The contamination of optical elements (mirrors and gratings) with carbon still is an issue when using soft x-ray synchrotron radiation. With an in-house developed HF-plasma treatment we are able to decontaminate our optics in-situ from carbon very efficiently. The cleaning device, a simple Al-antenna, is mounted in situ inside the mirror- and grating vacuum chambers. A systematic study of the HF-plasma cleaning efficiency was performed acquired with in-situ and exsitu methods for monitoring: An atomic force microscope (AFM) and a scanning tunneling microscope (STM) were used before and after the cleaning process to determine the surface morphology and roughness. Reflectivity angular scans using the reflectometer at the BESSY-II Metrology Station [1-3] allowed to estimate the thickness of the remaining Clayer after different cleaning steps and thereby helped us to determine the etching rate. Reflection spectra measurements in the range of 200 eV – 900 eV show the complete removal of Carbon from the optics without contaminating it with any other elements due to the plasma treatment. The data show that the plasma process improves the reflectivity and reduces the roughness of the surface. In addition to that, the region of the optical surface where the carbon has been removed becomes passivated.
Within our technology center for production of highly efficient precision gratings a versatile 4-circle UHV-reflectometer
for synchrotron radiation based at-wavelength characterization has been fabricated. The main feature is the possibility to
incorporate real live-sized gratings. The samples are adjustable within six degrees of freedom by a novel UHV-tripod
system, and the reflectivity can be measured at all incidence angles for both s- and p-polarization geometry. The
reflectometer has been setup in a clean room hutch and it is coupled permanently to the optics beamline PM-1 for the UV
and XUV range with the polarization adjustable to either linear or elliptical. The setup will be open to users by the end of
The design for a new XUV-Optics Beamline is presented. The collimated plane grating monochromator (PGM-)
beamline at a bending magnet is setup at the BESSY-II synchrotron radiation facility within the framework of the
blazed-grating production facility. Coupled to a versatile four-circle (ten axes) UHV- reflectometer as a permanent end
station the whole setup is dedicated to at-wavelength characterization and calibration of the in-house produced precision
gratings and novel nano-optical devices as well as mirrors, multilayered systems etc. It is also open to external projects
employing reflectometry, spectroscopy or scattering techniques. According to its purpose, this beamline has specific
features, such as: very high spectral purity, provided by two independent high order suppression systems, an advanced
aperture system for suppression of stray light and scattered radiation, a broad energy range between 10 eV and 2000 eV,
small beam divergence and spot size on the sample. Thus this Optics Beamline will become a powerful metrology tool
for reflectivity measurements in s- or p-polarisation geometry with linearly or elliptically polarized light on real optics up
to 360 mm length and 4 kg weight.
At the European X-ray Free Electron Laser facility one‐ or two‐ Si(111) channel (cut) crystal X‐ray monochromator (Kmonochromator) are planned for photon beam based alignment: gap tuning of the undulator segments and phase tuning of the phase shifters during commissioning and maintenance of the undulators. A prototype device has been built using a single channel-cut crystal and was characterized at PETRAIII synchrotron (at P01, which is the only beamline with two undulator segments) by applying different undulator adjustment methods, intended for the European XFEL, that use imaging and intensity detection. This paper presents the setup and the first results from the experimental qualification of the K-monochromator prototype.
This paper presents the outcome of ray tracing simulations for different optical schemes to be setup at the
European X-ray Free Electron Laser facility (XFEL.EU), Germany: one- or two- channel (cut) crystal X-ray
monochromators (K-Mono; using spontaneous radiation) are planned and designed mainly for photon beam
based alignment, which is gap tuning of the undulator segments and phase tuning of the phase shifters during
commissioning and maintenance of the undulators. The coherent SASE (Self Amplified Spontaneous Emission)
radiation will be monitored pulse-resolved by single-shot spectrometers of which two types are investigated: i) a
three element spectrometer, design proposed by Yabashi et al., which consists of a curved focusing mirror,
followed by a flat analyzer crystal and a 2D-detector.ii) a two element spectrometer based on a reflection zone
plate that reflects and focuses in one step, and a 2D-detector (currently under development).
The paper deals with the recent results of the experiments on soft X-ray imaging of various carbon-containing objects: biological samples, artificial carbon fibres, graphite slices, etc. The working wavelength was chosen to be 4.5 nm due to high penetration ability of these soft X-rays in the carbon materials. The experimental set-up included: laser plasma X-ray source (generated with the 2nd harmonics of Nd:YAG laser), scandium-based thin-film filter and highly reflective spherical multilayer mirror. The Co/C multilayer's reflectivity was measured to be about 15 % at normal incidence that was high enough to produce soft X-ray images using one nanosecond-long exposure. The work demonstrates a possibility to produce high contrast images outside "water window" region for study of relatively thick (tens of microns) samples that may lead to new fields of applications of the soft x-ray microscopy.
A raytracing code for zone plates incorporated in the BESSY raytracing program RAY is described. This option allows one to calculate intensity distributions in a focal plane of circular or linear zone plates considering diffraction limited resolution. Zone plate material properties are also taking into account using optical constants data tables. The complete code is available as PC-Windows version.
Sc/Si multilayers were designed for normal incidence reflectivity in the wavelength range from 35 to 50 nm and were deposited by dc-magnetron sputtering. X-ray scattering of CuKα radiation, transmission electron microscopy, atomic force microscopy and chemical analysis were used for the characterization of the multilayer structures. The normal incidence reflectivity was measured as a function of the wavelength, for different layer thickness ratios, number of layers and some important sputter parameters. Maximum reflectivities of 21% @ 38 nm and 54 % @ 46 nm for Sc/Si multilayer mirrors were achieved. Reflectivity up to 56 % @ 44.7 nm for a Sc/Si multilayers having enhanced interface structure
due to Cr diffusion barriers will be under discussion. The increase in reflectivity is consistent with multilayers having sharper and smoother interfaces. The evolutions of optical properties in the temperature range from 50°C to 250°C for classical Sc/Si and interface engineered Sc/Cr/Si/Cr multilayers will be compared.
Results of soft x-ray reflection measurements of Cr/Sc multilayer mirrors close to the Sc absorption edge at 3.11 nm are presented. Improvements in the deposition technology and the adjustment of the multilayer period with an accuracy of better than 0.01 nm to this absorption edge enabled a step forward towards soft x-ray mirrors with an adequate reflectance that allow the realization of normal incidence optical components in the water window. In particular, reflectivity measurements performed at the PTB reflectometer at BESSY II in Berlin revealed a reflectivity of R = 14.8% at an incidence
angle of θ = 1.5° and R = 15.0% at θ = 5°. Simulation results show that the interface widths between the Cr and Sc nanolayers are less than 0.4 nm. The annealing effect in short-period Cr/Sc multilayers was studied in the temperature range from 50°C to 500°C by X-ray scattering and transmission electron microscopy. Structural and phase transformations and the corresponding changes of the optical properties are presented and discussed.
Due to the unusual behavior of its optical constants the first transition element Sc with atomic configuration (3p64s23d) is a very attractive candidate for multilayer coatings optimized for the anomalous dispersion region of the 3p-3d transition around 28 eV (45 nm) and for the vicinity of the 2p absorption edge at 398 eV (3.12 nm), respectively. New normal incidence reflectivity data for Sc/Si at Sc 3p are shown with peak values up to 54% and for Cr/Sc at Sc 2p with peak values up to 17% are presented. The influence of optical performance on multilayer growth conditions and parameters are discussed in detail and the necessity of at-wavelength metrology for the final characterization is demonstrated. The results encourage e.g. applications for normal incidence optics used for high-power pulsed UV and x-ray laser systems and for x-ray microscopes operated in the water window.
An instrument for measuring polarization typically consists of a phase shifter and a linear polarizer. Up to 600 eV, periodic multilayer structures can be used for this purpose. They consist of alternating layers of two materials, one of which has an absorption edge in the photon energy region of interest. The phase shift of the transmitted beam and the intensity of the reflected beam show maxima at energies just below the edge. Phase shifters on 100 nm thick Si3N4 membranes and linear polarizers on Si wafers have been made by DC magnetron sputter deposition. The polarizers were designed to work at the Brewster angle, where only s-polarized radiation is reflected. The corresponding multilayer period decreases from 8.5 nm at 100 eV to 1.4 nm at 600 eV. A reflectance of 6.8% was obtained at 512 eV for 150(V/Ni). In order to extend polarization measurements into the 1 keV region, the use of magnetic effects like magnetic circular dichroism (MCD) is being explored. This effect has been measured in Co/C and FeCoV/Ti transmission multilayers close to the L2,3 edges of Co and Fe.
Ultrathin Cr/Sc-multilayers were systematically investigated using tuneable soft x-ray synchrotron and x-ray tube radiation. The multilayers were optimized either for use in normal incidence or at 45 degrees at photon energies around the L-absorption edges of Sc (399 eV) and Cr (574 eV), respectively, and K-absorption edge of C (283 eV). The high reflectivity of the multilayer mirrors allows to use them for the creation of multi-mirror systems for x-ray astronomy and microscopy and x-ray diagnostics of high-temperature plasma.
Laminar groove profiles promise a high suppression factor for the even orders of reflection gratings. For normal incidence mounts the theoretical suppression of the second order should be nearly perfect if the groove to land ratio of 1 : 1 is matched. Experimental experience with laminar gratings demonstrates that the suppression of the second order is not as good as expected from calculations. Once we understood that the behaviour of the second order contribution cannot be explained in terms of a mismatch of the groove to land ratio alone, we started to investigate the characteristics of laminar groove profiles in more detail by means of atomic force microscopy. The main discrepancy between the idealised laminar profile and the
measured profiles is the limited aspect angle of the edges of the grooves: the profiles are rather trapezoidal than laminar. Simulating the diffraction efficiency of the measured trapezoidal profiles revealed that the shallow aspect angle has a significant influence on the higher order diffraction efficiencies. Optimising groove profile parameters under assumption of a realistic aspect angle yielded essentially different values than the same procedure for idealised laminar profiles.
We present an experimental survey of the performance of various multilayer systems to be used in the soft x-ray range with special emphasis on the water window. The multilayers have been designed as high reflectance normal incidence mirrors and, for polarimetry purposes, as detectors for circularly polarized synchrotron radiation, respectively. Seven different multilayer systems with spacer materials of C or the transition metals Sc, Ti, V, Cr in combination with the absorber materials Fe, W and Ni were investigated. At the 1s- and 2p absorption edges, respectively, they show a strong resonant enhancement of the reflectance due to anomalous dispersion. By tailoring the layer thickness and the thickness ratio for use at and below the resonance energy in normal incidence ((theta) equals 90 degree(s)) and at (theta) equals 45 degree(s), respectively, an excellent performance with respect to reflectance, transmission and polarizance, respectively, in the water window was achieved for multilayers with period thicknesses down to 1.4 nm.
We present first experimental data on a novel type of optical element for synchrotron radiation applications in the x-ray region: namely laterally-graded aperiodic crystals on the basis of Si1-xGex alloys. The lattice parameter of such a gradient crystal containing up to some atomic % Ge in a Si single crystal changes nearly linearly along the plate of diffraction. Thus the variation of the Bragg angle of divergent incident light on the crystal can be compensated for. This opens up the possibility to operate a crystal monochromator in nearly crystal limited resolution in the whole energy range above 2 keV at the full vertical divergence without a collimating premirror. Simultaneously the reflected spectral intensity can be increased considerably as compared with a conventional Si-crystal monochromator.
X-ray multilayer supermirrors for the energy range up to 22 KeV have been theoretically studied and experimentally measured with synchrotron radiation. A multilayer mirror with 50 W/Si bi-layers of different thicknesses on an Si substrate has a smooth reflectivity of up to 32% in the whole energy range from 5 KeV to 22 KeV at a grazing incidence angle of 0.32 degrees.
The crossed field undulator independently proposed by Moiseev et al. and K. J. Kim generates short wavelength (photon energy above 35 eV) circularly polarized radiation. It is based on the coherent superposition of two mutually orthogonally polarized wavetrains generated in two `ordinary' undulators arranged one after the other along with electron beam axis. The superposition is achieved in a monochromator of sufficient spectral resolution. The relative phase is determined by the so called modulator located in between the two undulators. It is a three pole magnetic structure returning the electrons to the axis with a time delay with respect to the straight path of the order of an optical period.
Reflecting multilayers (ML) are widely used and their linearly polarizing property is well known. In particular an angle of incidence of 45 degree(s) theoretically leads to reflection of only the s-component. Kimura et al. used the phase shifting properties of a reflecting ML to measure circular polarization at 97 eV. A transmitting ML as phase shifting element for the same energy has been described and measured. In this paper we report on the use of a transmission ML as a phase shifting element at photon energies near the carbon K edge. Such devices can have applications in detecting and perhaps generation of circularly polarized soft x-rays.
The large lattice parameter (ao equals 23.44 angstroms) of cubic YB66 together with its vacuum compatibility, mechanical properties and resistance to radiation damage makes this material well suited for use as soft x-ray monochromator in the 1 - 2 keV region. Crystals obtained by various growth modes of an indirect heating floating zone (IHFZ) technique are characterized with x-ray topography and rocking curve measurements using both laboratory and synchrotron sources. The results indicate that high quality single crystals of YB66 large enough to accept at least 1 mrad of synchrotron beam can be produced.
Deposition possibility of the small d-spacing (d approximately 1 - 2 nm) multilayers on the basis of the material combinations W/Sb, W/B4C, Cr/Sb, Cr/Sc, Fe/Sc, and their utilization as dispersive and focusing elements for the photon energy range E > 0.3 keV have been investigated. The employment of the normal incidence spherical multilayers W/Sb and Cr(Fe)/Sc for imaging of a high-temperature laser-produced plasma within the `water window' spectral range (0.3 < E < 0.5 keV) are presented.