Micro-drilling of alkali-silicate glass with ultraviolet picosecond laser
Abstract
The low efficiency of UV-laser ablation of transparent alkali-silicate glass has been increased by means of irradiation by 60Co γ-quanta to doses 104 −107 Gy to induce intensive UV-visible coloration. Varying the picosecond pulse energy of Nd:YAG laser at 4-harmonics 266 nm within 1−9 mJ and pulse number, arrays and grids of holes were drilled with diameters from 9 to 40 µm on area up to 1×1 cm2 . Shock waves of 4−5 µm were generated by expanding plasma around ablated holes at focused pulse energy density >108 J/m2 and nanoscale crystallization occurred there. Besides, a submicron hole was drilled aside the central micron hole due to generation of vacuum UV harmonics. The combined effect of γ-irradiation followed by UV laser drilling has resulted in decrease of silicon and oxygen contents, and generation of fluorine that may be caused by photonuclear reactions 28Si14→19F9+ 33Т1; 16O8→44He2; 16О8+3Т1→19F9. Because of glass viscosity and relaxation during 2 months at 300 K, the exit diameter of drilled holes has increased up to the entry one. Such micro-scale grids can be used for separating liquid mixtures or cleaning water.