arXiv subjects

A. M. Fedotov

Publications and source records attributed to A. M. Fedotov.

At least 37 records · Page 2Linked to original sources

arXiv2015

Optimized multibeam configuration for observation of QED cascades

QED cascades in intense electromagnetic field can occur if the dynamical quantum parameter $χ$ of a seed electron, which in Compton units coincides with the electron proper acceleration, attains the order of unity. We derive general expression for $χ$ of an initially slow electron in an arbitrary electromagnetic field for a time range $t\ll 1/ω$, where $ω$ is the field carrier frequency. Using this formula, we consider a special field configuration of multiple colliding focused laser beams and optimize it to provide cascade development at laser power below $10$ PW and intensity of the order of $10^{23}$W/cm$^2$. Such parameters of the beams will be obtained with a new generation of laser facilities, particularly the ELI Beamlines, in the coming years.

physics.plasm-ph↗

arXiv2014

Radiation friction vs ponderomotive effect

The concept of ponderomotive potential is upgraded to a regime in which radiation friction becomes dominant. The radiation friction manifests itself in novel features of long-term capturing of the particles released at the focus and impenetrability of the focus from the exterior. We apply time scales separation to the Landau-Lifshitz equation splitting the particle motion into quivering and slow drift of a guiding center. The drift equation is deduced by averaging over fast motion.

physics.plasm-ph↗

arXiv2014

Collapse and revival of electromagnetic cascades in focused intense laser pulses

We consider interaction of a high-energy electron beam with two counterpropagating femtosecond laser pulses. Nonlinear Compton scattering and electron-positron pair production by the emitted photons result in development of an electromagnetic "shower-type" cascade, which however collapses rather quickly due to energy losses by secondary particles. Nevertheless, the laser field accelerates the low-energy electrons and positrons trapped in the focal region, thus giving rise to development of electromagnetic cascade of another type ("avalanche-type"). This effect of cascade collapse and revival can be observed at the electron beam energy of the order of several GeV and intensity of the colliding laser pulses of the level of $10^{24}$W/cm$^2$. This means that it can be readily observed at the novel laser facilities which are either planned for the nearest future, or are already under construction. The proposed experimental setup provides the most realistic and promissory way to observe the "avalanche-type" cascades.

physics.plasm-ph↗

arXiv2014

Accurate numerical simulation of radiation reaction effects in strong electromagnetic fields

The Landau-Lifshitz equation provides an efficient way to account for the effects of radiation reaction without acquiring the non-physical solutions typical for the Lorentz-Abraham-Dirac equation. We solve the Landau-Lifshitz equation in its covariant four-vector form in order to control both the energy and momentum of radiating particle. Our study reveals that implicit time-symmetric collocation methods of the Runge-Kutta-Nyström type are superior in both accuracy and better maintaining the mass-shell condition than their explicit counterparts. We carry out an extensive study of numerical accuracy by comparing the analytical and numerical solutions of the Landau-Lifshitz equation. Finally, we present the results of simulation of particles scattering by a focused laser pulse. Due to radiation reaction, particles are less capable for penetration into the focal region, as compared to the case of radiation reaction neglected. Our results are important for designing the forthcoming experiments with high intensity laser fields.

physics.plasm-ph↗

arXiv2013

Creation of electron-positron plasma with superstrong laser field

We present a short review of recent progress in studying QED effects of interaction of ultra-relativistic laser pulses with vacuum and $e^-e^+$ plasma. The development of laser technologies promises very rapid growth of laser intensities in close future already. Two exawatt class facilities (ELI and XCELS, Russia) in Europe are already in the planning stage. Realization of these projects will make available a laser of intensity $\sim 10^{26}$W/cm$^2$ or even higher. Therefore, discussion of nonlinear optical effects in vacuum are becoming urgent for experimentalists and are currently gaining much attention. We show that, in spite of the fact that the respective field strength is still essentially less than $E_S=m^2c^3/e\hbar=1.32\cdot 10^{16}$V/cm, the nonlinear vacuum effects will be accessible for observation at ELI and XCELS facilities. The most promissory for observation is the effect of pair creation by laser pulse in vacuum. It is shown, that at intensities $\sim 5\cdot 10^{25}$W/cm$^2$, creation even of a single pair is accompanied by development of an avalanchelike QED cascade. There exists an important distinctive feature of the laser-induced cascades, as compared with the air showers arising due to primary cosmic ray entering the atmosphere. In our case the laser field plays not only the role of a target (similar to a nucleus in the case of air showers). It is responsible also for acceleration of slow particles. It is shown that the effect of pair creation imposes a natural limit for attainable laser intensity. Apparently, the field strength $E\sim E_S$ is not accessible for pair creating electromagnetic field at all.

physics.plasm-ph↗

arXiv2013

Pair creation by collision of intense laser pulse with high-frequency photon beam

We consider pair creation by collision of a couple of counterpropagating electromagnetic pulses with arbitrary frequency ratio, mostly in the context of setup with collision of optical and coherent hard X- (or gamma-) ray pulses. This problem is non-perturbative and in general does not admit exact analytical solutions. We discuss several known approaches according to the ratio of the parameters. Certain regions of the parameter space are not covered by the existing approximations or models. We present a new simplified exactly solvable model with one of the pulses being a delta-pulse. This model partially fills the yet unexplored gap in the space of parameters. The shape of the momentum distribution of the created particles in such a model is discussed. Even though the model may not have immediate implications for the forthcoming experiments, it can still provide some hints for better understanding of the fully non-perturbative regime and vacuum instability in QED interactions of extremely strong and short laser pulses.

hep-ph↗

arXiv2013

Effect of laser polarization on QED cascading

Development of QED cascades in a standing electromagnetic wave for circular and linear polarizations is simulated numerically with a 3D PIC-MC code. It is demonstrated that for the same laser energy the number of particles produced in a circularly polarized field is greater than in a linearly polarized field, though the acquiring mean energy per particle is larger in the latter case. The qualitative model of laser-assisted QED cascades is extended by including the effect of polarization of the field. It turns out that cascade dynamics is notably more complicated in the case of linearly polarized field, where separation into the qualitatively different "electric" and "magnetic" regions (where the electric field is stronger than the magnetic field and vice versa) becomes essential. In the "electric" regions acceleration is suppressed and moreover the high-energy electrons are even getting cooled by photon emission. The volumes of the "electric" and "magnetic" regions evolve periodically in time, and so does the cascade growth rate. In contrast to the linear polarization the charged particles can be accelerated by circularly polarized wave even in "magnetic" region. The "electric" and "magnetic" regions do not evolve in time and cascade growth rate almost does not depend on time for circular polarization.

physics.plasm-ph↗

arXiv2011

Boost modes for a massive fermion field

We have shown that Wightman function of a free quantum field generates any complete set of solutions of relativistic wave equations. Using this approach we have constructed the complete set of solutions to 2d Dirac equation consisting of eigenfunctions of the generator of Lorentz rotations (boost operator). It is shown that at the surface of the light cone the boost modes for a fermion field contain $δ$-function of a complex argument. Due to the presence of such singularity exclusion even of a single mode with an arbitrary value of the boost quantum number makes the set of boost modes incomplete.

hep-th↗

arXiv2010

Laser field absorption in self-generated electron-positron pair plasma

Recently much attention has being attracted to the problem of limitations on the attainable intensity of high power lasers [A.M. Fedotov {\it et al.} Phys. Rev. Lett. \textbf{105}, 080402 (2010)]. The laser energy can be absorbed by electron-positron pair plasma produced from a seed by strong laser field via development of the electromagnetic cascades. The numerical model for self-consistent study of electron-positron pair plasma dynamics is developed. Strong absorption of the laser energy in self-generated overdense electron-positron pair plasma is demonstrated. It is shown that the absorption becomes important for not extremely high laser intensity $I \sim 10^{24}$ W/cm$^2$ achievable in the nearest future.

physics.plasm-ph↗

arXiv2010

QED cascades induced by circularly polarized laser fields

The results of Monte-Carlo simulations of electron-positron-photon cascades initiated by slow electrons in circularly polarized fields of ultra-high strength are presented and discussed. Our results confirm previous qualitative estimations [A.M. Fedotov, et al., PRL 105, 080402 (2010)] of the formation of cascades. This sort of cascades has revealed the new property of the restoration of energy and dynamical quantum parameter due to the acceleration of electrons and positrons by the field and may become a dominating feature of laser-matter interactions at ultra-high intensities. Our approach incorporates radiation friction acting on individual electrons and positrons.

hep-ph↗

arXiv2010

On the kinetic equation approach to pair production by time-dependent electric field

We investigate the quantum kinetic approach to pair production from vacuum by time-dependent electric field. Equivalence between this approach and the more familiar S-matrix approach is explicitly established for both scalar and fermion cases. For the particular case of a constant electric field exact solution for kinetic equations is provided and the accuracy of low-density approximation is estimated.

hep-ph↗

arXiv2010

Limitations on the attainable intensity of high power lasers

It is shown that even a single $e^-e^+$ pair created by a super strong laser field in vacuum would cause development of an avalanche-like QED cascade which rapidly depletes the incoming laser pulse. This confirms the old N. Bohr conjecture that the electric field of the critical QED strength $E_S=m^2c^3/e\hbar$ could never be created.

hep-ph↗

arXiv2006

Generation of harmonics by a focused laser beam in vacuum

Generation of odd harmonics by a super strong focused laser beam in vacuum is considered. The process occurs due to the plural light-by-light scattering effect. In the leading order of perturbation theory, generation of $(2k+1)$th harmonic is described by a loop diagram with $(2k+2)$ external incoming, and two outgoing legs. A frequency of the beam is assumed to be much smaller than the Compton frequency, so that the approximation of a constant uniform electromagnetic field is valid locally. Analytical expressions for angular distribution of generated photons, as well as for their total emission rate are obtained in the leading order of perturbation theory. Influence of higher-order diagrams is studied numerically using the formalism of Intense Field QED. It is shown that the process may become observable for the beam intensity of the order of $10^{27}\rm{W/cm}^2$.

hep-ph↗

arXiv2006

Quark and pion condensation in a chromomagnetic background field

The general features of quark and pion condensation in dense quark matter with flavor asymmetry have been considered at finite temperature in the presence of a chromomagnetic background field modelling the gluon condensate. In particular, pion condensation in the case of a constant abelian chromomagnetic field and zero temperature has been studied both analytically and numerically. Under the influence of the chromomagnetic background field the effective potential of the system is found to have a global minimum for a finite pion condensate even for small values of the effective quark coupling constant. In the strong field limit, an effective dimensional reduction has been found to take place.

hep-ph↗

arXiv2006

Dynamical Casimir Effect in a one-dimensional uniformly contracting cavity

We consider particle creation (the Dynamical Casimir effect) in a uniformly contracting ideal one-dimensional cavity non-perturbatively. The exact expression for the energy spectrum of created particles is obtained and its dependence on parameters of the problem is discussed. Unexpectedly, the number of created particles depends on the duration of the cavity contracting non-monotonously. This is explained by quantum interference of the events of particle creation which are taking place only at the moments of acceleration and deceleration of a boundary, while stable particle states exist (and thus no particles are created) at the time of contracting.

quant-ph↗

arXiv2004

Damping of electromagnetic waves due to electron-positron pair production

The problem of the backreaction during the process of electron-positron pair production by a circularly polarized electromagnetic wave propagating in a plasma is investigated. A model based on the relativistic Boltzmann-Vlasov equation with a source term corresponding to the Schwinger formula for the pair creation rate is used. The damping of the wave, the nonlinear up-shift of its frequency due to the plasma density increase and the effect of the damping on the wave polarization and on the background plasma acceleration are investigated as a function of the wave amplitude.

hep-ph↗

arXiv2003

Unruh quantization in presence of a condensate

We have shown that the Unruh quantization scheme can be realized in Minkowski spacetime in the presence of Bose-Einstein condensate containing infinite average number of particles in the zero boost mode and located basically inside the light cone. Unlike the case of an empty Minkowski spacetime the condensate provides the boundary conditions necessary for the Fulling quantization of the part of the field restricted only to the Rindler wedge of Minkowski spacetime.

hep-th↗

arXiv2003

Pair creation by homogeneous electric field from the point of view of an accelerated observer

With a special choice of gauge the operator of the Klein-Fock-Gordon equation in homogeneous electric field respects boost symmetry. Using this symmetry we obtain solutions for the scalar massive field equation in such a background (boost modes in the electric field). We calculate the spectrum of particles created by the electric field, as seen by an accelerated observer at spatial infinity of the right wedge of Minkowski spacetime. It is shown that the spectrum and the total number of created pairs measured by a remote uniformly accelerated observer in Minkowski spacetime are precisely the same as for inertial observers.

hep-th↗