X-ray scattering is typically used as a weak linear atomic-scale probe of matter. At high intensities, such as produced at free-electron lasers, nonlinearities can become important, and the probe may ...no longer be considered weak. Here we report the observation of one of the most fundamental nonlinear X-ray-matter interactions: the concerted nonlinear Compton scattering of two identical hard X-ray photons producing a single higher-energy photon. The X-ray intensity reached 4 × 1020 W cm-2, corresponding to an electric field well above the atomic unit of strength and within almost four orders of magnitude of the quantum-electrodynamic critical field. We measure a signal from solid beryllium that scales quadratically in intensity, consistent with simultaneous non-resonant two-photon scattering from nearly-free electrons. The high-energy photons show an anomalously large redshift that is incompatible with a free-electron approximation for the ground-state electron distribution, suggesting an enhanced nonlinearity for scattering at large momentum transfer.
X-ray sources continue to advance in both intensity and temporal domains, thereby opening new ways to analyze the structure and properties of matter, provided that the resultant x-ray images can be ...efficiently and quantitatively recorded. In this perspective we focus on specific limitations of pixel area x-ray detectors. Although pixel area x-ray detectors have also advanced in recent years, many experiments are still detector limited. Specifically, there is need for detectors that can acquire successive images at GHz rates; detectors that can accurately measure both single photon and millions of photons per pixel in the same image at frame rates of hundreds of kHz; and detectors that efficiently capture images of very hard x-rays (20 keV to several hundred keV). The data volumes and data rates of state-of-the-art detection exceeds most practical data storage options and readout bandwidths, thereby necessitating on-line processing of data prior to, or
in lieu
of full frame readouts.
A prototype ePix100 detector was used in small‐angle scattering geometry to capture speckle patterns from a static sample using the Linac Coherent Light Source (LCLS) hard X‐ray free‐electron laser ...at 8.34 keV. The average number of detected photons per pixel per pulse was varied over three orders of magnitude from about 23 down to 0.01 to test the detector performance. At high average photon count rates, the speckle contrast was evaluated by analyzing the probability distribution of the pixel counts at a constant scattering vector for single frames. For very low average photon counts of less than 0.2 per pixel, the `droplet algorithm' was first applied to the patterns for correcting the effect of charge sharing, and then the pixel count statistics of multiple frames were analyzed collectively to extract the speckle contrast. Results obtained using both methods agree within the uncertainty intervals, providing strong experimental evidence for the validity of the statistical analysis. More importantly it confirms the suitability of the ePix100 detector for X‐ray coherent scattering experiments, especially at very low count rates with performances surpassing those of previously available LCLS detectors.
A prototype unit of the ePix100 camera was used for coherent scattering studies at the Linac Coherent Light Source. The performance of the detector was tested over a broad range of incident flux from 23 down to 0.01 photons per pixel on average.
The Vertically Integrated Photon Imaging Chip (VIPIC) project explores opportunities of the three-dimensional integration for imaging of X-rays. The design details of the VIPIC1 chip are presented ...and are followed by results of testing of the chip. The VIPIC1 chip was designed in a 130 nm process, in which through silicon vias are embedded right after the front-end-of-line processing. The integration of tiers is achieved by the Cu-Cu thermo-compression or Cu-based oxide-oxide bonding. The VIPIC1 readout integrated circuit was designed for high timing resolution, pixel based, X-ray Photon Correlation Spectroscopy experiments typically using 8 keV X-rays at a synchrotron radiation facility. The design was done for bonding a Silicon pixel detector, however other materials can be serviced as long as the positive polarity of charge currents is respected.
The Vertically Integrated Photon Imaging Chip (VIPIC) was custom‐designed for X‐ray photon correlation spectroscopy, an application in which occupancy per pixel is low but high time resolution is ...needed. VIPIC operates in a sparsified streaming mode in which each detected photon is immediately read out as a time‐ and position‐stamped event. This event stream can be fed directly to an autocorrelation engine or accumulated to form a conventional image. The detector only delivers non‐zero data (sparsified readout), greatly reducing the communications overhead typical of conventional frame‐oriented detectors such as charge‐coupled devices or conventional hybrid pixel detectors. This feature allows continuous acquisition of data with timescales from microseconds to hours. In this work VIPIC has been used to measure X‐ray photon correlation spectroscopy data on polystyrene latex nano‐colliodal suspensions in glycerol and on colloidal suspensions of silica spheres in water. Relaxation times of the nano‐colloids have been measured for different temperatures. These results demonstrate that VIPIC can operate continuously in the microsecond time frame, while at the same time probing longer timescales.
Preliminary X‐ray correlation spectroscopy results from the novel three‐dimensional vertically integrated photon imaging chip (VIPIC) detector are presented.
Charge-pump detector for X-ray correlation spectroscopy Carini, Gabriella A.; Rehak, Pavel; Chen, Wei ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2011, Letnik:
649, Številka:
1
Journal Article
Recenzirano
A detector for the X-ray Correlation Spectroscopy (XCS) instrument at the Linac Coherent Light Source (LCLS) in Stanford (CA) is being developed at Brookhaven National Laboratory (BNL). The LCLS is ...the first operational X-ray free electron laser. It provides extremely bright coherent laser-like X-ray pulses with energy up to 8
keV, shorter than 100
fs and with a repetition rate that will go up to 120
Hz.
An ideal detector for XCS experiments should cover a large angular range with high efficiency and provide a proper resolution to resolve the speckle. The requirement for dynamic range is not particularly stringent while a fast readout is needed. In particular, the Charge Pump Detector has to be highly efficient at the energy of 8
keV, provide a dynamic range of 100 photons and a readout noise much better than one photon. The 1024×1024 pixels have to be read within the repetition rate of the laser pulses, that is faster than 8
ms. The pixel size of 56
μm×56
μm is a compromise between charge sharing and small pixel.
Working principle and details of the detector will be discussed.
A well-characterized wavefront is important for many x-ray
free-electron laser (XFEL) experiments, especially for single-particle
imaging (SPI), where individual biomolecules randomly sample a
...nanometer region of highly focused femtosecond pulses. We demonstrate
high-resolution multiple-plane wavefront imaging of an ensemble of
XFEL pulses, focused by Kirkpatrick–Baez mirrors, based on mixed-state
ptychography, an approach letting us infer and reduce experimental
sources of instability. From the recovered wavefront profiles, we show
that while local photon fluence correction is crucial and possible for
SPI, a small diversity of phase tilts likely has no impact. Our
detailed characterization will aid interpretation of data from past
and future SPI experiments and provides a basis for further
improvements to experimental design and reconstruction algorithms.
Single-particle diffraction from X-ray Free Electron Lasers offers the potential for molecular structure determination without the need for crystallization. In an effort to further develop the ...technique, we present a dataset of coherent soft X-ray diffraction images of Coliphage PR772 virus, collected at the Atomic Molecular Optics (AMO) beamline with pnCCD detectors in the LAMP instrument at the Linac Coherent Light Source. The diameter of PR772 ranges from 65-70 nm, which is considerably smaller than the previously reported ~600 nm diameter Mimivirus. This reflects continued progress in XFEL-based single-particle imaging towards the single molecular imaging regime. The data set contains significantly more single particle hits than collected in previous experiments, enabling the development of improved statistical analysis, reconstruction algorithms, and quantitative metrics to determine resolution and self-consistency.
Several sets of hexagonal Silicon Drift Detector (SDD) arrays were produced by Brookhaven National Laboratory (BNL) and by the commercial vendor, KETEK. These detector arrays were tested at BNL. Each ...array consists of 14 independent SDD detectors (pixels) and two additional test pixels located at two corners of the array. The side of the detector upon which the X-ray radiation is incident (window side) has a thin junction covering the entire active area. The opposite side (device side) contains a drift-field electrode structure in the form of a hexagonal spiral and an electron collecting anode. There are four guard rings surrounding the 14-pixel array area on each side of the detector. Within each array, seven pixels have aluminum field plates - interrupted spirals that stabilize the electric potential under the Si- SiO 2 interface, while the other seven do not. Three bias voltages are applied to control the drift field in the silicon volume; one is applied to a rectifying contact surrounding the central anode (one for each pixel), one is applied to the detector entrance window (common to the full array), and a third bias is applied to a contact on the outer portion of the spiral, common to all pixels in the array. Some arrays were recently tested in NSLS beam line U3C at BNL. For this work, we installed the complete assemblies in the vacuum and cooled them to -27degC. During this beam run, we collected spectra for energies ranging between 350 and 900 eV in several pixels, some with field plates and others without. The detailed testing results of several arrays are reported here.
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