RESUMEN
The study of Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities in a planar geometry at high energy densities at the National Ignition Facility (NIF) requires high spatial resolution imaging. We demonstrate the potential of Fresnel zone plates (FZPs) to achieve resolution that would unlock such studies. FZPs are circular aperiodic gratings that use diffraction to focus x rays and produce an image with high spatial resolution. Taking into account the NIF's challenging environment, we have designed a specific array of five FZPs for a zinc backlighter to take a radiograph of a target with 9 keV x rays. We measured a mean resolution for the FZP of 1.9µm±0.5µm and a ±1mm depth of focus at an x-ray calibration facility as well as a 2.3µm±0.4µm resolution on a resolution wire mesh shot on the NIF. We also performed an in-depth analysis of the image quality to assess the capability to resolve the small features present in RT and RM instabilities.
RESUMEN
Traditional multilayer reflective optics that have been used in the past for imaging at x-ray photon energies as high as 200 keV are governed by classical wave phenomena. However, their behavior at higher energies is unknown, because of the increasing effect of incoherent scattering and the disagreement between experimental and theoretical optical properties of materials in the hard x-ray and gamma-ray regimes. Here, we demonstrate that multilayer reflective optics can operate efficiently and according to classical wave physics up to photon energies of at least 384 keV. We also use particle transport simulations to quantitatively determine that incoherent scattering takes place in the mirrors but it does not affect the performance at the Bragg angles of operation. Our results open up new possibilities of reflective optical designs in a spectral range where only diffractive optics (crystals and lenses) and crystal monochromators have been available until now.
RESUMEN
The first X-ray free electron laser (XFEL) at keV energies will be the Linac Coherent Light Source (LCLS), located at the SLAC National Accelerator Laboratory. Scheduled to begin operation in 2009, this first-of-a-kind X-ray source will produce ultra-short X-ray pulses of unprecedented brightness in the 0.8 to 8 keV first harmonic photon energy regime. Much effort has been invested in predicting and modeling the XFEL photon source properties at the undulator exit; however, as most LCLS experiments are ultimately dependent on the beam focal spot properties it is equally as important to understand the XFEL beam at the endstations where the experiments are performed. Here, we use newly available precision surface metrology data from actual LCLS mirrors combined with a scalar diffraction model to predict the LCLS beam properties in the experiment chambers.