Photo-acoustic response of a single 430 nm gold particle: Semi-analytical model and picosecond ultrasonics measurements

A semi-analytical model is developed to calculate the elastic response of a gold submicronic particle embedded in a silica thin film, following a subpicosecond optical excitation. Real and imaginary parts of the transient reflectivity are then derived, accounting for elasto-optic contribution in the particle and in the matrix, as well as particle and film surface motion. The major contribution comes from the particle surface displacement. Picosecond ultrasonics measurements in a reflection configuration on a single 430 nm diameter gold particle confirm the conclusions of the model and demonstrates the suitability of this technique to investigate the opto-acoustic response of such submicronic particles.