Time-resolved probing of the acoustic field radiated by a single submicron gold particle

Abstract

Transient reflectivity pump-probe experiments are performed on a single gold particle to analyze the vibration of the particle as well as the propagation of the resulting GHz acoustic wave in the embedding medium. In a first part, the vibration of a single 430 nm diameter gold particle embedded in a silica matrix is investigated. A semi-analytical model is presented and demonstrates that the detection mechanism relies on an intrinsic common-path interferometer which directly images the particle interface displacement. The coherent phonon propagation inside the embedding medium is then studied in the case of a gold particle embedded in an agarose gel. A comparison between experimental results and calculations suggests a detection of the Brillouin scattering in agarose, so long as the Brillouin frequency at the considered probe wavelength matches the fundamental breathing mode frequency (or one of its harmonics) of the particle.