Ablation of black-Si by (Gauss-)Bessel femtosecond laser beams

TL;DR

This study compares femtosecond Gaussian and Gauss-Bessel laser beams for black-Si modification, revealing that Bessel beams enable more precise, deeper ablation at lower fluences, significantly reducing damage and enhancing near-IR transmittance.

Contribution

It demonstrates that Gauss-Bessel beams allow for more efficient and precise black-Si ablation with lower fluence and higher aspect ratios than Gaussian beams, advancing laser processing techniques.

Findings

Bessel beams achieve deeper, more precise ablation at lower fluences.

The aspect ratio of ablated grooves with Bessel beams is twice that of Gaussian beams.

Reflectivity of nanotextured black-Si is strongly reduced, with >95% transmittance in near-IR.

Abstract

Laser machining and modification of black-Si (b-Si) by femtosecond laser Gaussian (G-) and Gauss-Bessel (GB-) beams are compared at a wavelength of 1030 nm. The GB-beam was generated using a diffractive axicon lens and 10x demagnification optics. It was found that modification of b-Si well below (a factor 50x) the single pulse ablation fluence of 0.2 J/cm2 was possible, corresponding to ablation/melting of nano-needles. The width of modification was almost independent of pulse energy/fluence and had a width of 1/e2-intensity profile at the melting regime. For the GB-beam, the smallest width of laser modification at 0.2 J/cm2 threshold (at the center core) was close to the FWHM of the core of the GB-beam. The aspect ratio of the ablated groove on the surface of b-Si made by GB-beam was twice as large - up to 8 - compared to that achievable with G-beam, and it was at a lower fluence of 4 J/cm2 (50x reduction). Reflectivity of two-side nanotextured b-Si on plasma-thinned 70-micrometers thick Si was strongly reduced in the near-IR range, reaching transmittance >95% at 1.7-2.1 micrometres wavelengths.