Computational Modeling of Pulsed Laser-Induced Heating and Evaporation of Gold Nanoparticles

Pulsed-laser-induced size reduction of plasmonic nanoparticles in solution has long been known for a drawback resulting from polydispersed products. Recently, by adjusting external pressure, laser intensity, and excitation wavelength, the nanosecond pulsed-laser excitations of colloidal gold nanoparticles in pressurized aqueous solution were found to enable tuning of the particle size and size distribution. Nevertheless, the mechanism underlying the phenomenon is poorly understood. Here we propose a model based on temperature calculations via the two-temperature model coupled to a surface evaporation mechanism. Incorporating the temperature-induced plasmon band bleaching during the excitation is crucial. Our computational result indicated that the photothermal evaporation of gold nanoparticles of a given size occurred at temperatures below the boiling point of bulk gold, leading to a smaller particle diameter with increasing laser fluence; the result qualitatively explains the experiment. The method developed here to calculate temperature is applicable to various nanoscale experiments including surface-enhanced Raman spectroscopy, where a proper assessment is indispensable when treating photothermal effects of plasmonic nanoparticles under illumination by pulsed and focused continuous lasers.