Abstract

The phenomenon of light-induced acoustic pulse generations, i.e., photoacoustic (PA) effect, and light-induced thermal wave generation, i.e., photothermal (PT) effect, can be advantageously used to monitor properties of materials. For example, extremely narrow acoustic transients can be produced by pulsed lasers in condensed matter as well as in gases. The propagation of such narrow acoustic pulses can be monitored by contact methods using transducers or by noncontact methods using optical probe beams. Acoustic velocities, dimensions, and subsurface defects can be detected. Also, Fourier transforms of the PA pulse shape at different propagation distances provide the ultrasonic absorption spectrum of the material. PA generations are frequently due to PT heating effects by optical pulses; however, PT heating can also lead to other detectable effects like refractive-index transients or infrared thermal radiation variations. This talk reviews the modern applications of PA and PT monitoring of material properties as well as basic theories and measurements of the PA pulse generation effect.

© 1985 Optical Society of America