Vertically standing nano-pillars by ultrafast first-order Bessel beam

Abstract

The invariant longitudinal spatial profile of the Bessel beam makes it attractive for laser processing. We show a fast and simple process to generate high aspect ratio nano-pillars using a single ultrafast pulse shaped as higher order Bessel beam. The high pressure induced in the sapphire bulk results in the ejection of elongated structures. These nano-pillars can exceed 15 μm in height with a sub-μm diameter. The observed morphologies suggest a model with different material ejection processes, ranging from solid material extraction to hydrodynamic jets. High-resolution transmission electron microscopy of the crystalline structure provides support for our proposed model.