Fig. 1. Experimental equipment

Fig. 2. Schematic of detection process. (a) Three-dimensional detection process of defect samples by laser point source scanning; (b) two-dimensional detection by A-scan

Fig. 3. Visualized dynamic images of ultrasonic wave at 6.08 μs in cracks with different depths. (a) 485 μm; (b) 1482 μm; (c) 1865 μm; (d) 3125 μm

Fig. 4. Results of signal analysis. (a) Reflected wave signal received at point M; (b) spectrogram corresponding to (a); (c) transmitted wave signal at point N

Fig. 5. Relationship between surface wave coefficients and defect depth. (a) Reflection coefficient; (b) transmission coefficient

Fig. 6. B-scanning images of cracks with different depths in Y direction and at X=10 mm. (a) 485 μm; (b) 1482 μm; (c) 1865 μm; (d) 3125 μm