Brillouin observation of bulk and confined acoustic waves in silica microspheres

Abstract

Nine batches of loose monodisperse silica microspheres were investigated as a function of their diameter (140 nm to 4 μm). The Brillouin measurements were made at room temperatures using a (3+3)-pass tandem Fabry-Perot interferometer equipped with a silicon avalanche diode detector. It was observed that the dependence of the confined acoustic mode frequencies on the diameters of the loose silica microspheres accorded well with Lamb's theory. The results show bulk acoustic modes in the larger microspheres, suggesting that the limiting size of a particle is about three times their wavelength.