1,461 research outputs found
Self-compression and catastrophic collapse of photon bullets in vacuum
Photon-photon scattering, due to photons interacting with virtual
electron-positron pairs, is an intriguing deviation from classical
electromagnetism predicted by quantum electrodynamics (QED). Apart from being
of fundamental interest in itself, collisions between photons are believed to
be of importance in the vicinity of magnetars, in the present generation
intense lasers, and in intense laser-plasma/matter interactions; the latter
recreating astrophysical conditions in the laboratory. We show that an intense
photon pulse propagating through a radiation gas can self-focus, and under
certain circumstances collapse. This is due to the response of the radiation
background, creating a potential well in which the pulse gets trapped, giving
rise to photonic solitary structures. When the radiation gas intensity has
reached its peak values, the gas releases part of its energy into `photon
wedges', similar to Cherenkov radiation. The results should be of importance
for the present generation of intense lasers and for the understanding of
localized gamma ray bursts in astrophysical environments. They could
furthermore test the predictions of QED, and give means to create ultra-intense
photonic pulses.Comment: 4 pages, 1 figur
The Intense Radiation Gas
We present a new dispersion relation for photons that are nonlinearly
interacting with a radiation gas of arbitrary intensity due to photon-photon
scattering. It is found that the photon phase velocity decreases with
increasing radiation intensity, it and attains a minimum value in the limit of
super-intense fields. By using Hamilton's ray equations, a self-consistent
kinetic theory for interacting photons is formulated. The interaction between
an electromagnetic pulse and the radiation gas is shown to produce pulse
self-compression and nonlinear saturation. Implications of our new results are
discussed.Comment: 7 pages, 1 figure, version to appear in Europhys. Let
Nonlinear propagation of broadband intense electromagnetic waves in an electron-positron plasma
A kinetic equation describing the nonlinear evolution of intense
electromagnetic pulses in electron-positron (e-p) plasmas is presented. The
modulational instability is analyzed for a relativistically intense partially
coherent pulse, and it is found that the modulational instability is inhibited
by the spectral pulse broadening. A numerical study for the one-dimensional
kinetic photon equation is presented. Computer simulations reveal a
Fermi-Pasta-Ulam-like recurrence phenomena for localized broadband pulses. The
results should be of importance in understanding the nonlinear propagation of
broadband intense electromagnetic pulses in e-p plasmas in laser-plasma systems
as well as in astrophysical plasma settings.Comment: 16 pages, 5 figures, to appear in Phys. Plasma
Graviton mediated photon-photon scattering in general relativity
In this paper we consider photon-photon scattering due to self-induced
gravitational perturbations on a Minkowski background. We focus on four-wave
interaction between plane waves with weakly space and time dependent
amplitudes, since interaction involving a fewer number of waves is excluded by
energy-momentum conservation. The Einstein-Maxwell system is solved
perturbatively to third order in the field amplitudes and the coupling
coefficients are found for arbitrary polarizations in the center of mass
system. Comparisons with calculations based on quantum field theoretical
methods are made, and the small discrepances are explained.Comment: 5 pages, 3 figure
Prospects and limitations of wakefield acceleration in solids
Advances in the generation of relativistic intensity pulses with wavelengths
in the X-ray regime, through high harmonic generation from near-critical
plasmas, opens up the possibility of X-ray driven wakefield acceleration. The
similarity scaling laws for laser plasma interaction suggest that X-rays can
drive wakefields in solid materials providing TeV/cm gradients, resulting in
electron and photon beams of extremely short duration. However, the wavelength
reduction enhances the quantum parameter , hence opening the question of
the role of non-scalable physics, e.g., the effects of radiation reaction.
Using three dimensional Particle-In-Cell simulations incorporating QED effects,
we show that for the wavelength nm and relativistic amplitudes
-100, similarity scaling holds to a high degree, combined with
operation already at moderate , leading to photon
emissions with energies comparable to the electron energies. Contrasting to the
generation of photons with high energies, the reduced frequency of photon
emission at X-ray wavelengths (compared to at optical wavelengths) leads to a
reduction of the amount of energy that is removed from the electron population
through radiation reaction. Furthermore, as the emission frequency approaches
the laser frequency, the importance of radiation reaction trapping as a
depletion mechanism is reduced, compared to at optical wavelengths for
leading to similar .Comment: 9 pages, 7 figure
Spin induced nonlinearities in the electron MHD regime
We consider the influence of the electron spin on the nonlinear propagation
of whistler waves. For this purpose a recently developed electron two-fluid
model, where the spin up- and down populations are treated as different fluids,
is adapted to the electron MHD regime. We then derive a nonlinear Schrodinger
equation for whistler waves, and compare the coefficients of nonlinearity with
and without spin effects. The relative importance of spin effects depend on the
plasma density and temperature as well as the external magnetic field strength
and the wave frequency. The significance of our results to various plasmas are
discussed.Comment: 5 page
Dynamics of spin 1/2 quantum plasmas
The fully nonlinear governing equations for spin 1/2 quantum plasmas are
presented. Starting from the Pauli equation, the relevant plasma equations are
derived, and it is shown that nontrivial quantum spin couplings arise, enabling
studies of the combined collective and spin dynamics. The linear response of
the quantum plasma in an electron--ion system is obtained and analyzed.
Applications of the theory to solid state and astrophysical systems as well as
dusty plasmas are pointed out.Comment: 4 pages, 2 figures, to appear in Physical Review Letter
Instability and dynamics of two nonlinearly coupled laser beams in a plasma
We investigate the nonlinear interaction between two laser beams in a plasma
in the weakly nonlinear and relativistic regime. The evolution of the laser
beams is governed by two nonlinear Schroedinger equations that are coupled with
the slow plasma density response. We study the growth rates of the Raman
forward and backward scattering instabilities as well of the Brillouin and
self-focusing/modulational instabilities. The nonlinear evolution of the
instabilities is investigated by means of direct simulations of the
time-dependent system of nonlinear equations.Comment: 18 pages, 8 figure
Physics of the laser-plasma interface in the relativistic regime of interaction
The reflection of intense laser radiation from solids appears as a result of
relativistic dynamics of the electrons driven by both incoming and
self-generated electromagnetic fields at the periphery of the emerging dense
plasma. In the case of highly-relativistic motion, electrons tend to form a
thin oscillating layer, which makes it possible to model the interaction and
obtain the temporal structure of the reflected radiation. The modelling reveals
the possibility and conditions for producing singularly intense and short XUV
bursts of radiation, which are interesting for many applications. However, the
intensity and duration of the XUV bursts, as well as the high-energy end of the
harmonic spectrum, depends on the thickness of the layer and its internal
structure which are not assessed by such macroscopic modelling. Here we analyse
the microscopic physics of this layer and clarify how its parameters are bound
and how this controls outlined properties of XUV bursts.Comment: 9 pages, 5 figure
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