Laser generated acoustic emission in water

A Q-switched Nd-YAG laser light source (pulse duration of 8 ns with a maximum energy of 50 mJ at a wavelength of 1.064 μm) was launched through an optical fibre (core diameter 800 μm and a numerical aperture (NA) of 0.25) delivery system into a tank containing natural water. The resulting acoustic wave generated by thermoelastic process was picked up using a broadband AE transducer (frequency bandwidth of 0–1 MHz) placed along the optical axis of the optical fibre carrying the laser source. Results of the experiments show that, the mean square voltage of the photo-acoustic emission (PAE) generated decreases with increase in the source-to-transducer distance in the range of 10–50 mm. Also the measurements show a good degree of repeatability at different input laser power levels. The result of the experiment is compared with an analytical model that has been proposed for this configuration. Application for on-line monitoring of fluid based processes is envisaged.