Machining fused silica surface by continuous-wave CO2 laser beams and their nanostructure characterizations

Fused silica surface machined using continuous-wave CO2 laser beams with an energy density of 0.5 J/mm(2) presented U-shaped grooves (approximately 47 mu m-deep and 250 mu m-wide) and asymmetrical craters (2-5 mu m high). The fully reacted valley in the groove center exhibited porous microstructures and agglomerated silica nanoparticles in the size of 33-118 nm; whereas, the less reacted peak in the groove edge only presented uneven solidified films from silica ablations. Distinct morphologies in the valley and peak areas were supposed to result from the Gaussian energy distribution of laser beams. The selected area electron diffraction pattern suggested that the laser-reacted silica nanostructures were still amorphous with no obvious composition change. The x-ray photoelectron spectrometric results showed that both Si 2p and O 1s peaks shifted to higher energy sides, implying a more oxidized state of Si4+ and absorbed oxygen or hydroxides on nanostructured silica after CO2 laser machining.