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Shock Ignition is considered as a relatively robust and efficient approach to inertial confinement fusion. A strong converging shock, which is used to ignite the fuel, is launched by a high power laser pulse with intensity in the range of 1015 − 1016 W/cm2 (at the wavelength of 351 nm). In the lower end of this intensity range the interaction is dominated by collisions while the parametric instabilities are playing a secondary role. This is manifested in a relatively weak reflectivity and efficient electron heating. The interaction is dominated by collective effects at the upper edge of the intensity range. The stimulated Brillouin and Raman scattering (SBS and SRS respectively) take place in a less dense plasma and cavitation provides an efficient collisionless absorption mechanism. The transition from collisional to collisionless absorption in laser plasma interactions at higher intensities is studied here with the help of large scale one-dimensional Particle-in-Cell (PIC) simulations. The relation between the collisional and collisionless processes is manifested in the energy spectrum of electrons transporting the absorbed laser energy and in the spectrum of the reflected laser light.

Laser-plasma interaction is investigated for conditions relevant for the shock-ignition (SI) scheme of inertial confinement fusion using two-dimensional particle-in-cell (PIC) simulations of an intense laser beam propagating in a hot, large-scale, non-uniform plasma. The temporal evolution and interdependence of Raman- (SRS), and Brillouin- (SBS), side/backscattering as well as Two-Plasmon-Decay (TPD) are studied. TPD is developing in concomitance with SRS creating a broad spectrum of plasma waves near the quarter-critical density. They are rapidly saturated due to plasma cavitation within a few picoseconds. The hot electron spectrum created by SRS and TPD is relatively soft, limited to energies below one hundred keV.

We present an overview of the interpretation of laser plasma interaction (LPI) experiments carried out on the LIL facility. These multikilojoule experiments have been done using underdense foam targets at 0.351 μm laser light leading to high temperature and large plasmas. We discuss the interpretation using our different numerical tools: hydrodynamics simulations carried out with the code FCI2 to characterize the plasma, linear gain estimates with the postprocessor Piranah and paraxial simulations with the code HERA.

Manipulating and harnessing plasmonic phenomena in the ultra-relativistic regime reveal promising prospects for the use of surface plasma waves (SPW) to create high-energy particle and radiation sources in the next generation of multi-petawatt lasers. Indeed, relativistic high-charge electron bunches can be produced by SPW excited by ultra-high intensity femtosecond lasers impinging on a periodically modulated solid-density target. In this regime, there is good evidence that SPW excitation survives and that the produced electron bunches experience strong acceleration, thus emitting large amounts of electromagnetic radiation. Therefore, extending the study to ultra-high laser intensities (I > 10 21 W/cm2), the use of a resonant grating for SPW generation represents an interesting alternative to light sources, as the energy lost by electrons due to radiation emission is transferred to high-energy γ photons. In addition, we show that using a laser with wavefront rotation coupled with a tailored blazed grating improves photon emission in the ultra-relativistic regime of interaction. [ABSTRACT FROM AUTHOR]

Over the last two decades, the importance of fully ionized plasmas for the controlled manipulation of high-power coherent light has increased considerably. Many ideas have been put forward on how to control or change the properties of laser pulses such as their frequency, spectrum, intensity, and polarization. The corresponding interaction with a plasma can take place either in a self-organizing way or by prior tailoring. Considerable work has been done in theoretical studies and in simulations, but at present there is a backlog of demand for experimental verification and the associated detailed characterization of plasma-optical elements. Existing proof-of-principle experiments need to be pushed to higher power levels. There is little doubt that plasmas have huge potential for future use in high-power optics. This introduction to the special issue of Matter and Radiation at Extremes devoted to plasma optics sets the framework, gives a short historical overview, and briefly describes the various articles in this collection. [ABSTRACT FROM AUTHOR]

The forthcoming generation of multi-petawatt lasers opens the way to abundant pair production by the nonlinear Breit–Wheeler process, i.e. the decay of a photon into an electron–positron pair inside an intense laser field. In this paper we explore the optimal conditions for Breit–Wheeler pair production in the head-on collision of a laser pulse with gamma photons. The role of the laser peak intensity versus the focal spot size and shape is examined keeping a constant laser energy to match experimental constraints. A simple model for the soft-shower case, where most pairs originate from the decay of the initial gamma photons, is derived. This approach provides us with a semi-analytical model for more complex situations involving either Gaussian or Laguerre–Gauss (LG) laser beams. We then explore the influence of the order of the LG beams on pair creation. Finally we obtain the result that, above a given threshold, a larger spot size (or a higher order in the case of LG laser beams) is more favorable than a higher peak intensity. Our results match very well with three-dimensional particle-in-cell simulations and can be used to guide upcoming experimental campaigns. [ABSTRACT FROM AUTHOR]

Ultra-short high-power lasers can deliver extreme light intensities (≥ 10 20 W/cm2 and ≤ 30 f s) and drive large amplitude Surface Plasma Wave (SPW) at over-dense plasma surface. The resulting current of energetic electron has great interest for applications, potentially scaling with the laser amplitude, provided that the laser–plasma transfer to the accelerated particles mediated by SPW is still efficient at ultra-high intensity. By means of particle-in-cell simulations, we identify the best condition for SPW excitation and show a strong correlation between the optimum surface plasma wave excitation angle and the laser's angle of incidence that optimize the electron acceleration along the plasma surface. We also discuss how plasma density and plasma surface shape can be adjusted in order to push to higher laser intensity the limit of surface plasma wave excitation. Our results open the way to new experiments on forthcoming multi-petawatt laser systems. [ABSTRACT FROM AUTHOR]

Type-III-burst radio signals can be mimicked in the laboratory via laser-plasma interaction. Instead of an electron beam generating Langmuir waves (LWs) in the interplanetary medium, the LWs are created by a laser interacting with a millimeter-sized plasma through the stimulated Raman instability. In both cases, the LWs feed the Langmuir decay instability which scatters them in several directions. The resulting LWs may couple to form electromagnetic emission at twice the plasma frequency, which has been detected in the interplanetary medium, and recently in a laboratory laser experiment [Marquès et al., Phys. Rev. Lett. 124, 135001 (2020)]. This article presents the first numerical analysis of this laser configuration using particle-in-cell simulations, providing details on the wave spectra that are too difficult to measure in experiments. The role of some parameters is addressed, with a focus on laser intensity, in order to illustrate the behavior of the electromagnetic emission's angular distribution and polarization. [ABSTRACT FROM AUTHOR]

In this work, a quasi-neutral plasma grating is considered, generated by two counter-propagating identical laser beams. Typical time scales associated with such gratings are given by , where v0 is the electron quiver in the laser field of wavevector k. In most situations, the behavior of the grating can be characterized by a single parameter, µ, which is proportional to the ratio of background electron temperature to the square of the electron quiver velocity. Indeed, even for quasi-neutral gratings, electron pressure might play an important role, via adiabatic electron heating. The influence on grating formation and lifetime of other parameters involving the inclusion of dissipative effects or kinetic effects is also examined in detail. Finally, an approximated analytical solution to the fluid model is found and shows good agreement with first-principle simulations. [ABSTRACT FROM AUTHOR]

Solar radio emissions are electromagnetic waves emitted in the solar wind as a consequence of electron beams accelerated during solar flares or interplanetary shocks such as interplanetary coronal mass ejections. Different physical mechanisms have been suggested to describe their origin. A good understanding of the emission process would enable to infer the kinetic energy transferred from accelerated electrons to radio waves. Even if the electrostatic case has been extensively studied, full electromagnetic simulations were attempted only recently. In this work, we report large‐scale 2D3V electromagnetic particle‐in‐cell simulations that enable to identify the generation of both electrostatic and electromagnetic waves originated by a succession of plasma instabilities. They confirm that an efficient mechanism to generate solar radio emissions close to T2f, the harmonic of the plasma frequency, is a multistage model based on a succession of nonlinear three‐wave interaction processes. Through a parametric study of the electron beam parameters, we show that (i) the global efficiency of the multistep conversion mechanism from the electron beam kinetic energy to the T2f radio wave is independent of the beam parameters, approximately 10−5 in all tested configurations, while (ii) the directivity of the electromagnetic radio wave strongly depends on the origin electron beam. Those results represent a step forward toward the use of solar wind radio emissions, observed remotely, as a diagnostic for the properties of the electron beam located at the source of the radio emission, and therefore to eventually better characterize remotely electron acceleration mechanisms in space regions not directly accessible to in situ measurements. Key Points: We single out the successive steps of the generation mechanisms of solar radio emissionsWe quantify the energy transferred from energetic particles to radio waves and show it is independent of energetic particles parametersWe identify the directivity of the radio emissions and show its strong dependence on energetic particles parameters. [ABSTRACT FROM AUTHOR]

The role of density perturbations of the background plasma in the development of Langmuir waves generated by beam-plasma instabilities is a very debated issue in space physics. The presence of clumpy electrostatic wave-packets (in particular Langmuir waves), from in situ observations, is indeed puzzling. Several processes have been proposed to explain the formation of waveforms, such as Stochastic Growth Theory and trapping in eigenmodes. Here we explore another mechanism considering the seeding of the beam-plasma instability by density holes. We have performed several 1D-1V Vlasov simulations in the electrostatic limit. We show that in the presence of a density hole, a large amplitude solitary wave-packet of Langmuir waves is formed and that it evolves towards clumpier waveforms. Moreover, the large-amplitude wave-packets generated near the hole can reach saturation and accelerate the electrons of the beam: their velocity distribution is strongly distorted, leading to a multi-peaked structure that generates new unstable modes having phase velocities both larger and smaller than the average speed of the beam. The relationship between the wave amplitude and the characteristics of the density hole is also described, showing how the electron beam may select specific holes to generate enhanced localised Langmuir wave-packets. [ABSTRACT FROM AUTHOR]

A theoretical and numerical analysis is carried out for turbulent collisionless shocks mediated by the ion-Weibel instability during high-velocity plasma collisions. We develop a simple model based on the coalescence dynamics of the ion current filaments, which predicts the spatio-temporal evolution of the magnetic fluctuations formed in the upstream plasma region. From comparison with particle-in-cell simulations, our model is shown to correctly capture the magnetic-field and ion-beam properties during the early-time shock propagation. [ABSTRACT FROM AUTHOR]

Plasma amplification of low energy, a short (~100-500 fs) laser pulse by an energetic long (~10 ps) pulse via strong coupling Stimulated Brillouin Backscattering is investigated with an extensive analysis of one-dimensional particle-in-cell simulations. Parameters relevant to nowadays experimental conditions are investigated. The obtained seed pulse spectra are analyzed as a function of the interaction conditions such as plasma profile, pulses delay, and seed or pulse duration. The factors affecting the amount of energy transferred are determined, and the competition between Brillouin-based amplification and parasitic Raman backscattering is analyzed, leading to the optimization of the interaction conditions. [ABSTRACT FROM AUTHOR]

Different electron acceleration regimes in the evanescent field of a surface plasma wave are studied by considering the interaction of a test electron with the high-frequency electromagnetic field of a surface wave. The non-relativistic and relativistic limits are investigated. Simple scalings are found demonstrating the possibility to achieve an efficient conversion of the surface wave field energy into electron kinetic energy. This mechanism of electron acceleration can provide a high-frequency pulsed source of relativistic electrons with a well defined energy. In the relativistic limit, the most energetic electrons are obtained in the so-called electromagnetic regime for surface waves. In this regime, the particles are accelerated to velocities larger than the wave phase velocity, mainly in the direction parallel to the plasma-vacuum interface. [ABSTRACT FROM AUTHOR]

Red and yellow lines identify the wave-vectors produced by Raman [Eq. (1)] and LDI [Eq. (2)], respectively. Red and yellow lines identify the wave-vectors produced by SRS [Eq. (1)] and by the first LDI step [Eq. (2)], respectively. Magenta lines identify the wave-vectors produced by LDI [Eq. (3)]. [Extracted from the article]

Plasma media, by exciting Raman (electron) or Brillouin (ion) waves, have been used to transfer energy from moderately long, high-energy light pulses to short ones. Using multidimensional kinetic simulations, we define here the optimum window in which a Brillouin scheme can be exploited for amplification and compression of short laser pulses over short distances to very high power. We also show that shaping the plasma allows for increasing the efficiency of the process while minimizing other unwanted plasma processes. Moreover, we show that, contrary to what was traditionally thought (i.e., using Brillouin in gases for nanosecond pulse compression), this scheme is able to amplify pulses of extremely short duration. [ABSTRACT FROM AUTHOR]

Amplification of laser pulses based on the backscattering process in plasmas can be performed using either the response of an electron plasma wave or an ion-acoustic wave. However, if the pulse durations become very short and the natural spread in frequency a substantial amount of the frequency itself, the Raman and Brillouin processes start to mix. Kinetic simulations show the transition from a pure amplification regime, in this case strong-coupling Brillouin, to a regime where a considerable downshift of the frequency of the amplified pulse takes place. It is conjectured that in the case of very short pulses, multi-modes are excited which contribute to the amplification process. [ABSTRACT FROM AUTHOR]

The possibility of enhancing the emission of the ions accelerated in the interaction of a high intensity ultra-short (<100 fs) laser pulse with a thin target (<10λ0), via surface plasma wave excitation is investigated. Two-dimensional particle-in-cell simulations are performed for laser intensities ranging from 1019 to 1020 Wcm-2μm2. The surface wave is resonantly excited by the laser via the coupling with a modulation at the target surface. In the cases where the surface wave is excited, we find an enhancement of the maximum ion energy of a factor ∼2 compared to the cases where the target surface is flat. [ABSTRACT FROM AUTHOR]

Two-plasmon-decay (TPD) instability is investigated for conditions relevant for the shock-ignition (SI) scheme of inertial confinement fusion. Two-dimensional particle-in-cell simulations show that in a hot, large-scale plasma, TPD develops in concomitance with stimulated Raman scattering (SRS). It is active only during the first picosecond of interaction, and then it is rapidly saturated due to plasma cavitation. TPD-excited plasma waves extend to small wavelengths, above the standard Landau cutoff. The hot electron spectrum created by SRS and TPD is relatively soft, limited to energies below 100 keV, which should not be a danger for the fuel core preheat in the SI scenario. [ABSTRACT FROM AUTHOR]

The efficiency of laser overdense plasma coupling via surface plasma wave excitation is investigated. Two-dimensional particle-in-cell simulations are performed over a wide range of laser pulse intensity from 1015 to 1020 W cm-2 μm2 with electron density ranging from 25 to 100nc to describe the laser interaction with a grating target where a surface plasma wave excitation condition is fulfilled. The numerical studies confirm an efficient coupling with an enhancement of the laser absorption up to 75%. The simulations also show the presence of a localized, quasi-static magnetic field at the plasma surface. Two interaction regimes are identified for low (Iλ2 < 1017 W cm-2 μm2) and high (Iλ2 > 1017 W cm-2 μm2) laser pulse intensities. At 'relativistic' laser intensity, steady magnetic fields as high as ∼580 MG μm/λ0 at 7 × 1019 W cm-2 μm2 are obtained in the simulations. [ABSTRACT FROM AUTHOR]

A detailed description of stimulated Raman backscattering and related processes for the purpose of inertial confinement fusion requires multi-dimensional kinetic simulations of a full speckle in a high-temperature, large-scale, inhomogeneous plasma. In particular for the shock-ignition scheme operating at high laser intensities, kinetic aspects are predominant. High- (Iλo2~5×1015Wμm2/cm2) as well as low-intensity (Iλo2~1015Wμm2/cm2) cases show the predominance of collisionless, collective processes for the interaction. While the two-plasmon decay instability and the cavitation scenario are hardly affected by intensity variation, inflationary Raman backscattering proves to be very sensitive. Brillouin backscattering evolves on longer time scales and dominates the reflectivities, although it is sensitive to the intensity. Filamentation and self-focusing do occur for all cases but on time scales too long to affect Raman backscattering. [ABSTRACT FROM AUTHOR]

The shock ignition concept implies laser pulse intensities higher than 1015 W/cm2 (at the wavelength of 351 nm), which is the commonly accepted limit where the inverse bremsstruhlung absorption dominates. The transition from collisional to collisionless absorption in laser plasma interactions at higher intensities is studied in the present paper with the help of large scale one-dimensional particle-in-cell simulations. The initial parameters are defined by the hydrodynamic simulations corresponding to recent experiments. The simulations predict that a quasi-steady regime of laser plasma interaction is attained where the total laser energy absorption stays on the level of ∼65% in the laser intensity range 1015-1016 W/cm2. However, the relation between the collisional and collisionless processes changes significantly. This is manifested in the energy spectrum of electrons transporting the absorbed laser energy and in the spectrum of the reflected laser light. [ABSTRACT FROM AUTHOR]

A correction to the article "Stimulated Brillouin backscattering and ion acoustic wave secondary instability," published in the August, 20, 2009, issue of the journal is presented.

A study of the secondary instability of a finite-amplitude ion acoustic wave (IAW) affecting the saturation of stimulated Brillouin backscattering (SBS) of laser light in a plasma is presented. The secondary instability of the SBS IAW provides a nonlinear dissipation mechanism for the SBS IAW and can reduce the SBS reflectivity. To better understand the physics of the secondary instability and SBS, particle-in-cell kinetic simulations, analysis of dispersion relations, and integration of coupled mode equations have been undertaken and compared. Among the effects examined are the influences on the secondary instability of the frequency of the primary IAW, the second-harmonic IAW, and ion trapping in the primary SBS IAW which affects Landau damping and the IAW frequency. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) particle-in-cell numerical simulations of the interaction between a high-intensity short-pulse p-polarized laser beam and an overdense plasma are presented. It is shown that, under appropriate physical conditions, a surface plasma wave can be resonantly excited by a short-pulse laser wave, leading to strong relativistic electron acceleration together with a dramatic increase, up to 70%, of light absorption by the plasma. Purely 2D effects contribute to enhancement of electron acceleration. It is also found that the angular distribution of the hot electrons is drastically affected by the surface wave. The subsequent ion dynamics is shown to be significantly modified by the surface plasma wave excitation. [ABSTRACT FROM AUTHOR]

Two-dimensional particle-in-cell simulations of laser-plasma interaction using a plane-wave geometry show strong bursty stimulated Brillouin backscattering, rapid filamentation, and subsequent plasma cavitation. It is shown that the cavitation is not induced by self-focusing. The electromagnetic fields below the plasma frequency that are excited are related to transient soliton-like structures. At the origin of these solitons is a three-wave decay process exciting new modes in the plasma. The cavitation is responsible for a strong local reduction of the reflectivity and goes along with an efficient but transient heating of the electrons. Once heating ceases, transmission starts to increase. Local as well as global average reflectivities attain a very low value due to strong plasma density variations brought about by the cavitation process. On the one hand, the simulations confirm the existence of a new mechanism of cavity and soliton formation in nonrelativistic laser-plasma interaction in two dimensions, which was shown to exist in one-dimensional simulations [S. Weber, C. Riconda, and V. T. Tikhonchuk, Phys. Rev. Lett. 94, 055005 (2005)]. On the other hand, new aspects are introduced inherently related to the additional degree of freedom. [ABSTRACT FROM AUTHOR]

Short light pulse amplification using the stimulated Brillouin backscattering mechanism is considered. The novel feature is that the interaction process takes place in the strongly coupled regime and therefore the pulse compression is not limited by the ion-acoustic wave period. The mechanism is very efficient due to the large ratio of light frequency to the characteristic ion-acoustic wave frequency. Although large-amplitude ion-acoustic waves are generated and subsequent wave breaking takes place, the fluid and kinetic nonlinearities do not intervene with the amplification itself. [ABSTRACT FROM AUTHOR]

The role of ion and electron kinetic effects is investigated in the context of the nonlinear saturation of a driven ion acoustic wave (IAW) and its parametric decay into subharmonics. The simulations are carried out with a full–particle-in-cell (PIC) code, in which both ions and electrons are treated kinetically. The full-PIC results are compared with those obtained from a hybrid-PIC code (kinetic ions and Boltzmann electrons). It is found that the largest differences between the two kinds of simulations take place when the IAW is driven above the ion wave-breaking limit. In such a case of a strong drive, the hybrid-PIC simulations lead to a Berstein-Greene-Kruskal-like nonlinear IAW of a large amplitude, while in the full-PIC the IAW amplitude decays to a small level after a transient stage. The electron velocity distribution function is significantly flattened in the domain of small electron velocities. As a result the nonlinear frequency shift due to the electron kinetic effects compensates partly the nonlinear frequency shift due to the ion kinetic effects, allowing then for the parametric decay of the driven IAW into subharmonics. These observations lead to the conclusion that electron kinetic effects become important whenever the nonlinear effects come into play. [ABSTRACT FROM AUTHOR]

Numerical simulations and their theoretical interpretation of the formation of standing electromagnetic solitons produced in a regime of pulsating stimulated Brillouin scattering are presented. The localized field structures are stable, long-living entities and their physical properties are in very good agreement with theoretical predictions of electromagnetic solitons in a hot and dense plasma. They are the final outcome of a specific mode-coupling regime that can be attained for high laser intensities via the transient excitation of kinetic electrostatic nonlinear electron modes. [ABSTRACT FROM AUTHOR]

The stability of a driven coherent ion-acoustic wave (IAW) with regard to its decay into longer wavelengths is investigated. The effects of harmonic generation and wave dispersion are taken into account. The driver frequency and wave number do not necessarily satisfy the linear ion-acoustic wave dispersion relation, allowing a frequency mismatch between the driver frequency and the plasma linear-response frequency. The stability analysis is generally shown to involve a seven wave coupling in which the fundamental and the second-harmonic components of the equilibrium IAW couple to a low-frequency daughter wave and to their Stokes and anti-Stokes satellites. The general dispersion relation corresponding to this seven wave coupling is derived and solved numerically in three-dimensional geometry. A variety of branches of instabilities is found to appear. In order to classify these branches, an approximate dispersion relation is derived, corresponding to the Korteweg–de-Vries limit for the plasma low-frequency nonlinear behavior. This approximate dispersion relation makes it possible to obtain approximate expressions for the growth rate of each branch. The occurrence of each type of instability is discussed as a function of the sign and size of the frequency mismatch. The special case of one-dimensional geometry is also considered, making it possible to investigate the results of one-dimensional numerical simulations. [ABSTRACT FROM AUTHOR]

A kinetic mechanism for the saturation of Brillouin backscattering in the high-intensity regime is presented. The reflectivity goes through several characteristic phases and terminates in a low-level quasistationary state of a few percent. This low-level saturation is due to the creation of cavities in the plasma. The process responsible for cavity formation is linked to Coulomb explosions in the bulk plasma. Along with the cavity formation, particles are accelerated up to energies of 100 keV. Strong electron and ion heating and acceleration are the characteristics of this saturation mechanism for stimulated Brillouin backscattering. The cavities are filled with electrostatic and electromagnetic fields. Whereas the electrostatic ones are quickly dissipated, the electromagnetic ones are stable and have intensities up to 30 times the incident laser intensity. [ABSTRACT FROM AUTHOR]

The relativistic acceleration of electrons by the field of surface plasma waves created in the interaction between ultrashort high-intensity laser pulses with sharp-edged overdense plasmas has been investigated. It is shown that the initial phase of the wave experienced by the electrons play a leading part by yielding a well-defined peaked structure in the energy distribution function. This study suggests that resonant excitation of surface plasma waves could result in quasi-monokinetic energetic electron bunches. When the space charge field becomes too strong, this mechanism can evolve toward a true absorption process of the surface wave energy via an enhanced "vacuum heating" mechanism generalized to the case of surface plasma waves. [ABSTRACT FROM AUTHOR]

Analyzes the asymptotic stable response of the plasma to a dynamic magnetic excitation using the reduced magnetohydrodynamics resistive equation with antenna boundary conditions. Difference between the antenna frequency and the rotation frequency; Solution for magnetic flux function at the rational surface.

Examines the existence of modes solutions for magneto-whistler wave equations in a homogenous plasma. Derivation of mode equation; Physical properties of the mode; Computations of mode characteristics for high poloidal mode numbers.

In this erratum, (i) we repair a typographical error in Eq. (44) of our publication [D. Pesme, C. Riconda, and V. T. Tikhonchuk, Phys. Plasmas 12, 092101 (2005)] and (ii) we correct an algebraic mistake concerning the Korteweg-de-Vries (KdV) limits (44) and (49) of the general dispersion relation (39) of our publication. This algebraic error invalidates some of our statements concerning the existence of the decay H2 instability in the KdV limit. We consequently correct the approximate equation governing the decay H2 instability in the KdV limit. We display the corrected figures corresponding to the numerical solutions of the general dispersion relation (39). [ABSTRACT FROM AUTHOR]

Laser-generated plasma gratings are dynamic optical elements for the manipulation of coherent light at high intensities, beyond the damage threshold of solid-state-based materials. Their formation, evolution, and final collapse require a detailed understanding. In this paper, we present a model to explain the nonlinear dynamics of high-amplitude plasma gratings in the spatially periodic ponderomotive potential generated by two identical counterpropagating lasers. Both fluid and kinetic aspects of the grating dynamics are analyzed. It is shown that the adiabatic electron compression plays a crucial role as the electron pressure may reflect the ions from the grating and induce the grating to break in an X-type manner. A single parameter is found to determine the behavior of the grating and distinguish three fundamentally different regimes for the ion dynamics: completely reflecting, partially reflecting or passing, and crossing. Criteria for saturation and lifetime of the grating as well as the effect of finite ion temperature are presented. [ABSTRACT FROM AUTHOR]

Radiation reaction in the interaction of ultrarelativistic electrons with a strong external electromagnetic field is investigated using a kinetic approach in the nonlinear moderately quantum regime. Three complementary descriptions are discussed considering arbitrary geometries of interaction: a deterministic one relying on the quantum-corrected radiation reaction force in the Landau and Lifschitz (LL) form, a linear Boltzmann equation for the electron distribution function, and a Fokker-Planck (FP) expansion in the limit where the emitted photon energies are small with respect to that of the emitting electrons. The latter description is equivalent to a stochastic differential equation where the effect of the radiation reaction appears in the form of the deterministic term corresponding to the quantum-corrected LL friction force, and by a diffusion term accounting for the stochastic nature of photon emission. By studying the evolution of the energy moments of the electron distribution function with the three models, we are able to show that all three descriptions provide similar predictions on the temporal evolution of the average energy of an electron population in various physical situations of interest, even for large values of the quantum parameter χ. The FP and full linear Boltzmann descriptions also allow us to correctly describe the evolution of the energy variance (second-order moment) of the distribution function, while higher-order moments are in general correctly captured with the full linear Boltzmann description only. A general criterion for the limit of validity of each description is proposed, as well as a numerical scheme for the inclusion of the FP description in particle-in-cell codes. This work, not limited to the configuration of a monoenergetic electron beam colliding with a laser pulse, allows further insight into the relative importance of various effects of radiation reaction and in particular of the discrete and stochastic nature of high-energy photon emission and its back-reaction in the deformation of the particle distribution function. [ABSTRACT FROM AUTHOR]

The excitation of surface plasmons with ultra-intense (I ∼ 5 × 1019 W/cm2), high contrast (∼1012) laser pulses on periodically modulated solid targets has been recently demonstrated to produce collimated bunches of energetic electrons along the target surface [Fedeli et al., Phys. Rev. Lett. 116, 015001 (2016)]. Here, we report an extensive experimental and numerical study aimed to a complete characterization of the acceleration mechanism, demonstrating its robustness and promising characteristics for an electron source. By comparing different grating structures, we identify the relevant parameters to optimize the acceleration and obtain bunches of ∼650 pC of charge at several MeV of energy with blazed gratings. [ABSTRACT FROM AUTHOR]

The role of the global phase in the spatio-temporal evolution of the 3-wave coupled equations for backscattering is analyzed in the strong-coupling regime of Brillouin scattering. This is of particular interest for controlled backscattering in the case of plasma-based amplification to produce short and intense laser pulses. It is shown that the analysis of the envelope equations of the three waves involved, pump, seed, and ion wave, in terms of phase and amplitude fully describes the coupling dynamics. In particular, it helps understanding the role of the chirp of the laser beams and of the plasma density profile. The results can be used to optimize or quench the coupling mechanism. It is found that the directionality of the energy transfer is imposed by the phase relation at the leading edge of the pulse. This actually ensures continued energy transfer even if the intensity of the seed pulse is already higher than the pump pulse intensity. [ABSTRACT FROM AUTHOR]