Statistical and coherence properties of radiation from X-ray free electron lasers

TL;DR

This paper analyzes the statistical and coherence properties of X-ray free electron laser radiation, revealing universal scaling laws and Gaussian behavior before saturation, with implications for optimizing FEL performance.

Contribution

It introduces universal scaling relations for key FEL characteristics in the saturation regime based on numerical simulations and similarity techniques.

Findings

Gaussian statistics of FEL radiation before saturation

Universal scaling relations for efficiency, coherence time, and transverse coherence

Statistical properties of higher harmonics

Abstract

We describe statistical and coherence properties of the radiation from x-ray free electron lasers (XFEL). It is shown that the X-ray FEL radiation before saturation is described with gaussian statistics. Particularly important is the case of the optimized X-ray FEL, studied in detail. Applying similarity techniques to the results of numerical simulations allowed us to find universal scaling relations for the main characteristics of an X-ray FEL operating in the saturation regime: efficiency, coherence time and degree of transverse coherence. We find that with an appropriate normalization of these quantities, they are functions of only the ratio of the geometrical emittance of the electron beam to the radiation wavelength. Statistical and coherence properties of the higher harmonics of the radiation are highlighted as well.