Ultrasonic imaging of layered structures utilizing nondestructive subnanosecond photoacoustic pulse generation

We describe a photoacoustic ultrasonic imaging system that can provide separate acoustic information on a thick substrate and a thin coating simultaneously. This is achieved by generating an ultranarrow longitudinal pulse on the opaque layered sample, and detecting the series of substrate and coating echoes in high time resolution. The echo times, attenuations, and acoustic dispersions in each series provide information on the substrate or coating separately. New photoacoustic images of coatings and of substrates for coated ceramic substrates are presented.