a The behavior of phonon dispersion curve (red) close to the first Brillouin edge. Quasinormal modes (QNMs) fi,1 are depicted by blue points. The magenta arrows show the experimentally observed frequencies. b, c The quality factors (b) and coupling strength constant (c) for a set of QNMs close to a band gap (white rectangle). Quasinormal modes fi,1 are depicted by blue points. An orange point corresponds to f0,3 mode. The experimental amplitude of a signal, reflected from the same geometry phononic crystal measured in a separate experiment is shown in the inset. Three dips correspond to the excitation of modes f−2,1 = 3.248 GHz, f0,1 = 3.264 GHz and f0,3 = 3.283 GHz, which have the highest coupling strength. The experimental Q-factors extracted from the widths of these dips are Q−2,1 = 380, Q0,1 = 1050, Q0,3 = 950, which are in good agreement with calculated ones, shown on (b).