Laser Generation of Convergent Acoustic Waves and Applications to Materials Evaluation

A converging-wave technique for laser generation and detection of focused acoustic waves is described together with a number of applications to the nondestructive testing and characterization of industrial materials. An annular-shaped wave is produced by irradiating the inspected material with a laser beam focused through a suitable combination of spherical and conical lenses. The ultrasonic pulse reaches a relatively high amplitude in the center of convergence, where it is probed by a noncontact interferometric optical sensor. Applications to the ultrasonic characterization of ceramic materials, coating thickness evaluation, detection of delaminations in layered materials as well as crack inspection are described.

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