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Proceedings Paper

Quantitative measurement of laminar material properties and structure using time domain reflection imaging
Author(s): David Zimdars; Jeffrey White; G. Fichter; A. Chernovsky; S. L. Williamson
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Paper Abstract

Time domain terahertz (TD-THz) reflection imaging tomography can be used to investigate the laminar structure of objects. In a monostatic configuration, a sequence of pulses is generated by reflection from each discontinuity in index of refraction. Through analysis of the return pulses, the material absorption and index of refraction properties of each layer can be determined. TD-THz reflection tomography can be used to precisely measure the thickness of coatings such as yttria stabilized zirconia (YSZ) thermal barrier coatings (TBC) on aircraft engine turbine blades; paint on aircraft, ships, and cars; and other thin film measurement applications. In each of these cases, precise determination of the optical delay of the TD-THz pulses is required with as little as sub-10 femtosecond precision for pulses which can be greater than 500 fs in duration. We present a method to accurately measure optical delay between layers where the pulses are fit to a reference template. These are demonstrated to achieve micron scale accuracy in coating thickness. As an example, TD-THz non destructive evaluation (NDE) imaging is used to two-dimensionally map the thickness of YSZ TBCs on aircraft engine turbine blades. Indications of thermal degradation can be seen. The method is non-contact, rapid, and requires no special preparation of the blade.

Paper Details

Date Published: 15 April 2008
PDF: 8 pages
Proc. SPIE 6949, Terahertz for Military and Security Applications VI, 69490B (15 April 2008); doi: 10.1117/12.777603
Show Author Affiliations
David Zimdars, Picometrix, Inc. (United States)
Jeffrey White, Picometrix, Inc. (United States)
G. Fichter, Picometrix, Inc. (United States)
A. Chernovsky, Picometrix, Inc. (United States)
S. L. Williamson, Picometrix, Inc. (United States)

Published in SPIE Proceedings Vol. 6949:
Terahertz for Military and Security Applications VI
James O. Jensen; Hong-Liang Cui; Dwight L. Woolard; R. Jennifer Hwu, Editor(s)

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