Experimental study of directivity patterns of laser ultrasound in an unpolarized PZT ceramic in the thermoelastic regime

The experimental longitudinal directivity patterns of laser-generated ultrasound for both line and disc laser sources, in an unpolarized PZT-4 ceramic in the thermoelastic regime, are presented. The exciting source is a Q-switched Nd:YAG laser operating at the wavelength of 1.06 μm and having a pulse width of 8 ns and maximum pulse energy of 200 mJ. The acoustic pulses are detected by a 5 MHz piezoelectric ultrasonic transducer. The results show that there are noticeable differences between the directivity patterns in the non-metal PZT and those in the metal aluminium. Discussions of the observations are offered.