space charge field is nonuniform in REM and it decreases linearly from the left side (close to ion sheet) of REM to the right. Hence the electron layers on extreme left of REM experience strong force due to space charge field and at some instant when this force becomes stronger than the longitudinal component of the Lorentz force of laser, the dense electron sheet (REM) start to debunch (Figure 1(c)). We obtain the attosecond electron bunch counterpropagating to incident laser, as a result of debunching of the REM. We focus in this letter to explore the interaction of these attosecond left turning back (LTB) electron sheets with the rest over counter propagating incident laser pulse. Since the LTB electron sheets are accelerating due to both Coulomb interaction among the the electron sheets and Coulomb interaction between the electron sheets and the ion background of the target as shown in Figure 1(d). We see (as shown in Figure 1(e)) attosecond electron bunch co-streaming with the em solitary field of attosecond length after the
The multi-petawatt (PW) laser facilities under development will enable experimental investigations into the interaction of ultra-intenselaser pulses with plasma. Laser plasma interaction physics is an active area of research with many different aspects, including fast electron transport, 1 ion acceleration, 2, 3 absorption physics 4 and fundamental QED studies. 5, 6 Ion acceleration is a topic which will receive particular attention at multi-PW laser facilities due to its application to cancer therapies. 7 At the intensities which will be achieved with multi-PW systems, high energy ions are predicted to be achieved through radiation pressure acceleration (RPA), where the radiation pressure due to the laser light is sufficiently high to accelerate thinfoil targets to high velocities. RPA is expected to produce quasi-monoenergetic ion bunches, where the maximum energy has a fast scaling with the laser intensity. 8, 9 The maximum achievable ion energies may however be limited by QED effects, such
The dynamics of the PCDS in ultra-intenselaser interactions with thin foils, ranging in thickness from tens to hundreds of nanometres, has been investigated experimentally and numerically. The maximum PCDS velocity has been determined experimentally via measurements of the relativistic Doppler shift of second harmonic light produced at the laser focus. Coupled 2D PIC simulations are used to explore the spatial and temporal evolution of the PCDS for each target thickness investigated. Comparison of the experimental and numerical results with corresponding analytical models of the HB and LS modes of RPA reveal the target thickness ranges for which each mode dominates. The numerical results show that a hybrid model, starting with HB and transitioning to LS (when the compressed electron layer reaches the rear surface of the target) is required for thicknesses between the extreme cases. Measurements of the transmitted laser light reveal that at the thinnest targets considered, transparency reduces the radiation pressure, resulting in a lower maximum PCDS velocity.
Radiation reaction effects are typically overlooked in the LS regime of radiation pressure acceleration; since the targets can acquire relativistic velocities, the laser fields are strongly Doppler shifted, reducing the intensity which arrives at the target in its reference frame. This effect has been observed in a recent study by Del Sorbo et al , in which quantum effects are found to be quenched due to the high target velocity which can be obtained in the LS regime. That study used circularly polarized laser pulses, in which case electron heating via the oscillating component of the ponderomotive force is suppressed, and the targets undergo highly efficient acceleration. By contrast, here we consider linear polarization such that the electron heating effects are still present, allowing RR to influence the collective electron dynamics.
Another novel idea, ﬁrst suggested by Bulanov et al., is to treat the nonlinear density waves driven by an ultra- short intenselaser in underdense plasmas as ﬂying mir- rors . As compared to laser-foil scenarios, this scheme demands relatively gentle drive lasers [6, 7], and can be potentially operated at a high repetition rate using gas targets. In order to create such mirrors for eﬃcien- t backscattering, it is crucial to drive the plasma waves closely to the wavebreaking point, where the maximal electron ﬂuid velocity v m matches with the phase veloc-
Interaction of ultraintense laser pulse with solid foiltarget produces high fluxes of energetic electrons that can lead to secondary processes such as bright X and γ-ray emission , ion acceleration [2, 3], powerful terahertz (THz) radiation [4–9], etc. The mechanisms involved are of basic research interest in high energy density physics and the resulting particle bunches and radiation have many novel applications [1-9]. Powerful THz radiation has been detected at both the front and rear sides of the targets. Several mechanisms of THz emission from the target front have been proposed, including that of transient electron currents driven by the ponderomotive force , the antenna effect , and surface electron currents . However, an explanation for the recently reported  extremely powerful THz pulses emitted from the rear target surface is still lacking. It has been suggested that the radiation could be from the target-rear electron sheath, which is also responsible for target normal sheath acceleration (TNSA) of ions . In this model, a hot relativistic MeV electron bunch created by the laser impact is reflected by the intense sheath fields on both sides of the target. Dipole-like acceleration/deceleration induced radiation (bremsstrahlung) is thus emitted.
Yet some questions remain: how does the plasma maintain itself in such a seemingly stable state with density higher than a solid even in 1D? What traps the protons, preventing them from overshooting the electron front? Recently, we proposed  the self-organized double layer as a stably trapping mechanism in 1D. The electrons are trapped by the potential well formed by the balance of the radiation pressure and the electric force of the protons left behind, while protons are trapped in the accelerating frame by its inertial force while being accelerated by the electric field of the electron layer. This double layer allows the trapped protons to be accelerated as a monoenergetic group as the foil is accelerated by the radiation force as a whole. But a key question remains: what fraction of the protons are trapped and thus accelerated as monoenergetic ones? In this paper, we address these questions as well as the nature of proton trapping and test the role of the target thickness by employing an analytic and numerical study of the 1D Vlasov–Maxwell equations for protons and electrons.
. The transfer of momentum to the target as the laser reflects off its front surface can accelerate the target ions to high energies in quasi-monoenergetic bunches. The potential applications of the resulting beams of energetic ions include oncology  and the fast ignition approach to inertial confinement fusion [8, 9]. The effectiveness of the RPA mechanism is highest for targets which are just above the critical density (at which the plasma frequency is equal to the laser frequency) and is greatly reduced if the target undergoes relativistic self induced transparency (RSIT; caused by a reduction in the plasma frequency to below the laser frequency, due to the relativistic increase in the mass of the oscillating target electrons). Not only does the resultant laser propagation into the target volume reduce the radiation pressure on the surface, but it also heats the electrons in the bulk of the target, which enhances other acceleration mechanisms [10, 11, 12, 13]. The maximum ion energies which can be achieved using multi-PW laser systems may however be restricted by the onset of the radiation reaction (RR) force and QED effects (such as electron positron pair-production and stochastic photon emission), which become important at laser intensities exceeding 10 22 Wcm −2 .
Ultrafast laser-driven proton radiography shows that a large amplitude (thousands of Tesla) magnetic field is generated at the rear of foil targets irradiated by high-intensity laser pulse 18 . Robinson et al. has found that the self-generated magnetic field plays important role on the presence of the quasi-monoenergetic proton peaks for ultrathin foils 15 . To understand our observation for thick targets, we have carried out numerical simulations by the 2D3V PIC code KLAPS 19, 20 . The simulation parameters are similar to the experimental. The temporal and spatial resolutions in the simulations are dt=0.025τ 0 , and
Relativistically intense ( > 10 18 W · cm −2 for a laser wave- length of ' 1 µ m) laser–solid interactions provide a means to generate a compact source of highly energetic ions of ultrashort pulse duration [1, 2] . The resultant ion beams can be used in a wide range of science and applications, in- cluding isochoric heating of matter  , ultrafast probing of transient electric and magnetic fields  and micron-scale proton radiography  . There is also the potential to apply such beams to medical oncology  and fast-ignition inertial confinement fusion  . The maximum energy, energy spread, beam parameter selectivity and beam spatial profile require- ments for these potential applications drive the need to im- prove and optimize the underlying acceleration mechanisms. The most investigated laser-driven ion acceleration mecha- nism, target normal sheath acceleration (TNSA), occurs dur- ing intenselaser pulse interactions with thinfoil targets  . The formation of an electric field with strength on the order of T · V · m −1 at the target rear ionizes surface atoms
Acceleration of protons and heavier ions in interactions of intenselaser pulses with thin solid targets has received a great deal of experimental and theoretical interest since multi-MeV-energy ions were first demonstrated in 2000 [1–4]. Laser-generated ion beams have been shown to have a number of desirable properties, including high brightness (up to 10 13 ions in a picosecond bunch at the source) and low transverse and longitudinal emittance (about 100-fold better than beams produced from typical RF accelerators) . The interest in laser-accelerated ions is driven by the potential compactness and lower cost of these sources compared to more conventional accelerators. Among the many possible applications of laser-generated high-energy ion beams are the fast ignition approach to inertial confinement fusion , ion beam radiography , nuclear physics [8, 9] and therapeutic medicine [10–13]. The need to optimize and control this novel source of high-energy ions for applications is motivating a worldwide research effort on high-power laser-driven ion acceleration.
The interaction of an extreme ultraviolet (EUV) laser beam with a parylene foil was studied by experiments and simulation. A single EUV laser pulse of nanosecond duration focused to an intensity of 3 × 10 10 W cm − 2 perforated micrometer thick targets. The same laser pulse was simultaneously used to diagnose the interac- tion by a transmission measurement. A combination of 2-dimensional radiation- hydrodynamic and diffraction calculations was used to model the ablation, leading to good agreement with experiment. This theoretical approach allows predictive modelling of the interaction with matter of intense EUV beams over a broad range of parameters. C 2016 Author(s). All article content, except where other-
Ultra-intense lasers have been demonstrated to fit the geometric constraints of a tabletop laser. The ul- tra-intenselaser for Project New Orion is anticipated to likewise satisfy relevant geometric constraints and asso- ciated mass constraints for the associated launch vehicle. The ultra-intenselaser will provide an energy source derived from a magneto-hydrodynamic generator converting a portion of the propulsive thrust thermal/kinetic energy into electrical energy for operating the ultra-intenselaser. The generated electrical energy implies a need for a temporary storage medium, such as a supercapacitor. The selection of an appropriate energy storage me- dium will be a subject of pending refinement of the Project New Orion endeavor, such as further convergence of the design for the first stage propulsion system.
bremsstrahlung photons as a result of electron-nuclei interaction. Propulsion involving lasers through chemical rather than non-chemical interaction has been previously advocated by Phipps. The major utilities of the ultra-intenselaser derived antimatter ramjet are the capability to gen- erate antimatter without a complex storage system and the ability to decouple the antimatter ramjet propulsion system from the energy source. For instance the ultra-intenselaser and energy source could be terrestrial, while the ramjet could be mounted to a UAV as a propulsion system. With the extrapolation of current technologies, a sufficient number of pulses by ultra-intense las- ers are eventually anticipated for the generation of antimatter to heat the propulsive flow of a ramjet. Fundamental performance analysis is provided based on an ideal ramjet derivation that is modified to address the proposed antimatter ramjet architecture.
The resulting target heating and front surface plasma expansion profiles at given simulation times are shown in Figure 3. The ASE-only simulations (Figures 3(a) and 3(c)) show that the primary effect of the ASE pedestal is to heat the underdense region of the target and drive a low-temperature shock wave into the target, resulting in compression of the first micron depth of the target by ∼ 25%. The target heating and expansion driven by the ASE is relatively small. For the case in which the proton beam is added, we find that the first few tens of microns depth from the front surface of the target is heated to temperatures of ∼ 10 eV, as shown in Figure 3(b), with an exponential decrease in temperature to about 0.3 eV at a depth of 100 µm. Similar laser-driven proton heating profiles have been reported in other work  . Importantly, we find that the target front side expands faster into vacuum in response to this heating, resulting in slightly larger plasma scale length, compared to the case of ASE-only heating.
Soon after the first demonstration of the laser , the quest for a coherent light source at even shorter wavelengths emerged. Nowadays, intense, brilliant X-ray beams are ob- tained from large-scale synchrotrons and have become an indispensible tool in many areas of science and technology. These intense X-ray light sources allow resolving matter on the atomic level, give novel opportunities to condensed matter physics, enable the analysis of large biomolecules and thus help developing new materials or future drugs. Recently, free electron lasers have started operating in the X-ray regime providing X-ray pulses of unprecedented high brightness exceeding those from conventional synchrotron sources by orders of magnitude and now o ff ering time resolution on the femtosecond scale [2, 3]. These next generation light sources are now being built at several laboratories around the globe and will open a new era in many fields of science. However, due to their large cost and size, the number of those facilities will be naturally limited to only a few.
. We have deliberately used a pre-pulse to irradiate the target before the high power laser irradiation in order to establish a plasma of controlled scale-length into which the high power laser interacts. The scale-length of the plasma formed by the pre-pulse at the time of the high power laser irradiance is measured using transverse probe shadowgraphy. Electron energy and temper- ature measurements with the controlled density scale-length have been reported by Culfa et al 8,9 . This paper investigates the effects of the electrons accelerated through the target
90% of the generated positrons are ejected anisotropic and aft to the respective target. The me- chanisms for the laser-derived positron antimatter generation involve electron interaction with the nuclei based on bremsstrahlung photons that yield electron-positron pairs as a consequence of the Bethe-Heitler process, which predominates the Trident process. Given the constraints of the current and near future technology space, a pulsed space propulsion configuration is advocated for antimatter derived space propulsion, similar in concept to pulsed radioisotope propulsion. Antimatter is generated through an ultra-intenselaser on the scale of a Titan laser incident on a gold target and annihilated in a closed chamber, representative of a combustion chamber. Upon reaching a temperature threshold, the closed chamber opens, producing a pulse of thrust. The im- plication of the pulsed space propulsion antimatter architecture is that the energy source for the antimatter propulsion system can be decoupled from the actual spacecraft. In contrast to conven- tional chemical propulsion systems, which require storage of its respective propulsive chemical potential energy, the proposed antimatter propulsion architecture may have the energy source at a disparate location from the spacecraft. The ultra-intenselaser could convey its laser energy over a distance to the actual spacecraft equipped with the positron antimatter pulsed space propulsion system. Hydrogen is considered as the propulsive fluid, in light of its low molecular weight. Fun- damental analysis is applied to preliminarily define the performance of the positron antimatter derived pulsed space propulsion system. The fundamental performance analysis of the antimatter pulsed space propulsion system successfully reveals the architecture is viable for further evalua- tion.
A total number of 875 equally spaced 1-meter-long plastic ﬁbers are placed in close contact with the scintillator, to sample and guide the optical light signals out of the spectrometer. The ﬁber bundle was further wrapped with aluminum to avoid stray light. The cross-talk between channels was also checked using a point laser source to be <4%. Although the spatial resolution of the non-
An all-optical approach to laser-proton acceleration enhancement is investigated using the simplest of target designs to demonstrate application-relevant levels of energy conversion efficiency between laser and protons. Controlled deposition of laser energy, in the form of a double-pulse temporal envelope, is investigated in combination with thinfoil targets, in which recirculation of laser-accelerated electrons can lead to optimal conditions for coupling laser drive energy into the proton beam. This approach is shown to deliver a substantial enhancement in the coupling of laser energy to 5-30 MeV protons, compared to single pulse irradiation, reaching a record high 15 % conversion efficiency with a temporal separation of 1 ps between the two pulses and a 5 µm-thick Au foil. A 1D simulation code is used to support and explain the origin of the observation of an optimum pulse separation of ∼ 1 ps.