This PDF file contains the front matter associated with SPIE Proceedings Volume 10761, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

The European XFEL generates extremely short and intense X-ray laser pulses, with high coherence and diffraction limited divergence. Due to these outstanding characteristics of the beam, ultra-flat X-ray mirrors of ultimate precision are needed to enable a wave front preserving transport of photons from the source to the experimental hall. One of the experimental stations already in operation is the SPB/SFX (Single Particles, Clusters and Biomolecules / Serial Femtosecond Crystallography) station. This instrument is dedicated to coherent diffraction imaging of single particles and structure determination with serial femtosecond crystallography. The instrument is also designed to investigate the structure of these systems as a function of time, using the short X-ray pulses. The optics used in the photon transport tunnels as well as in the experimental station need to fulfill really challenging specifications; therefore, they need to be inspected with metrology devices and methods of comparable precision. This paper presents the metrological characterization of the micron focusing mirrors for the SPB/SFX scientific instrument done with a large aperture Fizeau interferometer. The micron focusing system consists of 2 pairs of mirrors; each pair contains one flat and one elliptical mirror. One pair is vertically reflecting and the other pair is horizontally reflecting. The central profile specification for the mirrors is less than 2 nm peak-to-valley (P-V) figure error over the main surface shape. The measurements performed in our lab are all done in grazing incidence setup and with the mirrors facing side. Analyzing these data we can account many important parameters, as the peak-to-valley of the central profile, the radius, the gravity compensation profile and the ellipse parameters. The micron focusing mirrors have been recently installed in the corresponding chamber of the SPB/SFX Optics Hutch and they will be used very soon for the next User Experiments Run.

The Linac Coherent Light Source (LCLS) of SLAC is upgrading the facility to a more flexible design, permitting both, high energy per pulse mode and High Repetition Rate mode. Two independent “sources” Soft and Hard X-ray will serve five of the existing beamlines and three completely new ones. We will present here, one of the new beamlines, mainly dedicated to Resonant Inelastic Scattering (RIXS) and Liquid Jet based experiments. The beamline is designed to deliver the beam to the floor upstairs of the existing experimental area by using a large deflection, grating based monochromator. The monochromator is designed to provide both, very high resolving power (E/ΔE<50,000) and transform limited low-resolution mode. To accommodate those very different operative modes, the footprint of the beam on the gratings is controlled to illuminate the proper amount of lines. An elliptical bendable mirror, in front of the monochromator, will create four different virtual sources, to cover the photon energy range from 250 to 1600 eV in both modes. After the monochromator, the beamline will serve three experimental stations installed in line. A pair of plan elliptical bendable mirrors, operating in the Kirkpatrick-Baez configuration, will focus the radiation in the proper experimental station. The focal spot size, will be controllable, permitting to adapt it to the need of the experiment. Another major requirement is to preserve the uniformity of the beam, out of focus, with a maximum intensity variation of less than 5%. This implies maintaining the shape error of all the optics to sub-nm levels, even in the presence of heat load. The design principle and performance of the three active mirrors and the impact on the monochromator and spot profile will be presented in details, together with some preliminary tests.

With the onset of high power XFELs and diffraction limited storage rings, there is a growing demand to maintain sub nanometer mirror figures even under high heat load. This is a difficult issue as the optimum cooling design for an optic is highly dependent on the power footprint on the mirror, which can be highly dynamic. Resistive Element Adjustable Length (REAL) cooling can be utilized to change the cooling parameters during an experiment to adapt for changing beam parameters. A case study of the new soft x-ray monochromator for the LCLS L2SI program is presented that utilizes this new capability to allow the beam to translate across the mirror for different operation modes, greatly simplifying the monochromator mechanics. Metrology of a prototype mirror will also be presented.

Nine bendable mirrors will be installed as part of the upgrade to Linac Coherent Light Source. To achieve the target performance, accurate elliptical shapes must be generated with these focusing mirrors to an accuracy in the order of 10⁴ to 10⁵. We briefly summarize the developmental work including surface metrology via stitching and actuator characterization as well as fitting algorithm to achieve shape control of a KB developmental prototype. The height error of the centerline shape generated by the current system is in the order of 3 nm for a one meter long silicon mirror. The most important limiting factor is metrology due to environmental control.

The Linac Coherent Light Source (LCLS) is undergoing an upgrade to a double source setup to provide eight experimental hutches (five existing and three new) with either high-repetition or high-intensity pulses and highly coherent X-ray beams. The photon transportation and distribution to each hutch relies on, among other elements, bendable mirrors. Given the coherence of the LCLS source, and to avoid introducing wavefront distortions beyond workable limits, the mirrors need to have extremely smooth surfaces, with a figure compliant with the nominal profile (usually elliptical). The effectiveness and the accuracy of the bending system and of the actuators over the entire length of the mirror (up to 1.2 m) need to be assessed by an appropriate metrology system. Long Trace Profilometry (LTP) is a suitable technique to characterize a slightly-curved surface mirror profile with very high sensitivity, provided that the optomechanical system implementation enables sensitivity and accuracy values compatible with the mentioned surface quality requirements. In this paper, we show the status and performance of the LTP under development at LCLS. The LTP essentially consists of an advanced optical head that endows a laser beam with sharp interferential features to increase its resolution and detects the optical lever of the beam reflected by the sample, plus a high-precision gantry system (Q-Sys) for accurate scanning of the mirror under test, under impact of its bending mechanics and cooling system. The measured results are compared to the simulated performance of the LTP, and we show the way of the oncoming improvement of the instrument.

The Linac Coherent Light Source (LCLS), a US Department of Energy Office of Science X-ray facility operated by the Stanford University, is being upgraded with a second source to provide eight beamlines (five existing and three under construction) with either high-repetition or high-intensity pulses and highly coherent X-ray beams. The photon transportation and distribution to each beamline relies on, among other elements, elliptically- bendable mirrors, often in Kirkpatrick-Baez (K-B) configuration. One of the crucial tasks in beamline design and performance prediction is the self-consistent simulation of the final point spread function of the complete optical system, simultaneously accounting for diffractive effects, mirror deformations, and surface finishing defects. Rather than using ray-tracing routines, which cannot manage diffractive effects, and rather than employing the first-order scattering theory, which cannot be applied when the optical path differences exceed the radiation wavelength, a wavefront propagation formalism can be used to treat all the aspects at the same time. For example, the WISE code, initially developed for astronomical X-ray mirrors at INAF-OAB, and subsequently used to simulate X-ray reflective systems at the Fermi light source, is now a part of the well-known OASYS simulation package. In this paper, we extend the model to a two-dimensional imaging and show performance simulations of two elliptical mirrors to form a complete Kirkpatrick-Baez system

We discuss experimental, analytical, and numerical methods recently developed at the Advanced Light Source (ALS) X˗Ray Optics Laboratory (XROL) for calibration and precision shaping of bendable x-ray mirrors. The methods are based on ex situ measurements with the mirrors using surface slope profilers available at the ALS XROL. The first realization of methods and dedicated software has allowed the optimization of the beamline performance of bendable mirrors by adjustment of the mirror shape to minimize the root-mean-square variation of residual (after subtraction of the ideal desired shape) slope deviations from ideal (specified) surface figure. Here, we further develop the methods that in application to elliptically bent mirrors adapt as a figure of merit the minimum of the rms size of the focused beam. The efficacy of the developed methods is demonstrated with examples of optimal tuning of an elliptically bendable cylindrical mirror designed for the ALS beamline 10.3.2.

Adjustable X-ray optics is the technology under study by SAO and PSU for the realization of the proposed X-ray telescope Lynx. The technology is based on thin films of lead-zirconate-titanate (PZT) deposited on the back of thermally formed thin substrates, and represents a potential solution to the challenging trade-off between high-surface quality and low mass, that limits the performance of current generation of X-ray telescopes. The technology enables the correction of mirror fabrication figure, mounting induced distortions, and on-orbit correction for variations in the mirror thermal environment. We describe the current state of development, presenting updated test data, anticipation of performances and expectations.

The only way to increase the sensitivity of X-ray telescopes without significantly increasing their size (compared to existing telescopes) is to use thinner mirror shells. However, to maintain the figure of thin mirror shells, their shape will need to be adjusted after they are mounted and/or actively controlled during flight. Here we describe progress toward developing a method that can be used to do both. The core of the concept is to coat thin (<500 μm) X-ray mirrors with a ~10 μm layer of magnetic smart material (MSM). When an external magnetic field is applied to the MSM layer it will expand or contract, changing the shape of the mirror. We have previously demonstrated that this method can be used to generate a single localized deformation on the surface of a test sample. Here we present work to study how two deformations affect each other. The first deformation that we created has a height of ~5 μm. The second deformation, generated by applying a magnetic field to the sample 4 mm from the first position, has a height of ~1 μm. It is likely that the second deformation is smaller than the first because the two areas where the magnetic field was applied were close to each other. This could have caused the MSM to already be partially expanded in the second area when the field was applied there.

Preserving the coherence and wavefront of a diffraction limited x-ray beam from the source to the experiment poses stringent quality requirements on the production processes for X-ray optics. In the near future this will require on-line and in-situ at-wavelength metrology for both, free electron lasers and diffraction limited storage rings. A compact and easy to move X-ray grating interferometry (XGI) setup has been implemented by the Beamline Optics Group at PSI in order to characterize x-ray optical components by determining the aberrations from reconstructing the x-ray wavefront. The XGI setup was configured for measurements in the moire mode and tested with focusing optic at Swiss Light Source, Diamond Light Source and LCLS. In this paper measurements on a bendable toroidal mirror, a zone plate, a single and a stack of beryllium compound refractive lenses (CRL) are presented. From these measurements the focal position and quality of the beam spot in terms of wavefront distortions are determined by analysing the phase-signal obtained from the XGI measurement. In addition, using a bendable toroidal mirror, we directly compare radius of curvature measurements obtained from XGI data with data from a long-trace profilometer, and compare the CRL wavefront distortions with data obtained by ptychography.

Imagine Optic (IO) is actively developing EUV to X-ray wavefront (WF) sensors since 2003 for applications on metrology of EUV to X-ray beams emitted by synchrotrons, free-electron lasers, plasma-based soft X-ray lasers and high harmonic generation. Our sensors have demonstrated their high usefulness for metrology of EUV to X-ray optics from single flat or curved mirrors to more complex optical systems (Schwarzschild, Kirkpatrick-Baez static or based on bender technology or with activators). Our most recent developments include the realization of a EUV sensor adapted to strongly convergent or divergent beams having numerical aperture as high as 0.15, as well as the production of a hard X-ray sensor working at 10 keV and higher energies, providing repeatability as good as 4 pm rms. We present a review of the developed sensors, as well as experimental demonstrations of their benefits for various metrology and WF optimization requirements.

In synchrotron radiation facilities, soft X-ray nanofocusing with mirrors remains a hurdle due to difficulties in mirror fabrication. We have been researching the use of ellipsoidal mirrors for soft X-ray nanofocusing. Information on the wavefront errors of focused beams is helpful for improving the focusing system. This study presents ptychographic wavefront measurements for a nanofocusing system with an ellipsoidal mirror. We developed a ptychography program and performed several simulations at 300 eV to investigate the theoretical accuracy of the wavefront measurements. The simulation results indicate that wavefront measurements with high accuracy are possible.

With the progresses achieved on the development of high quality, highly coherent soft X-ray (or EUV) sources from synchrotrons, free-electrons laser, high harmonics and plasma based soft X-ray laser, as well as for the need of always better optics for imaging (EUV lithography, EUV spatial telescopes, EUV microscopes), the demand on metrology is increasing very fast. Nowadays, many synchrotrons have developed metrology beamlines but with the limit of being too expensive and too large for transposing them to university-scale laboratories or optical firms. At Laboratoire d'Optique Appliquée, we have developed a compact and versatile metrology beamline to test at-wavelength different EUV optics, from single component to full assembly and adaptive optics. The beamline is based on the use of high harmonics generated by the interaction of a 35 fs, 4 kHz, 3 mJ laser with neutral gases. The high harmonics span from 10 to 50 nm and are fully coherent, collimated and exhibit a good wavefront of about lambda/5 rms. The beamline covers a footprint of about 5*1.5 m2 while the driving laser occupies about 4 m2. Itis composed of an interaction chamber where high harmonics are generated, a spectrometer and the metrology chamber (1.5m*0.7m) . We have tested many optical components from flat or curved mirrors to toroidal mirror or Schwarzschild microscope. We will present in detail the beamline as well as results from optic metrology. The beamline is also used for calibration of wavefront sensors. This beamline is well suited for testing EUV adaptive optic in any configurations.

The need for smaller focal spot sizes to meet the demands for higher resolution imaging is driving the adoption of adaptive optics in x-ray beamlines. Closed-loop control of the mirror shape, position, and orientation can greatly enhance the performance of these optics by allowing for rejection of perturbations. We demonstrate the performance of an array of interferometric absolute position sensors as a means of providing real-time feedback on shape changes of the reflecting surface of a bimorph mirror by comparison to a Fizeau interferometer.

We present an optical system based on two toroidal mirrors in a Wolter configuration to focus broadband XUV high harmonic radiation generated by the non-linear interaction of a fs, 10 Hz laser with neutral gas. The experiment was carried out at Lund University in collaboration with Laboratoire d’Optique Appliquée, ELI-ALPS and Imagine Optic. Optimization of the focusing optics alignment is carried out with the aid of an XUV Hartmann wavefront sensor commercialized by Imagine Optic. Back-propagation of the optimized wavefront to the focus yields a focal spot of 3.6 * 4.0 µm2 full width at half maximum, which is consistent with ray-tracing simulations that predict a minimum size of 3.0 *3.2 µm2. We will show also how the optimization of the high harmonic beam by the use of an infrared adaptive optic may help for compensating the residual aberrations of the Wolter, leading to a clear improvement of the focal spot.