Thermal interference-optical excitation of ultrasonic waves in condensed media

An investigation was made of an effective method for the excitation of ultrasonic waves in thin liquid films based on the pulsed heating of these films by an interference field of coherent radiation. The perturbations induced in the medium were measured from the diffraction of a cw laser beam. It is shown that the optimal conditions for the generation of monochromatic sound packets are achieved for exciting radiation having a pulse duration considerably shorter than the period of the acoustic waves. A method of determining the velocity and attenuation of the sound is proposed and the importance of edge effects in the relaxation processes of the perturbations is studied.