Optimization of a short-pulse-driven Si Heα soft x-ray backlighter

Abstract

High backlighter brightness is important to maximize the number of detected photons in radiography experiments and to minimize the background while backlighting high-energy-density plasmas with strong self-emission. Several different configurations were tested to improve the brightness of the Si He_α x-ray line emission at a photon energy of 1865 eV from high-energy (>1 kJ), short-pulse (∼20 ps), laser-driven backlighter targets. The emission from low-density SiO₂ foam targets, the effects of a laser prepulse, and Si targets with a CH “shield” that form a small cavity were compared to solid-density, flat Si targets. The CH “shield” targets showed the best performance with a>5×improvement in time-integrated emission and an x-ray pulse duration of ∼25 ps with no measurable spectral shift of the Si He_α emission line. A conversion efficiency from laser light into Si He_α photons on the order of 1 × 10^–5 was inferred from the data.