The use of a pulsed laser source for the generation of elastic waves in materials is investigated, taking into account optical penetration into the material. Under appropriate conditions, a significant feature of the laser‐generated elastic waveform is a precursor (sharp spike) signaling the arrival of the longitudinal wave. The shape of this precursor signal is strongly dependent on the optical and thermal properties of the material. This paper shows that the observed precursor can be understood through the use of models that account for optical penetration and thermal diffusion into the material.