86 research outputs found
Ion acceleration in "dragging field" of a light-pressure-driven piston
We propose a new acceleration scheme that combines shock wave acceleration
(SWA) and light pressure acceleration (LPA). When a thin foil driven by light
pressure of an ultra-intense laser pulse propagates in underdense background
plasma, it serves as a shock-like piston, trapping and reflecting background
protons to ultra-high energies. Unlike in SWA, the piston velocity is not
limited by the Mach number and can be highly relativistic. Background protons
can be trapped and reflected forward by the enormous "dragging field" potential
behind the piston which is not employed in LPA. Our one- and two-dimensional
particle-in-cell simulations and analytical model both show that proton
energies of several tens to hundreds of GeV can be obtained, while the
achievable energy in simple LPA is below 10 GeV.Comment: submitte
Bright X-ray source from a laser-driven micro-plasma-waveguide
Owing to the rapid progress in laser technology, very high-contrast
femtosecond laser pulses of relativistic intensities become available. These
pulses allow for interaction with micro-structured solid-density plasma without
destroying the structure by parasitic pre-pulses. This opens a new realm of
possibilities for laser interaction with micro- and nano-scales photonic
materials at the relativistic intensities. Here we demonstrate, for the first
time, that when coupling with a readily available 1.8 Joule laser, a
micro-plasma-waveguide (MPW) may serve as a novel compact x-ray source.
Electrons are extracted from the walls and form a dense self-organized helical
bunch inside the channel. These electrons are efficiently accelerated and
wiggled by the waveguide modes in the MPW, which results in a bright,
well-collimated emission of hard x-rays in the range of 1~100 keV.Comment: 5 pages, 4 figure
Axionlike-particle generation by laser-plasma interaction
Axion, a hypothetical particle that is crucial to quantum chromodynamics and
dark matter theory, has not yet been found in any experiment. With the
improvement of laser technique, much stronger quasi-static electric and
magnetic fields can be created in laboratory using laser-plasma interaction. In
this article, we discuss the feasibility of axion or axionlike-particle's
exploring experiments using planar and cylindrically symmetric laser-plasma
fields as backgrounds while probing with an ultrafast superstrong optical laser
or x-ray free-electron laser with high photon number. Compared to classical
magnet design, the axion source in laser-plasma interaction trades the
accumulating length for the source's interacting strength. Besides, a
structured field in the plasma creates a tunable transverse profile of the
interaction and improves the signal-noise ratio via the mechanisms such as
phase-matching. The mass of axion discussed in this article ranges from 1
\textmu eV to 1 eV. Some simple schemes and estimations of axion production and
probe's polarization rotation are given, which reveals the possibility of
future laser-plasma axion source in laboratory.Comment: 24 pages, 5 figure
Spin-dependent two-photon Bragg scattering in the Kapitza-Dirac effect
We present the possibility of spin-dependent Kapitza-Dirac scattering based
on a two-photon interaction only. The interaction scheme is inspired from a
Compton scattering process, for which we explicitly show the mathematical
correspondence to the spin-dynamics of an electron diffraction process in a
standing light wave. The spin effect has the advantage that it already appears
in a Bragg scattering setup with arbitrary low field amplitudes, for which we
have estimated the diffraction count rate in a realistic experimental setup at
available X-ray free-electron laser facilities
Proton Acceleration in a Laser-induced Relativistic Electron Vortex
We show that when a solid plasma foil with a density gradient on the front
surface is irradiated by an intense laser pulse at a grazing angle, around 80
degrees, a relativistic electron vortex is excited in the near-critical-density
layer after the laser pulse depletion. The vortex structure and dynamics are
studied using particle-in-cell simulations. Due to the asymmetry introduced by
nonuniform background density, the vortex drifts at a constant velocity,
typically 0.2 to 0.3 times the speed of light. The strong magnetic field inside
the vortex leads to significant charge separation; in the corresponding
electric field initially stationary protons can be captured and accelerated to
twice the velocity of the vortex (100-200 MeV). A representative scenario -
with laser intensity of 10^21 W/cm^2 -is discussed: two dimensional simulations
suggest that a quasi-monoenergetic proton beam can be obtained with a mean
energy 140 MeV and an energy spread of about 10%. We derive an analytical
estimate for the vortex velocity in terms of laser and plasma parameters,
demonstrating that the maximum proton energy can be controlled by the incidence
angle of the laser and the plasma density gradient.Comment: 15 pages, 8 figure
Generation of Intense High-Order Vortex Harmonics
This paper presents the method for the first time to generate intense
high-order optical vortices that carry orbital angular momentum in the extreme
ultraviolet region. In three-dimensional particle-in-cell simulation, both the
reflected and transmitted light beams include high-order harmonics of the
Laguerre-Gaussian (LG) mode when a linearly polarized LG laser pulse impinges
on a solid foil. The mode of the generated LG harmonic scales with its order,
in good agreement with our theoretical analysis. The intensity of the generated
high-order vortex harmonics is close to the relativistic region, and the pulse
duration can be in attosecond scale. The obtained intense vortex beam possesses
the combined properties of fine transversal structure due to the high-order
mode and the fine longitudinal structure due to the short wavelength of the
high-order harmonics. Thus, the obtained intense vortex beam may have
extraordinarily promising applications for high-capacity quantum information
and for high-resolution detection in both spatial and temporal scales because
of the addition of a new degree of freedom
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