All-optical scanning acoustic microscope: Rapid phase imaging

An all-optical version of a scanning acoustic microscope is presented. The electronic data acquisition system is a major advancement. It is capable of high speed acquisition of phase as well as amplitude images at 82 and 164 MHz. The approach is to use computer generated holograms to focus and distribute the generating laser light into multiple arcs. This results in the formation of a surface acoustic wave focus. The increase in the amplitude of the signal at the focus is important, since the signal-to-noise ratio must be greater than unity to avoid the use of digital averaging.