Photothermal measurements are increasingly attractive for thermal analysis of fragile nano-structured materials or as an in situ measurement for investigation of coupled thermal and mechanical properties. The most common thermal property measurements, including the laser flash and photothermal reflectance methods, have limited applicability due to stringent requirements on geometry, thermal, and optical properties of the material. In contrast, the mirage method typically does not require any sample modification and places a minimum number of restrictions on the sample geometry. This method uses a periodically modulated pump laser to heat a sample material and a probe beam to observe the resulting change in index of refraction of a gas above the sample. In this work, the experimental methodology and data analysis are generalized to allow more accurate measurement of low thermal diffusivity materials. The method expands upon the work of Ravi et al. (2002), but alternatively uses a numerical solution to the heat equations, more accurately capturing a square-wave heat application from the pump laser and nonzero probe beam height.
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