35 research outputs found
The FERMI beamline system: a unique tool for investigating matter at nano-scale
All natural sciences benefit from the use of electromagnetic radiation to probe the phenomena of nature. From the structure of atoms and molecules to their evolution in complex system for various energy conditions, photons have been proved to be an essential tool for exploring matter in all its form. The advent of Free Electron Lasers (FEL) has allowed to perform unprecedented experiments. The properties of the FEL radiation (transverse and longitudinal coherence, brightness, pulse length and energy bandwidth) allow to perform Coherent Diffraction Imaging at a nano-scale level, non-linear spectroscopy and to probe ultra-fast phenomena in a wide set of simple and complex systems. On the the hand the FEL radiation needs to be characterised, transported and focused in order to allow the users to perform the experiments. In this thesis the FERMI beamlines (the Italian FEL) are described in detail together with the outstanding technological and scientific experimental results
BGO relaxation dynamics probed with heterodyne detected optical transient gratings
We used optical laser pulses to create transient gratings (TGs) with sub-10
{\mu}m spatial periodicity in a Bismuth Germanate (310) (Bi4Ge3O12) single
crystal at room temperature. The TG launches phonon modes, whose dynamics were
revealed via forward diffraction of a third, time-delayed, heterodyne-detected
optical pulse. Acoustic oscillations have been clearly identified in a
time-frequency window not covered by previous spectroscopic studies and their
characteristic dynamic parameters have been measured as a function of
transferred momenta magnitude and direction.Comment: 6 pages, 4 figure
Transient grating spectroscopy on a DyCo thin film with femtosecond extreme ultraviolet pulses
Surface acoustic waves (SAWs) are excited by femtosecond extreme ultraviolet
(EUV) transient gratings (TGs) in a room-temperature ferrimagnetic DyCo
alloy. TGs are generated by crossing a pair of EUV pulses from a free electron
laser (FEL) with the wavelength of 20.8\,nm matching the Co -edge, resulting
in a SAW wavelength of \,nm. Using the pump-probe transient grating
scheme in a reflection geometry the excited SAWs could be followed in the time
range of -10 to 100\,ps in the thin film. Coherent generation of TGs by
ultrafast EUV pulses allows to excite SAW in any material and to investigate
their couplings to other dynamics such as spin waves and orbital dynamics
FEL stochastic spectroscopy revealing silicon bond softening dynamics
Time-resolved X-ray Emission/Absorption Spectroscopy (Tr-XES/XAS) is an
informative experimental tool sensitive to electronic dynamics in materials,
widely exploited in diverse research fields. Typically, Tr-XES/XAS requires
X-ray pulses with both a narrow bandwidth and sub-picosecond pulse duration, a
combination that in principle finds its optimum with Fourier transform-limited
pulses. In this work, we explore an alternative xperimental approach, capable
of simultaneously retrieving information about unoccupied (XAS) and occupied
(XES) states from the stochastic fluctuations of broadband extreme ultraviolet
pulses of a free-electron laser. We used this method, in combination with
singular value decomposition and Tikhonov regularization procedures, to
determine the XAS/XES response from a crystalline silicon sample at the
L2,3-edge, with an energy resolution of a few tens of meV. Finally, we combined
this spectroscopic method with a pump-probe approach to measure structural and
electronic dynamics of a silicon membrane. Tr-XAS/XES data obtained after
photoexcitation with an optical laser pulse at 390 nm allowed us to observe
perturbations of the band structure, which are compatible with the formation of
the predicted precursor state of a non-thermal solid-liquid phase transition
associated with a bond softening phenomenon
Widely tunable two-colour seeded free-electron laser source for resonant-pump resonant-probe magnetic scattering
International audienceThe advent of free-electron laser (FEL) sources delivering two synchronized pulses of different wavelengths (or colours) has made available a whole range of novel pump–probe experiments. This communication describes a major step forward using a new configuration of the FERMI FEL-seeded source to deliver two pulses with different wavelengths, each tunable independently over a broad spectral range with adjustable time delay. The FEL scheme makes use of two seed laser beams of different wavelengths and of a split radiator section to generate two extreme ultraviolet pulses from distinct portions of the same electron bunch. The tunability range of this new two-colour source meets the requirements of double-resonant FEL pump/FEL probe time-resolved studies. We demonstrate its performance in a proof-of-principle magnetic scattering experiment in Fe–Ni compounds, by tuning the FEL wavelengths to the Fe and Ni 3p resonances
The Low Density Matter (LDM) beamline at FERMI: Optical layout and first commissioning
The Low Density Matter (LDM) beamline has been built as part of the FERMI free-electron laser (FEL) facility to serve the atomic, molecular and cluster physics community. After the commissioning phase, it received the first external users at the end of 2012. The design and characterization of the LDM photon transport system is described, detailing the optical components of the beamline