arXiv subjects
Publications and source records attributed to Mattias Marklund.
We consider the Thomson scattering of an electron in an ultra-intense chirped laser pulse. It is found that the introduction of a negative chirp means the electron enters a high frequency region of the field while it still has a large proportion of its original energy. This results in a significant enhancement of the energy and intensity of the emitted radiation as compared to the case without chirping.
We derive a simple expression for the photon helicity and polarisation-flip probabilities in arbitrary background fields, in the low energy regime. Taking the background to model a focused laser beam, we study the impact of pulse shape and collision geometry on the probabilities and on ellipticity signals of vacuum birefringence. We find that models which do not account for pulse duration can overestimate all signals in near head-on collisions by up to an order of magnitude. Taking pulse duration into account, the flip probability becomes relatively insensitive to both angular incidence and the fine details of the pulse structure.
We propose and develop a general method of numerical calculation of the wave function time evolution in a quantum system which is described by Hamiltonian of an arbitrary dimensionality and with arbitrary interactions. For this, we obtain a general n-order single-step propagator, which could be used for the numerical solving of the problem with any prescribed accuracy. We demonstrate an applicability of the proposed approach by considering a propagation of an electron in focused electromagnetic field with vortex electric field component.
The Kelvin-Helmholtz instability in an ionized plasma is considered with a focus on the generation of magnetic field via the Biermann battery mechanisms. The problem is studied through direct numerical simulations of two counter-directed flows in 2D geometry. The simulations demonstrate the formation of eddies and their further interaction resulting in a large single vortex. At early stages, the generated magnetic field evolves due to the baroclinic term in the induction equation, revealing significantly different structures from the vorticity field, despite the fact that magnetic field and vorticity obey identical equations. At later times, the magnetic field exhibits complex behavior and continues to grow even after a hydrodynamic vortex has developed.
Vacuum birefringence is governed by the amplitude for a photon to flip helicity or polarisation state in an external field. Here we calculate the flip and non-flip amplitudes in arbitrary plane wave backgrounds, along with the induced spacetime-dependent refractive indices of the vacuum. We compare the behaviour of the amplitudes in the low energy and high energy regimes, and analyse the impact of pulse shape and energy. We also provide the first lightfront-QED derivation of the coefficients in the Heisenberg-Euler effective action.
We propose a new method of detecting radiation reaction effects in the motion of particles subjected to laser pulses of moderate intensity and long duration. The effect becomes sizeable for particles that gain almost no energy through the interaction with the laser pulse.
The electron mass shift in a laser field has long remained an elusive concept. We show that the mass shift can exist in pulses but that it is neither unique nor universal: it can be reduced by pulse shaping. We show also that the detection of mass shift effects in laser-particle scattering experiments is feasible with current technology, even allowing for the transverse structure of realistic beams.
We discuss the theory and phenomenology of pair annihilation, within an ultra-short laser pulse, to a single photon. The signature of this process is the uni-directional emission of single photons with a fixed energy. We show that the cross section is significantly larger than for two-photon pair annihilation in vacuum, with XFEL parameters admitting a much clearer signal than optical beams.
We consider the effects of radiation damping on the electron dynamics in a Gaussian beam model of a laser field. For high intensities, i.e. with dimensionless intensity a0 \gg 1, it is found that the dynamics divide into three regimes. For low energy electrons (low initial γ-factor, γ0) the radiation damping effects are negligible. At higher energies, but still at 2γ0 < a0, the damping alters the final displacement and the net energy change of the electron. For 2γ0 > a0 one is in a regime of radiation reaction induced electron capture. This capture is found to be stable with respect to the spatial properties of the electron beam and results in a significant energy loss of the electrons. In this regime the plane wave model of the laser field provides a good description of the dynamics, whereas for lower energies the Gaussian beam and plane wave models differ significantly. Finally the dynamics are considered for the case of an XFEL field. It is found that the significantly lower intensities of such fields inhibits the damping effects.
We give an exact, analytic, and manifestly gauge invariant account of pair production in combined longitudinal and transverse electromagnetic fields, both depending arbitrarily on lightfront time. The instantaneous, nonperturbative probability of pair creation is given explicitly along with the spectra of the final particle yield. Our results are relevant to high-intensity QED experiments now being planned for future optical and x-ray free electron lasers.
The process of protons transport in molecular water chains is of fundamental interest for many biological systems. Although many features of such systems can be analyzed using large-scale computational modeling, other features are better understood in terms of simplified model problems. Here we have tested, analytically and numerically, a model describing the classical proton hopping process in molecular water chains. In order to capture the main features of the proton hopping process in such molecular chains, we use a simplified model for our analysis. In particular, our discrete model describes a 1D chain of water molecules situated in an external protein channel structure, and each water molecule is allowed to oscillate around its equilibrium point in this system, while the protons are allowed to move along the line of neighboring oxygen atoms. The occurrence and properties of nonlinear solitary transport structures, allowing for much faster proton transport, are discussed, and the possible implications of these findings for biological systems are emphasized.
The generation of ultra-strong attosecond pulses through laser-plasma interactions offers the opportunity to surpass the intensity of any known laboratory radiation source, giving rise to new experimental possibilities, such as quantum electrodynamical tests and matter probing at extremely short scales. Here we demonstrate that a laser irradiated plasma surface can act as an efficient converter from the femto- to the attosecond range, giving a dramatic rise in pulse intensity. Although seemingly similar schemes have been presented in the literature, the present setup deviates significantly from previous attempts. We present a new model describing the nonlinear process of relativistic laser-plasma interaction. This model, which is applicable to a multitude of phenomena, is shown to be in excellent agreement with particle-in-cell simulations. We provide, through our model, the necessary details for an experiment to be performed. The possibility to reach intensities above 10^26 W/cm^2, using upcoming 10 petawatt laser sources, is demonstrated.
We investigate strong field vacuum effects using a phase space approach based on the Wigner formalism. We calculate the Wigner function in a strong null-field background exactly, using lightfront field theory. The Wigner function exhibits the distinct features of strong field QED: in particular we identify the effective mass in a laser pulse, compare it to the well-known mass shift in a periodic plane wave and identify signals of multi-photon absorption and emission. Finally, we show how to extend our results to describe vacuum pair production in colliding laser pulses.
We derive a fluid theory for spin-1/2 particles starting from an extended kinetic model based on a spin-projected density matrix formalism. The evolution equation for the spin density is found to contain a pressure-like term. We give an example where this term is important by looking at a linear mode previously found in a spin kinetic model.
We discuss pair creation in a strong laser background. Using lightfront field theory, we show that all the physics is contained in the lightfront momentum transfer from the laser, and probe, to the produced pair. The dependence of this momentum transfer on the geometry of the laser leads to resonance and diffraction effects in pair production spectra. The lightfront approach naturally explains the interpretation of laser-stimulated pair production as a multi-photon process creating pairs of an effective mass.
We consider stimulated pair production employing strong-field QED in a high-intensity laser background. In an infinite plane wave, we show that light-cone quasi-momentum can only be transferred to the created pair as a multiple of the laser frequency, i.e.\ by a higher harmonic. This translates into discrete resonance conditions providing the support of the pair creation probability which becomes a delta-comb. These findings corroborate the usual interpretation of multi-photon production of pairs with an effective mass. In a pulse, the momentum transfer is continuous, leading to broadening of the resonances and sub-threshold behaviour. The peaks remain visible as long as the number of cycles per pulse exceeds unity. The resonance patterns in pulses are analogous to those of a diffraction process based on interference of the produced pairs.
We review the effects of strong background fields in noncommutative QED. Beginning with the noncommutative Maxwell and Dirac equations, we describe how combined noncommutative and strong field effects modify the propagation of fermions and photons. We extend these studies beyond the case of constant backgrounds by giving a new and revealing interpretation of the photon dispersion relation. Considering scattering in background fields, we then show that the noncommutative photon is primarily responsible for generating deviations from strong field QED results. Finally, we propose a new method for constructing gauge invariant variables in noncommutative QED, and use it to analyse the physics of our null background fields.
We discuss a two-fold extension of QED assuming the presence of strong external fields provided by an ultra-intense laser and noncommutativity of spacetime. While noncommutative effects leave the electron's intensity induced mass shift unchanged, the photons change significantly in character: they acquire a quasi-momentum that is no longer light-like. We study the consequences of this combined noncommutative strong-field effect for basic lepton-photon interactions.