Observation of Subsurface Structures by Scanning Laser Photoacoustic Spectroscopy

Abstract
Aiming at the detection of the subsurface structure of the material, a new technique using a piezoelectric transducer (PZT) as a photoacoustic detector is presented and discussed. Aluminum foils with a groove under the surface were used as samples and the groove was detected by measuring the amplitude or the phase angle of the photoacoustic signal. By the use of a relatively high modulation frequency, a new elastic image as well as thermal image have been obtained.