Correcting thermal-emission-induced detector saturation in infrared reflection or transmission spectroscopy

TL;DR

This paper identifies and corrects errors in infrared spectroscopy caused by thermal emission from samples at high temperatures, improving measurement accuracy in reflectance and transmittance studies.

Contribution

It introduces optical attenuation and correction factors to mitigate detector saturation effects due to thermal emission in infrared spectroscopy.

Findings

Thermal emission causes significant measurement errors at high temperatures.

Optical attenuation enables convergence testing to correct errors.

Correction factors improve the accuracy of temperature-dependent IR measurements.

Abstract

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.