A quantitative theory of laser-generated ultrasound

The generation of broadband elastic waves in solids by laserpulses is a suitable tool for nondestructive evaluation. The basic equations for mathematical description of the generation mechanism follow directly from non-equilibrium thermodynamics and were recently presented by us in linearized from together with preliminary results in "A complete model for thermoelastic generation of ultrasound". In this contribution we go essentially beyond that by applying the basic equations to a complete system composed of laser, aluminium-specimen and capacitance transducer. The method of greens function and numerical integration is used to obtain solutions for the displacement field taking into account both the structure of different lasermodes and the finite area of the capacitance transducer. Finally we have computed the temporal behavior of the displacement field for different observation angles and reached an remarkable good qualitative and quantitative agreement with our carefully performed m easurements.