The advent of extreme ultraviolet (EUV) and soft x-ray free electron lasers (FELs) has enabled nonlinear optical experiments at wavelengths shorter than the visible-UV range. An important class of experiments is those based on the four-wave-mixing (FWM) approach, which are often based on interactions between pulses at different wavelengths. The exploitation of multiple EUV/soft x-ray wavelengths is not straightforward, but it can significantly expand the range of applications. In this manuscript we report on an experimental approach, based on the concomitant use of a non-collinear split-delay-and-recombination unit (“mini-Timer”) and on a two-color seeded FEL emission scheme (“twin-seed mode”). We used a diamond sample for demonstrating the capability of this setup of generating and detecting a FWM signal stimulated by two-color EUV FEL pulses. This approach can be further exploited for developing experimental methods based on non-linear EUV/x-ray optics.
Preserving the coherence and wavefront of a diffraction limited x-ray beam from the source to the experiment poses stringent quality requirements on the production processes for X-ray optics. In the near future this will require on-line and in-situ at-wavelength metrology for both, free electron lasers and diffraction limited storage rings. A compact and easy to move X-ray grating interferometry (XGI) setup has been implemented by the Beamline Optics Group at PSI in order to characterize x-ray optical components by determining the aberrations from reconstructing the x-ray wavefront. The XGI setup was configured for measurements in the moire mode and tested with focusing optic at Swiss Light Source, Diamond Light Source and LCLS. In this paper measurements on a bendable toroidal mirror, a zone plate, a single and a stack of beryllium compound refractive lenses (CRL) are presented. From these measurements the focal position and quality of the beam spot in terms of wavefront distortions are determined by analysing the phase-signal obtained from the XGI measurement. In addition, using a bendable toroidal mirror, we directly compare radius of curvature measurements obtained from XGI data with data from a long-trace profilometer, and compare the CRL wavefront distortions with data obtained by ptychography.
FERMI is the first seeded EUV-SXR free electron laser (FEL) user facility, and it is operated at Elettra Sincrotrone Trieste. Two of the four already operating beamlines, namely LDM (Low Density Matter) 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. A wafefront sensor is used as diagnostic for the characterization of the focused spot and for the optimization of the parameters of these active optical systems as well. The aim of this work is, first, to describe in detail the optimization procedure using the wavefront sensor through the minimization of the Zernike coefficients, and second, report on the final results obtained on the K-B optical system at the DiProI endstation. The wavefront sensor, mounted out of focus behind the DiProI chamber, allows to compute the intensity distribution of the FEL beam, typically a mix between several modes resulting in a ”noisy hyper-Gaussian” intensity profile, and the wavefront residual from ideal propagation shape and after tilt correction. Combining these two measures we can obtain the electric field of the wave out of focus. Propagating back the electric field we reconstruct the focal spot in far field approximation. In this way the sensor works as a diagnostic reconstructing the focal spot. On the other hand, after modelling the electric field with a Zernike polynomial it is easy and fast to optimize the mirror bending and the optical system angles by minimizing the aberrations, quantified in terms of Zernike coefficients. Since each coefficient corresponds to a single parameter, they can be minimized one at the time. 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 for DiProI of 5.5 μm x 6.2 μm at 32 nm wavelength, confirmed by the PMMA ablation imprints. The experimental results were 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 were found to be in agreement with the experimental measurements.
KEYWORDS: Spectroscopy, Free electron lasers, X-rays, Photons, X-ray optics, Mirrors, Diffraction gratings, Alternate lighting of surfaces, Current controlled current source
FERMI, the Italian Free Electron Laser user facility, provides VUV/soft x-ray photons pulses with unprecedented high brilliance and coherence. The unique design of EIS-TIMER is conceived to exploit such kind of non-linear coherent experiments to probe collective vibrational and electronic properties of matter at the nanoscale. After the proof of principle experiment successfully carried out at the DiProI beamline employing a simplified and compact setup (mini-TIMER), the EIS-TIMER beamline has been installed and commissioned. The beamlines employs 24 mirrors and three photon beams in order to create a wide set of transient grating able to reach Q vectors so far impossible to probe.
In the presentation the scientific case, the commissioning results as well as the future development of the beamline will be shown. The future project nano-TIMER will be described in detail with particular attention to it's unique optical scheme mainly composed by diffraction gratings.
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 optical layout of a reflective grating compressor specifically designed for extreme-ultraviolet FEL sources. The working principle is based on the use of a couple of constant-line-spaced gratings used at grazing incidence and illuminated in divergent light. The two possible grating configurations, namely the on-plane and off-plane, are analyzed and compared. The Group Delay Dispersion (GDD) introduced by the compressor is analytically analyzed and quantified. The spatial chirp also is considered, and its effect analyzed. The deviation from the ideal case in which the instrument is feed with a collimated beam is considered. The effect of the beam divergence on the compressor response is quantified and the attenuation of this effect by a “de-tuning” of the compressor is proposed. This solution avoids the use of a pre-collimating optics, therefore incrementing the total instrumental throughput. Finally, it is shown the optical design of an actual compressor for the FERMI FEL, that can be inserted in the optical path without any deviation or translation of the photon beam with respect to the nominal path.
C. Spezzani, E. Ferrari, E. Allaria, F. Vidal, L. Lounis, A. Ciavardini, R. Delaunay, F. Capotondi, E. Pedersoli, M. Coreno, C. Svetina, L. Raimondi, M. Zangrando, R. Ivanov, I. Nikolov, A. Demidovich, M. Danailov, G. De Ninno, H. Popescu, M. Eddrief, M. Kiskinova, M. Sacchi
Magnetization control without applying magnetic fields has potential for applications in sensors and devices. In Fe/MnAs/GaAs(001), the Fe magnetization can be modified by acting on the MnAs microstructure via temperature control, without applying external magnetic fields. Here we use an optical laser pulse to vary the local temperature and an x-ray free-electron laser pulse to probe the induced magnetic and structural dynamics in a time-resolved resonant scattering experiment, both pulses having ~100 fs duration. Modifications of the MnAs microstructure take place within a few ps, followed by a slower dynamics driven by thermal diffusion. We show that a single optical laser pulse can reverse the Fe magnetization locally, the process being driven not by the fast modifications of the MnAs structure, but rather by its slower return to equilibrium.
The FERMI FEL facility has begun delivering photons in 2011, becoming in late 2012 the first seeded facility open to external users worldwide. Since then, several tens of experiments have been carried out on the three operative endstations LDM, DiProI, and EIS-TIMEX. Starting from the commissioning phase, the transport and diagnostics system (PADReS) has been continuously developed and upgraded, becoming the indispensable interface between the machine and the experimental chambers. Moreover, PADReS itself has served as an active player for several machine studies as well as for various state-of-the-art experiments. In particular, some elements of PADReS have become key features to perform cutting edge experiments: the online energy spectrometer, the active optics refocusing systems, the split and delay line, and so on. For each of them the peculiar advantages will be described showing the actual implementation in the experiments. The experience gathered so far in fulfilling the needs of both machine and experimental physicists will be discussed, with particular emphasis on the solutions adopted in different scenarios. Recurrent requests and major difficulties will be reported so to give a glimpse about the standard tasks to be solved when preparing new and demanding experiments. Finally, some ideas and near-future improvements will be presented and discussed.
P. Finetti, E. Allaria, B. Diviacco, C. Callegari, B. Mahieu, J. Viefhaus, M. Zangrando, G. De Ninno, G. Lambert, E. Ferrari, J. Buck, M. Ilchen, B. Vodungbo, N. Mahne, C. Svetina, C. Spezzani, S. Di Mitri, G. Penco, M. Trovò, W. Fawley, P. Rebernik, D. Gauthier, C. Grazioli, M. Coreno, B. Ressel, A. Kivimäki, T. Mazza, L. Glaser, F. Scholz, J. Seltmann, P. Gessler, J. Grünert, A. De Fanis, M. Meyer, A. Knie, S. Moeller, L. Raimondi, F. Capotondi, E. Pedersoli, O. Plekan, M. Danailov, A. Demidovich, I. Nikolov, A. Abrami, J. Gautier, J. Lüning, P. Zeitoun, L. Giannessi
FERMI, based at Elettra (Trieste, Italy) is the first free electron laser (FEL) facility operated for user experiments in
seeded mode. Another unique property of FERMI, among other FEL sources, is to allow control of the polarization state
of the radiation. Polarization dependence in the study of the interaction of coherent, high field, short-pulse ionizing
radiation with matter, is a new frontier with potential in a wide range of research areas. The first measurement of the
polarization-state of VUV light from a single-pass FEL was performed at FERMI FEL-1 operated in the 52 nm-26 nm
range. Three different experimental techniques were used. The experiments were carried out at the end-station of two
different beamlines to assess the impact of transport optics and provide polarization data for the end user. In this paper
we summarize the results obtained from different setups. The results are consistent with each other and allow a general
discussion about the viability of permanent diagnostics aimed at monitoring the polarization of FEL pulses.
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.
The future beamline Magneto Dynamics (MagneDyn) will be devoted to study the electronic states and the local magnetic properties of excited and transient states of complex systems by means of the time-resolved X-ray absorption spectroscopy (TR-XAS) technique. The beamline will use the high energy source at FERMI covering the wavelength range from 60 nm down to 1.3 nm. An on-line photon energy spectrometer will allow to measure the spectrum with high resolution while delivering most of the beam to the end-stations. Downstream the beam will be possibly split and delayed, by means of a delay line, and then focused with a set of active KB mirrors. These mirrors will be able to focus the radiation in one of the two MagneDyn experimental chambers: the electro-magnet end-station and the Resonant Inelastic X-ray Scattering (RIXS) end-station. After an introduction of MagneDyn scientific case, we will discuss the layout showing the expected performances of the beamline.
Cristian Svetina, Nicola Mahne, Lorenzo Raimondi, Luca Rumiz, Marco Zangrando, Enrico Allaria, Filippo Bencivenga, Carlo Callegari, Flavio Capotondi, Davide Castronovo, Paolo Cinquegrana, Paolo Craievich, Ivan Cudin, Massimo Dal Forno, Miltcho Danailov, Gerardo D'Auria, Raffaele De Monte, Giovanni De Ninno, Alexander Demidovich, Simone Di Mitri, Bruno Diviacco, Alessandro Fabris, Riccardo Fabris, William Fawley, Mario Ferianis, Eugenio Ferrari, Lars Froehlich, Paolo Furlan Radivo, Giulio Gaio, Luca Giannessi, Maya Kiskinova, Marco Lonza, Benoit Mahieu, Claudio Masciovecchio, Ivaylo Nikolov, Fulvio Parmigiani, Emanuele Pedersoli, Giuseppe Penco, Mauro Predonzani, Emiliano Principi, Fabio Rossi, Claudio Scafuri, Claudio Serpico, Paolo Sigalotti, Simone Spampinati, Carlo Spezzani, Michele Svandrlik, Mauro Trovo, Alessandro Vascotto, Marco Veronese, Roberto Visintini, Dino Zangrando
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.
Kirkpatrick-Baez (K-B) active X-ray optics system is a good choice for focusing the free electron laser (FEL)
pulses delivered by FERMI, the first seeded EUV-SXR FEL user facility operated at Elettra Sincrotrone Trieste.
The present work reports the results obtained tuning this optical system used at the Diffraction and Projection
Imaging (DiProI) beamline in order to improve and optimize its performance in terms of quality and size of
the focal spot onto the sample controlling the fluence as well. To characterize the performance 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
allowed for optimizing the bending acting on the mirrors curvature and the angle positions (pitch and roll) of
the K-B system. The experimental results are compared with the predictions from simulations obtained using
the WISE code, starting from mirror actual surface metrology characterization. Filtering the Fourier transform
of the mirror surface profiles we have analyzed the impact of spatial wavelengths on the focal spot degradation.
From the wavefront measurements we have inferred a focal spot of 10 μm x 10 μm confirmed by the PMMA
ablation imprints. The results from simulations with the WISE code are in agreement with the measurements
and for different energies of the incident beam we established the threshold when the focal spot degradation is
not affected by the spatial wavelengths of the K-B mirror surfaces.
The development of Free Electron Laser sources is opening up the possibility to probe dynamics at the femtosecondnanometer time-length scales. A remarkable step forward towards this goal would be achieved by extending the Four Wave Mixing (FWM) approach at VUV/soft x-ray wavelengths. FWM-based techniques allow a coherent control in both the stimulating and probing processes of photon-induced excitations. We propose to exploit the FERMI@Elettra seeded Free Electron Laser (FEL) source to put on practice the VUV/soft x-ray FWM approach, yet theoretically conceived one decade ago. Moreover, the exploitation of VUV/soft x-ray wavelengths allows adding site-sensitivity to FWM methods by exploiting core resonances of selected elements in the sample.
FERMI@Elettra is a VUV/Soft X-ray Free Electron Laser (FEL) user facility under commissioning in Trieste, Italy. It provides a spatially coherent transform-limited photon beam in the sub-ps regime with high fluence and tunable wavelength. One of the FERMI beamlines, TIMEX, will be dedicated to the study of matter under extreme and metastable conditions, created and probed by the FEL radiation. Moreover, an active optics dedicated to perform the beam shaping at focus is needed in order to provide the necessary flat-top intensity distribution for heating the sample uniformly. In this work the principles of the beam shaping applied to the TIMEX beamline will be discussed as well as the adopted solution. Ray tracing simulations will be shown for theoretical mirror profiles as well as the metrological measurements with an interferometer and the Long Trace Profiler (LTP).
FERMI@Elettra, the Italian Free Electron Laser (FEL) source, is in an advanced commissioning phase, having already delivered radiation down to the endstations. The facility is routinely using the low energy branch (FEL1) to produce photons in the 65–20 nm range, while the 20–4 nm range will be covered by FEL2 that is now being commissioned. A dedicated system to collect, diagnose, transport and focus the radiation (PADReS) is used to provide informations about the photon beam intensity, position, spectral content, transverse coherence, and so on. The experience gathered so far, as well as the most recent results both from the diagnostic section and the
beam manipulation part are presented here.
FERMI@Elettra is a Free Electron Laser (FEL) under commissioning at Sincrotrone Trieste. It will
provide an almost fully coherent and transform limited radiation with a very high brilliance in the
VUV/Soft X-ray range. This article describes the working principles of the Variable Line Spacing
diffraction gratings applied to the photon energy spectrometer as well as the design concept, ray tracing
and efficiency simulations. Metrological results at various spatial frequencies of the optics involved
and the first characterization results with FEL radiation will be shown.
The Italian Free Electron Laser (FEL) facility FERMI@Elettra has started to produce photon radiation at the end of
2010. The photon beam is presently delivered by the first undulator chain (FEL1) that is supposed to produce photons in
the 100-20 nm wavelength range. A second undulator chain (FEL2) will be commissioned at the end of 2011, and it will
produce radiation in the 20-4nm range.
The Photon Analysis Delivery and Reduction System (PADReS) was designed to collect the radiation coming from both
the undulator chains (FEL1 and FEL2), to characterize and control it, and to redirect it towards the following beamlines.
The first parameters that are checked are the pulse-resolved intensity and beam position. For each of these parameters
two dedicated monitors are installed along PADReS on each FEL line. In this way it possible to determine the intensity
reduction that is realized by the gas reduction system, which is capable of cutting the intensity by up to four orders of
magnitude. The energy distribution of each single pulse is characterized by an online spectrometer installed in the
experimental hall. Taking advantage of a variable line-spacing grating it can direct the almost-full beam to the
beamlines, while it uses a small fraction of the beam itself to determine the spectral distribution of each pulse delivered
by the FEL.
The first light of FERMI@Elettra, delivered to the PADReS section in late 2010, is used for the first commissioning runs
and some preliminary experiments whose results are reported and discussed in detail.
FERMI@Elettra is a new free-electron-laser (FEL) facility, presently under commissioning, able to generate
subpicosecond photon pulses of high intensity in the far ultraviolet and soft X-ray range (λ=100-20 nm for
the present FEL1 source, extended in future to 4 nm with the FEL2 source). Here we briefly describe the
present status of the TIMEX end-station, devoted to perform experiments on condensed matter under extreme
conditions. The layout of the end-station, presently in the final stages of construction, is reported showing the
details of the optics and sample environment. The potential for transmission, reflection, scattering, as well as
pump-and-probe experiments is discussed taking into account that FEL pulses can heat thin samples up to
the warm dense matter (WDM) regime. The calculated deposited energy in selected elemental films, including
saturation effects, shows that homogeneous heating up to very high temperatures (1-10 eV for the electrons) can
be easily reached with a suitable tuning of the energy and focus of the soft x-ray pulses of FERMI@Elettra. The
results of the first test of the TIMEX end-station are also reported.
The irradiation effects of multiple ultrafast shots of laser beams with estimated fluences of some tens of
mJ/cm2 on a EUV Mo/Si multilayer have been studied. Irradiation damage has been induced by multiple shots of two
different lasers (100 fs 400 nm the first, 1.5 ns 46.9 nm the second). The study has been motivated by the need of
multilayer Mo/Si optics for the delay lines of the FEL source FERMI@Elettra, where these mirrors will be used to
reflect 100 fs pulses at 13 nm with a fluence of some mJ/cm2. The analysis has been performed by means of different
techniques as EUV and soft X-ray reflectivity, XPS, and Standing wave enhanced XPS. Simulations have been carried
on by means of an indigenously developed software OPAL (Optical Properties of Anisotropic Layers) for the
calculation of the absorbed energy by the stratified medium. AFM and SEM surface images have been also acquired. In
the irradiation at 400 nm, we observed a significant change in the multilayer performance at fluences of 100 mJ/cm2 and
above with a significant reduction of reflectivity. Spectroscopic analysis allowed to correlate the decrease of reflectivity
with the degradation of the multilayer stacking, ascribed to Mo-Si intermixing at the Mo/Si interfaces of the first few
layers, close to the surface of the mirror. Preliminary tests have been also performed on the sample irradiated at 46.9
nm.
FERMI@Elettra is a Free Electron Laser (FEL) user facility currently under construction at Sincrotrone Trieste,
Italy. It will provide a spatial coherent transform-limited beam in the sub-ps regime, covering the wavelength
range from 100 nm to 3 nm with the goal of 1 nm (by using third harmonics). The transform-limited beam is
supposed to have a natural energy bandwidth of the order of 50-100 meV. Nevertheless, one of the three future
beamlines, the one dedicated to Low Density Matter (LDM) studies, needs a monochromator to clean the signal.
It must cover the whole wavelength range with eventual omission of the lower energy part. We will report the
design of a fixed included angle monochromator employing three gratings. The optical system will be described,
and particular attention will be given to the constraints like the pulse broadening, the focus displacement and, of
course, the flux. Engineering constraints and manufacturers tolerances also taken into account will be presented,
too.
The FERMI@Elettra free electron laser (FEL) user facility is currently under construction at the Sincrotrone Trieste
laboratory in Trieste (Italy). It is a based on a seeded scheme that will provide an almost perfect transform limited beam
and fully spatial coherent. It will cover the wavelength range from 100 to about 3 nm and in a short future down to 1 nm
(by using higher harmonics). It is expected to be fully operative in the late summer of 2010. In this presentation we will
report the layout of the photon beam diagnostics section with the preliminary tests, the radiation transport system to the
experimental area, and the experimental hall facilities. A particular emphasis will be given to the optical solution and
constrains due to the need of preserving the wave front and to avoid damage on the different optical elements, including
slits, mirrors, gratings and all the diagnostic facilities. One of the main problems will be the necessity of using very large
grazing incidence angle (up to 45°) on multilayers and single coating mirrors. These elements are mandatory to perform
the transient grating experiments and to realize the delay lines, where time delay up to 1 nsec are required. This issue
poses a serious problem in terms of energy density delivered and adsorbed by the optics and great care must be taken
into the choice of the proper multilayer materials. Some studies on the reflectivity of multilayers and Carbon coated
mirrors will be reported as well as the diagnostic tools to monitor the quality of the optics in operative conditions.
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