Longitudinal Wave Precursor Signal from an Optically Penetrating Thermoelastic Laser Source

Date
1989
Authors
Conant, R.
Telschow, K.
Major Professor
Advisor
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Altmetrics
Authors
Research Projects
Organizational Units
Journal Issue
Department
Abstract

The thermoelastic laser ultrasonic source depends on the optical absorption of energy at the sample surface to produce a volumetric expansion. This paper presents the results of calculations and measurements on the effects of optical penetration of the laser beam into the sample and the elastic waveforms produced. A central result is prediction of a sharp longitudinal waveform that precedes the main waveform and is very similar to that observed with an ablative source (normal point force). The shape of this precursor signal is strongly dependent on the optical penetration depth of the material. A basic explanation of the origin of the precursor signal is given in terms of a one-dimensional model using point sources imbedded within the material. Experimental measurements on a material with a substantial optical penetration depth directly confirm calculations using 2-D integral transform techniques by taking into account the temperature variation with depth.

Comments
Description
Keywords
Citation
DOI