Transform-Limited X-Ray Pulse Generation from a High Brightness Self-Amplified Spontaneous Emission Free-Electron Laser

TL;DR

This paper introduces a novel method for generating transform-limited X-ray pulses from a free-electron laser by using repeated electron beam delays, significantly enhancing coherence length and spectral brightness without external seeding.

Contribution

The paper presents a new HB-SASE technique that increases FEL coherence length by two orders of magnitude, enabling transform-limited pulses at various X-ray wavelengths without external seeding.

Findings

Coherence length increased by ~100x over SASE

Generation of transform-limited soft X-ray pulses

Production of near transform-limited hard X-ray pulses

Abstract

A method to achieve High-Brightness Self-Amplified Spontaneous Emission (HB-SASE) in the Free Electron Laser (FEL) is described. The method uses repeated non-equal electron beam delays to de-localise the collective FEL interaction and break the radiation coherence length dependence on the FEL cooperation length. The method requires no external seeding or photon optics and so is applicable at any wavelength or repetition rate. It is demonstrated using linear theory and numerical simulations that the radiation coherence length can be increased by approximately two orders of magnitude over SASE with a corresponding increase in spectral brightness. Examples are shown of HB-SASE generating transform-limited FEL pulses in the soft X-ray and near transform-limited pulses in the hard X-ray. Such pulses may greatly benefit existing applications and may also open up new areas of scientific research.