SwissFEL is the Free Electron Laser (FEL) facility under construction at the Paul Scherrer institute (PSI), aiming to provide users with X-ray pulses of lengths down to 2 femtoseconds at standard operation. The measurement of the length of the FEL pulses and their arrival time relative to the experimental laser is crucial for the pump-probe experiments carried out in such facilities. This work presents a new device that measures hard X-ray FEL pulses based on the THz streak camera concept. It describes the prototype setup called pulse arrival and length monitor (PALM) developed at PSI and tested in Spring-8 Angstrom Compact Free Electron Laser (SACLA) in Japan. Based on the first results obtained from the measurements, we introduce the new improved design of the second generation PALM setup that is currently under construction and will be used in SwissFEL photon diagnostics.
After the successful demonstration of the hard X-ray self-seeding at LCLS, an effort to build a system for working in the soft X-ray region is ongoing. The idea for self-seeding in the soft X-ray region by using a grating monochromator was first proposed by Feldhauset. al. The concept places a grating monochromator in middle of the undulators and selects a narrow bandwidth “seed” from the SASE beam produced by the upstream section of undulators, which is then amplified to saturation in the downstream section of the undulators. The seeded FEL beam will have a narrower bandwidth approaching the transform limit. The challenge is to accommodate a monochromator and refocusing system as well as the electron beam magnetic chicane into a very limited space. The Soft X-raySelf Seeding system replaces only a single undulator section of ~ 4 m. Theoverall project and the expected FEL performances are described elsewhere. Here we present the detailed optical design solution, consisting of a fixed incidence angle toroidal blazed grating with variable groove density, a rotating plane mirror (the only required motion for tuning the energy) to redirect the selected monochromatic beam onto an exit slit, and two more mirrors, one sphere and one flat, to focus and overlap the ‘seed’ onto the electron beam in the downstream undulators.
Next-generation X-ray sources, based on the X-ray Free Electron Laser (XFEL) concept, will
provide highly coherent, ultrashort pulses of soft and hard X-rays with peak intensity many
orders of magnitude above that of a synchrotron. These pulses will allow studies of
femtosecond dynamics at nanometer resolution and with chemical selectivity. They will
produce coherent-diffraction images of organic and inorganic nanostructures without the
deleterious effects of radiation damage.
The planned XFEL at the Paul Scherrer Institut, the SwissFEL, is a fourth generation light source. Meanwhile the first
hard X - ray FEL was taken into operation, the LCLS at Stanford, USA. Two further hard XFELs are in construction.
One in Hamburg, Germany and the second at Spring - 8, Japan. Thanks to the beam properties of the XFEL, these new
sources promise to bring novel insights and breakthroughs in many scientific disciplines. For engineers and designers
new challenges arise in terms of material choice, damage thresholds and beam property conservation. The Swiss Light
Source optics group is currently working on the beamline optics design of the SwissFEL beamlines. The preliminary
optics design of the two undulator beamlines which serve six experiments is under preparation. In this article a
preliminary layout of the hard X - ray Aramis undulator beamline is presented. Several beamline designs have been
evaluated. Beam deflection and splitting via mirrors and diamonds is presented. The SwissFEL is planned to be
operational in 2016.
Synchrotron-based X-ray Tomographic Microscopy is a powerful technique for fast, non-destructive, high resolution quantitative volumetric investigations on diverse samples. At the TOMCAT (TOmographic Microscopy and Coherent radiology experimenTs) beamline at the Swiss Light Source (SLS), synchrotron light is delivered by a 2.9 T superbend. The main optical component, a Double Crystal Multilayer Monochromator, covers an energy range between 8 and 45
keV. The standard TOMCAT detector offers field of views ranging from 0.75x0.75 mm<sup>2</sup> up to 12.1x12.1mm<sup>2</sup> with a theoretical resolution of 0.37 μm and 5.92 μm, respectively. The beamline design and flexible endstation setup make a large range of investigations possible. In addition to routine measurements, which exploit the absorption contrast, the high coherence of the source also enables phase contrast tomography, implemented with two complementary techniques. Differential Phase Contrast (DPC) imaging has been fully integrated in terms of fast acquisition and data reconstruction. Scans of samples within an aqueous environment are also feasible. The second phase contrast method is a Modified Transport of Intensity approach that yields a good approximation of the 3D phase distribution of a weakly absorbing object from a single tomographic dataset. Typical acquisition times for a tomogram are in the order of few minutes, ensuring high throughput and allowing for semi-dynamical investigations and in-situ experiments. Raw data are automatically post-processed online and full reconstructed volumes are available shortly after a scan with minimal user intervention. In addition to a beamline overview, a selection of high-impact tomographic applications will be presented.
Over the last decade, synchrotron-based X-ray tomographic microscopy has established itself as a fundamental tool for non-invasive, quantitative investigations of a broad variety of samples, with application ranging from space research and materials science to biology and medicine. Thanks to the brilliance of modern third generation sources, voxel sizes in the micrometer range are routinely achieved by the major X-ray microtomography devices around the world, while the isotropic 100 nm barrier is reached and trespassed only by few instruments. The beamline for TOmographic Microscopy and Coherent rAdiology experiments (TOMCAT) of the Swiss Light Source at the Paul Scherrer Institut, operates a multimodal endstation which offers tomographic capabilities in the micrometer range in absorption contrast - of course - as well as phase contrast imaging. Recently, the beamline has been equipped with a full field, hard X-rays microscope with a theoretical pixel size down to 30 nm and a field of view of 50 microns. The nanoscope performs well at X-ray
energies between 8 and 12 keV, selected from the white beam of a 2.9 T superbend by a [Ru/C]<sub>100</sub> fixed exit multilayer monochromator. In this work we illustrate the experimental setup dedicated to the nanoscope, in particular the ad-hoc designed X-ray optics needed to produce a homogeneous, square illumination of the sample imaging plane as well as the magnifying zone plate. Tomographic reconstructions at 60 nm voxel size will be shown and discussed.
Time-resolved x-ray absorption fine structure (XAFS) spectroscopy with picosecond temporal resolution is a
new method to observe electronic and geometric structures of short-lived reaction intermediates. It combines an intense
femtosecond laser source synchronized to the x-ray pulses delivered into the microXAS beamline of the Swiss Light
Source (SLS). We present key experiments on charge transfer reactions as well as spin-crossover processes in
coordination chemistry compounds next to solvation dynamics studies of photogenerated atomic radicals.
Vascular factors associated with Alzheimer's disease (AD) have recently gained increased attention. To investigate changes in vascular, particularly microvascular architecture, we developed a hierarchical imaging framework to obtain large-volume, high-resolution 3D images from brains of transgenic mice modeling AD. In this paper, we present imaging and data analysis methods which allow compiling unique characteristics from several hundred gigabytes of image data. Image acquisition is based on desktop micro-computed tomography (µCT) and local synchrotron-radiation µCT (SRµCT) scanning with a nominal voxel size of 16 µm and 1.4 µm, respectively. Two visualization approaches were implemented: stacks of Z-buffer projections for fast data browsing, and progressive-mesh based surface rendering for detailed 3D visualization of the large datasets. In a first step, image data was assessed visually via a Java client connected to a central database. Identified characteristics of interest were subsequently quantified using global morphometry software. To obtain even deeper insight into microvascular alterations, tree analysis software was developed providing local morphometric parameters such as number of vessel segments or vessel tortuosity. In the context of ever increasing image resolution and large datasets, computer-aided analysis has proven both powerful and indispensable. The hierarchical approach maintains the context of local phenomena, while proper visualization and morphometry provide the basis for detailed analysis of the pathology related to structure. Beyond analysis of microvascular changes in AD this framework will have significant impact considering that vascular changes are involved in other neurodegenerative diseases as well as in cancer, cardiovascular disease, asthma, and arthritis.
Synchrotron-based X-ray Tomographic Microscopy (SRXTM) is nowadays a powerful technique for non-destructive,
high-resolution investigations of a broad kind of materials. High-brilliance and high-coherence third generation
synchrotron radiation facilities allow micrometer and sub-micrometer, quantitative, three-dimensional
imaging within very short time and extend the traditional absorption imaging technique to edge-enhanced
and phase-sensitive measurements. At the Swiss Light Source TOMCAT, a new beamline for TOmographic Microscopy and Coherent rAdiology experimenTs, has been recently built and started regular user operation in
June 2006. The new beamline get photons from a 2.9 T superbend with a critical energy of 11.1 keV. This makes
energies above 20 keV easily accessible. To guarantee the best beam quality (stability and homogeneity), the
number of optical elements has been kept to a minimum. A Double Crystal Multilayer Monochromator (DCMM)
covers an energy range between 8 and 45 keV with a bandwidth of a few percent down to 10<sup>-4</sup>. The beamline
can also be operated in white-beam mode, providing the ideal conditions for real-time coherent radiology. This
article presents the beamline design, its optical components and the endstation. It further illustrates two recently
developed phase contrast techniques and finally gives an overview of recent research topics which make intense
use of SRXTM.
State-of-the-art synchrotron-based microtomography devices have
nowadays to fulfill very stringent requirements in term of spatial
resolution, detection efficiency and data throughput. The most
used detection system is based on collecting the light produced by
a thin scintillation screen with microscope optics and conveying
it to a high-performance charge coupled device (CCD) camera. With
the chip-size of currently available CCDs installed at high
brilliance sources like the Swiss Light Source (SLS) raw data are
produced at rate of gigabyte/minute. It is crucial therefore to
provide the necessary infrastructure to be able to post-process
the data in real time, and provide to the user 3D information
immediately after the end of the scan. The visible-light-based
detection system is intrinsically limited by scintillation
properties, optical coupling and CCD granularity to a practical
limit of about 1 micron spatial resolution and efficiency of a few
percent. A novel detector, called Bragg magnifier, is one of the
techniques recently proposed to efficiently trespass the
micrometer barrier. It exploits two-dimensional asymmetric Bragg
diffraction from flat crystals to produce X-ray images with
magnification factors up to 150x150 and pixel sizes less than
100x100 nm<sup>2</sup>. The infrastructure devoted to microtomography
at the SLS is described, as well as some very promising
experiments. The layout of a novel, tomography dedicated beamline
is also presented.
A wide range of disorders are associated with alterations of the central and peripheral vascular system. Modified vascular corrosion casting using a newly developed polymer, allows for the first time hierarchical assessment of 3D vessel data in animals down to the level of capillaries. Imaging of large volumes of vasculature at intermediate resolution (16 μm) was performed using a desktop micro-computed tomography system. Subsequently regions of interest were identified for additional high resolution imaging (1.4 μm) at the X-ray Tomographic Microscopy (XTM) station of the Swiss Light Source (SLS). A framework for systematic hierarchical imaging and quantification was developed. Issues addressed included enhanced XTM data acquisition, introduction of local tomography, sample navigation, advanced post processing, and data combination. In addition to visual assessment of qualitative changes, morphometrical and architectural indices were determined using direct 3D morphometry software developed in house. Vessel specific parameters included thickness, surface, connectivity, and vessel length. Reconstructions of cerebral vasculature in mutant mice modeling Alzheimer's disease revealed significant changes in vessel architecture and morphology. In the future, a combination of these techniques may support drug discovery. Additionally, future ultra-high-resolution <i>in vivo</i> systems may even allow non-invasive tracking of temporal alterations in vascular morphology.
With the advent of high brilliance, third generation synchrotron
radiation sources, the spatial resolution of non-destructive X-ray
tomographic investigations can be scaled down to the micrometer or
even submicrometer range while the coherent nature of the
radiation extends the traditional absorption imaging techniques
towards edge-enhanced or phase-sensitive measurements. The
performance of the presently used detectors is limited by
scintillation properties, optical light coupling and charge
coupled device granularity which impose a practical limit of about
1 micrometer spatial resolution with efficiencies of a few
percent. We developed a detector called Bragg magnifier which
exploits double asymmetrical Bragg diffraction from flat crystals
to efficiently produce distortion- and aberrations-free X-ray
images with magnification factors up to 150x150 and pixel sizes of
less than 100x100nm<sup>2</sup>.
At the Material Science Beamline 4S of the Swiss Light Source (SLS), the X-ray Tomographic Microscopy (XTM) facility is entering its final construction phase. A high performance detector based on a scintillating screen optically coupled to a CCD camera has been developed and tested. MTF-responses of the detector system show spatial resolution down to the micrometer level. A second detector, which will provide a quantum jump in term of spatial resolution and efficiency, has been successfully simulated and will be integrated in the current device soon. A user- friendly graphical interface gives access to the main measurements parameters needed for a complete tomographic scan in absorption as well as in phase-contrast mode. The new instrumentation shall be used for the analysis of the physical structure and chemical composition of technical materials and biological samples, e.g. enabling non- destructive testing during the development of modern composite materials, or enabling pseudo-dynamic testing of bone samples to establish structure-function relationships in simulated osteoporosis.
We present the concept of an experiment that aims at probing in real-time photoinduced structural modifications in a large class of media ranging from biological systems to solid state materials using time-resolved X-ray spectroscopies (Extended X-ray Absorption Fine Structure-EXAFS or X-ray Absorption Near-Edge Structure-XANES) in the picosecond time domain. The principle of the experiment is based on the pump-probe scheme, where an ultrashort laser pulse induces a structural modification in a chemical, physical or biological system. The picosecond hard X-ray pulse from a synchrotron probes the evolution of the structure in real-time by means of an adjustable time delay between the pump and the probe pulses. The paper discusses the case of iodine in liquid solvents as a test bench of the technique.