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This numerical study is focused on electro-optic (EO) spatial decoding of transition radiation (TR) produced by a relativistic electron bunch passing through a metal foil. The calculations included the imaging of polychromatic transition radiation from an electron bunch and the process of EO spatial decoding. From an experimental perspective, a careful examination of the calculation approach of the data analysis is essential. Therefore, to thoroughly understand the process of signal generation and examine the possibility of adopting a less time-consuming treatment, comparative studies were conducted on detailed and simplified models of both transition radiation imaging and EO signal generation. All calculations are defined in SI units for the convenience of experimental measurements. For TR imaging, the results suggest that the simplified analytical model is sufficient to perform polychromatic calculations with considerable accuracy. For EO spatial decoding, we discussed the process of EO signal generation using 1D and 2D models. We found that the 1D model was sufficient for rapid data analysis. Furthermore, the temporal energy chirp was demonstrated to have a minimal impact on the shape of the EO signal. Because both the transverse and longitudinal profiles can be calculated with arbitrary distributions, this numerical study can facilitate measurements of 3D electron charge density profiles in both laser wakefield acceleration and conventional accelerator research., Comment: 22 pages, 21 figures, submitted to Physical Review Accelerators and Beams

High-order harmonics are ubiquitous in nature and present in electromagnetic, acoustic, and gravitational waves. They are generated by periodic nonlinear processes or periodic high-frequency pulses. However, this periodicity is often inexact, such as that in chirped (frequency-swept) optical waveforms or interactions with nonstationary matter -- for instance, reflection from accelerating mirrors. Spectra observed in such cases contain complicated sets of harmonic-like fringes. We encountered such fringes in our experiment on coherent extreme ultraviolet generation via BISER, and could not interpret them using currently available knowledge. Here, we present a comprehensive theory based on interference of harmonics with different orders fully explaining the formation of these fringes, which we call alloharmonics. Like atomic spectra, the complex alloharmonic spectra depend on several integer numbers and bear a unique imprint of the emission process, which the theory can decipher, avoiding confusion or misinterpretation. We also demonstrate the alloharmonics in simulations of gravitational waves emitted by binary black hole mergers. Further, we predict the presence of alloharmonics in the radio spectra of pulsars and in optical frequency combs, and propose their use for measurement of extremely small accelerations necessary for testing gravity theories. The alloharmonics phenomenon generalizes classical harmonics and is critical in research fields such as laser mode locking, frequency comb generation, attosecond pulse generation, pulsar studies, and future gravitational wave spectroscopy., Comment: 29 pages, 9 figures, 3 tables

Relativistic mirrors can be realized with strongly nonlinear Langmuir waves excited by intense laser pulses in underdense plasma. On reflection from the relativistic mirror the incident light affects the mirror motion. The corresponding recoil effects are investigated analytically and with particle-in-cell simulations. It is found that if the fluence of the incident electromagnetic wave exceeds a certain threshold, the relativistic mirror undergoes a significant back reaction and splits into multiple electron layers. The reflection coefficient of the relativistic mirror as well as the factors of electric field amplification and frequency upshift of the electromagnetic wave are obtained., Comment: 8 pages, 5 figures, submitted to Physics of Plasmas

Effects of ionization injection in low and high Z gas mixtures for the laser wake field acceleration of electrons are analyzed with the use of balance equations and particle-in-cell simulations via test probe particle trajectories in realistic plasma fields and direct simulations of charge loading during the ionization process. It is shown that electrons appearing at the maximum of laser pulse field after optical ionization are trapped in the first bucket of the laser pulse wake. Electrons, which are produced by optical field ionization at the front of laser pulse, propagate backwards; some of them are trapped in the second bucket, third bucket and so on. The efficiency of ionization injection is not high, several pC/mm/bucket. This injection becomes competitive with wave breaking injection at lower plasma density and over a rather narrow range of laser pulse intensity., Comment: 12 figures

Apart from maximizing the strength of optical electromagnetic fields achievable at high-intensity laser facilities, the collision of several phase-matched laser pulses has been theoretically identified as a trigger of and way to study various phenomena. These range from the basic processes of strong-field quantum electrodynamics to the extraordinary dynamics of the generated electron-positron plasmas. This has paved the way for several experimental proposals aimed at both fundamental studies of matter at extreme conditions and the creation of particle and radiation sources. Because of the unprecedented capabilities of such sources they have the potential to open up new opportunities for experimental studies in nuclear and quark-gluon physics. We here perform a systematic analysis of different regimes and opportunities achievable with the concept of multiple-colliding laser pulses (MCLP), for both current and upcoming laser facilities. We reveal that several distinct regimes could be within reach of multi-PW laser facilities., Comment: 15 pages, 12 figures

As an alternative to Compton backscattering and bremsstrahlung, the process of colliding high-energy electron beams with strong laser fields can more efficiently provide both cleaner and brighter source of photons in the multi-GeV range for fundamental studies in nuclear and quark-gluon physics. In order to favor the emission of high-energy quanta and minimize their decay into electron-positron pairs the fields must not only be sufficiently strong, but also well localized. We here examine these aspects and develop the concept of a laser-particle collider tailored for high-energy photon generation. We show that the use of multiple colliding laser pulses with 0.4 PW of total power is capable of converting more than 18% of the initial multi-GeV electron beam energy into photons, each of which carries more than half of the electron energy., Comment: 6 pages, 4 figures

A method for the asymmetric focusing of electron bunches, based on the active plasma lensing technique is proposed. This method takes advantage of the strong inhomogeneous magnetic field generated inside the capillary discharge plasma to focus the ultrarelativistic electrons. The plasma and magnetic field parameters inside the capillary discharge are described theoretically and modeled with dissipative magnetohydrodynamic computer simulations enabling analysis of the capillaries of rectangle cross-sections. Large aspect ratio rectangular capillaries might be used to transport electron beams with high emittance asymmetries, as well as assist in forming spatially flat electron bunches for final focusing before the interaction point., Comment: 16 pages, 7 figures, 1 table

We analyze the collision of a high energy electron beam with an oscillating electric and magnetic field configuration, which represents a three-dimensional standing electromagnetic wave. The radiating electrons are stopped at the distance of the order of or less than the electromagnetic wave wavelength, and become trapped near the electric field local maxima due to the nonlinear dependence of the radiation friction force on the electromagnetic field strength, while the quantum effects on the radiation friction remain negligible., Comment: 8 pages, 5 figures, 31 citations, 1 appendix

The multiple colliding laser pulse concept formulated in Ref. [1] is beneficial for achieving an extremely high amplitude of coherent electromagnetic field. Since the topology of electric and magnetic fields oscillating in time of multiple colliding laser pulses is far from trivial and the radiation friction effects are significant in the high field limit, the dynamics of charged particles interacting with the multiple colliding laser pulses demonstrates remarkable features corresponding to random walk trajectories, limit circles, attractors, regular patterns and Levy flights. Under extremely high intensity conditions the nonlinear dissipation mechanism stabilizes the particle motion resulting in the charged particle trajectory being located within narrow regions and in the occurrence of a new class of regular patterns made by the particle ensembles., Comment: 28 pages, 32 figures

In various media the elementary components can emit traveling waves such as electromagnetic, gravitational or acoustic types. If these elementary emitters are synchronized, the resulting emission is coherent. Moreover, the faster the emitters approach an observer, the more intense and directional their apparent emission is, with associated frequency increase. Multi-stream flows ubiquitously occur in media (such as with shock waves and jets in astrophysical and laboratory plasmas) and produce fast moving density singularities, where high concentration and synchronism can bring constructive interference. However, a singularity emitting such characteristic coherent radiation has not been demonstrated yet. We show this general phenomenon in laser-driven relativistic plasma, which is an ideal medium for realizing these effects in the laboratory under controllable conditions. Our experiments and simulations reveal bright coherent soft x-ray radiation from nanoscale electron density singularities in multi-stream plasma. They constitute a new compact x-ray source of ultrashort duration, demanded in numerous applications. In general, singularities can be bright sources of other types of traveling waves. Thus our findings open new opportunities in different fields of science. For example, gravitational wave generation, as proposed in ultrahigh-energy accelerators, can be significantly enhanced by intentionally induced density singularities in the particle bunches. Further, we anticipate that multi-stream flows in cosmic media can produce intense bursts of coherent electromagnetic and/or gravitational waves, especially at longer wavelengths which facilitate constructive interference. We can then expect to observe more directional short wavelength bursts from cosmic emitters approaching at relativistic speeds. Thus, we present a new framework for interpreting a broad range of experimental results.

Radiation pressure acceleration (RPA) is a highly efficient mechanism of laser-driven ion acceleration, with with near complete transfer of the laser energy to the ions in the relativistic regime. However, there is a fundamental limit on the maximum attainable ion energy, which is determined by the group velocity of the laser. The tightly focused laser pulses have group velocities smaller than the vacuum light speed, and, since they offer the high intensity needed for the RPA regime, it is plausible that group velocity effects would manifest themselves in the experiments involving tightly focused pulses and thin foils. However, in this case, finite spot size effects are important, and another limiting factor, the transverse expansion of the target, may dominate over the group velocity effect. As the laser pulse diffracts after passing the focus, the target expands accordingly due to the transverse intensity profile of the laser. Due to this expansion, the areal density of the target decreases, making it transparent for radiation and effectively terminating the acceleration. The off-normal incidence of the laser on the target, due either to the experimental setup, or to the deformation of the target, will also lead to establishing a limit on maximum ion energy., Comment: 17 pages, 6 figures

Efficient laser ion acceleration requires high laser intensities, which can only be obtained by tightly focusing laser radiation. In the radiation pressure acceleration regime, where the tightly focused laser driver leads to the appearance of the fundamental limit for the maximum attainable ion energy, this limit corresponds to the laser pulse group velocity as well as to another limit connected with the transverse expansion of the accelerated foil and consequent onset of the foil transparency. These limits can be relaxed by using composite targets, consisting of a thin foil followed by a near critical density slab. Such targets provide guiding of a laser pulse inside a self-generated channel and background electrons, being snowplowed by the pulse, compensate for the transverse expansion. The use of composite targets results in a significant increase in maximum ion energy, compared to a single foil target case., Comment: 16 pages, 9 figures

A nonlinear oscillator with an abruptly inhomogeneous restoring force driven by an uniform oscillating force exhibits stochastic properties under specific resonance conditions. This behaviour elucidates the elementary mechanism of the electron energization in the strong electromagnetic wave interaction with thin targets., Comment: 10 pages, 12 figures

In the ion acceleration by radiation pressure a transverse inhomogeneity of the electromagnetic pulse results in the displacement of the irradiated target in the off-axis direction limiting achievable ion energy. This effect is described analytically within the framework of the thin foil target model and with the particle-in-cell simulations showing that the maximum energy of accelerated ions decreases while the displacement from the axis of the target initial position increases. The results obtained can be applied for optimization of the ion acceleration by the laser radiation pressure with the mass limited targets., Comment: 9 pages, 7 figures

Radiation Pressure Acceleration relies on high intensity laser pulse interacting with solid target to obtain high maximum energy, quasimonoenergetic ion beams. Either extremely high power laser pulses or tight focusing of laser radiation is required. The latter would lead to the appearance of the maximum attainable ion energy, which is determined by the laser group velocity and is highly influenced by the transverse expansion of the target. Ion acceleration is only possible with target velocities less than the group velocity of the laser. The transverse expansion of the target makes it transparent for radiation, thus reducing the effectiveness of 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., Comment: 6 pages, 4 figures

We discuss a new compact gamma-ray source aiming at high spectral density, up to two orders of magnitude higher than currently available bremsstrahlung sources, and conceptually similar to Compton Sources based on conventional linear accelerators. This new source exploits electron bunches from laser-driven electron acceleration in the so-called self-injection scheme and uses a counter-propagating laser pulse to obtain X and gamma-ray emission via Thomson/Compton scattering. The proposed experimental configuration inherently provides a unique test-bed for studies of fundamental open issues of electrodynamics. In view of this, a preliminary discussion of recent results on self-injection with the FLAME laser is also given., Comment: 8 pages, 10 figures, 44 references - Channeling 2012 conference

We propose experiments on the collision of high intensity electromagnetic pulses with electron bunches and on the collision of multiple electromagnetic pulses for studying extreme field limits in the nonlinear interaction of electromagnetic waves. The effects of nonlinear QED will be revealed in these laser plasma experiments., Comment: 7 pages, 3 figures, 1 table; 15th Advanced Accelerator Concepts Workshop (AAC 2012), Austin, Texas, 10-15 June, 2012

When the ions are accelerated by the radiation pressure of the laser pulse, their velocity can not exceed the laser group velocity, in the case when it is less than the speed of light in vacuum. This is demonstrated in two cases corresponding to the thin foil target irradiated by a high intensity laser light and to the hole boring by the laser pulse in the extended plasma accompanied by the collisionless shock wave formation. It is found that the beams of accelerated at the collisionless shock wave front ions are unstable against the Buneman-lke and the Weibel-like instabilities which result in the ion energy spectrum broadening., Comment: 22 pages, 9 figures

We demonstrate a new high-order harmonic generation mechanism reaching the `water window' spectral region in experiments with multi-terawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving uJ/sr pulses. Harmonics are collectively emitted by an oscillating electron spike formed at the joint of the boundaries of a cavity and bow wave created by a relativistically self-focusing laser in underdense plasma. The spike sharpness and stability are explained by catastrophe theory. The mechanism is corroborated by particle-in-cell simulations.

A new diagnosis method for high energy ions utilizing a single CR-39 detector mounted on plastic plates is demonstrated to identify the presence of the high energy component beyond the CR-39's detection threshold limit. On irradiation of the CR-39 detector unit with a 25 MeV per nucleon He ion beam from conventional rf-accelerators, a large number of etch pits having elliptical opening shapes are observed on the rear surface of the CR-39. Detailed investigations reveal that these etch pits are created by heavy ions inelastically backscattered from the plastic plates. This ion detection method is applied to laser-driven ion acceleration experiments using cluster-gas targets, and ion signals with energies up to 50 MeV per nucleon are identified.

We propose the 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 for studying extreme field limits in the nonlinear interaction of electromagnetic waves. The regimes of dominant radiation reaction, which completely changes the electromagnetic wave-matter interaction, will be revealed in the laser plasma experiments. This will result in a new powerful source of ultra short high brightness gamma-ray pulses. A possibility of the demonstration of the electron-positron pair creation in vacuum in a 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., Comment: 33 pages, 5 figures, 1 table

Identified is a set of ballpark parameters for laser, plasma, and accelerator technologies that are defined for accelerated electron energies reaching as high as PeV. These parameters are carved out from the scaling laws that govern the physics of laser acceleration, theoretically suggested and experimentally explored over a wide range in the recent years. We extrapolate this knowledge toward PeV energies. In the density regime on the order of 10^16 cm^-3, it is possible to consider the application of the existing NIF (or LMJ) or its extended lasers to their appropriate retrofitting for this purpose. Although the ambition of luminosity is not pursued, such energies by themselves may allow us to begin to feel and study the physics of the 'texture of vacuum'. This is an example of fundamental physics exploration without the need of luminosity paradigm. By converting accelerated electrons with extreme energies to like energy gamma photons, and let them propagate through vacuum over a sufficient distance, these extremely high energy (and therefore short wavelength) photons experience smallest vacuum structures and fluctuations. If we can measure the arrival time differential and thus the gamma photon speed as a function of different energies such as 0.1 PeV vs 1 PeV, say within attoseconds accuracy, we can collect valuable data if and how gamma photons still obeys the premise of relativity or the vacuum texture begins to alter such fundamentals. The only method currently available to look at this problem may be to study astrophysical data of the primordial gamma ray bursts (GRBs), which are compared with the presently suggested approach., Comment: 18 pages, 1 figure, 1 table, submitted to Phys. Rev. ST-AB

The energy of the ions accelerated by an intense electromagnetic wave in the radiation pressure dominated regime can be greatly enhanced due to a transverse expansion of a thin target. The expansion decreases the number of accelerated ions in the irradiated region increasing the energy and the longitudinal velocity of remaining ions. In the relativistic limit, the ions become phase-locked with respect to the electromagnetic wave resulting in the unlimited ion energy gain. This effect and the use of optimal laser pulse shape provide a new approach for great enhancing the energy of laser accelerated ions., Comment: 30 pages, 9 figures, misprints corrected

Bright Ar K-shell x-ray with very little background has been generated using an Ar clustering gas jet target irradiated with an 800 mJ, 30 fs ultra-high contrast laser, with the measured flux of 1.1 x 10^4 photons/mrad^2/pulse. This intense x-ray source critically depends on the laser contrast and the laser energy and the optimization of this source with interaction is addressed. Electron driven by laser electric field directly via nonlinear resonant is proved in simulation, resulting in effective electron heating and the enhancement of x-ray emission. The x-ray pulse duration is demonstrated to be only 10 fs, as well as a source size of 20 um, posing great potential application for single-shot ultrafast x-ray imaging., Comment: 13 pages, 5 figures

We demonstrate generation of 10-20 MeV/u ions with a compact 4 TW laser using a gas target mixed with submicron clusters, corresponding to tenfold increase in the ion energies compared to previous experiments with solid targets. It is inferred that the high energy ions are generated due to formation of a strong dipole vortex structure. The demonstrated method has a potential to construct compact and high repetition rate ion sources for hadron therapy and other applications., Comment: 7 pages, 4 figures

An ultra-bright high-intensity X- and gamma-radiation source is proposed. A high-density thin plasma slab, accelerating in the radiation pressure dominant regime by a co-propagating ultra-intense electromagnetic wave, reflects a counter-propagating relativistically strong electromagnetic wave, producing strongly time-compressed and intensified radiation due to the double Doppler effect. The reflected light contains relativistic harmonics generated at the plasma slab, all upshifted with the same factor as the fundamental mode of the incident light., Comment: 6 pages, 3 figures. Submitted to Phys. Rev. Lett

Coulomb implosion mechanism of the negatively charged ion acceleration in laser plasmas is proposed. When a cluster target is irradiated by an intense laser pulse and the Coulomb explosion of positively charged ions occurs, the negative ions are accelerated inward. The maximum energy of negative ions is several times lower than that of positive ions. The theoretical description and Particle-in-Cell simulation of the Coulomb implosion mechanism and the evidence of the negative ion acceleration in the experiments on the high intensity laser pulse interaction with the cluster targets are presented., Comment: 4 pages