Laser generation of ultrasound in films and coatings

A model for the pulsed laser generation of ultrasound in an isotropic film on a semi-infinite substrate is presented. The model gives the time domain displacement of the system as a function of the density and mechanical prop erties of the film and substrate and the thermal properties of the film. Th e model has been verified experimentally using a 1 ns Nd:YAG laser source f or acoustic wave generation and a stabilized Michelson interferometer for d etection. Experimental and theoretical signals agree well for both the case of a fast layer on a slow substrate (zirconium nitride/steel) and a slow l ayer on a fast substrate (titanium/aluminum). (C) 1999 American Institute o f Physics. [S0003-6951(99)01923-3].