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High-power laser facilities give experimental access to fundamental strong-field quantum electrodynamics processes. A key effect to be explored is the nonlinear Breit-Wheeler process: the conversion of high-energy photons into electron-positron pairs through the interaction with a strong electromagnetic field. A major challenge to observing nonlinear Breit-Wheeler pair production experimentally is first having a suitable source of high-energy photons. In this paper we outline a simple all-optical setup which efficiently generates photons through the so-called $\gamma$-flash mechanism by irradiating a solid target with a high-power laser. We consider the collision of these photons with a secondary laser, and systematically discuss the prospects for exploring the nonlinear Breit-Wheeler process at current and next-generation high-power laser facilities., Comment: 12 pages, 8 figures

A microtube implosion driven by ultraintense laser pulses is used to produce ultrahigh magnetic fields. Due to the laser-produced hot electrons with energies of mega-electron volts, cold ions in the inner wall surface implode towards the central axis. By pre-seeding uniform magnetic fields on the kilotesla order, the Lorenz force induces the Larmor gyromotion of the imploding ions and electrons. Due to the resultant collective motion of relativistic charged particles around the central axis, strong spin current densities of ~ peta-ampere/cm2 are produced with a few tens of nm size, generating megatesla-order magnetic fields. The underlying physics and important scaling are revealed by particle simulations and a simple analytical model. The concept holds promise to open new frontiers in many branches of fundamental physics and applications in terms of ultrahigh magnetic fields., 22 pages, 7 figures

Dense high-energy monoenergetic proton beams are vital for wide applications, thus modern laser-plasma-based ion-acceleration methods are aiming to obtain high-energy proton beams with energy spread as low as possible. In this work, we put forward a quantum radiative compression method to postcompress a highly accelerated proton beam and convert it to a dense quasimonoenergetic one. We find that when the relativistic plasma produced by radiation-pressure acceleration collides head on with an ultraintense laser beam, large-amplitude plasma oscillations are excited due to quantum radiation reaction and the ponderomotive force, which induce compression of the phase space of protons located in its acceleration phase with negative gradient. Our three-dimensional spin-resolved quantum electrodynamics (QED) particle-in-cell simulations show that hollow-structure proton beams with a peak energy approximately GeV, relative energy spread of few percents, and number Np ∼1010 (or Np ∼109 with a 1% energy spread) can be produced in near-future laser facilities, which may fulfill the requirements of alternative applications, such as, for radiography of ultrathick dense materials, or as injectors of hadron colliders.

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 present a brief overview of physical processes in a plasma under the action of relativistically strong electromagnetic radiation generated by high-power lasers. Attention is focused on nonlinear waves in a laser plasma for the creation of compact electron accelerators. Then, we address the acceleration of plasma bunches by the radiation pressure of light, which is the most efficient regime of ion acceleration. Coherent hard electromagnetic radiation in the relativistic plasma is generated in the form of high harmonics and/or electromagnetic pulses, which are compressed and intensified after reflection from relativistic mirrors created by nonlinear plasma waves. These processes are of interest in view of the development of novel methods for acceleration of charged particles and the development of sources of bright and hard electromagnetic radiation.

Electron–positron pair production via Breit–Wheeler process requires laser intensities approaching 1024 W cm−2 due to the small cross-section. Here, we propose a mechanism for brilliant γ-ray emission and dense GeV pairs creation accompanied with high-harmonic generation by using plasma mirror and an ultra short pulse with the intensity of 3 × 1023 W cm−2. The laser is reflected by the solid surface after propagating tens of microns in a near-critical density plasma and breaks into short wave packets. The intensity of the reflected high order harmonic field is enhanced by the focusing and compression effects from the deformed oscillating mirror. The radiation trapped electrons emit γ-photons while colliding with the reflected attosecond pulses. The peak intensity of the γ-ray reaches 0.74 PW with the brilliance of 2 × 1024 s−1 mm−2 mrad−2 (0.1%BW)−1 (at 58 MeV). A GeV positron beam is obtained with density of 4 × 1021 cm−3 and a particle number of 5.6 × 109. Laser technology is rapidly developing to the point where pulse power and intensity are expected to reach such levels that new physical processes will be able to be studied for the first time. Using simulation the authors theoretically investigate the generation of high brilliance gamma rays and electron-positron pairs during extreme intense laser interaction with a specific target.

High order harmonic generation by extremely intense, interacting, electromagnetic waves in the quantum vacuum is investigated within the framework of the Heisenberg-Euler formalism. Two intersecting plane waves of finite duration are considered in the case of general polarizations. Detailed finite expressions are obtained for the case where only the first Poincar\'e invariant does not vanish. Yields of high harmonics in this case are most effective., Comment: 12 pages, 2 figures

In this article we use an electromagnetic Lagrangian constructed so as to include dispersive effects in the description of an electromagnetic wave propagating in the Quantum Electrodynamic Vacuum. This Lagrangian is Lorentz invariant, includes contributions up to six powers in the electromagnetic fields and involves both fields and their first derivatives. Conceptual limitations inherent to the use of this higher derivative Lagrangian approach are discussed. We consider the one-dimensional spatial limit and obtain an exact solution of the nonlinear wave equation recovering the Korteveg-de Vries type periodic waves and solitons given in S. V. Bulanov et al., Phys. Rev. D, 101, 016016 (2020)., 11 pages

Using analytical methods and computer simulations, we investigate physical processes which lead to the formation of ring-shaped electromagnetic and electron structures in laser-plasma interaction. We observe that as the intense laser pulse excites a nonlinear Langmuir wave in an underdense plasmas, a significant portion of the pulse is refracted outwards the propagation direction due to the interactions with thin, high-density electron walls surrounding the wave cavities. Because of the radial symmetry, the refracted light forms a distinct electromagnetic ring that encircles the driver pulse. The efficiency of the energy transfer to the electromagnetic ring is relatively high, so that the ring can generate its own Langmuir wave and trigger the electron self-injection, which results in a ring-shaped beam of high-energy electrons. The properties of the ring-shaped electromagnetic and electron beams depend on the parameters of the Langmuir wave cavity walls, thus they can be controlled by tuning the parameters of the laser and plasma. The ring structures could be applied as a drivers for acceleration of positively charged particles, or as a diagnostic to determine regimes and the overall efficiency of the laser-wakefield accelerator.

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

Dynamic mitigation for the tearing mode instability in the current sheet in collisionless plasma is demonstrated by applying a wobbling electron current beam. The initial small amplitude modulations imposed on the current sheet induce the electric current filamentation and the reconnection of the magnetic field lines. When the wobbling or oscillation motion is added from the electron beam having a form of a thin layer moving along the current sheet, the perturbation phase is mixed and consequently the instability growth is saturated remarkably, like in the case of the feed-forward control.

Dynamic mitigation for the tearing mode instability in the current sheet in collisionless plasmas is demonstrated by applying a wobbling electron current beam. The initial small amplitude modulations imposed on the current sheet induce the electric current filamentation and the reconnection of the magnetic field lines. When the wobbling or oscillatory motion is added from the electron beam having a form of a thin layer moving along the current sheet, the perturbation phase is mixed and consequently the instability growth is saturated remarkably, like in the case of the feed-forward control.

Magnetic reconnection driven by laser plasma interactions attracts great interests in the recent decades. Motivated by the rapid development of the laser technology, the ultra strong magnetic field generated by the laser-plasma accelerated electrons provides unique environment to investigate the relativistic magnetic field annihilation and reconnection. It opens a new way for understanding relativistic regimes of fast magnetic field dissipation particularly in space plasmas, where the large scale magnetic field energy is converted to the energy of the nonthermal charged particles. Here we review the recent results in relativistic magnetic reconnection based on the laser and collisionless plasma interactions. The basic mechanism and the theoretical model are discussed. Several proposed experimental setups for relativistic reconnection research are presented.

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.

We show that electron-positron pair production from the vacuum is possible via the strong Coulomb fields generated by micro-bubble implosions induced by ultra-high intensity lasers. Even in the case where the Coulomb fields are lower than the pair creation threshold, externally injected high energy electrons or photons could be used to generate pairs.

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.

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.

Coherent x-rays via the Burst Intensification by Singularity Emitting Radiation (BISER) mechanism are generated from relativistic plasma in helium gas target. A broad modulation of the BISER spectrum, which is significantly wider than the harmonic order, is observed and characterized. In particular, we found that the modulation period can be as large as 41 eV.

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

We propose a mechanism to generate a single intense circularly polarized attosecond x-ray pulse from the interaction of a circularly polarized relativistic few-cycle laser pulse with an ultrathin foil at normal incidence. Analytical modeling and particle-in-cell simulation demonstrate that a huge charge-separation field can be produced when all the electrons are displaced from the target by the incident laser, resulting in a high-quality relativistic electron mirror that propagates against the tail of the laser pulse. The latter is efficiently reflected as well as compressed into an attosecond pulse that is also circularly polarized.

We present an approach for direct measurement of ultrahigh laser intensities in the range \(10^{20}\)–\(10^{24}\) W/cm\(^2\). The method is based on the use of multiple sequential tunneling ionization of heavy atoms with adequately high ionization potentials. We show that, due to the highly nonlinear dependence of tunneling ionization rates on the electromagnetic field strength, an off-set in the charge distribution of ions appears to be clearly sensitive to the peak value of intensity in the laser focus. Based on the tunnel-ionization mechanism, a simple analytic theory helps in estimating the maximal charge state produced at a given laser intensity. Our theory also allows for calculating qualitatively a distribution in charge states generated in different zones of the laser focus. These qualitative predictions are in excellent agreement with numerical simulations of the tunneling cascades, developed in the interaction of a short tightly focused laser pulse with low-density noble gas targets. The method could be particularly useful and of instrumental demand in view of the expected commissioning of several new laser facilities, capable of delivering ultra-powerful light pulses in the above mentioned domain of intensities.

Using QED PIC and hydrodynamic simulations, we optimize the -flare generation scheme from the high power laser interaction with tailored target showing the efficient conversion of the laser pulse energy to -photons.

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.

The hodograph transformation is generally used in order to associate a system of linear partial differential equations to a system of nonlinear (quasilinear) differential equations by interchanging dependent and independent variables. Here we consider the case when the nonlinear differential system can be derived from a Lagrangian density and revisit the hodograph transformation within the formalism of the Lagrangian-Hamiltonian continuous dynamical systems. Restricting to the case of nondissipative, nondispersive one-dimensional waves, we show that the hodograph transformation leads to a linear partial differential equation for an unknown function that plays the role of the Lagrangian in the hodograph variables. We then define the corresponding hodograph Hamiltonian and show that it turns out to coincide with the wave amplitude. i.e., with the unknown function of the independent variables to be solved for in the initial nonlinear wave equation. (C) 2019 Elsevier B.V. All rights reserved.

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

Converging cylindrical electromagnetic fields in vacuum have been shown (Zababakhin and Nechaev Sov Phys JETP 6:345, 1958) to exhibit amplitude “cumulation”. It was found that the amplitude of self-similar waves increases without bounds at finite distances from the axis on the front of the fields reflected from the cylindrical axis. In the present paper, we propose to exploit this cylindrical cumulation process as a possible new path towards the generation of ultra-strong electromagnetic fields where nonlinear quantum electrodynamics (QED) effects come into play. We show that these effects, as described in the long wave-length limit within the framework of the Euler Heisenberg Lagrangian, induce a radius-dependent reduction of the propagation speed of the cumulation front. Furthermore, we compute the $$e^+{-}e^-$$ pair production rate at the cumulation front and show that the total number of pairs that are generated scales as the sixth power of the field amplitude.

The interplay between the frequency chirping of a broadband laser pulse and the longitudinal chromatic aberration of a focusing optic introduces the superluminal or subluminal behavior to a laser focus. In this paper, we present an analytic expression for an electric field describing a superluminal or subluminal femtosecond laser focus with orbital angular momentum. The analytic expression for a superluminal or subluminal laser focus is obtained through a diffraction integral, in which the focal length is replaced by a time-dependent focal length under the paraxial approximation, and the Fourier transformation. The speed and pulse duration of a laser focus are determined by the total group delay dispersion and a chromaticity parameter defined by the longitudinal chromatic aberration of a dispersive focusing optic. It is shown that it is possible to generate a several femtosecond superluminal orbital angular momentum laser focus in the focal region.

In a dissipative dynamic system driven by an oscillating force, a strong nonlinear highly oscillatory friction force can create a quasi-steady tug, which is always directed opposite to the ponderomotive force induced due to a spatial inhomogeneity of oscillations. When the friction-induced tug exceeds the ponderomotive force, the friction stabilizes the system oscillations near the maxima of the oscillation spatial amplitude., Comment: 7 pages, 2 figures, 1 appendix

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

As an advanced accelerator concept, laser wakefield acceleration, with its attractive acceleration gradient, has invoked great interest worldwide. The electron beams from laser wakefield acceleration were assumed to have the advantage of “jitterfree” or relatively small jitter, since the emergence of quasimonoenergetic bunch structures were considered to result from the trapping of electrons into the first bucket of the plasma wave. However, the emission times of the electron bunches from laser wakefield acceleration have not been real time monitored in experiments up to now. To examine this, we introduced the electro-optic spatial decoding method. The relative emission times of the electrons were observed to have variations with different plasma densities when using a laser with moderate intensity. The study shows that timing issues should not be ignored in some occasions of laser wakefield acceleration. The method used in this paper could be a candidate serving as a single-shot nondestructive electron bunch timing monitor for laser wakefield experiment and potential ultrafast pump-probe studies.

As an alternative to Compton backscattering and bremsstrahlung, the process of colliding high-energy 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., Comment: 6 pages, 4 figures