How to use disorder for guiding a broadband acoustic wave ?
Résumé
In 1989, the concept of transverse localization was introduced as a new form of localization of light in the sense of Anderson [H. De Raedt et al. Phys. Rev. Lett., vol. 62, no. 1, pp. 47-50, 1989.]. Recently T. Schwartz et al. [Nature, vol. 446, p. 52, 2007] reported the first experimental demonstration of this prediction. To do so, they studied the propagation of light in 2 dimensional disordered photonic lattices, and proved that light was indeed exponentially localized in the transverse plane. Here, we present an equivalent scheme to guide MHz-ultrasonic broadband waves. We explore propagation of MHz-ultrasound in a medium which is either ordered or disordered in the two transverse dimensions (x,y) but invariant in the propagation direction (z). Our samples are made of parallel arrangements of cylindrical scatterers (0.8mm in diameter) embedded in a soft elastic matrix. In the disordered case, the probe beam is laterally confined with an exponential transverse intensity profile, which gives the first demonstration of the transverse localization of acoustic waves. Moreover we prove that the typical dispersion experienced by the pulsed waves in the ordered sample is almost cancelled in the Anderson localized one, hence resulting in a spatio- temporally guided wave.
Domaines
Acoustique [physics.class-ph]
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