Tens Of Fs Research Articles

First-Principles Simulations of Salt-Concentrated Electrolytes for Li-Based Batteries: How Solvents Tune Solvation Structures and Li-Ion Conductivity

Salt-concentrated nonaqueous electrolytes, due to their special properties in increasing the stability of batteries by the formation of anion-derived solid electrolyte interphases (SEIs), have attracted considerable attention in recent years. Despite extensive efforts to explore the microscopic solvation structures of electrolyte solutions, a clear relationship between the microstructures and electrolyte performance, especially the Li-ion conductivity, is still in demand. In this work, we performed ab initio molecular dynamics (AIMD) simulations as well as density function theory (DFT) calculations for three as-designed electrolytes, namely lithium bis(fluorosulfonyl)imide (LiFSI) with acetonitrile (AN), 1,2-dimethoxyethane (DME), and 2,2-dimethyl-3,6,9-trioxa-2-siladecane (siloxane). We observed that for the above electrolytes at high concentrations, Li-ion conduction proceeds when the solvation structure changes from one form to another in a few tens of fs, involving the binding/debinding of both the solvent and FSI anion with the Li-center. The dynamics of binding between the solvents and Li decrease with the increase in the strength of the solvation sheath, which is influenced by the polarity of the solvent. The steric shielding effect was clearly detected in the siloxane-LiFSI system which became almost nonconductive at a concentration of 3 mol L–1. It should be noted that despite the high concentration of each electrolyte (≥5 mol L–1), there is still a certain amount of free solvents according to the simulation results. Our results deepen the understanding of the Li-ion conduction process in salt-concentrated electrolytes and provide guidelines for designing high-performance electrolytes.

Multifunctional all-fiber polarization-maintaining nonlinear pulse amplifier

A multifunctional all-fiber polarization-maintaining nonlinear amplifier system is proposed and investigated. Two Erbium-doped polarization-preserving gain fibers are used to amplify the seed laser and split into four output points with different transmission fibers to obtain four stable ultra-short pulses with different durations, which vary from tens of fs to ps level. And the output powers are tens of mW and can be changed with different output point. The seed laser in this process has a repetition rate of 113 MHz, a pulse duration of about 450fs, and different absorption coefficients for the two gain fibers. It is demonstrated that the proposed fiber laser with varied pulse duration can be potentially applied in laser detection, terahertz generation, and even different types of material processing.

Spectrally tunable high-power Yb:fiber chirped-pulse amplifier

Tailoring the properties of the driving laser to the need of applications often requires compromises among laser stability, high peak and average power levels, pulse duration, and spectral bandwidth. For instance, spectroscopy with optical frequency combs in the extreme/visible ultraviolet spectral region requires a high peak power of the near-IR driving laser, and therefore high average power, pulse duration of a few tens of fs, and maximal available spectral bandwidth. Contrarily, the parametric conversion efficiency is higher for pulses with a duration in the 100-fs range due to temporal walk-off and coating limitations. Here we suggest an approach to adjust the spectral characteristics of high-power chirped-pulse amplification (CPA) to the requirements of different nonlinear frequency converters while preserving the low-phase-noise (PN) properties of the system. To achieve spectral tunability, we installed a mechanical spectral shaper in a free-space section of the stretcher of an in-house-developed ytterbium-fiber-based CPA system. The CPA system delivers 100 W of average power at a repetition rate of 132.4 MHz. While gaining control over the spectral properties, we preserve the relative-intensity-noise and PN properties of the system. The high-power CPA can easily be adjusted to deliver either a spectrum ideal for mid-IR light generation (full width at half maximum of ∼ 11 nm , compressed pulse duration of 230 fs) or a spectrum ideal for highly nonlinear processes such as high-harmonic generation ( - 10 dB level of > 50 nm , transform-limited pulse duration of ∼ 65 fs ).

Deriving x-ray pulse duration from center-of-energy shifts in THz-streaked ionized electron spectra.

A fast and robust, yet simple, method has been developed for the immediate characterization of x-ray pulse durations via IR/THz streaking that uses the center of energy (COE) of the photoelectron spectrum for the evaluation. The manuscript presents theory and numerical models demonstrating that the maximum COEs shift as a function of the pulse duration and compares them to existing data for validation. It further establishes that the maximum COE can be derived from two COE measurements set at a phase of π/2 apart. The theory, model, and data agree with each other very well, and they present a way to measure pulse durations ranging from sub-fs to tens of fs on-the-fly with a fairly simple experimental setup.

Electron-Transfer-Induced Side-Chain Cleavage in Tryptophan Facilitated through Potassium-Induced Transition-State Stabilization in the Gas Phase.

Fragmentation of transient negative ions of tryptophan molecules formed through electron transfer in collisions with potassium atoms is presented for the first time in the laboratory collision energy range of 20 up to 100 eV. In the unimolecular decomposition process, the dominating side-chain fragmentation channel is assigned to the dehydrogenated indoline anion, in contrast to dissociative electron attachment of free low-energy electrons to tryptophan. The role of the collision complex formed by the potassium cation and tryptophan negative ion in the electron transfer process is significant for the mechanisms that operate at lower collision energies. At those collision times, on the order of a few tens of fs, the collision complex may not only influence the lifetime of the anion but also stabilize specific transition states and thus alter the fragmentation patterns considerably. DFT calculations, at the BHandHLYP/6-311++G(3df,2pd) level of theory, are used to explore potential reaction pathways and the evolvement of the charge distribution along those.

Femtosecond electronic structure response to high intensity XFEL pulses probed by iron X-ray emission spectroscopy

We report the time-resolved femtosecond evolution of the K-shell X-ray emission spectra of iron during high intensity illumination of X-rays in a micron-sized focused hard X-ray free electron laser (XFEL) beam. Detailed pulse length dependent measurements revealed that rapid spectral energy shift and broadening started within the first 10 fs of the X-ray illumination at intensity levels between 1017 and 1018 W cm-2. We attribute these spectral changes to the rapid evolution of high-density photoelectron mediated secondary collisional ionization processes upon the absorption of the incident XFEL radiation. These fast electronic processes, occurring at timescales well within the typical XFEL pulse durations (i.e., tens of fs), set the boundary conditions of the pulse intensity and sample parameters where the widely-accepted ‘probe-before-destroy’ measurement strategy can be adopted for electronic-structure related XFEL experiments.

Double chirp-taper x-ray free-electron laser for attosecond pump-probe experiments

In this paper we propose a double chirp-taper method to produce two subfemtosecond x-ray free-electron lasers (XFELs) using electron beams with sinusoidal energy modulation. The taper of the undulator is optimized to control the power profile of each XFEL pulse to obtain a single-spike power shape. We present start-to-end numerical simulations of this method to demonstrate the generation of two XFEL pulses with $\ensuremath{\sim}0.4\text{ }\text{ }\mathrm{fs}$ full width at half maximum, with a time separation tunable from 0 to tens of fs and energy separation limited by the available undulator tuning range. The output of this method provides a powerful tool for XFEL pump-probe experiments at the attosecond timescale.

Three-dimensional kinetic modeling of streamer propagation in a nitrogen/helium gas mixture

A fully resolved kinetic model (particle-in-cell and direct simulation Monte Carlo for particle/photon collisions) of a near atmospheric pressure ionization wave is presented here. Fully resolving the required numerical spatial (sub-μm) and temporal scales (tens of fs) for atmospheric pressure discharges in three-dimensions is still a challenging task on modern super computers. To keep the overall problem tractable, the total number of elements are reduced by only simulating a 10° wedge rather than a full 360° geometry. The ionization wave is generated in a needle-plane configuration with a gap size of 250 μm and a background of nitrogen and helium gas. A voltage of 1500 V is applied to the anode and an initial electron and ion density of 109 cm−3 is seeded in a region near the anode electrode tip and extending towards the cathode. As these initial electrons are swept away, photoionization and photoemission create new electrons and allow the ionization front to propagate towards the cathode. Results from the 90% N2, 10% He discharge indicate that photoionization has minimal impact on plasma formation processes and cathode photoemission is the dominant mechanism for new electrons. In the 90% He, 10% N2 discharge case, however, photoionization likely has an impact as the observed locations of photoionization occur far enough away from the ionization front to allow for sufficient avalanche processes that contribute to the propagation of the ionization wave. Additionally, the electron energy distribution functions in the 90% He, 10% N2 case indicate that there is less energy loss to the low lying molecular N2 electronic states as well as the vibrational and rotational modes. This leads to higher electron energies and faster plasma development times of ∼0.4 ns for the 90% He, 10% N2 case, and ∼1.5 ns for the 90% N2, 10% He case. In addition to analysis of the ionization wave results, the overall challenges associated with simulations near atmospheric pressure discharges in three-dimensions are discussed, including the limitations of the 10° wedge that produces, at least qualitatively, minimal 3D effects.

Ultrafast Intersystem Crossing vs Internal Conversion in α-Diimine Transition Metal Complexes: Quantum Evidence.

Whereas third row transition metal carbonyl α-diimine complexes display luminescent properties and possess low-lying triplet metal-to-ligand charge transfer (MLCT) states efficiently accessible by a spin-vibronic mechanism, first row analogues hold low-lying metal-centered (MC) excited states that could quench these properties. Upon visible irradiation, different functions are potentially stimulated, namely, luminescence, electron transfer, or photoinduced CO release, the branching ratio of which is governed by the energetics, the character, and the early time dynamics of the photoactive excited states. Simulations of ultrafast nonadiabatic quantum dynamics, including spin-vibronic effects, of [M(imidazole)(CO)3(phenanthroline)]+ (M = Mn, Re) highlight the role of the metal atom. An ultrafast intersystem crossing process, driven by spin-orbit coupling, populates the low-lying triplet states of [Re(imidazole)(CO)3(phen)]+ within the first tens of fs. In contrast, efficient internal conversion between the two lowest 1MLCT states of [Mn(imidazole)(CO)3(phen)]+ is mediated within 50 fs by vibronic coupling with upper MC and MLCT states.

Prospects of Using High-Intensity THz Pulses To Induce Ultrafast Temperature-Jumps in Liquid Water.

Ultrashort, high-intensity terahertz (THz) pulses, e.g., generated at free-electron laser facilities, allow for direct investigation as well as the driving of intermolecular modes in liquids like water and thus will deepen our understanding of the hydrogen bonding network. In this work, the temperature-jump (T-jump) of water induced by THz radiation is simulated for ten different THz frequencies in the range from 3 to 30 THz and five different pulse intensities in the range from 1 × 1011 to 5 × 1012 W/cm2 employing both ab initio molecular dynamics (AIMD) and force field molecular dynamics (FFMD) approaches. The most efficient T-jump can be achieved with 16 THz pulses. Three distinct T-jump mechanisms can be uncovered. For all cases, the T-jump mechanism proceeds within tens of femtoseconds (fs). For frequencies between 10 and 25 THz, most of the energy is initially transferred to the rotational degrees of freedom. Subsequently, the energy is redistributed to the translational and intramolecular vibrational degrees of freedom within a maximum of 500 fs. For the lowest frequencies considered (7 THz and below), translational and rotational degrees of freedom are heated within tens of fs as the THz pulse also couples to the intermolecular vibrations. Subsequently, the intramolecular vibrational modes are heated within a few hundred fs. At the highest frequencies considered (25 THz and above), vibrational and rotational degrees of freedom are heated within tens of fs, and energy redistribution to the translational degrees of freedom happens within several hundred fs. Both AIMD and FFMD simulations show a similar dependence of the T-jump on the frequency employed. However, the FFMD simulations overestimate the total energy transfer around the main peak and drop off too fast toward frequencies higher and lower than the main peak. These differences can be rationalized by missing elements, such as the polarizability, in the TIP4P/2005f force field employed. The feasibility of performing experiments at the studied frequencies and intensities as well as important issues such as energy efficiency, penetration depth, and focusing are discussed.

Lifetime and surface-to-bulk scattering off vacancies of the topological surface state in the three-dimensional strong topological insulators Bi2Te3 and Bi2Se3

We analyze the finite lifetimes of the topologically protected electrons in the surface state of Bi2Te3 and Bi2Se3 due to elastic scattering off surface vacancies and as a function of energy. The scattering rates are decomposed into surface-to-surface and surface-to-bulk contributions, giving us new fundamental insights into the scattering properties of the topological surface states (TSS). If the number of possible final bulk states is much larger than the number of final surface states, then the surface-to-bulk contribution is of importance, otherwise the surface-to-surface contribution dominates. Additionally, we find defect resonances that have a significant impact on the scattering properties of the TSS. They can strongly change the lifetime of the surface state to vary between tens of fs to ps at surface defect concentrations of 1 at%. We also see that the effective scattering angle shows a strong dependence on the Fermi surface warping. Our results compare fairly well with available experiments.

Radiation Damage in Macromolecular Crystallography.

Radiation damage inflicted on macromolecular crystals during X-ray diffraction experiments remains a limiting factor for structure solution, even when samples are cooled to cryotemperatures (~100 K). Efforts to establish mitigation strategies are ongoing and various approaches, summarized below, have been investigated over the last 15 years, resulting in a deeper understanding of the physical and chemical factors affecting damage rates. The recent advent of X-ray free electron lasers permits "diffraction-before-destruction" by providing highly brilliant and short (a few tens of fs) X-ray pulses. New fourth generation synchrotron sources now coming on line with higher X-ray flux densities than those available from third generation synchrotrons will bring the issue of radiation damage once more to the fore for structural biologists.

SACLAの高強度X線照射下の原子・分子の動的振舞い

We have investigated ultrafast electronic and nuclear dynamics in atoms, molecules and clusters induced by very intense（～50 μJ/μm2）, ultrashort（～10 fs） pulses generated by SACLA. At photon energy of 5.0～5.5 keV, we could identify that Xen+ with n up to 26 is produced, evidencing occurrence of deep inner-shell ionization and sequential electronic decay cycles repeated multiple times in the xenon atom within ～10 fs pulse duration. The results for momentum-resolved multiple ion coincidence study on iodine-contained organic molecules（iodomethane and 5-iodouracil）illustrates that the charges are produced by the cycles of deep inner-shell ionization of the iodine atom and sequential electronic decay and spread over the entire molecule within 10 fs, leading to Coulomb explosion. The measured momentum distributions and correlations are well reproduced by the model calculations. The results for electron spectroscopy on argon and xenon clusters, with help of model calculations, illustrate that nanoplasma is formed by the XFEL pulse in tens of fs, and continuous thermal emission from the plasma occurs in ps.

Practicing DSAM in aberrant domain: use of multi-disciplinary techniques

Measurement of level lifetime of nuclear states is of relevance in nuclear structure research as it provides us with an unique probe into the underlying microscopic structure of these states. Of the several experimental techniques for lifetime measurements, the Doppler Shift Attenuation Method (DSAM) is the one adopted for measuring lifetimes typically in the range of few tens of fs to few ps. The technique is based on the analysis of the observed Doppler affected gamma rays emitted by the recoils in flight. The crucial component in the related analysis is the simulation of the stopping process, of the residues of interest, in the target and the backing media. This requires calculation of the corresponding stopping powers and the same has been identified as one of the principal uncertainties in the extracted lifetime in DSAM. Traditionally the method is pursued with a thin target, for production of nuclei of interest, on a thick elemental backing wherein stopping process is perceived to occur. The present work in light of it's objectives uses a setup which is in sharp variance with the conventional scenario, such as the use of a thick molecular target, which contributes both to the production of the residues as well as their subsequent slowing down. This demanded extensive developments in the analysis procedure particularly in the domain of simulating the stopping process with due incorporation of the nuances of nuclear reaction kinematics besides subjecting the molecular medium to a detailed structural characterization, routinely carried out in the domain of material science. These developments have been used to extract the level lifetimes of nuclei at the interface of the sd & pf shells such as 26Mg, 29Si, and 32P.

Decoherence, control and attosecond probing of XUV-induced charge migration in biomolecules. A theoretical outlook.

The sudden ionization of a molecule by an attosecond pulse is followed by charge redistribution on a time scale from a few femtoseconds down to hundreds of attoseconds. This ultrafast redistribution is the result of the coherent superposition of electronic continua associated with the ionization thresholds that are reached by the broadband attosecond pulse. Thus, a correct theoretical description of the time evolution of the ensuing wave packet requires the knowledge of the actual ionization amplitudes associated with all open ionization channels, a real challenge for large and medium-size molecules. Recently, the first calculation of this kind has come to light, allowing for interpretation of ultrafast electron dynamics observed in attosecond pump-probe experiments performed on the amino acid phenylalanine [Calegari et al., Science 2014, 346, 336]. However, as in most previous theoretical works, the interpretation was based on various simplifying assumptions, namely, the ionized electron was not included in the description of the cation dynamics, the nuclei were fixed at their initial position during the hole migration process, and the effect of the IR probe pulse was ignored. Here we go a step further and discuss the consequences of including these effects in the photoionization of the glycine molecule. We show that (i) the ionized electron does not affect hole dynamics beyond the first femtosecond, and (ii) nuclear dynamics has only a significant effect after approximately 8 fs, but does not destroy the coherent motion of the electronic wave packet during at least few additional tens of fs. As a first step towards understanding the role of the probe pulse, we have considered an XUV probe pulse, instead of a strong IR one, and show that such an XUV probe does not introduce significant distortions in the pump-induced dynamics, suggesting that pump-probe strategies are suitable for imaging and manipulating charge migration in complex molecules. Furthermore, we show that hole dynamics can be changed by shaping the attosecond pump pulse, thus opening the door to the control of charge dynamics in biomolecules.

Double-resonance spectroscopy of radicals: higher electronic excited states of 1- and 2-naphthylmethyl, 1-phenylpropargyl and 9-anthracenylmethyl

Multiple pulsed-laser frequencies are used to extract the excitation spectra of Dn ← D0 transitions (n > 1) of the 1- and 2-naphthylmethyl, 1-phenylpropargyl and 9-anthracenylmethyl radicals. Bands are, respectively, observed at 27993, 27478, 32437 and 25063 cm−1, with respective widths (at half maximum) of 292, 290, 149 and 326 cm−1. On the basis of comparison with ab initio vertical excitation energies, the transitions for 2-naphthylmethyl, 1-phenylpropargyl and 9-anthracenylmethyl radical are assigned as D3 ← D0. The observed transition of 1-naphthylmethyl is ambiguously either or both D3 ← D0 and D4 ← D0. From the wide Lorentzian profiles observed, lifetimes of a few tens of fs are inferred, the spectral widths precluding this class of molecule from being responsible for the long-unidentified diffuse interstellar bands.

Table-top generation and spectroscopic study of ∼10 TPa high-energy density materials with C60+ hypervelocity (∼100 km/s) impact

The use of nanoparticles as flyers to create shock pressures exceeding 10 TPa and to investigate the matters in planetary or stellar interiors has been pursued by the author for two decades. Previous studies led by the author at Brookhaven National Lab (BNL) in 1994 proved that such ultra-strong shocks can be generated with charged bio and water nanoparticles by accelerating them with an electrostatic accelerator and impacting them on solids at ∼ 100 km/s. The author in 2008 showed that the BNL nanoplasmas produced intense bursts of soft x-rays (hv ∼ 100 eV) from optical decay of excimer-like Metastable Innershell Molecular State, MIMS, formed by inner-shell electron excitation. The conversion efficiency from the nano-flyer kinetic energy to the radiation energy was unexpectedly high, ∼38%, which was attributed to high efficiency pressure ionization conversion of impact energy to MIMS excitation energy and MIMS collective optical decay in tens of fs via Dicke Superradiance. Now, this paper reports an experimental study performed with C60 as a nano-flyer that permitted reduction of the size and complexity of the apparatus by orders of magnitude compared with the BNL one. The present results confirm the BNL results unambiguously, demonstrate a pathway to scaling up of soft x-ray intensity, and open doors to a wide range of applications from lithography to inertial fusion.

First electrons from the new 220 TW Frascati Laser for Acceleration and Multidisciplinary Experiments (FLAME) at Frascati National Laboratories (LNF)

A new era of laser based plasma accelerators is emerging following the commissioning of many high power laser facilities around the world. Extremely short (tens of fs) laser pulses with energy of multi-joules level are available at these newly built facilities. Here we describe the new 220TW FLAME facility. In particular we discuss the laser system general layout, the main measurements on the laser pulse parameters, the underground target area. Finally we give an overview of the first results of the Self-Injection Test Experiment (SITE), obtained at a low laser energy. This initial low laser energy experimental campaign was necessary for the validation of the radio-protection shielding (Esposito, 2011 [1]) we discuss here. With respect to our preliminary configuration, with a pulse duration of 30fs and a focusing optic of F/15, we discuss here the minimum laser energy requirements for electron acceleration and the forward transmitted optical radiation.

A multi-scale ab initio theoretical study of the production of free radicals in swift ion tracks in liquid water

Using a multi-scale theoretical approach from first principles, we show that the production of HO2 radicals in liquid water can be understood from the initial Coulomb explosion of doubly ionized water molecules. Based on the separation of time scales, we used three different theoretical models, each one associated with a specific time scale. The initial ∼1 fs of water radiolysis is taken care of with a Monte Carlo code whose basic ingredients are cross-sections. These have been calculated in the present work using the continuum distorted wave eikonal initial state (CDW-EIS) model framework. Our calculated cross-sections nicely demonstrate that double ionization of water molecules is one major event compatible with the experimental HO2 molecular rate production. The subsequent tens of fs following the double ionization of one water molecule of the liquid medium have been described with microscopic ab initio Car–Parrinello molecular dynamics simulations. Dynamics shows that the water Coulomb explosion leads to the formation of two H3O+ ions and an atomic oxygen atom. The final stage of the Coulomb explosion (up to the ms timescale) has been modelled with a chemical Monte Carlo code, assessing that the production of HO2 results from the O + OH → HO2 reaction in the liquid phase.

Laser–plasma accelerator: status and perspectives

Laser-plasma accelerators deliver high-charge quasi-monoenergetic electron beams with properties of interest for many applications. Their angular divergence, limited to a few mrad, permits one to generate a small gamma ray source for dense matter radiography, whereas their duration (few tens of fs) permits studies of major importance in the context of fast chemistry for example. In addition, injecting these electron beams into a longer plasma wave structure will extend their energy to the GeV range. A GeV laser-based accelerator scheme is presented; it consists of the acceleration of this electron beam into relativistic plasma waves driven by a laser. This compact approach (centimetres scale for the plasma, and tens of meters for the whole facility) will allow a miniaturization and cost reduction of future accelerators and derived X-ray free electron laser (XFEL) sources.