Nonuniformity imprint on the ablation surface of laser-irradiated targets

The first high-resolution (spatial and temporal) 2D images of the density region close to the ablation surface of laser-irradiated targets are obtained using a novel x-ray imaging technique. These show that laser intensity nonuniformities imprint themselves onto the cold target surface, even if these exist only on short {}10 ps time scales as is the case with a laser beam smoothed by induced spatial incoherence. This imprint phenomenon is interpreted in terms of the poor thermal smoothing under the conditions prevailing at the beginning of the pulse. It appears that the problem can be combatted by preforming a uniform plasma before interacting with the optical drive.