Coherent acoustic phonon 2 Coherent acoustic phonons 2 Electronic relaxation 2 Gold 2 Hypersound Lattice vibrations 2 Mechanical constraints 2 Mechanical oscillations 2 Metamaterial antennas 2 Nanoantennas 2 Phonons 2 Plasmonic nanostructures 2 Plasmons 2 Probes 2 Pump probe 2 Silica 2 Ultrashort pulses 2 Vibrations (mechanical) 2 gold-silica nanoantenna 2 hypersound 2 nanoresonator 2 pump-probe 2