Among the fourth-generation light sources, the Italian free-electron laser (FEL) FERMI is the only one operating in the high-gain harmonic generation (HGHG) seeding mode. FERMI delivers pulses characterized by a quasi transform limited temporal structure, photon energies lying in the extreme ultra-violet (EUV) region, supreme transversal and longitudinal coherences, high peak brilliance, and full control of the polarization. Such state of the art performances recently opened the doors to a new class of time-resolved spectroscopies, difficult or even impossible to be performed using self-amplified spontaneous sources (SASE) light sources. FERMI is currently equipped with three operating beamlines opened to external users (DiProI, LDM and EIS), while two more are under commissioning (MagneDYN and TeraFERMI). Here, we present the recent highlights of the EIS (Elastic and Inelastic Scattering) beamline, which has been purposely designed to take full advantage from the coherence, the intensity, the harmonics content, and the temporal duration of the pulses. EIS is a flexible experimental facility for time-resolved EUV scattering experiments on condensed matter systems, consisting of two independent end-stations. The first one (EIS-TIMEX) aims to study materials in metastable and warm dense matter (WDM) conditions, while the second end-station (EIS-TIMER) is fully oriented to the extension of four-wave mixing (FWM) spectroscopies towards the EUV spectral regions, trying to reveal the behavior of matter in portions of the mesoscopic regime of exchanged momentum impossible to be probed using conventional light sources.
The development of free electron laser (FEL) sources, which provide extreme ultraviolet (XUV) and soft x-ray radiation
of unprecedented coherence and almost transform-limited pulse structure, has opened up the realm of XUV/x-ray
non-linear optics. In particular, XUV four-wave-mixing (XFWM) experiments may allow, e.g., to probe correlations
among low-energy excitations and core states, and to access the “mesoscopic” wavevector range (0.1-1 nm-1), inaccessible
so far and fundamental to investigate nanostructures and disordered systems. In this manuscript we report on the latest
advances and future developments of the TIMER setup at FERMI (Elettra, Italy), specifically conceived for XFWM
experiments. In particular, we discuss the improvements on the XUV-probe and on the pump transport. Moreover, TIMER
and mini-TIMER (a test setup available at the DiProI end station) are also suitable for time-resolved second order nonlinear
experiments, which are intrinsically surface sensitive due to symmetry restrictions. We hereby discuss the foreseen
extension to the XUV of interface specific probing of electronic processes, for example charge and energy transfer, with
In this manuscript we report on a compact experimental set-up (“mini-TIMER”) conceived for transient grating (TG) experiments based on free electron laser (FEL) radiation. This set-up has been tested at the seeded FEL facility FERMI (Elettra, Trieste, Italy) and allowed us to observe the first FEL-stimulated TG signal. This experimental result is of the greatest relevance in the context of developing coherent non-linear optical methods into the extreme ultraviolet (EUV) and soft X-ray (SXR) range. Such a challenging task will be addressed in the next future at FERMI by using the present set-up and the forthcoming EIS-TIMER beamline, which is being installed at FERMI and will start the commissioning phase in the second semester 2015. The possibility to use TGs generated by FEL radiation at sub-optical wavelengths would allow developing EUV/SXR four-wave-mixing (FWM) applications, so far considered only theoretically and widely believed to be potentially able to provide major breakthroughs in several fields of science.
We describe the method of Heterodyne Near Field Speckles (HNFS) for the characterization of spatial and temporal coherence of radiation. The method relies on the statistical properties of the speckle field produced by spherical particles randomly distributed and suspended in a fluid. We report preliminary results obtained with broadband light sources. We discuss the results obtained with the Self-Amplified Spontaneous Emission free electron laser SPARC LAB. This method will enable to calibrate and realize a diagnostics for the X-ray, broadband betatron radiation emitted in laser-plasma accelerators.
FERMI is the first seeded EUV-SXR free electron laser (FEL) user facility operated at Elettra Sincrotrone
Trieste. Two of the three already operating beamlines, namely LDM (Low DensityMatter) and DiProI (Diffraction
and Projection Imaging), use a Kirkpatrick-Baez (K-B) active X-ray optics system for focusing the FEL
pulses onto the target under investigation. The present work reports on the final results obtained from the
optimization of the K-B optical system at the DiProI endstation. The aim of the optimization is to improve the
system performances in terms of quality and size of the focal spot onto the sample, controlling the fluence as
well. To characterize the performances and develop reliable and reproducible focusing procedures we performed
a campaign of measurements with several diagnostic systems, including a wavefront sensor mounted after the
DiProI chamber. Online wavefront measurements have made possible the optimization of the bending acting
on the mirror curvature and of the (pitch and roll) angle positions of the K-B system. From the wavefront
measurements we have inferred a focal spot of 8 μm x 9.5 μm, confirmed by the PMMA ablation imprints. The
experimental results are compared with the predictions from simulations obtained using the WISE code, starting
from the characterization of the actual mirror surface metrology. The results from simulations are in agreement
with the experimental measurements. Filtering the Fourier transform of the mirror surface profiles, using the
WISE code we have analyzed the impact of different spatial wavelengths on the focal spot degradation. For
different energies of the incident beam we established the threshold where the focal spot degradation is no longer
affected by the spatial wavelengths of the K-B mirror surfaces.
In the very last period we were starting to observe a degradation of the focal spot. After a metrology analysis
we concluded that the problem was due to a failure of the substrate material. We temporally solved the problem
checking the mounting, but we have planned an improvement of the material for the future.
Conference Committee Involvement (1)
Adaptive X-Ray Optics V
19 August 2018 | San Diego, California, United States