Photoacoustic signal generation and detection

Photoacoustic generation, i.e. light producing sound, can be due to a variety of causes and can be used for different applications. In the application area of acoustic imaging and non-destructive evaluation, photoacoustic generation is usually produced via the thermoelastic expansion effect due to the absorption of a pulsed or rapidly-modulated laser beam on an opaque surface. To obtain large amplitude acoustic waves or shock waves, the effect of photo-ablation of a thin-film on the surface can also be used. Detection of the photoacoustic pulse can be done either by contact transducer measurement or by non-contact optical measurement. Application of these effects in materials testing is described.