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

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, 1x10(15) W/cm(2) laser pulses incident on planar plastic targets, instantaneously affecting samples located similar to 0.7 mm away. An abrupt onset of strong absorption of an optical probe beam (lambda=532 nm) 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. (c) 2006 American Institute of Physics.