Shaping attosecond pulses via high-order harmonic generation driven by two mixed Laguerre-Gaussian vortex beams

Shaping the waveform of attosecond pulses is crucial for controlling electron dynamics and is typically achieved using a high-order harmonic generation (HHG) spectrum containing a minimum. Here, we propose a novel method for shaping attosecond pulses via HHG without carrying orbital angular momentum (OAM), driven by two mixed Laguerre-Gaussian vortex beams with oppositely signed OAMs. We show that the waveform of an attosecond pulse train synthesized using low-divergent, non-vortical high harmonics in the far field can be significantly regulated; specifically, the number of emission bursts within half an optical cycle of the driving laser increases to five compared to one or two bursts in the previous studies. We also show that the spectral structure of on-axis high harmonics in the far field, as well as the waveform of the resulting attosecond pulses, can be modified by varying the position or thickness of the gas medium. Additionally, we analyze the phase-matching mechanism of near-field harmonics, which generate on-axis harmonics in the far field after propagation. Transverse and longitudinal phase-matching mechanisms are identified for thin and thick gas media, respectively. We anticipate that this work will provide new insights into expanding the applications of employing vortex beams to drive the HHG process in gas media.