This PDF file contains the front matter associated with SPIE Proceedings Volume 10236, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Dynamical diffraction in a deformed (often bent) crystal is described by the Takagi equations ¹ which, in general, have to be solved numerically on a regular 2-D grid of points representing a planar cross section of the crystal in which the diffraction of an incident X-ray wavefront occurs . Presently, the majority of numerical approaches are based on a finite difference solving scheme^2-4 which can be easily implemented on a regular Cartesian grid but is not suitable for deformed meshes. In this case, the inner deformed crystal structure can be taken into account, but not the shape of the crystal surface if this differs substantially from a planar profile ^5,6.

Conversely, a finite element method (FEM) can be easily applied to a deformed mesh and serves very well to the purpose of modelling any incident wave on an arbitrarily shaped entrance surface ⁷ e.g. that of a bent crystal or a crystal submitted to a strong heat load ^8-10. For instance, the cylindrical shape of the surface of a strongly bent crystal plate can easily be taken into account in a FEM calculation. Bent crystals are often used as focusing optical elements in Xray beamlines ^11-13.

In the following, we show the implementation of a general numerical framework for describing the propagation of X-rays inside a crystal based on the solution of the Takagi equations via the COMSOL Multiphysics FEM software package (www.comsol.com). A cylindrically bent crystal will be taken as an example to illustrate the capabilities of the new approach.

We investigate the mechanisms involved in the modification of dielectric materials by ultrashort laser pulses. We show that the use of a double pulse (fundamental and second harmonic of a Ti–Sa laser) excitation scheme allows getting new insight in the fundamental processes that occur during the interaction. We first measure the optical breakdown (OB) threshold map (intensity of first pulse versus intensity of second pulse) in various materials (Al2O3, MgO, α-SiO2). Using a simple model that includes multiphoton excitation followed by carrier heating in the conduction band, and assuming that OB occurs when a critical amount of energy is deposited in the material, we can satisfactorily reproduce this evolution of optical breakdown thresholds. The results demonstrate the dominant role of carrier heating in the energy transfer from the laser pulse to the solid. This important phenomenon is also highlighted by the kinetic energy distribution of photoelectrons observed in a photoemission experiment performed under similar conditions of double pulse excitation. Furthermore, we show, in the case of α-SiO2, that the formation of self-trapped exciton is in competition with the heating mechanism and thus play an important role especially when the pulse duration exceeds a few 100 fs. Finally, also in quartz or silica, we observe that the initial electronic excitation plays a key role in the formation of surface ripples and that their characteristics are determined by the first pulse, even at intensities well below OB threshold. The consequence of all these experimental results in the domain of UV or VUV induce damage will be discussed. In particular we demonstrate the possibility to dramatically increase the ablation efficiency by VUV light by using such double pulse scheme.

Interest in high-resolution structure investigation has been zealous, especially with the advent of X-ray free electron lasers (XFELs). The intense and ultra-short X-ray laser pulses (~ 10 GW) pave new routes to explore structures and dynamics of single macromolecules, functional nanomaterials and complex electronic materials. In the last several years, we have developed XFEL single-shot diffraction imaging by probing ultrafast phase changes directly. Pump-probe single-shot imaging was realized by synchronizing femtosecond (<10 fs in FWHM) X-ray laser (probe) with femtosecond (50 fs) IR laser (pump) at better than 1 ps resolution. Nanoparticles under intense fs-laser pulses were investigated with fs XFEL pulses to provide insight into the irreversible particle damage processes with nanoscale resolution. Research effort, introduced, aims to extend the current spatio-temporal resolution beyond the present limit. We expect this single-shot dynamic imaging to open new science opportunity with XFELs.

Possible dose-rate effects in a plasmid DNA exposed to pulsed extreme ultraviolet (XUV) and soft x-ray (SXR) water window radiation from two different table-top plasma-based sources was studied. Dose delivered to the target molecule was controlled by attenuating the incident photon flux with aluminum thin foils as well as varying the DNA/buffer-salt ratio in the irradiated sample. Irradiated samples were analyzed using the agarose gel electrophoresis. Some additional bands were identified in gel electrophoretograms as results of a DNA cross-linking. They were inspected by atomic force microscopy (AFM). Yields of single- and double-strand breaks (Gy-1 Da-1) were determined as a function of incident dose rate. Both yields decreased with a dose rate increasing. The ratio of single- and double-strand breaks exhibited only a slight increase at elevated dose rates. In conclusion, complex and/or clustered damages do not seem to be initiated under these irradiation conditions.

Simple analytic equation is deduced to explain new physical phenomenon detected experimentally: growth of nano-dots (40–55 nm diameter, 8–13 nm height, 9.4 dots/μm² surface density) on the grazing incidence mirror surface under the three years irradiation by the free electron laser FLASH (5–45 nm wavelength, 3 degrees grazing incidence angle). The growth model is based on the assumption that the growth of nano-dots is caused by polymerization of incoming hydrocarbon molecules under the action of incident photons directly or photoelectrons knocked out from a mirror surface. The key feature of our approach consists in that we take into account the radiation intensity variation nearby a mirror surface in an explicit form, because the polymerization probability is proportional to it. We demonstrate that the simple analytic approach allows to explain all phenomena observed in experiment and to predict new effects. In particular, we show that the nano-dots growth depends crucially on the grazing angle of incoming beam and its intensity: growth of nano-dots is observed in the limited from above and below intervals of the grazing angle and the radiation intensity. Decrease in the grazing angle by 1 degree only (from 3 to 2 degree) may result in a strong suppression of nanodots growth and their total disappearing. Similarly, decrease in the radiation intensity by several times (replacement of free electron laser by synchrotron) results also in disappearing of nano-dots growth.

Boron carbide (B₄C) - due to its exceptional mechanical properties - is one of the few existing materials that can withstand the extremely high brilliance of the photon beam from free electron lasers (FELs) and is thus of considerable interest for optical applications in this field. However, as in the case of many other optics operated at modern accelerator-, plasma-, or laser-based light source facilities, B₄C-coated optics are subject to ubiquitous carbon contaminations. These contaminations - that are presumably produced via cracking of CH_x and CO₂ molecules by photoelectrons emitted from the optical components - represent a serious issue for the operation of the pertinent high performance beamlines due to a severe reduction of photon flux and beam coherence, not necessarily restricted to the photon energy range of the carbon K-edge. Thus, a variety of B₄C cleaning technologies have been developed at different laboratories with varying success [1]. Here, we present a study regarding the low-pressure RF plasma cleaning of a series of carbon-contaminated B₄C test samples via an inductively coupled O₂/Ar and Ar/H₂ remote RF plasma produced using the IBSS GV10x plasma source following previous studies using the same RF plasma source [2, 3]. Results regarding the chemistry, morphology as well as other aspects of the B₄C optical coatings and surfaces before and after the plasma cleaning process are reported.

Observations in the UV and EUV allow many diagnostics of the outer layers of the stars and the Sun so that more and more space telescopes are developed to operate in this fundamental spectral range. However, absorption by residual contaminants coming from polymers outgassing causes critical effects such as loss of signal, spectral shifts, stray light… Thus, a cleanliness and contamination control plan has to be defined to mitigate the risk of damage of sensitive surfaces. In order to specify acceptable cleanliness levels, it is paramount to improve our knowledge and understanding of contamination effects, especially in the UV/EUV range. Therefore, an experimental study has been carried out in collaboration between CNES and IAS, in the frame of the development of the Extreme UV Imager suite for the ESA Solar Orbiter mission; this instrument consists of two High Resolution Imagers and one Full Sun Imager designed for narrow pass-band EUV imaging of the solar corona, and thus very sensitive to contamination. Here, we describe recent results of performance loss measured on representative optical samples. Six narrow pass-band filters, with a multilayer coating designed to select the solar Lyman Alpha emission ray, were contaminated with different amounts of typical chemical species. The transmittance spectra were measured between 100 and 200 nm under high vacuum on the SOLEIL synchrotron beam line. They were compared before and after contamination, and also after a long exposure of the contaminated area to EUV-visible radiations.

Interaction of short-wavelength free-electron laser (FEL) beams with matter is undoubtedly a subject to extensive investigation in last decade. During the interaction various exotic states of matter, such as warm dense matter, may exist for a split second. Prior to irreversible damage or ablative removal of the target material, complicated electronic processes at the atomic level occur. As energetic photons impact the target, electrons from inner atomic shells are almost instantly photo-ionized, which may, in some special cases, cause bond weakening, even breaking of the covalent bonds, subsequently result to so-called non-thermal melting. The subject of our research is ablative damage to lead tungstate (PbWO4) induced by focused short-wavelength FEL pulses at different photon energies. Post-mortem analysis of complex damage patterns using the Raman spectroscopy, atomic-force (AFM) and Nomarski (DIC) microscopy confirms an existence of non-thermal melting induced by high-energy photons in the ionic monocrystalline target. Results obtained at Linac Coherent Light Source (LCLS), Free-electron in Hamburg (FLASH), and SPring-8 Compact SASE Source (SCSS) are presented in this Paper.

In this paper, we present an extension to our code, XCASCADE [Medvedev, Appl. Phys. B 118, 417], that enables to model time evolution of electron cascades following low-intensity X-ray excitation in various materials consisting of elements with atomic numbers Z = 1 - 92. The code is based on a classical Monte-Carlo scheme and uses atomistic cross sections to describe electron impact ionization. The new extended version, XCascade-3D, also tracks the electron trajectories with 3D spatial resolution. This model takes into account anisotropic scattering of electrons on atoms. We show that the calculated electron ranges in various materials are in a good agreement with the available data, confirming the potential for high accuracy applications at FEL pulse diagnostics.

In this contribution an analysis of influence of model parameters on the results of simulations of material properties under free-electron laser irradiation is presented. It is based on the in-house hybrid code XTANT (X-ray-induced Thermal And Nonthermal Transition; N. Medvedev et. al, Phys. Rev. B 91 (2015) 054113), which combines tight binding molecular dynamics for atoms with Monte Carlo treatment of high-energy electrons and core-holes, and Boltzmann collision integrals for nonadiabatic (electron-phonon) coupling. Different parameterizations of transferable tight binding method for silicon are analyzed, namely basis sets sp³ and sp³s*. The sp³ parameterization seems to provide a better agreement of the silicon damage threshold with experimental data. Further, the influence of different schemes of molecular dynamics periodic boundaries simulation is compared: constant volume vs Parrinello-Rahman constant pressure. Constant-volume scheme gives a better agreement with experimental transient properties, as could be expected. Parameters entering the calculations of optical properties are analyzed, showing virtually no effect on the outcome beyond trivial broadening of the peaks of the optical coefficients.

By methods of hard X-ray diffraction (λ=0.154 nm) and scanning electron microscopy the surface morphology of Sc/Si multilayer mirrors influenced with nanosecond pulses of discharge capillary laser (λ=46.9 nm) is studied. Under irradiation a relief of periodically alternating valleys and ridges is formed. The region of observed relief is extended over the space being ~10⁴ greater than the irradiated region. Periodic relief (periodicity of 2.2-2.3 μm) appears as a result of reaction between Sc and Si layers making valleys (Sc₃Si₅ silicide) and ridges (ScSi monosilicide). Each of periods has complex structure exactly repeated in neighbor periods. Mechanisms of periodic relief formation are discussed.

High brilliance sources in the EUV spectral range such as Synchrotron and Free Electron Lasers (FEL) are widely used in multiple scientific and technological applications thanks to their peculiar characteristics. One main technical problem of FEL is related to the rejection of high harmonics, seed laser, first stage photons, and diffuse light; in order to improve the quality of the beam delivered by these sources, a suitable optical system acting as band-pass filters is necessary. In this paper we discuss the optical and structure characterization of Nb/Zr and Zr/Nb self-stand transmittance filters, designed for 4.5 nm-20 nm wavelength ranges. In order to understand the properties of these bilayers filters, a campaign of measurements has been planned to be performed on Zr and Nb films on Si₃N₄ membrane windows and silicon substrates, deposited with e- beam deposition technique. Comparison of the results has been planned too. IMD transmittance and reflectance simulations, together with preliminary AFM and reflectance measurements will be shown in this work.