Open Access

Show Abstract ▼

Abstract: Ion beam figuring (IBF) is a powerful technique for figure correction of X-ray mirrors to a high accuracy. Here, recent technical advancements in the IBF instrument developed at Diamond Light Source are presented and experimental results for figuring of X-ray mirrors are given. The IBF system is equipped with a stable DC gridded ion source (120 mm diameter), a four-axis motion stage to manipulate the optic, a Faraday cup to monitor the ion-beam current, and a camera for alignment. A novel laser speckle angular measurement instrument also provides on-board metrology. To demonstrate the IBF system's capabilities, two silicon X-ray mirrors were processed. For 1D correction, a height error of 0.08 nm r.m.s. and a slope error of 44 nrad r.m.s. were achieved. For 2D correction over a 67 mm × 17 mm clear aperture, a height error of 0.8 nm r.m.s. and a slope error of 230 nrad r.m.s. were obtained. For the 1D case, this optical quality is comparable with the highest-grade, commercially available, X-ray optics.

Open Access

Show Abstract ▼

Abstract: The design of X-ray beamlines at synchrotrons and free electron lasers requires accurate theoretical modelling of the optical components, such as mirrors, multilayers, lenses, and monochromators. In response to this call, many software developers have stepped forward with freely available packages. Among those that have been used by the Optics & Metrology group of Diamond Light Source (DLS) are SHADOW [Citation1] and RAY [Citation2] for ray tracing, SRW [Citation3] and WISER [Citation4] for wavefront propagation, and xrt [Citation5] and OASYS [Citation6], which combine both types of simulations. These packages permit expert users to predict the performance of X-ray beamlines with a wide variety of optical designs. In many cases, however, it is desirable to have simple analytical formulas to determine whether the performance of a particular optical design will be acceptable. These can help designers eliminate underperforming options at an early stage. They are also easier to communicate to the suppliers that manufacture the optical components and to the engineers that install them. Diamond Light Source has recently treated several cases relevant to the planned Diamond-II upgrade to a diffraction-limited storage ring [Citation7]. First, the non-uniform structures that are always seen in unfocused beams after reflection by multilayers and mirrors have been simply related to the curvature of the wavefront. Second, software based on analytical expressions has been developed to help in the design of future soft X-ray beamlines. Third, thermal deformations of diffracting crystal monochromators, which are a major cause of beam distortion and intensity loss, are being evaluated with the aid of a new analytical model. Finally, Diamond Light Source has established an active program of inspecting crystals with X-ray topography, and crystals other than silicon are being considered as X-ray optics. Therefore, an ­extensible software package for the calculation of X-ray structure factors in crystals, especially those described in the literature by multiple conventions that cause confusion, has been published on GitHub. The immediate motivation has been to help Diamond’s beamlines take full advantage of the higher brightness of Diamond-II, but the main goal throughout has been to make beamline design as general and as simple for non-experts as possible. Much of our work has already been presented in this journal.

Open Access

Show Abstract ▼

Abstract: The ambient-pressure endstation and branchline of the Versatile Soft X-ray (VerSoX) beamline B07 at Diamond Light Source serves a very diverse user community studying heterogeneous catalysts, pharmaceuticals and biomaterials under realistic conditions, liquids and ices, and novel electronic, photonic and battery materials. The instrument facilitates studies of the near-surface chemical composition, electronic and geometric structure of a variety of samples using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy in the photon energy range from 170 eV to 2800 eV. The beamline provides a resolving power hν/Δ(hν) > 5000 at a photon flux > 1010 photons s−1 over most of its energy range. By operating the optical elements in a low-pressure oxygen atmosphere, carbon contamination can be almost completely eliminated, which makes the beamline particularly suitable for carbon K-edge NEXAFS. The endstation can be operated at pressures up to 100 mbar, whereby XPS can be routinely performed up to 30 mbar. A selection of typical data demonstrates the capability of the instrument to analyse details of the surface composition of solid samples under ambient-pressure conditions using XPS and NEXAFS. In addition, it offers a convenient way of analysing the gas phase through X-ray absorption spectroscopy. Short XPS spectra can be measured at a time scale of tens of seconds. The shortest data acquisition times for NEXAFS are around 0.5 s per data point.

Open Access

Show Abstract ▼

Abstract: Synchrotron radiation is emitted from a bending magnet source in a wide ray fan which is collected by the first optical element in a beamline. In order to maximize angular acceptance, and hence flux, it is beneficial to increase the length of this mirror and optical design requirements may necessitate that the optical surface be over 1 m in length. Such mirrors also require cooling as they may be subject to high heat loads from the incident radiation. Two beamlines, B07 and B24, at Diamond Light Source, UK, use 1.4 m long toroidal mirrors which utilize a similar side-clamped cooling manifold design. While this scheme has been successful in providing effective cooling of the mirror, it has also been discovered that it introduces deformation of the radius of curvature which is sufficient to alter the focusing characteristics of the mirror. At both beamlines, the horizontal focus of the beam was found to differ by up to several meter from the design position at the exit slit which resulted in poor flux throughput, reduced energy resolution and other side effects. A pencil beam scan method has been used to diagnose this issue and infer the position of the focus and mirror shape. Through the use of a standalone chiller to alter the temperature of the water within the cooling loop, it has been possible to correct the distortion of the radius and restore the focus to its nominal position.

Open Access

Show Abstract ▼

Abstract: Using the coupled wave approach (CWA), we introduce the analytical theory for alternate multilayer grating (AMG) operating in the single-order regime, in which only one diffraction order is excited. Differing from previous study analogizing AMG to crystals, we conclude that symmetrical structure, or equal thickness of the two multilayer materials, is not the optimal design for AMG and may result in significant reduction in diffraction efficiency. The peculiarities of AMG compared with other multilayer gratings are analyzed. An influence of multilayer structure materials on diffraction efficiency is considered. The validity conditions of analytical theory are also discussed.