal waveguide”. The numerical calculations for the phase-matching in LiNbO3, ZnTe, DAST and GaSe nonlinear optical crystals have been performed. The influence of THz radiation absorption on the efficiency of generation of coherent THz radiation in the system has been investigated.
关键词： optical rectification,femtosecond laser pulses,phase-matching,nonlinear-optical crystal,terahertz radiation
更新于2025-09-16 10:30:52
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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) - Frequency-and-polarization-controllable High-power THz Wave Generation Using Organic Nonlinear Optical Crystal
摘要： Arbitrary control of high-power THz polarization and frequency is studied by the numerical calculation based on the coupled wave approach. THz wave generation using organic crystals via optical rectification provides high conversion efficiency. To overcome the limitation of the generated THz field direction which comes from their optical anisotropy, we propose the synthesis of THz wave generated from two crystals whose optical axis are orthogonal each other. By the calculation, the linearly and circularly polarized THz wave generation by changing the time delay of two pump pulses is demonstrated.
关键词： optical rectification,organic nonlinear optical crystal,polarization control,frequency control,THz wave generation
更新于2025-09-16 10:30:52
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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) - Milliwatt-Class MHz Repetition-Rate THz Source Driven by a sub-100 fs High Power Thin-Disk Laser
摘要： We demonstrate optical rectification in GaP crystals thin-disk oscillator, nonlinearly driven by a 100 W-class compressed to sub-100 fs in a multi-pass cell. In optimized conditions, we obtain a power of 1.35 mW, which is the highest average power achieved in GaP so far. Additionally, we explore the effect of temperature of the crystal down to 77 K, showing that controlling the temperature of the crystal could be a key aspect for further power scaling and for handling thermal effects that become important at such high driving powers.
关键词： thin-disk laser,optical rectification,THz source,GaP crystals,high power
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) - Semiconductors as Highly Efficient Single and Multicycle Terahertz Sources
摘要： The low- (0.1-2 THz) and mid-frequency (2-20 THz) bands of the THz range can be accessed by optical rectification (OR) in LiNbO3 (LN) [1] and organic crystals [2], respectively. The low -frequency band is optimally fitting for acceleration of charged particle beams. However, further increasing the THz pulse energy and field strength is challenging. Semiconductors can be used as highly efficient terahertz sources if the pumping wavelength sufficiently long to eliminate two- and three-photon pump absorption and the associated free-carrier absorption in the THz range. At such long infrared pump wavelengths tilted-pulse-front (TPF) pumping has to be used for phase matching. Comparing to LN this angle is advantageously small (<30°), and contact-grating (CG) is feasible. In our experiment we demonstrated more than two orders of magnitude higher pump-to-THz conversion efficiency than before [3], using a pump wavelength of 1.7 μm. 14 μJ THz pulse energy at 0.7% efficiency were measured with a prism shape ZnTe source [4]. We also realized a monolithic ZnTe CG THz source and demonstrated the generation of THz pulses with up to 3.9 μJ energy and 0.3% efficiency (Fig. 1a) [5]. We will discuss the prospects and basic design aspects of long-wavelength-pumped semiconductor THz sources, including optimal pumping and phase-matching conditions [6]. Our calculations show that single-cycle THz pulses can be generated with 15 GW/cm2 pump intensity, 150 fs pump pulse duration and 2 THz phase- matching frequency with more than 3% conversion efficiency from an 8 mm thick GaP source (Fig 1b). We will also present our latest results on GaP CG design for three different pump wavelengths (1.76, 2.06 and 2.2 μm), symmetric and Littrow configurations, and four different phase-matching frequencies from 1 to 4 THz. The expected first order diffraction efficiencies are 76-81% which can be increased to >90% with additional anti-reflection coating for the corresponding pump wavelength. GaP in combination with a flexible and efficient pump source technology, such as the dual-chirped OPA [7], and the CG technology can be a highly efficient and versatile source of multicycle THz pulses too [8]. Conversion efficiencies up to 3% were predicted for 5 mm crystal length (Fig 1c). Based on this, producing multicycle THz pulses with about 1.2 mJ energy from a GaP contact-grating source of about 1 cm2 area is feasible by using intensity-modulated pump pulses with 40 mJ energy from a dual-chirped OPA [7]. For an optimal combination of THz frequency, pump intensity, and crystal length, efficiencies as high as 8% can be expected.
关键词： Tilted-pulse-front pumping,Optical rectification,Terahertz sources,Semiconductors,Contact-grating,Conversion efficiency
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) - Generation of a Few Cycle Terahertz Pulse in Aperiodically Poled Lithium Niobate by Sequence of Pump Pulses
摘要： It is shown that chirped aperiodically poled lithium niobate crystal is capable to generate powerful THz pulses with controllable number of THz field oscillations (from nearly single- to multi-cycles), when it is pumped by sequence of femtosecond laser pulses with chirped delays between adjacent pulses. The peak electric field strength of about 0.3 MV/cm (for non-focused THz beam) is predicted if intensity of each pump pulse in the sequence is 20 GW/cm2.
关键词： Optical rectification,Aperiodically poled lithium niobate,Terahertz pulse,Femtosecond laser pulses
更新于2025-09-11 14:15:04
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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 Pulse Generation Emitted from Slant-Stripe-Type PPLN Via Optical Rectification Effect
摘要： To generate THz wave efficiency, phase-matching condition and small absorption of THz waves in nonlinear crystal are required. PPLN has attracted attention as a promising candidate for nonlinear crystal for THz wave generation, since periodically poled lithium niobate (PPLN) can be controlled its phase matching condition by designing periodically-poled structure. In case of ultrashort pulse pumping, multi-cycle THz pulses are obtained from PPLNs via optical rectification effect [1]. In this case, THz pulses with an arbitrary frequency shift are expected to be obtained by optimizing the periodic structures of the PPLNs [1,2]. Utilizing this feature, it is expected that multi-cycled THz pulses can be applied to radar techniques with high resolution. However, the pulse length is limited by 10~30 ps owing to absorption of PPLN. Note that PPLNs have absorption coefficient of approximately a few tens cm-1 at room temperature [3]. To prevent absorption of the generated THz wave, slant-stripe-type PPLN crystal was proposed by Sasaki et-al [4]. The slanted-PPLN is designed that propagation direction of generated THz wave is perpendicular to the direction of pump beam. In this case, generated THz wave is emitted from side surface of the crystal. By setting pump beam as close to the lateral face of the crystal as possible, damping of the THz wave is small, due to the short path length in the nonlinear crystal. In case of two color ns pulse pumping (via difference frequency generation, DFG), efficient THz wave generation have been demonstrated. However, multi-cycled THz pulse by ultra-short pulse pumping (via optical rectification effect, OR) emitted from the slanted PPLN have not been demonstrated. As THz wave generation mechanisms are different in cases of DFG and OR, it is not certain whether multi-cycled THz pulse generate efficiently and propagate in the direction perpendicular to the pump beam via OR effect, similarly to the case of DFG. Our experiments were performed at room temperature. The slanted PPLN was pumped by femtosecond pulse (pulse width ~ 170 fs, wavelength ~ 1035 nm, repetition rate ~ 30 MHz). THz pulse was emitted from the side surface of the PPLN and detected by bolometer. Fig. 1 (a) shows the signal intensity of the bolometer as a function of intensity of pump power. It is confirmed that THz signal increased proportional to the square of the pump intensity increased. Fig. 1(b) shows THz wave intensity as a function of the polarization angle of the incident pump pulse. It is confirmed that the signal is maximized at 0 degree (parallel to polarization direction of the PPLN) and is minimized at 90 degree (perpendicular to the polarization) and is well fitted by cos4(cid:84) ((cid:84): polarization angle). Owing to these results, it is confirmed that the signal detected by the bolometer is THz pulse.
关键词： slant-stripe-type,THz pulse generation,multi-cycled THz pulses,optical rectification effect,PPLN
更新于2025-09-11 14:15:04
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Laser‐Driven Strong‐Field Terahertz Sources
摘要： A review on the recent development of intense laser-driven terahertz (THz) sources is provided here. The technologies discussed include various types of sources based on optical rectification (OR), spintronic emitters, and laser-filament-induced plasma. The emphasis is on OR using pump pulses with tilted intensity front. Illustrative examples of newly emerging applications are briefly discussed, in particular strong-field THz control of materials and acceleration and manipulation of charged particles.
关键词： plasma-based terahertz sources,optical rectification,spintronic emitters,terahertz pulses,strong-field terahertz–matter interactions
更新于2025-09-11 14:15:04