Thermoelastic Waves Generated by Line-focused Laser Sources

Laser-based ultrasonics has many industrial application in the area of nondestructive testing and evaluation (NDT and E), laser ultrasonic velocity and attenuation measurements to determine elastic constants and grain size of materials. The laser-generated ultrasonics has several advantages in NDT and E over many conventional transducers, such as the ability to achieve broad-banded excitation with high signal reproducibility and the possibility of generating a truly remote source of ultrasound by optical means on hot or rough samples and in hostile environments. The characteristics of the laser-based ultrasonic wave depend strongly on the optical penetration, thermal diffusion, elastic properties and geometry of materials as well as parameters of the exiting laser pulse including the shape, focus spot, and pulse width. A numerical analysis formulation is developed to simulate a generation of thermoelastic waves in homogeneous isotropic elastic half-space under a linefocused laser irradiation. Analytic solutions for surface displacements are obtained by employing integral transform methods to the transient elastodynamic equations. Inverse Fourier transform is numerically evaluated by making use of Filon's method and numerical inversion of the Laplace transform is performed on the basis of Crump-Durbin technique. The numerical results of the displacements and the tractions generated by a line-focused laser pulse on the surface of an aluminum block