Hybrid Femtosecond Laser and Ion-Implantation Processing for Controlled, Deep, High-Efficiency Ablation in Fused Silica

Abstract: Femtosecond laser modification of fused silica enables precise surface tailoring for the fabrication of micro-optical components such as microlenses and diffractive elements. However, the process is governed by laser-matter interactions where the local fluence determines the processing depth, often limiting control over feature geometry and efficiency. Here, we present a hybrid approach combining localized Au implantation (1.8 MeV Au2+ ions) into SiO2 samples with femtosecond laser irradiation (250 fs), effectively tuning the laser-matter interaction and resulting morphology. At both 515 nm and 1030 nm irradiation wavelengths, single-shot femtosecond pulses produce cylindrical craters with sharp edges and flat-bottom profiles. Independently of the fluence, these craters exhibit a constant depth of 550 nm, corresponding to the region of maximum Au concentration. The effect manifests already at moderate fluence (app. 4 J/sq.cm) and yields high ablation efficiency, up to 15 cubic micrometers per microjoule. The hybrid method also works effectively at lower implantation doses that preserve the excellent transmission of fused silica, offering a promising pathway for the high-quality fabrication of flat optical components such as binary phase masks, phase lenses, or fused-silica micromolds.