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Accuracy of subsurface temperature distributions computed from pulsed photothermal radiometry
D J Smithies1, T E Milner, B S Tanenbaum
1Beckman Laser Institute and Medical Clinic, University of California, Irvine 92612, USA.
Physics in Medicine and Biology
|October 2, 1998
Summary
Pulsed photothermal radiometry (PPTR) can determine subsurface temperature increases but has limitations. Accuracy decreases when chromophore layer thickness is less than 25% of its depth, affecting peak temperature and layer thickness calculations.
Area of Science:
- Physics
- Optical Engineering
- Materials Science
Background:
- Pulsed photothermal radiometry (PPTR) is a non-contact technique for measuring temperature changes in materials.
- It is used to analyze subsurface chromophore layers after laser irradiation.
- Understanding PPTR's limitations is crucial for accurate thermal analysis.
Purpose of the Study:
- To identify and analyze the inherent limitations of Pulsed Photothermal Radiometry (PPTR).
- To compute the temperature increase in subsurface chromophore layers using PPTR data.
- To assess the impact of various parameters on PPTR accuracy.
Main Methods:
- A time record of infrared emission from a test material was calculated.
- A non-negatively constrained conjugate gradient algorithm was employed for data analysis.
- Singular value decomposition was used to investigate the accuracy of computed temperature distributions.
Main Results:
- The algorithm accurately predicted the average depth and integral of temperature increase.
- Computed peak temperature increase was significantly underestimated when the thickness/depth ratio was below 25%.
- Computed chromophore layer thickness was overestimated under the same conditions.
Conclusions:
- PPTR accuracy is limited by the number of singular vectors representing the temperature increase.
- The thickness/depth ratio significantly impacts the accuracy of PPTR measurements.
- Careful consideration of these limitations is necessary for reliable subsurface thermal analysis using PPTR.