A hard X-ray delay line device capable of splitting single FEL X-ray pulses into two adjustable fractions and
recombining them with the goal of performing X-ray Photon Correlation Spectroscopy and pump - probe type
studies was designed. The performance of the device has been verified at the XPP and XCS instruments of
LCLS. The measured throughput of the device at 7.9 keV is 3.6%. The coherence properties of the LCLS beam
passing through the delay line were investigated by analyzing speckle patterns produced by single LCLS pulses.
A high speckle contrast of 0.69 was found, indicating the feasibility of performing coherence based experiments
with the delay line.
Hard x-ray point focusing by two crossed multilayer Laue lenses is studied using a full-wave modeling approach. This study shows that for a small numerical aperture, the two consecutive diffraction processes can be decoupled into two independent ones in respective directions. Using this theoretical tool, we investigate adverse effects of various misalignments on the 2D focus profile and discuss the tolerance to them. We also derive simple expressions that describe
the required alignment accuracy.
We have developed a prototype instrument with a novel interferometrically controlled differential scanning stage system. The system consists of 9 DC-motor-driven stages, 4 picomotor-driven stages, and 2 PZT-driven stages. A custom-built laser Doppler displacement meter system provides two-dimensional (2D) differential displacement measurement with subnanometer resolution between the zone-plate x-ray optics and the sample holder. The entire scanning system was designed with high stiffness, high repeatability, low drift, flexible scanning schemes, and possibility of fast feedback for differential motion. Designs of the scanning stage system, as well as preliminary mechanical test results, are presented in this paper.
Using Fresnel zone plates, a spatial resolution between 20 nm for soft x-rays and 70 nm for hard x-rays has been achieved. Improvement of the spatial resolution without loss of efficiency is difficult and incremental due to the fabrication challenges posed by the combination of small outermost zone width and high aspect ratios. We describe a novel approach for high-resolution x-ray focusing, a multilayer Laue lens (MLL). The MLL concept is a system of two crossed linear zone plates, manufactured by deposition techniques. The approach involves deposition of a multilayer with a graded period, sectioning it to the appropriate thickness, assembling the sections at the optimum angle, and using it in Laue geometry for focusing. The approach is particularly well suited for high-resolution focusing optics for use at high photon energy. We present a theory of the MLL using dynamic diffraction theory and Fourier optics.
We introduce a new design of tilted linear zone plates, which are named tapered tilted linear (TTL) zone plates. The purpose of the design is to increase efficiency while at the same time keeping the focal plane perpendicular to the optical path. In order to accomplish this, the zone radius and number of zones must become a function of position along the structure. Simulation work described in this paper shows improved optical performance over regular tilted linear zone plates.
Zone plates with depth to zone-width ratios as large as 100 are needed for focusing of hard x-rays. Such high aspect ratios are challenging to produce by lithography. We are investigating the fabrication of high-aspect-ratio linear zone plates by multilayer deposition followed by sectioning. As an initial step in this work, we present a synchrotron x-ray study of constant-period multilayers diffracting in Laue (transmission) geometry. Data are presented from two samples: a 200 period W/Si multilayer with d-spacing of 29 nm, and a 2020 period Mo/Si multilayer with d-spacing of 7 nm. By cutting and polishing we have successfully produced thin cross sections with section depths ranging from 2 to 12 μm. Transverse scattering profiles (rocking curves) across the Bragg reflection exhibit well-defined interference fringes originating from the depth of the sample, in agreement with dynamical diffraction theory for a multilayer in Laue geometry.
We have implemented in the undulator first-optics enclosure of the Massachusetts Institute of Technology-McGill University-IBM Corporation Collaborative Access Team Sector at the Advanced Photon Source an x-ray beamline and a spectrometer optimized for performing small-angle, wide- bandpass, coherent x-ray scattering experiments. We describe the novel features of this set-up. The performance of the beamline and the spectrometer has been characterized by measuring static x-ray speckle patterns form isotopically disordered aerogels. Statistical analysis of the speckle patterns has been performed from which we extract the speckle width sand contrast versus wave-vector transfer and sample thickness. The measured speckle widths and contrast are compared to direct numerical evaluations of the intensity correlation function. The calculated widths are in poor agreement with the measurements but the calculated contrast agrees well with the measured contrast.
This paper summarizes recent in situ x-ray analyses of the growth of GaAs by organometallic vapor phase epitaxy (OMVPE). This growth was carried out using tertiarybutylarsine (TBAs) and trimethylgallium (TMG) as the source materials. Examples of in situ x-ray measurements are given including x-ray absorption studies of gas phase behavior and x-ray scattering studies of layer-by-layer growth.