Imaging phonon eigenstates and elucidating the energy storage characteristics of a honeycomb-lattice phononic crystal cavity

作者：Paul H. Otsuka, R. Chinbe, Motonobu Tomoda, Osamu Matsuda, Y. Tanaka, Dieter M. Profunser, S. Kim, Heonsu Jeon, István A. Veres, A. A. Maznev, Oliver B. Wright · 发表于：Photoacoustics · 年份：2023 · DOI：10.1016/j.pacs.2023.100481 · 被引用次数：7 · 研究领域：Acoustic Wave Phenomena Research、Acoustic Wave Resonator Technologies、Ultrasonics and Acoustic Wave Propagation

We extend gigahertz time-domain imaging to a wideband investigation of the eigenstates of a phononic crystal cavity. Using omnidirectionally excited phonon wave vectors, we implement an ultrafast technique to experimentally probe the two-dimensional acoustic field inside and outside a hexagonal cavity in a honeycomb-lattice phononic crystal formed in a microscopic crystalline silicon slab, thereby revealing the confinement and mode volumes of phonon eigenstates-some of which are clearly hexapole in character-lying both inside and outside the phononic-crystal band gap. This allows us to obtain a quantitative measure of the spatial acoustic energy storage characteristics of a phononic crystal cavity. We also introduce a numerical approach involving toneburst excitation and the monitoring of the acoustic energy decay together with the integral of the Poynting vector to calculate the Q factor of the principal in-gap eigenmode, showing it to be limited by ultrasonic attenuation rather than by phonon leakage to the surrounding region.