Effective area is one of the most important parameters of x-ray telescopes. It can be increased by enlarging the entrance aperture or maximizing the reflectivity through the proper designing and optimization of the reflecting coating. A method to increase the reflectivity of grazing incidence x-ray mirrors in the 0.5- to 8-keV energy region is analyzed. The idea consists in the use of a trilayer reflecting coating instead of single-layer one (e.g., C/Ni/Pt mirror instead of Pt one). Deposition of low-absorbing medium-Z and low-Z layers onto the top of strongly absorbing high-Z material results in essential increase in the reflectivity while keeping the same width of the reflectivity plateau. In particular, C/Ni/Pt trilayer mirror demonstrates enhancement of the double reflection coefficient by a factor achieving 1.5 to 3.5 compared to that of Pt-coated mirror. The effective area of a telescope is also considerably increased. The experimental results are in a very good agreement with the theoretical predictions. In addition, the C/Ni/Pt trilayer mirror exhibits a reasonable thermal stability and a relatively low compressive stress of about −550 MPa.
The low efficiency of conventional single layer gratings at the tender X-ray region (E=1~5 keV) significantly limits the photon flux of the beamline and the development of related imaging and spectroscopy experiments in this region. To overcome this issue, multilayer coated gratings have been proposed and developed. The diffraction behavior of a multilayer grating is more complex than a single layer grating. To understand the diffraction behavior and exert the maximum potential of this new optics, we have built an analytical theory based on coupled wave theory. A high efficiency single order diffraction regime was first identified which means only one diffraction order will be excited with a certain incidence angle and structure parameters. This is applicable to blazed multilayer gratings (BMGs). To achieve maximum efficiency, the optimum grating and multilayer structures were analyzed. The highest theoretical efficiency of a BMG can reach the same value of the coated multilayer reflectance. Moreover, blazed multilayer gratings exhibit the advantage of high harmonics suppression. For the BMG, the conventional condition of maximal diffraction efficiency, Dsinα = nd, where D and d is the grating period and multilayer period, respectively, α is blaze angle, n is diffraction order, has been proved invalid. This is due to the contribution of anti-blaze facets to diffraction and effect of strongly asymmetric diffraction. Based on these, a Cr/C BMG was fabricated in collaboration with the Department for Nanometer Optics and Technology in BESSY-II. Maximum efficiency of up to 60% was demonstrated at 3 keV which is close to the theoretical prediction.
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.
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.
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