Observation of acoustic coherent backscattering

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Abstract
The coherent backscattering of an acoustic wave has been observed. The phenomenon is attributed to the weak localization of the wave and has been predicted for any kind of classical wave including light and acoustic waves. The laser diffraction method was applied to measure the intensity profile of the diffuse scattering of a 10 MHz ultrasonic pulse from an inhomogeneous medium including randomly dispersed polystyrene beads of 200 μm diameter as scatterers. The efficiency of the coherent backscattering was estimated to be 2, which agrees with the ideal value expected by theory. A direct visualization of the coherent backscattering was also carried out using the schlieren technique.