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Soft X-ray monochromators for synchrotron radiation sources have been continuously developed over the years, improving energy resolution and stability. Great effort has been made in improving the surface quality of the optics involved, reaching values permitting diffraction-limited images. Still, one problem has not been solved, nor fully understood, yet: groove placing errors. Nowadays, these are one of the major factors responsible for resolving the power reduction of diffraction-gratings-based X-ray monochromators. Despite decades of use of gratings, there is not yet a universally established method for predicting and simulating the effect of groove placing errors on monochromator performance. This is especially important in the new scenario of high-coherent X-ray sources, i.e. diffraction-limited storage rings and free-electron lasers. To address this problem, in this article an approach based on WISER (Wavefront propagatIon Simulation codE libRary) is presented. WISER is a physical optics simulation package, also available in the user-friendly Orange Synchrotron Radiation Suite - OASYS. Even though it was originally conceived to assess the focusing performance of X-ray mirrors in the presence of height defects, it perfectly simulates the performance of a periodic (or quasi-periodic) structure like a diffraction grating. In this article, the way to use WISER and its application to a specific case, e.g. the design of a monochromator for the upgrade of a beamline at the Advanced Light Source, are shown. A simple rule for estimating how well the grooves are placed on a grating, based on calculation of the Strehl ratio, is also presented. [ABSTRACT FROM AUTHOR]

The automated recognition of fossil planktonic foraminifera in thin section (TS) samples can bring benefit through reduction of time, costs, and human effort for biostratigraphic analyses. In this work we present the outcomes of an Eni internal Research and Development project aimed at evaluating the feasibility of automated recognition of microfossils by means of computer vision. We trained two Deep-Learning (DL) models to first identify fossil candidates within TS samples and subsequently classify selected taxa among 66 registered Oligocene-Miocene planktonic foraminifera species. In the step of fossil detection, we achieved a mean average precision of 81.4% in extracting bounding boxes containing fossils from raw TS photomicrographs. In the subsequent fossil classification step, we obtained a top-1 accuracy of 70% (i.e., in approximately 70% of cases, the label assigned by the biostratigraphers coincided with the model best guess) and a top-3 accuracy of 88% (i.e., in 88% of cases, it was included within the top-3 species predicted by the model). Given these promising performances, the fossil detection and classification pipeline has been deployed in a web application that indicates fossil-containing bounding boxes and suggests the top-3 most likely species for each sample. Biostratigraphers' corrections/confirmations are stored to be used for future re-trainings and incrementally improve the performances of the algorithms. • Automated recognition of Oligo-Miocene planktonic foraminifera at the thin section (TS) exam by means of computer vision. • Training of two Deep Learning (DL) models: 1) to detect fossils in TS samples and, 2) to classify selected taxa among 66 registered species. • Mean average precision of 81.4% in extracting fossils in bounding boxes from TS photomicrographs (i.e., fossil detection). • Top-1 accuracy of 70% and a top-3 accuracy of 88% (i.e., fossil classification). • Fossil detection and classification pipeline have been deployed in a user web application/dashboard. • The dashboard includes human validation processes and is aimed at performance improvement/incremental learning. [ABSTRACT FROM AUTHOR]

FERMI is the first and only seeded EUV‐SXR free‐electron laser (FEL) facility available to users; it operates at Elettra – Sincrotrone Trieste (Italy) and it presents five operating endstations. Three of them, namely LDM (Low Density Matter), DiProI (Diffraction and Projection Imaging) and MagneDyn (Magneto‐Dynamical studies), use a Kirkpatrick–Baez (KB) active X‐ray optics system to focus the FEL pulses into the experimental chambers. The present work reports on the final results of the upgraded KB Active Optics Systems (KAOS), which have been mechanically modified in order to improve stability and repeatability with respect to the original design. The results have been obtained on both the FERMI FEL lines, FEL1 and FEL2, and are particularly relevant for the latter as it is the low‐wavelength line recently opened to users. After a thorough description of the new mechanical layout of the system and the aspects that have been improved after the refurbishment, a set of simulations of the optical performances are presented. The code used to simulate the behavior of KAOS is WISEr, a physical‐optics‐based tool, which is freely accessible, and integrated into the Oasys platform, that takes into account the specific surface metrology characterization of the beamline mirrors, including figure errors and microroughness power spectral density. The results of WISEr are then used as a reference for the actual optimization of the optical system. This procedure relies heavily on a wavefront sensor (WFS) mounted out of focus to optimize the refocusing mirrors alignment as well as their curvature bending (by minimization of the coefficients of the Zernike wavefront expansion). Moreover, the WFS data are used to reconstruct the focal spot parameters by means of a back‐propagation of the electric field. Finally, these results are compared with those obtained after the FEL ablation of a PMMA layer positioned on the focal plane, and analyzed ex situ in a post‐mortem fashion. The mechanically refurbished optical system and the multi‐technique alignment approach, aimed at optimizing the mirrors' curvature, pitch and roll angles, allowed a focal spot of 1.8 µm × 2.4 µm at 4.14 nm wavelength (FEL2) to be inferred, confirmed by the PMMA ablation imprints. [ABSTRACT FROM AUTHOR]

In this work the longitudinal shifts of the focal plane of an ellipsoidal mirror induced by longitudinal shifts of the source and by the optical figure error of the mirror itself are investigated. The case of an ideal mirror illuminated by a Gaussian beam is considered first, deriving an analytical formula predicting the source‐to‐focus shift. Then the realistic case of a mirror affected by surface shape defects is examined, by taking into account metrological data and numerically solving the Huygens–Fresnel integral. The analytical and numerical solutions in the ideal and real cases are compared. Finally, it is shown that an additional dependence of the focal shift is introduced on the wavelength and the pointing angle of the source. Both effects are investigated by numerical computations. We limit the treatment in the XUV spectral range, choosing as a test bench the Kirkpatrick–Baez mirror system of the DiProI and LDM end‐stations and at the FERMI seeded free‐electron laser (FEL). The work is primarily aimed at disentangling the different causes of focal shift at FEL light sources, where source position, wavelength and pointing angle are either tunable or rapidly fluctuating. The method can be easily extended to parabolic reflectors and refractors (lenses) with other kinds of illuminating sources and wavelengths. [ABSTRACT FROM AUTHOR]

Abstract: X-ray mirrors with high focusing performances are in use in both mirror modules for X-ray telescopes and in synchrotron and FEL (Free Electron Laser) beamlines. A degradation of the focus sharpness arises in general from geometrical deformations and surface roughness, the former usually described by geometrical optics and the latter by physical optics. In general, technological developments are aimed at a very tight focusing, which requires the mirror profile to comply with the nominal shape as much as possible and to keep the roughness at a negligible level. However, a deliberate deformation of the mirror can be made to endow the focus with a desired size and distribution, via piezo actuators as done at the EIS-TIMEX beamline of FERMI@Elettra. The resulting profile can be characterized with a Long Trace Profilometer and correlated with the expected optical quality via a wavefront propagation code. However, if the roughness contribution can be neglected, the computation can be performed via a ray-tracing routine, and, under opportune assumptions, the focal spot profile (the Point Spread Function, PSF) can even be predicted analytically. The advantage of this approach is that the analytical relation can be reversed; i.e., from the desired PSF the required mirror profile can be computed easily, thereby avoiding the use of complex and time-consuming numerical codes. The method can also be suited in the case of spatially inhomogeneous beam intensities, as commonly experienced at synchrotrons and FELs. In this work we expose the analytical method and the application to the beam shaping problem. [Copyright &y& Elsevier]

Coherent light-matter interactions mediated by opto-magnetic phenomena like the inverse Faraday effect (IFE) are expected to provide a non-thermal pathway for ultrafast manipulation of magnetism on timescales as short as the excitation pulse itself. As the IFE scales with the spin-orbit coupling strength of the involved electronic states, photo-exciting the strongly spin-orbit coupled core-level electrons in magnetic materials appears as an appealing method to transiently generate large opto-magnetic moments. Here, we investigate this scenario in a ferrimagnetic GdFeCo alloy by using intense and circularly polarized pulses of extreme ultraviolet radiation. Our results reveal ultrafast and strong helicity-dependent magnetic effects which are in line with the characteristic fingerprints of an IFE, corroborated by ab initio opto-magnetic IFE theory and atomistic spin dynamics simulations. Coherent light-matter interactions mediated by opto-magnetic phenomena like the inverse Faraday effect are expected to provide a non-thermal pathway for ultrafast manipulation of magnetism. The authors use intense and circularly polarized pulses of extreme ultraviolet radiation to induce particularly strong effects in a ferrimagnetic GdFeCo alloy. [ABSTRACT FROM AUTHOR]

The scope of this paper is to outline the main marks and performances of the MagneDyn beamline, which was designed and built to perform ultrafast magnetodynamic studies in solids. Open to users since 2019, MagneDyn operates with variable circular and linear polarized femtosecond pulses delivered by the externally laser-seeded FERMI free-electron laser (FEL). The very high degree of polarization, the high pulse-to-pulse stability, and the photon energy tunability in the 50–300 eV range allow performing advanced time-resolved magnetic dichroic experiments at the K-edge of light elements, e.g., carbon and at the M- and N-edge of the 3d-transition-metals and rare earth elements, respectively. To this end, two experimental end-stations are available. The first is equipped with an in situ dedicated electromagnet, a cryostat, and an extreme ultraviolet Wollaston-like polarimeter. The second, designed for carry-in user instruments, hosts also a spectrometer for pump-probe resonant x-ray emission and inelastic spectroscopy experiments with a sub-eV energy resolution. A Kirkpatrick-Baez active optics system provides a minimum focus of ∼ 20 × 20 μ m2 FWHM at the sample. A pump laser setup, synchronized with the FEL-laser seeding system, delivers sub-picosecond pulses with photon energies ranging from the mid-IR to near-UV for optical pump-FEL probe experiments with a minimal pump-probe jitter of few femtoseconds. The overall combination of these features renders MagneDyn a unique state-of-the-art tool for studying ultrafast magnetic and resonant emission phenomena in solids. [ABSTRACT FROM AUTHOR]

The future Magneto Dynamics (MagneDyn) beamline 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 technique. The beamline will use FERMI's high-energy source covering the wavelength range from 60 nm down to 1.3 nm. An on-line photon energy spectrometer will allow spectra to be measured 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 Kirkpatrick-Baez mirrors. These mirrors will be able to focus the radiation in one of the two MagneDyn experimental chambers: the electromagnet end-station and the resonant inelastic X-ray scattering end-station. After an introduction of the MagneDyn scientific case, the layout will be discussed showing the expected performances of the beamline. [ABSTRACT FROM AUTHOR]

TeraFERMI is the new terahertz (THz) beamline for pump-probe studies on the femtosecond time-scale, under construction at the FERMI free-electron laser (FEL) facility in Trieste, Italy. The beamline will take advantage of the coherent radiation emitted by the spent electrons from the FEL undulators, before being dumped. This will result in short, coherent, high-power THz pulses to be used as a pump beam, in order to modulate structural properties of matter, thereby inducing phase transitions. The TeraFERMI beamline collects THz radiation in the undulator hall and guides it along a beam pipe which is approximately 30 m long, extending across the safety hutch and two shielding walls. Here the optical design, which will allow the efficient transport of the emitted THz radiation in the experimental hall, is presented. [ABSTRACT FROM AUTHOR]

The broadband nature of IRSR, together with the superior flux and higher brilliance are the key points of IR beamline scientific programs in 3rd generation SR rings. However, it is also well-established that the extraction of IRSR radiation from a bending magnet in the next-generation Diffraction Limited Storage Rings is a challenging task. The Elettra 3rd generation storage ring in Trieste (Italy) is implementing its upgrade program to Elettra 2.0 DLSR, the design of which offers the possibility of a suitable extraction port for IR light, with comparable extraction angles with respect to the present SISSI beamline. In this contribution we will present the results of the preliminary simulations run in Synchrotron Radiation Workshop on the expected performances of SISSI in Elettra 2.0. Considering the spatial constrains and the magnetic layout, also introduced here, two options for the IRSR source will be considered and benchmarked with the current SISSI beamline. [ABSTRACT FROM AUTHOR]

Laser‐slicing at a diffraction‐limited storage ring light source in the soft X‐ray region is investigated with theoretical and numerical modelling. It turns out that the slicing efficiency is favoured by the ultra‐low beam emittance, and that slicing can be implemented without interference to the standard multi‐bunch operation. Spatial and spectral separation of the sub‐picosecond radiation pulse from a hundreds of picosecond‐long background is achieved by virtue of 1:1 imaging of the radiation source. The spectral separation is enhanced when the radiator is a transverse gradient undulator. The proposed configuration applied to the Elettra 2.0 six‐bend achromatic lattice envisages total slicing efficiency as high as 10−7, one order of magnitude larger than the demonstrated state‐of‐the‐art, at the expense of pulse durations as long as 0.4 ps FWHM and average laser power as high as ∼40 W. [ABSTRACT FROM AUTHOR]

Abstract Experiments using high brightness X-rays are on the forefront of science due to the vast variety of knowledge they can provide. New Synchrotron Radiation (SR) and Free Electron Laser (FEL) light sources provide unique tools for advanced studies using X-rays. Top-level scientists from around the world are attracted to these beamlines to perform unprecedented experiments. High brightness, low emittance light sources allow beamline scientists the possibility to dream up cutting-edge experimental stations. X-ray optics play a key role in bringing the beam from the source to the experimental stations. This article explores the recent developments in X-ray optics. It touches on simulations, diagnostics, metrology and adaptive optics, giving an overview of the role X-ray optics have played in the recent past. It will also touch on future developments for one of the most active field in the X-ray science. [ABSTRACT FROM AUTHOR]

Time-resolved investigations have begun a new era of chemistry and physics, enabling the monitoring in real time of the dynamics of chemical reactions and matter. Induced transient optical absorption is a basic ultrafast electronic effect, originated by a partial depletion of the valence band, that can be triggered by exposing insulators and semiconductors to sub-picosecond extreme-ultraviolet pulses. Besides its scientific and fundamental implications, this process is very important as it is routinely applied in free-electron laser (FEL) facilities to achieve the temporal superposition between FEL and optical laser pulses with tens of femtoseconds accuracy. Here, a set of methodologies developed at the FERMI facility based on ultrafast effects in condensed materials and employed to effectively determine the FEL/laser cross correlation are presented. [ABSTRACT FROM AUTHOR]

An open-source database containing metrology data for X-ray mirrors is presented. It makes available metrology data (mirror heights and slopes profiles) that can be used with simulation tools for calculating the effects of optical surface errors in the performances of an optical instrument, such as a synchrotron beamline. A typical case is the degradation of the intensity profile at the focal position in a beamline due to mirror surface errors. This database for metrology (DABAM) aims to provide to the users of simulation tools the data of real mirrors. The data included in the database are described in this paper, with details of how the mirror parameters are stored. An accompanying software is provided to allow simple access and processing of these data, calculate the most usual statistical parameters, and also include the option of creating input files for most used simulation codes. Some optics simulations are presented and discussed to illustrate the real use of the profiles from the database. [ABSTRACT FROM AUTHOR]

A new high-performance method for the free-electron laser (FEL) focused beam diagnosis has been successfully tested at the FERMI FEL in Trieste, Italy. The novel pixelated phosphor detector (PPD) consists of micrometric pixels produced by classical UV lithography and dry etching technique, fabricated on a silicon substrate, arranged in a hexagonal geometry and filled with suitable phosphors. It has been demonstrated that the overall resolution of the system has increased by reducing the diffusion of the light in the phosphors. Various types of PPD have been produced and tested, demonstrating a high resolution in the beam profile and the ability to measure the actual spot size shot-to-shot with an unprecedented resolution. For these reasons, the proposed detector could become a reference technique in the FEL diagnosis field. [ABSTRACT FROM AUTHOR]

Measurement of the emission wavelength and the spectral content of the photon radiation is essential information for both machine and experimental physicists at a free-electron laser (FEL) user facility. Knowledge of the photon beam spectral properties is needed during the machine optimization and for performing machine studies ( i.e. monitoring the change of the FEL output as a function of the machine parameters). The experimentalists, on the other hand, need to know the photon beam spectral distribution of the source, shot to shot, to discriminate the acquired data. Consequently, the main requirement for the instrument, supposed to obtain this information, is the capability of working on-line and shot-to-shot, with minimal perturbation of the beam delivered to the experimental stations. Starting from the grating fundamental equations, the conceptual design of the FERMI Pulse-Resolved Energy Spectrometer: Transparent and On-line (PRESTO) is presented, explaining the optical design in detail. The performance of PRESTO, in terms of resolving power, efficiency and spectral response, is also discussed. Finally, some useful features beyond the usual measurement of the energy spectrum are reported, as they have been routinely used by both machine and experimental physicists. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Photon Analysis Delivery and REduction System of FERMI (PADReS) has been routinely used during the machine commissioning and operations of FERMI since 2011. It has also served the needs of several user runs at the facility from late 2012. The system is endowed with online and shot-to-shot diagnostics giving information about intensity, spatial-angular distribution, spectral content, as well as other diagnostics to determine coherence, pulse length etc. Moreover, PADReS is capable of manipulating the beam in terms of intensity and optical parameters. Regarding the optics, besides a standard refocusing system based on an ellipsoidal mirror, the Kirkpatrick-Baez active optics systems are key elements and have been used intensively to meet users' requirements. A general description of the system is given, together with some selected results from the commissioning/operations/user beam time. [ABSTRACT FROM AUTHOR]

The Diffraction and Projection Imaging (DiProI) beamline at FERMI, the Elettra free-electron laser (FEL), hosts a multi-purpose station that has been opened to users since the end of 2012. This paper describes the core capabilities of the station, designed to make use of the unique features of the FERMI-FEL for performing a wide range of static and dynamic scattering experiments. The various schemes for time-resolved experiments, employing both soft X-ray FEL and seed laser IR radiation are presented by using selected recent results. The ongoing upgrade is adding a reflection geometry setup for scattering experiments, expanding the application fields by providing both high lateral and depth resolution. [ABSTRACT FROM AUTHOR]

Abstract: To enhance the reflectivity of X-ray mirrors beyond the critical angle, multilayer coatings are required. Interface imperfections in the multilayer growth process are known to cause non-specular scattering and degrade the mirror optical performance; therefore, it is important to predict the amount of X-ray scattering from the rough topography of the outer surface of the coating, which can be directly measured, e.g., with an Atomic Force Microscope (AFM). This kind of characterization, combined with X-ray reflectivity measurements to assess the deep multilayer stack structure, can be used to model the layer roughening during the growth process via a well-known roughness evolution model. In this work, X-ray scattering measurements are performed and compared with simulations obtained from the modeled interfacial Power Spectral Densities (PSDs) and the modeled Crossed Spectral Densities for all the couples of interfaces. We already used this approach in a previous work for periodic multilayers; we now show how this method can be extended to graded multilayers. The upgraded code is validated for both periodic and graded multilayers, with a good accord between experimental data and model findings. Doing this, different kinds of defects observed in AFM scans are included in the PSD analysis. The subsequent data-model comparison enables us to recognize them as surface contamination or interfacial defects that contribute to the X-ray scattering of the multilayer. [Copyright &y& Elsevier]