[2] CITARELLA R, GIANNELLA V. Additive manufacturing in industry [J]. Applied Sciences, 2021, 11(2): 840.

[3] BHUSHAN B, CASPERS M. An overview of additive manufacturing (3D printing) for microfabrication [J]. Microsystem Technologies, 2017, 23: 1117-1124.

[4] ZHAO C, PARAB N D, LI X, et al. Critical instability at moving keyhole tip generates porosity in laser melting [J]. Science, 2020, 370(6520): 1080-1086.

[5] YIN Yan, ZHANG Yuan, DONG Kaiji, et al. The development of 3D printing technology and the current situation of controlling defects in SLM technology [J]. China Welding, 2020, 29(3): 9-19.

[8] CERNIGLIA D, MONTINARO N. Defect detection in additively manufactured components: laser ultrasound and laser thermography comparison [J]. Procedia Structural Integrity, 2018, 8:154-162.

[10] FENG W, ZHOU X, ZENG X, et al. Ultrasonic flaw echo enhancement based on empirical mode decomposition [J]. Sensors, 2019, 19(2):236.

[15] HONG Xiaobin, HUANG Liuwei, LIUFU Yonghong, et al. Laser ultrasonic scanning for detection of damage in copper pipelines using blind compressive sensing and the adjacent area difference coefficient [J]. Measurement Science and Technology, 2022, 33(6): 065202.

[18] MAO X, YANG Q, WANG X, et al. Application of variational mode decomposition and whale optimization algorithm to laser ultrasonic signal denoising [J]. Sensors, 2022, 23(1):354.

[19] GILLES J. Empirical wavelet transform [J]. IEEE Transactions on Signal Processing, 2013, 61(16): 3999-4010.