Single Shot Generation of High-Aspect-Ratio Nano-Rods from Sapphire by Ultrafast First Order Bessel Beam

Engineering the polarization and spatial phase of ultrafast laser pulses represents a compelling strategy for enhancing control over laser-matter interaction and enabling rapid and innovative nano-fabrication processes. Here, the single-shot, ultrafast laser fabrication of high-aspect-ratio, vertically standing nano-pillars with a diameter of approximate to 800 nm and height up to 15 mu m on the surface of sapphire, is reported. To achieve this, the distinctive properties of diffraction-free, first-order Bessel beams endowed with either radial or azimuthal polarization distributions, are harnessed under tight focusing conditions. The highly intense laser-matter interaction in this configuration generates a tubular-shaped, high-pressure field beneath the material surface, leading to the rapid expulsion of material across the surface. Three distinct regimes for the pillar generation are identified in addition to a mechanism based on the Rayleigh-Plateau theory that explains the distinct morphological regimes observed. The findings not only shed light on the underlying physical mechanisms of intense excitation of transparent dielectrics but also offer exciting prospects for the rapid fabrication of positive nano-structures and material compression across various fields of application. Single femtosecond laser pulses can produce high aspect ratio positive nanostructures. Using a higher-order Bessel beam, high pressure and temperature conditions are reached to enable the translation of a high aspect ratio nano-rod from the bulk of sapphire. Several morphologies of vertically-standing nanopillars can be generated and explained.image