[18a-E214-1~5] 22.1 Joint Session M "Phonon Engineering"

▲ [18a-E214-1] Two-dimensional Imaging of Zero-Group-Velocity Lamb Waves

〇Oliver B. Wright¹, Qingnan Xie², Sylvain Mezil¹, Paul H. Otsuka¹, Motonobu Tomoda¹, Jerome Laurent³, Zhonghua Chen², Osamu Matsuda¹ (1.Hokkaido Univ., 2.Nanjing Univ. S&T, 3.Institut Langevin)

Keywords:acoustics, photonics, ultrafast

Waveguides channel propagating waves with reduced losses thanks to the confined dimensions, and are widely used in optics and acoustics. They are dispersive, i.e., the phase and the group velocities differ. Zero-group-velocity (ZGV) modes are particular points in a dispersion relation where the group velocity vanishes whereas the phase velocity remains finite. These modes can be found in most waveguide geometries (e.g., fibres and cylinders) and have the advantages of combining reduced losses and high Q factor. Here we present the imaging of gigahertz zero-group velocity acoustic waves in a microscopic plate. Lamb waves in a bilayer consisting of a ~2 micron thickness silicon nitride plate coated with polycrystalline titanium are imaged by means of a time-resolved two-dimensional imaging technique using an ultrashort-pulse laser. We identify and isolate the first ZGV mode, its associated Q factor and its lifetime. Applications include nanoscale non-destructive testing and extension to imaging photonic ZGV in two dimensions.