Coverslip Induced Artifacts in High Resolution Scanning Laser Acoustic Microscope Images

Abstract

A critical component of the scanning laser acoustic microscope (SLAM) is the optical reflector which covers the object and defines a plane where the sound field is to be observed. Ideally, this reflector should have no influence of its own on the resulting acoustic image but should be a perfectly flexible optically reflecting layer imbedded within the medium used to couple sound into and out of the object. In practice, however, it is most conveniently realized by a more or less conventional mirror; an aluminum or gold coating on the face of an optically transparent solid plate. This paper examines some of the interactions which occur at this interface and the artifacts which appear in the image as a result. In particular, surface waves in the reflector generated at discontinuities in the sound field lead to fringes aligned with edges of the object.