Femtosecond Nanostructuring of Glass with Optically Trapped Microspheres and Chemical Etching

Aleksander Shakhov, Artyom Astafiev, Alexander Gulin, and Victor A. Nadtochenko

Laser processing with optically trapped microspheres is a promising tool for nanopatterning at sub-diffraction limited resolution in a wide range of technological and biomedical applications. In this paper, we investigate sub-diffraction limited structuring of borosilicate glass with femtosecond pulses in the near-field of optically trapped microspheres combined with chemical post-processing. Glass surface was processed by single laser pulses at 780 nm focused by silica microspheres and then subjected to selective etching in KOH, which produced pits in the laser affected zones (LAZs). Chemical post-processing allowed obtaining structures with better resolution and reproducibility. We demonstrate production of reproducible pits with diameter as small as 70 nm (λ/11). Complex 2-Dimensional structures with 100 nm (λ/8) resolution were written on the glass surface point by point with microspheres manipulated by optical tweezers. Furthermore, the mechanism of laser modification underlying selective etching was investigated with mass-spectrum analysis. We propose that increased etching rate of laser-treated glass result from change in its chemical composition and oxygen deficiency.

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