Fabricating ultrafine particles by laser ablation of microspheres.

摘要

In this work a new method for fabricating ultrafine glass particles that employs laser ablation of microspheres (LAM) has been developed and investigated. Pulsed-laser radiations with wavelengths of 249 nm, 0.53 ;Overall results showed that the mean diameter of particles generated was in the range from 60 to 120 nm, and particle size distributions were closely log-normal with small geometric standard deviations. Results also showed that at a fixed laser wavelength, the mean particle diameter was generally inversely proportional to laser fluence, while at a fixed laser fluence, the particle size is proportional to the laser wavelength. However, one exception occurred at the wavelength of 0.53 ;Three different mechanisms that governed the laser ablation of glass microspheres were found. Depending on the energy absorbed by the microspheres, the ultrafine particles were formed either by the explosive breakup of the microspheres in liquid-phase at low fluence levels (;A computer simulation, based on Lorentz-Mie theory, was performed to determine the heat absorption by glass microspheres irradiated by a laser pulse. By assuming the temperature independence of the microsphere's density, specific heat, and time dependence of laser pulse irradiation, we obtained initial results that showed that the local temperature and the volume-averaged temperature rises within the microsphere were a function of optical properties of the glass, microsphere size, laser wavelength, and fluence. These results helped to explain the observed nanoparticle size and size distribution.