Acoustic testing in a very small space based on a point sound source generated by laser-induced breakdown: Stabilization of plasma formation

This paper proposes a method of acoustic testing based on a point source generated by laser-induced breakdown in air. A high-power neodymium-yttrium- aluminum-garnet pulse laser is used in this system for generating the laser-induced breakdown in acoustic fields. Plasma formation can be realized by the laser-induced breakdown if the local intensity of the laser beam reaches 10¹⁵ W/m². The shock wave that is yielded by consuming a part of the plasma energy becomes a sound source. Assuming that the laser beam is focused to a small volume through a convex lens and the sound source by the laser induced-breakdown has nondirectional property, it is possible to create a point source with this technique. Securing the laser light path installs no device for acoustic excitation in acoustic fields. The system is validated by comparing the resonant frequencies of a very small space measured by the laser-induced breakdown and calculated by theoretical model.