Pulse-duration dependence of electron acceleration and betatron radiation in tightly focused laser wakefield acceleration

Betatron X-ray sources generated via laser wakefield acceleration (LWFA) hold strong potential for diverse applications. Recent progress in tightly focused, high-intensity LWFA has enabled high-charge electron bunches and enhanced betatron radiation. Systematic experimental scans of the laser pulse duration 𝜏FWHM, a key control parameter for both acceleration and radiation, remain challenging, motivating particle-in-cell simulations. Accordingly, we simulate tightly focused laser pulses propagating in underdense plasma and show that 𝜏FWHM governs transitions between distinct interaction regimes. An optimal duration range of 20–40 fs is identified, where direct laser acceleration contributes substantially and the conversion efficiencies from laser energy to electron energy and to X-ray energy are simultaneously maximized, reaching 70% and 0.4%, respectively, at ∼ 1 PW.