Immersion laser-induced ultrasound imaging of solids with complex macroscopic geometry of surface

In this paper a real-time experimental system and algorithms for immersion two-dimensional laser ultrasonic imaging of solids with complex geometry of surface are presented. Wideband probe ultrasonic pulse is generated photoacoustically in an opaque plate, which absorbs pulsed laser radiation. The back-scattered acoustic field is recorded by a multi-element piezoelectric array. The signals are used to reconstruct refraction-corrected ultrasonic images, which are post-processed to determine positions of the external and internal boundaries of the object. The numerical simulations are carried out to verify the developed algorithms. The proposed approach allowed measuring the positions of the boundaries of the polymethyl methacrylate (PMMA) sample with accuracy of ~0.1 mm in the direction of the probe beam propagation, and ~0.2-0.3 mm in the perpendicular direction.