Tailoring electron bunch quality in laser-plasma acceleration: a comparative study of Bessel-Gaussian and Gaussian laser profiles under variable plasma density geometries

Abstract

Controlling electron injection and beam quality in laser wakefield acceleration (LWFA) requires coordinated manipulation of both the driving laser structure and the plasma density profile. In this work, a systematic particle-in-cell (PIC) study is performed to investigate how longitudinal plasma density tailoring, characterized by the high-density plateau length Lhigh, interacts with laser pulse shaping to regulate electron injection and final beam properties. Gaussian (G) and zeroth-order Bessel– Gaussian (BG) laser pulses are compared under strictly equal total laser-energy conditions using multi- section plasma density profiles. The simulations show that BG pulses promote extended and repeated injection, resulting in higher trapped charge across all investigated values of Lhigh. This enhancement is accompanied by increased beam loading, which reduces the effective accelerating field and limits the attainable peak energy. In contrast, G pulses favor more localized injection with lower trapped charge but higher peak energy and improved spectral quality, particularly when the high-density plateau is removed (Lhigh = 0). Importantly, Lhigh is identified as a robust and practical control parameter for tuning injection duration and balancing charge–energy trade-offs for both laser drivers. Despite the distinct injection dynamics, no fundamental differences in transverse emittance behavior are observed between G and BG pulses for identical plasma configurations. Instead, the emittance evolution is governed by the timing and spatial localization of injected electrons, as controlled by the tailored density geometry. These results establish a design-oriented framework in which moderate laser pulse shaping, combined with longitudinal plasma density tailoring, provides complementary and experimentally accessible pathways for optimizing beam parameters in LWFA.