T his issue of SRN is focused on the problem of dealing with the high heat loads delivered to beamlines by current insertion devices. In thinking about this problem, the first question I asked myself was what topics were appropriate to include in this issue. There is, of course, the immediate problem of removing the heat from the white and pink beam optics to minimize thermal distortions. But it goes beyond that. With the many new synchrotrons and upgrades to existing storage rings recently completed or planned, which are now extending the diffraction limit of the source to higher X-ray energies, and the advent of free electron laser sources, the coherence properties of the beam and preserving those properties are becoming critical to conducting important scientific work; this is being driven by the development of advanced X-ray techniques that require high coherence, such as ptychography and coherent diffraction imaging (see, for example, Ref. [1]). From my perspective, the topic of high heat loads includes dealing with the heat load and minimizing the thermal distortions on the first several beamline optics, yes, but also involves the ability to sense and correct for the inevitable distortions that do occur, which involves diagnostics and wavefront sensors, and the ongoing development of various ingenious schemes for corrective optics. It also involves the advancement of beamline mechanics, stable enough to resist thermal drift and additional stresses on the optics under varying heat loads due to scattered radiation or thermal sinks from the optic cooling mechanisms, and beam position monitoring with feedback to correct for drifts when they occur. All of this requires advanced control systems to allow the various parts of the beamline to work properly together. Furthermore, there is the topic of advances in materials with properties such that they perform better under the thermal load due to the X-ray beam. This is certainly not an exhaustive list of strategies being considered to deal with the heat loads. For instance, there is also work being done on new insertion device designs that deflect a significant portion of the power off axis so that it can be intercepted by an aperture placed upstream of the first optical component [2, 3]. The point is that the problem is a many-headed hydra, and there are multiple efforts underway to do battle with the beast. What defines a high heat load? This is a fair question to ask, but difficult to answer with a number. The heat loads of insertion devices and their effects on the beamline optics, as well as strategies to deal with the problem, are significantly different if we are dealing with, say, a soft X-ray EPU-based beamline or a high energy beamline with a superconducting wiggler. The degree to which the thermal load will present a problem also depends upon the scientific techniques that will be enabled by the beamline. Perhaps it is best to define “high heat load” operationally: a heat load that presents technical challenges that are not readily met by existing well-developed solutions. The problem itself is not new. It has been recognized early on with the advent of dedicated synchrotron sources [4], but at this point in time we have the benefit of four decades of research, development, and experience in operating beamlines at synchrotron facilities. The steady progress over these years has led us to the current point: facing the challenge of delivering highly coherent beams to the sample interaction point with minimal degradation of the beam quality. A problem of this complexity cannot be solved by a single person; it requires the expertise of teams of talented engineers, scientists, and technicians working together to conceive, Guest Editorial Synchrotron Radiation News ISSN 0894-0886 is published bi-monthly. Coden Code: SRN EFR

Diffraction Enhanced Imaging (DEI) or Analyzer Based Imaging (ABI) uses a perfect crystal monochromator and matching analyzer to achieve sensitivity to X-ray refraction and ultra small-angle scattering on the order of 0.01 micro-radians. As such, a thermal bump on the crystal caused by photon heat load in the order of 1 W is detrimental. The heat load at the HEX (High Energy Engineering X-ray) super-conducting wiggler (SCW) beamline, under construction at the NSLS-II, is on the order of 1 kW. How do we reconcile the three orders of magnitude difference between the HEX source power and the DEI/ABI requirements? The solution involves using a double-crystal bent-Laue monochromator as pre-monochromator to prepare a beam with a large divergence and bandwidth that is matched to a flat symmetric crystal [333] post-monochromator. In the article, we will show through phase-space (X-ray wavelength vs. angle as viewed by a flat crystal) analysis and Dumond diagrams that there is indeed a unique bending radius that matches the double-crystal bent-Laue monochromator in phase space to the flat Bragg crystal. The matched system has the desirable feature that the phase space of the bent crystal’s output beam is much larger than that of the flat crystal,

We performed fully- and partially-coherent synchrotron emission and propagation simulations with the "Synchrotron Radiation Workshop" computer code to analyze the performance of two soft X-ray beamlines under development at the National Synchrotron Light Source II: Soft X-ray Nanoprobe (SXN), and Angle-Resolved Photoemission Spectroscopy (ARPES) and Resonant Inelastic X-ray Scattering (RIXS) Imaging (ARI). The SXN beamline intends to provide high flux and high spatial resolution coherent soft X-ray imaging capabilities using both zone plate and lensless coherent imaging techniques. The ARI beamline aims to perform high flux ARPES and RIXS experiments with a focal spot size at the sample approaching 100 nm using highly-demagnifying mirrors in Kirkpatrick-Baez geometry. To accurately calculate the resolution and the degree of X-ray coherence provided by the two state-of-the-art beamlines, partial coherence effects are required to be taken into account in wave optics simulations for these two beamlines. In this talk, beamline performance parameters such as spot size, degree of coherence, flux, and energy resolution at the sample are presented. The effects of mirror surface slope errors on beamline performance were studied and some suggestions for further optimization are discussed.

Diffraction gratings are key elements of soft X-ray synchrotron beamlines. Besides wavelength dispersion, specific parameters can be tailored to adjust the energy dependent efficiency and focusing, and to correct wavefront aberrations. As key elements of a beamline, any departure from the design values can severely reduce the overall performance. On the other hand, known non-conformities can often be corrected by slight adjustment of the alignment parameters. A careful and accurate metrology is therefore required before installation on the beamline. After presenting what variable line spacing gratings, variable groove depth gratings, and alternate multilayer gratings are, the use of the SOLEIL long trace profiler for the measurement of groove density variation along the surface and of the atomic force microscope for the groove geometry and roughness characterizations will be discussed. A few examples of grating metrology will be presented and analyzed with the help of optical simulations.

Many of the emergent properties in quantum materials manifest themselves as low-energy collective excitations involving entwined charge, spin, orbital, and lattice degrees of freedom. These propert...

As resolving power targets have increased with each generation of beamlines commissioned in synchrotron radiation facilities worldwide, diffraction gratings are quickly becoming crucial optical components for meeting performance targets. However, the metrology of variable-line-spacing (VLS) gratings for high resolution beamlines is not widespread; in particular, no metrology facility at any US DOE facility is currently equipped to fully characterize such gratings. To begin to address this issue, the Optics Group at the Advanced Photon Source at Argonne, in collaboration with SOLEIL and with support from Brookhaven National Laboratory (BNL), has developed an alternative beam path addition to the Long Trace Profiler (LTP) at Argonne's Advanced Photon Source. This significantly expands the functionality of the LTP not only to measure mirrors surface slope profile at normal incidence, but also to characterize the groove density of VLS diffraction gratings in the Littrow incidence up to 79 degrees, which covers virtually all diffraction gratings used at synchrotrons in the first order. The LTP light source is a 20mW HeNe laser, which yields enough signal for diffraction measurements to be performed on low angle blazed gratings optimized for soft X-ray wavelengths. We will present the design of the beam path, technical requirements for the optomechanics, and our data analysis procedure. Finally, we discuss challenges still to be overcome and potential limitations with use of the LTP to perform metrology on diffraction gratings.

We introduce a method for using Fizeau interferometry to measure the intrinsic resolving power of a diffraction grating. This method is more accurate than traditional techniques based on a long-trace profiler (LTP), since it is sensitive to long-distance phase errors not revealed by a d-spacing map. We demonstrate 50,400 resolving power for a mechanically ruled XUV grating from Inprentus, Inc.

We present the optical design of the Centurion soft X-ray resonant inelastic X-ray scattering (RIXS) spectrometer to be located on the SIX beamline at NSLS-II. The spectrometer is designed to reach a resolving power of 100 000 at 1000 eV at its best resolution. It is also designed to have continuously variable 2θ motion over a range of 112° using a custom triple rotating flange. We have analyzed several possible spectrometer designs capable of reaching the target resolution. After careful analysis, we have adopted a Hettrick-Underwood spectrometer design, with an additional plane mirror to maintain a fixed direction for the outgoing beam. The spectrometer can cancel defocus and coma aberrations at all energies, has an erect focal plane, and minimizes mechanical motions of the detector. When the beamline resolution is accounted for, the net spectral resolution will be 14 meV at 1000 eV. This will open up many low energy excitations to study and will expand greatly the power of soft X-ray RIXS.

For over a decade, synchrotron-based footprinting studies at the NSLS X28C beamline have provided unique insights and approaches for examining the solution-state structures of large macromolecular assemblies, membrane proteins, and soluble proteins, for time-resolved studies of macromolecular dynamics, and most recently for in vivo studies of RNA-protein complexes. The transition from NSLS to NSLS-II has provided the opportunity to create an upgraded facility for the study of increasingly complex systems; progress on the development of the XFP (X-ray Footprinting for In Vitro and In Vivo Structural Studies of Biological Macromolecules) beamline at NSLS-II is presented here. The XFP beamline will utilize a focused 3-pole wiggler source to deliver a high flux density x-ray beam, where dynamics can be studied on the microsecond to millisecond timescales appropriate for probing biological macromolecules while minimizing sample perturbation. The beamline optics and diagnostics enable adaptation of the beam size and shape to accommodate a variety of sample morphologies with accurate measurement of the incident beam, and the upgrades in sample handling and environment control will allow study of highly sensitive or unstable samples. The XFP beamline is expected to enhance relevant flux densities more than an order of magnitude from that previously available at X28C, allowing static and time-resolved structural analysis of highly complex samples that have previously pushed the boundaries of x-ray footprinting technology. XFP, located at NSLS-II 17-BM, is anticipated to become available for users in 2016.

A "source-to-sample" wavefront propagation analysis of the Electron Spectro-Microscopy (ESM) UV / soft X-ray beamline, which is under construction at the National Synchrotron Light Source II (NSLS-II) in the Brookhaven National Laboratory, has been conducted. All elements of the beamline - insertion device, mirrors, variable-line-spacing gratings and slits - are included in the simulations. Radiation intensity distributions at the sample position are displayed for representative photon energies in the UV range (20 - 100 eV) where diffraction effects are strong. The finite acceptance of the refocusing mirrors is the dominating factor limiting the spatial resolution at the sample (by similar to 3 mu m at 20 eV). Absolute estimates of the radiation flux and energy resolution at the sample are also obtained from the electromagnetic calculations. The analysis of the propagated UV range undulator radiation at different deflection parameter values demonstrates that within the beamline angular acceptance a slightly "red-shifted" radiation provides higher flux at the sample and better energy resolution compared to the on-axis resonant radiation of the fundamental harmonic.

Beamline X25 at the NSLS is one of the five beamlines dedicated to macromolecular crystallography operated by the Brookhaven National Laboratory Macromolecular Crystallography Research Resource group. This mini-gap insertion-device beamline has seen constant upgrades for the last seven years in order to achieve mini-beam capability down to 20 µm × 20 µm. All major components beginning with the radiation source, and continuing along the beamline and its experimental hutch, have changed to produce a state-of-the-art facility for the scientific community.

The biogeochemical cycle of Fe is intricately linked with that of organic matter. Cysteine represents an organic molecule with functionalities (O, S, N functional groups) and a C backbone that may mimic the functional groups present in organic matter from terrestrial and aquatic environments. In the present study we explore the redox speciation and coordination environment of Fe and the roles of the various ligand atoms of cysteine (C, N, S) in iron-organic redox coupling and transformations. The changes in oxidation state of Fe, C, N, and S in laboratory-synthesized Fe(II)–cysteine (synthesized from ferrous sulfate) and Fe(III)–cysteine (synthesized from ferric nitrate) complexes are monitored as a function of time using synchrotron X-ray absorption spectroscopy (Fe L2,3-edge XANES; C, N and S K-edge XANES; Fe K-edge EXAFS) and theoretical multiplet calculations using the program CTM4XAS (Charge Transfer Multiplet for X-ray Absorption Spectroscopy). CTM4XAS calculations show that 80% of the total Fe in both the Fe(II)–cysteine and the Fe(III)–cysteine complexes is present as Fe2+ initially (t=0), thus indicating preservation of Fe(II) in Fe(II)–cysteine and reduction of Fe(III) in Fe(III)–cysteine at initial conditions, the latter caused by an internal electron transfer reaction from S of –SH on the cysteine molecule. After 12months, however, ∼60% of the total Fe is present as Fe3+ in the Fe(II)–cysteine complex whereas ∼67% of the total Fe is present as Fe2+ in the Fe(III)–cysteine complex. The fact that a larger proportion of the Fe in the Fe(III)–cysteine complex remained reduced after 12months than that in the Fe(II)–cysteine complex suggests that the reduced Fe in Fe(III)–cysteine after 12months is further stabilized via preferential binding with the donor atoms of cysteine. Stabilization via preferential binding is supported by a coordination environment that changed from tetrahedral Fe2+ binding to S at a distance of 2.3Å at t=0 for both Fe(II,III)–cysteine complexes, to Fe3+ in an octahedral coordination with O/N atoms at a distance of 2.05Å (most prevalent in Fe(II)–cysteine) and Fe2+ in tetrahedral coordination with S/O/N atoms at an average distance of 2.15Å (most prevalent in Fe(III)–cysteine) at t=12months. Redox changes in the –NH2 and –SH groups of cysteine accompanied the Fe redox changes thus reflecting the true potential of cysteine as a redox ligand. Our studies of the Fe(II,III)–cysteine complexes add valuable information to the existing literature on the redox chemistry of Fe–cysteine systems by shedding light on the electron exchange pathways that may occur within the complexes and by providing a detailed depiction of the iron-ligand structure and coordination. The presence and persistence of Fe(II) or Fe(III) in complexes with soluble organics have implications for Fe biological availability and Fe mobility and transport in terrestrial as well as in aquatic environments.

Flux is a simple yet key indicator of overall beamline alignment. For many synchrotron measurements, the energy resolution and reproducibility are important characteristics as well. However. many beamlines do not have diffractometers capable of measuring the energy resolution in the experimental hutches. For absolute flux measurements, we have found that thickness calibrated Si photodiodes make very convenient, robust detectors capable of handling a wide flux range. For measuring the energy resolution, we have developed a simple, portable instrument analyzer applicable to any beamline with a scanning monochromator. This same instrument is capable of measuring the energy stability and reproducibility as well. We have used these to characterize many of the beamlines on the NSLS X-ray ring, and will present the methods and our experience to date to demonstrate their usefulness.

We present a dynamic monitoring method and monitoring system of grating angle, referred to as the Precise Angle Monitor (PAM), at U4B, a soft x-ray spherical grating monochromator (SGM) beam line at the National Synchrotron Light Source (NSLS). In an SGM, a photon energy scan is accomplished by rotating the grating angle precisely. After several decades of service, the monochromator at U4B developed instabilities that severely impacted the experimental program. Over several hours, either the spectral shape experienced distortions or the spectral peak shifted. In order to directly monitor the grating motion during scans, the optical head of a portable long trace profiler (PTLTP) was installed on U4B as the PAM. We find that the grating rotational motion is not ideal: (1) the scan steps are not smooth and there are high-frequency step angle errors; (2) there is also a low-frequency angle error; and (3) an unstable thermal expansion produces extra rotational error. Measurements of dynamic monitoring are presented, including grating rotation repeatability and thermal instability. The results illustrate the utility of dynamic monitoring of monochromator motion during actual operation.

The Multi-order Solar EUV Spectrograph (MOSES) is a slitless spectrograph designed to study solar He II emission at 303.8 Å (1 Å = 0.1 nm), to be launched on a sounding rocket payload. One difference between MOSES and other slitless spectrographs is that the images are recorded simultaneously at three spectral orders, m = -1, 0, +1. Another is the addition of a narrow-band multilayer coating on both the grating and the fold flat, which will reject out-of-band lines that normally contaminate the image of a slitless instrument. The primary metrics for the coating were high peak reflectivity and suppression of Fe XV and XVI emission lines at 284 Å and 335 Å, respectively. We chose B4C/Mg2Si for our material combination since it provides excellent peak reflectivity and rejection of out-of-band wavelengths. Measurements of witness flats at NIST indicate the peak reflectivity at 303.8 is 39.0% for a 15 bilayer stack, while suppression ranges from 7.5x to 12.9x at 284 Å and from 3.4x to 15.1x at 335 Å for the individual reflections in the optical path. We present the results of coating the MOSES flight gratings and fold flat, including the spectral response of the fold flat and grating as measured at NIST's SURF III and Brookhaven's X24C beamline, respectively.