Optical probing of acoustic waves on rough surfaces

The problem of optically measuring acoustic displacements on samples with rough surface texture is examined. A focusing lens system which increases the amount of scattered light collected from a rough surface is presented. A computer-controlled scanning system for an all-fiber-optic acoustic surface wave probe is described which electronically divides out surface reflectance changes encountered while measuring rough samples. The probe demonstrates the ability to optically measure acoustic displacements on surfaces with a roughness comparable to that produced by most common manufacturing processes. An image of the acoustic field surrounding a defect in an aluminum test sample is presented.