Nonlinear radiation pressure and stochasticity in ultraintense laser fields

Abstract

The drift acceleration due to radiation reaction for a single electron in an ultraintense plane wave (a = eE/mcω ∼ 1) of arbitrary waveform and polarization is calculated and shown to be proportional to a 3 in the high-a limit. The cyclotron motion of an electron in a constant magnetic field and an ultraintense plane wave is numerically found to be quasiperiodic even in the high-a limit if the magnetic field is not too strong, as suggested by previous analytical work. A strong magnetic field causes highly chaotic electron motion and the boundary of the highly chaotic region of parameter space is determined numerically and shown to agree with analytical predictions.PACS numbers: 52.40.Nk 52.35.MwIt has been known for many years that qualitative changes occur in the behavior of an electron moving in an electromagnetic plane wave when the dimensionless strength a = eE/mcω is of order unity. Recent advances in laser pulse compression and amplification [1] have made it possible to attain such ultraintense waves in the laboratory and led to new investigations of their properties. One important effect is that an electron moving in an ultraintense electromagnetic plane wave and also subjected to slowly varying "background" fields behaves approximately like a particle of enhanced mass mγ 0 = m 1 + e 2 A µ A µ /m 2 c 4 drifting in the background fields. Here A is the vector potential and γ 0 = 1 + a 2 /2 for a linearly polarized monochromatic wave. The fast motion in the wave can be rigorously averaged over if the background fields are sufficiently weak and the plane wave is not so strong that pair creation effects become significant.The first part of this Letter uses the guiding-center equations obtained in the derivation of the enhancedmass approximation [2] to calculate the drift acceleration of an electron in a plane wave due to the radiation damping and reaction forces. In a strong wave, the variation of the electron effective mass mγ over the wave orbit must be properly accounted for to obtain the correct drift acceleration. The average drift acceleration is the quantity of greatest interest because experiments and astrophysical phenomena typically involve many wave periods. The guiding-center equations provide the tools to carry out the averaging and determine the motion of electrons under the (previously calculated) Lorentz-Dirac radiation force [3,4]. The second part of this Letter considers the destruction of the enhanced-mass behavior and transition to stochasticity as the strength of the background fields is increased to violate the field-strength condition eB back /mcω wave ≪ 1 necessary for the enhanced-mass derivation. The breakdown of the enhanced-mass picture is shown numerically to predict the onset of stochasticity even for very strong wave intensity. Both the nonlinear radiation acceleration and the stochasticity are expected to be significant in astrophysical situations, and the first effect may well be visible in laboratory experiments with ultraintense laser pulses.Classical calculations are valid f...

Laser electron acceleration on curved surfaces

“…The acceleration takes place for the electrons which are injected into the laser field with the apporpriate initial phase. Various mechanisms of electron injection have been discussed in the literature: applied magnetic or electric fields [25][26][27][28][29], colliding laser pulses [30][31][32][33][34], superposition of traveling transverse and longitudinal waves [35] or a resonant excitation of surface plasma waves on a periodic surface structure [16,36]. Here, spontaneous magnetization may boost electron acceleration if it exceeds certain threshold value, similarly to the results in Refs.…”

“…Here, spontaneous magnetization may boost electron acceleration if it exceeds certain threshold value, similarly to the results in Refs. [26,27]. To unravel the injection mechanism, we performed a separate 3D modeling of the motion of test electrons in the given laser field with imposed constant magnetic field, with geometrical constraints simulating the target boundary.…”

Electron heating in the laser and static electric and magnetic fields

“…In this letter, we show that electron interactions with intense linearly polarized laser radiation and very general static electric and magnetic fields in a 2D slab approximation (including those considered in Refs. [1][2][3][4][5][6][7][8][9][10][11][12] can also be conveniently described in the framework of the 3/2 dimensional Hamiltonian approach. It allows us to utilize the fundamental results of previous studies on regular and stochastic motion in Hamiltonian systems (e.g., see Refs.…”

“…Some of them were the subjects of previous studies. [1][2][3][4][5][6][7][8][9][10][11][12] Case 1. We start with the case where both laser and static electric fields are in the y-direction, while the static magnetic field (depending only on the y-coordinate) is in the x-direction (similar to that considered in Refs.…”