Libor Sveda

Porosity Measurement Method by X-Ray Computed Tomography

This paper describes a new nondestructive approach for porosity measurement developed in response to a need for a more accurate porosity measuring method for solid samples. The conventional methods in X-ray CT imaging are based on image segmentation where a threshold is applied at a user-defined value. As a result, the uncertainty in the porosity measurement is introduced. Therefore, the new method, called the grey level method, which reflects the phenomenon of image processing and computation of ration between the volume of voids and the total volume of the entire sample, was considered and improved in term of image noise and artifacts. The volumes of 2D CT image as a surface are achieved by means of integrating the surface with operations relating to image histogram. The porosity value is given from the curve of a porosity distribution. Subsequently, the properties of individual pores were measured and comparison with conventional destructive method of porosity computation was carried out. Also limitations of industrial X-ray CT as well as their accuracy are discussed.

Recent progress with x-ray optics based on Si wafers and glass foils

We report on recent progress with development of astronomical X-ray optics based on thermally formed glass foils and on bent Si wafers. Experiments with thermal glass forming have continued adding wider range of evaluated and optimized parameters. Recent efforts with Si wafers have been focused on their quality improvements such as flatness and thickness uniformity in order to better meet the requirements of future X-ray astronomy projects applications, as well as on study of their surface quality, defects analysis, and methods for its reproducible measurement. The role of substrates quality in performance of final mirror arrays, as required by large future space X-ray astronomy experiments was also studied. The problem of increasing size of Si wafers, required for some X-ray optics applications, is also addressed. First results of irradiation tests of selected substrates are also reported and discussed.

X-ray imaging with compound refractive lens and microfocus x-ray tube

Compound refractive lenses (CRL), consisting of a lot number in-line concave microlenses made of low-Z material were studied. Lenses with focal length 109 mm and 41 mm for 8-keV X-rays, microfocus X-ray tube and X-ray CCD camera were used in experiments. Obtained images show intensity distribution of magnified microfocus X-ray source focal spot. Within the experiments, one lens was also used as an objective lens of the X-ray microscope, where the copper anode X-ray microfocus tube served as a source. Magnified images of gold mesh with 5 microns bars were obtained. Theoretical limits of CRL and experimental results are discussed.

Novel x-ray optics with Si wafers and formed glass

The thermally formed thin glass foils and optically shaped Si wafers are considered to belong to the most promising technologies for future large space X-ray telescopes. We present and discuss the recent progress in these technologies, as well as properties of test mirrors produced and tested. For both technologies, both flat and curved samples have been produced and tested. The achieved profile accuracy is of order of 1 micrometer or better, while the bending technologies maintain the intrinsic fine surface microroughness of substrates (better than 0.5 nm for glass and around 0.1 nm for Si wafers).

Astrophysics with LOBSTER

We report on astrophysical aspects of fully innovative very wide-field X-ray telescopes with high sensitivity. The prototypes are very promising, allowing the proposals for space projects with very wide-field Lobster-eye X-ray optics to be considered. The novel telescopes will monitor the sky with unprecedented sensitivity and angular resolution of order of 1 arcmin. They are expected to contribute essentially to study of various astrophysical objects such as AGN, SNe, Gamma-ray bursts (GRBs), X-ray flashes (XRFs), galactic binary sources, stars, CVs, X-ray novae, various transient sources, etc.

Novel technologies for x-ray multi-foil optics

The future large space X-ray telescopes in study (such as the ESAs XEUS) require novel approaches and innovative lightweight technologies. Although there are several alternative possibilities, in general the shaped thin glass foils and shaped Si wafers are considered to belong to the most promising ones. We present and discuss the recent progress in these technologies, as well as properties of test mirrors produced and tested. For both technologies, both flat and curved samples have been produced and tested. The achieved profile accuracy is of order of 1 micrometer or better, while the bending technologies maintain the intrinsic fine surface microroughness of substrates (better than 0.5 nm).

Astronomical lobster eye telescopes

We describe and discuss astronomical LOBSTER EYE X-ray telescopes based on Multi Foil Optics including recent results of the development and tests of advanced laboratory samples. An alternative proposal for a space experiment based on this optics - Lobster All Sky Monitor - is also briefly presented and discussed.

Slumping monitoring of glass and silicone foils for x-ray space telescopes

We developed a non-contact method for in-situ monitoring of the thermal slumping of glass and silicone foils to optimize this technology for the production of high quality mirrors for large aperture x-ray space telescopes. The telescopes crucial part is a high throughput, heavily nested mirror array with the angular resolution better than 5 arcsec. Its construction requires precise and light-weight segmented optics with surface micro-roughness on the order of 0.1 nm. Promising materials are glass or silicon foils shaped by thermal forming. The desired parameters can be achieved only through optimizing the slumping process. We monitored the slumping by taking the snapshots of the shapes every five minutes at constant temperature and the final shapes we measured with the Taylor Hobson profilometer. The shapes were parabolic and the deviations from a circle had the peak-to-valley values of 20-30 μm. The observed hot plastic deformation of the foils was controlled by viscous flow. We calculated and plotted the relations between the middle part deflection, viscosity, and heat-treatment time. These relations have been utilized for the development of a numerical model enabling computer simulation. By the simulation, we verify the materials properties and generate new data for the thorough optimization of the slumping process.

Lobster eye: technology and imaging properties

Lobster eye optics, as a wide field of view imaging system, is perfectly suited for x-ray astronomy but can be useful also in the lab. This paper presents a brief overview of the technologies developed in our group, where the glass and silicon mirrors are used to built up the Schmidt lobster eye design and mainly discuss the mirror design consequences on the resulting imaging properties of the system. Corrections of various image distortions and imperfections, either geometric, spectral or temporal in case of scanning observations have to be applied in order to get a valuable instrument. Several image processing methods are discussed and its strengths and weaknesses are shown for both astronomy and laboratory experiments.

Multi-foil optic condenser for a laser plasma EUV source

Design and development of the multi-foil optic (MFO) condenser for a gas puff laser plasma source for EUV lithography is presented. The MFO in general is a soft x-ray optic which consists of two perpendicular sets of very thin reflecting surfaces, where photons are reflected at grazing angles. The aim of the work was to design the condenser working for ~100 eV photons focusing from point to point ~40 cm distant. Initial design and simulations are described and compared to early experiments performed in visible light. The performance of the optic over the initial requirements is discussed. We also briefly discuss several other MFO modifications, including condensers and collimators for laboratory purposes or the wide field x-ray scanning modules for satellite astronomy.