Plenary sessions

Few-fs to as X-ray pulses at the European XFEL: characterization and applications 

Tommaso Mazza, Scientist in Gas Phase Soft X-Ray Physics , Scientific Instrument SQS, European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Germany

tommaso.mazza@xfel.eu

Abstract: X-ray Free Electron lasers (XFELs) are light sources with brilliance exceeding third generation synchrotrons by several orders of magnitude, delivering pulses made of many X-ray photons and with very short durations.

Pulse durations reaching down to the sub-femtosecond regime, implemented in pump-probe setups either exploiting multipulse delivery schemes or synchronized external sources, give access to the natural time scale of electronic motion. This opens the way to extending time-resolved experiments from the recording of molecular movies which capture nuclear dynamics by means of different probes, to measurements in which electronic movies with the appropriate time resolution can be recorded, or even electronic control can be exerted.

The exceptionally high x-ray pulse energies which can be delivered by FELs, on the other hand, pushed already in early stages the quest for observing strong field effects at nm-sized wavelengths. It can be shown that effective access to the corresponding high intensity conditions can only be obtained with attosecond pulses, in a similar manner as decades ago sub-ps pulses gave access to strong field pheonomenology in the optical regime.

With the first generation ever of isolated attosecond pulses by HHG process dating back only 20 years, attosecond science is still in its infancy, with the most prolific efforts dedicated to the investigation of light generation mechanisms. FEL scientists belong well in the photonics community; yet, due to their well defined user-oriented mission, FELs have also a strong drive towards the development of a standard delivery of sub-fs x-ray pulses for user operation.

In my contribution I will report on the experience at the European XFEL with the use of sub-fs x-ray pulses delivered by the FEL undulators. I will briefly tell on the generation technique and I will then describe the metrology approaches we developed and implemented for their characterization. Finally, I will show some results on first applications and will discuss the scientific perspectives of the current developments.

Tommaso Mazza is Senior Instrument Scientist at the Small Quantum Systems Instrument at the European XFEL. After his PhD at the University of Milan (2007) he dedicated to studies on isolated metal clusters designing and performing experiments with optical lasers, synchrotron and FEL sources as post-doc at the University of Milan and visiting scientist at the IMRAM institute in Japan. In 2011 he joined the European XFEL, dedicating to the development of the SQS instrument from the very beginning, and extending his scientific activities to the study of atomic and molecular systems.

He currently has a senior role in the SQS group with advanced expertise on x-ray beam transport and diagnostics, ion and electron spectroscopy. His research activities focus on non-linear interaction of atoms with x-rays, molecular dynamics upon photoexcitation, structural dynamics of complex metal clusters, and metrology techniques for FEL sources.

Challenges for intense and compact Compton sources - First X-ray production at ThomX

ThomX collaboration, Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 ORSAY, France

marie.jacquet@ijclab.in2p3.fr 

Abstract: Currently, there are increasing demands for access to bright, tunable, monochromatic X-ray sources in the fields of medicine (imaging and therapy), cultural heritage studies and preservation, and industrial applications (materials science). Synchrotrons are the best light sources in terms of energy tuning and brightness but there are strong constraints on their use and diffusion, such as their size, construction and operating costs and the high demand for beam times. Thanks to the increasing power of lasers, for a moderate cost and dimensions compatible with an experimental hall, compact Compton scattering sources can now provide a quasi-monochromatic X-ray beam of high flux and high brightness, compared to current laboratory sources (X-ray tubes). 

The French project ThomX is a demonstrator of such a source. The machine is installed at the Irène Joliot-Curie laboratory (IJCLab) on the Orsay campus of Université Paris-Saclay and is designed to produce a total average flux of 10^12-10^13 ph/s in an energy range from 45 keV to 90 keV with an average brightness of 10^10-10^11 ph/s /mm2/mrad2/0.1%bw. To achieve these performances, the electron bunches and laser pulses are stored respectively in a storage ring and a high-gain Fabry-Perot cavity. The first X-rays were produced in July 2023.

In this context, I will start by introducing the state of the art of the compact high-flux Compton sources, then I will give an overview of the ThomX source, from its construction to its commissioning, and outline the latest results and next steps to reach nominal flux.

During her PhD in the 90s and until the 2010s, Marie Jacquet carried out research in high-energy physics at large particle colliders (simulations of Standard Model processes, search for new particles, detector calibration, data analysis, Compton polarimetry): at the Large Electron-Positron Collider (LEP) at CERN, then at the Hadron-Electron Ring Accelerator (HERA) in Hamburg.

From the 2010s, she works on the Compton polarimeter at HERA and the expertise of the IJCLab laboratory in this area brought her to the field of Compton X-ray sources, then led her to join the ThomX project carried out by IJCLab (formerly LAL). Today, Marie Jacquet is the scientific manager of ThomX.