Calorimetric Measurement of Temperature Dependent Absorption in Copper

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Abstract
This paper reports the temperature dependence of optical absorption in copper as measured by laser rate calorimetry. It is found that the measured values of the temperature dependence agree well with the predictions of the simple Drude theory for wavelengths of 10.6 μm and 1.08 μm. At 0.647 μm the temperature dependence is stronger, due to the effect of interband transitions. Absolute values of the absorptance are measured to be somewhat higher than predicted by the simple Drude theory, indicating the importance of the anomalous skin effect and possibly other absorption mechanisms. After cycling to a temperature of 200°C or greater, a permanent increase in the room temperature absorptance is observed. This increased absorption is pronounced at 1.08 μm and 0.647 μm, whereas it is not observable at 10.6 μm. The permanent change is correlated with a change in the observed microstructure of the surface.