Optical detection of ultrasound on rough surfaces using speckle correlated spatial filtering

Abstract

There are numerous techniques for the optical detection of ultrasound but many of these are of very limited application on optically rough surfaces. Techniques that work on rough surfaces are often complicated, inefficient and expensive. In this paper a new technique for the optical detection of ultrasound on rough surfaces is presented. It is a variation on the knife-edge (KE) technique but adapted for rough surfaces by replacing the knife-edge with a speckle correlated spatial filter (SCSF) which is implemented using a spatial light modulator (SLM). This technique is conceptually and practically simple and may be implemented using relatively low cost components. It is also relatively general and may also be applied to the detection of small displacements in many circumstances.