Observation of harmonic lasing in the Angstrom regime at European XFEL

TL;DR

This paper reports the first demonstration of harmonic lasing at the European XFEL, including cascaded harmonic lasing, enabling access to higher photon energies up to 100 keV with improved beam properties.

Contribution

It presents the first successful operation of harmonic lasing cascade at an XFEL, extending the photon energy range and demonstrating new capabilities for high-energy X-ray generation.

Findings

Harmonic lasing achieved at 5.9 Å and 2.8 Å.

First operation of a harmonic lasing cascade (5th-3rd-1st).

Potential to reach photon energies up to 100 keV.

Abstract

Harmonic lasing provides an opportunity to extend the photon energy range of existing and planned X-ray FEL user facilities. Contrary to nonlinear harmonic generation, harmonic lasing can generate a much more intense, stable, and narrow-band FEL beam. Another interesting application is Harmonic Lasing Self-Seeding (HLSS) that allows to improve the longitudinal coherence and spectral power of a Self-Amplified Spontaneous Emission (SASE) FEL. This concept was tested at FLASH in the range of 4.5 - 15 nm and at PAL XFEL at 1 nm. In this paper we present recent results from the European XFEL where we successfully demonstrated harmonic lasing at 5.9 Angstrom and 2.8 Angstrom. In the latter case we obtained both 3rd and 5th harmonic lasing and, for the first time, operated a harmonic lasing cascade (5th-3rd-1st harmonics of the undulator). These results pave the way for reaching very high photon energies, up to 100 keV.