Applications of broadband laser-based ultrasound to materials testing
We discuss the role of broadband Lamb wave propagation for materials testing applications in metal and composite material plates. Using a high powered pulsed laser-acoustic source it was possible to initiate broadband acoustic pulses in the samples. The pulses were detected by non-contact, broadband optical receivers. Temporal and spatial sampling of the ultrasonic wavefield allowed simultaneous measurements of several separate Lamb wave modes. A recent development of the technique is described whereby a low power CW laser diode was used to generate Lamb waves in a steel sample at a significantly reduced peak power compared to the pulsed laser source. Digital modulation of the injection current to the diode coupled with correlation detection allowed observation of the low amplitude ultrasound propagating in the sample.
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