Showing papers on "Free electron model published in 2013"
TL;DR: The findings underscore, in agreement with recent studies of more esoteric soft matter systems, the prevalence of non-Gaussian yet Fickian diffusion in simple colloidal suspension with hard-sphere interactions.
Abstract: We show that free electrons can efficiently excite plasmons in doped graphene with probabilities of order one per electron. More precisely, we predict multiple excitations of a single confined plasmon mode in graphene nanostructures. These unprecedentedly large electron-plasmon couplings are explained using a simple scaling law and further investigated through a general quantum description of the electron-plasmon interaction. From a fundamental viewpoint, multiple plasmon excitations by a single electron provides a unique tool for exploring the bosonic quantum nature of these collective modes. Our study does not only open a viable path towards multiple excitation of a single plasmon mode by single electrons, but it also reveals graphene nanostructures as ideal systems for producing, detecting, and manipulating plasmons using electron probes.
121 citations
TL;DR: Angle-resolved photoemission spectroscopy reveals the presence of a two-dimensional electron gas at the surface of In(2)O(3)(111) and quantized subband states arise within a confining potential well associated with surface electron accumulation.
Abstract: Angle-resolved photoemission spectroscopy reveals the presence of a two-dimensional electron gas at the surface of ${\mathrm{In}}_{2}{\mathrm{O}}_{3}(111)$. Quantized subband states arise within a confining potential well associated with surface electron accumulation. Coupled Poisson-Schr\"odinger calculations suggest that downward band bending for the conduction band must be much bigger than band bending in the valence band. Surface oxygen vacancies acting as doubly ionized shallow donors are shown to provide the free electrons within this accumulation layer. Identification of the origin of electron accumulation in transparent conducting oxides has significant implications in the realization of devices based on these compounds.
92 citations
TL;DR: In this article, the authors show that free electrons can efficiently excite plasmons in doped graphene with probabilities in the order of one per electron and predict multiple excitations of a single plasmon mode in graphene nanostructures.
Abstract: We show that free electrons can efficiently excite plasmons in doped graphene with probabilities in the order of one per electron. More precisely, we predict multiple excitations of a single confined plasmon mode in graphene nanostructures. These unprecedentedly large electron-plasmon couplings are explained using a simple scaling law and further investigated through a general quantum description of the electron–plasmon interaction. From a fundamental viewpoint, multiple plasmon excitations by a single electron provide a unique platform for exploring the bosonic quantum nature of these collective modes. Not only does our study open a viable path toward multiple excitation of a single plasmon mode by a single electron, but it also reveals electron probes as ideal tools for producing, detecting, and manipulating plasmons in graphene nanostructures.
86 citations
TL;DR: It is demonstrated that the achieved quantum yield is high enough for use in rf photoinjectors operating as electron sources for MHz repetition rate x-ray free electron lasers.
Abstract: In this Letter, we report on the efficient generation of electrons from metals using multiphoton photoemission by use of nanostructured plasmonic surfaces to trap, localize, and enhance optical fields. The plasmonic surface increases absorption over normal metals by more than an order of magnitude, and due to the localization of fields, this results in over 6 orders of magnitude increase in effective nonlinear quantum yield. We demonstrate that the achieved quantum yield is high enough for use in rf photoinjectors operating as electron sources for MHz repetition rate x-ray free electron lasers.
81 citations
TL;DR: In this article, a physical model of the wave normal angle distribution along a field line is presented, which provides insight on how the wave norm distribution varies as chorus waves propagate away from the equatorial source region.
Abstract: [1] The propagation and attenuation characteristics of lower band and upper band chorus waves are investigated by ray tracing, and the evaluation of Landau damping based on an empirical suprathermal electron model derived from Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. The rate of Landau damping is found to increase at larger L-shell, for more oblique wave normal angles, and for higher geomagnetic activity. Damping is also larger on the nightside than on the dayside and is more pronounced in the upper band than in the lower band. These features can account for the statistical pattern of chorus waves observed away from the equatorial source region. A physical model of the wave normal angle distribution along a field line is presented, which provides insight on how the wave normal angle distribution varies as chorus waves propagate away from the equatorial source region. Our modeling shows that wave emissions at low latitudes (λ ≲ 30°) come predominately from the equatorial source at the same L-shell and that their wave normal angles increase with increasing latitude due to wave refraction caused by magnetic gradients and curvature. However, at high latitudes (λ ≳ 30°), the wave normal angle distribution along a particular field line is affected by chorus waves that arrive from an equatorial source at lower L because of significant cross-L propagation. As a consequence, the lower band wave normal angle tends to decrease with increasing latitudes, while the upper band wave normal angle can either increase or decrease depending on the equatorial source at lower L. The effect of cross-L propagation might also explain why observed wave normal angle distribution tends to become more field-aligned at high latitudes. Interestingly, the upper band chorus at such high latitudes originates from lower band waves originating near the equator at lower L. A global model of wave normal variation along a field line constructed in this study is not currently available from observations but is nonetheless critically important for evaluating bounce-averaged diffusion coefficients for future radiation belt modeling.
79 citations
TL;DR: An observation of interference effects in Compton scattering in the experiment held on the VEPP-2000 collider was reported and the explanation, proposed in terms of classical electrodynamics, is in agreement with QED calculations.
Abstract: In this Letter we report an observation of interference effects in Compton scattering in the experiment held on the VEPP-2000 collider. Infrared laser radiation was scattered head-on the 990 MeV electrons inside the dipole magnet, where an electron orbit radius is about 140 cm. It was observed that the energy spectrum of backscattered photons, measured by a HPGe detector, differs from that defined by the Klein-Nishina cross section and scattering kinematics of free electrons. The explanation of the effect, proposed in terms of classical electrodynamics, is in agreement with QED calculations.
59 citations
TL;DR: In this article, the electron self energy in the presence of the surface phonon-mediated electron-electron interaction focusing on how the linear chiral graphene dispersion is renormalized by surface phonons is calculated.
Abstract: We theoretically study various aspects of the electron-surface optical phonon interaction effects in graphene on a substrate made of polar materials. We calculate the electron self energy in the presence of the surface phonon-mediated electron-electron interaction focusing on how the linear chiral graphene dispersion is renormalized by the surface phonons. The electron self energy as well as the quasiparticle spectral function in graphene are calculated, taking into account electron-polar optical phonon interaction by using a many-body perturbative formalism. The scattering rate of free electrons due to polar interaction with surface optical phonons in a dielectric substrate is calculated as a function of the electron energy, temperatures, and carrier density. Effects of screening on the self energy and scattering rate are discussed. Our theory provides a comprehensive quantitative (and qualitative) picture for surface phonon interaction induced many-body effects and hot-electron relaxation in Dirac materials.
52 citations
TL;DR: In this article, the fluid-kinetic hybrid electron model is verified in global gyrokinetic particle simulation of linear electromagnetic drift-Alfvenic instabilities in tokamak.
Abstract: The fluid-kinetic hybrid electron model is verified in global gyrokinetic particle simulation of linear electromagnetic drift-Alfvenic instabilities in tokamak. In particular, we have recovered the β-stabilization of the ion temperature gradient mode, transition to collisionless trapped electron mode, and the onset of kinetic ballooning mode as βe (ratio of electron kinetic pressure to magnetic pressure) increases.
45 citations
TL;DR: Theoretical studies on the atomic and electronic structure of Agn−,0,+ clusters containing up to 15 atoms have been carried out using a gradient corrected density functional formalism as mentioned in this paper.
Abstract: Theoretical studies on the atomic and electronic structure of Agn−,0,+ clusters containing up to 15 atoms have been carried out using a gradient corrected density functional formalism. Our studies indicate that the atomic structures of the clusters undergo a transition from spherical to prolate to oblate shapes as a function of the number of valence electrons. Clusters with a valence count of 8 are shown to be highly stable and their stability is rooted in the filled 1S, 1P shells within a confined spherical nearly free electron gas. Clusters with 14 valence electrons are also shown to be highly stable, but their stability arises due to oblate geometrical distortions that lead to a splitting of the 1D shell with a large HOMO–LUMO gap. The large splitting is shown to account for the observed unusual inertness of these clusters in reactivity with oxygen. The theoretical findings are compared with the observed peaks in the photodetachment spectrum of the anionic species.
36 citations
TL;DR: This novel experimental approach can be employed to characterize the 3dPAD in the laboratory frame as well as in the molecular frame of larger molecules and can be further developed to highly sensitive analytic techniques in the gas phase, for instance for the identification of chiral molecules.
Abstract: We review the generation and tomographic reconstruction of designer electron wave packets, that is, electron wave packets with a tailored momentum distribution in the continuum. Generation is accomplished by means of multiphoton ionization of an atomic prototype using polarization-shaped femtosecond laser pulses. Both the electronic structure of the neutral and interference of matter wave packets in the continuum contribute to the final shape. For the measurement of the resulting threedimensional photoelectron angular distributions (3dPAD) we combine the established technique of velocity map imaging (VMI) with a tomographic reconstruction method. This novel experimental approach can be employed to characterize the 3dPAD in the laboratory frame as well as in the molecular frame of larger molecules. Due to its sensitivity to electronic structure this method can be further developed to highly sensitive analytic techniques in the gas phase, for instance for the identification of chiral molecules.
34 citations
TL;DR: Band gaps and exciton binding energies of undoped and Al-doped ZnO thin films were determined from optical absorption measurement based on the Elliott's exciton absorption theory.
Abstract: Band gaps and exciton binding energies of undoped and Al-doped ZnO thin films were determined from optical absorption measurement based on the Elliott’s exciton absorption theory. As compared to the undoped films, the doped films exhibit a band gap expansion and a reduction in the exciton binding energies due to the free electron screening effect, which suppresses the excitonic absorption and results in a blue shift of the absorption edge. The undoped and doped films show the same quantum size dependence, i.e. both the exciton binding energies and band gap energies increase with decreasing grain size of the oxides.
TL;DR: In this paper, the electronic stopping power of hydrogen and helium ions in Ag and Pt was determined, and the results were compatible with modeling the conduction band as a free electron gas with an energy-dependent effective number of electrons.
Abstract: In recent energy loss measurements, band structure effects in electronic stopping have been observed for materials with finite excitation thresholds, for example, noble metals such as Cu and Au. To further investigate the influence of the position of the $d$ band relative to the Fermi edge, electronic stopping of hydrogen and helium ions in Ag and Pt was determined. For Ag, the electronic stopping power exhibits a velocity dependence similar to Cu and Au. No particular effect due to the comparatively large $d$-band offset in Ag is found. In the case of Pt, the electronic stopping power is virtually velocity proportional for H${}^{+}$ ions and exhibits a distinct velocity dependence for He${}^{+}$ ions. For hydrogen the results are compatible with modeling the conduction band as a free electron gas with an energy-dependent effective number of electrons. For He${}^{+}$, however, the observed effects point towards an additional energy loss mechanism, e.g., by charge-exchange processes.
TL;DR: In this paper, optical absorption of Mg-doped AlInGaN layers using excitationposition dependent and polarization resolved photoluminescence from the slab-waveguide edge of a laser structure was studied.
Abstract: We studied optical absorption of Mg-doped AlInGaN layers using excitation-position dependent and polarization resolved photoluminescence from the slab-waveguide edge of a laser structure. The major absorption in the Mg-doped layers was found only when p-doping is activated. It increases with the removal of residual hydrogen, which in case of Mg doping is a p-type passivation impurity, and reversibly disappears after passivation by hydrogen. This absorption is weakly wavelength and temperature dependent, and isotropic. This can be attributed to acceptor-bound hole absorption, because those holes concentration is nearly equal to that of activated acceptors and weakly temperature dependent (unlike the free hole concentration, which is much lower and is an exponential function of temperature due to high ionization energy). The cross section of photon absorption on such activated acceptor was quantified to be in the order of 10−17 cm−2. The absorption cross section of free electrons was found to be at least one order of magnitude lower and below detection limit. The same technique was used to experimentally quantify band structure polarization components along basis directions for green InGaN quantum wells (QWs) grown on c- and semipolar planes. The A1 and B1 valence subbands of c-plane QW were found to comprise mostly |X⟩ and |Y⟩ states. There was rather minor amount of |Z⟩ states with average square fraction of only 0.02. In (20-21) plane, due to small band anticrossing near gamma-point, we observed highly polarized absorption edges of A1- and B1-subbands consisting mainly of |Y⟩ and |X⟩ states, respectively, and found their energy splitting to be ∼40 meV. For (11-22) plane with smaller band splitting and polarization, we observed polarization switching with indium (In) concentration greater than 30% in the QW (or photon energy less than 2.3 eV). We confirmed our study of valence band structures by optical gain measurements.
TL;DR: In this article, the contribution of free and bound electrons to the complex dielectric function of spherical silver NPs and their influence on the optical extinction spectra were analyzed, and the results obtained from the optimum fit are: Kbulk?=?2???1024 (coefficient for bound-electron contribution), Eg? =?1.91?eV (gap energy), EF?=?"4.12?ev (Fermi energy), and?b?=?1.5???1014?Hz (damping constant for bound electrons).
Abstract: The study of metal nanoparticles (NPs) is of great interest due to their ability to enhance optical fields on the nanometric scale, which makes them interesting for various applications in several fields of science and technology. In particular, their optical properties depend on the dielectric function of the metal, its size, shape and surrounding environment.This work analyses the contributions of free and bound electrons to the complex dielectric function of spherical silver NPs and their influence on the optical extinction spectra. The contribution of free electrons is usually corrected for particle size under 10?nm, introducing a modification of the damping constant to account for the extra collisions with the particle's boundary.For the contribution of bound electrons, we considered the interband transitions from the d-band to the conduction band including the size dependence of the electronic density states for radii below 2?nm. Bearing in mind these specific modifications, it was possible to determine optical and band energy parameters by fitting the bulk complex dielectric function. The results obtained from the optimum fit are: Kbulk?=?2???1024 (coefficient for bound-electron contribution), Eg?=?1.91?eV (gap energy), EF?=?4.12?eV (Fermi energy), and ?b?=?1.5???1014?Hz (damping constant for bound electrons).Based on this size-dependent dielectric function, extinction spectra of silver particles in the nanometric?subnanometric radius range can be calculated using Mie's theory, and its size behaviour analysed. These studies are applied to fit experimental extinction spectrum of very small spherical particles fabricated by fs laser ablation of a solid target in water. From the fitting, the structure and size distribution of core radius and shell thickness of the colloidal suspension could be determined. The spectroscopic results suggest that the colloidal suspension is composed by two types of structures: bare core and core?shell. The former is composed by Ag, while the latter is composed by two species: silver?silver oxide (Ag?Ag2O) and hollow silver (air?Ag) particles. High-resolution transmission microscopy and atomic force microscopy analysis performed on the dried suspension agree with the sizing obtained by optical extinction spectroscopy, showing that the latter is a very good complementary technique to standard microscopy methods.
TL;DR: In this paper, the effect of preexisting air plasma was investigated using two optical geometries: collinear and orthogonal pumping geometry, and possible mechanisms of the results were discussed in terms of the dynamics of free electrons in the air plasma.
Abstract: Terahertz (THz) wave generation process in air plasma was studied using femtosecond laser pulse pairs. The effect of preexisting air plasma was investigated using two optical geometries: collinear and orthogonal pumping geometry. When the air plasma is excited in collinear geometry, the power of the generated THz wave shows asymmetric dependence on the relative delay of these pulses. The asymmetry depends on the relative intensities of these pump pulses, and it disappears when the pulses have equal intensities. In the orthogonal pumping geometry, the power of the THZ wave generated by the main pump pulse decreases in the presence of the preexisting plasma generated by the prepulse, and it recovers as the relative delay between the prepulse and main pulses becomes longer. Possible mechanisms of the results are discussed in terms of the dynamics of free electrons in the air plasma.
TL;DR: In this article, a tight binding (TB) model is proposed for describing perovskite oxide heterostructures and surfaces, which provides a simple intuitive physical picture and yields, already with only two parameters, quantitatively much more reliable results consistent with experiment.
Abstract: Most recently, orbital-selective quantum well states of $d$ electrons have been experimentally observed in SrVO$_3$ ultrathin films [K. Yoshimatsu et. al., Science 333, 319 (2011)] and SrTiO$_3$ surfaces [A. F. Santander-Syro et. al., Nature 469, 189 (2011)]. Hitherto, one tries to explain these experiments by a nearly free electron (NFE) model, an approach widely used for delocalized electrons in semiconductor heterostructures and simple metal films. We show that a tight binding (TB) model is more suitable for describing heterostructures with more localized $d$ electrons. In this paper, we construct from first principles simple TB models for perovskite oxide heterostructures and surfaces. We show that the TB model provides a simple intuitive physical picture and yields, already with only two parameters, quantitatively much more reliable results, consistent with experiment.
TL;DR: In this paper, the authors investigated the synergetic effect of the SF6-N2 gas mixture, taking the effective temperature of the free electron Maxwell spectrum at the time of breakdown as an independent parameter.
Abstract: This paper investigates the synergetic effect of the SF6-N2 gas mixture, taking the effective temperature of the free electron Maxwell spectrum at the time of breakdown as an independent parameter. In this way, a direct link between a macroscopic variable (dc breakdown voltage of the mixture) and a fundamental microscopic variable (effective temperature) is established. Derivations are presented of expressions that relate the streamer mechanism breakdown voltage in an SF6-N2 gas mixture to the pd product (pressure×interelectrode distance), the percentage contribution of the N2 gas (χ), and the effective temperature of the spectrum of free electrons in the mixture (Td) at the time of breakdown (breakdown temperature). A new theoretical model for the dependence of the electron attachment coefficient (effective cross section) in the electronegative SF6 gas was used, which resulted in the final expression being different from the corresponding expressions obtained from other models. The obtained results were verified by experiments, under well controlled laboratory conditions. There was a high degree of agreement between the experimental and the theoretically calculated results.
TL;DR: In this article, the authors used two-pulse experiments to show that both limits can be exceeded by taking advantage of absorption seeded by free electrons or self-trapped excitons, depending on the pulse separation.
Abstract: There are natural limits to the spatial resolution and the deposited energy densities that can be achieved in femtosecond laser dielectric modification. These arise because of the threshold-like nature of nonlinear absorption. We use two-pulse experiments to show that both limits can be exceeded by taking advantage of absorption seeded by free electrons or self-trapped excitons, depending on the pulse separation.
TL;DR: Comparisons verify the theoretical model which estimates the proton or deuteron energy loss in partially ionized plasmas with experimental data finding a very close agreement, where both stoppings have the same dependence on target ionicity.
Abstract: In this work, proton and deuteron stopping due to free and bound electrons in partially ionized plasma targets is evaluated. The stopping of target free electrons is calculated using the dielectric formalism, well described in our previous works. In the case of target bound electrons, a short expression to calculate their contribution to the stopping is used, where mean excitation energies are obtained by means of the Hartree-Fock method. Experiments with different kinds of plasmas are analyzed. For LiH plasma, estimated plasma stopping fits experimental data very well, within the error bars, recognizing the well-known enhanced plasma stopping. In the case of CH${}_{2}$ plasma, we obtain, from estimated ionization, that total stopping power increases when target electron density does. Our estimations are very similar to experimental data which show the same behavior with target free and bound electron density. Finally, in Al plasma, we compare directly our calculations with experimental data finding a very close agreement, where both stoppings have the same dependence on target ionicity. All these comparisons verify our theoretical model which estimates the proton or deuteron energy loss in partially ionized plasmas.
TL;DR: In this article, the authors show that the electron energy distribution becomes non-continuous, with discrete peaks corresponding to specific inelastic collisions, and the relative magnitude of these peaks and shape of the energy distribution can be directly controlled by the parameter pressure times distance (pd) and the applied potential across the gap.
Abstract: Particle simulations of high-pressure microdischarges at gaps below 10 μm show that the electron energy distribution becomes non-continuous, with discrete peaks corresponding to specific inelastic collisions. The relative magnitude of these peaks and shape of the energy distribution can be directly controlled by the parameter pressure times distance (pd) and the applied potential across the gap. These parameters dictate inelastic collisions experienced by electrons and as both increase the distribution smooths into a Maxwellian-like distribution. By capitalizing on field emission at these dimensions, it is possible to control the energy distribution of free electrons to target specific, energy dependent reactions.
TL;DR: In this paper, the effect of dynamic interference of photoelectrons emitted with the same kinetic energy at different times during the rising and falling sides of the pulse predicted in [\emph{Ph.V. Demekhin and L.S. Cederbaum},
Abstract: The time-dependent Schrodinger equation for the hydrogen atom and its interaction with coherent intense high-frequency short laser pulses is solved numerically exactly by propagating the single-electron wave packets. Thereby, the wavefunction is followed in space and time for times longer than the pulse duration. Results are explicitly shown for 3 and 10 fs pulses. Particular attention is paid to identifying the effect of dynamic interference of photoelectrons emitted with the same kinetic energy at different times during the rising and falling sides of the pulse predicted in [\emph{Ph.V. Demekhin and L.S. Cederbaum}, Phys. Rev. Lett. \textbf{108}, 253001 (2012)]. In order to be able to see the dynamic interference pattern in the computed electron spectra, the photoelectron wave packet has to be propagated over long distances. Clearly, complex absorption potentials often employed to compute spectra of emitted particles cannot be used to detect dynamic interference. For the considered high-frequency pulses of 3 and 10 fs durations, this requires enormously large spatial grids. The presently computed photoionization and above-threshold ionization spectra are found to exhibit pronounced dynamic interference patterns. Where available, the patterns are in very good agreement with previously published results on the photoionization spectra which have been computed using a completely different method, thus supporting the previously made assumption that the above-threshold ionization processes are very weak for the considered pulse intensities and high carrier frequency. The quiver motion in space and time of a free electron in strong laser pulses is also investigated numerically. Finally, a discussion is presented of how fast the atom is ionized by an intense pulse.
TL;DR: The Italian free-electron laser, FERMI, now generates coherent soft X-rays in the water window (2.3-4.4 nm) by two-stage frequency upconversion of ultraviolet seed laser pulses using the 'fresh bunch' technique as discussed by the authors.
Abstract: The Italian free-electron laser, FERMI, now generates coherent soft X-rays in the water window (2.3–4.4 nm) by two-stage frequency upconversion of ultraviolet seed laser pulses using the 'fresh bunch' technique.
TL;DR: In this paper, the HartreeFock method and oscillator strength functions were used to calculate the stopping of free and bound electrons in a plasma target, respectively, and compared with an experiment in xenon plasmas finding a close agreement.
Abstract: In this work, proton stopping due to free and bound electrons in a plasma target is analyzed. The stopping of free electrons is calculated using the dielectric formalism, well described in previous literature. In the case of bound electrons, HartreeFock methods and oscillator strength functions are used. Differences between both stopping, due to free and bound electrons, are shown in noble gases. Then, enhanced plasma stopping can be easily estimated from target ionization. Finally, we compare our calculations with an experiment in xenon plasmas finding a close agreement.
TL;DR: A semi-analytical model for free electron production induced by multiphoton ionization in dielectric materials for short laser pulses at moderate intensities is presented and shows that significant deviations from the parabolic band approximation may occur.
Abstract: We present a semi-analytical model for free electron production induced by multiphoton ionization in dielectric materials for short laser pulses at moderate intensities. Within this approach, the laser-induced absorption is described through the Bloch–Volkov formalism, and the electronic structure of materials is evaluated through first-principles calculations. Results obtained for NaCl and KDP (KH2PO4) materials show that significant deviations from the parabolic band approximation may occur. When the laser intensity increases, high multiphotonic orders may become the predominant mechanisms outside the centre of the Brillouin zone.
TL;DR: In time domain II, about 46% of the second pulse is absorbed by a single photon due to the localized state, which is responsible for higher bonding strength compared with that prepared by single-pulse irradiation.
Abstract: The absorption mechanism of the second pulse is experimentally and theoretically investigated for high-efficiency microwelding of photosensitive glass by double-pulse irradiation using a femtosecond laser. The transient absorption change during the second pulse irradiation for various energies induced by the first pulse is measured at different delay times. The resulting effects depend on whether the delay time is 0–30 ps (time domain I) or 30– several ns (domain II). By solving rate equations for the proposed electronic processes, the excitation and relaxation times of free electrons in time domain I are estimated to be 0.98 and 20.4 ps, respectively, whereas the relaxation times from the conduction band to a localized state and from the localized state to the valence band in domain II are 104.2 and 714.3 ps, respectively. Single-photon absorption of the second pulse by free electrons dominates in domain I, resulting in high bonding strength. In time domain II, about 46% of the second pulse is absorbed by a single photon due to the localized state, which is responsible for higher bonding strength compared with that prepared by single-pulse irradiation.
TL;DR: In this paper, the scale separation between ions and the electrons is exploited to derive the reduced electron model, and a closed system of equations for the electron response to ion-scale turbulence is derived.
Abstract: In this paper, we extend the multiscale approach developed in Abel et al (2012 Rep. Prog. Phys. submitted) by exploiting the scale separation between ions and the electrons. The gyrokinetic equation is expanded in powers of the electron to ion mass ratio, which provides a rigorous method for deriving the reduced electron model. We prove that ion-scale electromagnetic turbulence cannot change the magnetic topology, and argue that to lowest order the magnetic field lies on fluctuating flux surfaces. These flux surfaces are used to construct magnetic coordinates, and in these coordinates a closed system of equations for the electron response to ion-scale turbulence is derived. All fast electron timescales have been eliminated from these equations. We also use these magnetic surfaces to construct transport equations for electrons and for electron heat in terms of the reduced electron model.
TL;DR: In this article, a collisional-radiative time-dependent module is implemented to study radiation transport in matter from ultrashort and ultraintense X-ray bursts.
TL;DR: In this paper, an ultrathin metal film deposited on dielectric plate supports low loss THz surface plasma wave (SPW), the SPW field falls off away from the metal film both inside the dielectrics as well as in free space.
Abstract: An ultrathin metal film deposited on dielectric plate supports low loss THz surface plasma wave (SPW). The SPW field falls off away from the metal film both inside the dielectric as well as in free space. Two lasers normally incident, from free space on the planar structure, exert a difference frequency ponderomotive force on the free electrons of the film and resonantly excite THz SPW. The ratio of SPW amplitude to lasers is 10−3 at laser intensity of 3 × 1012 W/cm2 at 1 μ m wavelength. The growth rate falls monotonically because at higher frequency the coupling of SPW is weak.
TL;DR: In this article, the effect of free electrons on the quality factor (Q) of a metallic nanomechanical resonator in the form of a thin elastic beam is investigated, and simple perturbation theory is used to calculate the rate at which an externally excited vibration mode decays due to its interaction with free electrons.
Abstract: We investigate the effect of free electrons on the quality factor (Q) of a metallic nanomechanical resonator in the form of a thin elastic beam. The flexural and longitudinal modes of the beam are modeled using thin beam elasticity theory, and simple perturbation theory is used to calculate the rate at which an externally excited vibration mode decays due to its interaction with free electrons. We find that electron-phonon interaction significantly affects the Q of longitudinal modes, and may also be of significance to the damping of flexural modes in otherwise high-Q beams. The finite geometry of the beam is manifested in two important ways. Its finite length breaks translation invariance along the beam and introduces an imperfect momentum conservation law in place of the exact law. Its finite width imposes a quantization of the electronic states that introduces a temperature scale for which there exists a crossover from a high-temperature macroscopic regime, where electron-phonon damping behaves as if the electrons were in the bulk, to a low-temperature mesoscopic regime, where damping is dominated by just a few dissipation channels and exhibits sharp non-monotonic changes as parameters are varied. This suggests a novel scheme for probing the electronic spectrum of a nanoscale device by measuring the Q of its mechanical vibrations.
TL;DR: In this paper, the Hartree-Fock-Slater method was used to calculate the photorecombination cross sections from photoionization cross sections (PICSs) calculated by relativistic random phase approximation (RRPA).
Abstract: Transition of an electron from a free to a bound state is critical in determining the qualitative shape of the spectrum in high-order-harmonic generation (HHG), and in tomographic imaging of orbitals. We calculate and compare the recombination amplitude, from a continuum state described by a plane wave and an outgoing scattering eigenstate, to the bound state for the noble gases that are commonly used in HHG. These calculations are based on the single active electron model and the Hartree-Fock-Slater method, using both the length form and the acceleration form of the dipole matrix element. We confirm that the recombination amplitude versus emitted photon energy strongly depends upon the wave function used to describe the free electron. Depending on the choice of the wave function and the dipole form, the square of the absolute value of the recombination amplitude can differ by almost two orders of magnitude near the experimentally measured Cooper minima. Moreover, only the outgoing scattering eigenstates with the length form roughly predict the experimentally observed Cooper minimum for Ar ($\ensuremath{\sim}50\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$) and Kr ($\ensuremath{\sim}85\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$). We provide a detailed derivation of the photorecombination cross sections from photoionization cross sections (PICSs) calculated by the relativistic random phase approximation (RRPA). For Ar, Kr, and Xe, we compare the total PICSs calculated using our recombination amplitudes with that obtained from RRPA. We find that PICS calculated using the outgoing scattering eigenstates with the length form is in better agreement with the RRPA calculations than the acceleration form.