Longitudinal wave generation in laser ultrasonics

Abstract

The purpose of this work is to conduct a detailed investigation of wave generation by thermal dipoles in laser-generated ultrasound. A simplified description of ultrasound generation is used to provide a clear explanation as to how longitudinal waves are generated by thermal dipoles. The effects of the shape and time dependence of the temperature distribution on the waveforms are illustrated. Studies such as this are needed in order to explain the shapes of laser-generated ultrasound waves for nondestructive materials testing, and to enable researchers to select optimum laser pulse parameters for specific applications. In particular, this work identifies the physical origins of the precursor.