Identification of laser-induced Lamb waves

We studied experimentally the ultrasonic propagating modes produced by a laser pulse of 532 nm while impinging on an aluminum plate. The beam, shaped as a line, induced various Lamb modes whose relative power varied with the laser line length. Identification of their mode was performed by detecting the ultrasonic modes with piezoelectric detectors along a propagation direction orthogonal to the line, and using two dimensional fast Fourier transform. Good agreement is observed between theoretical and experimental dispersion curves for the first fundamental symmetric and anti-symmetric modes. Results are shown for 12 and 24 mm laser line-length at 13.6 and 16.8 ns pulse-width.