Fig. 1. SAFT schematic of separated excitation and detection

Fig. 2. Relationship between arrival time of reflected sound waves and scan steps at different depths

Fig. 3. Schematic of sample structure used in numerical calculation

Fig. 4. Numerical simulation B-scan images for models (a) with and (b) without defect

Fig. 5. Difference between the B-scan image in the defective cases and the B-scan image in the perfect cases

Fig. 6. Propagation path of the signals A1 and B1 in Fig.5

Fig. 7. SAFT image of Fig.5

Fig. 8. SAFT image results of defects with different sizes. (a) d=0.5 mm; (b) d=0.8 mm

Fig. 9. Experimental B-scan image with scanning laser source

Fig. 10. Time-domain waveform obtained when excitation light is scanned to the 60th step

Fig. 11. SAFT image of Fig.9

Fig. 12. SAFT image of the perfect area