Yb 3+ /Er 3+ -codoped distributed feedback (YbEr-DFB) fibre grating lasers have been investigated for the detection of ultrasonic Lamb waves generated in an aluminium plate. Two sensor configurations have been investigated. A path-length-imbalanced readout Mach–Zehnder interferometer was used to measure the laser frequency shift induced by ultrasonic vibration. The resolution to out-of-plane displacement was 3 × 10 −15 m Hz −1/2 for a continuous ultrasonic wave at a frequency of 470 kHz. Ultrasonic waves were also detected by directly monitoring the laser output power. This simplified configuration is useful for tone burst AE signals generated by a low energy impact.
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Ye et al. (2004) studied this question.
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