Spatial and temporal coherence properties of single free-electron laser pulses

TL;DR

This paper experimentally characterizes the spatial and temporal coherence of the FLASH free-electron laser at 8.0 nm, revealing high coherence lengths and times, and a very high degeneracy parameter, surpassing other sources in the same energy range.

Contribution

It provides the first detailed measurements of spatial and temporal coherence properties of FLASH at 8.0 nm, demonstrating its exceptional coherence characteristics.

Findings

Transverse coherence length of 6.2 to 8.7 microns.

Coherence time of 1.75 femtoseconds.

Degeneracy parameter of 10^{10} to 10^{11}.

Abstract

The experimental characterization of the spatial and temporal coherence properties of the free-electron laser in Hamburg (FLASH) at a wavelength of 8.0 nm is presented. Double pinhole diffraction patterns of single femtosecond pulses focused to a size of about 10 microns by 10 microns were measured. A transverse coherence length of 6.2 microns in the horizontal and 8.7 microns in the vertical direction was determined from the most coherent pulses. Using a split and delay unit the coherence time of the pulses produced in the same operation conditions of FLASH was measured to be 1.75 fs. From our experiment we estimated the degeneracy parameter of the FLASH beam to be on the order of $10^{10}$ to $10^{11}$, which exceeds the values of this parameter at any other source in the same energy range by many orders of magnitude.