Variable coherence model for free-electron laser pulses

TL;DR

The paper presents the variable coherence model (VCM) for simulating FEL pulses, enabling continuous control over pulse noise characteristics while maintaining fixed average parameters, through systematic statistical analysis.

Contribution

It introduces a novel VCM that allows adjustable coherence width in FEL pulse simulations, extending prior models with continuous noise control capabilities.

Findings

VCM can generate FEL pulses from maximally random to fully coherent.

Statistical analyses show how coherence width affects sub-pulse properties.

Application to absorption simulation demonstrates VCM's practical relevance.

Abstract

We introduce the variable coherence model (VCM) for simulating free-electron laser (FEL) pulses generated through self-amplified spontaneous emission. Building on the established partial coherence model of [T. Pfeifer et. al, Opt. Lett. 35, 3441 (2010)], we demonstrate that the implementation of a variable coherence width allows for continuous control over the pulses' characteristic noise, while keeping the average pulse parameters such as the bandwidth fixed. We demonstrate this through systematic statistical analyses of the intensity and number of sub-pulses in VCM pulses, in both time and frequency. In particular, we analyze how the sub-pulse statistics are affected by the coherence width parameter. We perform our analyses across three distinct regimes of FEL parameters and demonstrate how the VCM can generate pulses that range from maximally random to fully coherent. Finally, we illustrate the effect of the VCM variable coherence width on an absorption simulation.