Compact, intense attosecond sources driven by hollow Gaussian beams

TL;DR

This paper demonstrates that using hollow Gaussian beams to drive high-order harmonic generation improves the efficiency and refocusing of attosecond pulses, enabling more powerful, compact attosecond light sources for advanced applications.

Contribution

The study introduces a novel method of shaping the driving laser into hollow Gaussian beams to enhance attosecond pulse generation and refocusing, reducing chromatic aberrations and increasing pulse energy.

Findings

HGBs efficiently redistribute laser energy in focus

Attosecond pulses generated on a ring with low divergence

Refocused attosecond pulses reach higher intensity

Abstract

High-order harmonic generation (HHG) 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 a high intensity, 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 (HGB). Our experimental and theoretical results reveal that HGBs efficiently redistribute the driving laser energy in the focus, where the harmonics are generated on a ring with low divergence, which furthermore decreases with increasing order. Although generated as a ring, the attosecond pulses can be refocused with greatly reduced chromatic spread, therefore reaching higher intensity. This approach enhances the intensity of refocused attosecond pulses and enables significantly higher energy to be delivered in the driving beam without altering the focusing conditions. These combined advantages open pathways for compact, powerful, tabletop, laser-driven attosecond light sources.