Fig. 1. Schematic diagram of photoacoustic signal generation by laser thermal expansion

Fig. 2. Four typical shapes of photoacoustic sources generated by laser thermal expansion. (a) Point source; (b) linear source; (c) planar source; (d) stereo source

Fig. 3. Schematic diagram of photoacoustic signal generated by linear source

Fig. 4. Schematic diagram of photoacoustic signal generated by planar source

Fig. 5. Pictures of soundproof pool

Fig. 6. Layout of experimental equipment

Fig. 7. Laser and laser spot reflection amplification equipment. (a) Laser picture; (b) laser spot reflection amplification equipment

Fig. 8. Time-domain signal of linear source (single waveform)

Fig. 9. Measured time-domain signals of linear source (9 consecutive normalized waveforms)

Fig. 10. Analysis results of correlation coefficients

Fig. 11. Simulation results of time-domain signals of planar sound source. (a) Single signal; (b) stacked signal with delay of 0.02 ms; (c) stacked signal with delay of 0.04 ms; (d) stacked signal with delay of 0.06 ms

Fig. 12. Measured time-domain signal of planar sound source (single waveform)

Fig. 13. Measured time-domain signals of planar sound source (nine consecutive waveforms)

Fig. 14. Analysis results of correlation coefficients