Influence of laser parameters on laser ultrasonic efficiency

Abstract

Laser ultrasonics is currently the optimal method for non-destructive testing of composite materials in the aerospace industry. The process is based on a laser-generated ultrasound wave which propagates inside the composite. The response at the material surface is detected and converted into a defect map across the aircraft. The design and optimisation of a laser system for this application is reviewed in this paper, together with the basic science involved. This includes the optimisation of laser parameters, such as output couplers and gas mixture, and the impact these choices have on the laser chemistry. The authors present a theory for the catalytic recombination of the gas which shows excellent agreement with experiment. Finally, an operating laser system for this application, yielding a six-fold improvement in performance over conventional laser systems, is described.