We argue that the principal features of the plastic flow behavior of Ta can be described a model that incorporates a two-component Peierls-type mechanism and an ``obstacle`` mechanism in series. We compare results of calculations based on such a model with flow data for unalloyed Ta before and after shock loading to 45 GPa for 1.8 {mu}s. Our data suggest that the shock loading changes only structural parameters.

This paper describes the use of Fourier techniques to characterize the transmitted and reflected wavefront of optical components. Specifically, a power spectral density, (PSD), approach is used. High power solid-state lasers exhibit non-linear amplification of specific spatial frequencies. Thus, specifications that limit the amplitude of these spatial frequencies are necessary in the design of these systems. Further, NIF optical components have square, rectangular or irregularly shaped apertures with major dimensions up-to 800 mm. Components with non-circular apertures can not be analyzed correctly with Zernicke polynomials since these functions are an orthogonal set for circular apertures only. A more complete and powerful representation of the optical wavefront can be obtained by Fourier analysis in 1 or 2 dimensions. The PSD is obtained from the amplitude of frequency components present in the Fourier spectrum. The shape of a resultant wavefront or the focal spot of a complex multicomponent laser system can be calculated and optimized using PSDs of the individual optical components which comprise the system. Surface roughness can be calculated over a range of spatial scale-lengths by integrating the PSD. Finally, since the optical transfer function (OTF) of the instruments used to measure the wavefront degrades at high spatial frequencies, the …

We argue that the principal features of the plastic flow behavior of tantalum can be described by a model that incorporates a two-component Peierls-type mechanism and an {open_quotes}obstacle{close_quotes} mechanism in series. We compare the results of calculations based on such a model with flow data for unalloyed tantalum before and after shock loading to 38 GPa for 1 {mu}s. Our data suggest that the shock loading changes only structural parameters.