Effects of Preplasma Scale Length and Laser Intensity on the Divergence of Laser-Generated Hot Electrons

Abstract

We report on a numerical study of the effects of preplasma scale length and laser intensity on the hot-electron (≥1 MeV) divergence angle using full-scale 2D3V (two dimensional in space, three dimensional in velocity) simulations including a self-consistent laser-plasma interaction and photoionization using the particle-in-cell code LSP. Our simulations show that the fast-electron divergence angle increases approximately linearly with the preplasma scale length for a fixed laser intensity. On the other hand, for a fixed preplasma scale length, the laser intensity has little effect on the divergence angle in the range between 10(18) and 10(21) W/cm(2). These findings have important implications for the interpretation of experimental results.

Effects of front-surface target structures on properties of relativistic laser-plasma electrons

“…Consequently there have been numerous efforts to increase the number and energy of the hot electrons as well as to increase the efficiency of the conversion of laser energy into hot electron energy. Most of these studies have emphasized the role of the laser pulse energy, duration, and intensity [7][8][9][10]; in addition, there is a robust literature describing the effect on electron energy of a "pre-plasma" on the front of the target [11][12][13].…”

Collimated fast electron beam generation in critical density plasma

“…Especially the magnetic field is known to function as an electron collimator [28][29][30] or scatterer. 26,27 Here, we explain the collimation mechanism as the result of the magnetic field.…”

“…This difference could be due to the scale length of the preplasma used in the PIC (1 lm). 26,27 Longer preplasma will produce electrons with a larger divergence due to Weibel instability growth. Figure 3(b) shows the electron energy spectra for both target cases from the simulation.…”

Effects of filamentation instability on the divergence of relativistic electrons driven by ultraintense laser pulses

“…The divergence measured in the experiments usually increases with laser intensity 10 , though some discrepancy exists among the different diagnostic techniques because each one is dependent on different parameters 11 . However, recent PIC simulations show that the RE divergence is approximately linearly proportional to the preplasma scale length for a fixed laser intensity, but is weakly dependent on the laser intensity for a fixed preplasma 12 . For a normally incident laser, the electron injection angle θ i = tan −1 √ 2/(γ − 1) is obtained from the electron's trajectory in an intense electromagnetic wave 13 , where γ is the electron relativistic factor.…”