EIS-Home

The Elastic and Inelastic Scattering (EIS) beamline consists of two separate end-stations (EIS-TIMEX and EIS-TIMER), dedicated to two different research projects. EIS-TIMEX is fully operational since July 2013 and it is devoted to study matter under extreme thermodynamic conditions on ultrafast timescales. EIS-TIMER is presently under construction/commissioning and it will be dedicated to wave-mixing experiments; we accept user proposals on the latter instrument starting from the present (fifth) call for proposals. 
The common aim of the two instruments is to exploit the time structure of the FERMI FEL source for performing time-resolved experiments through the pump-probe approach. Each end-station will exploit different key properties of the source, that operates in the 20-300 eV spectral range at the fundamental harmonics (up to 900 eV in the 3rd harmonics), delivering photon pulses of ~ 40-80 fs duration and ~100 uJ energy, with selectable photon wavelenght and polarization. Different types of multi-colour FEL emission schemes are also available.


EIS-TIMER 

Basic principles

EIS-TIMER end-station is a FEL-based four-wave-mixing instrument that will exploit the time structure, harmonic content and coherence properties of the FERMI source. EIS-TIMER is specially designed to exploit the transient grating (TG) approach. In TG-based experiments two non-collinear coherent FEL pulses (pump) are overlapped, in time and space, at the sample. Their interference originates a transient standing electromagnetic wave (i.e. the TG) with a spatial periodicity in the 1-100 nm range. The TG imposes a nanoscale modulation of sample parameters, whose time evolution can be monitored by measuring the diffraction of a third time-delayed coherent pulse (probe), which inpinges into the sample at the Bragg angle. The time-dependent diffracted signal encodes relevant information on several kinds of dynamics, ranging from slow (>ns scale) diffusion processes to fast (sub-fs scale) electron dynamics. The implementation of this experimental scheme, nowadays used only with optical lasers, to the EUV/soft X-ray range would be of relevance, e.g., for the physics of disordered systems, since it will make accessible the mesoscopic kinematic region (wavevectors in the 0.1-1 nm-1 range) that cannot be explored by available instruments. Nanoscale TG experiments could also allow sensitive probing of thin films/interfaces, transport properties and correlations in nanostructured materials.

The combination of the TG method and the multi-colour seeded FEL emission available at FERMI also allows for coherent Raman scattering (CRS) experiments. EUV/soft X-ray CRS can be a unique ultrafast probe for high-energy excitations, such as high-frequency vibrations or electronic excitations. A succesful test of FEL stimulated CRS has been recently carried out using the mini-TIMER setup and a "phase-matched" optical probe; CRS will be also available at EIS-TIMER. We finally mention that the wavelength tunability of FERMI enables the exploitation of EUV/soft X-ray core-resonances of selected atoms, which may be used to add atomic selectivity to both TG and CRS experiments.
 

EIS-TIMER and mini-TIMER

The mini-TIMER setup is also available for users at the DiProI end station (see here for further details). The main differences between EIS-TIMER and mini-TIMER are:

  • the range in the crossing angle (~ 2o-12o, continuously variable, at mini-TIMER and 18o, 27o90o or 105o at EIS-TIMER); 
  • the range in the time delay between the two FEL "pump" pulses (< 0.5 ps at mini-TIMER, up to ~7 ps at EIS-TIMER);
  • the possibility to use an EUV/soft X-ray probe at selected wavelength (17.8, 13.3, 6.7 and 3.2 nm; other wavelength may be possible upon request). In this case the pump wavelength has to be 3 times larger than the probe one.

 

The TIMER project has been partially financed by the ERC Grant N.202804-TIMER



Top panel: a simple sketch of a TG experiment. Bottom panel: the region of the energy-wavevector (ω-k) plane plane accessible by FEL-based TG (orange area) and CRS (cyan area) along with the typical range of sample excitations; the range probed by optical optical four-wave-mixing (yellow area) is limited to the low-k region by the long wavelength of optical photons. The main aim of TIMER is to use FEL-based TG to probe low-energy excitations (ω < 0.1 eV: phonons, thermal modes, etc.) in the 0.1-1 nm-1 k-range and FEL-based CRS to probe high-energy excitations (ω up to a few eV: high-frequency vibrations, excitons, etc.), and, more in general, to experimentally develop the wave-mixing approach in theEUV and soft X-ray range.


EIS TIMEX 

Basic principles

EIS-TIMEX end-station will exploit the high intensity, energy domain and time structure of the FEL to probe fundamental properties of dense matter under metastable and/or extreme thermodynamic conditions with sub-ps time resolution. The basic idea is to exploit the high peak power of the Fermi@Elettra source of a fs optical laser  to induce an efficient ultrafast (< ps) and almost isochoric heating (up to the 10's eV (~106 K) range) of bulk-like dense samples followed by a slower (~10 ps) isoentropic expansion. The energy deposited in the sample is large enough to stimulate a nonequilibrium condition characterized by hot electron temperatures and cold lattice followed by structural changes including phase transitions. Under specific conditions optically excited condensed matter can reach a Warm Dense Matter (WDM) thermodynamic regime. WDM is a poorly understood state of matter located "in between" the classical plasma and the condensed matter (see phase diagram on the right), where the atoms/ions behaviour is strongly coupled to the dense electron plasma despite the high temperature. The understanding of the WDM state represents a real challenge for researchers, and it would be of great relevance for several applications, such as: inertial fusion, extreme-state chemistry, high-pressure research, etc. The study of WDM properties and/or phase transitions dynamics in the 0.1-100 ps range will be done through a pump-probe (time-resolved) scheme, which can exploit either an optical (i.e., a fs laser) and/or a EUV probe (i.e., a second FEL pulse).

Highlights

RIXS experiments at EIS-TIMEX

We have designed and constructed a RIXS experimental endstation that allowed us to successfully measure the d-d excitations in KCoF3 single crystals at the cobalt M2,3-edge. The FEL-RIXS spectra show an excellent agreement with the ones obtained from the same samples at the MERIXS endstation of the MERLIN beamline at the Advanced Light Source storage ring (Berkeley, USA). For more details: Dell'Angela et al. Scientific Reports 6, 38796 (2016)

Long-lived hot electrons in Al 

We report a time-resolved study of the relaxation dynamics of Al films excited by ultrashort intense free-electron laser (FEL) extreme-ultraviolet pulses. The system response was measured through a pump-probe detection scheme, in which an intense FEL pulse tuned around the Al L2,3 edge (72.5 eV) acted as the pump, while a time-delayed ultrafast pulse probed the near-infrared (NIR) reflectivity of the Al film. Remarkably, following the intense FEL excitation, the reflectivity of the film exhibited no detectable variation for hundreds of fs. For more details: F. Bisio, E. Principi et al. PRB 96, 081119(R) (2017)

EUV stimulated emission from MgO

We give evidence for soft-x-ray stimulated emission from a magnesium oxide solid target pumped by EUV 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. 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. More details:  P. Jonnard et al. Structural Dynamics 4, 054306 (2017)

EIS-TIMER commissioning

On July 2015 we started the commissioning of the EIS-TIMER beamline; in this first two commissioning weeks we tested two FEL-pump branch-lines (crossing angle ~18o). We burned permanent gratings (panel a) on the sample and we observed a transient grating signal (panel b) by using of an optical (UV) probe. These first results show how FEL-pump/laser-probe experiments are already possible at EIS-TIMER; the next step is the implementation of the FEL probing.

mini-TIMER(@DiProI): demonstration of FEL-stimulated TG experiments 

We carried out the first four-wave-mixing (FWM) experiment stimulated by EUV transient gratings, using a special setup (mini-TIMER) hosted in the DiProI experimental chamber (see DiProI's website). A shetch of the experiment is reported in the picture below. The CCD image is the first FEL-stimulated FWM signal, that propagated downstream the sample along the "phase-matched" direction (kFWM). The results have been recently published in Nature [F. Bencivenga et al., Nature 520, 205 (2015)]; for more information see also the Elettra top-story.

Toward jitter-free pump-probe experiments at EIS-TIMEX

An innovative pump-probe FEL/laser  approach has allowed us to achieve a time-jitter of 6 fs at EIS-TIMEX. For more details see M. B. Danailov et al. Opt. Express 22, 12869 (2014)

User Area

The 7th call for proposal is open until 15th October 2017The experiments will be scheduled starting from October 2018.

The installation and commissioning of EIS-TIMEX experimental chamber is completed, although some upgrades are ongoing. The EIS-TIMER end-station is under construction/commissioning, user experiments will be scheduled in 2017. Some information to write proposals for TIMER can be found in the EIS-TIMER setup page
We invite all potential users and collaborators to discuss their proposals with the beamline staff. This is crucial for a careful assessment of the experiment feasibility and may lead to improvements in the proposed experimental plans and setups. Our website provides a wealth of information on experiment feasibility and proposal submission. For more info, please visit the user info section.



 
Last Updated on Wednesday, 30 August 2017 18:39