Many fields, from aerospace engineering to cultural heritage, can benefit from x-ray micro computed tomography (micro-CT). However, access to x-ray imaging tools remains limited for non-expert users. The UK’s National X-Ray Computed Tomography facility (NXCT) therefore aims to provide access and expert support to academia and industry. As part of the NXCT, at UCL we have developed a unique user facility with multi-scale and multi-contrast x-ray micro-CT capabilities. Our custom system has an x-ray generator with Molybdenum and Copper targets, which can be changed to adapt the energy to the needs of an imaging experiment. The x-rays are emitted on both sides of the source allowing for two imaging stations: one at mm-sized field-of-view (FOV) with resolutions of around 1μm, the “high-resolution station”; and one at cm-sized FOV with resolutions of around 10μm, the “large FOV station”. The high-resolution station is fitted with a custom mirror which gives a monochromatic beam at 17.5keV (for Mo) and 8keV (for Cu). Both stations can be operated with phase-contrast methods such as free-space propagation or beam tracking. Access to this new imaging facility, dedicated to academic and industrial users, is supported through free-at-the-point-of-access and paid schemes.
Practically, all modern x-ray diffractometers, SAXS, TXRF systems and many other laboratory X-ray instruments are equipped with multilayer X-ray optics. It is due to a much higher flux these instruments have comparing with those having no optics or having a grazing incidence optics without multilayer coatings. There are variety of the multilayer optics designs – from one bounce collimating parabolic mirror to four corners double bounce focusing mirrors. Design of multilayer optics depends on application, X-ray source parameters, requirements on divergence, focal spot, available room for the optics, manufacturing capability and cost. Key characteristics of the optics, requirements on multilayers d-spacing accuracy, optics slope errors, and substrates surface roughness are discussed in the paper. Different optics designs are considered including recently developed optics for a laboratory topography system and a Hybrid optics combining multilayer and crystal optics for XRR and XRD.
The NIST Extreme Ultraviolet (EUV) Reflectometry Facility was designed in the 1990s to accommodate the largest multilayer optics envisioned at that time. However, with increasing power requirements for an EUV scanner, source collection optics have grown larger and more steeply curved than the original design would allow. To accommodate these changes, the mechanical and operational parameters of the facility have been upgraded. To access the entire surface of a larger optic, an auxiliary off-axis rotation stage has been installed allowing an increase in maximum optic size from 350 mm to 450 mm. Likewise, to deal with the deeper sags and steeper slopes of these optics, we have had to significantly expand our data analysis capabilities. In order to make these measurements, the incident radiation is reflected out of the vertical plane, allowing for measurements of effectively unpolarized radiation, an advantage for EUV lithography optics such as source collectors.
Laser-produced plasma (LPP) sources for extreme ultraviolet lithography (EUVL) systems utilize CO2 lasers operating
with wavelength 10.6μm. Since multilayer-coated optics have high reflectivity for this infrared radiation (IR), a
significant and detrimental amount of IR is passed through the EUVL system. One method to remove the IR from the
system is to utilize a binary diffraction grating. When this grating is applied directly to the surface of the primary
collector optic of the source, the majority of the IR is diverted outside the radius of the exit aperture at the intermediate
focus (IF). This paper will report details on the performance of a full size (410mm diameter) Demonstration Collector
utilizing IR rejection (IRR) technology with the capability to produce over 125X suppression of IR, equaling the
performance of a IR spectral filter. Additional details will be reported on the technology development and use of a
glassy smoothing layer to enable high EUV performance, a weighted average multilayer reflectance of 50.9% for
unpolarized EUV radiation.
Johansson crystals have been known for many decades as x-ray optical elements with a high resolving power and small
foci. However, in the past their use in applications requiring a small focus and a narrow band pass were limited by
imperfections caused by the technologies applied to their manufacture. While high performance Johansson crystals
might have been achieved in some research facilities, such crystals were not commercially available. RIT has developed
a process for fabricating precision Johansson crystals. The fabrication maintains the crystal structure intact. The angular
precision of the bending process of atomic planes and the reflecting crystal surface is better than four arc seconds. In
this paper, we will present the basic aspects of the technology and the achievements with Silicon and Germanium
crystals.
Two-dimensional multilayer optics have been widely used for enhancing and monochromatizing x-ray beams for various diffraction applications. However, when they are applied to Mo Kα radiation, the performance suffers from the fact that multilayer optics can use only a very small portion of the source. This is because the rocking curve of a multilayer becomes narrower at higher energy. Comparing to the optics for the Cu Kα radiation, the throughput of the optics for Mo Kα depends heavily on how small the source is. Based on the theoretical ray-tracing study, we have designed, fabricated and tested a system combining a microfocusing x-ray source and a side-by-side multilayer optic. Initial test results agree well with the theoretical expectation. The flux gain for a sample smaller than 100 micrometers is about 9 fold compared to a system composing of 2 kW sealed tube and graphite monochromator. The resolution of a diffractometer can also be improved by configuring the optical path. This paper will discuss the system design, detailed comparison between this system and a sealed tube-graphite monochromator based system, and possible applications such as small molecule diffraction system. A theoretical comparison to a rotating anode based system will also be discussed.
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