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Ultrafast electron-lattice thermalization in copper and other noble metal nanoparticles
摘要： Using time-resolved ultrafast pump-probe spectroscopy we investigated the electron-lattice energy transfer in small copper nanospheres with diameters ranging from 3.2 to 23 nm, either embedded in a glass or dispersed in a solvent. Electron-lattice scattering rate is shown to increase with size reduction, in agreement with our previous results obtained on gold and silver nanoparticles in the low excitation regime. We attribute this effect to the reduction of the screening efficiency of electron–phonon interactions close to the nanoparticle surface. To understand the discrepancy between the results on the electron-lattice scattering in different metals reported in the literature (reduction, no dependence or increase with nanoparticle size), we discuss the experimental conditions required for the accurate determination of electron-lattice energy transfer time from time-resolved investigations in the weak and strong excitation regimes and present power-dependent experiments on gold nanospheres in solution. Our findings are derived from a theoretical analysis based on the two-temperature model predictions and on a complete modeling of the nanoparticle transient extinction cross-section through the resolution of Boltzmann equation in the presence of hot electrons.
关键词： pump-probe spectroscopy,copper nanoparticles,electron-lattice interactions,two-temperature model,ultrafast electron dynamics
更新于2025-09-23 15:23:52
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Numerical stability of time-dependent coupled-cluster methods for many-electron dynamics in intense laser pulses
摘要： We investigate the numerical stability of time-dependent coupled-cluster theory for many-electron dynamics in intense laser pulses, comparing two coupled-cluster formulations with full configuration interaction theory. Our numerical experiments show that orbital-adaptive time-dependent coupled-cluster doubles (OATDCCD) theory offers significantly improved stability compared with the conventional Hartree-Fock-based time-dependent coupled-cluster singles-and-doubles (TDCCSD) formulation. The improved stability stems from greatly reduced oscillations in the doubles amplitudes, which, in turn, can be traced to the dynamic biorthonormal reference determinants of OATDCCD theory. As long as these are good approximations to the Brueckner determinant, OATDCCD theory is numerically stable. We propose the reference weight as a diagnostic quantity to identify situations where the TDCCSD and OATDCCD theories become unstable.
关键词： time-dependent coupled-cluster theory,OATDCCD,Brueckner determinant,TDCCSD,intense laser pulses,numerical stability,many-electron dynamics
更新于2025-09-23 15:21:01
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Gain of electron orbital angular momentum in a direct laser acceleration process
摘要： Three-dimensional “particle in cell” simulations show that a quasistatic magnetic ?eld can be generated in a plasma irradiated by a linearly polarized Laguerre-Gauss beam with a nonzero orbital angular momentum (OAM). Perturbative analysis of the electron dynamics in the low intensity limit and detailed numerical analysis predict a laser to electrons OAM transfer. Plasma electrons gain angular velocity thanks to the dephasing process induced by the combined action of the ponderomotive force and the laser induced–radial oscillation. Similar to the “direct laser acceleration,” where Gaussian laser beams transmit part of its axial momentum to electrons, Laguerre-Gaussian beams transfer a part of their orbital angular momentum to electrons through the dephasing process.
关键词： orbital angular momentum,electron dynamics,magnetic field generation,Laguerre-Gauss beam,plasma
更新于2025-09-23 15:21:01
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Attosecond transient-absorption spectroscopy of polar molecules
摘要： We apply attosecond transient absorption spectroscopy (ATAS) to explore the effects of a nonzero permanent dipole on electron dynamics at the subfemtosecond scale, exemplified in the polar LiF molecule. In contrast with nonpolar systems, a familiar feature of the ATA spectra—the light-induced structures—are observed adjacent to a bright state. Moreover, a previously unobserved ladder structure is identified. The observations are analyzed in the context of a model based on fixed-nuclei adiabatic states, supported by full numerical simulations. Analytic calculations originating in the adiabatic model shed light on the nature and origins of the findings.
关键词： LiF molecule,attosecond transient absorption spectroscopy,electron dynamics,polar molecules,ladder structure,light-induced structures
更新于2025-09-23 15:21:01
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Electron dynamics in low pressure capacitively coupled radio frequency discharges
摘要： In low temperature plasmas, the interaction of the electrons with the electric field is an important current research topic that is relevant for many applications. Particularly, in the low pressure regime ((cid:1)10 Pa), electrons can traverse a distance that may be comparable to the reactor dimensions without any collisions. This causes “nonlocal,” dynamics which results in a complicated space- and time-dependence and a strong anisotropy of the distribution function. Capacitively coupled radio frequency (CCRF) discharges, which operate in this regime, exhibit extremely complex electron dynamics. This is because the electrons interact with the space- and time-dependent electric field, which arises in the plasma boundary sheaths and oscillates at the applied radio frequency. In this tutorial paper, the fundamental physics of electron dynamics in a low pressure electropositive argon discharge is investigated by means of particle-in-cell/Monte Carlo collisions simulations. The interplay between the fundamental plasma parameters (densities, fields, currents, and temperatures) is explained by analysis (aided by animations) with respect to the spatial and temporal dynamics. Finally, the rendered picture provides an overview of how electrons gain and lose their energy in CCRF discharges.
关键词： low pressure,particle-in-cell/Monte Carlo collisions simulations,electron dynamics,plasma parameters,capacitively coupled radio frequency discharges
更新于2025-09-23 15:21:01
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Electron excitation dynamics in a molecule modeled by valence-bond coupled localized electron wave packets; ????-?????μ?????±???¨é???-??3￠????????????????-????é???-???±èμ·?????¤????????ˉ??1;
摘要： A simple model of localized electron wave packets, floating and breathing Gaussians with non-orthogonal valence-bond spin-coupling, is demonstrated to produce an accurate high-harmonic generation (HHG) spectrum from an LiH molecule induced by an intense laser pulse. In contrast with the conventional molecular orbital picture in which the Li 2s and H 1s atomic orbitals are strongly mixed in the valence σ bonding orbital, the present calculation indicates that a superposition of independent responses of the electrons reproduces the spectrum in which the contribution of the H 1s electron dominates the characteristic plateau and cut-off of HHG.
关键词： High-harmonic generation,Electron dynamics,Valence-bond theory,Localized wave-packets
更新于2025-09-23 15:19:57
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Attosecond imaging of molecules using high harmonic spectroscopy
摘要： The availability of attosecond-duration extreme ultraviolet or soft X-ray light sources has opened up new fields of research in atomic and molecular physics. These pulses can be as short as 50 as, fast enough to freeze the motion of electrons within molecules, to resolve how electrons rearrange themselves after the removal of an electron and to study electron–electron correlations. Gas-phase molecules can be aligned in space using short laser pulses, permitting the measurement of molecular parameters in the molecular frame. Aligned molecules can be photoionized using a train of attosecond pulses, enabling the complete characterization of the partial waves making up the photoelectron angular distributions. Using a recolliding electron in the high harmonic process allows complex transition dipole matrix elements to be recorded (including their amplitude and phase) in the molecular frame. High harmonic spectroscopy makes it possible to image molecular orbitals and for unimolecular chemical reactions to be followed with femtosecond resolution. For example, the behaviour around conical intersections can be probed. Charge migration within molecules can be observed with sub-femtosecond resolution.
关键词： high harmonic spectroscopy,electron dynamics,charge migration,molecular orbitals,attosecond imaging
更新于2025-09-19 17:15:36
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Stimulated resonant inelastic x-ray scattering with chirped, broadband pulses
摘要： We present an approach for initiating and tracing ultrafast electron dynamics in core-excited atoms, molecules, and solids. The approach is based on stimulated resonant inelastic x-ray scattering induced by a single, chirped, broadband XUV or x-ray pulse. A first interaction with this pulse prepares a core-excited state wave packet by resonant core-excitation. A second interaction with the pulse at a later time induces the transition to valence-excited states, which is associated with stimulated emission. The preparation of the core-excited wave packet and the transition from the core-excited states to the valence-excited states occur at distinct chirp-dependent times. As a consequence, the stimulated emission carries information about the time evolution of the core-excited state wave packet.
关键词： XUV pulses,x-ray pulses,core-excited states,ultrafast electron dynamics,chirped pulses,stimulated resonant inelastic x-ray scattering
更新于2025-09-19 17:15:36
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[IEEE 2019 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization (NEMO) - Boston, MA, USA (2019.5.29-2019.5.31)] 2019 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization (NEMO) - A New Multipactor Effect Model for Dielectric-Loaded Rectangular Waveguides
摘要： Multipactor is an electron discharge that may appear in particle accelerators and microwave devices such as filters, multiplexers, and RF satellite payloads in satellite on-board equipment under vacuum conditions. When some resonance conditions are satisfied, secondary electrons get synchronized with the RF fields, and the electron population inside the device grows exponentially leading to a multipactor discharge. This multipactor discharge has some negative effects that degrade the device performance: increase of signal noise and reflected the device walls, outgassing, detuning of power, heating of resonant cavities, and even the partial or total destruction of the component. The main aim of this investigation is to show a new model for the analysis of multipactor effect in partially dielectric-loaded rectangular waveguides. For this purpose, a CAD software has been developed which allows the simulation and design of these structures out of the operation points in which this undesired multipactor effect occurs, including the main factors that drive it.
关键词： secondary emision yield,Dielectric-loaded rectangular waveguide,multipactor,electron dynamics
更新于2025-09-16 10:30:52
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Controlling circularly polarized high-order harmonic generation in molecules by intense tricircular laser pulses
摘要： We present a scheme to control circularly polarized high-order harmonic generation (HHG) in molecules, the source of extreme ultraviolet and x-ray pulses, by multiple frequency co- and counter-rotating circularly polarized laser pulses. Simulations are performed on the oriented single electron molecular ions with cyclic equilateral geometry, H2+ 3 , as benchmark models, by numerically solving time-dependent Schr?dinger equations. Results show that circularly polarized HHG can be produced with extended harmonic order cutoffs, which depend on the intensity ratio of ?elds and the ?eld-molecule symmetry. We describe the laser induced electron dynamics in a rotating frame to examine recollision dynamics and Coriolis effects. The resulting modulation of HHG spectra arises from a combination of two bicircular ?elds with counter-rotating and co-rotating components. It is also found that harmonic polarization is a function of the pulse frequencies and helicities, illustrating the importance of matching the ?eld-molecule symmetry. The results in principle illustrate a method for controlling circular polarization properties of harmonics in molecules.
关键词： tricircular laser pulses,molecules,electron dynamics,high-order harmonic generation,circularly polarized
更新于2025-09-16 10:30:52