2026/01/01 by Rodrigo Martín-Hernández, Melvin Redon, Ann-Kathrin Raab +9 · 1 voice
Physics and Astronomy · #Laser-Matter Interactions and Applications #Photorefractive and Nonlinear Optics #Spectroscopy and Quantum Chemical Studies
paper · doi:10.34133/ultrafastscience.0161
openalex publication_date 2026/01/01 · openalex created_date 2026/04/07 · openalex updated_date 2026/06/11
High-order harmonic generation enables the up-conversion of intense infrared or visible femtosecond laser pulses into extreme-ultraviolet attosecond pulses. However, the highly nonlinear nature of the process results in low conversion efficiency, which can be a limitation for applications requiring substantial pulse energy, such as nonlinear attosecond time-resolved spectroscopy or single-shot diffractive imaging. Refocusing of the attosecond pulses is also essential to achieve higher intensities but difficult in practice due to strong chromatic aberrations. In this work, we address both the generation and the refocusing of attosecond pulses by sculpting the driving beam into a ring-shaped intensity profile with no spatial phase variations, referred to as a hollow Gaussian beam. Our experimental and theoretical results reveal that hollow Gaussian beams efficiently redistribute the driving-laser energy in a ring-shaped area at focus, where the harmonics are generated with low divergence. In addition, unlike in standard Gaussian-driven schemes, this divergence decreases with increasing harmonic order. Although generated as a ring, our numerical simulations show that the attosecond pulses produced in such an extended area can be refocused with greatly reduced chromatic spread therefore enabling higher intensities—up to 3 times compared to those generated with Gaussian driving beams with the same Rayleigh length. This approach opens pathways for compact and powerful attosecond light sources driven by structured light beams.