Nondestructive evaluation of surface defects under dry/wet environment by the use of photoacoustic and photothermal electrochemical imaging

Nondestructive evaluation of surface defects fabricated on a metal plate has been performed by the use of a photoacoustic scheme and a photothermally-induced electrochemical detection scheme. An Ar laser beam is modulated with a mechanical chopper and is focused on a metal sample plate with a microscope objective lens. The laser beam is scanned with a pair of computer-controlled optical scanners. The principle of a photothermal electrochemical scheme is to detect an electrochemical current change caused by laser heating, instead of the sound wave detection in a photoacoustic scheme. A columnar hole fabricated on a metal sample surface was studied for each detection scheme under a dry/wet environment. (C) 1999 Elsevier Science Ltd. All rights reserved.