This PDF file contains the front matter associated with SPIE Proceedings Volume 7361, including the TItle Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

The European X-Ray Free Electron Laser will deliver high intensity ultrashort pulses of x-rays. The results of the x-ray interaction with matter in such a regime are not yet fully understood and the energy threshold for surface modifications remains unknown. The behavior of optical components under irradiation is a major issue for the European XFEL project. In fact some experiments rely on the coherence and high quality wave front of the beam and any degradation, even on the nanometer scale, of the x-ray optical components will affect the performance of these experiments. Hence investigation of radiation effects on materials is needed. We will describe the on-going program at the European XFEL which aims at developing new approaches for beamline design specific to FEL light source. Different tools are used in order to simulate the beam propagation and interaction with optical elements.

The FERMI@Elettra free electron laser (FEL) user facility is currently under construction at the Sincrotrone Trieste laboratory in Trieste (Italy). It is a based on a seeded scheme that will provide an almost perfect transform limited beam and fully spatial coherent. It will cover the wavelength range from 100 to about 3 nm and in a short future down to 1 nm (by using higher harmonics). It is expected to be fully operative in the late summer of 2010. In this presentation we will report the layout of the photon beam diagnostics section with the preliminary tests, the radiation transport system to the experimental area, and the experimental hall facilities. A particular emphasis will be given to the optical solution and constrains due to the need of preserving the wave front and to avoid damage on the different optical elements, including slits, mirrors, gratings and all the diagnostic facilities. One of the main problems will be the necessity of using very large grazing incidence angle (up to 45°) on multilayers and single coating mirrors. These elements are mandatory to perform the transient grating experiments and to realize the delay lines, where time delay up to 1 nsec are required. This issue poses a serious problem in terms of energy density delivered and adsorbed by the optics and great care must be taken into the choice of the proper multilayer materials. Some studies on the reflectivity of multilayers and Carbon coated mirrors will be reported as well as the diagnostic tools to monitor the quality of the optics in operative conditions.

Single shot radiation damage of bulk silicon induced by ultrashort XUV pulses was studied. The sample was chosen because it is broadly used in XUV optics and detectors where radiation damage is a key issue. It was irradiated at FLASH facility in Hamburg, which provides intense femtosecond pulses at 32.5 nm wavelength. The permanent structural modifications of the surfaces exposed to single shots were characterized by means of phase contrast optical microscopy and atomic force microscopy. Mechanisms of different, intensity dependent stages of the surface damage are described.

Ultra-fast soft x-ray lasers have opened a new area of laser-matter interactions which in most cases differ from the well understood interaction of UV-vis radiation with solid targets. The photon energy >30eV essentially exceeds the width of band gap in any known material and excites the electrons from the deep atomic and valence levels directly to the conduction band. Both thermal and non-thermal phenomena can occur in such a material being caused by electron thermalization and bond breaking, respectively. We report the first observation of non-thermal single-shot soft x-ray laser induced desorption occurring below the ablation threshold in a thin layer of poly (methyl methacrylate) - PMMA. Irradiated by the focused beam from the Free-electron LASer in Hamburg (FLASH) at 21.7nm, the samples have been investigated by an atomic-force microscope (AFM) enabling the visualization of mild surface modifications caused by the desorption. A model describing non-thermal desorption and ablation has been developed and used to analyze singleshot imprints in PMMA. An intermediate regime of materials removal has been found, confirming the model predictions. We also report below-threshold multiple-shot desorption of PMMA induced by high-order harmonics (HOH) at 32nm as a proof of an efficient material removal in the desorption regime.

We demonstrate a novel experimental method for efficient structural surface modification of various solids (PMMA, amorphous carbon) achieved by simultaneous action of XUV (21.6 nm), obtained from High-order Harmonic Generation (HHG), and Vis-NIR (410/820 nm) laser pulses. Although the fluence of each individual pulse was far below the surface ablation threshold, very efficient and specific material modification was observed after irradiation even by a single shot of mixed XUV/Vis-NIR radiation.

We have investigated nano-ablation of silica glass and ablation process using focused laser plasma soft Xrays. Laser plasma soft X-rays were generated by irradiation of a Ta target with Nd:YAG laser light. The soft X-rays were focused on silica glass plates using an ellipsoidal mirror at fluences up to 1 J/cm². In order to fabricate nano-trenches, a silica glass plate was irradiated with laser plasma soft X-rays through the windows of a line and space mask. We demonstrated fabrication of nano-trenches with a width of 50 nm. It should be noted that the feature size is more precise than that estimated from the thermal diffusion length for the 10-ns X-rays (i.e. 80 nm). Furthermore, the ablated area has a depth of 470 nm and a roughness of 1 nm after ten shots of irradiation. Thus, the X-ray irradiation technique have a significant feature of direct nanomachining. The ablation occurs at fluences F beyond a ablation threshould F_th and ablation depth per pulse D obeys the law D = 1/α ln(F/F_th), where α is an effective absorption coefficient. These results suggest that absorbed energy is accumulated in the absorbed region without energy diffusion until ablation occurs. In addition, time-resolved mass spectroscopy revealed that silica glass is broken into atomic ions and atomic neutrals during ablation. Because Si+ and O+ ions have kinetic energies of 10-30 eV, non-thermal process such as Coulomb explosion may be driving force behind the ablation. Such non-thermal process enables us to fabricate nano-structures on silica glass.

Extreme ultraviolet (EUV) is strongly absorbed in any material and can be transmitted only through very thin foils. The material surface after irradiation can remain unchanged or becomes modified in some way depending on radiation fluence and material properties. In some materials the surface changes may arise due to fast melting or boiling followed by solidification. In other cases photochemical or photothermal ablation can occur. It requires relatively high radiation fluence of the order of tens mJ/cm². A laser-plasma EUV source based on a gas puff target equipped with a proper optic can deliver such conditions. In this work EUV radiation coming from xenon or krypton plasma was focused using an ellipsoidal grazing incidence collector. Different kind of material samples were irradiated in the focal plane or at some distance behind the focal plane. This way different intensities were applied for irradiation of the samples. Irradiation was performed with 10 Hz repetition rate and different time duration varying from 1s to 2 min. Surface morphology after irradiation was investigated using a scanning electron microscope. In a case of some materials EUV intensity in the focal plane was sufficient for ablation. In other cases material ablation was not possible but surface structure was modified. Forms of the structures for a certain material depend both on EUV fluence in a single shot and the number of shots.

In recent years, technological developments in the area of extreme ultraviolet lithography (EUVL) have experienced great improvements. Currently, the application of EUV radiation apart from microlithography comes more and more into focus. Main goal of our research is to utilize the unique interaction between soft x-ray radiation and matter for probing, modifying, and structuring solid surfaces. In this contribution we present a setup capable of generating and focusing EUV radiation. It consists of a table-top laser-produced plasma source. In order to obtain a small focal spot resulting in high EUV fluence, a modified Schwarzschild objective consisting of two spherical mirrors with Mo/Si multilayer coatings is adapted to this source, simultaneously blocking unwanted out-of-band radiation. By demagnified (10x) imaging of the plasma an EUV spot of 5 μm diameter with a maximum energy density of ~0.72 J/cm² is generated (pulse length 8.8 ns). We present first applications of this integrated source and optics system, demonstrating its potential for high-resolution modification and structuring of solid surfaces. As an example, etch rates for PMMA, PC and PTFE depending on EUV fluences were determined, indicating a linear etch behavior for lower energy densities. In order to investigate changes of the chemical composition of PMMA induced by EUV radiation we present FTIR and NEXAFS measurements on irradiated samples. The latter were performed using the laboratory source tuned to the XUV spectral range around the carbon K-edge (λ ~ 4.4 nm) and a flat-field spectrometer. For showing the potential of this setup, first damage tests were performed on grazing incidence gold mirrors. For these thin Gold films, threshold energy densities could be determined, scaling linear with the film thickness.

We investigate theoretically the interaction of a semiconductor with an ultrashort high-intensity VUV laser pulse produced by new light source FLASH at DESY in Hamburg. Applying numerical simulations of excitations and ionization of electronic subsystem within a solid silicon target, irradiated with femtosecond laser pulse (25 fs, photon energy of 38 eV), the transient distribution of electrons within conduction band is obtained. The Monte Carlo method (ATMC) was extended in order to take into account the electronic band structure and Pauli's principle for electrons excited into the conduction band. Secondary excitation and ionization processes were included and simulated event by event as well. In the presented work the temporal distribution of the density of excited and ionized electrons, the energy of these electrons and their energy distribution function were calculated. It is demonstrated that due to the fact that part of the energy is spent to overcome ionization potentials, the final kinetic energy of free electrons is much less than the total energy provided by the laser pulse. We introduce the concept of an 'effective energy gap' for collective electronic excitation, which can be applied to estimate the free electron density after high-intensity VUV laser pulse. The effective energy gap depends on properties of the material as well as on the laser pulse.

Kinetic Boltzmann equations are used to model the ionization and expansion dynamics of xenon clusters irradiated with short, intense VUV pulses from free-electron-laser (FEL). This unified model includes all of the predominant interactions that contribute to the cluster dynamics induced by this radiation. The dependence of the evolution dynamics on cluster size and pulse fluence is investigated. It is found that the highly charged ions observed in the experiments are mainly due to Coulomb explosion of the outer shell of the cluster while ions formed in the interior of the cluster predominantly recombine with plasma electrons. As a result, a large fraction of neutral atoms is formed within the core, the proportion depending on the cluster size. The predictions of ion charge distribution, average ion charge and average energy absorbed per ion made with our model are found to be in good agreement with the experimental data. To our knowledge, our model is the first and only one that gives a full and quantitatively accurate description of all of the experimental data collected from irradiated atomic clusters at 100 nm photon wavelength.

The report will be devoted to the modelling of damage processes of the optical-cryogenic sensor at microscopic and macroscopic levels. The sensor is based on a new type of suspension of the probe of a supeconducting gravimeter. The interferometric method is provided coordinate measurement of the probe. The following main subjects will be covered by the report: (1) modelling of a supeconducting gravimeter; (2) modeling of a solid-state laser; (3) computer simulation of damage processes at microscopic and macroscopic levels; (4) response of thin films to intense short-wavelength radiation; (5) mathematical models for dynamic probabilistic risk assessment; (6) strategies for the design of optical components, and (7) software for modeling and prediction of ionizing radiation. For computer simulation of damage processes at microscopic and macroscopic levels the following methods are used: () statistical; (b) dynamical; (c) optimization; (d) acceleration modeling, and (e) mathematical modeling of laser functioning. Mathematical models of space ionizing radiation influence on gravimwter elements were developed for risk assessment in laser safety analysis.

We exposed standard Mo/Si multilayer coatings, optimized for 13.5 nm radiation to the intense femtosecond XUV radiation at the FLASH free electron laser facility at intensities below and above the multilayer ablation threshold. The interaction process was studied in-situ with reflectometry and time resolved optical microscopy, and ex-situ with optical microscopy (Nomarski), atomic force microscopy and high resolution transmission electron microscopy. From analysis of the size of the observed craters as a function of the pulse energy the threshold for irreversible damage of the multilayer could be determined to be 45 mJ/cm². The damage occurs on a longer time scale than the XUV pulse and even above the damage threshold XUV reflectance has been observed showing no measurable loss up to a power density of 10¹³ W/cm². A first explanation of the physics mechanism leading to damage is given.

A multilayer-coated 27-cm focal length parabola, optimized to reflect 13.5 nm wavelength at normal incidence, was used in multiple FLASH experiments and focused the beam to a sub-micron beam size. The intensity of the beam was measured indirectly from the depths of craters left by the FLASH beam on PMMA-coated substrates. Comparing simulated and experimental shapes of the craters we found the best match for a wavefront error of 0.45 nm, or λ/30. We further estimated that the FWHM of the focal spot was 350 nm and that the intensity in the focus was 10¹⁸ W/cm². The sub-micron FLASH beam provided extreme intensity conditions essential for warm dense matter experiments. The same optic was used in multiple experiments and survived the beam. However, after the first measurements, which took place over several days, the optical surface was contaminated. This contamination reduced the mirror reflectivity, which was partially recovered by oxygen plasma cleaning. However, even the partially cleaned multilayer-coated optic is still diffraction limited and can focus the beam in future experiments to a sub-micron beam size.

Three experiments were carried out to investigate carbon deposition and its mitigation on the surface of Mo/Si multilayer mirrors by EUV irradiation with the introduction of water vapor. In the first experiment of carbon deposition by EUV irradiation in the presence of n-decane gas as a hydrocarbon source, the reflectivity dropping rate of the multilayer mirror increases with increasing the n-decane pressure. In the second experiment of removing once-deposited carbon film by introducing water vapor, the carbon film was partly removed by EUV irradiation in the presence of water vapor. In the third experiment of carbon deposition mitigation by EUV irradiation in the coexistence of n-decane and water vapor, it was observed that carbon film deposition was mitigated by controlling the water vapor pressure. However, the mitigation effect on carbon deposition was not uniform for the EUV intensity, and a large non-linear dependency on the irradiation flux was observed.

A rasterscan test procedure [L. Lamaignère et al, Rev. Sci. Instrumen. 78, 103105 (2007)] has been implemented in order to determine low laser damage density of large aperture UV fused silica optics. This procedure was improved in terms of accuracy and repeatability. Tests have been carried on several facilities using several pulse durations and spatial distributions. We describe the equipment, test procedure and data analysis to perform this damage test with small beams (Gaussian beams, about 1mm @ 1/e, and top hat beams). Then, beam overlap and beam shape are the two key parameters which are taken into account in order to determine damage density. After data analysis and treatment, a repeatable metrology has been obtained. Moreover, the consideration of error bars on defects distributions permits to compare data between these installations. This allows us to reach reproducibility, a necessary condition in order to share results and to make reliable predictions of laser damage resistance.

Results of a novel X-ray laser application, aimed at understanding the microscopic effects involved in formation of laserinduced damage in optical materials exposed to sub-ns laser pulses, will be presented. Specifically, we studied thin plane beamsplitters that are presently the weakest element of the next generation of high-energy lasers (LMJ, NIF), with permanent damage threshold below 20 J/cm². Standard fused silica substrates and a model system, containing welldefined micron grooves as seeding sites to trigger damage when irradiated by 438 nm laser pulses, were in situ probed by a neon-like zinc X-ray laser delivering up to 10 mJ at 21.2 nm. The probing beamline employed a double Lloyd's mirror interferometer, used in conjunction with an imaging mirror to provide magnification of ~8. In conjunction with an array of in-situ optical diagnostics, one of the questions addressed was whether the damage (transient or permanent) on the rear surface of the beamsplitter occurs during or after the laser pulse, i.e. whether it is due to local electrical fields or to other processes. Another issue, examined by both the X-ray interferometric microscopy and the optical diagnostics, is whether a local rear-surface modification is associated with non-linear effects (self-focusing, filamentation) of the laser beam in the bulk.

The desktop capillary-discharge Ne-like Ar laser (CDL) providing 10-μJ nanosecond pulses of coherent 46.9-nm radiation with a repetition rate up to 12 Hz was developed and built at the Colorado State University in Fort Collins and then installed in Prague. The beam of the laser was focused by a spherical mirror covered with Si/Sc multilayer coating onto the surface of poly(methyl methacrylate) - PMMA. Interaction parameters vary by changing the distance between sample surface and beam focus. The samples were exposed to various numbers of shots. Analysis of damaged PMMA by atomic force (AFM) and Nomarski (DIC - differential interference contrast) microscopes allows not only to determine the key characteristics of the focused beam (e.g. Rayleigh's parameter, focal spot diameter, tight focus position, etc.) but also to investigate mechanisms of the radiation-induced erosion processes.

The beam of Free-Electron Laser in Hamburg (FLASH) tuned at either 32.5 nm or 13.7 nm was focused by a grazing incidence elliptical mirror and an off-axis parabolic mirror coated by Si/Mo multilayer on 20-micron and 1-micron spot, respectively. The grazing incidence and normal incidence focusing of ~10-fs pulses carrying an energy of 10 μJ lead at the surface of various solids (Si, Al, Ti, Ta, Si₃N₄, BN, a-C/Si, Ni/Si, Cr/Si, Rh/Si, Ce:YAG, poly(methyl methacrylate) - PMMA, stainless steel, etc.) to an irradiance of 10¹³ W/cm² and 10¹⁶ W/cm², respectively. The optical emission of the plasmas produced under these conditions was registered by grating (1200 lines/mm and/or 150 lines/mm) spectrometer MS257 (Oriel) equipped with iCCD head (iStar 720, Andor). Surprisingly, only lines belonging to the neutral atoms were observed at intensities around 10¹³ W/cm². No lines of atomic ions have been identified in UV-vis spectra emitted from the plasmas formed by the FLASH beam focused in a 20-micron spot. At intensities around 10¹⁶ W/cm², the OE spectra are again dominated by the atomic lines. However, a weak emission of Al⁺ and Al²⁺ was registered as well. The abundance ratio of Al/Al⁺ should be at least 100. The plasma is really cold, an excitation temperature equivalent to 0.8 eV was found by a computer simulation of the aluminum plasma OE spectrum. A broadband emission was also registered, both from the plasmas (typical is for carbon; there were no spectral lines) and the scintillators (on Ce:YAG crystal, both the luminescence bands and the line plasma emission were recorded by the spectrometer).

The efficiency of laser ablation drilling of metal and dielectric (ceramic, glasses, etc.) samples with single and multiple laser pulses per one laser shot was experimentally studied. The laser is operated on the fundamental (1064 nm) wavelength of Nd:YAG laser with 30 ns pulse length or its second (532 nm) and third (351 nm) harmonics, respectively. The laser shot repletion rate was 1 Hz. The pulses in train were separated by 25-45 μs interval. The crater depth and drilling speed dependence increasing on pulse number in multipulse train was studied. The laser ablation normalized per pulse energy in train dependence is not linear function. The strong ablation enhancement was observed. The optimal (in sense the total pulse energy using) drilling can be obtained with double pulse mode compared with 3 - 5 pulses. Nonlinear more than 6 fold increasing of crater depth produced by the second pulse in train was detected. The mechanism of selective increasing of the second pulse interaction efficiency with the hard target is discussed. Experimental results explained in terms of double pulse mode laser ablation model. Spectroscopy study of laser plasma was observed to confirm discussed model of high efficiency for two laser pulse laser ablation. Efficiency of double pulse mode compared with multipulse mode is discussed to be more perspective for various applications of laser ablation. The medicine (surgery, dentist, ophthalmology and so on) application is the most prospective, for instance, the teeth drilling or glaucoma perforation, can be done with smaller energy value.

Photoluminescence of scintillator materials based on intrinsic excitonic luminescence (PbWO₄), and on extrinsic luminescence from doped trivalent rare earth ions (RE³⁺), such as Y₃Al₅O₁₂:Ce ³⁺ and Lu₃Al₅O₁₂:Pr³⁺ was studied under excitation with free electron laser (FEL) light in the 50-100 eV energy range. In case of PbWO₄, non-exponential behavior in the initial part of decay curves was observed depending on the FEL pulse energy, and modeled in terms of the bimolecular self-quenching process. For the RE³⁺ doped samples, a reduction in light yield with increasing pulse energy is observed, which can be traced to saturation of the available RE³⁺ sites in the crystal due to the initial high concentration of electron-hole pairs after FEL excitation.

Transmittance and radiation induced absorbance in VUV-UV-visible spectral region were measured in several binary and complex fluoride single crystals at room temperature. Influence of the intentional doping and material stochiometry is demonstrated. X-ray induced coloration and degradation of transmittance characteristics are observed and discussed in terms of creation of various electron (F-like) and hole (VK- and H-like) centers and in terms of near band-edge transitions arising due to imperfect periodicity of the lattice in a general sense. It is shown that VUV characteristics cannot be derived or predicted from those observed in UV-visible spectral region.

We report on the results of fabrication and optoelectrical characterization of Gallium Nitride (GaN) based Extreme UltraViolet (EUV) photodetectors. Our devices were Schottky photodiodes with a finger-shaped rectifying contact, allowing better penetration of light into the active region. GaN layers were epitaxially grown on Silicon (111) by Metal- Organic-Chemical Vapor Deposition (MOCVD). Spectral responsivity measurements in the Near UltraViolet (NUV) wavelength range (200-400 nm) were performed to verify the solar blindness of the photodetectors. After that the devices were exposed to the EUV focused beam of 13.5 nm wavelength using table-top EUV setup. Radiation hardness was tested up to a dose of 3.3·10¹⁹ photons/cm². Stability of the quantum efficiency was compared to the one measured in the same way for a commercially available silicon based photodiode. Superior behavior of GaN devices was observed at the wavelength of 13.5 nm.

The development and properties of reflective coatings for the x-ray offset mirror systems of the Linac Coherent Light Source (LCLS) free-electron laser (FEL) are discussed in this manuscript. The uniquely high instantaneous dose of the LCLS FEL beam translates to strict limits in terms of materials choice, thus leading to an x-ray mirror design consisting of a reflective coating deposited on a silicon substrate. Coherent wavefront preservation requirements for these mirrors result in stringent surface figure and finish specifications. DC-magnetron sputtered B4C and SiC thin film coatings with optimized stress, roughness and figure properties for the LCLS x-ray mirrors are presented. The evolution of microstructure, morphology, and stress of these thin films versus deposition conditions is discussed. Experimental results on the performance of these coatings with respect to FEL damage are also presented.

Laser-based X-ray sources like laser-induced plasma (LIP) established as laboratory scale EUV- and soft X-radiation sources in many scientific fields. Concerning the relative low conversion efficiencies of about 0.5% to 1% one has to avoid scattered laser light reaching the X-ray optical setup. For this, thin metal filters with a thickness of a few hundred nanometres are used. Another purpose of the filter is to block high-speed ions, clusters and particles (debris) originating from the plasma, thus protecting the X-ray optics against damage. This is especially true when solid targets are used for plasma generation. Concerning the application of LIP sources, one needs to collect as much radiation as possible. Therefore X-ray optics with a high numerical aperture are required and the shielding filter has to be large and far-off the source or vice versa. Since large thin filters are very fragile, one has to find a compromise between these two parameters to achieve appropriate filter lifetime. In this work we describe the stage of experiments to learn more about the process of debris emission characteristics and the risk of damage to sensitive filters and X-ray optics. The experiments were carried out at a LIP source using a liquid nitrogen jet or an ethanol jet as target. Several types of metal foils are investigated at different distances to the source. Each filter is imaged onto a CMOS-Camera to examine the leakage of scattered laser light by debris-generated pinholes. The analysis of the experiments is carried out particularly with regard to the theoretical X-ray throughput versus lifetime of the different filter types.

This report concentrates on dynamic probabilistic risk analysis of optical elements for complex characterization of damages using physical model of solid state lasers and predictable level of ionizing radiation and space weather. The following main subjects will be covered by our report: (a) a solid-state laser model; (b) mathematical models for dynamic probabilistic risk assessment; and (c) software for modeling and prediction of ionizing radiation. A probabilistic risk assessment method for solid-state lasers is presented with consideration of some deterministic and stochastic factors. Probabilistic risk assessment is a comprehensive, structured, and logical analysis method aimed at identifying and assessing risks in solid-state lasers for the purpose of cost-effectively improving their safety and performance. This method is based on the Conditional Value-at-Risk measure (CVaR) and the expected loss exceeding Value-at-Risk (VaR). We propose a new dynamical-information approach for radiation damage risk assessment of laser elements by cosmic radiation. Our approach includes the following steps: (a)laser modeling, modeling of ionizing radiation influences on laser elements, (b) probabilistic risk assessment methods, and (c) risk minimization. For computer simulation of damage processes at microscopic and macroscopic levels the following methods are used: (a) statistical; (b) dynamical; (c) optimization; (d) acceleration modeling, and (e) mathematical modeling of laser functioning. Mathematical models of space ionizing radiation influence on laser elements were developed for risk assessment in laser safety analysis. This is a so-called 'black box' or 'input-output' model, which seeks only to reproduce the behaviour of the system's output in response to changes in its inputs. The model inputs are radiation influences on laser systems and output parameters are dynamical characteristics of the solid laser.

We evaluated basic characteristics of energetic plasma ions and neutrals, and of low-energy fragments (e.g. evaporated material and liquid micro-droplets) from a Tin (Sn) plasma produced by a CO2 (10.6 m) or Nd:YAG (1064 nm) laser. Experiments were performed with free-standing liquid droplet, semi-fixed liquid droplet and fixed solid droplet targets. Characteristics of energetic plasma ions, neutrals and fragments were measured by Faraday Cups, laser-induced fluorescence (LIF) imaging and shadowgraph imaging, respectively. The Sn ions were emitted towards the laser incident direction with a velocity of 10 ~ 100 km/s (kinetic energy of 0.06 ~ 6 keV) and the fragments (the majority of the target material) ejected in the same direction as laser pulse at a velocity of 10 ~ 500m/s. The neutrals were emitted in all directions from the target with a velocity of 5 ~ 40 km/s (kinetic energy of 0.015 ~ 1 keV).

EUV- and X-ray sources with laser like properties, e.g. free electron lasers, offer possibilities for many new experiments. In order to successfully plan and perform experiments at these high flux sources, it is necessary to know which kind of optics, exposed to the full beam, can be used. Due to the high intensities, it is not clear, whether transmissive diffractive optics are applicable, because these optics are usually fabricated on thin membranes, thus introducing additional absorption in the desired energy range. Since diffractive optics, especially zone plates, offer the possibility to achieve small spots when used as a focussing element and can also achieve good image quality in microscopic setups, their usage would facilitate many experiments, especially for their easy handling. As a proof of concept, we set up a zone plate based scanning transmission microscope at the unfocussed beamline BL3 at FLASH (DESY/Hamburg). The operating wavelength was 32 nm and 13.8 nm, respectively. While the first attempt, utilizing a zone plate composed of PMMA on silicon substrate failed due to ablation of the PMMA, a second zone plate (chromium on silicon nitride) was successfully used to focus the beam onto different samples (e.g. nickel-mesh and a silicon nitride structured sample). The resulting focal spot size was estimated from the acquired images to be in the range of 1 μm - 3μm in diameter. After several hours of exposure, no damage was visible to the optics. Beside the optics, different filters (Silicon/Zirconium, Zirconium and Aluminum) have been placed in the beam to evaluate possibilities to further reduce intensity which may be necessary if sensitive detectors are involved. All of the filters withstood the irradiation during the whole experiment.

Laser damage in KDP crystals has been studied since several years and more accurately with emergence of projects like LMJ (Laser MégaJoule, in France) or NIF (National Ignition Facility, in US). Laser damage tests are essentially performed at 351-nm wavelength (3ω), with regards to their optical behaviours on forementioned facilities. But only few data are available at 1064 nm (1ω) and at 532 nm (2ω), and even with wavelength-mixing more representative of operational conditions of KDP crystals. So in a first approach, we tried to carry out an identity chart of the crystal by performing mono-wavelength tests at 1ω, 2ω and 3ω. Then, a campaign of combination of multi-wavelength (typically 3ω and 1ω) tests has been started with several temporal delays between 3ω and 1ω pulses. These first results lead us to improve pre-existing modelling codes developed by CEA, which have proved their robustness to 3ω -experiment results. Foremost interests consist in implementing wavelength dependency and energy deposition mechanism as a consequence of our first observations on KDP.

Irradiation experiments were conducted at Prague Asterix Laser System (PALS) with the Ne-like zinc soft x-ray laser (SXRL) at 21.2 nm (58.5 eV) delivering up to 4 mJ (~4 x 10¹⁴ photons), 100-ps pulses in a narrowly collimated beam. The SXRL beam was focused using a 1 inch diameter off-axis parabolic mirror (f = 253 mm at 14 degrees) with a Mo:Si multilayer coating (R = 30% at 21 nm) placed 2825 mm from the SXRL. The diameter of the SXRL beam incident on the mirror was about 11 mm. Ablation experiments with a gradually attenuated beam were performed to determine the single-shot damage threshold of various materials. In this case, the sample was positioned at the tightest focus of the SXRL whose pulse energy was attenuated by aluminum filters of various thickness to adjust the fluence. Both the focal spot area and single-shot damage threshold were determined from the plot of damaged surface areas as a function of a pulse energy logarithm to dete. For PMMA, the focal spot area and the ablation threshold inferred from the data are S_foc = (1172±230) μm² and F_th = (1.25±0.4) J/cm², respectively. Inorganic materials have thresholds significantly higher than organic polymers, e.g., amorphous and monocrystalline silicon gave values 2.5 J/cm² and 4.2 J/cm², respectively. For prospective SASE FEL optical elements, the SiC coating is of great interest. Its damage threshold is of 20 J/cm², i.e., slightly lower than that of monocrystalline silicon. The thresholds determined with the 100-ps pulses from plasma-based, quasi-steady state SXRL are significantly higher than the thresholds obtained for 20-fs pulses provided by the SXR freeelectron laser in Hamburg. There is a difference in PMMA thresholds of two orders of magnitude for these two sources.

In recent years, technological developments in the area of extreme ultraviolet lithography (EUVL) have experienced great improvements. So far, intense light sources based on discharge or laser plasmas, beam steering and imaging optics as well as sensitive detectors are available. Currently, applications of EUV radiation apart from microlithography, such as metrology, high-resolution microscopy, or surface analysis come more and more into focus. In this contribution we present an overview on the EUV/XUV activities of the Laser-Laboratorium Göttingen based on table-top laser-produced plasma (LPP) sources. As target materials gaseous or liquid jets of noble gases or solid Gold are employed. Depending on the applications, the very clean but low intense gaseous targets are mainly used for metrology, whereas the targets for high brilliances (liquid, solid) are used for microscopy and direct structuring. For the determination of interaction mechanisms between EUV radiation and matter, currently the solid Gold target is used. In order to obtain a small focal spot resulting in high EUV fluence, a modified Schwarzschild objective consisting of two spherical mirrors with Mo/Si multilayer coatings is adapted to this source. By demagnified (10x) imaging of the Au plasma an EUV spot of 3 μm diameter with a maximum energy density of ~1.3 J/cm² is generated (pulse duration 8.8 ns). First applications of this integrated source and optics system reveal its potential for high-resolution modification and direct structuring of solid surfaces. For chemical analysis of various samples a NEXAFS setup was developed. It consists of a LPP, using gaseous Krypton as a broadband emitter in the water-window range, as well as a flat field spectrograph. The laboratory system is set to the XUV spectral range around the carbon K-edge (4.4 nm). The table-top setup allows measurements with spectral accuracy comparable to synchrotron experiments. NEXAFS-experiments in transmission and reflection are demonstrated. Beside chemical investigations, also microscopy applications are performed within the XUV spectral range. For this reason a water-window microscope was developed, based on a liquid argon LPP target. The XUV radiation is focused by a Cr/Sc multilayer mirror, leading to spectral narrow band radiation on the sample. For magnifying the sample, a Fresnel zone plate will be used with an outer zone width of 50 nm. Additionally to these applications, an EUV/XUV setup for structural analysis was developed. Using a spectral broad band emitting Xenon gaseous target combined with a grazing incidence optics (Kirkpatrick-Baez arrangement), it offers the possibility to perform angular resolved reflectivity-, diffraction- and scattering experiments as well as NEXAFS analysis in one setup. In completion to these experiments with LPP sources, an EUV/XUV Hartmann-type wavefront sensor has been developed in collaboration with DESY HASYLAB. It consists of a pinhole array, positioned in front of a XUV sensitive CCD camera with quantum converter. With custom-developed software the incident wavefront can be determined. This sensor is currently used at the free electron laser FLASH in Hamburg for beam characterization.

The utilization of nanostructured materials for modern applications gained more and more importance during the last few years. As examples super-fluorescent quantum dots, the use of carbon nano tubes (CNTs) in microelectronics, electrospun fibers in filter membranes, thin film coatings for solar cells, mirrors or LEDs, semiconductor electronics, and functionalized surfaces may be named to address only a few topics. To optimize the systems and enable the full range of capabilities of nanostructures a thorough characterization of the surface-near topography (e.g. roughness, thickness, lateral dimension) as well as of the chemical composition is essential. As a versatile tool for spatial and chemical characterization XUV reflectometry, scatterometry and diffractometry is proposed. Three different experimental setups have been realized evaluating spectral resolved reflectance under constant incidence angle, angular resolved reflectance at a constant wavelength, or a combined approach using laboratory scaled XUV sources to gain insight into chemical composition, film thickness and surface/interface roughness. Experiments on near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the carbon K-edge have been performed. The investigated systems range from synthetic polymers (PMMA, PI) over organic substances (humic acids) to biological matter (lipids), delivering unique spectra for each compound. Thus NEXAFS spectroscopy using a table-top XUV source could be established as a highly surface sensitive fingerprint method for chemical analysis. Future extended experiments will investigate the silicon L-edge where e.g. silicon oxide interlayers below high-k or other nano-layered material on Sisubstrates depict a technological important group of composite systems.