The Phase-Contrast Imaging Instrument at the Matter in Extreme Conditions Endstation at LCLS

We describe the Phase-Contrast Imaging instrument at the Matter in Extreme Conditions (MEC) endstation of the Linac Coherent Light Source. The instrument can image phenomena with a spatial resolution of a few hundreds of nanometers and at the same time reveal the atomic structure through X-ray diffraction, with a temporal resolution better than 100 femtosecond. It was specifically designed for studies relevant to High-Energy-Density Science and can monitor, e.g., shock fronts, phase transitions, or void collapses. This versatile instrument was commissioned last year and is now available to the MEC user community

Imaging Shock Waves in Diamond with Both High Temporal and Spatial Resolution at an XFEL

The advent of hard x-ray free-electron lasers (XFELs) has opened up a variety of scientific opportunities in areas as diverse as atomic physics, plasma physics, nonlinear optics in the x-ray range and protein crystallography. In this article, we access a new field of science by measuring quantitatively the local bulk properties and dynamics of matter under extreme conditions, in this case by using the short XFEL pulse to image an elastic compression wave in diamond. The elastic wave was initiated by an intense optical laser pulse and was imaged at different delay times after the optical pump pulse using magnified x-ray phase-contrast imaging. The temporal evolution of the shock wave can be monitored, yielding detailed information on shock dynamics, such as the shock velocity, the shock front width and the local compression of the material. The method provides a quantitative perspective on the state of matter in extreme conditions

Direct imaging of ultrafast lattice dynamics

Under rapid high-temperature, high-pressure loading, lattices exhibit complex elastic-inelastic responses. The dynamics of these responses are challenging to measure experimentally because of high sample density and extremely small relevant spatial and temporal scales. Here, we use an x-ray free-electron laser providing simultaneous in situ direct imaging and x-ray diffraction to spatially resolve lattice dynamics of silicon under high–strain rate conditions.We present the first imaging of a new intermediate elastic feature modulating compression along the axis of applied stress, and we identify the structure, compression, and density behind each observed wave. The ultrafast probe x-rays enabled time-resolved characterization of the intermediate elastic feature, which is leveraged to constrain kinetic inhibition of the phase transformation between 2 and 4 ns. These results not only address long-standing questions about the response of silicon under extreme environments but also demonstrate the potential for ultrafast direct measurements to illuminate new lattice dynamics

Refractive Hard X-Ray Nanofocusing at Storage Ring and X-Ray Free-Electron Laser Sources

Nanofocused hard x-ray beams are an essential tool at modern synchrotron radiation facilities. Tightly focused probe beams are mandatory to reach highest resolution in various x-ray microscopy schemes mapping the local elemental composition, chemical state, or atomic structure. Achievable spatial resolution is typically limited by the probe size itself and the applied dose. Both parameters are strongly dependent on the focusing quality and efficiency of x-ray optics used. This thesis focuses on the improvement of refractive hard x-ray optics. A new lens design is introduced that facilitates the use of coating techniques to fabricate lenses. This enables one to exploit x-ray optically favorable materials like aluminum oxide that were inaccessible beforehand. Experimental results proof the working principle of this new lens design and demonstrate the feasibility of aluminum oxide as a suitable material for refractive x-ray optics.In addition an aberration correction scheme based on a corrective phase plate, applicable to various x-rayoptics, is presented. On the example of beryllium lenses spherical aberrations are characterized by meansof ptychography. Based on this knowledge a corrective phase plate was designed and matched exactlyto the specific optical element. It consists of fused silica and is machined by laser ablation. Experimentson different synchrotron radiation facilities are performed, demonstrating a reduction in the strength ofspherical aberrations by an order of magnitude. The corrected optical element performs nearly at thediffraction limit, eliminating disadvantageous side lobes and increasing the peak intensity in the focalplane simultaneously. Benefits and possible new application fields for this aberration free, radiationhard, and efficient refractive hard x-ray optics are outlined

Refractive phase plates for aberration correction and wavefrontengineering

The short wavelength of X-rays allows in principle the creation of focal spot sizes down to a few nanometers and below. At the same time, this short wavelength and the resulting interaction with matter puts stringent requirements on X-ray optics manufacturing and metrology. With the transition from third-generation synchrotron sources to diffraction-limited storage rings of the fourth generation, more beamlines will operate at higher spatial coherence. Thus, more instruments will work with smaller focal spot sizes that are increasingly dominated by diffraction effects instead of a demagnification of the X-ray source. Consequently, the requirements of X-ray optics will increase to ensure best beam characteristics via diffraction-limited optics. Simultaneously, X-ray optics manufacturing strives to achieve higher numerical apertures to provide ever decreasing beam sizes. On the forefront of this development are highly specialized nanofocusing beamlines with X-ray optics that push focusing toward 10 nm [1–4] and have the ambitious goal to reach 1 nm spot sizes [5]. The fabrication of X-ray optics requires the most advanced technologies, such as lithographic nanofabrication for diffractive [6] and refractive optics [7], surface figuring with atomic precision for total reflection and multilayer mirrors [8], and thin-film technologies for multilayer optics [9]. All of these technologies have been developed over decades and further advances are expected in the future. Minuscule fluctuations or process anisotropies can cause shape deviations of the X-ray optic with a significant impact on focusing performance.Refractive phase plates in combination with a focusing optic are one solution to overcome these technological limitations. While the weak interaction of hard X-rays with matter and the resulting refractive index decrement δon the order of 10−6 pose a challenge for the fabrication of X-ray lenses [10], they allow for very precise control of the induced phase shift via thickness variations in a corrective optical element based on refraction. Even with a conservative shape accuracy of 1 μm for such an optical element, a correction of the wavefield error to <0.05 λ is possible. This exceeds both the Rayleigh criterion for the peak-to-valley wavefront error <0.25 λ and the Maréchal criterion for the RMS wavefront error <0.07 λ for a diffraction-limited optic. A key aspect for this correction scheme is an exact wavefield characterization upon which the design of the corrective element is based

Materials for x-ray refractive lenses minimizing wavefront distortions

Refraction through curved surfaces, reflection from curved mirrors in grazing incidence, and diffraction from Fresnel zone plates are key hard x-ray focusing mechanisms. In this article, we present materials used for refractive x-ray lenses. Important properties of such x-ray lenses include focusing strength, shape, and the material’s homogeneity and absorption coefficient. Both the properties of the initial material and the fabrication process result in a lens with imperfections, which can lead to unwanted wavefront distortions. Different fabrication methods for one-dimensional and two-dimensional focusing lenses are presented, together with the respective benefits and inconveniences that are mostly due to shape fidelity. Different materials and material grades have been investigated in terms of their homogeneity and the absence of inclusions. Single-crystalline materials show high homogeneity, but suffer from unwanted diffracted radiation, which can be avoided using amorphous materials. Finally, we show that shape imperfections can be corrected using a correction lens

Improved tungsten nanofabrication for hard X-ray zone plates

We present an improved nanofabrication method of high aspect ratio tungsten structures for use in high efficiency nanofocusing hard X-ray zone plates. A ZEP 7000 electron beam resist layer used for patterning is cured by a second, much larger electron dose after development. The curing step improves pattern transfer fidelity into a chromium hard mask by reactive ion etching using Cl2/O2 chemistry. The pattern can then be transferred into an underlying tungsten layer by another reactive ion etching step using SF6/O2. A 630 nm-thick tungsten zone plate with smallest line width of 30 nm was fabricated using this method and characterized. At 8.2 keV photon energy the device showed an efficiency of 2.2% with a focal spot size at the diffraction limit, measured at Diamond Light Source I-13-1 beamline

CRL optics and silicon drift detector for P06 Microprobe experiments at 35 keV

A provisional setup for X-ray microprobe experiments at 35 keV is described. It is based on compoundrefractive lenses (CRLs) for nanofocusing and a Vortex silicon drift detector with 2 mm sensorthickness for increased sensitivity at high energies. The Microprobe experiment (PETRA III) generallyuses Kirkpatrick-Baez mirrors for submicrometer focusing in the energy range of 5–21 keV.However, various types of scanning X-ray microscopy experiments require higher excitation energies.The CRL optics were characterized by X-ray ptychography and X-ray fluorescence (XRF) knife edgescans on a siemens star pattern and showed beam sizes down to 110 nm. The performance of the newsetup for microscopic X-ray diffraction (XRD)–XRF scanning X-ray microscopy measurements at35 keV is demonstrated on a cross-section of a painting fragment