We have used microelectromechanical systems (MEMS) to dynamically modulate synchrotron x-ray beams. By oscillating a small silicon crystal at 10s to 100s of kHz, we have demonstrated that the “time window” in which the Bragg condition is satisfied, and thus the time in which an x-ray pulse can be deflected by diffraction, can be significantly less than 1 ns. Here we discuss the optimization of x-ray optics to further improve device performance. We show that the time window can be reduced by matching the dispersion of a monochromator crystal to that of the MEMS crystal. We consider the case of an ideally perfect crystal and also treat the effects of strain and curvature, either of which broadens the crystal rocking curve and thus degrades the time window. A careful understanding of the effects of dispersion and x-ray wavelength produces time windows approaching the typical synchrotron pulse duration.
Time-resolved synchrotron x-ray measurements often rely on using a mechanical chopper to isolate a set of x-ray pulses. We have started the development of micro electromechanical systems (MEMS)-based x-ray optics, as an alternate method to manipulate x-ray beams. In the application of x-ray pulse isolation, we recently achieved a pulse-picking time window of half a nanosecond, which is more than 100 times faster than mechanical choppers can achieve. The MEMS device consists of a comb-drive silicon micromirror, designed for efficiently diffracting an x-ray beam during oscillation. The MEMS devices were operated in Bragg geometry and their oscillation was synchronized to x-ray pulses, with a frequency matching subharmonics of the cycling frequency of x-ray pulses. The microscale structure of the silicon mirror in terms of the curvature and the quality of crystallinity ensures a narrow angular spread of the Bragg reflection. With the discussion of factors determining the diffractive time window, this report showed our approaches to narrow down the time window to half a nanosecond. The short diffractive time window will allow us to select single x-ray pulse out of a train of pulses from synchrotron radiation facilities.
Synchrotron beamlines typically use macroscopic, quasi-static optics to manipulate x-ray beams. We present the use of dynamic microelectromechanical systems-based optics (MEMS) to temporally modulate synchrotron x-ray beams. We demonstrate this concept using single-crystal torsional MEMS micromirrors oscillating at frequencies of 75 kHz. Such a MEMS micromirror, with lateral dimensions of a few hundred micrometers, can interact with x rays by operating in grazing-incidence reflection geometry; x rays are deflected only when an x-ray pulse is incident on the rotating micromirror under appropriate conditions, i.e., at an angle less than the critical angle for reflectivity. The time window for such deflections depends on the frequency and amplitude of the MEMS rotation. We demonstrate that reflection geometry can produce a time window of a few microseconds. We further demonstrate that MEMS optics can isolate x rays from a selected synchrotron bunch or group of bunches. With ray-trace simulations we explain the currently achievable time windows and suggest a path toward improvements.
Grazing-Incidence Small Angle X-ray Scattering (GISAXS) offers the ability to probe large sample areas, providing three-dimensional structural information at high detail in a thin film geometry. In this study we exploit the application of GISAXS to structures formed at one step of the LiNe (Liu-Nealey) flow using chemical patterns for directed self-assembly of block copolymer films. Experiments conducted at the Argonne National Laboratory provided scattering patterns probing film characteristics at both parallel and normal directions to the surface. We demonstrate the application of new computational methods to construct models based on scattering measured. Such analysis allows for extraction of structural characteristics at unprecedented detail.
We demonstrate the use of electrostatically driven micro-electromechanical systems (MEMS) devices to control and deliver synchrotron x-ray pulses at high repetition rates. Torsional MEMS micromirrors, rotating at duty cycles of 2 kHz and higher, were used to modulate grazing-incidence x rays, producing x-ray bunches shorter than 10 μs. We find that dynamic deformation of the oscillating micromirror is a limiting factor in the duration of the x-ray pulses produced, and we describe plans for reaching higher operating frequencies using mirrors designed for minimal deformation.
A novel high-resolution x-ray powder diffractometer has been designed and commissioned at the bending magnet
beamline 11-BM at the Advanced Photon Source (APS), Argonne National Laboratory (ANL). This state-of-the-art
instrument is designed to meet challenging mechanical and optical specifications for producing high-quality powder
diffraction data with high throughput. The 2600 mm (H) X 2100 mm (L) X 1700 mm (W) diffractometer consists of
five subassemblies: a customized two-circle goniometer with a 3-D adjustable supporting base; a twelve-channel high-resolution crystal analyzer system with an array of precision x-ray slits; a manipulator system for a twelve scintillator x-ray detectors; a 4-D sample manipulator with cryo-cooling capability; and a robot-based sample exchange automation system.
The mechanical design of the diffractometer as well as the test results of its positioning performance are presented in
Conventional x-ray imaging relies on the differences in the absorption of the sample to provide image contrast. With the
small source sizes and large source-sample distances at synchrotrons, an additional mechanism, phase contrast, can come
into play. Phase effects, which include refraction and diffraction, can greatly enhance the image contrast. Phase contrast
is particularly useful in cases where the absorption contrast is weak. Added to this, the high x-ray flux available at
synchrotrons allows for unprecedented high-speed and high-resolution x-ray imaging. We demonstrate that high quality
time resolved images with sub-microsecond temporal and micrometer spatial resolutions are feasible. The range of
energy spectrum (5-150 keV) available at the Advanced Photon Source allows us to study a wide range of samples, from
soft tissues to high-Z materials. We will present preliminary results from the steel automobile fuel injectors and liquidair
We have demonstrated that a newly developed, ultrafast x-ray streak camera is sensitive to single x-ray pulses of highly monochromatic and unfocused synchrotron radiation at 8 keV. The high sensitivity was achieved by using CsI as the photocathode material. The individually measured x-ray pulses revealed that the bunch length was 120 ps long (full-width-at-half-maximum) and about 20-30 photon events were registered by streak camera in each pulse at the experimental conditions. The results demonstrated the feasibility of using this streak camera for single-shot experiments and using single x-ray pulses from the third-generation synchrotron sources with microfocused and/or polychromatic beams.
Building blocks with a nanoscale dimension (typically <100nm) have different properties compared with their bulk counterparts. For instance, the absorption and photoluminescence of semiconductor quantum dots show a strong size dependence [1, 2]. Charge injection onto a single quantum dot has to overcome a strong Coulomb charging energy. The magnetic moment of the surface atoms are strongly enhanced due to unquenched orbital moments in transition metal clusters . Fundamentally, all these new phenomena can be attributed to two major effects on the nanometer scale, namely the quantum confinement of charge and spin  and the low coordination of surface atoms . Development in colloidal chemistry during the past two decades has produced a variety of high quality nanoscale building blocks with many unique properties [6-10]. Although it is possible to study and utilize the physical properties of nanoparticles on a single particle level, it remains to be a technically challenging task. On the other hand, experiments on macroscopic 2D and 3D nanocrystal superlattices are more accessible. Self-assembly of nanocrystal building blocks not only provides a way to connect the nanoscale dimension to the macroscopic length scale, but it also creates a revolutionary new class of materials. New collective behavior is expected to emerge because of the strong coupling between building blocks [11, 12].
The detailed analysis of the fuel sprays has been well recognized as an important step for optimizing the operation of internal-combustion engines to improve efficiency and reduce emissions. However, the structure and dynamics of highly transient fuel sprays have never been visualized or reconstructed in three dimensions (3D) previously due to numerous technical difficulties. By using an ultrafast x-ray detector and intense monochromatic x-ray beams from synchrotron radiation, the fine structures and dynamics of 1-ms direct-injection gasoline fuel sprays were elucidated for the first time by a newly developed, ultrafast computed microtomography technique. Due to the time-resolved nature and the intensive data analysis, the Fourier transform algorithm was used to achieve an efficient reconstruction process. The temporal and spatial resolutions of the current measurement are 5.1 μs and 150 μm, respectively. Many features associated with the transient liquid flows are readily observable in the reconstructed spray. Furthermore, an accurate 3D fuel density distribution was obtained as the result of the computed tomography in a time-resolved manner. These results not only reveal the characteristics of automotive fuel sprays with unprecedented details, but will also facilitate realistic computational fluid dynamic simulations in highly transient, multiphase systems.
We demonstrated that the shot-to-shot timing jitter of a streak camera is reduced to 30 fs when it is triggered by a standard kilohertz laser with 1.2% RMS fluctuation. Such small jitter was obtained by improving the response time of deflection plates and the rise-time of a ramp pulse generated by a photoconductive switch, and by operating the photoconductive switch at the optimum working condition. The temporal resolution of the x-ray streak camera operating in accumulation mode is better than 600 femtosecond that is not limited by the timing jitter.
An x-ray streak camera operating in accumulation mode was developed for studying ultrafast dynamics at synchrotron facilities. A laser-triggered photoconductive switch was used as a sweeping unit to obtain low timing jitter. The fast rise time of the ramp pulse generated by the switch (90 ps) combined with the fast response of the traveling wave deflection plates (150 ps) significantly reduced the jitter caused by the shot-to-shot laser fluctuation. At ~1% rms (root mean square) laser energy fluctuation, the resolution of the camera is 1.1 ps when over 5000 laser shots were accumulated. This is two times better than that of the previous design with slower response (300 ps) deflection plates.
Construction of a single-pass free-electron laser (FEL) based on the self-amplified spontaneous emission (SASE) mode of operation is nearing completion at the Advanced Photon Source (APS) with initial experiments imminent. The APS SASE FEL is a proof-of-principle fourth-generation light source. As of January 1999 the undulator hall, end-station building, necessary transfer lines, electron and optical diagnostics, injectors, and initial undulators have been constructed and, with the exception of the undulators, installed. All preliminary code development and simulations have also been completed. The undulator hall is now ready to accept first beam for characterization of the output radiation. It is the project goal to push towards full FEL saturation, initially in the visible, but ultimately to UV and VUV, wavelengths.
This paper describes metrology of a vertically focusing mirror on the bending magnet beamline in sector-1 of the Advanced Photon Source, Argonne National Laboratory. The mirror was evaluated using measurements from both an optical long trace profiler and x-rays. Slope error profiles obtained with the two methods were compared and were found to be in a good agreement. Further comparisons were made between x-ray measurements and results from the SHADOW ray-tracing code.