A theory for the guided wave excitation by phase velocity scanning of a laser beam

A theory is presented for the propagation of guided waves excited by scanning a laser beam on a specimen at a constant velocity. Formulae are derived for the excitation by a point-focused laser beam as well as by a line-focused laser beam. It is deduced that such modes of guided waves are selectively excited whose phase velocities match the scanning velocity. In the case of Lamb waves, the feature of the wave propagation depends also on group velocities. It is shown that major characteristics of experimental observations previously made are explained with the present model