Acoustic Interference in Solids and Holographic Imaging

This paper reports a new technique for the visualization of ultrasonic interference in solids. The technique utilizes small (≈ 1 μm) polystyrene spheres suspended in a very thin liquid film formed on the surface of the solid. The nonlinear response of this film to acoustic waves is such that the spheres reveal the interference pattern present at the surface. There are two important advantages to this technique. The first is the simplicity of the technique, no elaborate equipment is required. The second is the easing of restrictions on ultimate resolution by our ability to visualize ultrasonic interference in solids.