Tunable multiple-scattering system

To study the propagation of multiply scattered waves, it is useful to have a medium in which the scattering properties can be easily controlled. Here, we describe such a system; it involves the propagation of ultrasonic surfa ce waves in a medium with an aligned, disordered pattern of grooves. Waves propagating parallel to the grooves see a homogeneous medium; waves propaga ting perpendicular to the grooves are strongly scattered. By varying the so urce-receiver distance and orientation with respect to the grooves, we are able to map out the transition from ballistic to diffusive propagation. In addition, by using an optical detection system we are able to measure the w ave motion inside the scattering medium. We measure the angle-dependent mac roscopic properties of the medium, such as the group velocity as well as th e mean-free path and the diffusion constant in the strong-scattering regime . (C) 2001 American Institute of Physics.