Conventional ultrasound testing technique usually employs a piezoelectric transducer to both generate and detect ultrasonic waves to perform non-destructive inspection. However, this type of transducer presents some drawbacks as: requirement of a coupling medium, high temperatures are not supported, narrow bandwidth, low spatial resolution, load the sample, and is hard to be used in complex geometries. In contrast, the laser ultrasonics technique can overcome these problems by taking advantage of the weightless non-contact nature of light, and both generation and detection of ultrasonic waves...