Direct femtosecond laser ablation of copper with an optical vortex beam

Abstract

Laser surface structuring of copper is induced by laser ablation with a femtosecond optical vortex beam generated via spin-to-orbital conversion of the angular momentum of light by using a q-plate. The variation of the produced surface structures is studied as a function of the number of pulses, N, and laser fluence, F. After the first laser pulse (N¼1), the irradiated surface presents an annular region characterized by a corrugated morphology made by a rather complex network of nanometer-scale ridges, wrinkles, pores, and cavities. Increasing the number of pulses (2<N<100), the surface texture progressively evolves towards larger structures, while the central, non-ablated area is gradually decorated by nanoparticles produced during laser ablation. At large number of pulses (200<N<1000), a micro-tip with a nanostructured surface forms in the center of the irradiated area, which eventually disappears at still larger number of pulses (N>1000) and a deep crater is formed. The nanostructure variation with the laser fluence, F, also evidences an interesting dependence, with a coarsening of the structure morphology as F increases. Our experimental findings demonstrate that direct femtosecond laser ablation with optical vortex beams produces interesting patterns not achievable by the more standard beams with a Gaussian intensity profile. They also suggest that appropriate tuning of the experimental conditions (F, N) can allow generating micro- and/or nano-structured surface for any specific application

Direct Femtosecond Laser Surface Structuring with Optical Vortex Beams Generated by a q-plate

“…Polarization is an intrinsic and key element of light and the use of laser beams with a spatially inhomogeneous state of polarization (SoP) is bringing out novel breakthroughs on the horizon of fs laser material processing 8 9 . The possibility to use vector optical fields to directly fabricate surface microstructures is emerging as a fascinating possibility and is proposed as an effective method for vector beams characterization 10 11 12 as well as for unconventional surface structuring 13 14 15 16 . One interesting possibility to obtain an unconventional distribution of SoP is provided by a beam with non-vanishing orbital angular momentum 17 .…”

Laser ablation of silicon induced by a femtosecond optical vortex beam

“…In particular, the current development of efficient beam converters generating powerful fs optical vortex pulses offers the possibility of observing new experimental aspects in this emerging topic [11][12][13][14][15]. The use of optical vortex (OV) beams in fs laser ablation and surface structuring has recently led to the generation of subwavelength ring structures on silicon or glass [12,13] and the production of surface microstructures on stainless steel, silicon, and copper [15][16][17][18]. These microstructures display a clear relationship with the spatial distribution of laser beam intensity and polarization.…”

Q-plate technology: a progress review [Invited]

“…Q-plates have been used quite extensively in the last four years to produce both pure OAM beams and vector-vortex beams to be used for laser ablation of metals and semiconductors. Amoruso and coworkers [88][89][90][91][92][93][94][95] have shown a variety of novel and interesting effects connected to the contemporary presence of structured wavefronts and ultra-short pulses. The central part of the ablated area (which corresponds to the hole of the doughnut, the singular point with vanishing intensity) is not affected by ablation, as one could expect, but only for low values of irradiation and number of shots.…”

“…The investigation of this multi-focus topic has continued in many directions: ablation on metal surfaces [88], the use of ablation patterns to characterize the Laguerre-Gauss vector beams [95], and the use of partially converted beams (or complex superpositions of OAM eigenstates) for generating non-standard shapes, which could be used, for instance, to create laser-ablated periodic sub-wavelength structures (meta-materials) [94].…”