Showing papers on "Total external reflection published in 2018"

Experimental study of EUV mirror radiation damage resistance under long-term free-electron laser exposures below the single-shot damage threshold

Abstract: The durability of grazing- and normal-incidence optical coatings has been experimentally assessed under free-electron laser irradiation at various numbers of pulses up to 16 million shots and various fluence levels below 10% of the single-shot damage threshold. The experiment was performed at FLASH, the Free-electron LASer in Hamburg, using 13.5 nm extreme UV (EUV) radiation with 100 fs pulse duration. Polycrystalline ruthenium and amorphous carbon 50 nm thin films on silicon substrates were tested at total external reflection angles of 20° and 10° grazing incidence, respectively. Mo/Si periodical multilayer structures were tested in the Bragg reflection condition at 16° off-normal angle of incidence. The exposed areas were analysed post-mortem using differential contrast visible light microscopy, EUV reflectivity mapping and scanning X-ray photoelectron spectroscopy. The analysis revealed that Ru and Mo/Si coatings exposed to the highest dose and fluence level show a few per cent drop in their EUV reflectivity, which is explained by EUV-induced oxidation of the surface.

Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces: a statistical analysis of the scattering contributions.

Abstract: Grazing incidence neutron scattering experiments offer surface sensitivity by reflecting from an interface at momentum transfers close to total external reflection. Under these conditions the penetration depth is strongly non-linear and may change by many orders of magnitude. This fact imposes severe challenges for depth resolved experiments, since the brilliance of neutron beams is relatively low in comparison to e.g. synchrotron radiation. In this article we use probability density functions to calculate the contribution of scattering at different distances from an interface to the intensities registered on the detector. Our method has the particular advantage that the depth sensitivity is directly extracted from the scattering pattern itself. Hence for perfectly known samples exact resolution functions can be calculated and visa versa. We show that any tails in the resolution function, e.g. Gaussian shaped, hinders depth resolved experiments. More importantly we provide means for a descriptive statistical analysis of detector images with respect to the scattering contributions and show that even for perfect resolution near surface scattering is hardly accessible.

A method for measuring the continuous dispersion spectrum of nonlinear refraction coefficients of materials

Abstract: In this paper, a method for measuring the continuous dispersion spectrum of nonlinear refraction coefficients of materials based on complex refractive index dispersion (CRID) measurement is proposed. This method involves measuring internal reflection spectra with a lab-made apparatus. From the determined CRIDs of a material with and without exciting light, the changes in refractive index over a wide spectral range can be obtained, from which the nonlinear refraction coefficients can be deduced. In addition, the RI changes at wavelengths far from the nonlinear range can be used to monitor the thermal effects. In this study, a methyl-red-doped poly(methyl methacrylate) (MR-PMMA) sample was investigated. A large nonlinear refraction coefficient on the order of 10 −1 cm 2 /W was observed. The results also show that the absolute value of nonlinear refraction coefficient of the MR-PMMA sample decreases with the increase of excitation intensity. Consequently, this study provides a powerful approach that has the potential to be applied in the study of the nonlinear properties of materials.

Peculiarities in the Formation of X-Ray Fluxes by Waveguide–Resonators of Different Construction

Abstract: The phenomenon of total external reflection (TER) of quasi-monochromatic X-ray radiation fluxes on a material interface and the effect of waveguide–resonator propagation of these fluxes in nanosize extended slit clearance, as well as a device operating on the basis of this effect—a planar X-ray waveguide–resonator—are briefly described. Experimental data on the formation of an X-ray flux by a composite X-ray waveguide–resonator are presented, and a model describing the decrease in the angular divergence of the formed flux without a decrease in the integral intensity is proposed. The model is based on the conception of partial angular tunneling of the radiation flux in the gap between two consequently mounted and mutually adjusted waveguide–resonators; the tunneling is implemented due to the interaction between interference fields of standing X-ray waves excited by the radiation transported by the slit clearance of these waveguide–resonators.

Grazing Incidence X-Ray Diffraction Study of Tantalum Thin Films

Abstract: The features of the analysis of thin films by small-angle X-ray reflectometry and grazing incidence X-ray diffractometry are considered by the example of tantalum films. In particular, it is shown that a substantial shift of the diffraction peak at small angles of incidence is associated with the refraction of X-rays near the angle of total external reflection. The results of the measurements are in good agreement with calculations. These factors should be considered in grazing incidence X-ray diffractometry to obtain a correct description of the distribution of the properties of thin films over their depth. It is demonstrated that the approach proposed in this paper can be used to determine the material constants (δ, β) and the thickness of tantalum films.

Development of an adjustable Kirkpatrick-Baez microscope for laser driven x-ray sources at CLPU

Abstract: A promising prototype of a highly adjustable Kirkpatrick-Baez (KB) microscope has been designed, built and tested in a number of laser driven x-ray experiments using the high power (200TW) VEGA-2 laser system of the Spanish Centre for Pulsed Lasers (CLPU). The presented KB version consists of two, perpendicularly mounted, 500{\mu}m thick Silicon wafers, coated with a few tens of nm layer of Platinum unlike the conventional, coated, millimetre thick glass substrates, affording more bending flexibility and large adjustment range. According to simulations, and based on total external reflection, this KB offers a broad-band multi-keV reflection spectra, allowing more spectral tunablity than conventional Bragg crystals. In addition to be vacuum compatible, the prototype is characterised by a relatively small size (21cm x 31cm x 27cm) and permits remote control and modification of both the radius of curvature (down to 10m) and the grazing incidence angle (up to 60mrad). A few examples of focusing performance tests, limitations and experimental campaign results are discussed.

Method for determining temperature of phase transitions in films and hidden layers of multi-layer structures of nanometer range of thicknesses

Abstract: FIELD: measuring equipment.SUBSTANCE: method for determining the temperature of phase transitions in films and hidden layers of multi-layer structures of nanometer range of thicknesses, a heated sample is irradiated with a flow of outgoing x-ray source, and the radiation reflected from the surface of the sample is recorded. According to the claimed invention, controlled heating of the sample is carried out, the heated sample is irradiated with a parallel beam of x-ray radiation under the critical angle of total external reflection, the radiation refracted by the sample is transmitted to a multi-reflection crystal-analyzer, and the beam reflected by the multi-reflection crystal analyzer is recorded by a detector. According to step-like change of intensity of refracted x-rays, the temperature of change of film material density is recorded at phase transition. In addition, the parallel x-ray beam is formed using a multi-reflection monochromator, which together with the multi-reflection crystal analyzer forms a circuit of a non-dispersive single-crystal spectrometer for recording small changes of critical angle Θc.EFFECT: increased determination accuracy of the melting point of films and individual layers of multi-layer structures of nanometer range of thicknesses in any combinations of film materials and substrates irrespective of their structure and transparency for optical radiation.2 cl, 1 dwg