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Proceedings Paper

Measurement and simulation of the laser-based thermo-elastic excitation and propagation of acoustic pulses for thin film and MEMS inspection
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Paper Abstract

Optical techniques for monitoring acoustic waves excited in thin films or micro-structures with ultrashort laser pulses are useful for the accurate and nondestructive evaluation as well as for the characterization of material properties. The pump-probe laser-based acoustic methods generate acoustic bulk waves in a thermo-elastic way by absorbing the pump laser pulses at the surface of the thin film. The acoustic waves are partly reflected at the interface of thin film and substrate. Back at the film surface the reflected acoustic wave causes a change of the optical reflection coefficient, which is measured by the probe laser pulse. One-dimensional, thermo-elastic models are developed to investigate the laser-based excitation and propagation of the longitudinal acoustic pulses in thin aluminium films. The change of the optical reflection coefficient is governed by the temperature distribution and the mechanical strain caused by the traveling acoustic pulse. The presented comparison of the simulation results of thin aluminium films with the pump-probe-measurements allows to determine film thickness or Young's modulus. Furthermore material properties like thermal conductivity and photoacoustic properties are estimated. The thermo-elastic modeling of the two-dimensional case and the resulting new possibility to use the pump-probe technique for the nondestructive evaluation of micro-structures is discussed. Further directions of the ongoing research project are presented.

Paper Details

Date Published: 7 June 2002
PDF: 10 pages
Proc. SPIE 4703, Nondestructive Evaluation and Reliability of Micro- and Nanomaterial Systems, (7 June 2002); doi: 10.1117/12.469627
Show Author Affiliations
Dieter Michael Profunser, Swiss Federal Institute of Technology Zurich (Switzerland)
Jacqueline Vollmann, Swiss Federal Institute of Technology Zurich (Switzerland)
Jurg Bryner, Swiss Federal Institute of Technology Zurich (Switzerland)
Jurg Dual, Swiss Federal Institute of Technology Zurich (Switzerland)


Published in SPIE Proceedings Vol. 4703:
Nondestructive Evaluation and Reliability of Micro- and Nanomaterial Systems
Norbert Meyendorf; George Y. Baaklini; Bernd Michel, Editor(s)

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