Intensity patterns of a focused electromagnetic spherical wave with aberration.

The laser pulse focused by a relativistic flying parabolic mirror can exceed the laser intensity focused by conventional physical focusing optics. Depending on the Lorentz γ-factor, the focal length of the relativistic flying mirror in the boosted frame of reference becomes much shorter than the incident beam size. The 4π-spherical focusing scheme is applied to describe such a focused field configuration. In this paper, a theoretical formalism has been developed to describe the field configuration focused by the 4π-spherical focusing scheme with an arbitrary phase error of an incident electromagnetic wave. The focused field configuration is described by the linear combination of the product of the spherical Bessel function and the spherical harmonics, resulting in the same expression as the multipole radiation. The mathematical expression showing the focused field for the femtosecond laser pulse, as well as the continuous wave, has been derived for the application to the femtosecond high-power laser. We show the three-dimensional intensity distribution near focus for the 4π-spherically focused electromagnetic field with phase error.

Propagation of intense electromagnetic pulse with a small conical phase shift induced by Axicon optics.

The conical phase shift induced by the axicon generates a non-diffracting Bessel beam. In this paper, we examine the propagation property of an electromagnetic wave focused by a thin lens and axicon waveplate combination, which induces a small amount of conical phase shift less than one wavelength. A general expression describing the focused field distribution has been derived under the paraxial approximation. The conical phase shift breaks the axial symmetry of intensity and shows a focal spot-shaping capability by controlling the central intensity profile within a certain range near focus. The focal spot-shaping capability can be applied to form a concave or flattened intensity profile, which can be used to control the concavity of a double-sided relativistic flying mirror or to generate the spatially uniform and energetic laser-driven proton/ion beams for hadron therapy.

Towards bright gamma-ray flash generation from tailored target irradiated by multi-petawatt laser.

One of the remarkable phenomena in the laser-matter interaction is the extremely efficient energy transfer to [Formula: see text]-photons, that appears as a collimated [Formula: see text]-ray beam. For interactions of realistic laser pulses with matter, existence of an amplified spontaneous emission pedestal plays a crucial role, since it hits the target prior to the main pulse arrival, leading to a cloud of preplasma and drilling a narrow channel inside the target. These effects significantly alter the process of [Formula: see text]-photon generation. Here, we study this process by importing the outcome of magnetohydrodynamic simulations of the pedestal-target interaction into particle-in-cell simulations for describing the [Formula: see text]-photon generation. It is seen that target tailoring prior the laser-target interaction plays an important positive role, enhancing the efficiency of laser pulse coupling with the target, and generating high energy electron-positron pairs. It is expected that such a [Formula: see text]-photon source will be actively used in various applications in nuclear photonics, material science and astrophysical processes modelling.

Superluminal-subluminal orbital angular momentum femtosecond laser focus.

The interplay between the frequency chirping of a broadband laser pulse and the longitudinal chromatic aberration of a focusing optic introduces the superluminal or subluminal behavior to a laser focus. In this paper, we present an analytic expression for an electric field describing a superluminal or subluminal femtosecond laser focus with orbital angular momentum. The analytic expression for a superluminal or subluminal laser focus is obtained through a diffraction integral, in which the focal length is replaced by a time-dependent focal length under the paraxial approximation, and the Fourier transformation. The speed and pulse duration of a laser focus are determined by the total group delay dispersion and a chromaticity parameter defined by the longitudinal chromatic aberration of a dispersive focusing optic. It is shown that it is possible to generate a several femtosecond superluminal orbital angular momentum laser focus in the focal region.

Dynamic mitigation of the tearing mode instability in a collisionless current sheet.

Dynamic mitigation for the tearing mode instability in the current sheet in collisionless plasmas is demonstrated by applying a wobbling electron current beam. The initial small amplitude modulations imposed on the current sheet induce the electric current filamentation and the reconnection of the magnetic field lines. When the wobbling or oscillatory motion is added from the electron beam having a form of a thin layer moving along the current sheet, the perturbation phase is mixed and consequently the instability growth is saturated remarkably, like in the case of the feed-forward control.

Relativistic flying forcibly oscillating reflective diffraction grating.

Relativistic flying forcibly oscillating reflective diffraction gratings are formed by an intense laser pulse (driver) in plasma. The mirror surface is an electron density singularity near the joining area of the wake wave cavity and the bow wave; it moves together with the driver laser pulse and undergoes forced oscillations induced by the field. A counterpropagating weak laser pulse (source) is incident at grazing angles, being efficiently reflected and enriched by harmonics. The reflected spectrum consists of the source pulse base frequency and its harmonics, multiplied by a large factor due to the double Doppler effect.

Relativistic slingshot: A source for single circularly polarized attosecond x-ray pulses.

We propose a mechanism to generate a single intense circularly polarized attosecond x-ray pulse from the interaction of a circularly polarized relativistic few-cycle laser pulse with an ultrathin foil at normal incidence. Analytical modeling and particle-in-cell simulation demonstrate that a huge charge-separation field can be produced when all the electrons are displaced from the target by the incident laser, resulting in a high-quality relativistic electron mirror that propagates against the tail of the laser pulse. The latter is efficiently reflected as well as compressed into an attosecond pulse that is also circularly polarized.

High-power γ-ray flash generation in ultraintense laser-plasma interactions.

When high-intensity laser interaction with matter enters the regime of dominated radiation reaction, the radiation losses open the way for producing short pulse high-power γ-ray flashes. The γ-ray pulse duration and divergence are determined by the laser pulse amplitude and by the plasma target density scale length. On the basis of theoretical analysis and particle-in-cell simulations with the radiation friction force incorporated, optimal conditions for generating a γ-ray flash with a tailored overcritical density target are found.

Proton acceleration to 40 MeV using a high intensity, high contrast optical parametric chirped-pulse amplification/Ti:sapphire hybrid laser system.

Using a high-contrast (10(10):1) and high-intensity (10(21) W/cm(2)) laser pulse with the duration of 40 fs from an optical parametric chirped-pulse amplification/Ti:sapphire laser, a 40 MeV proton bunch is obtained, which is a record for laser pulse with energy less than 10 J. The efficiency for generation of protons with kinetic energy above 15 MeV is 0.1%.

Temporal contrast enhancement of petawatt-class laser pulses.

We demonstrate the temporal contrast enhancement in a petawatt-class Ti:sapphire chirped-pulse amplification (CPA) laser system. An extra saturable absorber, introduced downstream after a low-gain optical parametric chirped-pulse amplification (OPCPA) preamplifier, has improved the temporal contrast in the system to 1.4×10(12) on the subnanosecond time scale at 70 TW power level. We have achieved 28 J of uncompressed broadband output energy with this system, indicating the potential for reaching peak powers near 600 TW.

Lorentz-Abraham-Dirac versus Landau-Lifshitz radiation friction force in the ultrarelativistic electron interaction with electromagnetic wave (exact solutions).

When the parameters of electron-extreme power laser interaction enter the regime of dominated radiation reaction, the electron dynamics changes qualitatively. The adequate theoretical description of this regime becomes crucially important with the use of the radiation friction force either in the Lorentz-Abraham-Dirac form, which possesses unphysical runaway solutions, or in the Landau-Lifshitz form, which is a perturbation valid for relatively low electromagnetic wave amplitude. The goal of the present paper is to find the limits of the Landau-Lifshitz radiation force applicability in terms of the electromagnetic wave amplitude and frequency. For this, a class of the exact solutions to the nonlinear problems of charged particle motion in the time-varying electromagnetic field is used.

Efficient generation of Xe K-shell x rays by high-contrast interaction with submicrometer clusters.

The interaction between a 25 TW laser and Xe clusters at a peak intensity of 1 × 10¹9 W/cm² has been investigated. Xe K-shell x rays, whose energies are approximately 30 keV, were clearly observed with a hard x-ray CCD at 3.4 MPa. Moreover, we studied the yield of the Xe K-shell x rays by changing the pulse duration of the laser at a constant laser energy and found that the pulse duration of 40 fs is better than that of 300 fs for generating Xe K-shell x rays.

High-energy ions from near-critical density plasmas via magnetic vortex acceleration.

Ultraintense laser pulses propagating in near-critical density plasmas generate magnetic dipole vortex structures. In the region of decreasing plasma density, the vortex expands both in forward and lateral directions. The magnetic field pressure pushes electrons and ions to form a density jump along the vortex axis and induces a longitudinal electric field. This structure moves together with the expanding dipole vortex. The background ions located ahead of the electric field are accelerated to high energies. The energy scaling of ions generated by this magnetic vortex acceleration mechanism is derived and corroborated using particle-in-cell simulations.

Schwinger limit attainability with extreme power lasers.

High intensity colliding laser pulses can create abundant electron-positron pair plasma [A. R. Bell and J. G. Kirk, Phys. Rev. Lett. 101, 200403 (2008)], which can scatter the incoming electromagnetic waves. This process can prevent one from reaching the critical field of quantum electrodynamics at which vacuum breakdown and polarization occur. Considering the pairs are seeded by the Schwinger mechanism, it is shown that the effects of radiation friction and the electron-positron avalanche development in vacuum depend on the electromagnetic wave polarization. For circularly polarized colliding pulses, these effects dominate not only the particle motion but also the evolution of the pulses. For linearly polarized pulses, these effects are not as strong. There is an apparent analogy of these cases with circular and linear electron accelerators to the corresponding constraining and reduced roles of synchrotron radiation losses.

Propagation-based phase-contrast enhancement of nanostructure images using a debris-free femtosecond-laser-driven cluster-based plasma soft x-ray source and an LiF crystal detector.

We demonstrate in-line phase-contrast imaging of nanothickness foils by using a relatively large, polychromatic, debris-free femtosecond-laser-driven cluster-based plasma soft x-ray source, and a high-resolution, large dynamic range LiF crystal detector. The spatial coherence length of radiation in our setup reached a value of 5 microm on the sample plane, which is enough to observe phase-contrast enhancement in the images registered by the detector placed only a few hundred micrometers behind the object. We have developed a tabletop soft x-ray emission source, which emits radiation within a 4pi sr solid angle, and which allows one to obtain contact and propagation-based phase-contrast imaging of nanostructures with 700 nm spatial resolutions. This advance could be of utility for metrology applications.

Observation of strong correlation between quasimonoenergetic electron beam generation by laser wakefield and laser guiding inside a preplasma cavity.

We use a one-shot measurement technique to study effects of laser prepulses on the electron laser wakefield acceleration driven by relativistically intense laser pulses (lambda=790 nm, 11 TW, 37 fs) in dense helium gas jets. A quasimonoenergetic electron bunch with an energy peak approximately 11.5 MeV[DeltaE/E approximately 10% (FWHM)] and with a narrow-cone angle (0.04pi mm mrad) of ejection is detected at a plasma density of 8 x 10(19) cm(-3). A strong correlation between the generation of monoenergetic electrons and optical guiding of the pulse in a thin channel produced by picosecond laser prepulses is observed. This generation mechanism is well corroborated by two-dimensional particle-in-cell simulations.

Soliton synchrotron afterglow in a laser plasma.

Coherent synchrotron radiation can be emitted by relativistic electromagnetic subcycle solitons dwelling in a low-temperature collisionless plasma. Using three-dimensional particle-in-cell simulations we show that solitons, left in a wake of a relativistically intense short circularly polarized laser pulse in the plasma, emit spiral electromagnetic wave, as a result of charge density oscillations in the wall of the soliton cavity. This high-frequency afterglow persists for tens of Langmuir periods.

Light intensification towards the Schwinger limit.

A method to generate ultrahigh intense electromagnetic fields is suggested, based on the laser pulse compression, carrier frequency upshift, and focusing by a counterpropagating breaking plasma wave, relativistic flying parabolic mirror. This method allows us to achieve the quantum electrodynamics critical field (Schwinger limit) with present-day laser systems.

Three-dimensional relativistic electromagnetic subcycle solitons.

Three-dimensional (3D) relativistic electromagnetic subcycle solitons were observed in 3D particle-in-cell simulations of an intense short-laser-pulse propagation in an underdense plasma. Their structure resembles that of an oscillating electric dipole with a poloidal electric field and a toroidal magnetic field that oscillate in phase with the electron density with frequency below the Langmuir frequency. On the ion time scale, the soliton undergoes a Coulomb explosion of its core, resulting in ion acceleration, and then evolves into a slowly expanding quasineutral cavity.