This paper uses particle-in-cell simulations and multi-objective Bayesian optimization to improve the efficiency and beam quality of laser wakefield acceleration. The authors focus on moderately short, sub-petawatt laser pulses and laser defocusing injection, which can create nanocoulomb electron bunches with an initially negative chirp. During subsequent acceleration the bunch undergoes an automatic two-step dechirping process, producing small energy spread without sacrificing charge. Optimization over laser and plasma parameters identifies a broad operating region with 10--30% laser-to-beam energy-transfer efficiency and percent-level energy spread. A representative case produces a roughly 420 MeV, 5.5 nC beam with 2% RMS energy spread using an 8.3 J, 7.2 fs laser pulse. The work argues that short-pulse operation and automated multi-objective search can jointly address efficiency, charge, and energy-spread constraints for compact accelerator applications.
- Demonstrated high-efficiency laser wakefield acceleration with moderately short laser pulses.
- Identified laser defocusing injection as a route to nanocoulomb, initially chirped electron beams.
- Explained the two-step dechirping mechanism that narrows the final energy spread.
- Used multi-objective Bayesian optimization to search the coupled laser-plasma design space.
- Reported operating points with high charge, percent-level energy spread, and up to 28% transfer efficiency.