Multi-mode laser-ultrasound imaging using Time-domain Synthetic Aperture Focusing Technique (T-SAFT)

• Published in: Photoacoustics (Munich) Vol. 27; p. 100370
• Main Authors: Ying, Kai-Ning, Ni, Chen-Yin, Dai, Lu-Nan, Yuan, Ling, Kan, Wei-Wei, Shen, Zhong-Hua
• Format: Journal Article
• Language: English
• Published: Germany Elsevier GmbH 01.09.2022; Elsevier
• Subjects: Defect detection; Laser ultrasound; Non-destructive Testing; Synthetic Aperture Focusing Technology (SAFT); Non-destructive Testing; Laser ultrasound; Synthetic Aperture Focusing Technology (SAFT); Defect detection
• ISSN: 2213-5979; 2213-5979
• DOI: 10.1016/j.pacs.2022.100370

The Synthetic Aperture Focusing Technique (SAFT) is an imaging algorithm used in laser ultrasonics (LU) to visualise the appearance of defects. However, ultrasound excited by a pulsed laser has the characteristics of wide bandwidth and multi-mode directivity patterns, leading to common problems in the SAFT process, such as low utilisation of ultrasound information and possible artefacts. To solve these problems, a Multi-mode Time-domain SAFT (MMT-SAFT) algorithm is proposed in this paper. The influence of ultrasonic directivity is discussed according to the imaging depth range, and imaging with multiple LU modes is performed to reduce artefacts. Simulations and experimental results prove the feasibility of the MMT-SAFT algorithm, which not only presents a clearer image of the upper part of defects but also improves image quality compared with time-domain SAFT using a single ultrasonic mode. The proposed technique can provide feasible directions for laser ultrasonic defect imaging. •Multi-mode T-SAFT algorithm suitable for LU detection is developed.•Ultrasonic directivity patterns are employed for further MMT-SAFT.•Improved MMT-SAFT imaging quality by selecting suitable imaging parameters.•Successfully imaged internal upper part of defect by all optics.