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Quantum chaos is reviewed from the viewpoint of “what is molecule?”, particularly placing emphasis on their dynamics. Molecules are composed of heavy nuclei and light electrons, and thereby the very basic molecular theory due to Born and Oppenheimer gives a view that quantum electronic states provide potential functions working on nuclei, which in turn are often treated classically or semiclassically. Therefore, the classic study of chaos in molecular science began with those nuclear dynamics particularly about the vibrational energy randomization within a molecule. Statistical laws in probabilities and rates of chemical reactions even for small molecules of several atoms are among the chemical phenomena requiring the notion of chaos. Particularly the dynamics behind unimolecular decomposition are referred to as Intra-molecular Vibrational energy Redistribution (IVR). Semiclassical mechanics is also one of the main research fields of quantum chaos. We herein demonstrate chaos that appears only in semiclassical and full quantum dynamics. A fundamental phenomenon possibly giving birth to quantum chaos is “bifurcation and merging” of quantum wavepackets, rather than “stretching and folding” of the baker’s transformation and the horseshoe map as a geometrical foundation of classical chaos. Such wavepacket bifurcation and merging are indeed experimentally measurable as we showed before in the series of studies on real-time probing of nonadiabatic chemical reactions. After tracking these aspects of molecular chaos, we will explore quantum chaos found in nonadiabatic electron wavepacket dynamics, which emerges in the realm far beyond the Born-Oppenheimer paradigm. In this class of chaos, we propose a notion of Intra-molecular Nonadiabatic Electronic Energy Redistribution (INEER), which is a consequence of the chaotic fluxes of electrons and energy within a molecule.

Abstract Dipolarization fronts (DFs) have been suggested as crucial energy conversion sites contributing significantly to global energy transfer in the magnetosphere. However, energy partitioning of DF‐driven energy transfer remains hitherto elusive. Using high‐cadence data from MMS spacecraft, we present a detailed investigation of energy flux densities at two DFs with/without surface ripples. We find that during both DF intervals, electron enthalpy flux increases dramatically, carries the greatest energy, and well correlates with local energy conversion. Poynting flux also increases but contributes to a relatively smaller portion. Ion enthalpy flux which in magnitude is slightly smaller than electron enthalpy flux barely changes. Particle kinetic energy and heat fluxes are negligible. Strong difference in energy fluxes observed by different spacecraft is found at the rippled DF, indicating three‐dimensional energy transport. These results indicate that energy budgets at the DFs are dominated by electron physics, rather than ion dynamics suggested by previous studies.

Herein we review a theoretical study of unidirectional π-electron rotation in aromatic ring molecules, which originates from two quasi-degenerate electronic excited states created coherently by a linearly polarized ultraviolet/visible laser with a properly designed photon polarization direction. Analytical expressions for coherent π-electron angular momentum, ring current and ring current-induced magnetic field are derived in the quantum chemical molecular orbital (MO) theory. The time evolution of the angular momentum and the ring current are expressed using the density matrix method under Markov approximation or by solving the time-dependent Schrödinger equation. In this review we present the results of the following quantum control scenarios after a fundamental theoretical description of coherent angular momentum, ring current and magnetic field: first, two-dimensional coherent π-electron dynamics in a non-planar (P)-2,2’-biphenol molecule; second, localization of the coherent π-electron ring current to a designated benzene ring in polycyclic aromatic hydrocarbons; third, unidirectional π-electron rotations in low-symmetry aromatic ring molecules based on the dynamic Stark shift of two relevant excited states that form a degenerate state using the non-resonant ultraviolet lasers. The magnetic fields induced by the coherent π-electron ring currents are also estimated, and the position dependence of the magnetic fluxes is demonstrated.

The electron dynamics in uniform magnetized capacitively coupled plasmas are investigated by using a one‐dimensional particle‐in‐cell simulation with a Monte Carlo collision model. It is found that the nonlinear dynamic behaviors of electrons are slightly modulated at weak magnetic fields, with more electron beams appearing during one sheath expansion. The electron beams are reversed before reaching the opposite electrode at moderate magnetic fields under the effect of Lorentz force. The discharge becomes very localized at very high magnetic fields, as the energetic electrons are confined in the vicinity of the sheath edge. The nonlocal to local transition of discharge characteristics is induced at different magnetic fields for various discharge frequencies. Generally, the discharge transition happens at stronger magnetic fields for high‐discharge frequencies. A quantitative relation between the discharge frequency and cyclotron frequency is given for the discharge transition. [ABSTRACT FROM AUTHOR]

Dipolarization fronts (DFs) have been suggested as crucial energy conversion sites contributing significantly to global energy transfer in the magnetosphere. However, energy partitioning of DF‐driven energy transfer remains hitherto elusive. Using high‐cadence data from MMS spacecraft, we present a detailed investigation of energy flux densities at two DFs with/without surface ripples. We find that during both DF intervals, electron enthalpy flux increases dramatically, carries the greatest energy, and well correlates with local energy conversion. Poynting flux also increases but contributes to a relatively smaller portion. Ion enthalpy flux which in magnitude is slightly smaller than electron enthalpy flux barely changes. Particle kinetic energy and heat fluxes are negligible. Strong difference in energy fluxes observed by different spacecraft is found at the rippled DF, indicating three‐dimensional energy transport. These results indicate that energy budgets at the DFs are dominated by electron physics, rather than ion dynamics suggested by previous studies. Plain Language Summary: Dipolarization fronts, earthward‐propagating transient magnetic structures, have been well documented to be crucial energy conversion sites contributing significantly to global energy transfer in the magnetosphere. However, owing to the limited capacity of previous spacecraft measurements, energy partition of energy transfer driven by the fronts remains not well understood so far. In this study, taking advantage of high‐resolution measurements from MMS which measure particle velocity distributions orders of magnitude faster than previous spacecraft, we present the first in‐situ investigation of energy flux densities at the fronts in the magnetotail. We reveal that energy budgets at the fronts are dominated by electron enthalpy flux and redistributed by electron flow moving along front ripples. Key Points: Electron enthalpy and Poynting fluxes carry the greatest energy and well correlate with local energy conversionIon energy flux which in magnitude is slightly smaller than electron energy flux barely changes across the frontsEnergy transport becomes three‐dimensional due to rippling effect induced by front surface waves [ABSTRACT FROM AUTHOR]

Betatron cooling, a plasma process losing particle energy in the perpendicular direction but reserving particle energy in the field‐aligned direction, is a consequence of magnetic depression under the conservation of magnetic moment. Such process has been widely studied in the Earth's magnetosphere but has never been reported in other planetary environment. Here, by utilizing the Mars Atmosphere and Volatile EvolutioN (MAVEN) measurements, we report two events of betatron cooling in the Martian magnetotail. In one of the events, betatron cooling occurs in the suprathermal and energetic ranges of electrons, whereas in the other event, it occurs in the thermal‐energy range. We quantitatively reproduce these two processes by using an analytical model. Gratifyingly, the cooling factor derived from the analytical model agrees well with the observation of magnetic depression. These results, for the first time demonstrating the betatron‐cooling effect beyond the Earth, are useful to understand the electron dynamics in the planetary magnetosphere. Plain Language Summary: Under conservation of the magnetic moment, electrons can lose energy in the perpendicular direction but reserve energy in the field‐aligned direction when magnetic field strength becomes weaker. Such process, called betatron cooling, has not been reported in the extraterrestrial planetary environment. Using the Mars Atmosphere and Volatile EvolutioN (MAVEN) data and an analytical model, for the first time, we quantitatively demonstrate and reproduce this cooling process of electrons in the Martian magnetotail, and the cooling factor derived from the analytical model agrees well with the observation. Our study promotes the understanding of the electron dynamics in the planetary magnetosphere. Key Points: We provide the first evidence of electron betatron cooling in Martian magnetotailWe quantitatively reproduce this cooling process by using an analytical modelThe cooling factor derived from the model agrees very well with the observation [ABSTRACT FROM AUTHOR]

State transition in the multiple-levels system has the great potential applications in the quantum technology. In this article we employ a deterministic approach in complex space to analyze the dynamics of the 1s–2p electron transition in the hydrogen atom. The electron’s spin motion is embodied in the framework of quantum Hamilton mechanics that allows us to examine the transition dynamics more precisely. The transition is driven by an oscillating electric field in the z-direction. The electron’s transition process can be visualized by monitoring its motion in the complex space. The quantum potential and the total energy proposed in this paper provide new indices to observe the dynamic changes of electrons in the transition process.

We construct explicitly potentials, Darboux matrix functions and corresponding solutions of Dirac, dynamical Dirac and Dirac–Weyl systems using generalised Bäcklund-Darboux transformation (GBDT) in the important case of nontrivial initial systems. In this way, we construct explicit solutions of systems with non-vanishing at infinity potentials, including steplike and power-law growth potentials. Thus, the constructed potentials (systems) differ fundamentally from the actively studied case of GBDT for the trivial initial systems. Generalised matrix eigenvalues A (not necessarily diagonal) and corresponding generalised matrix eigenfunctions Π (x) of the nontrivial initial systems are used in the GBDT constructions in this paper. Explicit expressions for these Π (x) are new and the method of deriving these expressions may be applied to various other important problems. The case of Dirac–Weyl system, which is of interest in electron dynamics and graphene theory is studied in greater detail, and generalised separation of variables appears in our approach to the study of this system. Explicit expressions for Weyl–Titchmarsh functions (in the form of pseudo-realisations) are derived. [ABSTRACT FROM AUTHOR]

Electronic response of crystalline diamond as well as high harmonic generation following irradiation by a single-cycle high-intensity laser pulse was calculated through modeling the dynamics in the framework of the time-dependent density functional theory. The frequencies of the applied laser pulses vary over visible regime with a timescale shorter than typical quantum dephasing. High harmonic yields, show substantial deviation from what is obtained from the power scaling law of perfect solids under longer cycle pulses due to the key role of strong nonlinear features of dynamics at high intensities. Further, the dynamical photon dressing of electronic states are monitored by Floquet quasi-static picture for ultrashort few cycle pulses. Our results show that dynamical bandgap is diminished as a function of increasing driven field frequency and the system changes into the dynamic metallization regimes that consequently leads to new hybridization of quasi static dressed bands particularly near high symmetrical points in the Brillouin zone. These Floquet hybridization can be used to produce coherent transport of charge on the scale of the huge number of lattice sites. Moreover, the pulse-induced phonon frequency variations that relate to bond softening and hardening, are connected to different order of Floquet dressed states. Importantly, it is found that dielectric response oscillation is directly proportional to the transient bandgap value so that entering into metallization mode preserves the polarization coherency. Based on the magnitude of calculated Keldysh parameter varies for dynamical bandgap, tunneling ionization is the dominant mechanism of excitation. [ABSTRACT FROM AUTHOR]

The toolbox for time-resolved direct measurements of electron dynamics covers a variety of methods. Since the experimental effort is increasing rapidly with achievable time resolution, there is an urge for simple and robust measurement techniques. Within this paper prove-of-concept experiments and numerical simulations are utilized to investigate the applicability of a new setup for the generation of ultrashort electron pulses in the energy range of 300 eV up to 1.6 keV. The experimental approach combines an in-vacuum liquid microjet and a few-cycle femtosecond laser system, while the threshold for electron impact ionization serves as a gate for the effective electron pulse duration. The experiments prove that electrons in the keV regime are accessible and that the electron spectrum can be easily tuned by laser intensity and focal position alignment with respect to the water jet. Numerical simulations show that a sub-picosecond temporal resolution is achievable.

An implementation of real‐time time‐dependent density functional theory (RT‐TDDFT) within the TURBOMOLE program package is reported using Gaussian‐type orbitals as basis functions, second and fourth order Magnus propagator, and the self‐consistent field as well as the predictor–corrector time integration schemes. The Coulomb contribution to the Kohn–Sham matrix is calculated combining density fitting approximation and the continuous fast multipole method. Performance of the implementation is benchmarked for molecular systems with different sizes and dimensionalities. For linear alkane chains, the wall time for density matrix time propagation step is comparable to the Kohn‐Sham (KS) matrix construction. However, for larger two‐ and three‐dimensional molecules, with up to about 5,000 basis functions, the computational effort of RT‐TDDFT calculations is dominated by the KS matrix evaluation. In addition, the maximum time step is evaluated using a set of small molecules of different polarities. The photoabsorption spectra of several molecular systems calculated using RT‐TDDFT are compared to those obtained using linear response time‐dependent density functional theory and coupled cluster methods. [ABSTRACT FROM AUTHOR]

Electron dynamics in gold (Aun) nanoparticles in the absence and presence of electric field is studied using molecular dynamics simulations. For this dynamics, motion of electrons is treated classically by considering a force field including Coulomb and van der Waals interaction potentials for the electron-electron (e--e-), electron-ionic core (e--Au+) and ionic core-ionic core (Au+-Au+) pairs of species. These electrons and ionic cores are set initially at the alternative sites of a set of identical twin fcc lattices. Electric current and conduction are evaluated for the Aun gold nanoparticles of different sizes (n = 2048, 2816, 3328, and 3840) in electric field of 0.001 V/Å strength. Results of this study show a non-linear dependence of electric conduction on the size of the gold nanoparticles. [ABSTRACT FROM AUTHOR]

The synthesis and structure of atomically precise Au130−xAgx (average x=98) alloy nanoclusters protected by 55 ligands of 4‐tert‐butylbenzenethiolate are reported. This large alloy structure has a decahedral M54 (M=Au/Ag) core. The Au atoms are localized in the truncated Marks decahedron. In the core, a drum of Ag‐rich sites is found, which is enclosed by a Marks decahedral cage of Au‐rich sites. The surface is exclusively Ag−SR; X‐ray absorption fine structure analysis supports the absence of Au−S bonds. The optical absorption spectrum shows a strong peak at 523 nm, seemingly a plasmon peak, but fs spectroscopic analysis indicates its non‐plasmon nature. The non‐metallicity of the Au130−xAgx nanocluster has set up a benchmark to study the transition to metallic state in the size evolution of bimetallic nanoclusters. The localized Au/Ag binary architecture in such a large alloy nanocluster provides atomic‐level insights into the Au−Ag bonds in bimetallic nanoclusters. [ABSTRACT FROM AUTHOR]

Drifting electron holes (DEHs), manifesting as sudden but mild dropout in electron flux, are a common phenomenon seen in the Earth's magnetosphere. It manifests the change of the state of the magnetosphere. However, previous studies primarily focus on DEHs during geomagnetically active time (e.g., substorm). Not until recently have quiet time DEHs been reported. In this paper, we present a systematic study on the quiet time DEHs. BeiDa Imaging Electron Spectrometer (BD‐IES) measurements from 2015 to 2017 are investigated. Twenty‐two DEH events are identified. The DEHs cover the whole energy range of BD‐IES (50–600 keV). Generally, the DEHs are positively dispersive with respect to energy. Time‐of‐flight analysis suggests the dispersion results from electron drift motion and gives the location where the DEHs originated from. Statistics reveal the DEHs primarily originated from the postmidnight magnetosphere. In addition, superposed epoch analysis applied to geomagnetic indices and solar wind parameters indicates these DEH events occurred during geomagnetically quiet time. No storm or substorm activity could be identified. However, an investigation into nightside midlatitude ground magnetic records suggests these quiet time DEHs were accompanied by Pi2 pulsations. The DEH‐Pi2 connection indicates a possible DEH‐bursty bulk flow (BBF) connection, since nightside midlatitude Pi2 activity is generally attributed to magnetotail BBFs. This connection is also supported by a case study of coordinated magnetotail observations from Magnetospheric Multiscale spacecraft. Therefore, we suggest the quiet time DEHs could be caused by magnetotail BBFs, similar to the substorm time DEHs. Key Points: Twenty‐two drifting electron hole (DEH) events during geomagnetically quiet time were identified from 2‐year BD‐IES measurementThe DEHs initially occur in the postmidnight magnetosphere, then drift with electrons, and are dispersed by the driftGiven a negative phase space density radial gradient, electron inward transport induced by bursty bulk flow results in the DEHs [ABSTRACT FROM AUTHOR]

Tiny-sized particles under the scheme of monolayer assembly, comprising gold atoms, developed at a different processing time in a pulse-based process. For a different processing time, atoms bind into different tiny particles under the placing packets of nanoshape energy where they elongate as per arrangement and when in one-dimensional arrays, they convert into structures of smooth elements. For different processing time and where tiny particles possess triangular shape, they pack to develop extended shapes where development rate of an anisotropic particle is not more than milliseconds. Increasing the processing time of solution upto certain duration increases the number of developing tiny particles in a triangular-shape, so, their extended shapes also. Uniformly adjacent orientation of electrons in atoms of tiny-shaped particle is because of exerting uniform surface force along their opposite poles as per gained potential energy where stretching of their clamped energy knots remains orientation-based. At a different processing time, inter-spacing distance of spotted intensity spots in selective area photons reflection patterns of particles remains the same as for the case of the structures of smooth elements visualized through transmission microscope high-resolution images. When the forceful coinciding of two parallel structures of smooth elements occurs, they bind into single element structure (of smooth element) by overlying a bit on the inner sides, thus, giving it double width where certain filled-state electrons and unfilled energy knots (belonging to sides of elongated atoms of parallel structures of smooth elements) coordinate to adhere. This study discusses the formation (development) of tiny particles (tiny-sized particles) followed by their extended shapes (large-sized particles) at different processing time of gold solution while employing a pulse-based electron–photon solution-interface process where they become the origin of physics and chemistry of materials by discussing many commonly known phenomena and processes, so, opening the alternative routes to design materials and explore science. [ABSTRACT FROM AUTHOR]

Recently, highly accurate multi-configuration time-dependent Hartree electron dynamics calculations demonstrated the efficient long-range energy transfer inter-Coulombic decay (ICD) process to happen in charged semiconductor quantum dot (QD) pairs. ICD is initiated by intraband photoexcitation of one of the QDs and leads to electron emission from the other within a duration of about 150 ps. On the same time scale electronically excited states are reported to relax due to the coupling of electrons to acoustic phonons. Likewise, phonons promote ionisation. Here, the QDs' acoustic breathing mode is implemented in a frozen-phonon approach. A detailed comparison of the phonon effects on electron relaxation and emission as well as on the full ICD process is presented, which supports the previous empirical finding of ICD being the dominant decay channel in paired QDs. In addition the relative importance of phonon–phonon, phonon–electron and electron–electron interaction is analysed. [ABSTRACT FROM AUTHOR]

The ability to produce ultrashort, high-brightness X-ray pulses is revolutionizing the field of ultrafast X-ray spectroscopy. Free-electron laser (FEL) facilities are driving this revolution, but unique aspects of the FEL process make the required characterization and use of the pulses challenging. In this paper, we describe a number of developments in the generation of ultrashort X-ray FEL pulses, and the concomitant progress in the experimental capabilities necessary for their characterization and use at the Linac Coherent Light Source. This includes the development of sub-femtosecond hard and soft X-ray pulses, along with ultrafast characterization techniques for these pulses. We also describe improved techniques for optical cross-correlation as needed to address the persistent challenge of external optical laser synchronization with these ultrashort X-ray pulses. [ABSTRACT FROM AUTHOR]

The electron rolling pin distribution, showing electron pitch angles primarily at 0°, 90°, and 180°, has recently been observed behind dipolarization fronts (DFs) and explained using an analytical model. However, the energy range of such distribution has been unknown so far, owing to the low‐resolution data in previous spacecraft missions. Here using the high‐resolution measurements of Magnetospheric Multiscale, we reveal the energy range of electron rolling pin distribution behind DFs for the first time. We find that such distribution appears only above 1.7 keV, falling well into the suprathermal energy range. Below 1.7 keV, electrons exhibit a Maxwell distribution, while above 1.7 keV, they exhibit a power law distribution. In addition, such distribution appears primarily in the growing phase of the flow and disappears quickly in the decaying phase. During the formation of the rolling pin distribution, electrons are gyrotropic. These findings have greatly improved our knowledge of electron dynamics around DFs. Plain Language Summary: Examining the electron pitch angle distribution can help us understand the electron dynamics behind dipolarization fronts (DFs). Up to now, the energy range of electron rolling pin distribution, which shows electron pitch angles primarily at 0°, 90°, and 180°, has been unknown, owing to the low‐resolution data in previous spacecraft missions. Here using the high‐resolution Magnetospheric Multiscale measurements, we reveal the energy range of electron rolling pin distribution behind DFs for the first time. Our findings can significantly improve the knowledge of electron dynamics around DFs. Key Points: Rolling pin distribution appears only above 1.7 keV, falling well into suprathermal energy rangeBelow 1.7 keV, electrons have Maxwell distribution; above 1.7 keV, they have power law distributionDuring the formation of the rolling pin distribution, electrons are gyrotropic [ABSTRACT FROM AUTHOR]

Electrons driven from atom or molecule by intense dual-color laser fields can coherently radiate high harmonics from extreme ultraviolet to soft X-ray, as well as an intense terahertz (THz) wave from millimeter to sub-millimeter wavelength. The joint measurement of high-harmonic and terahertz spectroscopy (HATS) was established and further developed as a unique tool for monitoring electron dynamics of argon from picoseconds to attoseconds and for studying the molecular structures of nitrogen. More insights on the rescattering process could be gained by correlating the fast and slow electron motions via observing and manipulating the HATS from atoms and molecules. We also propose the potential investigations of HATS of polar molecules, and solid and liquid sources. [ABSTRACT FROM AUTHOR]

Highlights • Numerical study of the double photoionization process in He-like and Be-like ions. • Probing the mechanisms of the two-electron ejection by EUV and soft X-ray photons. • Demonstration of how the behavior of the two electrons of any ion can be predictable. Abstract We numerically investigate the removal of the two outer electrons in the X = He, Li + , C 4 + , Be, B + and Ne 6 + targets by the absorption of a single photon of energy in the extreme UV/soft X-ray spectral region. Our theoretical method to describe the behavior of the electrons in the presence of the laser field is based on a spectral approach of configuration interaction type to solve the time-dependent Schrödinger equation. The probe of the electron dynamics in the different systems shows that the way the outer electrons will leave their parent X system is systematically dictated by the amount of excess photon energy available to them relative to the ionization potential of the corresponding X + ion. [ABSTRACT FROM AUTHOR]

Abstract This work highlights the direct impact of selecting acceptor moiety for organic dyes on the electron dynamics at faster time scales, in which overlooked photo-physical properties are present on semiconductor surfaces with specific acceptor moieties. Four top-performing dyes of indoline family (D131, D102, D149, and D205) sharing the same donor moiety, but through different acceptor groups, were selected and compared with respect of electron injection process, using ultrafast transient-infrared probe. The presence of rhodanine moiety at the acceptor unit in D102, D149 and D205, shows an additional slow electron injection process, of picosecond time-scale, on the low band-gap semiconductor, TiO 2. This slow process is expected to be present due to a twisted intramolecular charge transfer/isomerized state of the excited dye prior to electron injection. This isomerized state reduces as well the detrimental electron recombination process rates, and results of high performance in solar cells based on these rhodanine dyes. Replacing the rhodanine moiety by a cyano-acrylic group in D131 dye shows faster electron injection and recombination processes, due to the lower dipole moment present in the excited state, hindering the formation of an isomerized state. These findings will aid to enhance the organic dyes design used in dye sensitized solar cells, in which designed photo-physical processes on semiconductor surfaces can increase the efficiencies of the solar cells. [ABSTRACT FROM AUTHOR]

We study the coupled charge-lattice dynamics in the commensurate charge density wave (CDW) phase of the layered compound 1T-TaS 2 driven by an ultrashort laser pulse. For describing its electronic structure, we employ a tight-binding model of previous studies including the effects of lattice distortion associated with the CDW order. We further add on-site Coulomb interactions and reproduce an energy gap at the Fermi level within a mean-field analysis. On the basis of coupled equations of motion for electrons and the lattice distortion, we numerically study their dynamics driven by an ultrashort laser pulse. We find that the CDW order decreases and even disappears during the laser irradiation while the lattice distortion is almost frozen. We also find that the lattice motion sets in on a longer time scale and causes a further decrease in the CDW order even after the laser irradiation. [ABSTRACT FROM AUTHOR]

We investigate strong field ionization of an atomic gas in a plasmonically enhanced field resulting from the illumination of a nanometer-sized structure with ultrafast laser pulse. We use perturbation theory to derive an approximate solution for electron’s motion following ionization. These analytical estimates are corroborated by the time-dependent Schrödinger equation and classical trajectory Monte Carlo simulations. Notably, our approach can be used to obtain electron energy spectra without having to rely on numerical simulations. This allows for a deeper study of the dependence of electron energy spectrum on the properties of the near-field, suggesting electric field sensor applications. We derive an analytical expression for the location of the peak of the higher-energy structure (HES) as a function of laser parameters and near-field decay length. We find a particularly strong dependence of the energy peak on laser frequency, with lower frequencies causing a significant upward shift in the final electron energies. Combined with control of the width of the HES, which can be done by changing the size of the nanostructure, this points to the possibility of using nanotips as sources of ultrashort electron beams of tunable energy.

Highlights • The novel endstation combines different time-resolved X-ray spectroscopy techniques. • Electron dynamics in the fs-ns time scale can be accessed. • Laser/synchrotron are used as pump/probe sources for time resolved NEXAFS and XPS. Abstract In this report we illustrate the instrumental developments involving the branchline of the ALOISA beamline at the Elettra synchrotron, with the setup of the ANCHOR-SUNDYN endstation. The ANCHOR experimental chamber is designed for the study of in-situ prepared organo-metallic hybrid interfaces, by means of synchrotron based soft x-ray spectroscopic techniques. SUNDYN is a femtosecond pulse width laser setup, optimized for the optical pump of organic systems. It has been integrated in the ANCHOR endstation in order to perform time resolved spectroscopies at MegaHertz repetition rate. By combining resonant photoemission spectroscopy and pump-probe X-ray spectroscopies in the same chamber, we can study the dynamics of the electronic structure of organo-metallic interfaces from the femtosecond to the nanosecond timescales. We provide here a detailed description of this setup and discuss some case study measurements obtained during the commissioning of the apparatus. [ABSTRACT FROM AUTHOR]

The electron dynamics within thin current sheets plays a key role both for the process of magnetic reconnection and other energy transfer mechanisms but, from an observational point of view, is not well understood. In this paper we report observations of a reconnecting current sheet with intermediate guide field BG=0.5Bin, where Bin is the magnetic field amplitude in the inflow regions. The current sheet width is comparable to electron spatial scales. It shows a bifurcated structure and is embedded within the magnetopause current layer with thickness of several ion scales. The electron scale current sheet has strong out‐of‐plane and in‐plane currents, Hall electric and magnetic fields, a finite magnetic field component normal to the current sheet, and nongyrotropic electron distributions formed due to finite gyroradius effects at the boundary of the current sheet. Comparison between test particle simulations and electron data shows that electrons approaching from the edge of the largest magnetic curvature are scattered to perpendicular pitch angles in the center of the current sheet while electrons entering from the opposite side remain close to field aligned. The comparison also shows that an observed depletion in phase space at antiparallel pitch angles can be explained if an out‐of‐plane electric field, which due to the guide field is close to antiparallel to the magnetic field, is present in the center of the current sheet. This electric field would be consistent with the reconnection electric field, and we therefore interpret the depletion of electron phase space density as a manifestation of ongoing reconnection. Key Points: A reconnecting electron scale current sheet is observed inside a filamented magnetopause current layerDue to a guide magnetic field and related magnetic curvature, electrons entering from opposite sides have different behaviorThe presence of an out‐of‐plane electric field can explain observed electron distributions [ABSTRACT FROM AUTHOR]

Abstract: Mirror‐mode structures are widely observed in space plasma environments. Although plasma features within the structures have been extensively investigated in theoretical models and numerical simulations, relatively few observational studies have been made, due to a lack of high‐cadence measurements of particle distributions in previous space missions. In this work, electron dynamics associated with mirror‐mode structures are studied based on Magnetospheric Multiscale observations of electron pitch angle distributions. We define mirror‐mode peaks/troughs as the region where the magnetic field strength is greater/smaller than the mean field. The observations show that most electrons are trapped inside the mirror‐mode troughs and display a donut‐like pitch angle distribution configuration. Besides the trapped electrons in mirror‐mode troughs, we find that electrons are also trapped between ambient mirror‐mode peaks and coexisting untrapped electrons within the mirror‐mode structure. Analysis shows that the observed donut‐like electron distributions are the result of betatron cooling and the spatial dependence of electron pitch angles within the structure. [ABSTRACT FROM AUTHOR]

Correlated motion of electrons in the He atom irradiated with linearly polarised light is discussed. Mixing of the 2pz orbital into the 1s orbital is interpreted as motion of an electron along the z-axis. The transitions to the configurations (1s)(2pz) and (2pz)(2pz) from (1s)(1s) are described by using 1s-2pz hybridised orbitals with variable coefficients of hybridisation, in other words, by using the Thouless parameters. The quasi-eigenstates of the atom in stationary light are obtained on the basis of the Floquet formalism, and the behaviour of the Thouless parameters is analysed. Trajectories of time evolution of the Thouless parameters are found to be useful to grasp the motion of electrons. Shapes of the trajectories are classified into four modes: (1) two electrons try to stay away from each other due to Coulomb repulsion, (2) one of the electrons is solely driven to run, (3) two electrons are driven to travel together and (4) two electrons run anti-parallel with each other. The conditions of intensity and frequency of light causing these four modes are clarified and summarised in a kind of phase diagram. [ABSTRACT FROM AUTHOR]

Femtosecond laser pulse train induced breakdown of fused silica was studied by investigating its plasma emission and the ablated crater morphology. It was demonstrated that the electron dynamics in the ablated fused silica play a dominant role in the emission intensity of induced plasma and the volume of material removal, corresponding to the evolution of free-electron, self-trapped excitons, and the phase change of the fused silica left over by the first pulse. For a fluence of 11 J/cm 2 , the maximum plasma intensity of double-pulse irradiation at an interpulse delay of 120 ps was about 35 times stronger than that of a single-pulse, while the ablated crater was reduced by 27% in volume. The ionization of slow plume component generated by the first pulse was found to be the main reason for the extremely high intensity enhancement for an interpulse delay of over 10 ps. The results serve as a route to simultaneously increase the spatial resolution and plasma intensity in laser-induced breakdown spectroscopy of dielectrics. [ABSTRACT FROM AUTHOR]

A wide range of ultrafast phenomena in various atomic, molecular and condense matter systems is governed by electron dynamics. Therefore, the ability to image electronic motion in real space and real time would provide a deeper understanding of such processes and guide developments of tools to control them. Ultrashort light pulses, which can provide unprecedented time resolution approaching subfemtosecond time scale, are perspective to achieve real-time imaging of electron dynamics. This task is challenging not only from an experimental view, but also from a theory perspective, since standard theories describing light-matter interaction in a stationary regime can provide erroneous results in an ultrafast case as demonstrated by several theoretical studies. We review the theoretical framework based on quantum electrodynamics, which has been shown to be necessary for an accurate description of time-resolved imaging of electron dynamics with ultrashort light pulses. We compare the results of theoretical studies of time-resolved nonresonant and resonant X-ray scattering, and time- and angle-resolved photoelectron spectroscopy and show that the corresponding time-resolved signals encode analogous information about electron dynamics. Thereby, the information about an electronic system provided by these time-resolved techniques is different from the information provided by their time-independent analogues. [ABSTRACT FROM AUTHOR]

• Optical properties of indium tin oxide for low photon intensities and during irradiation with an intense ultrashort laser pulse. • A rate equation model for free electron dynamics in indium tin oxide is developed. • Thermal ionization of electronic states within the band gap is relevant for describing the electron dynamics in indium tin oxide during and after the laser excitation. • In heavily doped indium tin oxide the cascade ionization dominates the multiphoton ionization. The mechanisms of ultrafast laser-induced free electron generation and the effect of the free electrons on the transient optical properties in indium tin oxide is investigated by means of numerically solving rate equations and ultrafast transient experiments. A dynamical model for the transient optical properties of indium tin oxide thin films during excitation with an ultrashort laser pulse with fluences between 0.4 J cm − 2 to 2.3 J cm − 2 is developed and compared to pump probe microscopy during and after excitation with laser pulses. In the non-excited case, thin film interferences dominate the shape of the reflection spectrum. During laser excitation, (quasi-)free electron dynamics drastically alter the optical properties. The temporal evolution of the (quasi-)free electron density is numerically computed using rate equations for irradiation with laser pulses with various peak fluences for a pulse duration of 700 fs and a central wavelength of 1056 nm. We found that a thermal ionization term that takes electronic states within the band gap into account has to be considered to reproduce the reflectivities obtained by pump probe measurements. Additionally, we found that cascade ionization dominates the multiphoton ionization for indium tin oxide. [ABSTRACT FROM AUTHOR]