Point source in a phononic grating: stop bands give rise to phonon-focusing caustics
Author(s)Maznev, Alexei; Veres, Istvan A.; Profunser, Dieter M.; Every, Arthur G.; Matsuda, Osamu; Wright, Oliver B.; ... Show more Show less
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We use locally-excited gigahertz surface phonon wavepackets in microscopic line structures of different pitches to reveal profound anisotropy in the radiation pattern of a point source in a grating. Time-domain data obtained by an ultrafast optical imaging technique and by numerical simulations are Fourier transformed to obtain frequency-filtered real-space acoustic field patterns and k-space phononic band structure. The numerically-obtained k-space images are processed to reveal an intriguing double-horn structure in the lowest-order group-velocity surface, which explains the observed non-propagation sectors bounded by caustics, noted at frequencies above the bottom of the first stop band. We account for these phonon-focusing effects, analogous to collimation effects previously observed in two- and three-dimensional lattices, with a simple analytical model of the band structure based on a plane wave expansion. As the frequency is increased, a transition to dominant waveguiding effects along the lines is also documented.
DepartmentMassachusetts Institute of Technology. Department of Chemistry
New Journal of Physics
Veres, Istvan A. et al. “Point Source in a Phononic Grating: Stop Bands Give Rise to Phonon-focusing Caustics.” New Journal of Physics 14.12 (2012): 123015.
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