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We present results from a pitcher-catcher experiment utilizing a proton beam generated with nanostructured targets at a petawatt-class, short-pulse laser facility to induce proton-boron fusion reactions in a secondary target. A 45-fs laser pulse with either 400 nm wavelength and 7 J energy, or 800 nm and 14 J, and an intensity of up to 5 × 1021 W/cm2 was used to irradiate either thin foil targets or near-solid density, nanostructured targets made of boron nitride (BN) nanotubes. In particular, for 800 nm wavelength irradiation, a BN nanotube target created a proton beam with about five times higher maximum energy and about ten times more protons than a foil target. This proton beam was used to irradiate a thick plate made of boron nitride placed in close proximity to trigger 11B (p, α) 2α fusion reactions. A suite of diagnostics consisting of Thomson parabola ion spectrometers, postshot nuclear activation measurements, neutron time-of-flight detectors, and differentially filtered solid-state nuclear track detectors were used to measure both the primary proton spectrum and the fusion products. From the primary proton spectrum, we calculated (p, n) and (α,n) reactions in the catcher and compare with our measurements. The nuclear activation results agree quantitatively and neutron signals agree qualitatively with the calculations, giving confidence that primary particle distributions can be obtained from such measurements. These results provide new insights for measuring the ion distributions inside of proton-boron fusion targets.

The reflection of a laser pulse by a relativistic-moving mirror is one of the fundamental problems encountered in highpower laser and plasma interactions. It is well known that a laser pulse reflected by a relativistic-flying mirror experiences the intensification, frequency up-shift, and shortening of pulse duration. Thus, it is of fundamental interest to have a mathematical solution expressing the intensity distribution of a laser pulse reflected by a relativistic-flying parabolic mirror. In this paper, we present analytical and mathematical formulae describing the electromagnetic field of a laser pulse reflected and focused by the relativistic-flying parabolic mirror.

The electron density singularity formed at the joining area of relativistic wake wave and bow waves has been proposed as a novel relativistic electron mirror regime to reflect the counter-propagating electromagnetic pulse [1]. Coherent hard electromagnetic radiation is generated by the reflection, compression and frequency upshift from the electron density singularity. In this paper, detailed description of this regime is provided, and new features are shown. The electromagnetic fields reflected by the electron density singularity are investigated via multi-dimensional particle-in-cell simulations.

We are reviewing the high-average and high peak-power fs-laser sources and experimental areas currently in operation and preparation for user operation. This includes the 1 kHz, 15fs, 50mJ, Allegra laser based on OPCPA-technology. Short pulse 5ps-CPA thin disc lasers pump a series of OPCPA crystals ensuring a high contrast output. The Allegra laser enters the experimental area E1 with a number of end-stations for user experiments. The HAPLS (sub-30fs, Ti: Sapphire) laser pumped by a high-average power frequency converted DPSSL is currently delivering 500 TW, 3.3 Hz pulses via a stable vacuum beam transport system with a pointing stability around 1rad to the experimental areas for plasma physics experiments (E3) and ion acceleration (E4) with the ELIMAIA station. Both areas are fully equipped with target chambers and focusing optics for experimental operation and user assisted commissioning. The Nd:Glass laser Aton provides 1.5 kJ pulses and is currently being compressed to 10 PW in a large compressor tank. A second oscillator allows shaped pulse ns-operation at kJ level or future combination of 1 PW pulses and kJ shaped ns-pulses for advanced WDM or fusion experiments in the E3 area. A new laser disc liquid cooling technology enables repetition rates of 1 shot/minute allowing a much higher data acquisition for this kind of experiments. Furthermore we will report on the first experiments and the future experimental plans as well as on the prospects for user operation.

Combination of revolutionary high-repetition-rate high-power laser technology and the latest achievements in laser-plasma accelerators (LPAs) opens the way to develop a new generation of laser-driven compact free-electron lasers (FEL). The LPA electron beam brightness is extremely high due to a low normalized emittance (less than 0.5 µm) and high peak current (multi kA), resulting from an ultra-short e-beam duration (few fsec), which makes such beam extremely attractive for the production of high power pulses of the coherent photon radiation. In the frame of this report, we overview the laser-driven FEL research program at ELI-Beamlines (near Prague, Czech Republic), which aims to demonstrate the self-amplified spontaneous emission (SASE) regime with a generation of the coherent photon radiation starting from the extreme ultraviolet wavelength range. A possible extension of this research program to the X-ray FEL regime will be discussed.

In this work we investigated the use of a plasma shutter in the form of a thin foil for laser-driven ion acceleration enhancement. It is shown with the help of 3D particle-in-cell simulations that the laser pulse intensity can be increased and its profile steepened after burning through the plasma shutter. The enhanced intensity profile has a positive effect on the subsequent ion acceleration from the main foil, significantly increasing the maximal ion energy. The pre-expansion of the plasma shutter caused by prepulses is investigated using 2D hydrodynamic simulations. A scheme using a double plasma shutter configuration (the first one filtering out the prepulses and the second one shaping the main pulse) is proposed.

We present a regime where an ultra-intense laser pulse interacting with a foil target results in high $\gamma$-photon conversion efficiency, obtained via three-dimensional quantum-electrodynamics particle-in-cell simulations. A single-cycle laser pulse is used under the tight-focusing condition for obtaining the $\mathrm{\lambda}^3$ regime. The simulations employ a radially polarized laser as it results in higher $\gamma$-photon conversion efficiency compared to both azimuthal and linear polarizations. A significant fraction of the laser energy is transferred to positrons, while a part of the electromagnetic wave escapes the target as attosecond single-cycle pulses., Comment: 6 pages, 5 figures

The question of electromagnetic field intensification towards the values typical for strong field Quantum Electrodynamics is of fundamental importance. One of the most promising intensification schemes is based on the relativistic-flying mirror concept, which shows that the electromagnetic radiation reflected by the mirror will be frequency up-shifted by a factor of 4 gamma^2 (gamma: the Lorentz factor of the mirror). In laser-plasma interactions, such a mirror travels with relativistic velocities and typically has a parabolic form, which is advantageous for light intensification. Thus, a relativistic-flying parabolic mirror reflects the counter-propagating radiation in a form of focused and flying electromagnetic wave with a high frequency. The relativistic-flying motion of the laser focus makes the electric and magnetic field distributions of the focus complicated, and the mathematical expressions describing the field distributions of the focus is important. We present analytical expressions describing the field distribution formed by an ideal flying mirror having a perfect reflectance over the entire surface and wavelength range. The peak field strength of an incident laser pulse with a center wavelength of lambda_0 and an effective beam radius of w_e is enhanced by a factor proportional to gamma^3 (w_e/lambda_0) in the relativistic limit. Electron-positron pair production is investigated in the context of invariant fields based on the enhanced electromagnetic field. The pair production rate under the relativistic-flying laser focus is modified by the Lorentz gamma-factor and the beam radius-wavelength ratio (w_e/lambda_0). We show that the electron-positron pairs can be created by colliding two counter-propagating relativistic-flying laser focuses in vacuum, each of which is formed when a 180 TW laser pulse is reflected by a relativistic-flying parabolic mirror with a gamma = 12.2.

High power laser science and engineering 9, e30 (2021). doi:10.1017/hpl.2021.16, Published by Cambridge Univ. Press, Cambridge

Using an analytical model and computer simulation, we show that the wakefield driven by an ultrashort laser pulse in high-density plasma periodically reverses its polarity due to the carrier-envelope phase shift of the driver. The wakefield polarity reversal occurs on spatial scales shorter than the typical length considered for electron acceleration with the laser-wakefield mechanism. Consequently, the energies of accelerated electrons are significantly affected. The results obtained are important for the laser-wakefield acceleration under the conditions relevant to present-day high-repetition-rate laser systems.

In an experiment performed with a high-intensity and high-energy laser system, $\ensuremath{\alpha}$-particle production in proton-boron reaction by using a laser-driven proton beam was measured. $\ensuremath{\alpha}$ particles were observed from the front and also from the rear side, even after a 2-mm-thick boron target. The data obtained in this experiment have been analyzed using a sequence of numerical simulations. The simulations clarify the mechanisms of $\ensuremath{\alpha}$-particle production and transport through the boron targets. $\ensuremath{\alpha}$-particle energies observed in the experiment and in the simulation reach 10--20 MeV through energy transfer from 20--30 MeV energy incident protons. Despite the lower cross sections for protons with energy above the sub-MeV resonances in the proton-boron reactions, ${10}^{8}$--${10}^{9}\phantom{\rule{4pt}{0ex}}\ensuremath{\alpha}$ particles per steradian have been detected.

The main effort of the laser-driven ion acceleration community is aimed to improve particle beam features (energy, charge, divergence, monochromaticity) and to demonstrate reliable approaches to be used for multidisciplinary applications. An ion acceleration target area based on unique laser capabilities is available at ELI-Beamlines (Extreme Light Infrastructure) in the Czech Republic; it is called ELIMAIA (ELI Multidisciplinary Applications of laser-Ion Acceleration) and aims to provide stable, fully characterized and tuneable beams of particles accelerated by multi-Petawatt-class lasers and to offer them to the user community for multidisciplinary applications. The ELIMAIA section dedicated to ion focusing, selection, characterization and irradiation is named ELIMED (ELI MEDical and multidisciplinary applications). Thanks to ELIMED, very high-dose-rate (around Gy/min) controlled proton and ion beams, with energy ranging from 5 to 250 MeV, will be transported up to an in-air section dedicated to absolute and relative dosimetry of the laser-generated ions. A transmission, dual-gap air ionisation chamber will allow an on-line, non-destructive characterization of the ion dose at the user sample irradiation point. The uncertainty in the final dose released onto the sample is expected to be well below 5$\%$. An ELIMED radiobiology pilot experiment is scheduled in 2021, during which in-vitro cell irradiations will be carried out with well-controlled proton beams. In this work, the status of the ELIMED/ELIMAIA beamline will be reported along with a complete description of the main dosimetric systems and of their calibrations carried out at conventional accelerators.

Interaction of an electron with the counter-propagating electromagnetic wave is studied theoretically and with the particle-in-cell simulations in the regime of quantum radiation reaction. We find the electron energy in the center of the laser pulse, as it is a key factor for testing the non-linear quantum electrodynamics vacuum properties in the laser-electron collision in the regime of multi-photon Compton scattering and vacuum Cherenkov radiation. With multiparametric analysis we provide the conditions on electron initial energy for reaching the center of the laser pulse and emitting Cherenkov photons.

The TERESA (TEstbed for high REpetition-rate Sources of Accelerated particles) target area, recently commissioned with the L3-HAPLS laser at Extreme Light Infrastructure (ELI)-Beamlines, is presented. Its key technological sections (vacuum and control systems, laser parameters and laser beam transport up to the target) are described, along with an overview of the available plasma diagnostics and targetry, tested at relativistic laser intensities. Perspectives of the TERESA laser&ndash, plasma experimental area at ELI-Beamlines are briefly discussed.

We present preliminary results on generation of energetic α-particles driven by lasers. The experiment was performed at the Institute of Laser Engineering in Osaka using the short-pulse, high-intensity, high-energy, PW-class laser. The laser pulse was focused onto a thin plastic foil (pitcher) to generate a proton beam by the well-known TNSA mechanism which, in turn, was impinging onto a boron-nitride (BN) target (catcher) to generated alpha-particles as a result of proton-boron nuclear fusion events. Our results demonstrate generation of α-particles with energies in the range 8–10 MeV and with a flux around 5 × 10^9 sr^−1.

Author(s): Jeong, TM; Bulanov, SV; Sasorov, PV; Korn, G; Koga, JK; Bulanov, SS | Abstract: The scattering of high-power probe laser pulses by tightly focused ultrastrong laser pulses has been investigated through a semiclassical approach using a perturbative method based on the Born approximation. Under a 4π-spherically-focused ultrastrong light field, the electric permittivity and magnetic permeability tensors for vacuum are calculated from the Euler-Heisenberg Lagrangian to show the nonlinear birefringent property of vacuum. And, from permittivity and permeability tensors, the scattering potential is derived for the Born approximation. The first-order solution of the Born approximation is taken as an electric field scattered from the 4π-spherically-focused laser pulse when a probe laser pulse propagates through the focused laser field. The differential cross section of the nonlinear birefringent vacuum is derived, and the number of photons scattered from the nonlinear birefringent vacuum is analyzed in the laser power range of 10-1000 PW.

Singularities in multi-stream flows of relativistic plasmas can efficiently produce coherent high-frequency radiation, as exemplified in the concepts of the Relativistic Flying Mirror [Bulanov et al., Phys. Rev. Lett. 91, 085001 (2003)] and Burst Intensification by Singularity Emitting Radiation [Pirozhkov et al., Sci. Rep. 7, 17968 (2017)]. Direct observation of these singularities is challenging due to their extreme sharpness (tens of nanometers), relativistic velocity, and transient non-local nature. We propose to use an ultrafast (a few light cycles) optical probe for identifying relativistic plasma singularities. Our estimations and Particle-in-Cell simulations show that this diagnostic is feasible.

Although the interaction of a flat-foil with currently available laser intensities is now considered a routine process, during the last decade emphasis is given to targets with complex geometries aiming on increasing the ion energy. This work presents a target geometry where two symmetric side-holes and a central-hole are drilled into the foil. A study of the various side-holes and central-hole length combinations is performed with 2-dimensional particle-in-cell simulations for polyethylene targets and a laser intensity of 5.2x10^21 W cm^-2. The holed-targets show a remarkable increase of the conversion efficiency, which corresponds to a different target configuration for electrons, protons and carbon ions. Furthermore, diffraction of the laser pulse leads to a directional high energy electron beam, with a temperature of ~40 MeV or seven times higher than in the case of a flat-foil. The higher conversion efficiency consequently leads to a significant enhancement of the maximum proton energy from holed-targets., 22 pages, 10 figures

Relativistic mirrors in laser plasmas offer a promising way for development of compact and tunable sources of coherent short-wavelength radiation. Here we investigate recoil effects on reflection of high-intensity laser pulses from such mirrors.

The ELI-ELBA scientific program is devoted to the experimental investigation of different fundamental scientific problems by using a combination of multi-PW and sub-PW lasers available at the ELI-Beamlines research facility. The core plasma technology used is laser wakefield acceleration, which is needed to produce ultra-relativistic electron beams in extremely short distances by using very high accelerating gradients (>100 MeV/mm). ELI-ELBA experiments driven by multi-PW laser systems aim at the acceleration of multi-GeV electron beams for counter-propagating them with intense (>1020 W/cm2) laser pulses in order to study novel regimes of electromagnetic field interaction with matter and quantum vacuum. Different techniques of electron injection inside the plasma wave are investigated and compared, with the goal of producing stable and reproducible electron beams. Among the techniques investigated, the best results have been obtained with shock assisted ionization injection, where the injection of the electron inside the plasma waves is limited transversally by the ionization potential of high Z gas and longitudinally by plasma density tailoring.(/p)(p)ELI-ELBA experiments driven by TW laser systems aim at the understanding of laser wakefield acceleration in near critical density plasmas. Moreover, these laser systems can be operated at kHz repetition rate, resulting in an increased average beam power which is of interest for multi-disciplinary applications of laser wakefield acceleration, including medical imaging, radiobiology, and non-destructive testing. In order to successfully perform laser wakefield acceleration with TW kHz laser systems, the laser time duration has to be carefully tuned. In fact, single cycle laser pulses will limit the accelerating length and, on the other hand, laser pulses longer than the plasma wavelength might lead to laser defocusing induced by the plasma waves. (/p)(p)In the presentation the actual status of the beamline will be presented, along with recent experimental and theoretical results obtained as part of the group activity.

In the limit of extremely intense electromagnetic fields the Maxwell equations are modified due to the photon-photon scattering that makes the vacuum refraction index depend on the field amplitude. In presence of electromagnetic waves with small but finite wavenumbers the vacuum behaves as a dispersive medium. We show that the interplay between the vacuum polarization and the nonlinear effects in the interaction of counter-propagating electromagnetic waves can result in the formation of Kadomtsev-Petviashvily solitons and, in one-dimension configuration, of Korteveg-de-Vries type solitons that can propagate over a large distance without changing their shape., 16 pages, 5 figures

For developing a laser boron fusion reactor driven by picosecond laser pulses of more than 30 petawatts power, advances are reported about computations for the plasma block generation by the dielectric explosion of the interaction. Further results are about the direct drive ignition mechanism by a single laser pulse without the problems of spherical irradiation. For the sufficiently large stopping lengths of the generated alpha particles in the plasma results from other projects can be used., 10 pages, 5 figures, extended tex from lectures on 5th and 6th June 2017in Shanghai/China

ELI-Beamlines (ELI-BL), one of the three pillars of the Extreme Light Infrastructure endeavour, will be in a unique position to perform research in high-energy-density-physics (HEDP), plasma physics and ultra-high intensity (UHI) (>1022W/cm2) laser–plasma interaction. Recently the need for HED laboratory physics was identified and the P3 (plasma physics platform) installation under construction in ELI-BL will be an answer. The ELI-BL 10 PW laser makes possible fundamental research topics from high-field physics to new extreme states of matter such as radiation-dominated ones, high-pressure quantum ones, warm dense matter (WDM) and ultra-relativistic plasmas. HEDP is of fundamental importance for research in the field of laboratory astrophysics and inertial confinement fusion (ICF). Reaching such extreme states of matter now and in the future will depend on the use of plasma optics for amplifying and focusing laser pulses. This article will present the relevant technological infrastructure being built in ELI-BL for HEDP and UHI, and gives a brief overview of some research under way in the field of UHI, laboratory astrophysics, ICF, WDM, and plasma optics. Keywords: High-energy-density-physics, Ultra-high-intensity, Warm dense matter, Laboratory astrophysics, High repetition rate lasers, Plasma optics, Inertial confinement fusion, Laser–plasma interaction, Relativistic plasmas, PACS Codes: 52.25.Fi, 52.27.Ep, 52.27.Ny, 52.35.Mw, 52.38.Fz, 52.38.Dx, 52.38.Kd, 52.38.Mf, 52.57.-z, 52.65.-y, 52.72.+v

Relativistic mirrors can be realized with strongly nonlinear Langmuir waves excited by intense laser pulses in underdense plasma. On reflection from the relativistic mirror the incident light affects the mirror motion. The corresponding recoil effects are investigated analytically and with particle-in-cell simulations. It is found that if the fluence of the incident electromagnetic wave exceeds a certain threshold, the relativistic mirror undergoes a significant back reaction and splits into multiple electron layers. The reflection coefficient of the relativistic mirror as well as the factors of electric field amplification and frequency upshift of the electromagnetic wave are obtained., 8 pages, 5 figures, submitted to Physics of Plasmas

We present the results of theoretical studies of formation and evolution of the current sheet in a colliosionless plasma during magnetic reconnection in relativistic limit. Relativistic magnetic reconnection is driven by parallel laser pulses interacting with underdense plasma target. Annihilation of laser created magnetic field of opposite polarity generates strong non-stationary electric field formed in between the region with opposite polarity magnetic field accelerating charged particles within the current sheet. This laser-plasma target configuration is discussed in regard with the laboratory modeling of charged particle acceleration and gamma flash generation in astrophysics. We present the results of 3-dimensional kinetic simulations and theoretical studies on the formation and evolution of the current sheet in a collisionless plasma during magnetic field annihilation in the ultra-relativistic limit. Annihilation of oppositively directed magnetic fields driven by two laser pulses interacting with underdense plasma target is accompanied by an electromagnetic burst generation. The induced strong non-stationary longitudinal electric field accelerates charged particles within the current sheet. Properties of the laser-plasma target configuration are discussed in the context of the laboratory modeling for charged particle acceleration and gamma flash generation in astrophysics.

Apart from maximizing the strength of optical electromagnetic fields achievable at high-intensity laser facilities, the collision of several phase-matched laser pulses has been theoretically identified as a trigger of and way to study various phenomena. These range from the basic processes of strong-field quantum electrodynamics to the extraordinary dynamics of the generated electron-positron plasmas. This has paved the way for several experimental proposals aimed at both fundamental studies of matter at extreme conditions and the creation of particle and radiation sources. Because of the unprecedented capabilities of such sources they have the potential to open up new opportunities for experimental studies in nuclear and quark-gluon physics. We here perform a systematic analysis of different regimes and opportunities achievable with the concept of multiple-colliding laser pulses (MCLP), for both current and upcoming laser facilities. We reveal that several distinct regimes could be within reach of multi-PW laser facilities., Comment: 15 pages, 12 figures

Three main paths are being developed within the ELI research program for transforming driving laser pulses into bursts of bright short wavelength radiation: high-order harmonic generation in gases, plasma X-ray sources and sources based on relativistic electron beams accelerated in laser plasma. For each of these research areas, dedicated beamlines are built to provide a unique combination of X-ray sources to the scientific community. The application of these beamlines has a well-defined balance between fundamental science and applications in different fields of science and technology. Here we summarize the current status of those user beamlines and we introduce new diagnostics devices developed within the implementation phase of the project, namely compact XUV spectrometer and beam profiler that is using only one fixed detector and an imaging Michelson interferometer with increased sensitivity for low density gas jet characterization.

International audience; The Time-of-Flight (TOF) technique coupled with semiconductorlike detectors, as silicon carbide and diamond, is one of the most promising diagnostic methods for high-energy, high repetition rate, laser-accelerated ions allowing a full on-line beam spectral characterization. A new analysis method for reconstructing the energy spectrum of high-energy laser-driven ion beams from TOF signals is hereby presented and discussed. The proposed method takes into account the detector’s working principle, through the accurate calculation of the energy loss in the detector active layer, using Monte Carlo simulations. The analysis method was validated against well-established diagnostics, such as the Thomson parabola spectrometer, during an experimental campaign carried out at the Rutherford Appleton Laboratory (UK) with the high-energy laser-driven protons accelerated by the VULCAN Petawatt laser.

The nuclear reaction known as proton-boron fusion has been triggered by a subnanosecond laser system focused onto a thick boron nitride target at modest laser intensity (∼10^{16}W/cm^{2}), resulting in a record yield of generated α particles. The estimated value of α particles emitted per laser pulse is around 10^{11}, thus orders of magnitude higher than any other experimental result previously reported. The accelerated α-particle stream shows unique features in terms of kinetic energy (up to 10 MeV), pulse duration (∼10 ns), and peak current (∼2 A) at 1 m from the source, promising potential applications of such neutronless nuclear fusion reactions. We have used a beam-driven fusion scheme to explain the total number of α particles generated in the nuclear reaction. In this model, protons accelerated inside the plasma, moving forward into the bulk of the target, can interact with ^{11}B atoms, thus efficiently triggering fusion reactions. An overview of literature results obtained with different laser parameters, experimental setups, and target compositions is reported and discussed.

Capillary discharges are widely used in many experiments devoted to laser-plasma interaction as a simple tool to create plasma with required parameters. One of the application of these experiments is laser-plasma accelerators (LPA) of charged particles. Such LPAs are able to accelerate electrons bunch to more that a GeV on the centimeters distances [1]. Essential part of these experiments is capillary discharge. It is used to create plasma waveguide in order to channel an accelerating laser pulse. The long (several decimetres) and thin (several microns) capillary is needed to achieve maximum acceleration but its fabrication is laborious and unreasonably expensive for the LPA experiments. Also capillary can be damaged by electric current pulse that is used to create plasma waveguide. Additional heating of the plasma channel by a nanosecond laser pulse is used in order to avoid these limitations [2]. Propagation of a heater laser through the plasma waveguide deepens it further in the vicinity of the capillary axis. Recent experiments show positive effect of such heating on the final acceleration of the electrons. This leads to a problem of choosing optimal parameters to achieve maximal acceleration. Consistent numerical modeling of plasmadynamics and laser pulse propagation in plasma channel is required to maintenance and optimise the future experiments. The magnetohydrodynamic (MHD) code MARPLE [3] previously used for discharge simulations [3-5] was improved by taken into account additional heating due to laser radiation. Results of simulations that were done for the BELLA experimental facility will be presented at the conference. The work was supported in part by the Competitiveness Program of MEPhI No.02.A03.21.0005, basic research program of the Project 3-OMN RAS, U.S. DOE under Contract No.DE-AC02-05CH11231, EU Reg.Dev.Fund Ns.CZ.02.1.01/0.0/0.0/15 008/0000162 and CZ.02.1.01/0.0/0.0/15_003/0000449 and by the MoEYaS of the Czech Republic No.LQ1606. [1] W.Leemans et al. Phys. Rev. Lett. 113, 245002 (2014) [2] N.Bobrova et al. Phys. Plasmas 20, 020703 (2013) [3] G.Bagdasarov et al. Phys. Plasmas 24, 053111 (2017) [4] G.Bagdasarov et al. Phys. Plasmas 24, 083109 (2017) [5] G.Bagdasarov et al. Phys. Plasmas 24, 123120 (2017)

We will be giving an overview on the development of the “ELI-beamline facility” being currently implemented and opened as a user facility within the Extreme Light Infrastructure (ELI) project based on the European ESFRI (European Strategy Forum on Research Infrastructures) process. ELI-Beamlines is the high-energy, repetition-rate laser pillar of the ELI (Extreme Light Infrastructure) project. The main objective of the ELI-Beamlines facility is the delivery of ultra-intense high-energy pulses for high field experiments and the generation and applications of high-brightness X-ray sources and accelerated particles. The high power laser systems currently prepared and used for the generation of higher repetition rate sources of x-rays and particles are L1 (Allegra) a 1 kHz diode pumped laser produced sub-20fs OPCPA system and the L3 (HAPLS) a 10 Hz, 1 PW (30fs) laser using as the active medium Ti:sapphire with new gas cooled diode pumped Nd doped Glass pump laser. The lasers will be able to provide focused intensities attaining >1018-21 Wcm-2 suitable for generation of x-rays and particles (electrons and ions). We will discuss the infrastructure concerning the availability of experimental areas, including secondary sources of particles and x-rays in the wavelength range between 20 eV-100 keV and few Mev and their practical implementation at the ELI-Beamline user facility. The sources are either based on direct interaction of the laser beams with gaseous targets (high order harmonics) or will first accelerate electrons which then will interact with laser produced wigglers (Betatron radiation) or directly injected into undulators (laser driven LUX or later X-FEL). The direct interaction (collision) of laser accelerated electrons with the intense focused laser again will lead to short pulse high energy radiation via Compton or Thomson scattering for different applications opening also the route to fundamental physics investigations in high intensity interaction due to the 4 gamma 2 Lorentz boost of the intensity seen by high energy (GeV- > 106) electrons.

Using quantum electrodynamics particle-in-cell simulations, we optimize the gamma flare (γ-flare) generation scheme from interaction of high power petawatt-class laser pulse with tailored cryogenic hydrogen target having extended preplasma corona. We show that it is possible to generate an energetic flare of photons with energies in the GeV range and total flare energy being on a kilojoule level with an efficient conversion of the laser pulse energy to γ-photons. We discuss how the target engineering and laser pulse parameters influence the γ-flare generation efficiency. This type of experimental setup for laser-based γ source would be feasible for the upcoming high power laser facilities. Applications of high intensity γ ray beams are also discussed. The paper on this research project is submitted to Physics of Plasmas and available at arXiv:1809.09594

When coherent electromagnetic radiation generated by powerful laser system is tightly focused, pursuing the aim to achieve the highest value of intensity possible, it may be challenging estimating this intensity with a sufficient degree of accuracy. If the energy of a laser pulse, its duration, time profile and focal spot radius are known, evaulation of the maximal intensity is straightforward. However, for high power (sub-petawatt and above) femtosecond laser systems, the inherent uncertainties of these four parameters (except maybe the pulse duration) are rather high, so that different estimation models of the laser intensity in the focus may substantially disagree. Presently, the question of whether or not intensities above 10^21 W/cm2 have ever been achieved remains debatable, although values of this order and above are the main goal of the two Extreme Light Infrastructure (ELI) pillars. In this context, a reliable method allowing to calibrate ultrahigh laser intensities becomes of even higher demand. Here we discuss the reliability of a method for the measurement of ultrahigh laser intensities, based on the effect of tunneling field ionization of heavy atoms and ions. To this end, we employ the highly nonlinear dependence of tunneling ionization rates on the laser intensity. This nonlinearity leads to the emergence of steep plateaus in the distribution of charge states in the laser focus and in such a way to allowing estimate, with a high degree of certainty, the laser intensity at focus.

As an alternative to Compton backscattering and bremsstrahlung, the process of colliding highenergy electron beams with strong laser fields can more efficiently provide both cleaner and brighter source of photons in the multi-GeV range for fundamental studies in nuclear and quark-gluon physics. In order to favor the emission of high-energy quanta and minimize their decay into electron-positron pairs the fields must not only be sufficiently strong, but also well localized. We here examine these aspects and develop the concept of a laser-particle collider tailored for high-energy photon generation. We show that the use of multiple colliding laser pulses with 0.4 PW of total power is capable of converting more than 18 % of the initial multi-GeV electron beam energy into photons, each of which carries more than half of the electron energy

A novel regime of high frequency radiation generation via reflection at the electron density spikes in under- dense plasma is proposed. Intense driver laser pulse propagating in underdense plasma forms dense electron singularities near the front part of the bow waves, moving at relativistic velocity. By irradiating a source pulse counterpropagating to the electron density singularities, it is reflected and compressed, producing ultrashort coherent high order harmonics with frequency upshift.

Laser wakefield acceleration (LWFA) using high repetition rate mJ-class laser systems brings unique opportunities for a broad range of applications. In order to meet the conditions required for the electron acceleration with lasers operating at lower energies, one has to use high density plasmas and ultrashort pulses. In the case of a few-cycle pulse, the dispersion and the carrier envelope phase effects can no longer be neglected. In this work, the properties of the wake waves generated by ultrashort pulse lasers in near-critical density plasmas are investigated. The results obtained may lead to enhancement of the quality of LWFA electron beams using kHz laser systems., Comment: 9 pages; presented at SPIE Optics + Optoelectronics, 2019, Prague, Czech Republic

Nowadays by using the optical parametric chirped-pulse amplification (OPCPA) technique it is reasonable to expect the laser pulse energy up to 10 Joules with the repetition rate of 10-25 Hz. Development of such laser systems with the pulse compression down to 30 fs opens a way to build compact free-electron laser (FEL) based on the laser wakefield acceleration (LWFA). Combination of new laser development with constant improvement of the LWFA electron beam parameters has great potential in future development of the compact high repetition rate FEL, which is extremely demanded by the X-ray user community. The LWFA-driven FEL project called “LUIS" is currently under preparation at ELI-Beamlines in Czech Republic in collaboration with University of Hamburg. The LUIS project aims to experimentally demonstrate the stable and reliable generation of X-ray photons with a wavelength below 5 nm for user applications. An overview of the LUIS project including design features and a description of all the instrumentation used to characterize the laser, plasma, electron beam, photon generation and other subsystems will be presented in the frame of this report. The main challenges and future development of the laser-driven compact X-ray free electron laser with the radiation wavelength less than nm will also be discussed.

We propose a production of well-collimated and quasi-mono-energetic ion beams through the interaction of high- intensity laser pulse with thin overdense double layer targets. The target consists of heavy and light material layer with the modulations at the interface between them. Using extensive 2D3V PIC simulations we show that a relativistic Richtmyer-Meshkov like instability results in the generation of collimated quasi-mono-energetic beams of light ions. We compare the effects of modulations at the surface of single layer targets and at the interface between two different particle species of double layer targets. It is shown that initially small perturbations are amplified during the laser-target interaction leading to the formation of low-density regions at the positions determined by the initial perturbation geometry and high-density plasma bunches between them. The bunches, with higher density than the density in the initial foil are then accelerated by the laser radiation pressure, leading to the generation of quasi-mono-energetic, collimated ion beams.

We analyze theoretically the properties of two counter-propagating electromagnetic waves within the framework of the long wavelength approximation corresponding to the Heisenberg–Euler formalism in quantum electrodynamics (QED). We obtain a novel solution for electromagnetic shocks in QED vacuum and investigate the properties of the solution, the wave steepening and subsequent generation of higher order harmonics and electromagnetic shock wave formation with electron–positron pair generation at the shock wave front.

We study two counter-propagating electromagnetic waves in the vacuum within the framework of the Heisenberg-Euler formalism in quantum electrodynamics. We show that the non-linear field equations decouple for ordinary wave case and can be solved exactly. We solve the non-linear field equations assuming the solution in a form of a Riemann wave. We discuss the properties of the nonlinear electromagnetic wave propagating in the quantum vacuum, such as the wave steepening, subsequent generation of high order harmonics and electromagnetic shock wave formation with electron-positron pair generation at the shock wave front., 11 pages, 5 figures