Oliver Wright speaking on "Tracking surface phonons on phononic crystals", September 13, 2007

Tracking surface phonons on phononic crystals

Periodic elastic structures, or phononic crystals, promise diverse applications in the control of propagating sound. These acoustic metamaterials, with one-, two- or three- dimensional periodicity in their acoustic impedance, possess stop bands where the elastic waves are heavily damped. We track broadband surface phonon wave packets in 1D and 2D microscopic phononic crystals in two dimensions and in real time with an ultrafast optical technique. The eigenmode distribution and the 2D acoustic band structure are obtained from spatiotemporal Fourier transforms of the data up to 1 GHz. We find stop bands at the zone boundaries for both leaky-longitudinal and Rayleigh waves, and show how the structure of individual acoustic eigenmodes in k-space depends on Bloch harmonics and on mode coupling. We also track phonon pulses in phononic crystal waveguides and cavities.

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