Positronium in intense laser fields

The dynamics and radiation of positronium is investigated in intense laser fields.Comment: 13 pages, 3 figure

Microscopic laser-driven high-energy colliders

The concept of a laser-guided $e^+e^-$ collider in the high-energy regime is presented and its feasibility discussed. Ultra-intense laser pulses and strong static magnetic fields are employed to unite in one stage the electron and positron acceleration and their head-on-head collision. We show that the resulting coherent collisions in the GeV regime yield an enormous enhancement of the luminosity with regard to conventional incoherent colliders

Semi-classical limitations for photon emission in strong external fields

The semi-classical heuristic emission formula of Baier-Katkov [Sov. Phys. JETP \textbf{26}, 854 (1968)] is well-known to describe radiation of an ultrarelativistic electron in strong external fields employing the electron's classical trajectory. To find the limitations of the Baier-Katkov approach, we investigate electron radiation in a strong rotating electric field quantum mechanically using the Wentzel-Kramers-Brillouin approximation. Except for an ultrarelativistic velocity, it is shown that an additional condition is required in order to recover the widely used semi-classical result. A violation of this condition leads to two consequences. First, it gives rise to qualitative discrepancy in harmonic spectra between the two approaches. Second, the quantum harmonic spectra are determined not only by the classical trajectory but also by the dispersion relation of the effective photons of the external field

Electron Polarization in Ultrarelativistic Plasma Current Filamentation Instabilities

Plasma current filamentation of an ultrarelativistic electron beam impinging on an overdense plasma is investigated, with emphasis on radiation-inducedelectron polarization. Particle-in-cell simulations provide the classification and in-depth analysis of three different regimes of the current filaments, namely, the normal filament, abnormal filament, and quenching regimes. We show that electron radiative polarization emerges during the instability along the azimuthal direction in the momentum space, which significantly varies across the regimes. We put forward an intuitive Hamiltonian model to trace the origin of the electron polarization dynamics. In particular, we discern the role of nonlinear transverse motion of plasma filaments, which induces asymmetry in radiative spin flips, yielding an accumulation of electron polarization. Ou results break the conventional perception that quasi-symmetric fields are inefficient for generating radiative spin-polarized beams, suggesting the potential of electron polarization as a source of new information on laboratory and astrophysical plasma instabilities

Polarization operator approach to electron-positron pair production in combined laser and Coulomb fields

The optical theorem is applied to the process of electron-positron pair creation in the superposition of a nuclear Coulomb and a strong laser field. We derive new representations for the total production rate as two-fold integrals, both for circular laser polarization and for the general case of elliptic polarization, which has not been treated before. Our approach allows us to obtain by analytical means the asymptotic behaviour of the pair creation rate for various limits of interest. In particular, we consider pair production by two-photon absorption and show that, close to the energetic threshold of this process, the rate obeys a power law in the laser frequency with different exponents for linear and circular laser polarization. With the help of the upcoming x-ray laser sources our results could be tested experimentally.Comment: 10 pages, 3 figure

High-brilliance ultra-narrow-band x-rays via electron radiation in colliding laser pulses

A setup of a unique x-ray source is put forward employing a relativistic electron beam interacting with two counter-propagating laser pulses in the nonlinear few-photon regime. In contrast to Compton scattering (CS) sources, the envisaged x-ray source exhibits an extremely narrow relative bandwidth of $10^{-5}$ to $10^{-4}$, comparable to the x-ray free-electron laser (XFEL). The brilliance of the x-rays can be $2 - 3$ orders of magnitude higher than a state-of-the-art CS source, while the angle spreading of the radiation is much smaller. By tuning the laser intensities and the electron energy, one can realize either a single peak or a comb-like x-ray source around keV energy. The laser intensity and the electron energy in the suggested setup are rather moderate, rendering this scheme compact and table-top size, as opposed to XFEL and synchrotron infrastructures

Ultrarelativistic electrons in counterpropagating laser beams

The dynamics and radiation of ultrarelativistic electrons in strong counterpropagating laser beams are investigated. Assuming that the particle energy is the dominant scale in the problem, an approximate solution of classical equations of motion is derived and the characteristic features of the motion are examined. A specific regime is found with comparable strong field quantum parameters of the beams, when the electron trajectory exhibits ultrashort spike-like features, which bears great significance to the corresponding radiation properties. An analytical expression for the spectral distribution of spontaneous radiation is derived in the framework of the Baier-Katkov semiclassical approximation based on the classical trajectory. All the analytical results are further validated by exact numerical calculations. We consider a non-resonant regime of interaction, when the laser frequencies in the electron rest frame are far from each other, avoiding stimulated emission. Special attention is devoted to settings when the description of radiation via the local constant field approximation fails and to corresponding spectral features. Periodic and non-periodic regimes are considered, when lab frequencies of the laser waves are always commensurate. The sensitivity of spectra with respect to the electron beam spread, focusing and finite duration of the laser beams is explored.Comment: 23 papes, 10 figure

Ultra-strong laser pulses: streak-camera for gamma-rays via pair production and quantum radiative reaction

We show that a strong laser pulse combined with a strong x-ray pulse can be employed in a detection scheme for characterizing high-energy $\gamma$-ray pulses down to the zeptosecond timescale. The scheme employs streak imaging technique built upon the high-energy process of electron-positron pair production in vacuum through the collision of a test pulse with intense laser pulses. The role of quantum radiation reaction in multiphoton Compton scattering process and limitations imposed by it on the detection scheme are examined