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Resolving fine spectral features in lattice vibrational modes using femtosecond coherent spectroscopy
摘要： We show resolution of fine spectral features within several Raman active vibrational modes in potassium titanyl phosphate (KTP) crystal. Measurements are performed using a femtosecond time-domain coherent anti-Stokes Raman scattering spectroscopy technique that is capable of delivering equivalent spectral resolution of 0.1 cm?1. The Raman spectra retrieved from our measurements show several spectral components corresponding to vibrations of different symmetry with distinctly different damping rates. In particular, linewidths for unassigned optical phonon mode triplet centered at around 820 cm?1 are found to be 7.5±0.2 cm?1, 9.1±0.3 cm?1, and 11.2±0.3 cm?1. Results of our experiments will ultimately help to design an all-solid-state source for sub-optical-wavelength waveform generation that is based on stimulated Raman scattering.
关键词： damping rates,potassium titanyl phosphate,Raman active vibrational modes,femtosecond coherent spectroscopy,spectral resolution
更新于2025-09-23 15:21:01
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Plasmon-enhanced inelastic scattering by 2D and 3D superlattices made of silver nanocrystals
摘要： The lattice dynamics of natural crystals, artificial superlattices, or self‐organized nanocrystals intimately mix confinement, coupling, periodicity, and dissipative effects. The low wavenumber vibrational response of the new class of nanomaterials called “supercrystals” does contain relevant information concerning finite size effects on atomic movements inside each nanocrystal, mechanical coupling between adjacent nanocrystals, coherent behavior of the total assembly due to its superperiodicity, and finally finite‐time effects due to damping. All these aspects concerning the dynamical behavior of silver supercrystals has been analyzed using plasmon resonance Raman scattering. Owing to the highly uniform size and chemical environment of the nanocrystals, the confinement and homogeneous damping of their fundamental vibrations are carefully analyzed. The signature of their internal atomic arrangements, as a reminiscence of bulk phonons, is also explored. It is shown that for low particles diameter (?5 nm), deviations from the continuum elastic approximation occur and that the vibrational response is more sensitive to atomic arrangements and surface effects inside the nanocrystals than to spatial coherence effects between them.
关键词： atomistic simulations,supercrystals,damping,low wavenumber,metallic nanocrystals
更新于2025-09-23 15:21:01
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[IEEE 2018 International Conference on Optical MEMS and Nanophotonics (OMN) - Lausanne (2018.7.29-2018.8.2)] 2018 International Conference on Optical MEMS and Nanophotonics (OMN) - Selective Infiltration Damping of MEMS Scanning Mirrors
摘要： Quasi-static MEMS scanning mirrors are used for optical beam steering on arbitrary trajectories. They have to provide a broad mechanical bandwidth depending on the desired speed. In this work an approach by passive damping of the MEMS mirrors with gel droplets is described, that allows to increase the usable bandwidth. In order to achieve this, a dielectric gel is dispensed into the mirrors' structure. The appropriate infiltration method is presented. Static and dynamic properties such as maximum tilt angle and frequency response are investigated. Furthermore the reduction of parasitic effects like the coupling of the two axes of the mirror is discussed.
关键词： damping,frequency response,viscoelastic gel,scanning mirror,MEMS
更新于2025-09-23 15:21:01
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[IEEE 2019 International Conference on Optical MEMS and Nanophotonics (OMN) - Daejeon, Korea (South) (2019.7.28-2019.8.1)] 2019 International Conference on Optical MEMS and Nanophotonics (OMN) - Multimodal and Multifunctional Plasmonic Nanostructures and Techniques
摘要： State-space current control enables high dynamic performance of a three-phase grid-connected converter equipped with an LCL filter. In this paper, observer-based state-space control is designed using direct pole placement in the discrete-time domain and in grid-voltage coordinates. Analytical expressions for the controller and observer gains are derived as functions of the physical system parameters and design specifications. The connection between the physical parameters and the control algorithm enables automatic tuning. Parameter sensitivity of the control method is analyzed. The experimental results show that the resonance of the LCL filter is well damped, and the dynamic performance specified by direct pole placement is obtained for the reference tracking and grid-voltage disturbance rejection.
关键词： Active damping,current control,LCL filter,grid-connected converter,parameter sensitivity,sensorless state feedback
更新于2025-09-23 15:19:57
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Quantum correlations of two qubits beyond entanglement in two lossy cavities linked by a waveguide
摘要： We explore the quantum correlations (QCs) of two non-interacting two-level systems (qubits). Each qubit is embedded in an open cavity, the cavities are linked by an optical fiber and leak photons to the external environment. The quantum correlations are investigated via three different quantifiers (measurement-induced nonlocality, geometric quantum discord and negativity) under the effects of the coupling of the qubit-cavity and the fiber-cavity interactions as well as the cavity dissipations. It is found that the generation of QCs and their sudden birth and death phenomena, depend not only on the qubit-cavity and fiber-cavity couplings, but also on the initial states. The robustness of the QCs against the cavity dissipations can be enhanced in the regime of the ultra-strong cavity-fiber coupling. We convey that it is possible to control the quantum correlations, as well as to reduce the effect of cavity dissipation.
关键词： Non-local correlations,Cavity damping,Optical fiber
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Full-mode analysis of the plasmon oscillations of 2D electron gas subjected to electric field
摘要： Plasmon dispersion law including wave vector dependencies of the oscillation frequency, !′(q), and the damping !′′(q) of 2D electron gas subjected to the steady-state electric field were analyzed in the frameworks of general kinetic theory of collisionless plasma. Two particular cases of ungated and gated 2D electron gas were considered. We found that the spectra of 2D plasmons have the following peculiarities: multi-branched character, strong dependence of Landau damping vs dielectric surrounding of 2D gas, the strong non-reciprocal dispersion with respect to the direction of electron drift, existence of an extended instability range of wave vectors where plasmons propagating along the electron drift have essential increment of oscillations, !′′>0. Also, the effect of the mode interaction under applied field was identified.
关键词： plasmon instability,THz plasmonics,non-reciprocity,Landau damping
更新于2025-09-23 15:19:57
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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) - Enhancement of EQE for MBE grown InAs/GaAs Quantum Dot Solar Cell with Back Reflector
摘要： The human ankle joint plays a critical role during walking and understanding the biomechanical factors that govern ankle behavior and provides fundamental insight into normal and pathologically altered gait. Previous researchers have comprehensively studied ankle joint kinetics and kinematics during many biomechanical tasks, including locomotion; however, only recently have researchers been able to quantify how the mechanical impedance of the ankle varies during walking. The mechanical impedance describes the dynamic relationship between the joint position and the joint torque during perturbation, and is often represented in terms of stiffness, damping, and inertia. The purpose of this short communication is to unify the results of the first two studies measuring ankle mechanical impedance in the sagittal plane during walking, where each study investigated differing regions of the gait cycle. Rouse et al. measured ankle impedance from late loading response to terminal stance, where Lee et al. quantified ankle impedance from pre-swing to early loading response. While stiffness component of impedance increases significantly as the stance phase of walking progressed, the change in damping during the gait cycle is much less than the changes observed in stiffness. In addition, both stiffness and damping remained low during the swing phase of walking. Future work will focus on quantifying impedance during the "push off" region of stance phase, as well as measurement of these properties in the coronal plane.
关键词： Human ankle,ankle impedance,ankle damping,ankle stiffness
更新于2025-09-23 15:19:57
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Generalized Rayleigh surface waves in a piezoelectric semiconductor half space
摘要： In this paper, plane strain surface waves, also named generalized Rayleigh surface waves, in a transversely isotropic piezoelectric semiconductor half space are investigated. The governing equations of generalized Rayleigh surface waves include the equations of motion, Gauss’ law of electrostatics and the conservation of charge. Based on the basic theory of elastic-dynamic equations, the governing equations are deduced as equations related to the displacement, the electric potential and the perturbation of the carrier density and are solved analytically. We discuss dispersion curves and the attenuation tendency of generalized Rayleigh waves for real wave number cases. The results reveal that the semiconductor should lead to phase velocity decreasing, and the anomalous dispersion and damping of generalized Rayleigh waves. However, enough in-plane biasing electric field along the wave propagation should lead to the amplification of the waves. The influence of the out-plane biasing electric field is so slight that it can be omitted. These properties should be reproduced in the case of real frequencies. The results obtained may provide theoretical guidance for the design of high-performance surface acoustic wave devices made of piezoelectric semiconductors.
关键词： Damping,Piezoelectric semiconductor,Generalized Rayleigh surface,Biasing electric field
更新于2025-09-19 17:15:36
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Hot carriers generated by plasmons: where are they are generated and where do they go from there?
摘要： A physically transparent unified theory of optically and plasmon-induced hot carrier generation in metals is developed with all the relevant mechanisms included. Analytical expressions that estimate the carrier generation rates, their locations, energies and directions of motion are obtained. Among four mechanisms considered: interband absorption, phonon and defect assisted absorption, electron-electron scattering assisted absorption, and surface –collision assisted absorption (Landau damping), it is the last one that generates hot carriers which are most useful for practical applications in photo detection and photo catalysis.
关键词： plasmons,Landau damping,photo detection,hot carriers,absorption mechanisms,photo catalysis
更新于2025-09-19 17:15:36
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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) - The Journey from Manipulating Single Quantum Systems to Quantum Information Processing
摘要： The quality factor of a resonator represents the decay of vibrational energy over time, and is directly related to the frequency response and other key parameters that determine performance of inertial sensors and oscillators. Accurate prediction of the quality factor is essential for designing high-performance microelectromechanical (MEMS) devices. Several to the quality factor. Due to computational complexity, highly simplified models for the dominant dissipation mechanism, such as Zener’s model for thermoelastic dissipation (TED), are often the intuition provided by these models employed. However, is inadequate to predict the quality factor of more complex designs and can be highly misleading. In this paper, we construct complete, quantitative, and predictive models with finite-element methods for the intrinsic energy dissipation mechanisms in MEMS resonators using full anisotropic representation of crystalline silicon and the temperature dependence of all parameters. We find that TED is often a more significant source of damping than has been assumed, because of the previously neglected role of crystalline anisotropy and small geometric features, such as etch release holes—all of which can now be included in practical models. We show that these models, along with simpler scaling models for extrinsic dissipation mechanisms, explain measurements of quality factor in diverse sets of MEMS resonators with unprecedented accuracy.
关键词： internal friction,frequency response,micromechanical resonators,microelectromechanical devices,thermal-mechanical coupling,thermoelastic dissipation,geometry,resonance,systems,Capacitive sensors,damping,energy dissipation,frequency-domain analysis
更新于2025-09-19 17:13:59