Three-dimensional particle-in-cell simulations show that the periodic solid-state structures irradiated by intense ($\sim 10^{19}$ W/cm${}^2$) laser pulses can generate collimated electron bunches with energies up to 30 MeV (and acceleration gradient of $11.5$ GeV/cm), if the microstructure period is equal to the laser wavelength. A one-dimensional model of piecewise acceleration in the microstructure is proposed and it is in a good agreement with the results of numerical simulations. It shows that the acceleration process for relativistic electrons can be theoretically infinite. In the simulations, the optimal target parameters (the width of the microstructure elements and the microstructure period) are determined. The explored parameters can be used for proof-of-principle experiments demonstrating an ultrahigh gradient acceleration by a number of identical and mutually coherent laser pulses [A. Pukhov et al., Eur. Phys. J. Spec. Top. 223, 1197 (2014)].
In this letter we report on an experimental study of high harmonic radiation generated in nanometer-scale foil targets irradiated under normal incidence. The experiments constitute the first unambiguous observation of odd-numbered relativistic harmonics generated by the $\vec{v}\times\vec{B}$ component of the Lorentz force verifying a long predicted property of solid target harmonics. Simultaneously the observed harmonic spectra allow in-situ extraction of the target density in an experimental scenario which is of utmost interest for applications such as ion acceleration by the radiation press…
In simulations of a 10PW laser striking a solid we demonstrate the possibility of producing a pure electron-positron plasma by the same processes as those thought to operate in high-energy astrophysical environments. A maximum positron density of 10^26/m^3 is achieved, seven orders of magnitude greater than achieved in previous experiments. Additionally, 35% of the laser energy is converted to a burst of gamma-rays of intensity 10^22W/cm^2, potentially the most intense gamma-ray source available in the laboratory. This absorption results in a strong feedback between both pair and gamma-ray pro…
The problem of harmonics generation in nanotargets is considered at the range of parameters (a nanotarget diameter and a pump laser intensity) when the oscillation amplitude of an electron in a target is much larger than the target width. Electron motion in charged nanotargets in the presence of a laser field of different (non-relativistic) strength is considered. It is demonstarted that for lasers of infrared frequencies clusters do not posess strong enough potential to bound electrons with large oscillation amplitudes. Opposite to clusters, nanofilms were found to be very perspective targets…
The inelastic interaction between heavy ions and an electron plasma in the presence of an intense radiation field (RF) is investigated. The stopping power of the test ion averaged with a period of the RF has been calculated assuming that $ω_{0} >ω_{p}$, where $ω_{0}$ is the frequency of the RF and $ω_{p}$ is the plasma frequency. In order to highlight the effect of the radiation field we present a comparison of our analytical and numerical results obtained for nonzero RF with those for vanishing RF. It has been shown that the RF may strongly reduce the mean energy loss for slow ions while incr…
We investigate bulk ion heating in solid buried layer targets irradiated by ultra-short laser pulses of relativistic intensities using particle-in-cell simulations. Our study focuses on a CD2-Al-CD2 sandwich target geometry. We find enhanced deuteron ion heating in a layer compressed by the expanding aluminium layer. A pressure gradient created at the Al-CD2 interface pushes this layer of deuteron ions towards the outer regions of the target. During its passage through the target, deuteron ions are constantly injected into this layer. Our simulations suggest that the directed collective outwar…
A theoretical model is developed for the interaction of intense femtosecond laser pulses with solid targets on the basis of the two-temperature equation of state for an irradiated substance. It allows the description of the dynamics of the plasma formation and expansion. Comparison of available experimental data on the amplitude and phase of the complex reflection coefficient of aluminum with the simulation results provides new information on the transport coefficients and absorption capacity of the strongly coupled Al plasma over a wide range of temperatures and pressures.
Non-equilibrium processes following the irradiation of atomic clusters with short pulses of vacuum ultraviolet radiation are modelled using kinetic Boltzmann equations. The dependence of the ionization dynamics on the cluster size is investigated. The predictions on: (i) the maximal and average ion charge created, (ii) ion charge state distribution, (iii) average energy absorbed per atom, (iv) spatial charge distribution, and (v) thermalization scales are obtained for spherical xenon clusters containing: 20, 70, 2500 and 90000 atoms. These clusters were exposed to single rectangular pulses of …
The kinetic Boltzmann equation is used to model the non-equilibrium ionization phase that initiates the evolution of atomic clusters irradiated with single pulses of intense vacuum ultraviolet radiation. The duration of the pulses is < 50 fs and their intensity in the focus is < 10^{14} W/cm^2. This statistical model includes various processes contributing to the sample dynamics at this particular radiation wavelength, and is computationally efficient also for large samples. Two effects are investigated in detail: the impact of the electron heating rate and the effect of the plasma environment…
A scheme for generating intense high-harmonic optical vortices is proposed. It relies on spin-orbit interaction of light when a relativistically-strong circularly polarized laser pulse irradiates a micro-plasma-waveguide. The intense laser field drives a strong surface wave at the inner boundary of the waveguide, which leads to high-order harmonic generation as the laser traveling inside. For a circularly polarized drive laser, the optical chirality is imprinted to the surface wave, which facilitates conversion of spin angular momentum of the fundamental light into orbital angular momenta of t…
The effects of a radiation field (RF) on the interaction process of a relativistic electron beam (REB) with an electron plasma are investigated. The stopping power of the test electron averaged with a period of the RF has been calculated assuming an underdense plasma, $ω_{0} >ω_{p}$, where $ω_{0}$ is the frequency of the RF and $ω_{p}$ is the plasma frequency. In order to highlight the effect of the radiation field we present a comparison of our analytical and numerical results obtained for nonzero RF with those for vanishing RF. In particular, it has been shown that the weak RF increases the …
Energy spectra and angular distributions have been measured of electrons that are emitted upon disassembly of $Xe_{150000}$ following irradiation by intense (10$^{15}-10^{16}$ W cm$^{-2}$) laser pulses whose durations are varied over the 100-2200 fs range. The cluster explosion dynamics occur in the hydrodynamic regime. Electron emission is found to be unexpectedly asymmetric and exhibits a resonance when the laser pulse duration is $\sim$1 ps. These results are rationalized by extending the hydrodynamic model to also take into account the force that the light field exerts on the polarization …
PIConGPU modeling of nanoplasma formation in helium nanodroplets irradiated by intense femtosecond laser pulses
Max-Planck-Institut für Kernphysik（马克斯·普朗克核物理研究所）；Helmholtz-Zentrum Dresden - Rossendorf, Center for Advanced Systems Understanding (CASUS)（德累斯顿-罗森多夫亥姆霍兹中心，先进系统理解中心）；Helmholtz-Zentrum Dresden - Rossendorf（德累斯顿-罗森多夫亥姆霍兹中心）；Institute of Physics, University of Kassel（卡塞尔大学物理研究所）；Department of Physics and Quantum Center of Excellence for Diamond and Emerging Materials, Indian Institute of Technology Madras（马德拉斯印度理工学院物理系与钻石及新兴材料量子卓越中心）；ELI Beamlines facility, The Extreme Light Infrastructure ERIC（极亮基础设施欧洲利益协调实体 ELI光束线设施）
A very simple "geometrical" model of a fountain is analyzed to evaluate the net flow on the ground resulting from the superposition of the source and the falling streams. On this basis we suggest a scaling for the magnetic field generated at the rear surface of high-intensity laser-irradiated solid targets due to the "fountain effect" related to fast electrons escaping in vacuum.
Particle-in-cell (PIC) simulation results of sustained acceleration of electron-positron (e+e-) plasmas by comoving electromagnetic (EM) pulses are presented. When a thin slab of overdense e+e- plasma is irradiated with linear-polarized ultra-intense short laser pulses from both sides, the pulses are transmitted when the plasma is compressed to thinner than ~ 2 relativistic skin depths. A fraction of the plasma is then captured and efficiently accelerated by self-induced JxB forces. For 1 micron laser and 1021Wcm-2 intensity, the maximum energy exceeds GeV in a picosecond.
The generation of electron surface oscillations in overdense plasmas irradiated at normal incidence by an intense laser pulse is investigated. Two-dimensional (2D) particle-in-cell simulations show a transition from a planar, electrostatic oscillation at $2ω$, with $ω$ the laser frequency, to a 2D electromagnetic oscillation at frequency $ω$ and wavevector $k>ω/c$. A new electron parametric instability, involving the decay of a 1D electrostatic oscillation into two surface waves, is introduced to explain the basic features of the 2D oscillations. This effect leads to the rippling of the plasma…
Three dimensional Particle-In-Cell simulations describing the interaction of a short intense laser pulse with thin foils are presented. It is observed that the laser generated electron current decays into magnetically isolated filaments. The filaments grow in scale and magnitude by reconnection. Two different laser wavelengths are considered. The spatial separation of the filaments varies for the two wavelengths. Many current filaments carry net electric currents exceeding the Alfven current considerably.
We present a novel scheme to obtain robust, narrowband, and tunable THz emission by using a nano-dimensional overdense plasma target that is irradiated by two counter-propagating detuned laser pulses. So far, no narrowband THz sources with a field strength of GV/m-level have been reported from laser-solid interaction. We report intense THz pulses at beat-frequency ($\simeq$30THz) generated due to strong plasma current produced by the beat ponderomotive force in the colliding region, with an unprecedentedly high peak field strength of 11.9GV/m and spectral width $(Δf/f$$\simeq$$5.3\%)$ from 2D …
Propagation of short and ultra-intense laser pulses in a semi-infinite space of overdense hydrogen plasma is analyzed via fully-relativistic, real geometry particle-in-cell (PIC) simulations including radiation friction. The relativistic transparency and hole-boring regimes are found to be sensitive to the transverse plasma field, backward light reflection, and laser pulse filamentation. For laser intensities approaching $I\sim10^{24}$ W/cm$^2$ the direct laser acceleration of protons, along with ion Coulomb explosion, results in their injection into the acceleration phase of the compressed el…
Light carries angular momentum as spin and orbital components. The spin-orbit interaction (SOI) of light refers to phenomena in which the spin (left or right circular polarisation) affects the spatial degrees of freedom. Recently, interest in SOI has surged, as it provides physical insight into the behaviour of polarised light at subwavelength scales, and allows for spin-controlled manipulation of light. Most studies are performed with low intensity, leaving the role SOI plays in the relativistic laser-plasma interaction, characterised by nonlinearity, less understood. Here, using 3D particle-…
The harmonic emission from cluster nanoplasmas subject to short, intense infrared laser pulses is analyzed by means of particle-in-cell simulations. A pronounced resonant enhancement of the low-order harmonic yields is found when the Mie plasma frequency of the ionizing and expanding cluster resonates with the respective harmonic frequency. We show that a strong, nonlinear resonant coupling of the cluster electrons with the laser field inhibits coherent electron motion, suppressing the emitted radiation and restricting the spectrum to only low-order harmonics. A pump-probe scheme is suggested …
Emission of high energy gamma rays via the non-linear inverse Compton scattering process (ICS) in interactions of ultra-intense laser pulses with thin solid foils is studied using particle-in-cell simulations. It is shown that the angular distribution of the ICS photons has a forward-oriented two-directional structure centred at an angle $\vartheta = \pm 30^\circ$, a value predicted by a theoretical model based on a standing wave approximation to the electromagnetic field in front of the target, which only increases at the highest intensities due to faster hole boring, which renders the approx…
We propose a semi-classical approach based on the Vlasov equation to describe the time-dependent electronic dynamics in a bulk simple metal under an ultrashort intense laser pulse. We include in the effective potential not only the ionic Coulomb potential and mean-field electronic Coulomb potential from the one-body electron distribution but also the exchange-correlation potential within the local density approximation (LDA). The initial ground state is obtained by the Thomas-Fermi model. To numerically solve the Vlasov equation, we extend the pseudo-particle method, previously used for nuclei…
A three dimensional Particle-In-Cell simulation describing the interaction of an intense laser beam with a plasma slab is presented. It is observed that the laser generated electron current decays into magnetically isolated filaments. The filaments grow in scale and magnitude by a merging process in the course of which the field topology changes. The opposite process also takes place occasionally. The laser driven charge and energy flows and the reconnecting magnetic field mutually interact. At the end of the merging process flows and fields are confined close to the laser irradiated surface o…
Generation of terahertz radiation by an oscillating discharge, excited with short laser pulses, may be controlled by geometry of the irradiated target. In this work, an annular target with a thin slit is considered as an efficient emitter of secondary radiation when driven by a short intense laser pulse. Under the irradiation, a slit works as a diode, which is quickly filled by dense plasma, closing the circuit for a travelling discharge pulse. Such a diode defines the discharge pulse propagation direction in a closed contour, enabling its multiple passes along the coil.The obtained oscillatin…
Compact acceleration of a tightly collimated relativistic electron beam with high charge from a laser-plasma interaction has many unique applications. However, currently the well-known schemes, including laser wakefield acceleration from gases and vacuum laser acceleration from solids, often produce electron beams either with low charge or with large divergence angles. In this work, we report the generation of highly collimated electron beams with a divergence angle of a few degrees, quasi-monoenergetic spectra peaked at the MeV level, and extremely high charge ($\sim$100 nC) via a powerful su…
Balmer spectra are investigated which are obtained from hydrogen droplets irradiated by ultra-short intense laser pulses. A unified quantum statistical description of bremsstrahlung, the Stark broadening and the van der Waals profile of hydrogen spectral lines is used, which allows to include many-particle effects. Analyzing the line profiles, a low ionization degree of a dense plasma is inferred, where the main contribution to the spectral line shape originates from the interaction with the neutral components. Effective temperatures and densities of the radiating microplasma are deduced. A dy…
A novel radiation pressure acceleration (RPA) regime of heavy ion beams from laser-irradiated ultrathin foils is proposed by self-consistently taking into account the ionization dynamics. In this regime, the laser intensity is required to match with the large ionization energy gap when the successive ionization of high-Z atoms passing the noble gas configurations [such as removing an electron from the helium-like charge state $(\text{Z}-2)^+$ to $(\text{Z}-1)^+$]. While the target ions in the laser wing region are ionized to low charge states and undergo rapid dispersions due to instabilities,…
Ionization Dynamics in Intense Laser-Produced Plasmas
Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Laboratory for Laser Energetics（激光能量学实验室）；University of Alberta（阿尔伯塔大学）；Department of Physics, University of Alberta（阿尔伯塔大学物理系）；Department of Physics and Astronomy, University of Rochester（罗切斯特大学物理与天文系）；University of Rochester（罗切斯特大学）
Hard x-ray emission (20 - 200 keV) from plasmas produced by intense laser pulses on nanoparticle coated targets is compared with that from optically polished targets. The yield enhancement offered by nanoparticles is studied under different prepulse conditions. It is observed that the enhancement reduces when the nanoparticle coated target is irradiated with a prepulse with intensity greater than 10^13 W/cm^2. When the prepulse intensity exceeds 10^14 W/cm^2, the enhancement vanishes completely. This is attributed to preplasma formation on nanoparticles their subsequent structural modifcation …
We study the excitation of electron currents in a transparent cell of sub-millimeter size filled by an atomic gas and illuminated by an intense two-color femtosecond laser pulse. The pulse consists of a strong fundamental component and its second harmonic of low intensity, both circularly polarized. We show that for sufficiently small $20μ$m cells the plasma oscillation excited by asymmetric ionization is almost spatially homogeneous within the interaction volume. This coherent dipole plasma oscillation results in a remarkably efficient conversion of the electron energy into that of radiation …
A cascaded ion acceleration scheme is proposed by use of ultrashort laser-irradiated microtubes. When the electrons of a microtube are blown away by intense laser pulses, strong charge-separation electric fields are formed in the microtube both along the axial and along the radial directions. By controlling the time delay between the laser pulses and a pre-accelerated proton beam injected along the microtube axis, we demonstrate that this proton beam can be further accelerated by the transient axial electric field in the laser-irradiated microtube. Moreover, the collimation of the injected pro…
Bright Ar K-shell x-ray with very little background has been generated using an Ar clustering gas jet target irradiated with an 800 mJ, 30 fs ultra-high contrast laser, with the measured flux of 1.1 x 10^4 photons/mrad^2/pulse. This intense x-ray source critically depends on the laser contrast and the laser energy and the optimization of this source with interaction is addressed. Electron driven by laser electric field directly via nonlinear resonant is proved in simulation, resulting in effective electron heating and the enhancement of x-ray emission. The x-ray pulse duration is demonstrated …
In this paper we describe the physical processes that lead to the generation of Giant Electro- Magnetic Pulses (GEMP) on powerful laser facilities. Our study is based on experimental mea- surements of both the charging of a solid target irradiated by an ultra-short, ultra-intense laser and the detection of the electromagnetic emission in the GHz domain. An unambiguous correlation between the neutralisation current in the target holder and the electromagnetic emission shows that the source of the GEMP is the remaining positive charge inside the target after the escape of fast electrons accelera…
An overdense plasma layer irradiated by an intense light can exhibit dramatic nonlinear-optical effects due to a relativistic mass-effect of free electrons: highly-multiple hysteresises of reflection and transition, and emergence of gigantic "rogue waves". Those are trapped quasi-soliton field spikes inside the layer, sustained by an incident radiation with a tiny fraction of their peak intensity once they have been excited by orders of magnitude larger pumping. The phenomenon persists even in the layers with "soft" boundaries, as well as in a semi-infinite plasma with low absorption.
The paper reports the results of two-dimensional particle-in-cell simulations of proton beam acceleration at the interactions of a 130 fs laser pulse of intensity from the range of 10^21-10^23 W/cm^2, predicted for the Extreme Light Infrastructure (ELI) lasers currently built in Europe, with a thin hydrocarbon (CH) target. A special attention is paid to the effect of the laser pulse intensity and polarization (linear-LP, circular-CP) as well as the target thickness on the proton energy spectrum, the proton beam spatial distribution and the proton pulse shape and intensity. It is shown that for…
The dynamics of an electron bunch irradiated by two focused colliding super-intense laser pulses and the resulting gamma and electron-positron production are studied. Due to attractors of electron dynamics in a standing wave created by colliding pulses the photon emission and pair production, in general, are more efficient with linearly polarized pulses than with circularly polarized ones. The dependence of the key parameters on the laser intensity and wavelength allows to identify the conditions for the cascade development and gamma-electron-positron plasma creation.
In order to achieve a high quality, i. e. monoergetic, intense ion beam, we propose the use of a double layer target. The first layer, at the target front, consists of high-Z atoms, while the second (rear) layer is a thin coating of low-Z atoms. The high quality proton beams from the double layer target, irradiated by an ultra-intense laser pulse, are demonstrated with three dimensional Particle-in-Cell simulations.
A model of an electron-beam-plasma system is introduced to model the electrical breakdown physics of low-pressure nitrogen irradiated by an intense pulsed electron beam. The rapidly rising beam current induces an electric field which drives a return current in the plasma. The rigid-beam model is a reduction of the problem geometry to cylindrical coordinates and simplifications to Maxwell's equations that are driven by a prescribed electron beam current density. The model is convenient for comparing various reductions of the plasma dynamics and plasma chemistry while maintaining a good approxim…
The Schwinger limit could be approached by focusing to its diffraction limit the light reflected by a plasma mirror irradiated by a multi-petawatt laser. We explore numerically the interaction between such intense light and matter. We find that the interaction with a relativistic counterpropagative electron beam would enable the exploration of the fully nonperturbative regime of strong-field quantum electrodynamics (SF-QED), while the interaction with an initially solid target leads to a profusion of SF-QED effects that retroact on the laser-plasma interaction. We observe in both scenarios the…
This paper studies the interaction of laser-driven $γ$-photons and high energy charged particles with high-Z targets through Monte-Carlo simulations. The interacting particles are taken from particle-in-cell simulations of the interaction of a tightly-focused ultraintense laser pulse with a titanium target. Lead is chosen as the secondary high-Z target owing to its high cross section of the giant dipole resonance and electron-positron pair production. The results reveal an ultra-short ultra-relativistic collimated positron population and their energy spectra, angular distribution, and temporal…
The ability of an intense laser pulse to propagate in a classically over-critical plasma through the phenomenon of relativistic transparency is shown to facilitate the generation of strong plasma magnetic fields. Particle-in-cell simulations demonstrate that these fields significantly enhance the radiation rates of the laser-irradiated electrons, and furthermore they collimate the emission so that a directed and dense beam of multi-MeV gamma-rays is achievable. This capability can be exploited for electron-positron pair production via the linear Breit-Wheeler process by colliding two such dens…
Monoenergetic ion bunch generation and acceleration from double layer thin foil target irradiated by intense linearly polarized (LP) laser pulse is investigated using two-dimensional (2D) particle-in-cell (PIC) simulations. The low-Z ions in the front layer of the target are accelerated by the laser-driven hot electrons and penetrate through the high-Z ion layer to generate a quasi-monoenergetic ion bunch, and this bunch will continue to be accelerated by the quasi-stable electrostatic sheath field which is formed by the immobile high-Z ions and the hot electrons. This mechanism offers possibi…
Microscopy X-ray Imaging enriched with Small Angle X-ray Scattering for few nanometer resolution reveals shock waves and compression in intense short pulse laser irradiation of solids
Surfaces covered with nanostructures, such as nanowire arrays, have shown to facilitate a significantly higher absorption of laser energy as compared to flat surfaces. Due to the efficient coupling of the laser energy, highly energetic electrons are produced, which in turn can emit intense ultrafast X-ray pulses. In the present work we use full three dimensional PIC simulations to analyze the behavior of arrays of carbon nanowires $400 nm$ in diameter, irradiated by a $λ_0 = 400 nm$ laser pulse of $60 fs$ duration at FWHM and a vector potential of $a_0 = 18$. We analyze the ionization dynamics…
We study electron acceleration within a sub-critical plasma channel irradiated by an ultra-intense laser pulse ($a_0>100$ or $I>10^{22}~\mathrm{W/cm^2}$). In this regime, radiation reaction significantly alters the electron dynamics. This has an effect not only on the maximum attainable electron energy but also on the phase-matching process between betatron motion and electron oscillations in the laser field. Our study encompasses analytical description, test-particle calculations and 2-dimensional particle-in-cell simulations. We show single-stage electron acceleration to multi-GeV energies w…
The energy of the ions accelerated by an intense electromagnetic wave in the radiation pressure dominated regime can be greatly enhanced due to a transverse expansion of a thin target. The expansion decreases the number of accelerated ions in the irradiated region increasing the energy and the longitudinal velocity of remaining ions. In the relativistic limit, the ions become phase-locked with respect to the electromagnetic wave resulting in the unlimited ion energy gain. This effect and the use of optimal laser pulse shape provide a new approach for great enhancing the energy of laser acceler…
We examine the effect of cluster size on the interaction of Ar$_{55}$-Ar$_{2057}$ with intense extreme ultraviolet (XUV) pulses, using a model we developed earlier that includes ionization via collisional excitation as an intermediate step. We find that the dynamics of these irradiated clusters is dominated by collisions. Larger clusters are more highly collisional, produce higher charge states, and do so more rapidly than smaller clusters. Higher charge states produced via collisions are found to reduce the overall photon absorption, since charge states of Ar$^{2+}$ and higher are no longer p…
Surface plasmon (SP) excitation in intense laser interaction with solid target can be exploited for enhancing secondary emissions, in particular efficient acceleration of high charge electron bunches. Previous studies have mostly used grating coupling to allow SP excitation, which requires stringent laser contrast conditions to preserve the structural integrity of the target. Here we show via simulations that efficient SP electron acceleration for currently available short pulse lasers can occur in a flat foil irradiated at parallel or grazing incidence ($\sim 5^\circ$ with the target surface)…
Coulomb implosion mechanism of the negatively charged ion acceleration in laser plasmas is proposed. When a cluster target is irradiated by an intense laser pulse and the Coulomb explosion of positively charged ions occurs, the negative ions are accelerated inward. The maximum energy of negative ions is several times lower than that of positive ions. The theoretical description and Particle-in-Cell simulation of the Coulomb implosion mechanism and the evidence of the negative ion acceleration in the experiments on the high intensity laser pulse interaction with the cluster targets are presente…
