Steeply curved free-form x-ray mirrors, represented by monolithic ellipsoidal or Wolter mirrors, are required for submicron focusing without chromatic aberrations in the soft x-ray region. Such mirrors require a different approach to surface machining and metrology than conventional mirrors with small sags, such as Kirkpatrick-Baez or plane mirrors. A few examples of the fabrication of Wolter mirrors have been reported, in which surface measurements using a surface profilometer with a contact probe were used for figure correction. However, owing to differences in measurement methods and fabrication difficulties, the fabrication performance has not been fully evaluated on a comparative basis. In this study, a high-precision plane mirror was fabricated using the same process as that used for steeply curved free-form mirrors. The figure measurement accuracy was comparatively evaluated, and the results suggested the possibility of achieving a figure accuracy of 5nm in PV and 0.7nm in RMS in steeply curved free-form mirror fabrication.

The surface figure of x-ray mirrors can be improved by differential deposition of thin films. To achieve the required corrections, WSi2 layers of variable thickness were deposited through beam-defining apertures of different openings. The substrates were moved in front of the particle source with specific velocity profiles that were calculated with a deconvolution algorithm. Two different DC magnetron sputter systems were used to investigate the correction process. Height errors were evaluated before and after each iteration using off-line visible light surface metrology. Four 300mm long flat Si mirrors were used to study the impact of the initial shape errors on the performance of the correction approach. The shape errors were routinely reduced by a factor of 20 to 30 down to levels below 0.5nm RMS.

Wolter mirrors fabricated by high-precision Ni electroforming process have been applied as focusing optics for x-ray telescopes. The typical replication accuracy is on the order of 100nm. For higher resolution observations, the figure accuracy is required to be improved. Recently, we have been developing an efficient figure correction method using an Si layer on Wolter mirror. Film thickness of Si can be measured with accuracy of 1nm level by thickness measurement gauge. Si is removed under wet process so that the figure accuracy improves. In this study, we developed a fluid jet polishing system especially for removing Si layer on the inner surface of Wolter mirrors. Surface roughness remained unchanged at 0.3nm in RMS (root mean square) value before and after processing to a depth of 133nm. For demonstration, a sine curve with a length of 10mm and PV (peak to valley) of 160nm was processed on Si on a plane surface, resulting in a processing accuracy of 25nm in PV and 6.7nm in RMS.

A fully automated, high resolution method to measure the variable line density of a spherical grating is presented. The assessment of the line density requires an accurate evaluation of the first order diffraction angle, from which the line spacing is calculated. The optic characteristics (curvature, variable line density, length) make the measurement of this angle difficult to achieve, due to the limited dynamic range of the typical long trace profiler (LTP) used as a detector. We developed a new, fully automated method to assess the line density N(w) of a 280mm-long spherical grating (R≈65m). N(w) and the curvature of the optics could be measured on the same setup without intermediate realignment of the sample. The principle: the grating position is scanned with the linear stage while a feedback loop between the LTP detector and the round table maintains the Littrow condition. The angle of the round table is recorded as function of grating position. The accuracy of the angle assessment is then improved by subtracting the recorded residual angle measured by the LTP. Our method avoids stitching and overcomes the dynamic range limit of typical LTP instruments while it still benefits from the high resolution offered by its detector. The line density of the grating under test was determined with an estimated accuracy of ΔN of 5mm⁻¹ for a central line density of 1160mm⁻¹ . This method can be also applied to shape measurements of long steeply curved mirrors, whose accurate curvature evaluation is limited by the dynamic range of the typical LTP.

Binary pseudo-random array (BPRA) test samples are useful devices for calibrating the instrument transfer function (ITF) of Fizeau interferometers, interferometric microscopes, and other optical and non-optical surface and wavefront metrology instruments. The intrinsic white noise character of the power spectral density (PSD) function of the BPRA pattern simplifies the extraction of the ITF from the measured PSD. The ITF determined in a dedicated calibration experiment can be used to reconstruct the surface height profile from the measured data, effectively enhancing the instrument’s spatial resolution. For a high confidence reconstruction procedure, a reliable analytical model of the IFT is desirable. Usually, the model accounts for the contributions to the ITF related the imperfections of the instrument’s optical and detector systems. Here, we experimentally demonstrate that in the case of surface height metrology with Fizeau interferometers, the PSD measurements and, therefore, the efficacy of the ITF calibration of the tool, are strongly affected by the instrument data acquisition and processing procedures, as well as by the shape of the optic under test and its alignment with respect to the interferometer.

High-accuracy metrology is vitally important in manufacturing ultra-high-quality free-form mirrors designed to manipulate x-ray light with nanometer-scale wavelengths. The current capabilities and possibility for improvements in x-ray mirror manufacturing are limited by inherent imperfections of the integrated metrology tools. In the case of Fizeau interferometry, metrology tools are currently calibrated with super-polished flat test-standard/reference mirrors. This is acceptable for measuring slightly curved x-ray optics. However, for even moderately curved aspherical x-ray mirrors the flat-reference calibration is not sufficiently accurate and stitching Fizeau interferometer-based surface metrology is used to mitigate the problem. But still, the retrace and aberration errors, as well as the limited spatial resolution, described with the instrument transfer function (ITF), can be transferred into the optical surface topography of x-ray mirrors obtained in stitching metrology. For ITF calibration, we have developed an original technique, based on test standards structured as two-dimensional (2D) highly-randomized (HR) binary pseudo-random arrays (BPRAs). The technique employs the unique properties of the HR BPRA patterns in the spatial frequency domain., i.e. the inherent 2D power spectral density of the HR BPRA pattern has a deterministic white-noise-like character that allows direct determination of the ITF with uniform sensitivity over the entire spatial frequency range and field-of-view of an instrument. Here, we explore technological, metrological, and analytical aspects essential for calibration of the retrace and aberration errors of Fizeau interferometers using different types of tilted test samples, including a super-polished reference mirror for the re-trace calibration and the uniformly redundant array (URA) BPRA standards for the geometrical distortion (aberration) calibration. While the first method was previously demonstrated by researchers at DIAMOND Light Source, a method based on the URA BPRA is described and demonstrated here for the first time. We outline the design and fabrication process used in fabrication of URA BPRA test standards, and present the results of application of the URA BPRA standards demonstrating the high efficacy of our approach to geometrical distortion calibration of Fizeau interferometers. We also discuss the possible sources of unexpected peculiarities of the systematic errors, including an astigmatic character of the retrace error, observed with Fizeau interferometers at the Advanced Light Source X-Ray Optics Laboratory.

CMMs (Coordinate Measuring Machines) can measure the geometric tolerances of various mechanical components, but even the most accurate CMM have submicron accuracy, which makes it difficult to use them for evaluating optical components. On the other hand, more accurate μ-CMMs that can measure small optical components have also been developed. Our μ-CMM (UA3P) has three high-precision plane mirrors to construct three-dimensional orthogonal XYZ coordinates and uses a frequency-stabilized HeNe laser as the length scale. By scanning the surface of the object with a tactile-type probe, it is possible to measure the profile of optical components such as aspherical or free-form mirrors and lenses with an accuracy of less than 50nm. In this paper, by using a high accurate flat bar mirror whose profile has been measured by National Institute of Advanced Industrial Science and Technology (AIST) and making error table to correct the profile of the Z reference mirror installed in the machine, we could reduce the profile error of Z reference mirror within 24nm on the 400mm square in the XY plane. For tactile-type measurement machine, if the measurement range is large, the measurement time may be over an hour. Even in such the case of long-time measurements, we verified a method of configuring the profile of measured surfaces by referring to base axis data measured in a short period of time, and confirmed that profile waviness can be detected with 10nm precision by comparison with an interferometer. The advantage of a mechanical tactile measuring machine is that it can evaluate the profile without being influenced by the profile of the object. This means that our μ-CMM can perform highly accurate absolute profile measurement and evaluation for large-area free-form samples that are difficult to measure with an interferometer.

The QUATI (Quick X-Ray Absorption Spectroscopy for Time and space resolved experiments) beamline will be dedicated to high-quality x-ray absorption spectroscopy experiments, with temporal and spatial resolution on a millisecond scale and in situ conditions: XANES, EXAF and XES. The beam extracted from a bending magnet source (3.2T) is collimated vertically by a cylindrical mirror (bounce up deflecting) located at 15m from the source inside the frontend, passes a double crystal monochromator (24m), and is then focused by a toroidal mirror (bounce down deflecting) located at 30m from the source. Both mirrors have an optical length of 1.2m and are equipped with a mechanical bender. The surface quality of both mirrors in the low spatial frequency range is characterized by the Long Trace Profiler (LTP). Five gravity compensators evenly distributed along the mirror are adjusted manually. With the optics measured in its orientation as in the beamline, a height error of less than 20nm PV for the M1 mirror and less than 40nm PV for the M2 mirror was achieved. The final height error adjusted by the gravity compensators is slightly better than the pure polishing due to the low frequency nature of the deformation caused by gravity. The result attends the project specifications for the QUATI beamline. Additionally, mechanical stability and temporal accommodation of the mirrors in the bending system were investigated.

We consider the specification of hard x-ray monochromator crystals for both high-efficiency and diffraction-limited optical performance in the new era of ultra-high-brightness x-ray light sources. Within a double-crystal monochromator, thermal distortions resulting from intense beams can significantly affect the wavefront quality and reduce the total transmitted power. In two case studies, we model the performance of a water-cooled and a cryogenically-cooled monochromator on a working protein crystallography beamline at the Advanced Light Source. The cryo-cooling model appears capable of exceeding diffraction-limited performance specifications while preserving over 99% of the optimal transmitted power. The water-cooled system may perform well for beamlines that are not brightness-limited but does not come close to achieving this high-performance goal.

Ion-beam figuring (IBF) capable of providing sub-nanometer shape accuracy, is often used for fabrication of ultra-precise x-ray optics. However, in the case of gratings, the optical surface may degrade during the following ruling procedure or etching processes. This leads to the necessity for a post-ruling surface correction to recover the ultra-precise shape of the optics, while the IBF substrate finish prior the ruling could be omitted. If so, the gratings can be made using relatively inexpensive substrates produced with conventional mechanical or chemical-mechanical polishing with medium optical surface quality and then processed with a post-ruling IBF to bring the shape to the sub-nanometer accuracy. The key question is whether the grating grooves survive the IBF treatment. In this work we investigate the possibility of post-production IBF correction for lamellar x-ray gratings. A 200 lines/mm lamellar grating made using a lambda/20 Si substrate was processed with IBF to achieve a sub-nanometer flat optical surface of the final grating. We report on impact of the IBF process on groove profile, surface roughness, and diffraction efficiency of the grating.

In this study, we address the challenge of enhancing image quality and spatial resolution in computed tomography (CT) imaging by introducing simulation and fabrication of high aspect ratio, point-like transmission targets. Utilizing advanced electroplating techniques, traditionally employed in the fabrication of Through Substrate Via (TSV) interconnects for CMOS circuitry, we successfully embed copper targets within silicon substrates. This method allows us to create high-aspect- ratio features specifically designed for x-ray transmission targets, resulting in micro targets that exhibit a volume increase compared to conventional evaporated surface targets. Furthermore, we present simulation results of the x-ray spectrum generated by these targets, demonstrating their potential to significantly improve both image quality and spatial resolution in CT applications. Our findings suggest that leveraging advanced fabrication techniques can open new avenues for the development of enhanced imaging technologies in medical diagnostics and beyond.

Magnetic smart materials (MSMs) offer an alternative to the typical piezo-electric actuators currently used to control X-ray optics on beamlines. MSMs, combined with an overcoating of a magnetic hard material, create a deformable mirror that can operate in a power-off mode. The non-reflective side of the mirror is coated with an MSM and the magnetic hard overcoat. The process works by using an electromagnet (EM) to impose a magnetic field in the bilayer of the MSM and the magnetic hard overcoat, causing the mirror to deflect. Once the EM is turned off, the mirror settles into a new shape within minutes, which can remain intact for days. Since the EM is not fixed to the mirror, the exact placement of the magnetic field can be adjusted by relocating the EM. This feature allows for fine-scale adjustments and avoids the “dead pixel” replacement problem common with piezo patches attached to the mirror. Here, we provide a progress report based on laboratory-produced data.