Laser-generated MHz elastic waves from metallic-liquid interfaces

The thermoelastic generation of MHz waves from a three-layer structure consisting of a transparent substrate with an evaporated metallic film in contact with a liquid is described. Results with laser excitation indicate the magnitude of the strain wave to be strongly dependent on the expansion coefficient of the liquid and thickness of the metal film. The data are compared to a three-medium one-dimensional theory. Some practical applications such as nondestructive evaluation are discussed using this structure.