Theory of Pulsed Photothermal Radiometry for Transmission and Lateral Geometries

概要

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Pulsed photothermal radiometry (PPTR) employs a pulsed laser excitation to heat a sample and the resulting change in emitted IR radiation is detected remotely, which gives rise to the PPTR signal. A theory for analysing experimental data is considered for transmission geometry where excitation and detection are on opposite sides of the sample, and lateral geometry where excitation and detection are on the same side, but laterally displaced. For transmission geometry it is shown in detail how absorption coefficients at the excitation and detection wavelengths, $\alpha$ and $\beta$ respectively, appear in a symmetrical way in this theory. In doing this an alternative way of calculating PPTR signals is introduced using a Laplace transform technique. For lateral geometry a similar symmetry for disc excitation and detection areas, with radii $r_{1}$ and $r_{0}$, is also demonstrated. The Laplace transform technique is also used to give signal expressions for transmission geometry which converge quickly for small values of time. Furthermore, ways of applying the theory to experimental data in order to extract material properties $\alpha$, $\beta$ and thermal diffusivity $D$ are developed.
2005-08-15