A. Zarei, G. Li, F. Pourboghrat, S. Pilla
University of Delaware, Delaware, United States
Keywords: Laser Ultrasonic Testing, Composite Materials, Spatial Modulation, Waves Convergence, Convergent Laser Beams
Laser Ultrasonic Testing (LUT) is a noncontact, nondestructive technique for rapid, accurate inspection and characterization of materials, from small components to large structures. Its main limitation is the low signal-to-noise ratio (SNR), constrained by the material’s ablation threshold. This challenge is especially severe in composites due to their low ablation threshold, dissipative nature, anisotropy, and heterogeneous composition. While prior studies have explored temporal and spatial modulation of laser pulses, the potential of wave convergence, focusing generated ultrasonic waves to a single detection point to boost amplitude and SNR, has been overlooked. In this work, we derive laser beam shapes that cause specific wave types (longitudinal, Rayleigh, or Love) to converge at a target point in a composite material. These mathematically defined beam profiles are implemented in finite element simulations to evaluate their effectiveness. The results confirm that tailored beam shaping can significantly enhance the amplitude of the targeted wave mode while maintaining fluence below the ablation threshold, thereby achieving substantial SNR improvements. This approach offers a powerful pathway for highly accurate, fast, online, in-service, and noncontact inspection of advanced materials, with strong potential to improve defect detection sensitivity in advanced materials.