Simulation of laser-generated ultrasonic waves in layered plates

A model is presented for the pulsed laser generation of ultrasound in isotr opic layered plates. The stresses and displacements of the plate have been formulated in the Hankel and Laplace transform domains using the Thompson t ransfer matrix approach. The time domain response has been obtained by nume rically inverting the transforms. Several numerical results are presented s howing the normal surface displacement in the following configurations: sin gle-layer film on a semi-infinite substrate, two layers on a semi-infinite substrate, and three-layer plates. The model provides a useful tool for the determination of which modes are generated by a laser source in a layered system. It can also be used to determine how sensitive the modes are to sma ll changes in density, thickness, or elastic properties of the layers and t o help in the selection of experimental parameters (laser spot size, pulse length, and source to receiver distance) for optimal sensitivity. (C) 2001 Acoustical Society of America.