Experimental study on ultrasonic bulk field induced by oblique laser

The directivity patterns of the ultrasonic field induced by an oblique laser are investigated. The longitudinal wave and shear wave are respectively received by a piezoelectric transducer and an electromagnetic acoustic transducer in a state of micro ablation. At first, according to the ultrasound speeds, the signal types are determined. Then the directivity patterns are obtained by drawing peak to peak curve in the polar coordinate. The directivity patterns with normal axis of longitudinal wave do not change obviously for incidence angles in the range of 0-60, and angles for the maximum amplitude of shear wave still remain at 35 and -35. However, the main lobe of the directivity patterns for shear wave is sensitive to the incidence angle. In another word, shear wave amplitude near the normal increases with the incidence angle, especially when the inclined angle is no less than 45.