Fig. 1. Schematic of defect location detection. (a) Starting point; (b) middle point; (c) terminal point

Fig. 2. Schematic of defect size detection. (a) Detection of defect with diameter Φ₁; (b) detection of defect with diameter Φ₂

Fig. 3. Schematic of Comsol finite element simulation model

Fig. 4. Interaction process between laser ultrasonic and internal defect. (a) t=2.05 μs; (b) t=2.50 μs; (c) t=3.60 μs; (d) t=4.15 μs; (e) t=4.50 μs; (f) t=5.00 μs

Fig. 5. Schematic of each-mode ultrasonic wave propagation

Fig. 6. Scanning schematic and calculation results when pump laser fixed and probe laser movable. (a) Schematic of scanning form; (b) calculation results of received signals

Fig. 7. Finite element simulation results when pump laser fixed and probe laser movable. (a) B-scan result with defects; (b) B-scan result without defects; (c) difference between B-scan results with and without defects

Fig. 8. Scanning schematic and calculation results of received signals when pump laser and probe laser simultaneously movable. (a) Schematic of scanning form; (b) block 1; (c) block 2; (d) block 3

Fig. 9. Laser ultrasonic detection system. (a) Schematic of system; (b) experimental image of system

Fig. 10. Experiment on shear wave velocity measurement. (a) Experimental diagram; (b) experimental result

Fig. 11. Diagram of 45 steel block to be detected. (a) Three-dimensional diagram; (b) physical diagram

Fig. 12. Scanning schematic of defects detected by laser ultrasonic diffraction bulk wave method

Fig. 13. Experimental results of B-scan for each defect. (a) defect 1; (b) defect 2; (c) defect 3

Fig. 14. Schematic of calculation of defect location and size

Fig. 15. Relative errors from defect diffraction bulk wave detection method