This PDF file contains the front matter associated with SPIE Proceedings Volume 11109, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists

A new Aperture Centring Device (ACenD) for precisely positioning small apertures with respect to the autocollimator’s optics has been developed. With the new device, differences in the angle response of autocollimators between the calibration at a laboratory and their subsequent application in the slope measuring profilers are significantly minimized. Evaluation of the device with a circular aperture size of d=2.5 mm was carried out in different laboratories. It was verified that the ACenD is capable of achieving a reproducible aperture alignment < 0.1 mm. The device is a substantial aid for the operation of slope measuring profilometers and enables the measurable, documentable, and transferable positioning of apertures that did not exist before.

Autocollimators are excellent measuring tools for many applications, such as adjustments or characterizations of precision mechanics, optics and instruments. Autocollimators have several characteristic error sources due to misalignment or nonideality of the collimator lens, the light source and the sensor. To fully characterize errors related to simultaneous engagement of both measurement axes of the autocollimator a two directional angle generator is necessary.

In this paper, VTT MIKES interferometric 2-directional small angle generator (I2D-SAG) with updated model for calibration of autocollimators is described. It generates angles around 2 orthogonal axes with high accuracy. The maximum range of the I2D-SAG is ±1000” for both axes. In calibration of a high quality autocollimator a standard uncertainty below 0.01” can be reached.

In addition, preliminary results of a comparison of I2D-SAG and PTB Spatial Angle Autocollimator Calibrator (SAAC) instrument are presented. This is the first comparison between 2D autocollimator calibration systems. In this comparison, a good agreement was reached in characterization of an electronic autocollimator over 900”×900” range.

For new light sources, like X-ray free-electron lasers (FELs), highly precise diffraction-limited optics are needed, which are leading to ambitious requirements for the X-ray mirrors used in those facilities. For appropriate beam focusing and alignment, a control of the shape on the single-nanometre precision level is necessary, which generates high demands on the manufacturers and on the metrology. To face these questions, the project MooNpics – Metrology On One-Nanometer-Precise Optics was established. With a European-wide round-robin test, the goal is to push the frontiers in mirror metrology in Europe to single-nanometre figure error precision.

Within the MooNpics project, a special mirror holder for long X-ray mirrors was developed that provides reproducible and well defined mounting conditions in each participating laboratory. The goal is to understand mechanical and stress influences and hence to improve mounting methods. Before the actual start of the roundrobin, measurements were done to investigate the influence of the mirror mounting. A procedure was developed to reduce the induced stresses and increase the reproducibility with regard to the planned round-robin.

X-ray optics, desired for beamlines at free-electron-laser and diffraction-limited-storage-ring x-ray light sources, must have almost perfect surfaces, capable of delivering light to experiments without significant degradation of brightness and coherence. To accurately characterize such optics at an optical metrology lab, two basic types of surface slope profilometers are used: the long trace profilers (LTPs) and nanometer optical measuring (NOM) like angular deflectometers, based on electronic autocollimator (AC) ELCOMAT-3000. The inherent systematic errors of the instrument’s optical sensors set the principle limit to their measuring performance. Where autocollimator of a NOM-like profiler may be calibrated at a unique dedicated facility, this is for a particular configuration of distance, aperture size, and angular range that does not always match the exact use in a scanning measurement with the profiler. Here we discuss the developed methodology, experimental set-up, and numerical methods of transferring the calibration of one reference AC to the scanning AC of the Optical Surface Measuring System (OSMS), recently brought to operation at the ALS Xray Optics Laboratory. We show that precision calibration of the OSMS performed in three steps, allows us to provide high confidence and accuracy low-spatial-frequency metrology and not ‘print into’ measurements the inherent systematic error of tool in use. With the examples of the OSMS measurements with a state-of-the-art x-ray aspherical mirror, available from one of the most advanced vendors of X-ray optics, we demonstrate the high efficacy of the developed calibration procedure. The results of our work are important for obtaining high reliability data, needed for sophisticated numerical simulations of beamline performance and optimization of beamline usage of the optics. This work was supported by the U. S. Department of Energy under contract number DE-AC02-05CH11231.

We present recent advancements in the Optical Metrology Laboratory (OML) at Diamond Light Source. Improvements in optical manufacturing technology, and demands from beamlines at synchrotron and free electron laser facilities, have made it a necessity to routinely characterize X-ray mirrors with slope errors < 100 nrad rms. The Diamond-NOM profiler can measure large, fully assembled optical systems in a sideways, upwards, or downwards facing geometry. Examples are provided of how it has recently characterized several challenging systems, including: actively bent mirrors; clamped monochromator gratings in a downward-facing geometry; and four, state-of-the-art, elliptically bent, long mirrors with slope errors < 100 nrad rms. The NOM’s components and data analysis procedures are continuously updated to stay ahead of the ever-increasing quality of X-ray optics and opto-mechanics. The OML’s newest instrument is a Zygo HDX 6” Fizeau interferometer. A dedicated support frame and motorized translation and rotation stages enable sub-aperture images to be stitched together using in-house controls and automation software. Cross-comparison of metrology data, including as part of the MooNpics collaboration, provides a valuable insight into the nature of optical defects and helps to push optical fabrication to a new level of quality.

We demonstrate a novel One-Dimensional Ion-Beam Figuring (1D-IBF) solution from Brookhaven National Laboratory. Three improvements are introduced to the new 1D-IBF system. First, the misalignment of the coordinate systems between the metrology and the 1D-IBF hardware is minimized by integrating both the sample mirror and the Beam Removal Function (BRF) mirror into a single mirror holder. The measured BRF center is then used as a reference to calibrate the coordinate correspondence. Second, a Constrained Linear Least-Squares (CLLS) algorithm with a coarse-to-fine scheme is proposed to keep the non-negativity of the dwell time as well as ensure it smoothly duplicate the required removal amount. Third, a dwell time slicing strategy is used to smooth the implementation of the dwell time in the real 1D-IBF fabrication process. Experimental results demonstrate that the proposed 1D-IBF solution reduces the residual profile errors to sub-nanometer Root Mean Square (RMS) for both flat and spherical mirrors.

Meeting the ever-increasing performance demands of X-ray beamlines at modern synchrotrons, such as Diamond Light Source (DLS), requires the use of ultra-high-quality X-ray mirrors with surface deviations of less than a few nanometres from their ideal shape. Ion beam figuring (IBF) is frequently used for creating mirrors of this precision, but achieving the highest accuracy is critically dependent on careful alignment and precise metrology of defects on the optical surface. Multiple iterations of measurement and correction are typically required, and convergence towards the requisite shape can be a slow process. DLS have designed and built an in-house IBF system that comprises a large diameter DC gridded ion source, and a 4-axis motion stage for manipulating the mirror being figured. Additionally, a slope measuring profilometer for in-situ metrology, and an imaging system for alignment, are also built into the system. The advantages of incorporating these extra components are twofold: fast metrology feedback after each figuring run will considerably reduce the time required to perform multiple figuring iterations; and alignment and indexing errors will be drastically reduced when transferring the optic. Complemented by the Optical Metrology Laboratory at DLS and at-wavelength X-ray measurements on the Test beamline B16, it is expected that this system will enable rapid development and testing of high-quality mirrors with novel designs for micro- and nano-focussing of X-rays.

The Materials Imaging and Dynamics (MID) station is located at the SASE2 undulator beamline of European XFEL and has become operational in 2019. The MID instrument operates in the medium to hard X-ray range (5 - 25 keV) and its scientific focus is on time-resolved coherent X-ray scattering and diffraction studies in materials science, with particular interest in ultrafast pump-probe experiments where the pump can be either X-rays, an optical laser beam or a pulsed magnetic field. The optical setup of the MID instrument includes two vertically offset mirrors equipped with cryogenic cooling. The top mirror will be employed for grazing incidence experiments on liquid surfaces, and the bottom mirror will be used to spatially overlap two split beams generated by a “split and delay” line. The mirrors are 500 mm long and are coated with boron carbide (B4C) and platinum (Pt) in two adjacent stripes. Deterministic mirror polishing is done to compensate the gravitational sag in order to achieve a perfectly flat mirror when it is installed. The requirements were very challenging for the surface shape and the needed ion-beam deterministic polishing, so also the coating process had to be performed and monitored with particular care. We present the metrological characterization of the mirrors, carried out before and after the B4C and Pt coating, and performed with a large aperture Fizeau interferometer. The measurements were made at European XFEL’s metrology lab in grazing incidence setup and with the mirrors facing sideways. Analyzing these data, we can deduce many important parameters, as the peak-to-valley of the central profile, the bending radius, and the gravity compensation profile. We show metrological results before and after coating and give details about the calculations performed to decide whether the mirror shapes are still complying with specifications after all these processes.

An ongoing collaboration among four US Department of Energy (DOE) National Laboratories has demonstrated key technology prototypes and software modeling tools required for new high-coherent flux beamline optical systems. New free electron laser (FEL) and diffraction-limited storage ring (DLSR) light sources demand wavefront preservation from source to sample to achieve and maintain optimal performance. Fine wavefront control was achieved using a novel, roomtemperature cooled mirror system called REAL (resistive element adjustable length) that combines cooling with applied, spatially variable auxiliary heating. Single-grating shearing interferometry (also called Talbot interferometry) and Hartmann wavefront sensors were developed and used for optical characterization and alignment on several beamlines, across a range of photon energies. Demonstrations of non-invasive hard x-ray wavefront sensing were performed using a thin diamond single-crystal as a beamsplitter.

To achieve an ultrahigh resolution for soft X-ray beamlines at Taiwan Photon Source (TPS), the slope error of a highly precise grating is required on level of 0.1 μrad (rms) under thermal loading with various curvatures. On the beamline, some optics are usually operating under high power density from undulator magnet, the thermal load will introduce a thermal bump on the optics profile and degrade the beamline performance, such as energy resolution and beam size. To realize the high resolution goal, a specially designed bender with 25 actuators for the grating is designed and a In situ long trace profiler (LTP) with precision of 0.1 μrad (rms) has been developed to measure the mirror profile in soft X-ray beamlines. This article introduces the design and construction of in situ LTP. It can provide a feedback guideance for the adjustment of actuators of bender mechanism to achieve the optium profile. A suitable adjustment procedure from the input of in-situ LTP , performance of bender and energy spectrums are presented. There are several benders as the active mirrors and active gratings in operation in TPS 41A resonant inelastic X-ray scattering (RIXS) and TPS 45A angle-resolved photoemission spectroscopy (ARPES) beamlines. In the meantime, three in situ LTPs have been developed to monitor the grating profile under the thermal load in the beamlines. They are providing a feedback to measure the surface figure and to find the optimal surface profile. They would increase our efficiency to reach the energy resolving power of 35,000 and 28,000 in the RIXS and ARPES beamlines, respectively.

There is growing interest at synchrotron light and X-ray free electron laser facilities to explore and improve the dynamic performance of piezoelectric bimorph deformable X-ray mirrors. Many beamlines, especially those dedicated to Macromolecular Crystallography, need to measure hundreds of samples per day. Shorter acquisition time requires rapid changes in the focus of the X-ray beam to condense the maximum photon density onto the sample. This is necessary to match the X-ray beam to the dimensions of the sample, or to probe variable sized regions of larger samples. Fine control of the X-ray beam becomes crucial for ensuring the highest quality of scientific data and increased throughput. Previous work at Diamond Light Source successfully changed the X-ray beam focus and stabilised it in under 10 seconds using piezoelectric bimorph deformable mirrors. Further updates to the controls software of the programmable HV-ADAPTOS high-voltage power supply (from CAEN / S.RI. Tech) now make it possible to control individual electrodes at 1 Hz using custom voltage profiles. This allows localized compensation of piezo creep, thus improving X-ray beam shape, significantly reducing stabilisation time, and eliminating curvature drift. For ex-situ validation, dynamic changes in the surface of the bimorph mirror need to monitored in real-time with sufficient spatial sensitivity. In this paper, we show that the active optical surface of a bimorph mirror (from Thales-SESO) can be accurately changed with sub-nanometre height sensitivity by dynamically monitoring the mirror’s surface using an array of high-speed (up to 200 kHz) Zygo ZPS™ absolute interferometric displacement sensors mounted in an independent metrology frame.

The Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL is a soft X-ray beamline aiming to unravel electronic, spin and structural properties of materials in ultrafast processes at the nanoscale. Various experimental techniques offered at SCS have different requirements in terms of beam size at the sample. Kirkpatrick-Baez (KB) refocusing optics equipped with mechanical benders allows for independent change of the horizontal and vertical beam size. We report here on the first characterization of the SCS KB mirrors by means of a novel diffraction-based technique which images the beam profile on a 2D pixelated detector. This approach provides a quick characterization of micrometer beam sizes. Results are compared with metrology measurements obtained with a non-contact slope profiler.

An EUV Stokes polarimeter designed for operation up to 150 eV photon energy has been fabricated and commissioned (with red, green and violet light). The polarimeter consists of two identical 4-mirror optical groups acting as a phase retarder and analyser respectively. Each group is capable of independent azimuthal rotation about the beam without deviating the beam. The mirrors are gold coated and operating at 80° angle of incidence. Such an instrument can determine both the full Stokes vector of the incoming light and the optical constants (polarizance and phase delay) of the optical elements of the polarimeter, which are then translated into the optical constants (n and k) for gold and compared to the literature values.

An ellipsoidal mirror is a soft X-ray reflective focusing device. We are developing precise ellipsoidal mirrors based on an electroforming process. To improve the fabrication process, three-dimensional shape measurements with a high accuracy are required. In this research we develop a method to measure ellipsoidal shapes by industrial X-ray computed tomography (CT). The X-ray CT process consists of measuring the mirror shape and determining the parameters of the ellipsoid. We also evaluate the reproducibility of X-ray CT measurements and clarify that the accuracy is at the 5-m level.

Compound refractive lenses (CRLs) are widely used as focusing optics at X-ray synchrotron beamlines. For example, the Advanced Photon Source Upgrade (APS-U) beamlines will utilize a large number of CRLs. These lenses must be of high quality to preserve the wavefront and coherence properties of the new source. Therefore, they must be evaluated for quality control and performance before installation and use. At the APS, singlegrating Talbot interferometry has been the primary at-wavelength characterization method because of its high speed, and the ability to provide accurate, quantitative measurements. However, even though the measurement of a single lens is fast, the characterization of a large number of lenses is time consuming due to the time spent on mounting and alignment of individual samples. To adapt the method for testing large quantities of lenses, a fast evaluation system was developed, which includes the use of a lens cartridge for rapid sample change and alignment and an automated python script for batch data analysis. In this work, the optical specifications of refractive lenses are discussed. Measurement and data analysis procedures are also shown in details for testing individual lenses.

Tight XFEL focusing is very important for significantly enhancing photon flux density, which is highly demanded by users exploring nonlinear X-ray optics. However, focusing XFEL down to 10 nm or less is so difficult from the viewpoints of both optical fabrication and optical alignment. The former can be overcome using techniques of wavefront sensing and fine shape correction. For the latter, techniques for directly measuring beam size on the focus without an influence of vibration of nanobeam are required. We have developed a technique for determining the size of nanobeam on the focus using an intensity interferometer, based on the Hanbury Brown and Twiss effect, of X-ray fluorescence emitted from a thin film inserted into the focus. The spatial coherence of X-ray fluorescence observed far from the focus depends on the distance from the focus and emission region of X-ray fluorescence. Therefore, the measured coherence can determine the size of X-ray nanobeam. This method has advantages that vibration of nanobeam does not affect the result and the setup is so simple. A demonstration experiment was performed using a 100 nm focusing system based on total reflection KB mirrors at SACLA. X-ray fluorescence (8 keV) emitted from a thin Cu film by irradiation of focused XFEL pulses (12 keV) was detected shot-by-shot with a dual MPCCD. Analyses of approximately 1000 images based on the autocorrelation revealed that the beam size obtained with this method is in good agreement with one obtained with the wire scan method.

We investigate and compare the spatial (lateral) resolution, or more generally, the optical/instrumental transfer function (OTF/ITF) of surface slope measuring profilometers of two different types that are commonly used for high accuracy characterization of x-ray optics at the long-spatial-wavelength range. These are an autocollimator based profiler, Optical Surface Measuring System (OSMS), and a long trace profiler, LTP-II, both available at the Advanced Light Source (ALS) X˗Ray Optics Lab (XROL). In the OSMS, an ELCOMAT-3000 electronic auto-collimator, vertically mounted to the translation carriage and equipped with an aperture of 2.5 mm diameter, is scanned along the surface under test. The LTP˗II OTF has been measured for two different configurations, a classical two-beam pencil-beam-interferometry and a single-Gaussian-beam deflectometry. For the ITF calibration, we apply a recently developed method based on test surfaces with one-dimensional (1D) linear chirped height profiles of constant slope amplitude. Analytical expressions for the OTFs, empirically deduced based on the experimental results, are presented. We also discuss the application of the results of the ITF measurements and modeling to improve the surface slope metrology with state-of-the-art x-ray mirrors. This work was supported by the U. S. Department of Energy under contract number DE-AC02-05CH11231.

Slope-measuring deflectometry allows the non-contact measurement of curved surfaces such as ultra-precise elliptical cylindrical mirrors used for the focusing of synchrotron light. This paper will report on the measurement of synchrotron mirrors designed to guide and focus synchrotron light in the variable polarization beamline P04 at the PETRA III synchrotron at DESY (Hamburg). These mirrors were optimized by deterministic finishing technology based on topography data provided by slope-measuring deflectometry. We will show the results of the mirror inspection and discuss the expected beamline performance by ray-tracing results.

In order to give a complete evaluation of the beamline’s performance, x-ray mirrors should be measured by advanced surface metrology technique. How to improve spatial resolution of the surface profilers with long trace is one of the important issues for metrology lab. In this paper, we present our newly developed surface slope profiler with focused beam to sample the surface under test. This system has capability to measure precision optics with both high accuracy and spatial resolution. The systematic error of the instrument is also improved for large aperture footprint in the focusing lens considering the lateral beam shift effect. The characterization experiments of the optical head and the scanning measurement of the sample have been carried out to verify the performance of the profiler with accuracy of sub-100 nrad.

For on-line surface measurement of transparent optical elements, phase measuring deflectometry (PMD) is a very promising method. However, the parasitic reflection from the rear surface is an existing problem for PMD to measure transparent element. A parasitic reflection eliminating method using binary pattern is proposed, the principle of which is described in detail. And the proposed method is implemented on a transparent window glass with a thickness of about 10mm. The surface shape result shows a good agreement with the interferometer data with a sub-wavelength level accuracy.

The goal of an in situ Long Trace Profiler (LTP) is to adjust the mirror to 0.1 μrad Root Mean Square (RMS) under thermal load. Here we introduce the measurement configuration for in situ LTP. To avoid lens aberration, the moving optical head keeps the optical paths constant, and the reference beam is used to the correct of the unavoidable air bearing errors. The window glass in this test has a rather high optical quality, with a flatness of 1/150 (RMS) over 120 × 20 mm. The optical quality of the window was specified to be ± 1 μrad slope distortion in an aperture length of 100 mm. The window glass deformation for the air pressure was calculated by the Finite Element Method (FEM) software (ANSYS). The window glass deformation results can be fitting by the Zernike polynomial, and then bring it into the sequential optical ray tracing software (ZEMAX), and evaluating the window glass effect on the LTP measurement results. By this approach, we found that this has a constant error. Thus, the window glass air pressure error can be effectively removed from the measurement result to reveal the real mirror profile. Using the in situ LTP measuring result and the data iteration process, the bendable mirror can control the optical surface locate profile and thereby minimize the thermal distort effect. The slope error will be reduced to 0.1 μrad at the thermal load.

With the progressive development in synchrotron radiation facilities and free electron lasers (FELs), the requirement of the X-ray mirror is getting higher with tighter specifications. It challenges the X-ray mirror metrology in two major application scenes. On one hand, a reliable mirror measurement technique is needed to provide trustable feedback to the deterministic polishing in mirror fabrication or re-polishing process. On the other hand, it demands a more accurate mirror metrology technique to offer better services for the X-ray mirror inspection at synchrotrons and FELs to control the quality of X-ray mirrors to be installed into beamlines. Since the stitching interferometry can provide two-dimensional laterally extendable (stitched) results with sub-nanometer height resolution and precision, several stitching interferometric techniques are studied for synchrotron mirror metrology. It is not only to enhance the mirror inspection capability in NSLS-II optical metrology laboratory but also to act in concert with the ongoing ion beam figuring project at NSLS-II. Various stitching methods with different stitching parameters are investigated at our stitching interferometric platform. Some experimental results are revealed to demonstrate the validity and performance of the developed system and stitching methods.

In 2019, the Institut für angewandte Photonik (IAP) e. V. in cooperation with Nano Optics Berlin (NOB) GmbH and SIOS Meßtechnik GmbH has made an important progress in the technology for precision soft X-ray optics – the development of three-dimensional (3-D) reflection zone plates (RZPs) with diffractive compensation of slope errors. 2-D mapping of spherical and toroidal grating substrates was used for the metrology of their individual profile. Based on these data, the inscribed grating structure, which corrects the slope error distribution, was computed. The correction algorithm has been implemented as a Python script, and first pilot samples of slope error compensated RZPs are in fabrication process. The 3-D device can replace two or three components in an optical scheme and, therefore, reduce absorption losses by several orders of magnitude. Beyond, the fabrication of customized 3-D Fresnel structures on curved substrates promises considerable improvements for efficiency, resolution and energy range in wavelength dispersive applications. As an example, we present simulations for a compact instrument within (150 – 250) eV. Further development of this approach toward commercial availability will enable the design and construction of compact soft Xray monochromators and spectrometers with unique parameters.