Abstract
Using a photoacoustic effect, a non-destructive and non-contact defect detection has been studied. A low power semiconductor laser which has a power of 10mW is used as a light source. Because a photoacoustic signal is very low in this case, a proper condition of an acoustic sensor which detects the photoacoustic signal needs to be find. As a result of measuring a propagation characteristic of the photoacoustic signal, the photoacoustic signal propagates forward intensely, so the acoustic sensor is set in front of an object. An increase of the photoacoustic signal called an edge effect is observed on an edge of the object. A small defect which has a diameter of about 1.5mm can be detected. It has a high resolution in the defect detection and some adjacent defects which have a gap of 0.1mm can be detected because the laser light can be focused to the extremely small spot.
