Laser-induced plasma shock wave excitation technique with acoustic lens

(Lamb wave generation)

Abstract

We propose a method with a controllable ability of amplitudes and frequency ranges in excitation forces generated by laser-induced plasma (LIP) shock wave. To control these amplitudes and frequency ranges, we use an acoustic lens to focus the shock wave spreading spherically. When the pulsed laser beam is irradiated in air, reaching a threshold of 1015 W/m2 in air, plasma is formed. Then plasma is rapidly expanded through the ambient, resulting in shock wave generated at the origin of LIP position. A portion of the shock wave is applied to target structures as an impulse excitation force, because the LIP shock wave is a spherical wave. We generate Lamb waves on an aluminum plate using the shock wave focused by an acoustic lens, adjusting the amplitudes and the frequency components of the excitation force. From this, we realize that the generated Lamb waves have approximately three times larger amplitudes and lower frequency components compared with the conventional LIP excitation method.