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Proceedings Paper

Resolution Limitations In Photothermal Radiometric Imaging
Author(s): S J Sheard; M G Somekh
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Paper Abstract

In scanned photothermal radiometric imaging a sample is periodically heated using an intensity modulated laser beam. Absorption of the light energy generates a thermal wave which diffuses into the bulk of the sample. The resulting changes in surface temperature are measured using a focused infrared detector. One of the principal advantages of thermal waves is that they provide a convenient means for performing non-contacting subsurface imaging. Often a very tightly focused laser spot size is used as the heat source, which allows excellent surface resolution. In this case, however, the physics of image formation and the factors limiting the subsurface resolution need to be carefully considered. This paper presents a simple but rigorous Fourier transform analysis which enables one to calculate the temperature distribution throughout a material with a finite sized source and detection area. We plot results for various detector/source dimensions and develop criteria to determine whether attenuation or spreading of the thermal wave limits the spatial resolution. In addition the analysis is particularly useful for determining the range of validity of the simple one dimensional model which is often used to interpret experimental results.

Paper Details

Date Published: 3 October 1988
PDF: 6 pages
Proc. SPIE 0917, Recent Developments and Applications of Infrared Analytical Instruments, (3 October 1988); doi: 10.1117/12.945588
Show Author Affiliations
S J Sheard, University College London (England)
M G Somekh, University College London (England)


Published in SPIE Proceedings Vol. 0917:
Recent Developments and Applications of Infrared Analytical Instruments

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