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

Abstract

X rays at high photon energies are needed to backlight and image large objects 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 from un-needed low energy components. As the x-ray energy increases, the secondary effect of the interactions of the x rays with the filter or attenuator material must be addressed. This is especially true when one considers using 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 absolute x-ray yield and conversion efficiency with laser energy and power. This investigation is part of the study to determine the feasibility of high-energy backlighters using Ge emission near 10.3 keV. We will also show how these results apply to imaging at larger x-ray energies.