Fluorescence concerns in high energy x-ray yield scaling and imaging studies

X rays at high photon energies are needed to backlight and image large obje cts of high opacity on large lasers, such as the National Ignition Facility , or large pulsed power facilities, such as ATLAS. Attenuators and filters are usually used to bring the signals to scale and to filter the x rays fro m un-needed low energy components. As the x-ray energy increases, the secon dary effect of the interactions of the x rays with the filter or attenuator material must be addressed. This is especially true when one considers usi ng the very high energy x rays from the hot electrons generated during the interaction of intense lasers with high Z materials. We will show how these concerns can be quantified and reduced in at least one case; an experiment on the OMEGA laser facility, designed to investigate the scaling of absolu te x-ray yield and conversion efficiency with laser energy and power. This investigation is part of the study to determine the feasibility of high-ene rgy backlighters using Ge emission near 10.3 keV. We will also show how the se results apply to imaging at larger x-ray energies. (C) 2001 American Ins titute of Physics.