Combining sub-micron spatial resolution full-field-imaging with the penetration property of high-energy x-rays (> 50 keV) offers numerous applications, such as the ability to observe cracks and voids associated with the onset of failure in engineering materials, complementing x-ray diffraction microscopy probes. Progress in the development of adding such an imaging capability at the Advanced Photon Source high-energy x-ray undulator beamline 1-ID is reported. An initially tested, long baseline configuration had 18-21× x-ray image magnification with compound refractive lenses (as objective) placed 1.8 m after the specimen, and a two-dimensional detector located at a 32–37 m additional distance, in a different experimental station. Later, a more compact set-up of 3.5× magnification with a ≈6 m sample-to-detector separation, fitting within a single end-station, was tested. Both set-ups demonstrated 500 nm level spatial resolutions at energies within the 45–50 keV range. Phase contrast artifacts are present, and are discussed in view of the goal of achieving tomography capability, at even higher resolution, in such an instrument with high x-ray energies.
High-energy x-rays from a synchrotron source are well suited for numerous applications, such as studies of
materials structure and stress in bulk or extreme environments. Some of these methods require high spatial
resolution. Planar kinoforms are shown to focus monochromatized undulator radiation in the 50–100 keV
range down to 0.2–1.5 μm beam sizes at 0.25–2 m focal distances. These lenses were fabricated by reactive ion
etching of silicon. At such high x-ray energies, these optics can offer substantial transmission and lens aperture.
Saw-tooth refractive lenses (SRL) provide a comparatively attractive option for X-ray focusing for various reasons, including their simple, continuous tunability in energy and focal length. Optimal focusing of a conventional SRL at short focal lengths is limited by the SRL’s length in relation to the focal length. Three approaches to overcome this limitation are described. Analytical solutions verified with ray-tracing are presented. These are bending, variation of the saw-tooth tip angles, and variation of the period.
Compound refractive lenses (CRLs) are effective for collimating or focusing high-energy x-ray beams (50 - 100 keV) and can be used in conjunction with crystal optics in a variety of configurations, as demonstrated at the 1-ID undulator beamline of the Advanced Photon Source. As a primary example, this article describes the quadrupling of the output flux when a collimating CRL, composed of cylindrical holes in aluminum, is inserted in between two successive monochromators -- a modest energy resolution premonochromator followed by a high-resolution monochromator. The premonochromator is a cryogenically cooled, divergence-preserving, bent double-Laue Si(111) crystal device delivering an energy width ΔE/E ~10-3, sufficient for most experiments. The high-resolution monochromator is a four-reflection, flat Si(111) crystal system resembling two channel-cuts in a dispersive arrangement, reducing the bandwidth to ΔE/E < 10-4, as required for some applications. Tests with 67 keV and 81 keV photon energies show that the high-resolution monochromator, having a narrow angular acceptance of a few μrad, exhibits, a four-fold throughput enhancement due to the insertion of a CRL which reduces the premonochromatized beam's vertical divergence from 29 μrad to a few μrad. The ability to focus high-energy x-rays with CRLs having long focal lengths (tens of meters) is also shown by creating a line focus of 70 - 90 μm beam height in the beamline end-station with both the modest-energy-resolution and high-energy- resolution monochromatic x-rays.
Design, fabrication, testing, and performance of an x-ray lens assembly are described. The assembly consists of a number of precisely stacked and aligned parts, each of which is a section of an extruded aluminum piece having 16 parabolic cavities. The wall thickness between adjacent cavities is 0.2 mm. By stacking a number of long, extruded parts and cutting the assembly diagonally, a variable-focus lens system is derived. Moving the lens horizontally allows the incident beam to pass through fewer or more cavities focusing the emerging beam at any desired distance from the lens.
The variable focus aluminum lens has been used at the Advanced Photon Source to collimate a monochromatic, 8 keV undulator beam. Results indicate collimation consistent with theoretical expectations.
We use Fresnel zone plates as focusing optics in hard x-ray microprobes at energies typically between 6 and 30 keV. While a spatial resolution close to 0.1 μm can currently be achieved, highest spatial resolution is obtained only at reduced diffraction efficiency due to manufacturing limitations with respect to the aspect ratios of zone plates. To increase the effective thickness of zone plates, we are stacking several identical zone plates on-axis in close proximity. If the zone plates are aligned laterally to within better than an outermost zone width and longitudinally within the optical near-field, they form a single optical element of larger effective thickness and improved efficiency and reduced background from undiffracted radiation. This allows us both to use zone plates of moderate outermost zone width at energies of 30 keV and above, as well as to increase the efficiency of zone plates with small outermost zone widths particularly for the energy range of 6 - 15 keV.
The diffraction of femtosecond x-ray pulses by crystals will play a central role in the development of the optics of x-ray free-electron lasers (XFELs). Making use of Fourier analysis, we calculate the temporal dynamical diffraction of an incident delta function by single- and double- symmetric Bragg crystal monochromators. The time-dependent intensity of ultrashort XFEL pulses diffracted by perfect crystals is discussed. Our simulations show modifications in the time structure of incident 8 keV, 280-fs-duration, microbunched XFEL pulses after diffraction by the crystal optics. Finally, we investigate the statistical fluctuations of the time-integrated intensity from shot to shot.
X-ray free-electron lasers (XFELs) designed to operate at approximately 1A wavelengths are currently being proposed by several laboratories as the basis for the next (4th) generation of synchrotron radiation sources. The unique radiation properties of these proposed sources, which include 200 fs pulse duration and peak beam brilliance in excess of 1033 photon (2 .1%-bw mrad2 mm2), offer the possibility of ultrafast time-resolved experiments, perhaps down to 10- fs resolution levels using pulse compression or slicing techniques. Motivated by such potential applications, this paper addresses the relevant instrumentation issue of perfect crystal dynamical diffraction of ultrashort x-ray pulses when the pulse lengths become comparable to the extinction length scales. The basic calculations reported here show the transient time-dependent diffraction from perfect crystals excited by plane-wave delta-function electromagentic impulses. Time responses have been calculated for 8 keV photon energy, for reflected and transmitted beams in both Bragg and Laue cases. Interesting diffraction effects arise, and their implications for XFEL optics are discussed.
High-pressure-Bridgman grown CdZnTe x-ray detectors 1.25 approximately 1.7 mm thick were tested using monochromatic x-rays of 30 to 100 keV generated by a high energy x-ray generator. The results were compared with a commercially available 5 cm thick Nal detector. A linear dependence of the counting rate versus the x-ray generator tube current was observed at 58.9 keV. The measured pulse height of the photopeaks shows a linear dependence on energy. Electron and hole mobility-lifetime products were deduced by fitting bias dependent photopeak channel numbers at 30 keV x-ray energy. Values of 2 X 10-3 cm2/V and 2 X 10-4 cm2/V were obtained for (mu) (tau) e and (mu) (tau) p, respectively. The detector efficiency of CdZnTe at a 100 V bias was as high as, or higher than 90 percent compared to a Nal detector. At x-ray energies higher than 70 keV, the detection efficiency becomes a dominant factor and decreases to 75 percent at 100 keV.