We report the development of a practical instrument that enables depth-resolved midinfrared spectra to be measured in a noncontacting, nondestructive way on samples of arbitrary shape and size and without any prior preparation of the surface. The technique used, thermal emission decay Fourier transform infrared (TED-FTIR) spectroscopy combines time-domain optothermal radiometry with step-scanning FTIR spectroscopy. The instrument uses purpose-designed optics and software to measure optothermal transients at a predetermined number of interferometer path differences, from which depth-resolved spectra in the range 700–1800 cm−1 with a resolution of 12 cm−1 can be calculated. The depth range is limited by the optical and thermal properties of the sample, being ∼10 μm for common organic materials.
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