X-ray preheating of window materials in direct-drive shock-wave timing experiments

Abstract

The optical properties of x-ray preheated planar-window materials relevant for shock-wave timing experiments were studied on the OMEGA Laser System. The x-ray radiation was generated by 100 ps, 1×1015W∕cm2 laser pulses incident on planar plastic targets, instantaneously affecting samples located ∼0.7mm away. An abrupt onset of strong absorption of an optical probe beam (λ=532nm) and a temporally varying refractive index were measured in polystyrene and diamond windows. The behavior of diamond windows exposed to x rays is consistent with a simple model based on the generation of free charge carriers. Polystyrene windows showed indications of optical transitions due to molecular states that are created by the ionizing radiation.