Polarization dependent spike formation on black silicon via ultrafast laser structuring

TL;DR

This study investigates how different laser polarizations affect the formation and optical properties of micro-cones on black silicon surfaces, revealing polarization-dependent structural and absorption characteristics.

Contribution

It provides a comparative analysis of how linear, circular, and azimuthal laser polarizations influence micro-structure formation and optical absorption in black silicon.

Findings

Linear polarization causes asymmetric elliptical micro-cones with variable absorption.

Azimuthal polarization results in omni-directional elliptical cones with angle-independent absorption.

Circular polarization produces symmetrical conical structures with consistent optical properties.

Abstract

A comparative experimental and theoretical investigation is presented that centres on the effects of structuring black silicon surfaces with linearly, circularly and azimuthally polarized laser pulses under SF6 ambient atmosphere. It is shown that the asymmetric elliptical micro-cone formations induced by linearly polarized beams result in variable light absorption due to their spatial asymmetry. By contrast, the use of azimuthally polarized beams leads to an omni-directionality of the elliptical cone orientation which is dependent on the local electric field during laser scanning. The locally variant electric field state that is azimuthally polarized leads to a selective conical orientation for the induced structures. The omni-directional conical distribution induced by azimuthal polarization produces similar, angle-independent absorption in the visible spectrum with the symmetrical conical structures that could only be realized with circularly polarized beams.