Single-pulse ultrafast-laser machining of high aspect nano-holes at the surface of SiO2

Use of high numerical aperture focusing with negative longitudinal spherical aberration is shown to enable deep (> 10 mu m), high aspect ratio, nano-scale-width holes to be machined into the surface of a fused-silica (SiO2) substrate with single pulses from a 200 fs, 4 mu J Ti-Sapphire laser source. The depths of the nano-holes are characterized by use of a non-destructive acetate replication technique and are confirmed by imaging of sectioned samples with a dual focused ion beam/scanning electron microscope.