Study of quasimonoenergetic electron bunch generation in self-modulated laser wakefield acceleration using TW or sub-TW ultrashort laser pulses

Abstract

This work presents a study on laser wakefield electron acceleration in the self-modulated regime (SM-LWFA) using 50-fs laser pulses with energy on the mJ scale, at λ = 0.8 μm, impinging on a thin H 2 gas jet. Particle-in-cell simulations were performed using laser peak powers ranging from sub-terawatt to a few terawatts and plasma densities varying from the relativistic self-focusing threshold up to values close to the critical density. The differences in the obtained acceleration processes are discussed. Results show that bunched electron beams with full charge on the nC scale and kinetic energy in the MeV range can be produced and configurations with peak density in the range 0.5-5 × 10 20 atoms/cm 3 generate electrons with maximum energies. In this range, some simulations generated quasimonoenergetic bunches with ∼0.5% of the total accelerated charge and we show that the beam characteristics, process dynamics, and operational parameters are close to those expected for the blowout regime. The configurations that led to quasimonoenergetic bunches from the sub-TW SM-LWFA regime allow the use of laser systems with repetition rates in the kHz range, which can be beneficial for practical applications.

Creation and spatial-temporal characterization of gas targets and plasmas for laser-electron acceleration

“…In 2021, our research group and collaborators published a work [58] using PIC simulations to study the generation of MeV electron bunches in the SM-LWFA regime, driven by a few TW and sub-TW laser pulses. This kind of investigation had already been explored by our group since 2017, motivating the work described in this PhD thesis, and resulting in publications in international conference proceedings [111,112] .…”

“…For the simulations of interest for this work, the ramps are 80 μm long, and the plateau has 40 µm, defining a total diameter of 200 µm with 120 µm of FWHM, as shown by the blue line in Figure 3.2. The published work [58] studied the acceleration as a function of the plateau electron density after ionization (among other parameters), and in Figure 3.2shows the case for 6 = 2×10 20 cm -3 , along with the corresponding local plasma wavelength (red dashed line, disregarding local relativistic and density variation effects during the pulse propagation).…”

“…Furthermore, once there is only an ionization per atom, the plasma density 6 should be the same as the neutral gas molecular density Y for saturated ionization. Source: Adapted from MALDONADO, E. P., et al [58] .…”

“…Another alternative to generate MeV electron bunches with peak powers of a few TW at kHz operation rates is the self-modulated LWFA (SM-LWFA) regime [55,56,57] , with the additional advantage of not requiring laser pulse compression to a few fs in contrast to the LWFA using few cycle pulses. The SM-LWFA can generate bunches with a total charge in the nC range (two orders of magnitude higher than LWFA) [58,59] , which makes these bunches attractive for applications where a high dose of radiation is required [59,60,61] . Promising results showed recently the possibility of accelerating electron bunches to MeV using a laser with peak powers as low as 40 GW and pulse energy of ~1.3 mJ [62] .…”

“…Particle-in-cell (PIC) simulations have been showing us the possibility to generate tens of MeV electron bunches by SM-LWFA, using TW or sub-TW laser pulses and gaseous targets with submillimetric dimensions [58,111,112,113,114] . In addition to computational PIC simulation support, we are currently focusing efforts on several developments required for a LWFA installation, such as a source of high-peak-power laser pulses [115] , proper gaseous and plasma target creation [116,117] , and development and implementation of diagnostic tools to assist and monitor the experiments [118,119] .…”