Formation of nanofibers and microspheres by femtosecond laser ablation of chalcogenide glasse

Abstract

Formation of nano-fibers ranging from 30 to 300 nm in diameter and exceeding the length of one millimeter was observed during explosive ablation of As2S3 glass by femtosecond pulses at high fluence (> 5 J/cm2) irradiation of the 800 nm wavelength, 160 fs duration pulses in air. However, the spheres of up to several microns in diameter are found to form competing with nano-fiber formation and significantly deteriorating their morphology. The formation of these spheres is explained by the free energy minimization of explosively ablating liquid jets combined with the onset and evolution of the thermo-capillary forces at the local perturbations of the geometry and temperature. Performed thermal analysis suggests that the good nano-fiber morphology can be preserved by increasing the air pressure or ablation in water which shortens the characteristic cooling and solidification time of the liquid jets, and inhibits the development of the small geometrical perturbations into the large spheres.