Laser-based ultrasound technique for testing and characterization

Abstract

Ultrasonics is being used as a nondestructive testing and evaluation (NDT&E) technique in many areas such as material testing, pre-service qualification, online quality control, process monitoring, in-service inspection, medical diagnosis etc. Although ultrasonic techniques using piezoelectric effect-based sensors (PZT's) have been a topic of intense research and are widely employed in the area of NDT&E, some drawbacks associated with these techniques limit the applications. Some of these drawbacks are the requirement of couplant, loading of the test specimen by the transducer, limited spatial resolution due to the physical dimensions of the transducers, limited bandwidth, critical temperature dependence, need of a primary calibration technique etc. Laser ultrasonic technique has been found to be a suitable alternative that can overcome many of the drawbacks associated with PZT based systems. In this paper, we discuss the details of the mechanisms involved in laser based remote ultrasound generation and detection techniques. We also present the details of a laser-based ultrasound facility developed in our laboratory with a few experimental results and its potential applications to testing and materials characterisation.