Tracing X-rays through an L-shaped laterally graded multilayer mirror: a synchrotron application

A mirror for lab-based quasi-monochromatic parallel x-rays

A multilayered parabolic mirror with six W/Al bilayers was designed and fabricated to generate monochromatic parallel x-rays using a lab-based x-ray source. Using this mirror, curved bright bands were obtained in x-ray images as reflected x-rays. The parallelism of the reflected x-rays was investigated using the shape of the bands. The intensity and monochromatic characteristics of the reflected x-rays were evaluated through measurements of the x-ray spectra in the band. High intensity, nearly monochromatic, and parallel x-rays, which can be used for high resolution x-ray microscopes and local radiation therapy systems, were obtained.

Performance of a collimating L-shaped laterally graded multilayer mirror for the IXS analyzer system at NSLS-II

The L-shaped laterally graded multilayer mirror is a vital part of the ultrahigh-energy and momentum-resolution inelastic X-ray scattering spectrometer at the National Synchrotron Light Source II. This mirror was designed and implemented as a two-dimensional collimating optic for the analyzer system. Its performance was characterized using a secondary large-divergence source at the 30-ID beamline of the Advanced Photon Source, which yielded an integrated reflectivity of 47% and a collimated beam divergence of 78 µrad with a source size of 10 µm. Numerical simulations of the mirror performance in tandem with the analyzer crystal optics provided details on the acceptance sample volume in forward scattering and defined the technical requirements on the mirror stability and positioning precision. It was shown that the mirror spatial and angular stability must be in the range <8.4 µm and <21.4 µrad, respectively, for reliable operation of the analyzer.

High-quality quartz single crystals for high-energy-resolution inelastic X-ray scattering analyzers

High-quality quartz (α-SiO₂) crystals are characterized, and their use for inelastic X-ray scattering analyzers is presented and discussed.

Spherical analyzers are well known instruments for inelastic X-ray scattering (IXS) experiments. High-resolution IXS experiments almost always use Si single crystals as monochromators and spherical analyzers. At higher energies (>20 keV) Si shows a high energy resolution (<10 meV), at an exact symmetric back-diffraction condition, since the energy resolution is given by the real part of the susceptibility or polarizability. However, at low energies (<10 keV), high energy resolution is difficult to achieve with Si. α-SiO₂ (quartz) can be an option, since it offers high energy resolution at low energies. In this work, the characterization of high-quality α-SiO₂ is presented. Such characterization is made by high-resolution rocking curve, topography and lattice parameter mapping in different samples from a single block. X-ray optics with α-SiO₂ for IXS at lower energies (from 2.5 to 12.6 keV) with medium to high energy resolution (from 90 to 11 meV) are proposed and theoretically exploited.

Development of a multilayer mirror for high-intensity monochromatic x-ray using lab-based x-ray source

A parabolic, multilayer x-ray mirror, which can be used with a general lab-based x-ray source, was designed and fabricated. A glass substrate for the mirror was fabricated. Its surface was determined by following the rotation of a parabolic curve and was polished precisely. On the substrate surface, six W/Al bilayers were deposited to form the multilayer mirror. The effects of the mirror on x-ray images were investigated based on the calculated modulation transfer function (MTF) and image intensity values. Higher MTF and intensity values of an x-ray image were obtained using the mirror.

Investigation of multilayer X-ray optics for the 6 keV to 20 keV energy range

The X-ray optics group at the Swiss Light Source in co-operation with RIT (Rigaku Innovative Technologies) have investigated seven different multilayer samples. The goal was to find an ideal multilayer structure for the energy range between 6 keV and 20 keV in terms of energy resolution and reflectivity. Such multilayer structures deposited on substrates can be used as X-ray monochromators or reflecting synchrotron mirrors. The measured reflectivities agree with the simulated ones. They cover a reflectivity range from 45% to 80% for energies between 6 keV and 10 keV, and 80% to 90% for energies between 10 keV and 20 keV. The experimentally measured energy resolution of the samples lies between 0.3% and 3.5%.

Dispersive spread of virtual sources by asymmetric X-ray monochromators

The principles of the virtual source spread (spatial broadening) phenomenon induced by angular dispersion in asymmetric X-ray Bragg reflections are illustrated, from which the virtual source properties are analyzed for typical high-resolution multiple-crystal monochromators, including inline four-bounce dispersive monochromators, back-reflection-dispersion monochromators and nondispersive nested channel-cut monochromators. It is found that dispersive monochromators can produce spread virtual sources of a few millimetres in size, which may prevent efficient microfocusing of the beam as required by inelastic X-ray scattering spectroscopy and other applications. Possible schemes to mitigate this problem are discussed. The analyses may provide important guidelines for designing and optimizing modern high-precision synchrotron X-ray optics and beamline instrumentation for spectroscopy, imaging and nanofocusing applications.

Synchrotron X-ray tests of an L-shaped laterally graded multilayer mirror for the analyzer system of the ultra-high-resolution IXS spectrometer at NSLS-II

Characterization and testing of an L-shaped laterally graded multilayer mirror are presented. This mirror is designed as a two-dimensional collimating optics for the analyzer system of the ultra-high-resolution inelastic X-ray scattering (IXS) spectrometer at National Synchrotron Light Source II (NSLS-II). The characterization includes point-to-point reflectivity measurements, lattice parameter determination and mirror metrology (figure, slope error and roughness). The synchrotron X-ray test of the mirror was carried out reversely as a focusing device. The results show that the L-shaped laterally graded multilayer mirror is suitable to be used, with high efficiency, for the analyzer system of the IXS spectrometer at NSLS-II.

An alternative scheme of angular-dispersion analyzers for high-resolution medium-energy inelastic X-ray scattering

The development of medium-energy inelastic X-ray scattering optics with meV and sub-meV resolution has attracted considerable efforts in recent years. Meanwhile, there are also concerns or debates about the fundamental and feasibility of the involved schemes. Here the central optical component, the back-reflection angular-dispersion monochromator or analyzer, is analyzed. The results show that the multiple-beam diffraction effect together with transmission-induced absorption can noticeably reduce the diffraction efficiency, although it may not be a fatal threat. In order to improve the efficiency, a simple four-bounce analyzer is proposed that completely avoids these two adverse effects. The new scheme is illustrated to be a feasible alternative approach for developing meV- to sub-meV-resolution inelastic X-ray scattering spectroscopy.

Achromatic nested Kirkpatrick-Baez mirror optics for hard X-ray nanofocusing

The first test of nanoscale-focusing Kirkpatrick-Baez (KB) mirrors in the nested (or Montel) configuration used at a hard X-ray synchrotron beamline is reported. The two mirrors are both 40 mm long and coated with Pt to produce a focal length of 60 mm at 3 mrad incident angle, and collect up to a 120 µm by 120 µm incident X-ray beam with maximum angular acceptance of 2 mrad and a broad bandwidth of energies up to 30 keV. In an initial test a focal spot of about 150 nm in both horizontal and vertical directions was achieved with either polychromatic or monochromatic beam. The nested mirror geometry, with two mirrors mounted side-by-side and perpendicular to each other, is significantly more compact and provides higher demagnification than the traditional sequential KB mirror arrangement. Ultimately, nested mirrors can focus larger divergence to improve the diffraction limit of achromatic optics. A major challenge with the fabrication of the required mirrors is the need for near-perfect mirror surfaces near the edge of at least one of the mirrors. Special polishing procedures and surface profile coating were used to preserve the mirror surface quality at the reflecting edge. Further developments aimed at achieving diffraction-limited focusing below 50 nm are underway.

Feasibility of in-line instruments for high-resolution inelastic X-ray scattering

Inelastic X-ray scattering instruments in operation at third-generation synchrotron radiation facilities are based on backreflections from perfect silicon crystals. This concept reaches back to the very beginnings of high-energy-resolution X-ray spectroscopy and has several advantages but also some inherent drawbacks. In this paper an alternate path is investigated using a different concept, the `M(4) instrument'. It consists of a combination of two in-line high-resolution monochromators, focusing mirrors and collimating mirrors. Design choices and performance estimates in comparison with existing conventional inelastic X-ray scattering instruments are presented.