Final electron distribution for both 3D simulations.
Experimental electron distribution for collision at .
Comparison between experimental data and 3D simulations results. (a) Beam energy evolution as a function of collision position. (b) Beam charge evolution as a function of collision position (only the charge in the quasimonoenergetic part is taken into account).
(a) Evolution of the peak normalized vector potential during propagation for 2D and 3D simulations with focal plan position at . (b) On-axis longitudinal electric field, at .
(a) On-axis pump pulse field at four different positions inside the plasma. (b) Corresponding pump pulse spatial shape.
Phase-space plots of electrons in a vacuum undergoing the collision of two long and positive-circularly polarized laser pulses with and . The results come from a 1D simulation. (a) During the collision: Electrons are oscillating in the potential created by the force , responsible for the periodicity. (b) After the collision: Electrons which have gained momentum during the collision are now propagating freely. The plasma has been heated by the collision.
Electron distributions as a function of the longitudinal momentum for the four polarization cases. The distributions are plotted at collision time. The collision occurs at the beginning of a homogenous plasma with a density . The laser parameters are the same as those described in Sec. II, except .
On-axis longitudinal electric field for the four polarization cases. The fields are plotted at collision time. The two vertical lines delimit the collision region. Results from the same 3D simulations as in Fig. 7.
Separatrix and trajectory of an electron initially at rest (fluid trajectory) for a given wakefield.
(a) Longitudinal momentum evolution with time of a representative test electron. The particle initially at rest undergoes the collision of two parallel linearly polarized pulses (same parameters as in Fig. 7) and will then be trapped in the wake. Its evolution is separated in three phases: (1) chaotic evolution during collision leading to a momentum gain, (2) propagation through the inhibited wakefield region, and (3) acceleration by the regular wakefield. (b) Electron phase evolution with time. The position of the pump and injection laser is added. The graphical widths of the laser pulses in the phase direction correspond to their FWHM length.
Superposition of the on-axis wakefield and of the plasma phase-space distribution after the collision. The first wake bucket is represented. Data are from a 3D simulation with collision at .
(a) Superposition of the on-axis wakefield and of the plasma phase-space distribution. The two first wake buckets are represented. (b) Plot of the corresponding energy distribution. Data are from a 3D simulation with collision at .
Comparison between three 3D simulations with different collision positions. (a) Electron distributions as a function of longitudinal momentum during collision. (b) On-axis wakefield during collision. The two vertical lines delimit the collision region. (c) Plot of the unperturbed plasma wave separatrices and the trajectories in the phase-space of particles initially at rest (fluid trajectories).
Evolution of the peak normalized vector potential during propagation for three different focal plan positions (2D simulations).
2D simulations results. Evolution of the beam parameters as a function of the collision position. Three different focal plan positions are compared. (a) Beam energy. (b) Beam charge in the quasimonoenergetic part. (c) Charge trapped in the first wake bucket.
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