Interface reaction characterization and interfacial effects in multilayers

The performance of multilayer structures as x-ray, soft x-ray and extreme ultraviolet optics is dependent on the nature of the interfaces between constituent layers. Interfacial structure and the interaction between atoms at interfaces have also been demonstrated to have significant impact on the physical properties of multilayer materials in general and thus on their performance in other applied areas. As short summary of the approaches to characterization of interfaces in multilayer structures is presented as background. Two new techniques for the experimental evaluation of interfacial structure and interfacial structure effects are then considered and examples presented. Model calculations for one of these techniques which support the experimental results are also presented. In conclusion these results are reviewed of and an assessment of their implications relative to multilayer development given

Effect of stress-triaxiality on void growth in dynamic fracture of metals: a molecular dynamics study

The effect of stress-triaxiality on growth of a void in a three dimensional single-crystal face-centered-cubic (FCC) lattice has been studied. Molecular dynamics (MD) simulations using an embedded-atom (EAM) potential for copper have been performed at room temperature and using strain controlling with high strain rates ranging from 10^7/sec to 10^10/sec. Strain-rates of these magnitudes can be studied experimentally, e.g. using shock waves induced by laser ablation. Void growth has been simulated in three different conditions, namely uniaxial, biaxial, and triaxial expansion. The response of the system in the three cases have been compared in terms of the void growth rate, the detailed void shape evolution, and the stress-strain behavior including the development of plastic strain. Also macroscopic observables as plastic work and porosity have been computed from the atomistic level. The stress thresholds for void growth are found to be comparable with spall strength values determined by dynamic fracture experiments. The conventional macroscopic assumption that the mean plastic strain results from the growth of the void is validated. The evolution of the system in the uniaxial case is found to exhibit four different regimes: elastic expansion; plastic yielding, when the mean stress is nearly constant, but the stress-triaxiality increases rapidly together with exponential growth of the void; saturation of the stress-triaxiality; and finally the failure.Comment: 35 figures, which are small (and blurry) due to the space limitations; submitted (with original figures) to Physical Review B. Final versio

MONOCHROMATIC X-RAY AND XUV IMAGING WITH MULTILAYER OPTICS

The development of techniques for the fabrication of multilayer coated mirrors which can function as energy selective X-ray and XUV mirrors at normal incidence has greatly expanded the options available to the astronomical spectroscopist. We have developed a rocket spectroheliograph which utilizes multilayer optics in three configurations : i) As Cassegrain telescopes for imaging at 256 Å (He II) and 173 Å (Fe IX, X ) ; ii) As tertiary mirrors used with a conventional Wolter I telescope for imaging at 44 Å (Si XI, XII), 173 Å, and 256 Å ; iii) As off-axis spherical mirrors for imaging at 44 Å and 256 Å. We report on laboratory images and performance measurements obtained with these optical systems, and briefly on Solar Observations

Modeling and demonstration of a saturated Ni-like Mo X-ray laser

The technique of using a nsec pulse to preform and ionize the plasma followed by a psec pulse to heat the plasma has enabled us to achieve saturated laser output for low-Z neon-like and nickel-like ions driven by small lasers with less than ten joules of energy. In this work we present and model recent experiments done using the COMET laser at Lawrence Livermore National Laboratory to illuminate slab targets of Mo up to 1 cm long with a one joule, 600 ps prepulse followed 700 psec later by a five joule, one psec drive pulse. The experiments demonstrate saturated output on the Ni-like Mo [MATH] laser line at 18.9 nm. The small signal gain and gain length product are estimated by measuring the laser output versus target length. Experiments are done using multilayer mirrors to obtain two-dimensional images of the output aperture of the laser and to measure the total laser energy as a function of various parameters such as the delay between the short and long pulses and the energy of the two pulses. To model the experiments the LASNEX code is used to calculate the hydrodynamic evolution of the plasma and provide the temperatures and densities to the XRASER code, which then does the kinetics calculations to determine the gain. The temporal and spatial evolution of the plasma is studied both with and without radiation transport included for the [MATH] Ni-like Mo resonance lines. High gains are predicted for both the [MATH] laser line at 18.9 nm and the [MATH] photopumped line which is observed to lase at 22.6 nm

XUV polarimeter for undulator radiation measurements

A polarimeter for x-ray and vacuum ultraviolet (XUV) radiation was built to measure the spatial spectral dependence of the polarization of the light produced by the new undulator at the U5 beamline at NSLS. The fourth-harmonic radiation was measured, and it does not agree with predictions based on ideal simulation codes in the far-field approximation. 13 ref., 7 figs