High-intensity airborne sound generated by irradiation of nanosecond laser pulse to water-immersed optical absorber

Abstract

Abstract A high-intensity and small-size laser-induced airborne sound source was developed for application to non-contact and non-destructive testing. A laser target composed of a polycarbonate (PC) plate and a black fluoro-rubber (FKM) film immersed in circulating water was used as the sound source. The maximum sound pressure of about 15.2 kPa was obtained at a distance of about 11 mm from the surface of the laser target when a pulsed laser with its energy of about 110 mJ was irradiated to a 0.1 mm thick FKM film immersed in circulating water. The ratio of maximum pressure to the irradiation energy was stabilized up to 60 shots of pulsed laser irradiation. The maximum sound pressure of about 18 kPa was obtained through the 50 mm length cylindrical PC pipe of 3.2 mm in diameter when a pulsed laser at an energy of 120 mJ was irradiated to a 0.5 mm thick FKM film immersed in circulating water.