CHARACTERIZATION OF LASER-ULTRASOUND SIGNALS FROM AN OPTICAL-ABSORPTION LAYER WITHIN A TRANSPARENT FLUID

Characteristics of laser-ultrasound signals are presented from photoac oustic interaction with a layered, optically absorbing medium surround ed by a transparent fluid. A thermoelastic model is presented describi ng the interaction, with signal predictions in the fluid arising from polymer transducer detection. By taking the optical absorption coeffic ient and finite layer thickness into account, the amplitude and shape of transient elastic waves are calculated for both forward and backwar d travelling directions. Additionally, wave interaction with the PVDF transducer has been characterised using a discrete-time algorithm for the transducer response. With just three constants to define transduce r response characteristics, the response function may be used to predi ct voltage signal. Good agreement with experimental waveforms is demon strated, so that the response function may form the basis of system mo delling when miniature laser-ultrasound probes are used in various app lications.