We will discuss the optical design for a proposed beamline at NSLS-II, a late-third generation storage ring source, designed to exploit the spatial coherence of the X-rays to extract high-resolution spatial information from ordered and disordered materials through Coherent Diffractive Imaging, executed in the Bragg- and forward-scattering geometries. This technique offers a powerful tool to image sub-10 nm spatial features and, within ordered materials, sub-Angstrom mapping of deformation fields. Driven by the opportunity to apply CDI to a wide range of samples, with sizes ranging from sub-micron to tens-of-microns, two optical designs have been proposed and simulated under a wide variety of optical configurations using the software package Synchrotron Radiation Workshop. The designs, their goals, and the results of the simulation, including NSLS-II ring and undulator source parameters, of the beamline performance as a function of its variable optical components is described.
At the Lawrence Livermore National Laboratory (LLNL) we have engineered a silicon prototype sample that can be used to reflect focused hard x-ray photons at high intensities in back-scattering geometry.1 Our work is motivated by the need for an all-x-ray pump-and-probe capability at X-ray Free Electron Lasers (XFELs) such as the Linac Coherent Light Source (LCSL) at SLAC. In the first phase of our project, we exposed silicon single crystal to the LCLS beam, and quantitatively studied the x-ray induced damage as a function of x-ray fluence. The damage we observed is extensive at fluences typical of pump-and-probe experiments. The conclusions drawn from our data allowed us to design and manufacture a silicon mirror that can limit the local damage, and reflect the incident beam before its single crystal structure is destroyed. In the second phase of this project we tested this prototype back-reflector at the LCLS. Preliminary results suggest that the new mirror geometry yields reproducible Bragg reflectivity at high x-ray fluences, promising a path forward for silicon single crystals as x-ray back-reflectors.
The recent success of the X-ray Free Electron Lasers has generated great interests from the user communities of a wide range of scientific disciplines including physics, chemistry, structural biology and material science, creating tremendous demand on FEL beamtime access. Due to the serial nature of FEL operation, various beam-sharing techniques have been investigated in order to potentially increase the FEL beamtime capacity. Here we report the recent development in using thin diamond single crystals for spectrally splitting the FEL beam at the Linac Coherent Light Source, thus potentially allowing the simultaneous operation of multiple instruments. Experimental findings in crystal mounting and its thermal performance, position and pointing stabilities of the reflected beam, and impact of the crystal on the FEL transmitted beam profile are presented.
The Linear Coherent Light Source (LCLS), a free electron laser operating from 250eV to10keV at 120Hz, is opening windows on new science in biology, chemistry, and solid state, atomic, and plasma physics<sup>1,2</sup>. The FEL provides coherent x-rays in femtosecond pulses of unprecedented intensity. This allows the study of materials on up to 3 orders of magnitude shorter time scales than previously possible. Many experiments at the LCLS require a detector that can image scattered x-rays on a per-shot basis with high efficiency and excellent spatial resolution over a large solid angle and both good S/N (for single-photon counting) and large dynamic range (required for the new coherent x-ray diffractive imaging technique<sup>3</sup>). The Cornell-SLAC Pixel Array Detector (CSPAD) has been developed to meet these requirements. SLAC has built, characterized, and installed three full camera systems at the CXI and XPP hutches at LCLS. This paper describes the camera system and its characterization and performance.
An inline diagnostics device was developed to measure the intrinsic shot-to-shot intensity and position fluctuations of
the SASE-based LCLS hard X-ray FEL source. The device is based on the detection of back-scattered X-rays from a
partially-transmissive thin target using a quadrant X-ray diode array. This intensity and position monitor was tested for
the first time with FEL X-rays on the XPP instrument of the LCLS. Performance analyses showed that the relative
precision for intensity measurements approached 0.1% and the position sensitivity was better than 5 μm, limited only by
the Poisson statistics of the X-rays collected in a single shot.
Results of coherent diffractive imaging experiments performed with soft X-rays (1-2 keV) at the Linac Coherent
Light Source are presented. Both organic and inorganic nano-sized objects were injected into the XFEL beam
as an aerosol focused with an aerodynamic lens. The high intensity and femtosecond duration of X-ray pulses
produced by the Linac Coherent Light Source allow structural information to be recorded by X-ray diffraction
before the particle is destroyed. Images were formed by using iterative methods to phase single shot diffraction
patterns. Strategies for improving the reconstruction methods have been developed. This technique opens
up exciting opportunities for biological imaging, allowing structure determination without freezing, staining or
The penetrating nature and atomic-scale wavelength of X-ray radiation
makes the possibility of an X-ray microscope a very exciting prospect.
Unfortunately, existing X-ray optics are far less efficient than
their visible light counterparts. An attractive alternative to optics
is computational inversion of the far-field coherent X-ray diffraction (CXD), which can be measured using modern X-ray sources.
Thus we seek to defeat the so-called phase problem by iteratively seeking a set of phases consistent with the CXD measurement and some physical real-space constraints. We have found the behavior of fitting algorithms to be qualitatively different for simulated diffraction patterns and measured coherent X-ray intensity patterns. We will compare the convergence of the inversion of CXD patterns from simply shaped metal crystals with simulation.