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[IEEE 2019 Workshop on Recent Advances in Photonics (WRAP) - Guwahati, India (2019.12.13-2019.12.14)] 2019 Workshop on Recent Advances in Photonics (WRAP) - Effect of M <sup>2</sup> parameter of the fiber and the laser on the efficiency of coupling between them
摘要： We present a study on the dependence of coupling efficiency between an optical fiber and a laser on their M2 factors viz. Mf2 and M2, respectively. It is observed that the coupling efficiency is maximum for M2/ Mf2 < 1. This gives a fair idea for selection of optical fibers in coupling laser beams to optical fibers.
关键词： mode mixer,coupling efficiency,M2 factor,Optical fiber,knife edge method
更新于2025-09-23 15:21:01
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Split-off states in tunnel-coupled semiconductor heterostructures for ultrafast modulation of spin and optical polarization
摘要： We present a theoretical analysis of the split-off states emerging due to a tunnel coupling between a remote bound state and a semiconductor quantum well (QW). The on-site Coulomb repulsion and the spin splitting of the bound state have been considered. The split-off states emerge in the band gap of the QW and reveal themselves as two solitary peaks in the photoluminescence (PL) from the QW. The peaks have opposite circular polarization and their spectral position strongly depends on the tunnel coupling strength. We suggest a mechanism of ultrafast PL polarization switching by means of electrical modulation of the tunnel coupling by an external gate. The obtained results open a new possibility for the spin and optical polarization control in nanoscale systems.
关键词： split-off states,photoluminescence,optical polarization,semiconductor heterostructures,tunnel coupling,spin polarization
更新于2025-09-23 15:21:01
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Intermolecular vibrational energy transfer enabled by microcavity strong lighta??matter coupling
摘要： Selective vibrational energy transfer between molecules in the liquid phase, a difficult process hampered by weak intermolecular forces, is achieved through polaritons formed by strong coupling between cavity photon modes and donor and acceptor molecules. Using pump-probe and two-dimensional infrared spectroscopy, we found that the excitation of the upper polariton, which is composed mostly of donors, can efficiently relax to the acceptors within ~5 picoseconds. The energy-transfer efficiency can be further enhanced by increasing the cavity lifetime, suggesting that the energy transfer is a polaritonic process. This vibrational energy-transfer pathway opens doors for applications in remote chemistry, sensing mechanisms, and vibrational polariton condensation.
关键词： intermolecular interactions,strong light–matter coupling,polaritons,microcavity,vibrational energy transfer
更新于2025-09-23 15:21:01
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Numerical Modeling of Acousto-Plasmonic Coupling in Metallic Nanoparticles
摘要： We describe a computational approach to study the acousto-plasmonic coupling in metallic nanoparticles. We use the high level multiphysics finite element software FreeFEM developed at Laboratoire Jacques-Louis Lions of Pierre and Marie Curie University (Paris). Our numerical method determines one after the other the acoustic modes of the nanoparticles and the modulation of the electromagnetic properties. The transfer of the deformed geometries between acoustic and electromagnetic simulations is realized by an update of the nodal coordinates situated at the boundary between the nanoparticle and its host medium, and using a mesh deformation algorithm based on radial basis function interpolation. Thus we theoretically investigate different coupling mechanisms between confined vibrations and surface plasmons: shape effect, electron density effect due to changes of the nanoparticle volume and inter-band transitions effect which is evaluated by the deformation potential mechanism.
关键词： acousto-plasmonic coupling,radial basis function interpolation,FreeFEM,finite element method,metallic nanoparticles
更新于2025-09-23 15:21:01
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Slow photoelectron velocity-map imaging of cold C7? and C9?
摘要： High-resolution anion photoelectron spectra of cryogenically cooled C7? and C9? clusters obtained using slow photoelectron velocity-map imaging are presented, providing insight into the vibronic structure of neutral C7 and C9. These spectra yield accurate measurements of vibrational frequencies for the neutral clusters as well as electron affinities of 3.3517(4) and 3.6766(14) eV for C7 and C9, respectively. In the C7? spectrum, transitions involving the previously unreported v1 and v2 symmetric stretching modes, as well as the v9, v10, and v11 asymmetric bending modes, are assigned. Spin–orbit splitting is observed for several transitions in this spectrum, giving an energy difference of 28(6) cm?1 between the 2Π1/2g and 2Π3/2g spin–orbit levels of the C7? anion. In the spectrum of C9?, transitions involving the previously unreported symmetric stretch v1 and the asymmetric bend v11 are observed. In both spectra, several features are assigned to Franck-Condon forbidden transitions involving the doubly degenerate v10 and v11 modes of C7 and the v13 and v14 modes of C9. The appearance of these transitions is attributed to Herzberg-Teller coupling between the electronic states of the neutral clusters. Additional FC-forbidden transitions to states previously observed in gas-phase infrared experiments are observed and attributed to vibronic coupling between the electronic states of the anion, resulting in non-totally symmetric character in the anion’s full vibrational ground state. Finally, consideration of the energy dependence of detachment cross sections and Dyson orbital analyses reveal that addition of more carbon atoms to the linear chain results in photodetachment from delocalized molecular orbitals with increasing nodal structure, leading to threshold photodetachment cross sections that differ considerably from simple symmetry considerations.
关键词： Herzberg-Teller coupling,Franck-Condon forbidden transitions,anion photoelectron spectroscopy,vibronic structure,carbon clusters,slow photoelectron velocity-map imaging
更新于2025-09-23 15:21:01
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Biaryl Crossa??Coupling Enabled by Photoa??Induced Electron Transfer
摘要： We report a protocol for aryl cross-coupling of electron-deficient aryl halides with electron-rich (hetero)arenes that is driven solely by violet light. This process takes advantage of formation of photo-excited state of electron-deficient aryl halides, that are reduced by electron-rich (hetero)arenes to form a pair of aryl anion and cation radicals. The resulting aryl anion radicals of aryl halides undergo mesolysis of the carbon-halogen bond to generate aryl radicals, that are coupled most likely with aryl cation radicals to afford functionalized biaryls.
关键词： Single-electron-transfer,Visible light,Anion radicals,Aryl radicals,Cross-coupling
更新于2025-09-23 15:21:01
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<i>Ab Initio</i> Spin-Strain Coupling Parameters of Divacancy Qubits in Silicon Carbide
摘要： Cubic silicon carbide is an excellent platform for integration of defect qubits into established wafer-scale device architectures for quantum information and sensing applications, where a divacancy qubit, which is similar to the negatively charged nitrogen-vacancy (NV) center in diamond, has favorable coherence properties. We demonstrate by means of density-functional-theory calculations that for most types of distortion the 3C divacancy exhibits slightly smaller spin-strain coupling parameters but greater spin-stress coupling parameters in comparison with the diamond NV. We predict that high-quality 3C-SiC thin films hosting divacancy qubits are prospective platforms for quantum-enhanced pressure-sensor devices.
关键词： spin-strain coupling,quantum sensing,density-functional theory,divacancy qubits,silicon carbide
更新于2025-09-23 15:21:01
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Propulsion effects after laser ablation in water, confined by different geometries
摘要： A Nd:YAG laser with 7-ns pulses and pulse energies up to 10 mJ is used to induce an optical breakdown in the front surface of an aluminum rod, covered by a water layer. The rod is part of a ballistic pendulum. In this way, we study the propulsion effects by means of coupling coefficient and energy-conversion efficiency with respect to different confining geometries, volumes of water applied to the front surface of the rod, and the distance of this surface from the laser-beam focus. Holes with different dimensions are drilled on the target surface and filled with different volumes of water to examine the influence of the confinement by the liquid (a free boundary) and a solid-surface geometry on laser ablation effects. The rod movement and the water ejection after laser ablation are acquired by a high-speed camera with 10k frames per second. The results show that the confinement by cavity substantially increases the propulsion effects by shaping the ejected flow of the liquid; while the cavitation bubble, induced inside the water layer, plays a significant role in propulsion efficiency. From the presented results, it follows that the laser-propelled rod carries below 0.5% of the total mechanical energy after propulsion, while the rest of this energy represents the kinetic energy of the ablated water. As expected, moving the target surface away from the focal position decreases the ablative-propulsion efficiency. When the focus is moved inside the solid target, the decrease occurs due to lower conversion of the pulse energy into the energy of the cavitation bubble. If the focus is moved from the surface outward, the bubble moves towards the liquid–gas interface and it is not able to efficiently eject all the liquid from the target.
关键词： Cavitation bubble,Coupling coefficient,Laser propulsion,Nanosecond laser,Energy-conversion efficiency,Laser ablation
更新于2025-09-23 15:21:01
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[IEEE 2020 IEEE International Conference on Power Electronics, Smart Grid and Renewable Energy (PESGRE) - Cochin, India (2020.1.2-2020.1.4)] 2020 IEEE International Conference on Power Electronics, Smart Grid and Renewable Energy (PESGRE2020) - Power Optimized Architecture based Converter and Its Control for Single Phase Grid-Tied Solar Photovoltaic System
摘要： This paper proposes a power optimized based converter and its control for low voltage solar photovoltaic (PV) modules. For the grid tied solar PV system, the dc-bus voltage must be maintained more than a minimum level for its satisfactory working. In optimized architecture, each PV module is connected with a non isolated high gain DC-DC converter. These converters boost up the PV voltage as well as harvest the maximum solar energy. In the case of shadow, aging and fast change in solar insolation profile on each PV modules; it is able to harvest the maximum power. For maximum power harvesting, fuzzy logic control (FLC) is used. Each PV module with high gain DC-DC converter is connected at the common DC link. The DC power is converted into AC power by using voltage source Inverter (VSI). The VSC is controlled to stabilize dc-link voltage, synchronize with grid supply and to achieve low total harmonic distortion (THDs) in grid current under feeding non linear loads. For switching of a VSC, hysteresis control is used. Proposed model is developed using MATLAB 2015a and results are obtained under various operating conditions.
关键词： single phase grid,voltage source inverter (VSI),DC-DC converter,photovoltaic (PV) system,point of common coupling (PCC),high gain,maximum power harvesting (MPH)
更新于2025-09-23 15:21:01
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A Facile Approach to the Synthesis of n-Type π-Conjugated Hyperbranched Polymers
摘要： A facile approach for the synthesis of an n-type π-conjugated hyperbranched polymer, namely hyperbranched polypyridinebenzene, is proposed based on the copolymerization of 1,3,5-tribromobenzene (BeBr3) and 2,5-dibromopyridine via chain-growth condensation polymerization catalyzed by Ni(dppp)Cl2. The use of BeBr3 as a branching unit simplifies the synthesis of n-type π-conjugated hyperbranched polymers, compared with a similar hyperbranched polymer prepared from 2,4,6-tribromopyridine (PyBr3) and 2,5-dibromopyridine requiring a lengthy synthetic route to give the starting material PyBr3. The results of UV-Vis spectroscopy and cyclic voltammetry suggest that our synthesized polymer retains its hyperbranched structure, which is beneficial in electrochemical doping.
关键词： Cross-coupling,Doping,Polypyridine,Chain-growth condensation
更新于2025-09-23 15:21:01