Longitudinal space charge assisted echo seeding of a free-electron laser with laser-spoiler noise suppression

Kirsten Hacker

doi:10.1103/physrevstab.17.090702

Abstract

Seed lasers are employed to improve the temporal coherence of free-electron laser (FEL) light. However, when these seed pulses are short relative to the particle bunch, the noisy, temporally incoherent radiation from the unseeded electrons can overwhelm the coherent, seeded radiation. In this paper, a technique to seed a particle bunch with an external laser is presented in which a new mechanism to improve the contrast between coherent and incoherent free electron laser radiation is employed together with a novel, simplified echo-seeding method. The concept relies on a combination of longitudinal space charge wakes and an echo-seeding technique to make a short, coherent pulse of FEL light together with noise background suppression. Several different simulation codes are used to illustrate the concept with conditions at the soft x-ray free-electron laser in Hamburg, FLASH.

Highlights

Short-wavelength, high-brightness light sources, like free-electron lasers (FELs) driven by particle accelerators, are in demand for experiments studying ultrafast processes in matter
When the temporal coherence of FEL light is determined by the shot noise of an electron beam, as in self-amplified spontaneous emission (SASE), it is poor [13,14,15], but if it is determined by an external seed laser, the FEL light takes on the excellent temporal coherence properties of the external laser in the region that has been seeded
The electron bunch would be much longer than the femtosecond duration seed, so that with the best observed 25 fs synchronization between electron beam and external laser in an FEL facility [16], the seed laser would hit the electron bunch on every shot, but a

Summary

Introduction

Short-wavelength, high-brightness light sources, like free-electron lasers (FELs) driven by particle accelerators, are in demand for experiments studying ultrafast processes in matter. The seeding method described in this paper combines seeded LSCA SASE suppression with a short, echo-seeded pulse of temporally coherent FEL radiation.

Results

Conclusion