arXiv subjects

Daniel Seipt

Publications and source records attributed to Daniel Seipt.

30 records · Page 2Linked to original sources

arXiv2018

Mode truncations and scattering in strong fields

Truncating quantum field theories to a dominant mode offers a non-perturbative approach to their solution. We consider here the interaction of charged scalar matter with a single mode of the electromagnetic field. The implied breaking of explicit Lorentz invariance prompts us to compare instant-form quantisation and front-form, with the latter yielding significant simplifications when light-front zero modes are included. Using these field theory results we reassess the validity of existing first-quantised approaches to depletion effects in strong laser fields, and propose an alternative interpretation based on the dressing approach to QED and its infra-red structure.

hep-th↗

arXiv2018

Electron spin polarization in realistic trajectories around the magnetic node of two counter-propagating, circularly polarized, ultra-intense lasers

It has recently been suggested that two counter-propagating, circularly polarized, ultra-intense lasers can induce a strong electron spin polarization at the magnetic node of the electromagnetic field that they setup. We confirm these results by considering a more sophisticated description that integrates over realistic trajectories. The electron dynamics is weakly affected by the variation of power radiated due to the spin polarization. The degree of spin polarization differs by approximately 5\% if considering electrons initially at rest or already in a circular orbit. The instability of trajectories at the magnetic node induces a spin precession associated with the electron migration that establishes an upper temporal limit to the polarization of the electron population of about one laser period.

physics.plasm-ph↗

arXiv2017

Back-reaction on background fields: a coherent state approach

There are many situations in which a strong electromagnetic field may be approximated as a fixed background. Going beyond this approximation, i.e. accounting for the back-reaction of quantum process on the field, is however challenging. Here we develop an approach to this problem which is a straightforward extension of background field methods. The approach follows from the observation that scattering in an on-shell background is equivalent to scattering between coherent states; we show that by deforming these states one can model back-reaction. Focussing on intense laser-matter interactions, we provide examples which model beam depletion and, furthermore, introduce an extremisation principle with which to determine the level of depletion in a given scattering process.

hep-th↗

arXiv2017

Volkov States and Non-linear Compton Scattering in Short and Intense Laser Pulses

The collision of ultra-relativistic electron beams with intense short laser pulses makes possible to study QED in the high-intensity regime. Present day high-intensity lasers mostly operate with short pulse durations of several tens of femtoseconds, i.e. only a few optical cycles. A profound theoretical understanding of short pulse effects is important not only for studying fundamental aspects of high-intensity laser matter interaction, but also for applications as novel X- and gamma-ray radiation sources. In this article we give a brief overview of the theory of high-intensity QED with focus on effects due to the short pulse duration. The non-linear spectral broadening in non-linear Compton scattering due to the short pulse duration and its compensation is discussed.

physics.plasm-ph↗

arXiv2016

The effect of bound state dressing in laser assisted radiative recombination

We present a theoretical study on the recombination of a free electron into the ground state of a hydrogen-like ion in the presence of an external laser field. Emphasis is placed on the effects caused by the laser dressing of the residual ionic bound state. To investigate how this dressing affects the total and angle-differential cross section of laser assisted radiative recombination (LARR) we apply first-order perturbation theory and the separable Coulomb-Volkov-continuum ansatz. Using this approach detailed calculations were performed for low-$Z$ hydrogen like ions and laser intensities in the range from $I_L=10^{11}\text{W/cm}^2$ to $I_L=10^{13}\text{W/cm}^2$. It is seen that the total cross section as a function of the laser intensity is remarkably affected by the bound state dressing. Moreover the laser dressing becomes manifest as asymmetries in the angular distribution and the (energy) spectrum of the emitted recombination photons.

physics.atom-ph↗

arXiv2016

Analytical results for non-linear Compton scattering in short intense laser pulses

We study in detail the strong-field QED process of non-linear Compton scattering in short intense plane wave laser pulses of circular polarization. Our main focus is placed on how the spectrum of the back-scattered laser light depends on the shape and duration of the initial short intense pulse. Although this pulse shape dependence is very complicated and highly non-linear, and has never been addressed explicitly, our analysis reveals that all the dependence on the laser pulse shape is contained in a class of three-parameter master integrals. Here we present completely analytical expressions for the non-linear Compton spectrum in terms of these master integrals. Moreover, we analyse the universal behaviour of the shape of the spectrum for very high harmonic lines.

hep-ph↗

arXiv2016

Temporal laser pulse shape effects in nonlinear Thomson scattering

The influence of the laser pulse temporal shape on the Nonlinear Thomson Scattering on-axis photon spectrum is analyzed in detail. Using the classical description, analytical expressions for the temporal and spectral structure of the scattered radiation are obtained for the case of symmetric laser pulse shapes. The possibility of reconstructing the incident laser pulse from the scattered spectrum averaged over interference fringes in the case of high peak intensity and symmetric laser pulse shape is discussed.

physics.plasm-ph↗

arXiv2015

Determination of the carrier envelope phase for short, circularly polarized laser pulses

We analyze the impact of the carrier envelope phase on the differential cross sections of the Breit-Wheeler and the generalized Compton scattering in the interaction of a charged electron (positron) with an intensive ultra-short electromagnetic (laser) pulse. The differential cross sections as a function of the azimuthal angle of the outgoing electron have a clear bump structure, where the bump position coincides with the value of the carrier phase. This effect can be used for the carrier envelope phase determination.

hep-ph↗

arXiv2015

Dynamical Schwinger process in a bifrequent electric field of finite duration: survey on amplification

The electron-positron pair production due to the dynamical Schwinger process in a slowly oscillating strong electric field is enhanced by the superposition of a rapidly oscillating weaker electric field. A systematic account of the enhancement by the resulting bifrequent field is provided for the residual phase space distribution. The enhancement is explained by a severe reduction of the suppression in both the tunneling and multiphoton regimes.

hep-ph↗

arXiv2014

Lifting shell structures in the dynamically assisted Schwinger effect in periodic fields

The dynamically assisted pair creation (Schwinger effect) is considered for the superposition of two periodic electric fields acting a finite time interval. We find a strong enhancement by orders of magnitude caused by a weak field with a frequency being a multitude of the strong-field frequency. The strong low-frequency field leads to shell structures which are lifted by the weaker high-frequency field. The resonance type amplification refers to a new, monotonously increasing mode, often hidden in some strong oscillatory transient background which disappears during the smoothly switching off the background fields, thus leaving a pronounced residual shell structure in phase space.

hep-ph↗

arXiv2006

Quasi-Particle Description of Strongly Interacting Matter: Towards a Foundation

We confront our quasi-particle model for the equation of state of strongly interacting matter with recent first-principle QCD calculations. In particular, we test its applicability at finite baryon densities by comparing with Taylor expansion coefficients of the pressure for two quark flavours. We outline a chain of approximations starting from the Phi-functional approach to QCD which motivates the quasi-particle picture.

hep-ph↗

arXiv2006

Isentropic Equation of State of Two-Flavour QCD in a Quasi-Particle Model

We examine the isentropic QCD equation of state within a quasi-particle model being adjusted to first principle QCD calculations of two quark flavours. In particular, we compare with Taylor expansion coefficients of energy and entropy densities and with the isentropic trajectories describing the hydrodynamical expansion of a heavy-ion collision fireball.

hep-ph↗