  We found that temperature-dependent infrared spectroscopy measurements (i.e.,
reflectance or transmittance) using a Fourier-transform spectrometer can have
substantial errors, especially for elevated sample temperatures and collection
using an objective lens (e.g., using an infrared microscope). These errors
arise as a result of partial detector saturation due to thermal emission from
the measured sample reaching the detector, resulting in nonphysical apparent
reduction of reflectance or transmittance with increasing sample temperature.
Here, we demonstrate that these temperature-dependent errors can be corrected
by implementing several levels of optical attenuation that enable "convergence
testing" of the measured reflectance or transmittance as the thermal-emission
signal is reduced, or by applying correction factors that can be inferred by
looking at the spectral regions where the sample is not expected to have a
substantial temperature dependence.
