This PDF file contains the front matter associated with SPIE Proceedings Volume 12578, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The X-ray Free Electron Laser (XFEL) is uniquely characterised by its high-brilliance (≥ 10E12 photons/pulse), high spatial coherence and ultrashort (fs) pulses, in the wavelength range spanning over 30 keV from soft to hard x-ray regimes [1,2]. Much of the mainstream interests focus on the powerfulness of the beam it delivers, meanwhile increasing cases of (x-ray) optical and electronical components damages are rapidly emerging – many of them designed and considered to be “radiation tolerant”. This signals that there is still, afterall, insufficient understandings to short- to long-term radiation effects on materials at various degrees. The talk will target on the observations and examples from the European XFEL – one of the most intense XFEL facility in the world. The case study includes some (unintended) instant damages by X-rays, phase modification effects only observed in transmitted pulse profile but not under visible microscope, and controversy results where the long-term radiation fatigues can only explain. I will also note on how such effects could alter the x-ray pulse wavefront (WF) distortion and its effect ranging from radiation deposition mechanism, to (in)ability to reach diffraction limited foci, and limitations to spectral correlations between spectrometers. The general effect goes well beyond ‘bad quality’ beam and may determine the capability and the scientific goal of the experiment altogether. [1] Tschentscher, T. et al, Applied Sciences (Basel) 7, 592 (2017). [2] Decking, W. et al, Nature Photonics 14, 391 (2020).

The European X-Ray Free-Electron Laser (EuXFEL) generates highly brilliant x-ray radiation with photon energies of typically 0.3 to 20 keV, with pulse energies of several mJ, and a beam diameter of approximately 0.5 mm at 9 keV at a distance of 250 m from the source. The beam is pulsed with pulse durations smaller than 100 fs. Luminescent screens along the beam transport path are used for beam diagnostics, to visualise the beam position and transverse shape. The EuXFEL beam can reach the damage threshold of the different screen materials already within a few pulses. Care has to be taken about permissible beam conditions, and the most suitable screens must be selected for a desired application. This contribution reports on the experiences with radiation damage of luminescent screens from different materials (YAG:Ce, diamond:B, BN) during the recently accomplished 5 years of user operation of EuXFEL and gives examples of different types of degradation: from slight degradations by structural changes of screens and surface damage up to screen fracture. Under the particular pulse structure of the EuXFEL radiation at 9 keV photon energy, YAG screens withstand up to 0.5 J/mm² of incident pulse energy accumulated over successive radiation pulses, respectively 40 J/mm² for diamond.

This contribution deals with interactions of short-wavelength laser radiation with solids and their thermal and non-thermal consequences. A brief overview is given on materials behavior under exposure to an intense XUV/x-ray laser pulse. Differences between thermal and non-thermal processes contributing to the melting of solids and related phase transition phenomena are discussed. Various methods and techniques - both theoretical and experimental - making possible to estimate a portion of thermalized energy within the total pulse energy deposited in solids are described as well. Initial experiments performed with the NIR thermal imaging camera (FLIR A6700sc) revealed spatio-temporal distribution of temperatures on the surface of an aluminum foil target exposed to mid-UV radiation emitted by KrF excimer laser. A prospective use of this technique at XUV/x-ray laser facilities is proposed and discussed.

Optical elements for Extreme ultraviolet (EUV) Photolithography fall into several categories: most notably mirrors, but also (transmissive) beam splitters, spectral filters, diffusers, sensors and fiducial reference plates. All these components are challenged to the extreme by the stringent demands of photolithography at roughly 10 nm resolution, and the high-power EUV sources of up to 500 W today. This puts stringent requirements on materials, manufacturing and pretreatments of EUV optical elements, and requires deep understanding of the interaction between these optical elements and the EUV irradiation and the low-pressure background gas. While much is known about the interaction between EUV and mirrors, also elements like membranes are integral parts of today’s lithography tools. In this paper, we will give an overview of these interactions, and will dive deeper in the recent improvements in highpower transmissive membranes, and will also address some options being considered to extend the power limits even further to beyond 1000 W.

X-ray Free Electron Laser (XFEL) radiation may transform diamond into graphite. Two X-ray pulses were used; the first as pump to trigger the phase transition and the second as probe performing X-ray diffraction. The experiment was performed at the SACLA XFEL facility at the beamline 3 experimental hutch 5. The samples were polycrystalline diamond. The pump and probe photon energies were 7 and 10.5 keV, respectively, and the delay between the X-ray pulses was varied from 0 to 286 fs. To provide a range of energy densities, the X-ray focus was adjusted between 150 nm and 1 um. The (111), (220) and (311) diffraction peaks were observed. The intensity of each diffraction peak decreased with time indicating a disordering of the crystal lattice. From a Debye-Waller analysis, the root-mean-square (rms) atomic displacement perpendicular to particular lattice planes are calculated. At higher fluences, the rms atomic displacement perpendicular to the (111) planes is significantly larger than that perpendicular to the (220) or (311) planes. By accepting two successive XFEL pulses at a time delay of 33 ms, graphite (002) diffraction was observed beginning at a threshold dose of 1.7 eV/atom. The experimental results will be compared with calculations using a hybrid model based on tight-binding molecular dynamics.

This proceeding discusses the impact of XUV/X-ray irradiation on materials, and how their response is affected by temperature, size, and structure. When materials are exposed to intense XUV/X-ray irradiation, they undergo a series of processes ultimately leading to observable structure modification and damage. These effects were studied with a hybrid simulation tool XTANT-3. The code combines several methods in one interconnected model: the photon absorption and electron cascades are simulated with transport Monte Carlo; nonequilibrium kinetics of slow electrons (in the valence and the bottom of the conduction band) is traced with the Boltzmann equation; modeling evolution of the electronic structure and interatomic potential is done with the transferable tight binding method; and the response of the atomic system is simulated with the molecular dynamics. Combining these methods enabled the tracing of the essential effects of irradiation. This brief review summarizes the recent results obtained with this simulation tool.

The ELI Beamlines project as one pillar of the Extreme Light Infrastructure ERIC provides laser-driven secondary sources of EUV/XUV, X-ray and relativistic charged particles offering unique pump/probe experimental schemes for dynamic studies on the ultrafast time-scale. Moreover, these sources can be coupled together offering experimental schemes beyond the IR-laser-driven pump/probe approach. While the majority of facility scientific equipment is in progress of installation, numerous secondary beamlines have already been validated. Here we present secondary sources of XUV radiation via high harmonic generation (HHG) in gases and hard X-ray Cu-Ka source as well as user endstations that were connected to the beamline. The ELI Beamlines HHG/PXS supports experiments in three scientific end stations: MAC, ELIps, and T-REX, while plasma betatron source and lUIS will serve their own beamlines and endstations.

The ablation imprints method is a well-established approach to thoroughly characterising fluence distributions [J/cm2] of focused short-wavelength free-electron laser beams. For visible and near-infrared laser beams, fluence distribution of the focused beam can also be measured by other means, for example, by projecting a magnified image of the focal spot onto a camera. We studied the viability of the ablation imprints method in the visible and near-infrared spectral range and compared it to the above-mentioned conventional approach. Furthermore, we compared the effects of the X-ray, visible, and near-infrared radiation on the ablation damage. We characterised an X-ray astigmatic focused beam at the Small Quantum Systems instrument of the EuXFEL. At the Prague Asterix Laser System, we successfully characterised the focal spot at 438 nm. At 1315 nm, the ablation imprints method produced partially satisfactory results, and we compared these results with conventional methods. We conclude that the ablation imprints method can characterise focused laser beams in the visible and near-infrared spectral range.

We study theoretically the response of polymers to ultrafast XUV irradiation. To determine damage threshold doses of polymers from the alkene group, we use the hybrid simulation toolkit XTANT-3 [1]. The code models nonequilibrium electron kinetics, the energy exchange between electrons and atoms via electron-ion (electron-phonon) coupling, nonthermal modification of the interatomic potential, and the induced atomic response. For each of examined polymers, we demonstrate that nonthermal damage is the main mechanism of response to irradiation. At low doses, local defects are formed (hydrogen detachment, cross-linking), whereas with the increase of the dose, molecular disintegration leads to the formation of metallic liquid. [1] N. Medvedev, V. Tkachenko, V. Lipp, Z. Li, B. Ziaja, 4open. 1 (2018) 3

Nowadays, the mass production of micro- and nano-structures for highly integrated electronic circuits is dominated by extreme ultraviolet lithography (EUVL). This is multiple step processing the key step of which is represented by a transfer and demagnification of structural motif from either reflective or transmission masks with electromagnetic radiation having a typical wavelength of 13.5 nm delivered most frequently from optimized laser-produced plasma sources. Thus a latent micro/nano-structure is created in a suitable resist which should be etched. Then, a series of further processing steps should be applied to create a wanted 3D structure in an electronic device. Nevertheless, the number of processing steps can be reduced if an EUV/x-ray laser-induced materials erosion (desorption/ablation) would be engaged in manufacturing the micro/nano-structures. In this contribution, it will be discussed whether structures with sufficiently small details can be produced by intense extreme ultraviolet and x-ray radiation directly at an acceptable level of quality, with a high yield. Pulse duration and wavelength effects will be elucidated in both ablation and desorption modes of materials erosion. Special attention will be paid to processes, both thermal and nonthermal, which could blur the structural motif. Their investigation should help to eliminate them creating well developed structures having sharp edges.

In this contribution we share results of our experimental investigations on the role of EUV on carbon and silicon deposition in hydrogen environment. In our experiments we found no signs of EUV induced deposition of silicon. Moreover we show that it is possible to increase the rate of EUV induced deposition of carbon with respect to that of silicon. This could possibly be used to mitigate silicon growth on optical surfaces.

In the last decades, extreme ultraviolet (EUV) multilayer coatings have proved to be key components in the development and success of telescope imagers onboard space missions to image the solar corona. More recently, we have been able to significantly increase the efficiency, to develop new functionality and to extend the range of operation of EUV multilayer coatings, thanks to the development and optimization of new material combinations and new coating designs. Furthermore, multilayer mirrors with high efficiency, good stability, enhanced selectivity and/or broad bandwidth and phase controlled are key components to manipulate the ultra-short pulses generated by coherent sources. In this presentation, we will review the recent development of EUV multilayer optics for solar imaging, in particular for the two Solar Orbiter EUV telescopes, which produced the closest images of the Sun in 2022 with the first dual-band EUV coatings. We will also discuss multilayer mirrors for pico-, femto- and attosecond sources, including the recent development of a delay line with advanced multilayer optics for the femto/attosecond beamlines in Paris-Saclay (ATTOLAB). We will finally discuss the problem of inaccuracies in the available EUV optical properties of materials that makes it difficult to design and calibrate such instruments. We will discuss solutions to improve the accuracy in the determination of optical properties.

Ultrafast irradiation of matter induces a variety of processes in both electronic and atomic systems, intricately affecting each other. To model photoabsorption, nonequilibrium electron kinetics, decays of atomic holes, energy exchange with atoms of the target, nonthermal modification of interatomic potential, and induced atomic dynamics need to be accounted for to understand ensuing damage, the standard practice is to employ hybrid (combined, multiscale) methods. We discuss two examples of such models: XTANT-3 [1] and TREKIS-4 [2]. XTANT-3 combines Monte Carlo (MC), tight-binding molecular dynamics (MD), and Boltzmann collision integrals. It models nonequilibrium electron cascades (only in time), evolution of electronic structure, nonthermal melting, electron-phonon coupling [3], but limited to a few 100-1000s atoms. TREKIS-4 combines MC with classical MD, tracing electronic cascades in space (1d, 2d, or 3d), including relativistic energies. Classical MD models ~10^4-10^5 of atoms, approximately including nonthermal effects in covalent materials, but cannot trace evolution of the electronic structure and interatomic potential. [1] N. Medvedev, et al., 4open. 1 (2018) 3. [2] N. Medvedev, et al., Adv. Theory Simulations. (2022) 2200091. [3] N. Medvedev, J. Phys. Condens. Matter. 32 (2020) 435401.

We have modified the electrical properties of rutile TiO2 with a 17 keV X-ray beam about 50x50 nm2 in size. We have drawn a conducting channel in an insulating matrix, guided the electroforming of a conducting filament and modified the rectifying properties of a Schottky barrier. We have also observed changes in the surface morphology and a more intense Raman activity in the irradiated regions. Computer simulations show that temperature spikes at the nanoscale are expected in correspondence with the synchrotron pulses, and preliminary measurements via single crystal X-ray diffraction confirm that local heating takes place during irradiation.

We report on ion emission from plasma produced on thick targets irradiated with nanosecond and femtosecond pulses delivered by mid-ultraviolet and soft x-ray lasers, respectively. To distinguish between different ion acceleration mechanisms, the maximum kinetic energy of ions produced under different interaction conditions is plotted versus laser fluence. The transformation of the time-of-flight detector signal into ion charge density distance-of-flight spectra makes it possible to determine the mean kinetic energy of the fastest ion groups based on the influence of the acoustic velocity of ion expansion. This allows obtaining additional characteristics of the ion production. The final energy of the group of fast ions determined using the ion sound velocity model is an order of magnitude larger in the fs-XFEL interaction than in the ns-UV one. On the contrary, the ablation yield of ions in our experiment is seven orders of magnitude greater when applying ns-UV laser pulses, not only due to higher energies of UV laser pulses, but also due to a significant difference in interaction and ion formation mechanisms.

A proper spatial characterization of a laser beam profile is indisputably important for any laser-mater experiment as well as for protection of beamline optical elements. Method of ablation and desorption imprints provides thorough beam profile analysis applicable to a broad range of photon energies. This method, however, often requires up to thousands of shots which must be then manually analyzed. Here we present method based on deep learning image segmentation model which is able to substitute human element currently indispensable in this time-consuming ex situ post processing. It is a part of AbloCAM project – an universal device for semi-automatic beam profile analysis.