Fig. 1. Lamb wave dispersion curves in 20 μm thick Mg-Li alloy. (a) Phase speed; (b) group speed

Fig. 2. Calculation flow chart of mixed calculation method

Fig. 3. Schematic of finite element model of laser ultrasonic

Fig. 4. Time-domain curve and spectrum of ultrasonic wave received at 12.1 mm from surface to loading center. (a) Time-domain curve of ultrasonic wave; (b) spectrum of S0 mode

Fig. 5. B sweep diagram of Lamb wave in Mg-Li alloy foil

Fig. 6. Results of two-dimensional Fourier transform. (a) S0 mode; (b) A0 mode

Fig. 7. Time-domain waveforms for S0 original data or after band-pass filtering at different points

Fig. 8. Schematic of excitation point and measurement points on aluminum foil

Fig. 9. Signals received at 5 mm away from excitation point. (a) Time-domain curve of ultrasonic wave; (b) one-dimensional Fourier transformation curve of S0

Fig. 10. Time-domain signal received at 5 mm and 10 mm from excitation point and signal delay. (a) Time-domain signals; (b) delay time