The laser-ultrasonic technique is a promising tool in the field of the mechanical characterization of materials [1,2]. The use of a laser is associated to three temporal convolutions related to the source parameters (the spot size, the pulse duration and the wavelength of the excitation) [3,4]. For a given wavelength, the evaluation of the mechanical properties of low-damage threshold materials in the thermoelastic regime, requires a compromise between the space distribution and the pulse duration of the excitation. An enlargement of the spot or an increase of the pulse duration introduces delays on the arriving times of the acoustic waves and consequently affects the accuracy of the velocity measurement. In the case of a non-metallic material, a third effect related to the optical penetration might be considered.