Band structure and slow waves experimental and theoretical characterization in an high frequency 1D phononic crystal

We present heterodyne detected transient grating (HD-TG) measurements on 1D surface corrugated Phononic Crystal (PC) with characteristic band edge wave vector of $\pi/5$ $\mu$m$^{-1}$. This experimental investigation enables both the direct band diagram characterization of surface waves and a direct measurement of the group velocity dispersion. The experimental data are compared to the simulations performed with the structural-mechanic module of a finite element method software. In this work we show the presence of two band gaps, observe distinct types of surface waves and, for the first time to our knowledge, measure extremely slow waves in correspondence of the band edge wave vector.