Nanostructuring of surfaces by ultra-short laser pulses

Nanostructuring of an extended surface area is performed by ultra-short-pulse laser ablation in the low-fluence regime. A layer of micrometer-sized quartz spheres is used as a lens array in direct contact with the sample. The thickness of a transparent spacer layer under the spheres is adjusted so that the sample is struck by an array of well-focused spots. The threshold character of the ablation process allows the formation of sub-diffraction-limited structures, down to 500-nm holes with 800-nm light. The deposition of the lens array directly on the surface makes the technique broadly applicable, also to samples that show great variations in height.