Fig. 1. Surface morphology of 30Cr3 before and after immersion. (a) Before immersion; (b) After immersion

Fig. 2. Laser and acoustic signal acquisition system

Fig. 3. Waveform diagram of laser cleaning acoustic signal under different energy densities. (a) Time domain waveform diagram; (b) Frequency domain waveform diagram

Fig. 4. Cross-section appearance of high strength steel before and after cleaning under different laser energy density. (a)-(c) Uncleaned; (d) 5.5 J/cm²; (e) 10.1 J/cm²; (f) 13.6 J/cm²

Fig. 5. Short-time average amplitude of cleaning sound signal at different energy densities

Fig. 6. Fitted regression equations for microbial layer removal thickness and short-time average amplitude means

Fig. 7. Three-dimensional surface appearance of the template to be cleaned with similar roughness

Fig. 8. RMS and KU of the cleaned acoustic signals

Fig. 9. The three-dimensional morphology after cleaning. (a) Uncleaned; (b) 8.8 J/cm²; (c) 11.8 J/cm²; (d) 15 J/cm²; (e) 16 J/cm²; (f) 17.6 J/cm²

Fig. 10. Correspondence between cliff factor and roughness and segmented linear regression equation

Fig. 11. Instantaneous frequency diagram of cleaning sound signal at high energy density and macro-morphology after cleaning. (a)-(d) 16.0 J/cm²; (b)- (e) 16.8 J/cm² ; (c)-(f) 17.6 J/cm²

Fig. 12. Distribution of hardness test points

Fig. 13. Surface hardness after cleaning at different energy densities