Laser-ultrasonics: From the laboratory to industry

A broad overview of the field of laser-ultrasonics is presented. This overview draws from developments at the Industrial Materials Institute of the National Research Council of Canada as well as elsewhere. The principles of generation and detection are presented, stressing a few key characteristics of laser-ultrasonics: the material is actually the emitting transducer and transduction is made by light, thus eliminating any contact. These features carry both advantages and limitations that are explained. Another feature, which has been an impediment, is actually the complexity of the "laser-ultrasonic transducer", but in spite of this complexity, it can be made very reliable for use in severe industrial environments. It also can be very cost effective for a number of applications. Three applications that are now used in industry are presented: the inspection of polymer matrix composites used in aerospace, the measurement of thin layers in microelectronics and the thickness gauging of hot steel tubing in production. Technological aspects, such as interferometer design, detection lasers and others are also discussed. As an overall conclusion, laser-ultrasonics that was for a long time a laboratory curiosity has definitely now made its transition to industry. Nevertheless, developments should continue to improve performance, to make it well adapted to specific inspection or characterization tasks and more affordable.