Calibration of Microscope-coupled Fourier Transform Infrared Spectrometers for CW and Modulated Light Emission Measurements

Measurement of low power infrared light emission spectra from microstructures can be challenging, but is of key importance in several research fields. Fourier transform infrared spectrometers (FTIR) can be used for characterizing such weak light emitters, but this requires additional custom user calibration compared to traditional FTIR measurements of, e.g., transmission or reflection. These calibration techniques are well documented for standalone FTIR instruments but not for microscope coupled-FTIRs, even though such an architecture greatly simplifies collection of light from micro and nano scale structures. We propose and demonstrate a calibration method for microsope-FTIRs based on the well-known emissivity of doped silicon at high temperature. With this method, we measure responsivity and noise floor of a recently installed microscope-FTIR instrument (Bruker\textsuperscript{\textcopyright} Invenio\textsuperscript{\textregistered} R coupled with a Hyperion II microscope), which is found to be within theoretically predicted values. The method is demonstrated for two different detectors (Mercury Cadmium Telluride and Indium Antimonide), in both continuous wave (CW) and modulated (step-scan) emission measurements mode.