Time-resolved investigation of laser-induced shape transformation of silver nanoparticles

Abstract

Laser-induced permanent shape transformation dynamics of glass-embedded silver nanoparticles is investigated by a pulse-pair irradiation technique, where the nanoparticles are irradiated by pairs of time-delayed femtosecond laser pulses. The temporal evolution of surface plasmon extinction bands is obtained up to a time delay of 1 ns. We find that the aspect ratio of the modified nanoparticles, i.e., the observed dichroism, reduces rapidly to a minimum level within 20 ps after the laser irradiation. From that interpulse delay onward, the resulting aspect ratio stays at that minimum level until 100 ps. Subsequently, for longer time delays, the aspect ratio increases again until 1 ns. Temperature modeling of the nanoparticle-glass system gives evidence that the intermediately reduced dichroism is due to the high diffusion mobility that emitted silver ions can possess within a shell of heated glass around the nanoparticle, in a time window of 100 ps. For longer time delays the size of the heated glass shell gets reduced, thereby limiting the range of ionic diffusion. The theoretical estimations confirm the experimental results and suggest that the nanoparticle shape changes depend strongly on the thermal situation induced to the surrounding glass.