Seeded x-ray free-electron laser generating radiation with laser statistical properties

TL;DR

This paper demonstrates experimentally that a seeded free-electron laser (FEL) in the XUV range exhibits laser-like statistical properties, paving the way for quantum optics applications using FEL radiation.

Contribution

It provides the first experimental evidence that seeded FELs can behave as lasers in terms of statistical properties, unlike previous chaotic FEL sources.

Findings

Seeded FELs exhibit laser-like statistical properties.

HBT interferometry confirms the laser-like behavior.

First steps towards quantum optics experiments with FELs.

Abstract

The invention of optical lasers led to a revolution in the field of optics and even to the creation of completely new fields of research such as quantum optics. The reason was their unique statistical and coherence properties. The newly emerging, short-wavelength free-electron lasers (FELs) are sources of very bright coherent extreme-ultraviolet (XUV) and x-ray radiation with pulse durations on the order of femtoseconds, and are presently considered to be laser sources at these energies. Most existing FELs are highly spatially coherent but in spite of their name, they behave statistically as chaotic sources. Here, we demonstrate experimentally, by combining Hanbury Brown and Twiss (HBT) interferometry with spectral measurements that the seeded XUV FERMI FEL-2 source does indeed behave statistically as a laser. The first steps have been taken towards exploiting the first-order coherence of FELs, and the present work opens the way to quantum optics experiments that strongly rely on high-order statistical properties of the radiation.