Fig. 1. Raman-Nath diffraction principle

Fig. 2. Geometric relationship between photoelectric detection sensitive unit and diffracted light at limit frequency

Fig. 3. Schematic of tracing principle

Fig. 4. Principle of acousto-optic effect

Fig. 5. Contrast experiment between laser sensing and ultrasonic transducer methods

Fig. 6. Time domain feature comparison between laser sensing and ultrasonic transducer methods. (a) Laser sensor method; (b) ultrasonic transducer method

Fig. 7. Frequency domain feature comparison between laser sensing and ultrasonic transducer methods. (a) Transmitting center frequency is 550 kHz; (b) transmitting center frequency is 500 kHz

Fig. 8. Acousto-optic diffraction signal diagrams under different numbers of pulse excitation. (a) The number of pulse excitation is 1; (b) the number of pulse excitation is 3; (c) the number of pulse excitation is 6; (d) the number of pulse excitation is 9

Fig. 9. Comparison of laser sensing signals when initial phase of excitation signals is different (0° initial phase signal is taken as reference signal). (a) Initial phase is 45°；(b) initial phase is 90°；(c) initial phase is 135°；(d) initial phase is 180°

Fig. 10. Relationship between excitation initial phase and laser sensing initial phase

Fig. 11. Schematic of experimental device

Fig. 12. Laser sensor and sound source devices. (a) Three-dimensional modeling diagram of receiving terminal; (b) actual underwater experiment test diagram of receiving terminal; (c) three-dimensional modeling diagram of transmitting terminal; (d) actual experiment diagram of transmitting terminal

Fig. 13. Actual acousto-optic measurement signal

Fig. 14. Picture of line tracing. (a) Step length is 25 mm; (b) step length is 5 mm

Fig. 15. Experimental results of arbitrary step length