Radiation-reaction trapping of electrons in extreme laser fields

Direct laser acceleration: A model for the electron injection from the walls of a cylindrical guiding structure

We use analytical methods and particle-in-cell simulation to investigate the origin of electrons accelerated by the process of direct laser acceleration driven by high-power laser pulses in preformed narrow cylindrical plasma channels. The simulation shows that the majority of accelerated electrons are originally located along the interface between the channel wall and the channel interior. The analytical model based on the electron hydrodynamics illustrates the underlying physical mechanism of the release of electrons from the channel wall when irradiated by an intense laser, the subsequent electron dynamics, and the corresponding evolution of the channel density profile. The quantitative predictions of the total charge of released electrons and the average electron density inside the channel are validated by comparison with the simulation results.

Generation of High-Density High-Polarization Positrons via Single-Shot Strong Laser-Foil Interaction

We put forward a novel method for producing ultrarelativistic high-density high-polarization positrons through a single-shot interaction of a strong laser with a tilted solid foil. In our method, the driving laser ionizes the target, and the emitted electrons are accelerated and subsequently generate abundant γ photons via the nonlinear Compton scattering, dominated by the laser. These γ photons then generate polarized positrons via the nonlinear Breit-Wheeler process, dominated by a strong self-generated quasistatic magnetic field B^{S}. We find that placing the foil at an appropriate angle can result in a directional orientation of B^{S}, thereby polarizing positrons. Manipulating the laser polarization direction can control the angle between the γ photon polarization and B^{S}, significantly enhancing the positron polarization degree. Our spin-resolved quantum electrodynamics particle-in-cell simulations demonstrate that employing a laser with a peak intensity of about 10^{23}  W/cm^{2} can obtain dense (≳10^{18}  cm^{-3}) polarized positrons with an average polarization degree of about 70% and a yield of above 0.1 nC per shot. Moreover, our method is feasible using currently available or upcoming laser facilities and robust with respect to the laser and target parameters. Such high-density high-polarization positrons hold great significance in laboratory astrophysics, high-energy physics, and new physics beyond the standard model.

Positron Generation and Acceleration in a Self-Organized Photon Collider Enabled by an Ultraintense Laser Pulse

We discovered a simple regime where a near-critical plasma irradiated by a laser of experimentally available intensity can self-organize to produce positrons and accelerate them to ultrarelativistic energies. The laser pulse piles up electrons at its leading edge, producing a strong longitudinal plasma electric field. The field creates a moving gamma-ray collider that generates positrons via the linear Breit-Wheeler process-annihilation of two gamma rays into an electron-positron pair. At the same time, the plasma field, rather than the laser, serves as an accelerator for the positrons. The discovery of positron acceleration was enabled by a first-of-its-kind kinetic simulation that generates pairs via photon-photon collisions. Using available laser intensities of 10^{22}  W/cm^{2}, the discovered regime can generate a GeV positron beam with a divergence angle of around 10° and a total charge of 0.1 pC. The result paves the way to experimental observation of the linear Breit-Wheeler process and to applications requiring positron beams.

Effect of radiation-reaction on charged particle dynamics in a focused electromagnetic wave

The effect of radiation-reaction force on the dynamics of a charged particle in an intense focused light wave is investigated using the physically appealing Hartemann-Luhmann equation of motion. It is found that, irrespective of the choice of initial conditions, radiation reaction force causes the charged particle to cross the focal region, provided the particle is driven into regions where the radiation reaction force dominates over the Lorentz force, thus enhancing the forward energy gained by the particle from the intense light wave. This result is in sharp contrast to the well known result, derived in the absence of radiation reaction forces, where for certain initial conditions the particle reflects from the high intensity region of the focused light wave, thereby losing forward energy. From the perspective of energy gain, our studies clearly show that the parameter space for forward energy gain which is reduced by ponderomotive effects is compensated by radiation reaction effects. These results, which are of relevance to the present day direct laser acceleration schemes of charged particle, also agrees with that obtained using the well known Landau-Lifshitz equation of motion.

Ultra-intense laser field amplification from a petawatt-class laser focusing in moderate density plasma

The rapid development of laser technologies promises a significant growth of peak laser intensity from 10²² W/cm² to >10²³ W/cm², allowing the experimental studies of strong field quantum-electrodynamics physics and laser nuclear physics. Here, we propose a method to realize the ultra-intense laser field amplification of petawatt-class laser pulse in moderate density plasma via relativistic self-focusing and tapered-channel focusing. Three-dimensional particle-in-cell simulations demonstrate that almost an order of magnitude enhancement of laser intensity is possible even though the γ-ray radiation results in massive laser energy loss. In particular, with a seed laser intensity of ∼10²³ W/cm², duration of 82.5 fs and power of 31 petawatt, one can obtain ∼10²⁴ W/cm² intensity and up to ∼60% energy conversion efficiency from the initial seed laser to the focused laser in plasma with density of 3.3 × 10²²/cm³. This may pave the way to the new research field of ultra-intense laser plasma interaction in the upcoming laser facilities.

Particle dynamics governed by radiation losses in extreme-field current sheets

Particles moving in current sheets under extreme conditions, such as those in the vicinity of pulsars or those predicted on upcoming multipetawatt laser facilities, may be subject to significant radiation losses. We present an analysis of particle motion in model fields of a relativistic neutral electron-positron current sheet in the case when radiative effects must be accounted for. In the Landau-Lifshitz radiation reaction force model, when quantum effects are negligible, an analytical solution for particle trajectories is derived. Based on this solution, for the case when quantum effects are significant an averaged quantum solution in the semiclassical approach is obtained. The applicability region of the solutions is determined and analytical trajectories are found to be in good agreement with those of numerical simulations which account for radiative effects. Based on these results we demonstrate that radiation reaction itself can provide a mechanism of pinching even within a given field consideration.

Retrieving Transient Magnetic Fields of Ultrarelativistic Laser Plasma via Ejected Electron Polarization

Interaction of an ultrastrong short laser pulse with nonprepolarized near-critical density plasma is investigated in an ultrarelativistic regime, with an emphasis on the radiative spin polarization of ejected electrons. Our particle-in-cell simulations show explicit correlations between the angle resolved electron polarization and the structure and properties of the transient quasistatic plasma magnetic field. While the magnitude of the spin signal is the indicator of the magnetic field strength created by the longitudinal electron current, the asymmetry of electron polarization is found to gauge the islandlike magnetic distribution which emerges due to the transverse current induced by the laser wave front. Our studies demonstrate that the spin degree of freedom of ejected electrons could potentially serve as an efficient tool to retrieve the features of strong plasma fields.

Generation of Ultrarelativistic Monoenergetic Electron Bunches via a Synergistic Interaction of Longitudinal Electric and Magnetic Fields of a Twisted Laser

We use 3D simulations to demonstrate that high-quality ultrarelativistic electron bunches can be generated on reflection of a twisted laser beam off a plasma mirror. The unique topology of the beam with a twist index |l|=1 creates an accelerating structure dominated by longitudinal laser electric and magnetic fields in the near-axis region. We show that the magnetic field is essential for creating a train of dense monoenergetic bunches. For a 6.8 PW laser, the energy reaches 1.6 GeV with a spread of 5.5%. The bunch duration is 320 as, its charge is 60 pC, and density is ∼10^{27}  m^{-3}. The results are confirmed by an analytical model for the electron energy gain. These results enable development of novel laser-driven accelerators at multi-PW laser facilities.

Spin-polarized proton beam generation from gas-jet targets by intense laser pulses

A method of generating spin-polarized proton beams from a gas jet by using a multipetawatt laser is put forward. With currently available techniques of producing prepolarized monatomic gases from photodissociated hydrogen halide molecules and petawatt lasers, proton beams with energy ≳50 MeV and ≈80% polarization are proved to be obtained. Two-stage acceleration and spin dynamics of protons are investigated theoretically and by means of fully self-consistent three-dimensional particle-in-cell simulations. Our results predict the dependence of the beam polarization on the intensity of the driving laser pulse. Generation of bright energetic polarized proton beams would open a domain of polarization studies with laser driven accelerators and have potential application to enable effective detection in explorations of quantum chromodynamics.

Direct laser acceleration of electrons assisted by strong laser-driven azimuthal plasma magnetic fields

A high-intensity laser beam propagating through a dense plasma drives a strong current that robustly sustains a strong quasistatic azimuthal magnetic field. The laser field efficiently accelerates electrons in such a field that confines the transverse motion and deflects the electrons in the forward direction. Its advantage is a threshold rather than resonant behavior, accelerating electrons to high energies for sufficiently strong laser-driven currents. We study the electron dynamics via a test-electron model, specifically deriving the corresponding critical current density. We confirm the model's predictions by numerical simulations, indicating energy gains two orders of magnitude higher than achievable without the magnetic field.

Energy gain by laser-accelerated electrons in a strong magnetic field

This paper deals with electron acceleration by a laser pulse in a plasma with a static uniform magnetic field B_{*}. The laser pulse propagates perpendicular to the magnetic field lines with the polarization chosen such that (E_{laser}·B_{*})=0. The focus of the work is on the electrons with an appreciable initial transverse momentum that are unable to gain significant energy from the laser in the absence of the magnetic field due to strong dephasing. It is shown that the magnetic field can initiate an energy increase by rotating such an electron, so that its momentum becomes directed forward. The energy gain continues well beyond this turning point where the dephasing drops to a very small value. In contrast to the case of purely vacuum acceleration, the electron experiences a rapid energy increases with the analytically derived maximum energy gain dependent on the strength of the magnetic field and the phase velocity of the wave. The energy enhancement by the magnetic field can be useful at high laser amplitudes, a_{0}≫1, where the acceleration similar to that in the vacuum is unable to produce energetic electrons over just tens of microns. A strong magnetic field helps leverage an increase in a_{0} without a significant increase in the interaction length.

Extremely brilliant GeV γ-rays from a two-stage laser-plasma accelerator

Recent developments in laser-wakefield accelerators have led to compact ultrashort X/γ-ray sources that can deliver peak brilliance comparable with conventional synchrotron sources. Such sources normally have low efficiencies and are limited to 107-8 photons/shot in the keV to MeV range. We present a novel scheme to efficiently produce collimated ultrabright γ-ray beams with photon energies tunable up to GeV by focusing a multi-petawatt laser pulse into a two-stage wakefield accelerator. This high-intensity laser enables efficient generation of a multi-GeV electron beam with a high density and tens-nC charge in the first stage. Subsequently, both the laser and electron beams enter into a higher-density plasma region in the second stage. Numerical simulations demonstrate that more than 1012 γ-ray photons/shot are produced with energy conversion efficiency above 10% for photons above 1 MeV, and the peak brilliance is above 1026 photons s-1 mm-2 mrad-2 per 0.1% bandwidth at 1 MeV. This offers new opportunities for both fundamental and applied research.

Absorption and opacity threshold for a thin foil in a strong circularly polarized laser field

We show that a commonly accepted transparency threshold for a thin foil in a strong circularly polarized normally incident laser pulse needs a refinement. We present an analytical model that correctly accounts for laser absorption. The refined threshold is determined not solely by the laser amplitude, but by other parameters that are equally or even more important. Our predictions are in perfect agreement with particle-in-cell simulations. The refined criterion is crucial for configuring laser plasma experiments in the high-field domain. In addition, an opaque foil steepens the pulse front, which can be important for numerous applications.

Radiation reaction as an energy enhancement mechanism for laser-irradiated electrons in a strong plasma magnetic field

Conventionally, friction is understood as a mechanism depleting a physical system of energy and as an unavoidable feature of any realistic device involving moving parts. In this work, we demonstrate that this intuitive picture loses validity in nonlinear quantum electrodynamics, exemplified in a scenario where spatially random friction counter-intuitively results in a highly directional energy flow. This peculiar behavior is caused by radiation friction, i.e., the energy loss of an accelerated charge due to the emission of radiation. We demonstrate analytically and numerically how radiation friction can dramatically enhance the energy gain by electrons from a laser pulse in a strong magnetic field that naturally arises in dense laser-irradiated plasma. We find the directional energy boost to be due to the transverse electron momentum being reduced through friction whence the driving laser can accelerate the electron more efficiently. In the considered example, the energy of the laser-accelerated electrons is enhanced by orders of magnitude, which then leads to highly directional emission of gamma-rays induced by the plasma magnetic field.

Laser-Particle Collider for Multi-GeV Photon Production

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 a 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 multi-GeV electrons passing through the high-field region into photons, each of which carries more than half of the electron initial energy.

Laser-driven plasma pinching in e^{-}e^{+} cascade

The cascaded production and dynamics of electron-positron plasma in ultimately focused laser fields of extreme intensity are studied by three-dimensional particle-in-cell simulations with the account of the relevant processes of quantum electrodynamics (QED). We show that, if the laser facility provides a total power above 20 PW, it is possible to trigger not only a QED cascade but also pinching in the produced electron-positron plasma. The plasma self-compression in this case leads to an abrupt rise of the peak density and magnetic (electric) field up to at least 10^{28}cm^{-3} and 1/20 (1/40) of the Schwinger field, respectively. Determining the actual limits and physics of this process might require quantum treatment beyond the used standard semiclassical approach. The proposed setup can thus provide extreme conditions for probing and exploring fundamental physics of the matter and vacuum.

Effects of Involved Laser Photons on Radiation and Electron-Positron Pair Production in one Coherence Interval in Ultra Intense Lasers

Electron radiation and γ photon annihilation are two of the major processes in ultra intense lasers (UIL). Understanding their behavior in one coherence interval (CI) is the basis for UIL-matter interaction researches. However, most existing analytic formulae only give the average over many CIs. Present understanding of these two multi-photon processes in one CI usually assume that they emit forward and their spectra have a cutoff at the energy of the electron/γ. Such assumptions ignore the effects of involved laser photons (EILP). We deduced the formulae for these two processes in one CI with EILP included and give the conditions for the EILP to be significant. Strong EILP introduces new behaviors into these two processes in one CI, such as large angle emission and emit particles above the usually assumed cutoff. Simulations show that the EILP would be significant when laser intensity reaches 2 × 10²² W/cm², which is within the reach of state-of-art lasers.

Intense, directional and tunable γ-ray emission via relativistic oscillating plasma mirror

A mechanism for high energy γ-photon generation based on laser-plasma accelerator is proposed. The laser pulse with a peak intensity of 10²²W/cm² accelerates the electron beam to GeV by the laser wakefield effect. A solid Aluminium target serves as a plasma mirror which is located at the rear side of a gas jet and reflects the laser pulse. High order harmonics are generated due to the Doppler effect experienced by the incident laser. The collisions of the reflected attosecond pulses and the energetic electron beam provide a large cross section for nonlinear Compton scattering and produce a collimated γ-photon flux. The mechanism generates GeV photons with a pulse duration given by the duration of the electron beam.

Relativistic Doppler-boosted γ-rays in High Fields

The relativistic Doppler effect is one of the most famous implications of the principles of special relativity and is intrinsic to moving radiation sources, relativistic optics and many astrophysical phenomena. It occurs in the case of a plasma sail accelerated to relativistic velocities by an external driver, such as an ultra-intense laser pulse. Here we show that the relativistic Doppler effect on the high energy synchrotron photon emission (~10 MeV), strongly depends on two intrinsic properties of the plasma (charge state and ion mass) and the transverse extent of the driver. When the moving plasma becomes relativistically transparent to the driver, we show that the γ-ray emission is Doppler-boosted and the angular emission decreases; optimal for the highest charge-to-mass ratio ion species (i.e. a hydrogen plasma). This provides new fundamental insight into the generation of γ-rays in extreme conditions and informs related experiments using multi-petawatt laser facilities.

QED cascade saturation in extreme high fields

Upcoming ultrahigh power lasers at 10 PW level will make it possible to experimentally explore electron-positron (e-e+) pair cascades and subsequent relativistic e-e+ jets formation, which are supposed to occur in extreme astrophysical environments, such as black holes, pulsars, quasars and gamma-ray bursts. In the latter case it is a long-standing question as to how the relativistic jets are formed and what their temperatures and compositions are. Here we report simulation results of pair cascades in two counter-propagating QED-strong laser fields. A scaling of QED cascade growth with laser intensity is found, showing clear cascade saturation above threshold intensity of ~1024 W/cm2. QED cascade saturation leads to pair plasma cooling and longitudinal compression along the laser axis, resulting in the subsequent formation of relativistic dense e-e+ jets along transverse directions. Such laser-driven QED cascade saturation may open up the opportunity to study energetic astrophysical phenomena in laboratory.

Unexpected impact of radiation friction: enhancing production of longitudinal plasma waves

We study the penetration of ultra-intense (intensity I [Formula: see text] 10^23-24 W/cm²) circularly polarized laser pulses into a thick subcritical plasma layer with accounting for radiation friction. We show that radiation pressure is enhanced due to radiation friction in the direction transverse to the laser pulse propagation, and that for stronger and longer laser pulses this mechanism dominates over the ordinary ponderomotive pressure, thus resulting in a substantionaly stronger charge separation than anticipated previously. We give estimates of the effect and compare them with the results of one and two dimensional particle-in-cell simulations. This effect can be important for laser-based acceleration schemes.

Experimental evidence of quantum radiation reaction in aligned crystals

Quantum radiation reaction is the influence of multiple photon emissions from a charged particle on the particle's dynamics, characterized by a significant energy-momentum loss per emission. Here we report experimental radiation emission spectra from ultrarelativistic positrons in silicon in a regime where quantum radiation reaction effects dominate the positron's dynamics. Our analysis shows that while the widely used quantum approach is overall the best model, it does not completely describe all the data in this regime. Thus, these experimental findings may prompt seeking more generally valid methods to describe quantum radiation reaction. This experiment is a fundamental test of quantum electrodynamics in a regime where the dynamics of charged particles is strongly influenced not only by the external electromagnetic fields but also by the radiation field generated by the charges themselves and where each photon emission may significantly reduce the energy of the charge.

The experimental evidence of radiation reaction has so far been elusive. Here the authors provide the signature of radiation reaction in quantum electrodynamics by observing the radiation reaction effects when high-energy positrons emit radiation while propagating through a  silicon crystal.

Extreme plasma states in laser-governed vacuum breakdown

Triggering vacuum breakdown at laser facility is expected to provide rapid electron-positron pair production for studies in laboratory astrophysics and fundamental physics. However, the density of the produced plasma may cease to increase at a relativistic critical density, when the plasma becomes opaque. Here, we identify the opportunity of breaking this limit using optimal beam configuration of petawatt-class lasers. Tightly focused laser fields allow generating plasma in a small focal volume much less than λ³ and creating extreme plasma states in terms of density and produced currents. These states can be regarded to be a new object of nonlinear plasma physics. Using 3D QED-PIC simulations we demonstrate a possibility of reaching densities over 10²⁵ cm⁻³, which is an order of magnitude higher than expected earlier. Controlling the process via initial target parameters provides an opportunity to reach the discovered plasma states at the upcoming laser facilities.

Ultra-bright γ-ray flashes and dense attosecond positron bunches from two counter-propagating laser pulses irradiating a micro-wire target

We propose a novel scheme to generate ultra-bright ultra-short γ-ray flashes and high-energy-density attosecond positron bunches by using multi-dimensional particle-in-cell simulations with quantum electrodynamics effects incorporated. By irradiating a 10 PW laser pulse with an intensity of 10²³ W/cm² onto a micro-wire target, surface electrons are dragged-out of the micro-wire and are effectively accelerated to several GeV energies by the laser ponderomotive force, forming relativistic attosecond electron bunches. When these electrons interact with the probe pulse from the other side, ultra-short γ-ray flashes are emitted with an ultra-high peak brightness of 1.8 × 10²⁴ photons s^-1mm^-2mrad^-2 per 0.1%BW at 24 MeV. These photons propagate with a low divergence and collide with the probe pulse, triggering the Breit-Wheeler process. Dense attosecond e^-e⁺ pair bunches are produced with the positron energy density as high as 10¹⁷ J/m³ and number of 10⁹. Such ultra-bright ultra-short γ-ray flashes and secondary positron beams may have potential applications in fundamental physics, high-energy-density physics, applied science and laboratory astrophysics.

Brilliant petawatt gamma-ray pulse generation in quantum electrodynamic laser-plasma interaction

We show a new resonance acceleration scheme for generating ultradense relativistic electron bunches in helical motions and hence emitting brilliant vortical γ-ray pulses in the quantum electrodynamic (QED) regime of circularly-polarized (CP) laser-plasma interactions. Here the combined effects of the radiation reaction recoil force and the self-generated magnetic fields result in not only trapping of a great amount of electrons in laser-produced plasma channel, but also significant broadening of the resonance bandwidth between laser frequency and that of electron betatron oscillation in the channel, which eventually leads to formation of the ultradense electron bunch under resonant helical motion in CP laser fields. Three-dimensional PIC simulations show that a brilliant γ-ray pulse with unprecedented power of 6.7 PW and peak brightness of 10²⁵ photons/s/mm²/mrad²/0.1% BW (at 15 MeV) is emitted at laser intensity of 1.9 × 10²³ W/cm².

Influence of e^{-}e^{+} creation on the radiative trapping in ultraintense fields of colliding laser pulses

The behavior of a thin plasma target irradiated by two counterpropagating laser pulses of ultrahigh intensity is studied in the framework of one- and two-dimensional particle-in-cell simulations. It is found that above an intensity threshold, radiative trapping can focus electrons in the peaks of the electromagnetic field. At even higher intensities, the trapping effect cannot be maintained according to the increasing influence of electron-positron pair production on the laser-plasma dynamics.

Dense GeV electron-positron pairs generated by lasers in near-critical-density plasmas

Pair production can be triggered by high-intensity lasers via the Breit–Wheeler process. However, the straightforward laser–laser colliding for copious numbers of pair creation requires light intensities several orders of magnitude higher than possible with the ongoing laser facilities. Despite the numerous proposed approaches, creating high-energy-density pair plasmas in laboratories is still challenging. Here we present an all-optical scheme for overdense pair production by two counter-propagating lasers irradiating near-critical-density plasmas at only ∼10²² W cm⁻². In this scheme, bright γ-rays are generated by radiation-trapped electrons oscillating in the laser fields. The dense γ-photons then collide with the focused counter-propagating lasers to initiate the multi-photon Breit–Wheeler process. Particle-in-cell simulations indicate that one may generate a high-yield (1.05 × 10¹¹) overdense (4 × 10²² cm⁻³) GeV positron beam using 10 PW scale lasers. Such a bright pair source has many practical applications and could be basis for future compact high-luminosity electron–positron colliders.

High power lasers can produce electron-positron pairs at GeV energies, but doing so through laser–laser collisions would require exceedingly high intensities. Here the authors present an all-optical scheme for pair production by irradiating near-critical-density plasmas with two counter-propagating lasers.

Characteristics of betatron radiation from direct-laser-accelerated electrons

Betatron radiation from direct-laser-accelerated electrons is characterized analytically and numerically. It is shown here that the electron dynamics is strongly dependent on a self-similar parameter S(≡n_{e}/n_{c}a_{0}). Both the electron transverse momentum and energy are proportional to the normalized amplitude of laser field (a_{0}) for a fixed value of S. As a result, the total number of radiated photons scales as a_{0}^{2}/sqrt[S] and the energy conversion efficiency of photons from the accelerated electrons scales as a_{0}^{3}/S. The particle-in-cell simulations agree well with the analytical scalings. It is suggested that a tunable high-energy and high-flux radiation source can be achieved by exploiting this regime.

All-optical bright γ-ray and dense positron source by laser driven plasmas-filled cone

An all-optical scheme for bright γ-rays and dense e^-e⁺ pair source is proposed by irradiating a 10²² W/cm² laser onto a near-critical-density plasmas filled Al cone. Two-dimensional (2D) QED particle-in-cell (PIC) simulations show that, a dense electron bunch is confined in the laser field due to the radiation reaction and the trapped electrons oscillate transversely, emitting bright γ-rays forward in two ways: (1) nonlinear Compton scattering due to oscillation of electrons in the laser field, and (2) Compton backwardscattering resulting from the bunch colliding with the reflected laser by the cone tip. Finally, the multi-photon Breit-Wheeler process is initiated, producing abundant e^-e⁺ pairs with a density of ∼ 10²⁷m^-3. The scheme is further demonstrated by full 3D PIC simulations, which indicates a positron number up to 2 × 10⁹. This compact γ-rays and e^-e⁺ pair source may have many potential applications, such as the laboratory study of astrophysics and nuclear physics.

Towards manipulating relativistic laser pulses with micro-tube plasma lenses

Efficient coupling of intense laser pulses to solid-density matter is critical to many applications including ion acceleration for cancer therapy. At relativistic intensities, the focus has been mainly on investigating various laser beams irradiating initially overdense flat interfaces with little or no control over the interaction. Here, we propose a novel approach that leverages recent advancements in 3D direct laser writing (DLW) of materials and high contrast lasers to manipulate the laser-matter interactions on the micro-scales. We demonstrate, via simulations, that usable intensities ≥10(23) Wcm(-2) could be achieved with current tabletop lasers coupled to micro-engineered plasma lenses. We show that these plasma optical elements act as a lens to focus laser light. These results open new paths to engineering light-matter interactions at ultra-relativistic intensities.

Quantum Radiation Reaction: From Interference to Incoherence

We investigate quantum radiation reaction in laser-electron interactions across different energy and intensity regimes. Using a fully quantum approach which also accounts exactly for the effect of the strong laser pulse on the electron motion, we identify in particular a regime in which radiation reaction is dominated by quantum interference. We find signatures of quantum radiation reaction in the electron spectra which have no classical analogue and which cannot be captured by the incoherent approximations typically used in the high-intensity regime. These signatures are measurable with presently available laser and accelerator technology.

Impact of quantum effects on relativistic electron motion in a chaotic regime

The impact of quantum effects on electron dynamics in a plane linearly polarized standing wave with relativistic amplitudes is considered. Using spectral analysis of Lyapunov characteristic exponents with and without radiation losses we show that the contraction effect of phase space due to the radiation reaction force in the classical form does not occur in the quantum case when the discreteness of photon emission is taken into account. It is also demonstrated that electron bunch kinetics has a diffusion solution rather than the d'Alambert type solution as in the classical description. For this case, we applied the Markov chain formalism and showed that this method gives exact characteristics of electron bunch evolution, such as motion of the center of mass and electron bunch dimensions.

Nonlinear increase of X-ray intensities from thin foils irradiated with a 200 TW femtosecond laser

We report, for the first time, that the energy of femtosecond optical laser pulses, E, with relativistic intensities I > 10(21)  W/cm(2) is efficiently converted to X-ray radiation, which is emitted by "hot" electron component in collision-less processes and heats the solid density plasma periphery. As shown by direct high-resolution spectroscopic measurements X-ray radiation from plasma periphery exhibits unusual non-linear growth ~E(4-5) of its power. The non-linear power growth occurs far earlier than the known regime when the radiation reaction dominates particle motion (RDR). Nevertheless, the radiation is shown to dominate the kinetics of the plasma periphery, changing in this regime (now labeled RDKR) the physical picture of the laser plasma interaction. Although in the experiments reported here we demonstrated by observation of KK hollow ions that X-ray intensities in the keV range exceeds ~10(17)  W/cm(2), there is no theoretical limit of the radiation power. Therefore, such powerful X-ray sources can produce and probe exotic material states with high densities and multiple inner-shell electron excitations even for higher Z elements. Femtosecond laser-produced plasmas may thus provide unique ultra-bright X-ray sources, for future studies of matter in extreme conditions, material science studies, and radiography of biological systems.