High-order harmonic generation with radially chirped annular beams in the overdriven regime: Spectral extension and coherent high-flux radiation
Phys. Rev. A 112, 013505 – Published 2 July, 2025
DOI: https://doi.org/10.1103/95xh-351z
Abstract
High-order harmonic generation (HHG) with simultaneously high energy and high photon flux remains a fundamental challenge in strong-field physics. In this study, we introduce a method employing radially chirped annular (RCA) beams to significantly enhance HHG efficiency and coherence. RCA beams, which enable symmetric simultaneous spatio-temporal focusing with precise control, satisfy the essential requirements for efficient HHG: they can maximize laser intensity at the target while spatially separating the driving field from the harmonics in the far field. The 2D 1 carrier-resolved pulse propagation simulations demonstrate that, in the presence of plasma-induced defocusing, the RCA beam resists lateral spreading and maintains a more consistent phase front across the beam due to its spatio-spectral structure. Interestingly, the beam profile also exhibits dual chirp behavior, with positive chirping observed on axis and negative chirping off axis. RCA-driven harmonics demonstrate position-independent yield stability relative to the focal point, while remaining highly structured, broader in spectrum, more intense, and less divergent than those generated with conventional Gaussian beams. Moreover, harmonics achieve more spectral extension in the cutoff region and can generate attosecond pulses with durations nearly twice as short and intensities 1.5 times higher than conventional methods, along with enhanced phase stability across the generated harmonics. These findings suggest RCA beams hold strong potential for applications requiring high-flux coherent extreme ultraviolet and soft-x-ray radiation, opening transformative possibilities for advancing attosecond science and ultrafast spectroscopy.
