Mechanical properties of materials may be obtained from the inversion of ultrasonic Lamb wave dispersion curves. In order to do this broadband excitation and detection of ultrasound is required. As sample size and, in particular, thickness, are reduced to those of microstructures, ultrasound frequencies in the range of the gigahertz region will be required. We look at two possible cw laser excitation techniques which, having far lower peak powers than the more frequently used Q-switched lasers, therefore give a negligible risk of damaging the sample through ablation. In the first method the modulation frequency of a sinusoidally modulated laser is swept over the required range. In the second, the laser is modulated with a series of square pulses whose timing is given by a PRBS (pseudo random binary sequence) in the form of a modified m-sequence.

Date Published: 7 April 2009
PDF: 11 pages
Proc. SPIE 7293, Smart Sensor Phenomena, Technology, Networks, and Systems 2009, 72930Y (7 April 2009); doi: 10.1117/12.816362

Published in SPIE Proceedings Vol. 7293:
Smart Sensor Phenomena, Technology, Networks, and Systems 2009
Norbert G. Meyendorf; Kara J. Peters; Wolfgang Ecke, Editor(s)