Description
One of the most fundamental yet experimentally untested processes is the generation of electron-positron pairs through the interaction of an intense field with the quantum vacuum, i.e., the nonlinear Breit-Wheeler process. Achieving this requires field strengths surpassing the Schwinger critical limit of $1.3\times10^{18}$V/m to induce pair production directly from the vacuum [1].
To investigate pair creation via the nonlinear Breit-Wheeler process, an all-optical experimental setup has been proposed at the Centre for Advanced Laser Applications (CALA), utilizing the ATLAS-3000 laser system [2]. In the experiment, the ATLAS-3000 laser beam will be split into two parts: one beam, known as the collider laser, will have approximately 9.5 J of energy, and the other part, called the LWFA beam, with more than 25 J of energy, will be used to accelerate electron beams to energies up to 2.5 GeV for generating bremsstrahlung $\gamma$-photons that will then interact with the collider laser.
To achieve such experimental laser parameters, the division of the full 28 cm RMS diameter of the ATLAS-3000 beam can be performed in two different configurations: a D-shaped and a ring-shaped split. However, evaluating the electron accelerator's performance with both structured near-fields (NF) of the LWFA beam is still necessary to identify which splitting method delivers electron beams with stable performance and the required parameters for the pair-production experiment. To this end, we conducted an experimental campaign at the JETi-200 laser system at the Helmholtz Institute Jena to determine the optimal laser beam splitting for the pair-production experiment at CALA.
Here, we present a performance comparison between the electron beams accelerated using both proposed split methods and the full, unsplit laser beam by varying the laser normalized vector potential $a_0$. Other parameters, such as plasma electron density, pulse duration, focusing geometry, and energy before the split, were kept fixed.
[1] V. I. Ritus, J. Sov. Laser Res. 6, 5 (1985)
[2] F. C. Salgado et al., New J. Phys. 23, 105002 (2021).
