Three dimensional particle-in-cell simulations of electron beams created via reflection of intense laser light from a water target

Abstract

We present 3D Particle-in-Cell (PIC) modeling of an ultra-intense laser experiment by the Extreme Light group at the Air Force Research Laboratory (AFRL) using the PIC code LSP. This is the first time PIC simulations have been performed in 3D for this experiment which involves an ultra-intense, short-pulse (30 fs) laser interacting with a water jet target at normal incidence. These 3D PIC simulation results are compared to results from 2D(3v) PIC simulations for both 5.4 • 10 17 W cm −2 and 3 • 10 18 W cm −2 intensities. Comparing the 2D(3v) and 3D simulation results, the laser-energyto-ejected-electron-energy conversion efficiencies were comparable, but the angular distribution of ejected electrons show interesting differences with qualitative differences at higher intensity. An analytic plane-wave model is discussed which provides some explanation for the angular distribution and energies of ejected electrons in the 2D(3v) simulations. We also performed a 3D simulation with circularly polarized light and found a significantly higher conversion efficiency and peak electron energy, which is promising for future experiments.

Particle-in-cell simulations of electron acceleration from relativistic interaction of mid-infrared laser interactions with near solid density matter

“…Because of the similarity to earlier work in Ref. 2, it is unsurprising that the model compares favorably to the 780 nm results shown in Fig. 2.…”

“…Ponderomotive steepening was also present in the 3D PIC simulations of near-IR-laser interactions that we published in Ref. 2, although for brevity, we did not highlight this result. Figure 5 provides essentially the first compelling evidence that this effect should persist in mid-IR experiments of this kind.…”

“…We also overplot with solid lines the results from an analytic model described in Ref. 2. This model considers that the back-directed electrons are ejected at high speed into a pulsed plane wave that approximates the reflected laser pulse.…”

“…For all simulations, the initial conditions included a liquid-density water slab target with some assumed pre-plasma scale length similar to earlier studies. 1,2 In all simulations, a laser is normally incident onto the water slab. We use the following Cartesian coordinate system for these simulations: the positive x-axis is the direction of the laser, the y-axis is the polarization direction, and the z-axis is the axis of the water column, which is assumed to be the axis of symmetry in the 2D(3v)/ PIC simulations.…”

Relativistic electron acceleration by mJ-class kHz lasers normally incident on liquid targets

“…In the presently studied case of normal-incidence laser-target interaction, p-polarization-dependent electron acceleration mechanisms are suppressed. However, three recently published experimental and computational papers [18][19][20] have demonstrated how a wide spray (±40 • cone) of electrons can be accelerated to >120 keV with 1.5% laserto-electron energy conversion efficiency in the laser reflection direction for few-mJ, 10 18 W cm −2 , normal-incidence interactions. A standing wave and direct laser acceleration theoretical framework was developed in Orban et al [19] to provide a physical interpretation of this normal-incidence, extremely-high-efficiency electron acceleration by a mJ-class relativistic laser.…”