- 标题
- 摘要
- 关键词
- 实验方案
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Effective tuning of isotropic and anisotropic properties of quantum dots and rings by external fields
摘要： The combined effects of intense THz laser field, magnetic field and in-plane electric field on electronic states and intraband optical properties of single isotropic quantum dots and rings are investigated using the non-perturbative Floquet theory in the high-frequency limit. Here we show that the change of the electric field direction for fixed values of intense THz laser field parameter can recover the degeneracy of the excited states and the dipole-allowed transition intensities in a quantum dot. Additionally, it is shown that in isotropic quantum rings the intense THz laser and the in-plane electric field create unusual Aharonov-Bohm oscillations. For fixed values of the intense THz laser field parameter, the amplitudes of Aharonov-Bohm oscillations can be effectively tuned by changing the electric field direction. Furthermore, for fixed values of the electric field strength and the laser field parameter the intraband optical properties can be effectively tuned by changing the electric field direction. Therefore, it can be asserted that circular quantum dots or circular rings in the intense THz laser field are equivalent to anisotropic quantum dots or rings respectively, and the electric field direction effectively tunes the single-electron energy spectrum and intraband optical properties of these structures.
关键词： External electric and magnetic fields,Isotropic and unisotropic properties of QDs and QRs,Intraband optical properties of QDs and QRs,Intense THz laser field
更新于2025-09-12 10:27:22
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Coupled Quantum Wells
摘要： Intersubband transitions in ZnO material systems are predicted to be promising candidates for infrared and terahertz (THz) optoelectronic devices due to their unusual material properties. In particular, the temperature performance of THz quantum cascade lasers is postulated to be significantly enhanced using ZnO material systems due to their large optical phonon energy. Taking a step forward toward that goal, intersubband transitions in ZnO/MgxZn1?xO asymmetric coupled quantum wells are observed on a nonpolar m plane ZnO substrate. Two absorption peaks are observed in the energy range from approximately 250 meV to approximately 410 meV at room temperature, unambiguously demonstrating the interwell coupling in the asymmetric coupled quantum wells. A theoretical model taking into account the interaction between intersubband transitions shows reasonable overall agreement with the experimental results, thus proving the strong coupling nature of the investigated system. As the building block of complex quantum structures based on intersubband transitions, the results presented show great potential applications of ZnO/MgxZn1?xO material systems in infrared and THz optoelectronics and physics.
关键词： intersubband transitions,ZnO,optoelectronics,quantum wells,THz,infrared
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) - THz surface phonon polariton generation in GaP photonic waveguide
摘要： Generation of THz wave using surface phonon polariton and difference frequency generation in GaP stripe is investigated. Here, we present our preliminary results and show that mixing a TE and a TM mid-IR mode propagating along a [100] crystal axis is more efficient than the usual optical configuration along a [110] axis under transverse pump modes for efficient THz generation.
关键词： photonic waveguide,surface phonon polariton,GaP,difference frequency generation,THz
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) - Terahertz Physics of Graphene, Possibly The Most Nonlinear Material We Know
摘要： In this presentation gigantic THz-range optical nonlinearity of graphene will be demonstrated and explained. In particular, nonlinear THz conductivity and saturable absorption, and extremely efficient THz high harmonics generation in graphene will be presented and explained within a framework of a simple thermodynamic model of THz-graphene interaction.
关键词： nonlinearity,high harmonics generation,saturable absorption,THz,graphene
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) - THz response of metallic structures to femtosecond laser pulses
摘要： The talk is devoted to the nonlinear effects in metallic structures (like gratings and nanoparticle arrays) irradiated by femtosecond laser pulses. Possible mechanisms of delayed THz response and specific non-quadratic nonlinear regimes of conversion are analyzed. In contrast to previous models, only low-frequency currents inside the metal are considered without involving electron emission and acceleration. Special attention is paid to the role of plasmonic resonances at optical frequency in the enhancement of low-frequency nonlinear response.
关键词： femtosecond laser pulses,plasmonic resonances,metallic structures,nonlinear effects,THz response
更新于2025-09-12 10:27:22
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Terahertz detection with an antenna-coupled highly-doped silicon quantum dot
摘要： nanostructured dopant-based silicon (Si) transistors are promising candidates for high-performance photodetectors and quantum information devices. For highly doped Si with donor bands, the energy depth of donor levels and the energy required for tunneling processes between donor levels are typically on the order of millielectron volts, corresponding to terahertz (THz) photon energy. Owing to these properties, highly doped Si quantum dots (QDs) are highly attractive as THz photoconductive detectors. Here, we demonstrate THz detection with a lithographically defined and highly phosphorus-doped Si QD. We integrate a 40 nm-diameter QD with a micrometer-scale broadband logarithmic spiral antenna for the detection of THz photocurrent in a wide frequency range from 0.58 to 3.11 THz. Furthermore, we confirm that the detection sensitivity is enhanced by a factor of ~880 compared to a QD detector without an antenna. These results demonstrate the ability of a highly doped-Si QD coupled with an antenna to detect broadband THz waves. By optimizing the dopant distribution and levels, further performance improvements are feasible.
关键词： logarithmic spiral antenna,silicon quantum dot,terahertz detection,broadband THz waves,photoconductive detectors
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) - Temporal Ghost Imaging with Wavelength Conversion
摘要： Ghost imaging is a non-direct measurement technique that uses the correlation between multiple probing patterns and the integrated signal measured after transmission (or reflection) through an object. [1] The resolution of the technique is determined by the characteristic length scale of the probing patterns fluctuations and/or the resolution with which they can be measured. Originally demonstrated in the spatial domain to reconstruct images of real physical objects, ghost imaging has been recently extended to the time-domain to measure ultrafast signals at telecom wavelengths [2]. In this work, we experimentally demonstrate ultrafast ghost imaging in the time-domain where the correlated intensities have completely different wavelengths. This wavelength-conversion temporal ghost-imaging scheme exploits fully the benefit of ghost imaging opening up new possibilities for ultrafast imaging in spectral regions where sensitive and/or fast detectors are not available and in particular the mid-infrared or THz range.
关键词： temporal domain,mid-infrared,ultrafast imaging,Ghost imaging,wavelength conversion,THz range
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) - Numerical Simulations of THz Generation with two-Color Mid-Infrared Laser Pulse and Relative Phase Control
摘要： The generation of terahertz (THz) radiation by two-color laser pulse induced gas plasma is an actively researched topic since its exploration [1]. It is a tabletop, powerful spectroscopic tool in the far-infrared spectral regime. The THz spectroscopy is capable to identify chemicals in a nondestructive way [2]. It is capable to generate THz radiation by remotely more than 100m from the laser system [3], the remote sensing of the THz radiation also possible [4]. By the combination of the former mentioned features, the THz spectroscopy is a powerful tool to identify drugs, poisons and explosives with remotely in a nondestructive way.
关键词： spectroscopy,relative phase control,gas plasma,two-color mid-infrared laser pulse,THz generation
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) - Theoretical Investigation of the Optimal Nonlinear Crystal Thickness for THz Generation from two-Color Laser Pulse Ionized Gas under Different Laser Pulse Parameters
摘要： The generation of terahertz (THz) radiation by two-color laser pulse induced gas plasma is an actively researched topic since its exploration. It is a tabletop, powerful spectroscopic tool in the far-infrared spectral regime. It is possible to generate THz radiation by remotely more than 100m from the laser system, the remote sensing of the THz radiation also possible. Furthermore, the THz spectroscopy is capable to identify chemicals in a nondestructive way. By the combination of the former mentioned features, the THz spectroscopy is a powerful tool to identify drugs, poisons and explosives with remotely in a nondestructive way. One of the drawbacks of the THz radiation generated from two-color laser pulse induced gas plasma is the low efficiency. In the last two decades many publications have been published about increasing the efficiency of this method. Spectrally shaped fundamental beam has been proved to be an effective way to control the generated THz field properties. Using a step phase plate is demonstrated to enhance the generated THz intensity with a factor of two. Combining the fundamental, the second harmonic and the third harmonic beams also increase the THz pulse generation efficiency. Increasing the fundamental laser pulse wavelength has proved to be improve the generation efficiency. In this publication, we examined the nonlinear crystal thickness effect on the THz generation from two-color laser pulse induced gas plasma. It was found the at a given fundamental pulse energy and pulse duration there is an optimal thickness for the nonlinear crystal, where the THz generation is the most effective as seen on Fig. 1. In case of a thinner crystal, than the optimal crystal thickness, the second harmonic generation effectivity decrease, which entails the THz generation effectivity also decrease. In case of thicker crystal, than the optimal crystal thickness, the material dispersion decreases both the fundamental and its second harmonic’s peak power, which entails the THz generation effectivity decrease. The optimal nonlinear crystal thickness was examined in the function of the fundamental laser pulse energy, pulse duration, central wavelength and the nonlinear crystal distance from the focal spot. It was found that all the former mentioned parameters have a great impact on the optimal nonlinear crystal thickness. In conclusion, choosing the proper crystal parameters considering the laser and the setup parameters are a crucial point of the THz generation from two-color laser pulse induced gas plasma.
关键词： optimal thickness,two-color laser pulse,gas plasma,nonlinear crystal thickness,THz generation
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