Optical measurement of deformation fields and surface processes with digital speckle correlation

This thesis presents a detailed investigation of Digital Speckle Correlation (DSC) as a tool for the measurement of three-dimensional deformation fields and surface processes, i.e. changes in the microstructure of the surface. The method is based on a detailed analysis of the changes in the speckle field that is scattered from a laser-illuminated rough surface, using digital image processing. The extremely simple and robust optical setup is suited for uses in harsh environments outside the laboratory, e.g. in Non-Destructive Testing (NDT) applications. In the first part of the thesis, a new technique is presented to determine the complete deformation field, in particular the hitherto inaccessible out-of-plane component. The measurement relies on the analysis of the spectral properties of the decorrelation which is caused by local tilt. The accuracy of the measurement is about one tenth of the used wavelength, and thus comparable to interferometric techniques (e.g. ESPI). In the second part, different theoretical approaches to describe the scattering at random rough surfaces, including perturbation theory, Kirchhoff theory and the two-scale model, are advanced to determine the correlation of the scattered speckle fields in terms of parameters of the surface microstructure changes. The theoretical relations are verified by comparative measurements with high resolution scanning force microscopy (SFM) and by correlation measurements under a variation of experimental parameters. The results allow for the first time a quantitative whole-field monitoring of surface processes by remote optical means.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Oldenburg

Year

2002

Author dc:creator

• Fricke-Begemann, Thomas

• [Keine Schlagwörter von Autor/in vergeben.]

Repository record source_url

http://oops.uni-oldenburg.de/219

OAI identifier oai:identifier

oai:oops.uni-oldenburg.de:219