This PDF file contains the front matter associated with SPIE Proceedings Volume 9515, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

The presentation will focus on the Status of Implementation of the project Extreme Light Infrastructure – Nuclear Physics (ELI-NP), project co-financed by the European Regional Development Fund, and the research opportunities at the future European Center for Scientific Research.

This paper discusses some aspect of the experimental effort in high field science (up to 10²² W/cm²) done with the high peak power (>200TW) laser system at the Advanced Laser Light Source facility (ALLS). A maximum intensity of 10²² W/cm² has been achieved on target. The present experiments explore the acceleration of electrons directly by the laser field (DLFA) in the transition between the relativistic and ultra-relatisitic regimes. Electrons are accelerated to multi-MeV energies using radially (TM₀₁) and azimuthally (TE₀₁) polarized modes and the contribution of various acceleration processes is briefly discussed.

High-order harmonic generation of high intensity ultra-short laser pulses by means of laser produced plasmas are discussed. Since with plasma targets there is no limitation on applicable laser intensity the generated harmonics can be substantially intense. Recent results of experiments and computer simulations on the high-order harmonic generation are briefly reviewed. Main attention is paid to the analysis of basic mechanisms of high-order harmonic generation from overdense and underdense plasma targets irradiated by relativistically intense laser pulses.

Overview of the laser systems being built for ELI-Beamlines is presented. The facility will make available high-brightness multi-TW ultrashort laser pulses at kHz repetition rate, PW 10 Hz repetition rate pulses, and kilojoule nanosecond pulses for generation of 10 PW peak power. The lasers will extensively employ the emerging technology of diode-pumped solid-state lasers (DPSSL) to pump OPCPA and Ti:sapphire broadband amplifiers. These systems will provide the user community with cutting-edge laser resources for programmatic research in generation and applications of high-intensity X-ray sources, in particle acceleration, and in dense-plasma and high-field physics.

A tight focusing scheme using a low f-number focusing optic is frequently considered as an effort to efficiently increase a peak intensity of a high power laser. In this paper, we present a method for describing the focal spot of a femtosecond laser pulse which is formed in the spatio-temporal region under low f-number (f-number ≤ 1) focusing conditions. In the method, transverse and longitudinal electromagnetic (EM) fields for a monochromatic wave are calculated in the focal plane and its vicinity, and then, in order to precisely describe the femtosecond focal spot in the spatio-temporal domain, the calculated monochromatic EM fields are coherently superposed with a given amount of spectral bandwidth and phase. The accuracy and validity of the method are tested and compared to results obtained with Fourier transform method under high f-number conditions. The single electron trajectory under a strong longitudinal field formed by a low f-number optic is presented to emphasize the importance of the tight focusing scheme.

Recently several ultrahigh intensity Chirped Pulse Amplification (CPA) laser systems have reached petawatt output powers [1, 2] setting the next milestone at tens or even hundreds petawatts for the next three to ten years [3, 4]. These remarkable results were reached when laser amplifiers (opposite to Optical Parametric Amplification (OPA) [5]) were used as final ones and from them Ti:Sapphire crystals supposed to be the working horses as well in the future design of these laser systems. Nevertheless, the main limitation that arises on the path toward ultrahigh output power and intensity is the restriction on the pumping and extraction energy imposed by Transverse Amplified Spontaneous Emission (TASE) [6] and/or transverse parasitic generation (TPG) [7] within the large aperture of the disc-shape amplifier volume.

Various spin effects are expected to become observable in light-matter interaction at relativistic intensities. Relativistic quantum mechanics equipped with a suitable relativistic spin operator forms the theoretical foundation for describing these effects. Various proposals for relativistic spin operators have been offered by different authors, which are presented in a unified way. As a result of the operators’ mathematical properties only the Foldy-Wouthuysen operator and the Pryce operator qualify as possible proper relativistic spin operators. The ground states of highly charged hydrogen-like ions can be utilized to identify a legitimate relativistic spin operator experimentally. Subsequently, the Foldy-Wouthuysen spin operator is employed to study electron-spin precession in high-intensity standing light waves with elliptical polarization. For a correct theoretical description of the predicted electron-spin precession relativistic effects due to the spin angular momentum of the electromagnetic wave has to be taken into account even in the limit of low intensities.

With the continuing development of laser systems, new important and so-far unexplored fields of research related to interaction of ultra-intense laser beams with matter are opening. At intensities of the order of 10²² W=cm², electrons may be accelerated in the electromagnetic field of the laser wave and achieve such a high energy that they can enter the regime affected by the radiation reaction. Due to the non-linear Thomson and Compton scattering the accelerated electrons emit photons. The interaction of emitted photons with the laser field may result in effective generation of electron-positron pairs by means of the Breit-Wheeler process. In this work we study the influence of laser pulse polarization on gamma-ray generation during interaction of two colliding and tightly focused laser pulses with a low density target composed of electrons. This paper focuses on evolution of electron trajectories and key parameters χ_e (probability of photon emission) and χ_γ(probability of pair generation) in the laser field. These interactions are studied using 2D PIC simulations. It is shown that in the case of circularly polarized and tightly focused laser beams, electrons are not following circular trajectories at the magnetic node of the standing wave established in the focus, which leads to lowering the radiation emission efficiency.

The matrix element of the Compton scattering in the presence of strong electromagnetic field in plasma is considered. The calculation is performed employing two novel wavefunctions, numerical and analytical, describing the dynamics of the particle in the electromagnetic field. The impact of the analytical approximation on the matrix element of the scattering process is investigated.

The most promising approach for detecting WISPs (Weakly Interacting Slim Particles) is to use their small coupling to photons, which detection is easy, even at the single particle level. This is what is done in “light shining through the wall” experiments, which are based on the probability that a photon may be converted into a WISP, which would traverse a light-tight wall without interacting, then have a chance of being converted back into a photon with the same frequency and direction as the original one¹. Because of the smallness of the WISPs-photon couplings, it is valuable to use the highest photon fluxes available together with a high magnetic field. In the near future, another interesting hidden-sector particle can be searched for on laser facilities, namely a hidden-sector photon (HP), also called paraphoton or dark photon. Indeed, the recent WMAP-7 observations and interpretations² hint for an extra neutrino-like particle (the total number of neutrino species is found to be 4.34 ± 0.87 with 68% Confidence Level), which could be accounted for by a hidden photon with a mass μ and a HP-photon coupling χ in the parameters range accessible with laser shots. At ELIBeamlines, there will be a 1.5-kJ laser (L4) running at 1 shot per mn; it is therefore possible to have a dedicated LSW experiment inside one of the facility rooms that would take advantage both of the large number of photons delivered and of the “high repetition rate” of this laser.

LFEX is the world’s largest high-energy petawatt laser. So far it delivers 3 kJ/1 ps and is planed to finally deliver 10 kJ/10-20 ps. It has been constructed and became partially operational since 2008, and with full beams since 2014. LFEX is synchronized to nsec Gekko-XII laser for variety of experiments with nsec and psec simultaneous laser beams irradiating the targets for fast ignition and other high-energy density physics.

The performance of a 0.1-Hz-repetition-rate, 30-fs, 1.5-PW Ti:sapphire laser which is using for research on high field physics in APRI-GIST is presented. The charged particles (electrons and protons) are accelerated and an efficient x-ray generation is demonstrated using the PW laser. Protons are accelerated up to 80 MeV when an ultra-thin polymer target is irradiated by a circularly-polarized PW laser pulse. Electrons are accelerated to multi-GeV level with a help of injector and accelerator scheme. In the relativistic harmonic generation experiment, the harmonic order is dramatically extended, by optimizing the intensity of pre-pulse level, up to 164^th that corresponds to 4.9 nm in wavelength and the experimental results can be explained by the oscillatory flying mirror model. The upgrade of the PW laser to the multi-PW level is under way.

Several signatures of quantum radiation reaction are investigated in the interaction of an electron beam with superstrong focused laser pulses in the radiation dominated regime. Analytic expressions for the electromagnetic fields of an ultrashort, tightly focused, laser pulse in vacuum are derived from scalar and vector potentials, using on equal footing two small parameters connected with the waist size of the laser beam and its duration. Due to the combined effect of the laser focusing and radiation reaction the angular spread of the main photon-emission region has a prominent maximum at an intermediate pulse duration and decreases along the further increase of the pulse duration, and the spectral bandwidth monotonically decreases with rising pulse duration. Those signatures can be used to distinguish the quantum radiation reaction with the classic radiation reaction and are measurable with currently available laser systems.

Radiation reaction radically influences the electron motion in an electromagnetic standing wave formed by two super-intense colliding laser pulses. Depending on the laser intensity and wavelength, the quantum corrections to the electron motion and the radiation reaction force can be independently small or large, thus dividing the parameter space into 4 regions. When radiation reaction dominates, the electron motion evolves to limit cycles and strange attractors. This creates a new framework for high energy physics experiments on the interaction of energetic charged particle beams and colliding super-intense laser pulses.

An alternative way may be possible for igniting solid density hydrogen-¹¹B (HB11) fuel. The use of >petawatt-ps laser pulses from the non-thermal ignition based on ultrahigh acceleration of plasma blocks by the nonlinear (ponderomotive) force, has to be combined with the measured ultrahigh magnetic fields in the 10 kilotesla range for cylindrical trapping. The evaluation of measured alpha particles from HB11 reactions arrives at the conclusion that apart from the usual binary nuclear reactions, secondary reactions by an avalanche multiplication may cause the high gains, even much higher than from deuterium tritium fusion. This may be leading to a concept of clean economic power generation.

In the framework of the ELI-Beamlines project, the HELL (High energy ELectron by Laser) platform will host an electron beamline with a dual aim: to explore innovative concepts of laser driven electron acceleration and to deliver a stable and reliable electron beam to external users, according to their specific needs. Because of this, it is crucial to identify the possible applications and their respective range of parameters. In order to accomplish this goal, Monte Carlo simulations of electron radiography and radiotherapy are performed and discussed. Once identified those parameter spaces, a beam transport line is studied and presented for each energy range. Finally, beam diagnostics are discussed.

The laser-driven Thomson scattering light source generates x-rays by the scattering of a high-energy electron beam off a high-intensity laser pulse. We have demonstrated that this source can generate collimated, narrowband x-ray beams in the energy range 0.1-12 MeV. In this work, we discuss recent results on the application of this source for radiography and photonuclear studies. The unique characteristics of the source make it possible to do this with the lowest possible dose and in a low-noise environment. We will also discuss recent experimental results that study nuclear reactions above the threshold for photodisintegration and photofission. The tunable nature of the source permits activation of specific targets while suppressing the signal from background materials.

Experimental demonstration of multi-charged heavy ion acceleration from the interaction between the ultra-intense short pulse laser system and the metal target is presented. The laser pulse of <10 J laser energy, 36 fs pulse width, and the contrast level of ~10¹⁰ from 200 TW class Ti:sapphire J-KAREN laser system at JAEA is used in the experiment. Almost fully stripped Fe ions accelerated up to 0.9 GeV are demonstrated. This is achieved by the high intensity laser field of ∼ 10²¹Wcm⁻² interacting with the solid density target. The demonstrated iron ions with high charge to mass ratio (Q/M) is difficult to be achieved by the conventional heavy ion source technique in the accelerators.

The burning process of high density (about 10¹⁸cm^-3), high temperature (tens to hundreds of keV) plasma trapped by a high mirror-like magnetic field in a Compact Magnetic Fusion (CMF) device is numerically investigated.. The initial high density and high temperature plasma in the CMF device is produced by ultrashort high intensity laser beam interaction with clusters or thin foils, and two fuels, D-T and p-¹¹B are studied. The spatio-temporal evolution of D-T and p-¹¹B plasmas, the production of alphas, the generated electric fields and the high external applied magnetic field are described by a 1-D multifluid code. The initial values for the plasma densities, temperatures and external applied magnetic field (about 100 T) correspond to high β plasmas. The main objectives of the numerical simulations are: to study the plasma trapping, the neutron and alpha production for both fuels, and compare the effect of the external applied magnetic field on the nuclear burning efficiency for the two fuels.. The comparisons and the advantages for each fuel will be presented. The proposed CMF device and the potential operation of the device within the ELI-NP pillar will be discussed.

Laser plasma physics is a field of big interest because of its implications in basic science, fast ignition, medicine (i.e. hadrontherapy), astrophysics, material science, particle acceleration etc. 100-MeV class protons accelerated from the interaction of a short laser pulse with a thin target have been demonstrated. With continuing development of laser technology, greater and greater energies are expected, therefore projects focusing on various applications are being formed, e.g. ELIMAIA (ELI Multidisciplinary Applications of laser-Ion Acceleration). One of the main characteristic and crucial disadvantage of ion beams accelerated by ultra-short intense laser pulses is their large divergence, not suitable for the most of applications. In this paper two ways how to decrease beam divergence are proposed. Firstly, impact of different design of targets on beam divergence is studied by using 2D Particlein-cell simulations (PIC). Namely, various types of targets include at foils, curved foil and foils with diverse microstructures. Obtained results show that well-designed microstructures, i.e. a hole in the center of the target, can produce proton beam with the lowest divergence. Moreover, the particle beam accelerated from a curved foil has lower divergence compared to the beam from a flat foil. Secondly, another proposed method for the divergence reduction is using of a magnetic solenoid. The trajectories of the laser accelerated particles passing through the solenoid are modeled in a simple Matlab program. Results from PIC simulations are used as input in the program. The divergence is controlled by optimizing the magnetic field inside the solenoid and installing an aperture in front of the device.

Relativistically induced transparency regime has been already achieved experimentally by the expansion of ionized solid target during laser-target interaction for relatively longer laser pulses (about 500 fs), but not for ultrashort pulses (about 30 fs), where the expansion is not significant, and, thus, too high laser intensity (close to 10²³ W/cm²) is required. However, when ultrashort intense laser pulse at higher harmonic frequency irradiates a thin solid foil, the target may become relativistically transparent for significantly lower laser pulse intensity compared with the irradiation at fundamental laser frequency. The relativistically induced transparency results in an enhanced heating of hot electrons as well as increased maximum energy of accelerated ions and their numbers. When fundamental laser frequency is converted to the third harmonics, we observed the increase of maximum energy of accelerated protons and numbers of high energy protons by factor of 2 in our two-dimensional particle-in-cell simulations. Lengthening of the laser pulse due to frequency conversion should not decrease the energy and numbers of accelerated protons. The proposed scheme enables to accelerate protons to energies over 250 MeV by ultrashort laser pulse of maximum intensity below 10²² W/cm² irradiating 200 nm thick solid foil.

Magnetic reconnection is regarded as a fundamental phenomenon in space and laboratory plasmas. It converts magnetic energy to kinetic energy of plasma particles through the topological rearrangements of the magnetic field lines. Magnetic reconnection is believed to play an important role in the solar systems, such as solar flares and coronal mass ejections. Observations of rapid energy release in solar flare and the global convection pattern within the magnetosphere are strongly suggestive that reconnection must be occurring. With the development of laser technology, high power laser facilities have made great progress in recent decades. Ultra powerful pulse with TW and PW are available now. As a result, the laser-matter interaction enters regimes of interest for laboratory astrophysics such as magnetic reconnection. J. Y. Zhong et al.1 reported an experiment about Xray source emission by reconnection outflows. Two intense lasers with long pulse duration are focused on the solid Aluminum target to generate hot electrons. In this paper, we employ a hydrogen foam target with near critical density to investigate the reconnection. Two parallel ultra intense pulses are injected into the target. By the effect of laser wakefield acceleration, two strong electron beam are generated and both of them induce a magnetic dipole structure. With the expansion of the dipole, magnetic field annihilation occurs in the center part of the target. The induced electric field and particle acceleration are detected in the simulations as evidence for magnetic reconnection. The effects of separation distance between two laser pulses and laser intensity on magnetic reconnection are also discussed.

Relativistic solitons arising from the interaction of an intense laser pulse with underdense plasmas are investigated. We show the formation and evolution of the relativistic solitons in a collisionless cold plasma with two dimensional particle-in-cell simulations. Such a kind of solitons will evolve into postsolitons if the time scale is longer than the ion response time. Generally, a substantial part of the pulse energy is transformed into solitons during the soliton formation. This fairly high efficiency of electromagnetic energy transformation can play an important role in the interaction between the laser pulse and the plasma. The energy exchange between the electromagnetic field and the kinetic energy of the soliton is discussed. In homogeneous plasmas, the solitons tend to stay close to the region where they are generated and dissipate due to the interaction with surrounding particles eventually. While the laser pulse propagates through inhomogeneous plasmas, the solitons are accelerated along the plasma density gradient towards lower density.

Radiochromic film (RCF) based multichannel diagnostics utilizes the concept of a stack detector comprised of alternating layers of RCFs and shielding aluminium layers. An algorithm based on SRIM simulations is used to correct the accumulated dose. Among the standard information that can be obtained is the maximum ion energy and to some extend the beam energy spectrum. The main area where this detector shines though is the geometrical characterization of the beam. Whereas other detectors such as Thomson parabola spectrometer or Faraday cups detect only a fraction of the outburst cone, the RCF stack placed right behind the target absorbs the whole beam. A complete 2D and to some extend 3D imprint of the ion beam allows us to determine parameters such as divergence or beam center shift with respect to the target normal. The obvious drawback of such diagnostics is its invasive character. But considering that only a few successful shots (2-3) are needed per one kind of target to perform the analysis, the drawbacks are acceptable. In this work, we present results obtained with the RCF diagnostics using both conventional accelerators and laser-driven ion beams during 2 experimental campaigns.

The quadrupole lens free multiple profile emittance measurement method is an adaptation of the standard multiple profile monitor method for electron beam emittance measurement which was tested at PW laser system. This single shot technique allows to obtain the emittance from beam profile radii fit by means of Twiss (Courant-Snyder) parameters. Lanex scintillating screens were used as profile monitors due to their high yield of visible photons. However, on the other hand, the screen is a source of multiple Coulomb scattering which can influence the beam profile on the following screens at relatively low electron energies. Nevertheless, the contribution of the multiple scattering can be effectively subtracted from the signal by e.g. Bayes unfolding. For high energy beams (E > 0.5 GeV), the multiple scattering contribution is negligible. The presented diagnostics is easy to be implemented into standard experimental setups without any special requests for alignment procedure. Moreover, it can be useful in the optimization phase of the laser plasma accelerator where beam fundamental parameters (energy, energy spread, divergence, pointing) typically fluctuate shot-to- shot.

The stability of accleration of ions in the RPDA regime against transversal shift of the cluster target relative to gaussian and supergaussian laser pulses is considered. It is shown that the maximum energy of ions decreases while the shift increases, as the target escapes the acceleration domain. The effect of self-focusing for the supergaussian pulse profile is found and interpreted. An analytical approach based on the relativistic mirror model is developed. We also conduct PIC simulations that prove our theoretical estimations. The results obtained can be applied to the optimization of ion acceleration by the laser radiation pressure with mass-limited targets.