A constant pressure gas flowmeter using a directly driven diaphragm bellows as a volume displacer was studied. This flowmeter is perfectly vacuum-sealed, does not contain elastomers and liquids that would prevent outgassing at elevated temperatures and can achieve a smaller ratio of the final volume to the displaced volume than when bellows are used, so that the uncertainty in generating small flow rates can be small. As, when a bellows is used in the volume displacer, the displaced volume cannot be calculated from the geometric dimensions and its dependence on the displacement is non-linear, a sensitive method had to be developed for measuring this dependence. The uncertainty in measuring the displaced volume by this method and the achieved uncertainty of the flowmeter were determined.

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Dust grains are sputtered at every environment containing energetic ions (i.e., ions with energies of several kiloelectronvolts). In the laboratory, only the beam experiments would fulfill these conditions; however, in the space, ions of these energies can be found even in the solar wind. It was suggested that the sputtering is one of the most important destruction processes of micrometer-sized dust grains, and on the other hand, it would be a source of heavy species in the interplanetary medium. We simulate the space environment by trapping the dust grains in an electrodynamic quadrupole trap and by influencing them by the ion beam with a variable energy up to 5 keV. The grains are charged to high surface potentials, and thus, a strong electric field near the surface can affect the sputtering rate. The finite size and the small curvature radius of grains play an important role in the quantification of sputtering efficiency. We propose a simple sputtering model for spherical grains and compare its predictions with measurements. An interpretation of the preliminary results obtained on gold microspheres bombarded by argon ions indicates that not only the grain mass but also the grain shape is changing in the course of our experiment. We suggest that similar effects can occur in the space if the dust is exposed to collimated ion beams.

The multi-mJ, 21-nm soft-x-ray laser at the PALS facility was focused onto the surfaces of amorphous carbon (a-C) coatings, developed for heavily loaded XUV/x-ray optical elements. AFM (Atomic Force Microscopy) images show a 3-micrometer expansion of the irradiated material. Raman spectra, measured with an Ar + laser microbeam in both irradiated and unirradiated areas, confirm a high degree of graphitization in the irradiated layer. In addition to this highfluence (~ 1 J/cm 2 ), single-shot experiment, it was necessary to carry out an experiment to investigate the consequences of prolonged XUV irradiation at relatively low fluence. A high-order harmonic (HH) beam generated at the LUCA facility of the CEA/Saclay Research Center was used as a source of short-wavelength radiation delivering high-energy photons to the surfaces at a low single-shot fluence but with high-average power. a-C irradiated at low fluence, (< 0.1 mJ/cm 2 ) by many HH shots exhibits an expansion of several nanometers. Although it is a less dramatic change of surface morphology than that due to single-shot x-ray-laser exposures, even the observed nanometer-sized changes caused on an a-C surface by an HH beam could influence the reflectivity of a grazing incidence optical element. These results seem to be important for estimating damage to surfaces of highly irradiated optical elements developed for guiding and focusing the ultra-intense XUV/x-ray beams provided by the new generation of sources (VUV FEL and XFEL in Hamburg; LCLS in Stanford) because, up to now, only melting and vaporization, and not graphitization, have been taken into account.

An irreversible response of inorganic scintillators to intense soft xray laser radiation was investigated at the FLASH (Free-electron LASer in Hamburg) facility. Three ionic crystals, namely, Ce:YAG (cerium-doped yttrium aluminum garnet), PbWO 4 (lead tungstate), and ZnO (zinc oxide), were exposed to single 4.6 nm ultra-short laser pulses of variable pulse energy (up to 12 μJ) under normal incidence conditions with tight focus. Damaged areas produced with various levels of pulse fluences, were analyzed on the surface of irradiated samples using differential interference contrast (DIC) and atomic force microscopy (AFM). The effective beam area of 22.2 ± 2.2 μm 2 was determined by means of the ablation imprints method with the use of poly(methyl methacrylate) -PMMA. Applied to the three inorganic materials, this procedure gave almost the same values of an effective area. The single-shot damage threshold fluence was determined for each of these inorganic materials. The Ce:YAG sample seems to be the most radiation resistant under the given irradiation conditions, its damage threshold was determined to be as high as 660.8 ± 71.2 mJ/cm 2 . Contrary to that, the PbWO 4 sample exhibited the lowest radiation resistance with a threshold fluence of 62.6 ± 11.9 mJ/cm 2 . The threshold for ZnO was found to be 167.8 ± 30.8 mJ/cm 2 . Both interaction and material characteristics responsible for the damage threshold difference are discussed in the article.

Time-resolved emission spectroscopy was employed to detect excited species formed by the laser ablation of Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O targets at atmospheric pressure. The emission spectra at times of up to 100 ns are characterized by the broadband emission of high-density plasma; for longer times, sharp atomic and ionic lines were found (Bi, Sr+, Sr, Ca+, Ca, and Cu for the ablation of Bi-Sr-Ca-Cu-O and Y, Y+, Ba+, and Cu for the ablation of Y-Ba-Cu-O). At times greater than 30 μs (Bi-Sr-Ca-Cu-O) or 2 μs (Y-Ba-Cu-O) primarily excited metal oxides occurred in the plasma. Experiments in oxygen, nitrogen, argon, and helium atmosphere indicate that part of the excited metal oxides are formed by reaction of the excited species with molecular or atomic oxygen.

A real-time and accurate characterization of the X-ray beam size is essential to enable a large variety of different experiments at free-electron laser facilities. Typically, ablative imprints are employed to determine shape and size of µm-focused X-ray beams. The high accuracy of this state-of-the-art method comes at the expense of the time required to perform an ex-situ image analysis. In contrast, diffraction at a curved grating with suitably varying period and orientation forms a magnified image of the X-ray beam, which can be recorded by a 2D pixelated detector providing beam size and pointing jitter in real time. In this manuscript, we compare results obtained with both techniques, address their advantages and limitations, and demonstrate their excellent agreement. We present an extensive characterization of the FEL beam focused to ≈1 µm by two Kirkpatrick-Baez (KB) mirrors, along with optical metrology slope profiles demonstrating their exceptionally high quality. This work provides a systematic and comprehensive study of the accuracy provided by curved gratings in real-time imaging of X-ray beams at a free-electron laser facility. It is applied here to soft X-rays and can be extended to the hard X-ray range. Furthermore, curved gratings, in combination with a suitable detector, can provide spatial properties of µm-focused X-ray beams at MHz repetition rate.

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