Attosecond electron bunch generation by an intense high-order harmonic pulse interacting with a thin target

Abstract Laser-accelerated electron bunches and the secondary radiation sources they produce exhibit a unique temporal resolution for probing ultrafast physical processes owing to their ultrashort pulse duration. The inherently short temporal profile of these pulses leads to extremely high peak bunch currents, thereby enabling a wide range of practical applications. In this study, 
 we propose and numerically investigate a method
 for generating such bunches by utilizing high-order harmonics through laser-plasma interaction as the driving pulse, which subsequently interacts with a thin target to produce an attosecond electron bunch.
 Two-dimensional particle-in-cell simulation results demonstrate that, using a driving laser with an intensity of $I_0 \approx 1.2\times10^{21}$~W/cm$^2$ (corresponding to $a_0 = 30$), it is possible to successfully generate an attosecond electron bunch exhibiting the following characteristics: 
 a duration of approximately \(100\;\mathrm{as}\),
an estimated charge on the order of a few \(\mathrm{100\;pC}\),
a geometric emittance of \(\sim4.9\times10^{-1}\;\mathrm{mm \cdot mrad}\),
and a divergence angle of \(\sim17^{\circ}\) (\(\sim0.3\;\mathrm{rad}\)).
 Moreover, by systematically analyzing the effects of laser intensity and target positioning, we identified an optimized set of simulation parameters. Under these optimal conditions, the attosecond electron bunch maintained a duration of approximately 130 as over seven laser periods. This study establishes a solid foundation for generating ultrashort electron bunches using a simple configuration and opens new prospects for their application in advanced high-energy physics and attosecond science experiments.