Experimental data for the linear thermal expansion coefficient of diamond available in the literature were analyzed and carefully selected to produce a representative dataset, which was fit with a ...multi-frequency Einstein model (R. Reeber, 1975) using a limited number of effective independent oscillators. In the temperature range of 10–300 K, the fits were constrained using the high-accuracy data (S. Stoupin and Yu. Shvyd’ko, 2011). It was found that the multi-frequency model precisely describes the available data from 10 K to approximately 1000 K. Above 1000 K, discrepancies were found, which suggest presence of anharmonic effects in diamond and/or influence of defects. The obtained semi-empirical formulas can be used as convenient continuous approximations for the thermal expansion coefficient in modeling thermoelastic behavior of diamond components subjected to large temperature variations.
Display omitted
•Existing experimental data are approximated with 4-term Einstein model.•The approximation accurately describes the data from 10 K to 1000 K.•Above 1000 K, the best fit to the model requires a high-frequency term.
The Linac Coherent Light Source (LCLS) is an X-ray free-electron laser at the SLAC National Accelerator Laboratory, which has been operating since 2009 for a wide range of scientific research. The ...free-electron laser process at LCLS is based on self-amplified spontaneous emission (SASE) where spontaneous emission from the initial electron beam shot noise is amplified by its interaction with the electrons over a long magnetic undulator. Although SASE is very effective, producing tremendously powerful, ultrashort X-ray beams, the start-up from noise leaves poor temporal coherence and a broad, noisy spectrum. We present experimental results of a new method, suggested by colleagues at DESY, allowing self-seeding using X-rays from the first half of the undulator to seed the second half through a diamond-based monochromator, producing near Fourier-transform-limited X-ray pulses with 0.4-0.5 eV bandwidth at 8-9 keV. These results demonstrate self-seeding at ångstrom wavelengths with a relative bandwidth reduction of 40-50 with respect to SASE.
Abstract
Large laser facilities have recently enabled material characterization at the pressures of Earth and Super-Earth cores. However, the temperature of the compressed materials has been largely ...unknown, or solely relied on models and simulations, due to lack of diagnostics under these challenging conditions. Here, we report on temperature, density, pressure, and local structure of copper determined from extended x-ray absorption fine structure and velocimetry up to 1 Terapascal. These results nearly double the highest pressure at which extended x-ray absorption fine structure has been reported in any material. In this work, the copper temperature is unexpectedly found to be much higher than predicted when adjacent to diamond layer(s), demonstrating the important influence of the sample environment on the thermal state of materials; this effect may introduce additional temperature uncertainties in some previous experiments using diamond and provides new guidance for future experimental design.
The fabrication and performance evaluation of single‐crystal diamond refractive X‐ray lenses of which the surfaces are paraboloids of revolution for focusing X‐rays in two dimensions simultaneously ...are reported. The lenses were manufactured using a femtosecond laser micromachining process and tested using X‐ray synchrotron radiation. Such lenses were stacked together to form a standard compound refractive lens (CRL). Owing to the superior physical properties of the material, diamond CRLs could become indispensable wavefront‐preserving primary focusing optics for X‐ray free‐electron lasers and the next‐generation synchrotron storage rings. They can be used for highly efficient refocusing of the extremely bright X‐ray sources for secondary optical schemes with limited aperture such as nanofocusing Fresnel zone plates and multilayer Laue lenses.
A double‐crystal diamond (111) monochromator recently implemented at the Linac Coherent Light Source (LCLS) enables splitting of the primary X‐ray beam into a pink (transmitted) and a monochromatic ...(reflected) branch. The first monochromator crystal, with a thickness of ∼100 µm, provides sufficient X‐ray transmittance to enable simultaneous operation of two beamlines. This article reports the design, fabrication and X‐ray characterization of the first and second (300 µm‐thick) crystals utilized in the monochromator and the optical assemblies holding these crystals. Each crystal plate has a region of about 5 × 2 mm with low defect concentration, sufficient for use in X‐ray optics at the LCLS. The optical assemblies holding the crystals were designed to provide mounting on a rigid substrate and to minimize mounting‐induced crystal strain. The induced strain was evaluated using double‐crystal X‐ray topography and was found to be small over the 5 × 2 mm working regions of the crystals.
PDF
