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
Stimulated emission is a fundamental process in nature that deserves to be investigated and understood in the EUV and X-ray regimes. Today this is definitely possible through high energy density FEL beams. In this context, we show evidence for soft x-ray stimulated emission from a MgO solid target pumped by extreme ultraviolet FEL pulses formed in the regime of travelling-wave amplified spontaneous emission in backward geometry. Our results combine two effects separately reported in previous works: emission in a privileged direction and existence of a material-dependent threshold, for the stimulated emission. We have developed a theoretical framework, based on coupled rate and transport equations taking into account the solid density plasma state of the target. Our model, accounts for both observed mechanisms that are the privileged direction for the stimulated emission of the Mg L2,3 characteristic emission and the pumping threshold.
Extreme Ultraviolet (EUV) multilayer (ML) technology has been intensively applied in many scientific and technological fields such as solar physics and photolithography. More recently, the advent of free electron lasers (FEL) emitting bright sub-ps pulses with very high quality in term of intensity stability, coherence and temporal shape has encouraged the usage of multilayer coatings also in the transport and manipulation of FEL radiation. In fact, conventional single layers coated mirrors provide negligible reflectance in the EUV spectral range whereas ML mirrors can reach high efficiency at normal incidence without affecting the pulses characteristics. Such optical elements have been also exploited at FERMI@ELETTRA FEL where novel multilayer coatings specifically conceived for pump and probe experiment and ultrafast absorption spectroscopy have been designed. The main results are reported.
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 present the design and characterization of a compact and portable spectrometer realized for photon in-photon out
experiments (in particular X-Ray Emission Spectroscopy, XES), in particular tailored to be used at the FERMI freeelectron-
laser (FEL) at ELETTRA (Italy). The spectrometer can be installed on different end stations at variable
distances from the target area both at synchrotron and FEL beamlines. Different input sections can be accommodated in
order to fit the experimental requests, with/without an entrance slit and with/without an additional relay mirror. The
design is compact in order to realize a portable instrument within a total footprint of less than one square meter. The
instrument is based on the use of two flat-field grazing-incidence gratings and an EUV-enhanced CCD detector to cover
the 25-800 eV spectral range, with spectral resolution better than 0.2%. The absolute response of the spectrometer, has
been measured in the whole spectral region of operation, allowing calibrated measurements of the photon flux. The
characterization on the Gas Phase beamline at ELETTRA Synchrotron as instrument for XES and some experimental
data of the FEL emission taken at EIS-TIMEX beamline at FERMI, where the instrument has been used for photon beam
diagnostics, are presented.
FERMI@Elettra is the first seeded VUV/soft X-ray FEL source. It is composed of two undulatory chains: the low energy branch (FELl) covering the wavelength range from 20 nm up to 100 nm, and the high energy branch (FEL2, employing a double stage cascade), covering the wavelength range from 4 nm up to 20 nm. At the end of 2012 FELl has been opened to external users while FEL2 has been turned on for the first time having demonstrated that a double cascade scheme is suitable for generating high intensity coherent FEL radiation. In this paper we will share our experience and will show our most recent results for both FERMI FELl and FEL2 sources. We will also present a brand new machine scheme that allows to perform two-colour pump and probe experiments as well as the first experimental results.