In this article, we concentrate on the optical penetration and laser pulse duration effects on the features of the ultrasonic waves generated in a solid by a laser impact. We consider the simple case of a uniform irradiation of the sample, which we describe with the help of a simple analytical one-dimensional model. In spite of its simplicity, this model clearly highlights the competition that occurs between two temporal convolution sources, related to the optical penetration and the laser pulse duration, respectively, to produce the longitudinal arrivals on the rear side of the sample. The model is also used for an accurate description of the features of the longitudinal precursor. ©1997 American Institute of Physics.