When an intensive pulsed laser or ion beam impinging a material surface gradually loses its energy and heating the material along the passing path of the beams, a pulsed ultrasonic wave can be excited due to a thermal source distributed along the depth direction. We deduce an expression and calculate the epicenter displacement of ultrasound. Investigation results show that: the waveform of displacement depends on the distribution depth, the type of thermal source, the properties of samples, and the ratio between the thickness of the absorption layer and the duration of excitation beam. The detail process, results and discussions are presented. © 2003 American Institute of Physics