Stochastic electron heating in an interference field of several laser pulses of a picosecond duration

Abstract

Efficient electron acceleration and heating is demonstrated in a multimode structure created by interference of several laser beams of a relativistic intensity and a picosecond duration near a sharp target boundary. Electron energization proceeds in two steps, with a slow stochastic heating followed by a fast regular acceleration in a resonance interaction with one of wave packets. It results in formation of a population of energetic electrons with an exponential distribution in energy characterized by a high effective temperature and a sharp cutoff. Hot electron characteristics depend on the number of crossing laser beams and their respective angles. This process is an example of efficient electron heating in vacuum by electromagnetic fields without participation of electrostatic plasma waves. It might contribute to creation of a superthermal particle population with an effective temperature significantly exceeding the common ponderomotive scaling.

Electron dynamics in counter-propagating laser waves

“…where m ≡ k 1 /ω is the resonant harmonics, δ j i is the Kronecker symbols, and C N (α, β) is the generalized Bessel function [24,34]. Notice that similar results were obtained in [19,24] by using multidimensional Hamiltonian methods. For Px = 0, one can show that K x ≈ K2 .…”

“…For Py = 0, we see that the phase in equation ( 19) corresponding to Chirikov-like mapping is twice that in equation ( 12) for A 1 polarized along with A. As a result, the stochastic condition can be found from equations (12,19) as…”

“…One kind of direct laser acceleration is to consider electrons in multiple laser pulses [13][14][15][16][17][18][19], where the mechanism of electron acceleration can be attributed to an onset of stochasticity when the amplitudes of the perturbing (weaker) laser waves exceed some threshold values [16][17][18][19] and the maximum electron energy can be well beyond the ponderomotive scaling. It was shown that the most efficient stochastic heating is to consider two counter-propagating laser waves [17,18].…”

“…However, due to the multidimensional spatio-temporal characteristics of the laser waves and strong nonlinearity of the dynamics of relativistic electrons in these waves, the analytic investigations of stochastic electron acceleration in the colliding laser waves in earlier studies are rather limited and the approaches used are quite complicated [16,18,[21][22][23][24], while the numerical simulations, which can shed some light on the criterion for stochastic electron motion in multiple laser waves [17][18][19], are only valid within the simulated parameter range. Therefore, more complete theoretical analysis is needed to have a better understanding of the electron dynamics in the counter-propagating laser waves.…”

Novel approach to stochastic acceleration of electrons in colliding laser fields

“…The electron dynamics in counter-propagating laser waves [1][2][3] has attracted a great deal of interest, and the stochastic acceleration was thought to be the reason for high energized electron tails observed in laserplasma interaction [4][5][6][7][8][9][10]. However, due to the multidimensional spatio-temporal characteristics of the laser waves and strong nonlinearity of the dynamics of relativistic electrons in these waves, the analytic investigations of stochastic electron acceleration in the colliding laser waves in earlier studies have been limited to either non-relativistic case [4,5] or the stochastic instability near the separatrices using quite complicated multidimensional Hamiltonian approach [6,7,11].…”