Measuring the spatial irradiance profile of the infrared beam in a fourier transform infrared spectrometer

Abstract This article presents a practical method for measuring the spatial irradiance distribution of the infrared (IR) beam emitted by a globar in a Fourier Transform Infrared (FTIR) spectrometer. The approach, intended for students with access to standard FTIR instrumentation, provides insights into the inhomogeneity of the IR beam profile, which can be well approximated by a Gaussian distribution. By recording just a few spectra using different apertures and applying a numerical fitting, the method enables the determination of the irradiance distribution width. Beyond offering a deeper understanding of beam characteristics in FTIR spectroscopy, this technique serves as a useful diagnostic tool for monitoring the performance and long-term stability of the spectrometer source. Its simplicity and low experimental requirements make it particularly well suited for instructional settings.