Directivity measurements in aluminum using a laser ultrasonics system

• Published in: Journal of physics. Conference series 2011-01, Vol.278 (1), p.012032-4
• Main Authors: Sakamoto, J M S, Tittmann, B R, Baba, A, Pacheco, G M
• Format: Article
• Language: English
• Subjects: Ablation; Aluminum; Amplitudes; Directivity; Frequency ranges; Lasers; Longitudinal waves; Mach-Zehnder interferometers; Neodymium lasers; Physics; Pulse duration; Semiconductor lasers; Spots; Ultrasonics; Ultrasound; YAG lasers
• ISSN: 1742-6596; 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/278/1/012032

A laser ultrasonics system was setup to measure the directivity (angular dependence pattern) of the amplitude of ultrasonic waves generated in aluminum samples. A pulsed Nd:YAG laser operating at 1064 nm optical wavelength, with typical pulse width (FWHM) of 8 ns, and energy per pulse of 450 mJ, was used to generate the ultrasound waves in the samples. The laser detection system was a Mach-Zehnder interferometer with typical noise-limited resolution of 0.25 nm (rms), frequency range from 50 kHz to 20 MHz, and measurement range from −75 nm/V to +75 nm/V. Two different optical spot sizes of the Nd:YAG laser were used to generate waves in the ablation regime: one was focused and the other was unfocused. Using the obtained data, the directivity graphics were drawn and compared with the theoretical curves, showing a good agreement. The experiments showed the directivity as a function of the optical spot size. For a point ultrasonic source (or focused optical spot), the directivity shows that the longitudinal waves present considerable amplitude in all directions. For a larger ultrasonic source (or an unfocused optical spot) the directivity shows that the longitudinal waves are generated with the higher amplitudes inside angles around ±10°.