Statistical properties of the radiation from SASE FEL operating in a post-saturation regime with and without undulator tapering

TL;DR

This paper analyzes the statistical and coherence properties of SASE XFEL radiation in the post-saturation regime, comparing effects of undulator tapering on efficiency and coherence.

Contribution

It provides a detailed comparison of XFEL performance with and without undulator tapering in the post-saturation regime, focusing on practical European XFEL parameters.

Findings

Tapering improves efficiency and coherence properties.

Post-saturation regime maintains significant coherence.

Undulator tapering enhances X-ray FEL performance.

Abstract

We describe statistical and coherence properties of the radiation from x-ray free electron lasers (XFEL) operating in the post-saturation regime. We consider practical case of the SASE3 FEL at the European XFEL. We perform comparison of the main characteristics of the X-ray FEL operating in the post-saturation regime with and without undulator tapering: efficiency, coherence time and degree of transverse coherence.