We review a number of instruments employed in a high-intensity J-KAREN-P laser-solid interaction experiment and discuss the applicability of the diagnostics to the best target position determination with a ~10 μm accuracy, while the focal spot size was ~1 μm and peak intensity was up to 7×1021 W/cm2. We discuss both front- and back-side diagnostics, some of them operated in the infrared, visible and ultraviolet ranges, while others in the extreme ultraviolet, soft X-ray and gamma-ray ranges. We found that the applicability of some of the instruments to the best at-focus target position determination depends on the thickness of the target.
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.
As an alternative to Compton backscattering and bremsstrahlung, the process of colliding highenergy electron beams with strong laser fields can more efficiently provide both cleaner and brighter
source of photons in the multi-GeV range for fundamental studies in nuclear and quark-gluon physics.
In order to favor the emission of high-energy quanta and minimize their decay into electron-positron
pairs the fields must not only be sufficiently strong, but also well localized. We here examine
these aspects and develop the concept of a laser-particle collider tailored for high-energy photon
generation. We show that the use of multiple colliding laser pulses with 0.4 PW of total power is
capable of converting more than 18 % of the initial multi-GeV electron beam energy into photons,
each of which carries more than half of the electron energy
A novel regime of high frequency radiation generation via reflection at the electron density spikes in under- dense plasma is proposed. Intense driver laser pulse propagating in underdense plasma forms dense electron singularities near the front part of the bow waves, moving at relativistic velocity. By irradiating a source pulse counterpropagating to the electron density singularities, it is reflected and compressed, producing ultrashort coherent high order harmonics with frequency upshift.
Laser wakefield acceleration (LWFA) using high repetition rate mJ-class laser systems brings unique opportunities for a broad range of applications. In order to meet the conditions required for the electron acceleration with lasers operating at lower energies, one has to use high density plasmas and ultrashort pulses. In the case of a few-cycle pulse, the dispersion and the carrier envelope phase effects can no longer be neglected. In this work, the properties of the wake waves generated by ultrashort pulse lasers in near-critical density plasmas are investigated. The results obtained may lead to enhancement of the quality of LWFA electron beams using kHz laser systems.
This work is dedicated to the multiparametric numerical simulations of the dynamics of electron vortices - one of the coherent structures that can form due to the interaction of high-intensity laser pulses with plasmas. Using a two-dimensional Particle-in-Cell simulations it is demonstrated that the postsoliton stage of the evolution of the electron vortex is described well by the ”snow plow” model. The dependence between the parameters of the vortex and the characteristic time of the vortex boundary disintegration is absorbed.
Electron vortices appear in the wake of a finite length laser pulse propogating in the underdense plasma. Usually they form two chains of vortices with opposite signs of the magnetic fields locked inside an electron cavity. Using 2D PIC simulations, we discuss the effects of evolution of single and binary electron vortices. Single electron vortices, though being in a quasistationary state on electron timescales, evolve on ion timescales, leading to anisotropic multishell ion motion. Binary electron vortices may be subject to complex motions, which can be described by the point-vortex solutions of Hasegawa-Mima equation. When the finite radius effects come into play, we observe effects as magnetic field annihilation with the subsequent fast electron bunch generation and secondary vortex formation.
The laser group velocity plays a crucial role in laser driven acceleration of electrons and ions. In particular, a highly efficient mechanism of laser driven ion acceleration, Radiation Pressure Acceleration, has a fundamental limit on the maximum attainable ion energy, which is determined by the group velocity of the laser. However there is another limiting factor that may shed the group velocity effects. It is due to the transverse expansion of the target, which happens in the course of a tightly focused laser pulse interaction with a thin foil. Transversely expanding targets become increasingly transparent for radiation thus terminating the acceleration. Utilization of an external guiding structure for the accelerating laser pulse may provide a way of compensating for the group velocity and transverse expansion effects.
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.
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 χe (probability of photon emission) and χγ(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.
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.
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.
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.
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.
We discuss the key important regimes of electromagnetic field interaction with charged particles. Main attention is paid to the nonlinear Thomson/Compton scattering regime with the radiation friction and quantum electrodynamics effects taken into account. This process opens a channel of high efficiency electromagnetic energy conversion into hard electromagnetic radiation in the form of ultra short high power gamma ray flashes.
We present experimental results, theory, and simulations demonstrating two novel sources of coherent X-ray radiation
generated in the relativistic laser (>1018W/cm2) interaction with easily accessible, repetitive, and debris-free gas jet
targets. The first source is based on a relativistic mirror reflecting a counter-propagating laser pulse. A strongly nonlinear
breaking wake wave driven by an intense laser pulse can act as a semi-transparent relativistic flying mirror. Such a
mirror directly converts counter-propagating laser light into a high-frequency (XUV or X-ray) ultrashort pulse due to the
double Doppler effect. In the experimental demonstration with the 9 TW J-KAREN laser, the flying mirror generated in
a He gas jet partially reflected a 1 TW pulse, providing up to ~1010 photons, 60 nJ (~1012 photons/sr) in the XUV range
(12.8-22 nm). The second source is demonstrated with the laser power ranging from 9 to 170 TW in experiments with
the J-KAREN and Astra Gemini lasers. The odd and even order harmonics generated by linearly as well as circularly
polarized pulses are emitted forward out of the gas jet. The 120 TW laser pulses produce harmonics with ~3×1013photons/sr (~600 μJ/sr) in the 120±5 eV spectral range. The observed harmonics cannot be explained by previously
known mechanisms (atomic harmonics, betatron radiation, nonlinear Thomson scattering, etc.). We introduce a novel
mechanism of harmonic generation based on the relativistic laser-plasma phenomena (self-focusing, cavity evacuation,
bow wave generation), mathematical catastrophe theory which explains the formation of structurally stable electron
density singularities, spikes, and collective radiation of a compact charge driven by a relativistic laser.
The critical electric field of quantum electrodynamics, called also the Schwinger field, is so strong that it produces
electron-positron pairs from vacuum, converting the energy of light into matter. Since the dawn of quantum
electrodynamics, there has been a dream on how to reach it on Earth. With the rise of laser technology this field has
become feasible through the construction of extremely high power lasers or/and with the sophisticated use of nonlinear
processes in relativistic plasmas. This is one of the most attractive motivations for extremely high power laser
development, i.e. producing matter from vacuum by pure light in fundamental process of quantum electrodynamics in
the nonperturbative regime. Recently it has been realized that a laser with intensity well below the Schwinger limit can
create an avalanche of electron-positron pairs similar to a discharge before attaining the Schwinger field. It has also been
realized that the Schwinger limit can be reached using an appropriate configuration of laser beams. In experiments on
the collision of laser light and high intensity electromagnetic pulses generated by relativistic flying mirrors, with
electron bunches produced by a conventional accelerator and with laser wake field accelerated electrons the studying of
extreme field limits in the nonlinear interaction of electromagnetic waves is proposed. The regimes of dominant
radiation reaction, which completely changes the electromagnetic wave-matter interaction, will be revealed. This will
result in a new powerful source of high brightness gamma-rays. A possibility of the demonstration of the electronpositron
pair creation in vacuum via multi-photon processes can be realized. This will allow modeling under terrestrial
laboratory conditions neutron star magnetospheres, cosmological gamma ray bursts and the Leptonic Era of the
Universe.
Electromagnetic wave generation in the extreme ultraviolet (XUV) and infrared (IR) wavelength range occurs
during the interaction of intense short laser pulses with underdense plasmas. XUV pulses are generated through
laser light reflection from relativistically moving electron dense shells (flying mirrors). A proof-of-principle and
an advanced experiment on flying mirrors are presented. Both of the experiments demonstrated light reflection
and frequency upshift to the XUV wavelength range (14-20 nm). The advanced experiment with a head-on
collision of two laser pulses exhibited the high reflected photon number. IR radiation, which is observed in the
forward direction, has the wavelength of 5 μm and dominantly the same polarization as the driving laser. The
source of the IR radiation is attributed to emission from relativistic solitons formed in the underdense plasma.
An ultra-bright high-power X-ray and γ-ray source is proposed. A relativistic flying mirror reflects a counterpropagating
electromagnetic radiation causing its frequency multiplication and intensification, while the role of
the mirror is played by a solid-density thin plasma slab accelerating in the radiation pressure dominant regime.
Frequencies of high harmonics generated at the flying mirror by a relativistically strong counter-propagating
radiation undergo multiplication with the same factor as the fundamental frequency of the reflected radiation,
approximately equal to the quadruple of the square of the mirror Lorentz factor. The theory of the reflectivity
of a moving thin plasma slab is presented.
We present the theory of the attosecond pulse generation by a relativistically intense few-cycle laser pulse interacting
with a thin plasma slab. In the limit of high plasma density or in the case of two identical pulses irradiating plasma from
opposite sides, the electron displacement in the direction perpendicular to the plasma slab is negligible. Electrons
moving along the plasma slab form the sliding mirror. The relativistic dynamics of the electrons result in the generation
of the phase-locked high order harmonics. After spectral filtering, isolated attosecond pulses with the duration less than
200 as can be obtained. We also find a very efficient regime of the attosecond pulse train generation without any
spectral filtering with the energy conversion efficiency into the main peak of about 3%.
The results of the theoretical consideration and two dimensional Particle in Cell simulation of electron acceleration with
a short-pulse intense laser propagating through a finite length underdense plasma layer are presented. The fast electron
energy spectrum and emittance are analyzed for moderate to high intensity and for different plasma density. It is shown
that for laser pulse lengths above the plasma wake wavelength the wake field accelerated electrons are further
accelerated by the electromagnetic wave.
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