Abstract
Nanosecond-resolved shadowgraphs and optical emission spectra were observed for the laser ablation of a silver plate in water to investigate the formation process of nanoparticles. Optical emissions, a shockwave, and a cavitation bubble were generated sequentially from the target surface after laser irradiation. In the optical emission spectra, continuous bands were observed, which were probably attributable to bremsstrahlung and/or electron–ion recombination. These findings suggest that materials emitted by laser ablation were confined by the surrounding water causing high pressure, which etches the target surface. Results show that nanoparticles are formed in the cavitation bubbles rather than in the bulk water from materials that were emitted via both direct laser ablation and secondary etching. In addition, a second shockwave was observed upon the collapse of the cavitation bubble, indicating that another secondary etching process might accompany nanoparticle formation.