Self-Seeded Free-Electron Lasers with Orbital Angular Momentum

TL;DR

This paper introduces a novel self-seeded free-electron laser technique to generate high-power x-ray beams with orbital angular momentum, overcoming optical challenges at high intensities.

Contribution

A new self-seeded FEL method that uses an optical element to generate and amplify OAM in x-ray beams, reducing thermal load and enabling high-power OAM pulses.

Findings

OAM seed pulse power can be amplified by over 100 times

Generated OAM pulses reach peak powers of tens of gigawatts

Method enables high-repetition-rate, high-power OAM x-ray pulses

Abstract

X-ray beams carrying orbital angular momentum (OAM) are an emerging tool for probing matter. Optical elements, such as spiral phase plates and zone plates, have been widely used to generate OAM light. However, these optics are challenging to use at x-ray free-electron lasers (XFELs) due to the high impinging intensities. Here, we propose a self-seeded FEL method to produce intense x-ray vortices. Unlike passive filtering after amplification, an optical element will be used to introduce the helical phase in the linear regime, significantly reducing the thermal load on the optical element. The generated OAM pulse is then used as a seed and significantly amplified. Theoretical analysis and numerical simulations demonstrate that the power of the OAM seed pulse can be amplified by more than two orders of magnitude, reaching peak powers of several tens of gigawatts. The proposed method paves the way for high-power and high-repetition-rate OAM pulses of XFEL light.