PhotonMEADOW23

Sep 12, 2023, 8:30 AM → Sep 14, 2023, 6:00 PM Europe/Rome

Trieste, Italy

The PhotonMEADOW23 will be held in Trieste from the 12th to the 14th of September 2023, at the International Centre for Theoretical Physics (ICTP). This event will merge two workshops: the "MEADOW - 10 years after" and the "PhotonDiag 2023":

• MEADOW - 10 years after aims at celebrating the 10th anniversary of the original MEADOW2013, the "MEtrology, Astronomy, Diagnostics and Optics Workshop" that was held in the same venue in 2013
   
• PhotonDiag 2023 represents the 6th edition of the "FELs of Europe Workshop on FEL Photon Diagnostics, Instrumentation, and Beamlines Design"

 

Combining the two workshops, there will be the opportunity to focus on several topics such as:

• X-ray optics design, realization and metrology (SR, FEL and Astronomy)
• Beamline design and simulation (SR and FEL)
• Photon diagnostics for FELs and synchrotrons
• Wavefront sensing (SR, FEL and Astronomy): simulations, instrumentation, measurements
• Time-related beam properties - temporal characterisation of electron, FEL, and laser beams
• Science instruments and detectors
• Scientific computing, machine learning and large data management
   

Tuesday, September 12

Welcome and Institutional

1 Welcome

Speaker: Marco Zangrando (Elettra Sincrotrone Trieste and CNR-IOM)

2 Operation and Upgrade of Elettra and FERMI

Speaker: Prof. Alfonso Franciosi (Elettra Sincrotrone Trieste)

X-ray optics design, realization and metrology: X-ray optics design, realization and metrology - 1

3 Correction of X-ray wavefront errors using adaptable refractive correctors

Imperfection in X-ray focusing optical elements result in phase errors which when propagated to the focal plane cause broadening of the focused beam profile. A useful concept is the X-ray wavefront which is a surface of constant phase and for ideal focusing this is a spherical surface centred on the focal point. Aberrations in optical elements cause a deviation of the wavefront from this ideal surface and give rise to loss of spatial resolution at the focus.
For 4th generation X-ray sources emitting X-rays with high spatial coherence, the requirement for achieving close to diffraction limited focusing is that the rms wavefront error should be a small fraction of the X-ray wavelength. This implies rms wavefront errors at the picometre level, which is highly demanding, and often this is beyond the limits of fabrication.

X-ray wavefront correction is a developing field in which special optical elements are inserted into the optical path to compensate the X-ray wavefront errors introduced by imperfect optics. I will describe design, fabrication and testing of wavefront correcting optical elements that use the weak refraction of X-rays to advance the X-ray phase with a variation in refractor thickness along one transverse direction giving a position dependent phase correction. Using a pair of refractors, the correction can be made adaptable to dynamically match the optical element allowing compensation for time dependent changes and for an X-ray energy independent correction. A pair of correctors can be used to separately correct the wavelength along two orthogonal directions.

Speaker: David Laundy (Diamond Light Source)

4 Blazed Soft X-Ray Gratings Fabricated by Grey-Tone Electron-Beam Lithography and Thermal Oxidation of Silicon

Blazed gratings are an essential element for instruments used at free electron laser and synchrotron facilities in soft and tender X-ray ranges. Their application ranges from beamline monochromators and spectrometer analyzers to self-seeding and pulse compression elements. These gratings are commonly made by mechanical ruling, however, the production time of high-quality blazed gratings has become a major bottleneck due to technological challenges in their fabrication and few suppliers only.
In this presentation, we report on a novel method for the production of next-generation X-ray diffraction gratings based on grey-tone electron-beam lithography (EBL) and thermal oxidation of silicon. This new technology gives advantage of high flexibility regarding the grating design, allowing for enhanced optical performance as well as novel optical functionalities. This EBL technique with its high resolution allows for the fabrication of several gratings with different pitches and/or blazed angles on the same substrate.
We will also present the at-wavelength characterization of manufactured blazed gratings. The measurements were done at the Optics beamline at BESSY II. The diffraction efficiency over the soft X-ray energy range, as well as the dispersion of the gratings, was investigated. The results show that the measured gratings match the required surface roughness, high diffraction efficiency, and very low diffuse scattering noise.

Speaker: Nazanin Samadi (Paul Scherrer Institute)

10:30 AM Coffee break - 1

X-ray optics design, realization and metrology: X-ray optics design, realization and metrology - 2

5 Synchrotron- and substrate-induced structural modifications in adventitious carbon layer on beamline optical elements

The XRD2 and XPRESS beamlines of Elettra, the Italian synchrotron facility, share a multipole semiconducting wiggler as photon source. XRD2 receives light from the central portion of the photon beam while a Si(111) beam splitter, at an incident angle of 4.5°, reflects a side portion of the radiation cone towards XPRESS. Upon dismounting, the crystal showed an unexpected, longitudinal, 4 mm-wide stripe on the optical element surface, clearly correlated with the beam footprint.

We will show the structural and chemical characterization performed in trying to understand what occurred to the crystal surface. Fizeau Interferometry revealed that the stripe was a relatively bulky bump, roughly 500 nm high at the initial incident point of the beam, and gradually decreasing along the crystal. Interestingly, X-ray Diffraction did not show any local variation of the Si crystal lattice parameter, ruling out any possible thermally-induced deformation. Finally, Infrared and Raman Spectroscopy allowed us ascertaining the adventitious carbon composition of the bump, also suggesting a non-amorphous layer and its hybridization states.

This study highlights the role played by carbon, as a common and diffuse contaminant, on affecting the performances of X-ray optical elements. Moreover, it confirms the occurrence of significant structural changes in the carbon layer, as the result of complex interactions with the substrate, i.e. the optical element surface, and the synchrotron radiation.

Speaker: Roberta Totani (ELETTRA SINCROTRONE TRIESTE)

6 Diamond-VeNOM: a high-speed slope profiler for characterising X-ray mirrors

We present the Diamond-VeNOM (velocity-NOM): a high-speed slope profiler of X-ray optics. With recent improvements in the fabrication quality of X-ray mirrors, the systematic errors of optical profilers are no longer negligible. For optics with slope errors << 100 nrad rms, repeated scans with the mirror oriented in a range of configurations are required to null experimental errors and improve measurement accuracy. This process is effective, but time consuming. To solve this problem, we have developed a dynamic profilometer system, whereby the optical surface is pitched in synchronization with translation of the scan head. Multiple autocollimators are used to simultaneously monitor the optical surface, parasitic angular errors of the air-bearing scan head, and angular rotation of the optic under test. A significant increase in measurement speed is achieved using new Elcomat5000 autocollimators with a 250 Hz acquisition rate. Based on 1 kHz feedback from motion encoders, a PandA input/output box triggers mechanical shutters to simultaneously block the beam path of each autocollimator when the motion stages reach a series of user-defined positions or angles. This enables synchronization of variable-speed translation and pitch trajectories with data acquisition from multiple autocollimators. This new innovation reduces the burden of post-processing data alignment and enables more sophisticated motion trajectories, including on-the-fly, automated nulling of the optical surface to reduce systematic errors. We demonstrate that fly-scanning, combined with the speed enhancement of the new autocollimators, leads to a 20X time efficiency of the Diamond-VeNOM compared to the Diamond-NOM’s traditional step-scans, without loss of data quality.

Speaker: Dr Simon Alcock (Diamond Light Source Ltd)

7 Experiences and Challenges with X-ray Optics for the LCLS

In the past 5 years, the LCLS Optics Metrology Laboratory has measured and encountered numerous types of extreme x-ray optics in various phases, i.e. from prototyping to qualifying the bare optics to the fully assembled optics systems. In this presentation, selected examples of optic work will be shared for illustrating the interesting experience working with optics for the LCLS, and the lessons learned. The hope is to create awareness in the community on what may be expected from such scale and magnitude of facility upgrade.

Speaker: Dr May Ling Ng (SLAC National Accelerator Laboratory)

8 Characterization of silicon pore optics for the ATHENA observatory in the PTB laboratory at BESSY II

For new astrophysics X-ray observatories like the Advanced Telescope for High ENergy Astrophysics (ATHENA), mirror surfaces of several hundred m² are required. As such an area is not achievable with a single mirror in space, the silicon pore optics (SPO) technology will be utilized. In the PTB laboratory at BESSY II, two dedicated beamlines are in use for their characterization with monochromatic radiation at 1 keV and a low divergence well below 2 arc sec: the X-ray Pencil Beam Facility (XPBF 1), providing a pencil beam of about 100 μm x 100 μm since 2005, and the X-ray Parallel Beam Facility (XPBF 2.0) where since 2016 beam sizes up to 7.5 mm x 7.5 mm are available while maintaining the low beam divergence. The SPOs are aligned and scanned with in-vacuum hexapods, and two electronic autocollimators are used to guaranty a hexapod positioning accuracy of 0.7 arc sec. A movable CCD-based camera system at a distance of 5 m or 12m to the SPO registers the direct and the reflected beam. The positioning of the detector can by verified by a laser tracker. XPBF 2.0 is not only used to characterize mirror stacks, but also to control the focusing properties of mirror modules (MM) - consisting of 4 mirror stacks - during their assembly at the beamline. The energy-dependent reflectance of a MM with Ir coating has been measured at two other beamlines in the entire photon energy range from 0.2 to 10 keV.

Speaker: Michael Krumrey (Physikalisch-Technische Bundesanstalt)

9 Updates on optical metrology for synchrotron mirrors at NSLS-II

In most synchrotron applications, X-ray mirror slope specification is an important parameter for applications using a partially coherent X-ray beam. The slope error is typically specified at the sub 100 nrad RMS for mirrors up to 1000 mm long by 50 mm wide. For applications using diffraction-limited X-ray beams, height specification is a more relevant parameter to maintain and focus the beam at the diffraction limit. The typical specification is at 1 nm or even sub-nm RMS level.
These requirements, whether specified in slope or height, bring enormous challenges to synchrotron mirror metrology. This task requires dedicated metrology instruments to accurately characterize these high-precision mirrors when typical surface shapes can be flat, circular cylinders, off-axis elliptical cylinders, or even two-dimensional curved shapes. Several metrology instruments have been developed at NSLS-II to tackle these challenges to characterize these high-precision synchrotron mirrors.
With several years of research and development, our group at the NSLS-II has established a procedure for optical metrology and mirror fabrication using ion beam figuring. In our workflow, a stitching interferometer prototype based on a Fizeau interferometer is used as an in-process inspection tool to provide feedback to an ion beam figuring instrument for synchrotron optics fabrication. When the mirror is under specification, it will be inspected by other metrology instruments to make cross-validation. Various metrology instruments, including the stitching shack-Hartmann instrument, the nano-accuracy surface profiler, and the micro-stitching white light interferometer, are used as final inspection tools to characterize the optics fabricated in-house or supplied by vendors.

Speaker: Dr Mourad Idir (Brookhaven National Laboratory)

12:40 PM Conference Photo

1:00 PM Lunch

X-ray optics design, realization and metrology: X-ray optics design, realization and metrology - 3

10 Highly efficient multilayer-coated blazed and laminar gratings for tender X-ray energy range

Multilayer coating on top of high line density blazed gratings can increase its diffraction efficiency up to one order of magnitude for a selected diffraction order. In combination with multilayer coated pre-mirror in plane grating monochromator (PGM) the total instrument transmission can be increased in hundreds of times. In our developments on multilayer-coated blazed gratings (MLBG) we have reached experimentally efficiency up to 60% [1,2] in tender energy range where single coated grating would demonstrate only few percent. After several successful prototypes the real MLBG were designed and installed in c-PGM at u41-TXM-beamline at BESSY-II [3].
The key factor of high performance MLBG is in correct optimization of both multilayer and grating profile parameters to each other [4]. Our current developments are focused on extension of operating energy range, employing ML coating on laminar profile (MLLG) and tuning the optimization in order to significantly increase grating angular dispersion (i.e. an instrument energy resolution) with minimal losses in the grating efficiency. In our contribution, we are presenting our latest successful experiments with broad energy range MLBG, high efficiency MLLG and MLBG optimized for higher diffraction orders. Together with this, we are going to discuss possibilities to reach highest of possible resolving power with MLBG and challenges connected with that.
[1] A. Sokolov et al., Opt. Express 27(12), 16833 (2019)
[2] F. Senf et al., Optics Express 24(12), 13220 (2016)
[3] S. Werner et al., Small Methods 7(1), 2201382 (2023)
[4] Q. Huang et al., Opt. Express 28, 821 (2020)

Speaker: Dr Andrey Sokolov (Helmholtz-Zentrum Berlin fur Materialien und Energie, BESSY II)

11 Development of stitching interferometry and ion beam figuring methods for high precision X-ray mirrors

Driven by the fast development of the new generation storage ring and free-electron laser facilities, X-ray mirrors with nanometer figure accuracy, complex shape and large size are widely demanded. These optics are being developed in Tongji University using stitching interferometry and ion beam figuring technique. Stitching interferometry is commonly used for the 2-D figure metrology of X-ray mirrors, while the accumulated angular error among neighboring subapertures and the systematic error within each subaperture are affecting the stitching accuracy. A method to correct the angular error using low-frequency profiles measured by other instruments is studied, called ‘mixed stitching’. It directly obtains the stitching angles from the 1-D profile along one direction of the entire tested mirror which further correct the relative angles fitted from algorithm. The stitching accuracy can be both improved either by a commercial contact profiler or a high-precision slope measurement system and the minimum figure error of below 1 nm RMS can be achieved. The shape error of a single subaperture is studied and reduced by calibration of the reference mirror and lateral resolution of the Fizeau interferometer. Based on these improvements, the measured figure accuracy of elliptical mirror using simple global stitching algorithm was improved to 1.5 nm RMS. Based on the high-precision stitching interferometry, mirrors with maximum length of 500mm and figure height error of 1nm RMS were manufactured and some of them have been applied in the synchrotron radiation facility. These results will be presented and discussed.

Speaker: Prof. Qiushi Huang (Tongji University)

12 Next Generation of Mirror Benders at LCLS

The ongoing upgrades of the Linac Coherent Light Source (LCLS) at SLAC aim to further expand the capabilities of X-ray free electron lasers by delivering photon energies up to 20 keV at 1 MHz repetition rates. To support these advancements, significant improvements are being made to the beamlines, particularly through the implementation of new bendable mirror systems capable of operating under these extreme conditions. The design of these upgraded benders builds upon the success of previous generation systems at LCLS, improving aspects such as cooling, mounting and kinematics, twist correction, stability, and overall performance. This talk will provide an overview of the upgrade efforts and highlight the key features and advancements of the new mirror bender systems.

Speaker: William Lane (SLAC)

3:20 PM Coffee break

Beamline design and simulation: Beamline design and simulation - 1

13 The Optics of the Athos Soft X-ray Beamlines at SwissFEL

SwissFEL is a free electron laser, comprising of two undulator lines with three endstations each: covering 2 – 12.7 keV (up to 1.5 mJ) and 0.25 – 2 keV (up to 5.0 mJ), respectively.
We present the design and commissioning of the ATHOS soft x-ray optics, starting with the overall beamline-layout and the optical components inside the front-end: a gas attenuator, a thin foil based solid-state attenuator, slits and a photon-beam diffusor, dispersing the x-ray beam and protecting the beam-stopper.
Inside the optics hutch a horizontal deflection mirror separates the bremsstrahlung and the x-rays. To ensure a common beam-path behind the monochromator, for mono- and pink-beam operation, two vertical offset mirrors can move into the beam instead of the monochromator. We discuss the design and performance of these in-house build mirror-systems. The monochromator has an upward deflecting grating, accommodating different beam-heights at the endstations. We present commissioning results for the monochromator using an ionisation chamber, a scintillation screen based 2D-detector and a 1D-detector with improved resolution for also characterising the spectrum of attosecond pulses.
There are horizontal deflection mirrors between the monochromator (common to all three endstations) and the exit slits (specific to the endstations) to steer the beam towards the corresponding experiment.
Each endstation has a KB-mirror system to focus the beam onto the sample. We use slit scanning to optimise its focal spot size. A laser-based pointing system (upstream of the KB) coincides with the x-ray beam, enabling sample alignment ahead of the beamtime.

Speaker: Dr Ulrich Hilmar Wagner (PSI)

14 BEaTriX, the new facility to measure the modular X-ray optics of the ATHENA telescope with an expanded and parallel X-ray beam

BEaTriX (Beam Expander Testing X-ray) is a unique facility developed at the INAF-Osservatorio Astronomico Brera (Merate, Italy) to test ATHENA’s X-ray mirror. The commissioning has been successfully completed, and the facility is now open to users.
The unique BEaTriX X-ray beam approximates the one created by an astronomical source (collimated and large), and it is re-created in a small lab (about 9 m × 18 m) thanks to an innovative design. A microfocus X-ray source produces a divergent beam which is conditioned by a parabolic mirror and a set of silicon crystals, one of which is asymmetrically cut with respect to the lattice planes. The first beam line, at the energy of 4.51 keV, is operative. The beam is collimated to < 3 arcsec, with a flux of 60 photons/s/cm2. Its size (170 mm × 60 mm) is sufficiently large to cover the entrance pupil of the ATHENA Silicon Pore Optics Mirror Modules (MM), generating an image at its focal length of 12 m. Its small size and vacuum modular compartments ensure a fast test rate, enabling the X-ray acceptance tests (PSF and Effective Area) of the ATHENA Silicon Pore Optics Mirror Modules (MM) at their production rate (2 MM/day), at 4.51 and 1.49 keV.
Giving the excellent results of the 4.51 keV beam-line, we have started the development of the second 1.49 keV beam line to be implemented in Merate, and a feasibility study to replicate the facility at the cosine premises, with beamlines at 1.49 and 6.4 keV

Speaker: Dr Bianca Salmaso (INAF - Osservatorio Astronomico Brera)

15 Closing the gap - towards tender X-rays by means of multi-layer coated gratings as monochromator optics

State-of-the-art soft X-ray beamlines use collimated plan-grating monochromators (cPGM) as monochromatizing devices. Multi-Layer (ML) coated plane gratings and mirrors allow to extend the available photon energy range of cPGM’s towards the so-called tender X-ray photon energy range (up to 5 keV) providing a significantly higher photon flux. This X-ray energy regime covers L- and M-absorption edges of most of the transition and rare-earth metals as well as K-edges of lighter elements such as silicon, sulfur and phosphorus. Recently such a ML based monochromator setup became operational at the U41-PGM1-XM beamline at the BESSY-II storage ring in Berlin. This beamline upgrade enabled for the first-time high resolution spectro-microscopic applications using photon energies up to 3keV. And extend its possibilities to support research e.g. on the field of life-science, semiconductor development and battery research. We will report on the design, commissioning and performance of this beamline and discuss possible options for new developments on the field of beamlines and end-stations in the tender-X-ray energy range (up to 5keV) at existing and future new accelerator-based photon sources.

Speaker: Frank Siewert (Helmholtz Zentrum Berlin)

16 Scattering effect from mirror surface defects: analytical and simulation approach

The scattering properties of mirror surfaces are strongly dependent on the surface structure and radiation incidence angle, for a given photon energy. In particular, in Free Electron Laser and Synchrotron X-ray photon transport beamlines, the perturbation of the scattering effect is often dominant in the Point Spread Function (PSF) degradation. The perturbation theory explains the surface Power Spectral Density (PSD) - scattering link, its main result being a simple linear relationship between the scattered intensity distribution and the PSD, expressed as a function of the surface spatial wavelength. The PSD can be assembled from various surface profile measurements, such as optical interferometry, profilometry, and Atomic Force Microscopy. Mathematically, the PSD is the square of the surface profile’s Fourier transform, or, equivalently, the Fourier transform of the auto-covariance function of the surface profile. Given the PSD of a non-ideal mirror surface, the mathematical form of the observed scattering is provided by the well-consolidated first-order perturbation theory.

The present work discusses the degradation of the PSF due to the scattering in grazing incidence geometry, from Extreme Ultra Violet to Hard X-ray photon energies. We analyzed a simple optical system constituted by a plane mirror and a set of Kirkpatrick-Baez plane-elliptical mirrors, taking into account the complete PSD of the mirrors.
The issue is discussed by comparing a first-order scattering theoretical approach and simulations performed with SHADOW (raytracing), Synchrotron Radiation Workshop (SRW, wave optics based), WISEr (wave optics based), and SHADOW’s Hybrid extension. The results obtained should be useful in facing this issue.

Speaker: Lorenzo Raimondi (Elettra-Sincrotrone Trieste)

17 Design plane varied-line-spacing grating in complex optical layout using step-by-step ray tracing method

Varied-line-spacing grating is a key optical element in the light facilities, concerning lithography, holography, tomography, as well as spatially resolved monochromator/spectrometer. In the last decades, the grooves parameters of varied-line-spacing gratings are necessary to be strictly deduced through the light path function and the Fermat's principle. This method is of great importance to analytically solve the spot focusing, correcting aberrations and compressing the pulse stretching. However, one needs to develop sophisticated light path function with Taylor expansion, and even with the efforts, coma and aberrations in high order cannot be totally corrected. In this article, we report a visual and universal method to analytically calculate the groove parameters for plane varied-line-spacing grating in a Hettrick-Underwood type spectrometer using step-by-step ray tracing, and have a great agreement with the Fermat's principle with Maclaurin series. Additionally, we use a semi-analytic approach to fast find out the focus point for a whole energy range based on the ray-tracing method. This framework provides new insights into optical design, manufacture, and metrology.

Speaker: Meiyi Wu (Institute of Advanced Science Facilities)

Wednesday, September 13

Beamline design and simulation: Beamline design and simulation - 2

18 X-ray photon transport simulators comparison: which will win?

The race toward completing several next-generation X-ray light source facilities around the world has been running hot since a few years. This has created the need to accurately simulate the performances of the beamlines before they are built, so as to make sure the optimal layout has been chosen. To this end, the optical community has at its disposal several simulation tools, most of them incorporated into a single framework, Oasys.
The aim of this work is to highlight the strengths and weaknesses of three among the most commonly used software tools, namely SHADOW, Synchrotron Radiation Workshop (SRW), and WISEr, the first being a raytracer, while the last two are concerned with wave optics. For completeness, we included in our analysis also SHADOW’s Hybrid extension.
In order to compare the different codes, we propagate a photon beam at different energies through a simple optical system, constituted by a plane mirror and a set of Kirkpatrick-Baez plane-elliptical mirrors.
We compare different diffraction effects, as well as the effects of the mirrors’ figure errors.
The results obtained should be useful in choosing a specific simulation tool for a specific task in beamline design, while at the same time clarifying to new users the strengths and limits of each of the codes.

Speaker: Dr Matteo Altissimo (Elettra Sincrotrone Trieste SCpA)

19 Active grating for monochromatization in the extreme-ultraviolet spectral region

The monochromatization of radiation in the extreme ultraviolet spectral region is accomplished by using diffraction gratings at grazing incidence. In the most general case, the grating is roto-translated to perform the wavelength scanning. Different optical configurations have been proposed until now, both using plane and concave gratings and with uniform or variable line spacing.
In this work we propose the use of a bendable grating as dispersing element. The control of the curvature radius of this optical element permits to perform at the same time the spectral selection and the focalization of the selected spectral component. As a consequence, the number of the optical elements is reduced from three to two: the grating and a focusing mirror.
We will present a low-cost mechanical implementation of this optical concept in which a thin plane diffraction grating, with a flat at rest optical surface, is bended by the use of a mechanical device to an almost cylindrical shape.
The device has been tested in the 13-50 eV energy region, showing very good focal properties with very low residual aberrations. To quantify these aberrations, the shape of the bended surface has been measured using a wavefront sensor.
Possible applications of the proposed solution are both in large-scale facilities such as FELs or synchrotrons, but also in table-top setups, such as those exploiting high-order harmonic generation.

Speaker: Fabio Frassetto (CNR-Institute for Photonics and Nanotechnologies, Via Trasea 7, 35131, Padova, Italy)

20 The new Pulse-Length Preserving Double Monochromator Beamline at FLASH

FLASH, the soft X-ray free-electron laser (FEL) in Hamburg provides high-brilliance ultrashort femtosecond pulses at MHz repetition rate for user experiments. For high resolution spectroscopic and dynamical studies in various research fields a small FEL energy bandwidth and ultrashort pulses are a prerequisite. While single grating monochromators provide high-energy resolution they introduce a pulse-front tilt which effectively elongates the longitudinal pulse profile, thus decreasing the time resolution. In order to preserve a short pulse duration and still monochromatize the FEL radiation, the new pulse-length preserving monochromator beamline FL23 at FLASH2 uses a double-grating design. A first grating disperses the radiation and an intermediate slit reduces the spectral bandwidth, a second grating operating in compensating configuration turns back pulse front tilt, thereby preserving the ultrashort photon pulses.
The open port beamline covers the spectral range between 1.3 nm and 20 nm with a spectral resolving power of approximately 2000. The beamline can also be operated in a single grating configuration in order to maximize the transmission at the high energy end. The bendable Kirkpatrick-Baez mirror system provides flexible microfocusing at the experiment. A femtosecond optical laser synchronized to the FEL will be provided for pump-probe experiments. The beamline concept and design has been developed using ray tracing simulations and confirmed by wavefront propagation simulations.
Here, the pulse-length preserving double monochromator beamline concept will be introduced, the different operation modes and expected photon parameters at the experimental station will be discussed and the first commissioning results will also be shown.

Speaker: Guenter Brenner

21 OASYS and DABAM: Two important projects born after MEADOW-2013. Status and Perspectives

We present two significant projects, namely OASYS (OrAnge SYnchrotron Suite)
and DABAM (DAta BAse for mirror Metrology), which emerged as notable outcomes from MEADOW2013. Both projects have had a considerable impact on the field of X-ray science and have provided valuable resources for researchers and scientists.

OASYS [1], an open-source software suite developed for the simulation and analysis of X-ray beamlines, has been instrumental in enhancing the design and optimization of beamlines in upgraded storage rings. Through its comprehensive toolset (add-ons), OASYS facilitates ray tracing, wavefront propagation, source modeling, and data analysis, thereby enabling researchers to study X-ray optics and simulate beamline performance. OASYS continues to evolve, incorporating new features and functionalities to meet the challenges of the X-ray science community.

DABAM [2] is a collaborative project aimed at creating a comprehensive database for mirror profiles measured in the metrology laboratories of synchrotron facilities and research institutions worldwide. DABAM serves as a centralized repository of information on the error profile characteristics of mirrors used in X-ray beamlines. DABAM facilitates the simulation of real mirrors in ray tracing and wavefront propagation simulations and is completely integrated into the OASYS environment.

This talk discusses the status and ongoing developments of both projects. It highlights the impact of OASYS and DABAM in adapting and upgrading many beamlines to the new low-emittance storage rings in operation (EBS-ESRF), being implemented (APS-U), or in project (ALS-U, etc).

[1] http://dx.doi.org/10.1117/12.2274263
[2] http://dx.doi.org/10.1107/S1600577516005014

Speaker: Dr Manuel Sanchez del Rio (ESRF)

Wavefront sensing

22 Developing high numerical aperture EUV Lithography at FELs

Extreme ultraviolet lithography (EUVL) is considered to be the future method of mass production of integrated circuits on chips. For long time, Free-Electron Lasers (FELs) have been proposed to accomplish the challenges of EUVL, i.e., a suitable power optical light source and the scanning speed of the wafer. According to this, we developed a two-steps EUVL experiment at FLASH using a Schwarzschild objective:
First, the Schwarzschild objective (SO) is aligned using at-wavelength wavefront sensor optimized for beams with a high numerical aperture. The phase measurements acquired with the wavefront sensor were analyzed using Fourier Demodulation (FD), an approach based on Fourier transformation analysis of repeating patterns. FD can recover the phase and the intensity and overcomes the measurement challenges of a SO pattern: 1) a huge magnification downstream the focus with attendant spherical aberration; 2) an obscuration of the central area; and 3) a discontinuous annular pattern divided into three lobes.
Secondly, the micrometer-sized focus of the Schwarzschild is used to demonstrate imaging. The Schwarzschild objective is used here in an on-axis geometry to image transparent samples on photosensitive material. Based on ray tracing, it is expected that the imprinted structures will have a resolution of approximately 100 nm (RMS focus-size). We will investigate state-of-the-art EUV components related to EUVL such as multilayer mirrors and photoresists submitted to intense EUV radiations.
Here the methods used in the first and the second step of this experiment will be presented and the results of the measurements will be discussed.

Speaker: Mabel Ruiz Lopez (DESY)

23 Wavefront sensing : Investigating FEL sources and Optics tuning

For the past 10 years, wavefront sensing has been a crucial component of Free Electron Laser (FEL) facilities. Not only does it help evaluate the quality of the wavefront delivered on the sample and optimize optical systems, but it also opens the door to the new, intriguing field of source metrology. Because of the complexity of the emission process, important parameters such as the effective source position and dimension may be a-priori not known and depend on the required machine optimization. Therby, the idea of aiming wavefront sensing at source characterization is captivating because of its shot-to-shot operability and accuracy, making it suitable as feedback for machine-tuning operations.In such a scenario, the interplay of both source and optics is determinant for the quality of the delivered spot. Here, we will report on the recent advances in both fields at the FERMI XEUV seeded-FEL facility.
On the optics side, we will discuss the application of Hartmann wavefront sensing for pushing to the limit the capabilities of the KAOS active focusing system when operated far away from its ordinary working range. This is necessary to deliver a near collimated beam, and it is becoming increasingly common with the use of auxiliary diffractive optics used to deliver OAM beams.
On the source metrology side, we will show how distinct machine configurations may affect the emitted wavefront, inspect subtle parameters, such as phase shifter, dispersive section currents and the seed delay.

Speaker: Michele Manfredda (ELETTRA)

11:00 AM Coffee Break

Wavefront sensing

24 Wavefront metrology and beam propagation in the EUV/X-ray spectral range

Proper in-situ fine-adjustment of the optical elements is crucial for an optimal performance of beam lines at synchrotron or free-electron laser facilities, considering that even slight misalignments of the grazing incidence mirrors can already deteriorate the focal spot. Real-time wavefront monitoring represents a valuable tool for reduction of these aberrations. In particular, wavefront sensors based on the Hartmann technique are well suited for this purpose as they afford rather compact setups and can be employed for both coherent and partially coherent radiation.
A Hartmann-type wavefront sensor was developed for the EUV and soft X-ray range in cooperation with DESY / Hamburg. From the simultaneous recording of wavefront and beam profile, prediction of the propagation behaviour of the beam is possible. In particular, focal intensity distributions can be computed, considering also the spatial coherence properties of the FEL beam. The latter were accessed experimentally for FLASH, using caustic scans and a subsequent evaluation of the Wigner distribution function. The improved Hartmann sensors are now routinely applied for fine-tuning of grazing incidence focusing mirrors of the free electron lasers FLASH and European XFEL / Hamburg.
Nevertheless, due to the many non-orthogonal degrees of freedom of these focusing optics, an optimal adjustment using wavefront metrology can be still very time-consuming. Within the new project “FEL Focus” fast machine learning algorithms based on wavefront data are developed in order to automate the fine-adjustment of FEL optics. Such an automated system control will greatly reduce the workload of the measuring station staff.

Speaker: Dong Du Mai (Institut für Nanophotonik Göttingen e.V.)

25 Hard X-ray Hartmann wavefront sensor for focus optimization of Compound Refractive Lenses at the European X-ray Free Electron Laser

The intense X-ray FEL beam delivered by European X-ray Free Electron Laser (EuXFEL) facility gives rise to strong challenges for the optics and their diagnostic. It is important to have an accurate knowledge of the single pulse X-ray wavefront, which affects focal plane intensity and profile, spot size, and spatial resolution, as well as centroid location within the focal plane. Wavefront sensing is important for quantitatively understanding the aligning of X-ray optical components and for conducting scientific experimental analysis. The Hartmann hard X-ray Wavefront sensor (HXWFS) enables measurements over a wide range of energies, as is common on X-ray instruments, with simplified mechanical requirements and is compatible with the high average power pulses delivered by EuXFEL. Hartmann sensor is composed of a grid of holes and a 2D detector that is tightly bound together with mechanics as a single device. Furthermore, the use of a hole array makes the sensor achromatic; wavefront measurement can be performed over a broad energy range. We will present recent preliminary results of the characterization of the focus scheme of SPB/SFX hutch compound refractive lenses (CRLs) at 9.3 keV photon energy using HXWFS (from the Imagine Optic, France) and Talbot wavefront sensor (diamond phase grating + scintillator-based camera) device. It is used to provide real-time measurement of the focal spot by CRLs of a beamline at strategic positions such as at the interaction of sample position.

Speaker: Dr Naresh Kujala (EuXFEL)

26 High-resolution hard X-ray Hartmann wavefront sensor

Wavefront sensing is a powerful tool enabling a variety of applications ranging from characterization and alignment of passive or active optical systems to non-destructive testing and phase imaging. Indeed, in the recent past, high-resolution Hartmann sensors have facilitated translating the applications of wavefront sensing to the extreme ultraviolet and X-ray spectral range.

In this work, we report on the performances of a high-resolution hard X-ray Hartmann wavefront sensor (HASO HXR) compatible with a broad photon energy range (5 - 25 KeV). The given sensor exhibits a spatial sampling of 20 μm, offering 100×100 sampling points over a field of view of 2×2 mm^2. To assess the performance of the hard X-ray wavefront sensor, we utilize Instrumentation Facility BM05 at European Synchrotron Radiation Facility (ESRF), Grenoble, France. The calibration performed at 14 KeV (88.57 pm) indicates at-energy root-mean-square (RMS) wavefront measurement accuracy and repeatability of 112 pm and 6 pm, respectively. Moreover, post-calibration, we utilize the HASO HXR to perform phase imaging of different polymeric wires at 14 KeV. Through relative wavefront measurement, i.e., detecting the wavefront with and without the sample, the Hartmann-based approach offers the possibility of extracting absorption, deflection, and phase images in X-ray spectral range.

On the one hand, the high-resolution hard X-ray Hartmann wavefront sensor can be a critical tool for easing the characterization and alignment of optical systems in the stated energy range. On the other hand, as a potential application, the presented results demonstrate HASO-HXR-enabled wavefront sensing for hard X-ray phase imaging.

Speaker: Guillaume Dovillaire

27 Recent developments in X-ray speckle-based techniques at Diamond Light Source

Over the last decade, X-ray speckle-based techniques have been extensively developed for advanced imaging and high precision metrology of X-ray optics. The speckle-based techniques have gained popularity due to their relatively simple experimental requirements and ease of use. At Diamond, we have worked extensively since 2012 to enhance the technique and to apply it to a range of X-ray imaging and metrology applications[1-3]. In this presentation, we are going to present our recent developments of these techniques and their latest applications. First, we show that the omnidirectional differential phase and dark-field images can be simultaneously extracted from a single speckle data set[4] . Further, we demonstrate the link between the irregular patterns in the far-field intensity image and the local wavefront curvature through beamline measurements and optics theory [5]. Finally, we have extended our techniques to the temporal applications [6] and have shown that it is possible to achieve very fast temporal measurements using conventional hardware. This new technique has great potential for time-resolved or real-time applications for X-ray instrumentation.

Reference
[1] S. Berujon, H. Wang, et al, Phys. Rev. A 86, 063813 (2012).
[2] H. Wang, Y. Kashyap, et al, Phys. Rev. Lett. 114, 103901 (2015).
[3] H. Wang, Y. Kashyap, et al, Sci. Rep. 6, 20476 (2016).
[4] H. Wang and K. Sawhney, Proc. Natl. Acad. Sci. U.S.A. 118, 2022319118 (2021).
[5] L. Hu, H. Wang, et al, Opt. Express 29, 4270 (2021).
[6] L. Hu, H. Wang, O. Fox, and K. Sawhney, Opt. Express 30, 33259 (2022).

Speaker: Hongchang Wang (Diamond Light Source)

1:00 PM Lunch

Poster Session

3:40 PM Coffee Break

Sponsors' Presentations

16:00 - 16:10 FMB Oxford
16:10 - 16:20 XRNanotech
16:20 - 16:30 Imagine Optic
16:30 - 16:40 Axilon
16:40 - 16:50 JJ X-Ray
16:50 - 17:00 Horiba

Facility Reports

Social dinner

Thursday, September 14

Scientific computing, machine learning and large data management

28 Advancements in X-ray Wavefront Sensing and At-wavelength Metrology at the Advanced Photon Source

The Advanced Photon Source (APS) has achieved significant advancements in X-ray wavefront sensing and at-wavelength metrology, which are essential for optimizing the performance of X-ray optics and synchrotron beamlines. A notable breakthrough is the development of the coded-mask-based wavefront sensing technique, which merges the advantages of grating interferometry and speckle tracking. Capitalizing on this technique, two wavefront sensor prototypes have been engineered: one featuring adjustable zoom capabilities catering to varying beam conditions and resolutions and a second, more compact and cost-effective model adaptable for different beamline configurations. In terms of at-wavelength metrology, the technique has been used to evaluate the quality and performance of hundreds of lenses of different materials and types, mirrors, crystals, and windows for APS and the APS upgrade projects. The characterization results are critical to ensure optimal performance of the beamline instrument and, ultimately, the scientific experiments. For wavefront sensing, the applications are diverse, concentrating particularly on beamline diagnostics and wavefront control, which are vital for the precise adjustment and preservation of X-ray beam quality. Plans are underway to design and fabricate wavefront sensors customized for each APS upgrade beamline, promising further performance enhancements. Furthermore, a specialized application of these advancements is their integration into adaptive optics systems as feedback mechanisms for real-time wavefront control.

Speaker: Dr Xianbo Shi (Argonne National Laboratory)

29 A new user-friendly tool for simulating the efficiency of multilayer gratings

In recent years, several x-ray facilities have begun to use multilayer gratings (MLGs) in plane-grating monochromators thanks to their vastly superior efficiencies in the tender x-ray range compared to traditional single-layer gratings (SLGs). However, most of the software tools normally used for simulating the efficiencies of SLGs are not able to simulate MLGs. As a result several x-ray beamline designers have resorted to purchasing stand-alone proprietary software to calculate the efficiencies of MLGs. However this approach can lead to other complications, especially since many proprietary software packages have been designed with rather different scientific applications in mind.

Here we present a new MATLAB-based software tool being developed at Diamond Light Source (DLS) for simulating the efficiencies of both SLGs and MLGs for x-ray beamlines. At its core our software uses a freely-available program (GD-Calc from KJ Innovation) which calculates grating efficiencies via the Rigorous Coupled Wave Analysis method. Our aim is to provide a user-friendly software tool for simulating grating efficiencies which only requires a MATLAB license. Moreover, as the code is fully-integrated into MATLAB, we believe that our software will help streamline the design optimisation of future SLGs and MLGs. We will present our latest grating efficiency simulations and validate them against complementary simulations using established software such as REFLEC. The existing user interface for the software will be described and we will outline our plans for future software developments. Finally, we will summarise our plans for multilayer gratings at DLS in the context of the Diamond-II upgrade.

Speaker: Andrew Walters (Diamond Light Source)

30 Efficient simulation and AI surrogate models for real-time optimisation

In order to aid the design and development of optical elements, such as Reflection Zone Plates, and automate the process of aligning optics in both spectrometers and beamlines, we have developed new simulation software as well as deep learning AI methods.

RAY-X, our open-source state-of-the-art physics-based ray tracing software is designed to utilise modern GPUs to reduce trace time of simulated beamlines and allow for easier multi-processing of tasks. RAY-X fundamentally restructures the architecture of the well-known RAY and RAY-UI software [1, 2] and uses the Vulkan framework [3], an industry leading graphics and computing API, to provide high efficiency, cross-platform access to modern GPUs.

The capabilities of RAY-X have afforded us the capacity to generate large datasets in order to train complex neural networks as surrogate models for both beamlines and Spectrometers. These surrogate models have inference times of milliseconds and can therefore be deployed in situ at beamlines for the purpose of automated real-time alignment of optical elements.

References:
1. F. Schäfers, “RAY - The BESSY Raytrace Program”, in: Modern Developments in X-Ray and Neutron Optics, Springer Series in Modern Optical Sciences, eds A. Erko, M. Idir, Th. Krist, A.G. Michette, Vol. 137, 9–41 (2008) https://doi.org/10.1007/978-3-540-74561-7_2
2. RAY-UI: New features and extensions. AIP Conference Proceedings 2054, 060034 (2019) https://aip.scitation.org/doi/abs/10.1063/1.5084665
3. https://www.khronos.org/vulkan/

Speaker: Peter Feuer-Forson (Helmholtz Zentrum Berlin)

31 A New Ray Trace Computer Program For Radiation Safety

A new computer program has been created to assist in radiation safety ray trace operation for Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory. In contrast to historical method which has been performed manually using drafting tools on CAD softwares, the computer-based calculation propagate the illumination boundaries automatically and accurately using phase space method. This method differs from ray-based sampling method available in most commercial ray tracing packages and avoids the risk of under-sampling.
With a native graphical user interface, the program is easy to operate and allows for near real-time feedback on placements and motional ranges of components with regard to beam containment. By replacing manual construction of ray trace drawings, significant time saving is achieved (from week to second) and potential human errors avoided. Such reduction in overhead also allows beam line safety considerations to enter early in the design iterations and potentially avoid engineering effort for costly modifications later on.

Speaker: Dr Lance Lee (SLAC National Accelerator Laboratory)

10:30 AM Coffee Break

Photon diagnostics for FELs and synchrotrons

32 XFEL sub-10 nm focusing with 10^22 W/cm^2 intensity: wavefront corrected mirror and focus characterization

We have developed a sub-10 nm focusing system to achieve an ultraintense X-ray laser field with 10^22 W/cm^2 intensity at SACLA. For the sub-10 nm focusing optics, an advanced KB (AKB) mirror system based on Wolter-type III geometry has been adopted. One of the remarkable challenges was the fabrication of steeply curved mirrors with radii of curvature of ~3 m with a shape accuracy of 1 nm. We applied an X-ray wavefront correction scheme using a single-grating interferometer and a differential deposition technique. The horizontal mirror pair was corrected twice and the vertical pair once, resulting in the wavefront error of λ/15 rms which satisfies Maréchal’s criterion. The focus characterization was performed by single-grating interferometry and ptychography. Both methods consistently indicated a focusing spot size of 7 × 7 nm^2, while the 2nd-order aberration term, i.e. astigmatism, contained slight uncertainty. To accurately measure astigmatism, we employed speckle interferometry that directly measures the on-focus beam size. From the speckle measurements, remained 3 µm astigmatism was identified and corrected faithfully. Consequently, XFEL 7 nm focusing spot with 1.45 × 10^22 W/cm^2 intensity has been achieved.

Speaker: Jumpei Yamada (Osaka University & RIKEN SPring-8 Center)

33 X-ray Gas Monitor operation at European XFEL above 25 keV

X-ray Gas Monitors (XGMs) are operated at European XFEL for non-invasive single-shot pulse energy measurements and average beam position monitoring. The basic mechanism is photo-ionization of rare gas atoms. They are used for machine SASE tuning and for sorting single-shot experimental data according to the pulse energy. The XGMs were developed at DESY based on the specific requirements of European XFEL. In this contribution we will present the XGM operation at photon energies above 25 keV. We will discuss how we extrapolated the cross-sections and ion-mean-charges with an increased uncertainty into these high photon energies and how we want to improve the precision of these values in the future. For the XGM single-shot signal we use the Huge Aperture MultiPlier (HAMP), because the standard X-ray Gas Monitor Detectors (XGMDs) do not give reliable signal-to-noise above 18 keV even at highest operating gas pressures. We will present single-shot correlations between consecutive XGMs operated with HAMP. We discovered an intra-train non-linearity of the HAMP signal and studied operation parameters to mitigate this effect. Additionally, we will report the limit of the single-shot resolution which we found at 4.5 MHz where the HAMP peaks are overlapping.

Speaker: Dr Theophilos Maltezopoulos (European XFEL)

34 Development of X-ray Ionization Beam Position Monitor for PAL-XFEL Soft X-ray

The Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL) operates hard X-ray and soft X-ray beamlines for scientific experiments with providing intense ultrashort X-ray pulses based on the self-amplified spontaneous emission (SASE) process. X-ray Free-Electron Laser is characterized by strong pulse-to-pulse fluctuations due to the SASE process. Thus, online photon diagnostics are very important for the rigorous measurements. The photo-absorption and emission concept using solid materials is very limited in the soft X-ray beamline diagnostics. Instead, the gas monitoring detectors (GMDs) that utilize the photo-ionization of the gas are installed at the optics hutch and the experimental hall of the soft X-ray beamline, and employed for monitoring the beam intensity status and for normalizing the experimental data. To track the beam position at the soft X-ray beamline in addition to those intensity monitors, we developed a X-ray ionization beam position monitor (XIBPM). The XIBPM uses ionization of either residual gas in the vacuum or Kr gas injected, and microchannel plate with phosphor. The XIBPM was installed at the experimental hall, and it was tested separately for horizontal and vertical beam position monitoring. Electrostatic field-map of the XIBPM is analyzed using the CST (Computer Simulation Technology) Studio Suite, and multiparticle tracking studies on the field-maps obtained from the CST Studio Suite are in progress to quantitatively analyze and identify error components. Here, we introduce the newly developed XIBPM about a basic structure and test results and a design optimization considering beam-gas interaction and particle tracking on a realistic field-map.

Speaker: Dr HyoJung Hyun (Pohang Accelerator Laboratory)

35 Silicon Carbide ultra-thin membranes for X-ray beam position and intensity monitoring

In this work, the performances of thin (0.5um-10um) Silicon Carbide (SiC) membranes as in-line X-ray Beam Position Monitors (XBPM) for synchrotron beams presented and compared with commercial single- and poly-crystalline diamond ones. Results show that SiC devices can reach superior transparencies with respect to diamond, thanks to the realisation of <2um thick sensors, while allowing for much larger active areas and zero-voltage operating conditions.
Given the obtained experimental and theoretical results and availability of electronic-grade epitaxies on up to 8inch wafers, we expected that SiC will substitute diamond in most X-ray beam monitoring applications, even in the cases of extreme X-ray power densities, such as pink and white beams. This is because, in such conditions, although the material properties of diamond are superior, SiC, thanks to the larger sensors sizes, allows for better heat dissipations and -overall- device reliability.
At the conference an overview of the different SiC XBPM products realised by SenSiC GmbH (including beam and center stops: intensity and position sensors), as well as preliminary results on XFEL beam monitoring, will be presented.

Speakers: Massimo Camarda (SenSiC GmbH), Dr Christoph Arrell (PSI)

36 AI-driven real-time optics control system to achieve aberration-free coherent wavefronts at 4th-generation synchrotron radiation and free electron laser beamlines

When dealing with experiments conducted at 4th-generation synchrotron radiation and free electron laser beamlines, the primary challenge for X-ray optical elements lies in achieving and maintaining focused X-ray beams of high intensity, possessing near-perfect wavefront quality and exceptional stability. Optical elements necessitate more stringent specifications compared to other applications due to the shorter wavelength and ultra-small emittance of the radiation generated by these sources. In the case of diffraction-limited light sources producing coherent photons, it is crucial to preserve well-controlled wavefronts. The degradation of the wavefront proves detrimental to phase-sensitive imaging techniques such as Tomography. For coherent X-ray scattering experiments employing techniques like X-ray Photon Correlation Spectroscopy, Coherent Surface Scattering Imaging, and Coherent X-ray Diffraction Imaging, wavefront uniformity holds particular significance. X-ray optics must be manufactured with a near-perfect shape, and automatically and consistently align and focus the beam according to experimental requirements. Furthermore, they should be capable of providing real-time correction in response to wavefront deformations. At the APS, we have successfully demonstrated the practical application of two methods: i) utilizing a Neural Network (NN) model to autonomously control deformable mirrors with remarkable precision and control. The NN is trained to establish a time-dependent relationship between the hardware setup and the wavefront properties during experiments. ii) Employing Bayesian optimization with Gaussian processes to automatically align and stabilize the focusing optical systems of hard X-ray synchrotron radiation beamlines. This approach utilizes ultra-realistic digital twins constructed using the OASYS simulation framework and enables effective steering of the optical assembly.

Speaker: Luca Rebuffi (Argonne National Laboratory)

1:00 PM Lunch

Time-related beam properties - temporal characterisation of electron, FEL, and laser beams: Time-related beam properties

37 A New Electro-Optic Detection Scheme for Recording Electron Bunch Shapes With High Resolution and Record Recording Length

Non-destructive, single-shot recording of longitudinal bunch profiles is a prerequisite for accelerator commissioning and operation. A common strategy for the measurement of ultra-short electron bunches is to sample the Coulomb field with femtosecond laser pulses. However, recording electric field evolution in single-shot with THz bandwidth is a largely open problem and has been recognized as a fundamental bottleneck.
We present here a novel electro-optic sampling strategy that is theoretically capable to overcome this limit, and achieve femtosecond resolution for any recording length. This new conceptual approach is based on mathematical concepts from photonic time stretch theory and information diversity in radio-frequency communication. We show numerically and experimentally that this approach enables recording of THz electric field and electron bunch shapes in single-shot with high bandwidth than previous spectral decoding single shot techniques.
This technique opens the way to ultrafast electric field shape characterization with femtosecond resolution in new situations, including longitudinal bunch profile monitoring, studies of microbunching instabilities, and THz pulses generated at free-electron lasers.

Speaker: Eléonore Roussel (Univ. Lille, CNRS, PhLAM - Physique des Lasers, Atomes et Molécules)

38 X-ray pulse shortening via nonlinear absorption and diffraction

Controlling optical properties with nonlinear light-matter interactions, which has been the justification of optical lasers, remains largely unexplored in the hard X-ray region. By combining nanofocusing optics and stable X-ray pulses from SACLA, we are testing various concepts of nonlinear devices to control the temporal and spectral properties of XFEL pulses. In this talk, I will discuss our recent experimental studies on X-ray pulse shortening through nonlinear absorption processes [1] and the reduction of atomic scattering factors at high intensity [2,3].

[1] I. Inoue et al., Phys. Rev. Lett. 127, 163903 (2021).
[2] I. Inoue et al., Phys. Rev. Lett. 126, 117403 (2021).
[3] I. Inoue et al., arXiv:2304.05948.

Speaker: Ichiro Inoue (RIKEN SPring-8 Center)

39 Single-shot temporal characterization of fundamental and harmonic ultra-short FEL Pulses

FLASH, the free-electron laser in Hamburg, operates in the self-amplified spontaneous emission (SASE) regime, leading to a unique combination of energy, spectrum, arrival time and pulse duration. So it is critical to be able to determine the pulse duration and arrival time of each pulse. THz field-driven streaking has the potential to deliver single-shot pulse duration information basically wavelength-independent and over a large dynamic range (in pulse duration and FEL energy)[1,2].

In addition, using THz streaking, the single-shot pulse duration has been measured over a wide range from 10fs to 350fs (FWHM) [2] and correlations with other photon beam parameters have been investigated [3]. Furthermore, the study included an examination of the impact of the number of undulators on the pulse duration contributing to lasing, which was compared to results from 1D and 3D FEL simulations [4]. Furthermore, we will show the excellent agreement of the XUV pulse arrival time measured by streaking with the electron arrival time.

In SASE FELs, nonlinear energy modulation of the electron bunch gives rise to natural harmonics of the fundamental wavelength. The pulse duration of these harmonics can be determined as well using THz streaking, which employs the same scheme used for the fundamental pulse duration. In this regard, we have conducted measurements and simulations to determine the pulse duration of the third harmonic and to observe its evolution along the undulators.

1-I.Grguraš et al.,Nat. Photon. 6(2012)
2-R.Ivanov et al.,J. Phys. B 53(2020)
3-I.Bermúdez et al.,Opt. Exp. 29(2021)
4-M.Bidhendi et al.,Appl. Sci. 12(2022)

Speaker: Mahdi M. Bidhendi (Deutsches Elektronen-Synchrotron DESY)

40 Photon arrival time monitoring with few fs measurement uncertainty at MHz rate

Pump and probe technique with X-ray free electron lasers (XFEL) is a powerful tool to study ultrafast X-ray matter interactions and subsequent ultrafast dynamics. It requires precise characterization of X-ray temporal properties, i.e. relative X-ray arrival time with respect to external optical laser pulses, X-ray pulse duration, and structure, preferably on a shot-to-shot basis.
In this contribution, we will give an overview of the X-ray temporal diagnostics techniques and present our X-ray/optical cross-correlation-based timing tools that can work at up to 1.13 MHz repetition rates with an ultrahigh measurement accuracy of down a few fs at the European XFEL.

Speaker: Jia Liu (European XFEL)

3:30 PM Coffee Break

Science instruments and detectors

41 A Diamond Sensor for Position Resolving Measurements at the European XFEL

The European X-ray Free Electron Laser (XFEL) facility produces extremely intense and short X-ray pulses, where the diagnostics of the X-ray beam properties is of critical importance. Besides existing diagnostic components, utilization of a diamond sensor was proposed to achieve radiation hard, non-invasive beam position and pulse energy measurements for hard X-rays. In particular, at very hard X-rays diamond-based sensors become a useful complement to gas-based devices which lose sen-
sitivity due to significantly reduced gas cross-sections. The measurements performed with a diamond sensor consisting of a 40 μm thick electronic grade single crystal chemical-vapour-deposition diamond with position-sensitive resistive electrodes in a duo-lateral configuration are presented in this work. The results show, for the first time to the best of our knowledge, that the diamond sensor delivers pulse-resolved beam position within less than 1% uncertainty at 2.25 MHz, and can be a valuable tool
for X-ray Free Electron Lasers, especially for the coming high repetition rate machines, enabling applications such as beam based alignment and intra-pulse-train position feedback.

Speaker: Tuba CONKA YILDIZ (European XFEL)

42 Detector developments at PSI

Developments of cutting-edge X-ray detectors are largely driven by experiments at large photon science facilities, i.e. the synchrotron radiation sources and free-electron lasers (FELs) which enable a wealth of investigations in different subjects. At PSI, we develop hybrid X-ray detectors for these facilities as well as for the next-generation radiation sources, namely diffraction-limited storage-rings and high repetition rate FELs. Their applications include but are not limited to scattering and diffraction imaging experiments for pixel detectors and XES, XRD, ED-XAS and XPD for strip detectors. Using different sensors, i.e. the Low Gain Avalanche Diodes (LGADs) and high-Z sensors, the hybrid X-ray detectors are able to cover a large energy range from hundreds of eV to hundreds of keV.

In this talk, I will introduce the detector developments at PSI and their broad applications in various scenarios. In particular, I will present Gotthard-II, a silicon microstrip detector capable of imaging up to 2720 frames at 4.5 MHz frame rate and 400 kHz continuously in beam diagnostic applications. Examples include their usage in the HIgh REsolution hard X-ray single-shot spectrometer (HIREX) for temporal energy resolution diagnostic and in the Photon Arrival time Monitor (PAM) for X-ray pulses arrival time jitter measurement. Finally, the new possibilities of Gotthard-II and the other hybrid detectors in combination with LGAD sensors for measurements in the soft and tender X-ray energy range, as well as the prospects for the next generation high-speed continuous imaging Gotthard-III with a frame rate greater than 1 MHz will be discussed.

Speaker: Jiaguo Zhang (Paul Scherrer Institut)

43 High-NA hard X-ray in-line holography with advanced KB optics based on Wolter type-III geometry

Hard X-ray imaging techniques employing bright-field images, such as bright-field microscopy and in-line holography, offer the benefit of capturing a wide field of view without the need to scan the sample. However, the spatial resolution of these techniques has been limited by the numerical aperture (NA) of hard X-ray optics.

Advanced KB optics based on Wolter type-III geometry is highly efficient and stable, with dramatically higher NA than conventional KB mirrors. This optical system uses multilayer mirrors to increase the NA and employs a Wolter type-III configuration to ensure robustness. By using this technology, the sub-10 nm focusing system at SACLA can attain a high NA of 0.01 and 40% efficiency while maintaining the sub-10 nm focusing for half a day.

Our research aims to develop a phase-contrast imaging technique with high spatial resolution and a wide field of view by combining in-line holography with the Advanced KB optics based on Wolter type-III geometry. To verify the efficacy of this approach, we conducted a proof-of-concept experiment employing the SACLA sub-10 nm focusing system. We used nanoparticles as test samples to evaluate the performance. The reconstructed data from this experiment confirmed a spatial resolution of 100nm. In this presentation, we will discuss findings from the simulation and demonstration experiments, and address the challenges identified for future work.

Speaker: Gota Yamaguchi (RIKEN SPring-8 Center)

44 Correcting for the loss in degree of polarization caused by beamline optics

The impact from optics on circular, elliptical, and inclined linear polarized light at synchrotron beamlines is known and understood but perhaps not always addressed. This impact is of particular interest for beamlines operating below ~150 eV and it becomes severe for energies below 40-60 eV, depending on the beamline’s optical layout. The Bloch beamline at MAXIV Laboratory is designed for angular and spin resolved photoemission spectroscopy, generally operating in the 15-200 eV energy range. It is sourced by a quasi-periodic elliptically polarizing undulator that delivers circular polarization and linear polarization at any inclination.

We have designed a compact 4-reflections polarimeter that can be inserted into the focus of the synchrotron beam in the experimental station’s analysis chamber and determine the actual polarization of the light at the sample. Based on this information we can set the undulator gap, helical phase, and inclined phase in an unconventional configuration to compensate the impact from the beamline optics on the polarization and deliver a high degree of circular or linear inclined polarized light to the users.

At present the polarimeter has been commissioned and is in operation while the undulator compensation procedure is still in its commissioning phase. Here we report the design and the design considerations of the polarimeter, the undulator compensation procedure, and first experimental results.

Speaker: Mats Leandersson (MAXIV Laboratory)

45 Closing remarks

Speaker: Marco Zangrando (Elettra Sincrotrone Trieste and CNR-IOM)